{
 "instance": {
  "cma-20211231.htm": {
   "axisCustom": 7,
   "axisStandard": 41,
   "contextCount": 825,
   "dts": {
    "calculationLink": {
     "local": [
      "cma-20211231_cal.xml"
     ]
    },
    "definitionLink": {
     "local": [
      "cma-20211231_def.xml"
     ]
    },
    "inline": {
     "local": [
      "cma-20211231.htm"
     ]
    },
    "labelLink": {
     "local": [
      "cma-20211231_lab.xml"
     ]
    },
    "presentationLink": {
     "local": [
      "cma-20211231_pre.xml"
     ]
    },
    "schema": {
     "local": [
      "cma-20211231.xsd"
     ],
     "remote": [
      "http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xl-2003-12-31.xsd",
      "http://www.xbrl.org/2003/xlink-2003-12-31.xsd",
      "http://www.xbrl.org/2005/xbrldt-2005.xsd",
      "http://www.xbrl.org/2006/ref-2006-02-27.xsd",
      "http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd",
      "http://www.xbrl.org/lrr/role/net-2009-12-16.xsd",
      "http://www.xbrl.org/lrr/role/reference-2009-12-16.xsd",
      "https://www.xbrl.org/2020/extensible-enumerations-2.0.xsd",
      "https://www.xbrl.org/dtr/type/2020-01-21/types.xsd",
      "https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd",
      "https://xbrl.fasb.org/srt/2021/elts/srt-roles-2021-01-31.xsd",
      "https://xbrl.fasb.org/srt/2021/elts/srt-types-2021-01-31.xsd",
      "https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd",
      "https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.xsd",
      "https://xbrl.fasb.org/us-gaap/2021/elts/us-types-2021-01-31.xsd",
      "https://xbrl.sec.gov/country/2021/country-2021.xsd",
      "https://xbrl.sec.gov/dei/2021q4/dei-2021q4.xsd"
     ]
    }
   },
   "elementCount": 1090,
   "entityCount": 1,
   "hidden": {
    "http://fasb.org/us-gaap/2021-01-31": 34,
    "http://www.comerica.com/20211231": 11,
    "http://xbrl.sec.gov/dei/2021q4": 4,
    "total": 49
   },
   "keyCustom": 150,
   "keyStandard": 678,
   "memberCustom": 47,
   "memberStandard": 93,
   "nsprefix": "cma",
   "nsuri": "http://www.comerica.com/20211231",
   "report": {
    "R1": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "dei:DocumentAnnualReport",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "document",
     "isDefault": "true",
     "longName": "000010001 - Document - Document And Entity Information",
     "role": "http://www.comerica.com/role/DocumentAndEntityInformation",
     "shortName": "Document And Entity Information",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "dei:DocumentAnnualReport",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R10": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210081002 - Disclosure - Fair Value Measurements",
     "role": "http://www.comerica.com/role/FairValueMeasurements",
     "shortName": "Fair Value Measurements",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R100": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-8",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForOtherArrangements",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240654042 - Disclosure - Short-term Borrowings Short-term Borrowings (Narrative) (Details)",
     "role": "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsNarrativeDetails",
     "shortName": "Short-term Borrowings Short-term Borrowings (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-8",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForOtherArrangements",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R101": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShortTermDebtTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i216f3fdf24d044d99daa954d30c7ef8e_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShortTermBorrowings",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240664043 - Disclosure - Short-term Borrowings Short-term Borrowings (Summary of Short-term Borrowings) (Details)",
     "role": "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails",
     "shortName": "Short-term Borrowings Short-term Borrowings (Summary of Short-term Borrowings) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShortTermDebtTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i216f3fdf24d044d99daa954d30c7ef8e_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShortTermBorrowings",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R102": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-8",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalHomeLoanBankDebt",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240694044 - Disclosure - Medium- And Long-Term Debt (Narrative) (Details)",
     "role": "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
     "shortName": "Medium- And Long-Term Debt (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-8",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalHomeLoanBankDebt",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R103": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfDebtInstrumentsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LongTermDebt",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240704045 - Disclosure - Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details)",
     "role": "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails",
     "shortName": "Medium- And Long-Term Debt (Schedule Of Medium- And Long-Term Debt) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfDebtInstrumentsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i0b3ed52dfb684b16921674b645a08c55_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:OtherLongTermDebt",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R104": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfMaturitiesOfLongTermDebtTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240714046 - Disclosure - Medium- And Long-Term Debt Schedule of Maturities of Medium- and Long-term Debt (Details)",
     "role": "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails",
     "shortName": "Medium- And Long-Term Debt Schedule of Maturities of Medium- and Long-term Debt (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfMaturitiesOfLongTermDebtTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R105": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "4",
      "first": true,
      "lang": "en-US",
      "name": "cma:DepositorySharesIssued",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240734047 - Disclosure - Shareholders' Equity Shareholders' Equity (Narrative) (Details)",
     "role": "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails",
     "shortName": "Shareholders' Equity Shareholders' Equity (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "4",
      "first": true,
      "lang": "en-US",
      "name": "cma:DepositorySharesIssued",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R106": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240764048 - Disclosure - Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Income (Loss)) (Details)",
     "role": "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
     "shortName": "Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Income (Loss)) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ife8ca6d914994af685183bf219d43e8c_I20181231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R107": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240794049 - Disclosure - Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details)",
     "role": "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
     "shortName": "Net Income Per Common Share (Basic And Diluted Net Income Per Common Share) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-5",
      "lang": "en-US",
      "name": "us-gaap:WeightedAverageNumberOfSharesOutstandingBasic",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R108": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "5",
      "first": true,
      "lang": "en-US",
      "name": "cma:Stockoptionsexcludedbecauseexercisepricesweregreaterthanaveragemarketpriceofshares",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240804050 - Disclosure - Net Income Per Common Share (Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation) (Details)",
     "role": "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
     "shortName": "Net Income Per Common Share (Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "5",
      "first": true,
      "lang": "en-US",
      "name": "cma:Stockoptionsexcludedbecauseexercisepricesweregreaterthanaveragemarketpriceofshares",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R109": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240834051 - Disclosure - Share-Based Compensation Share-Based Compensation (Narrative) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
     "shortName": "Share-Based Compensation Share-Based Compensation (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R11": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210151003 - Disclosure - Investment Securities",
     "role": "http://www.comerica.com/role/InvestmentSecurities",
     "shortName": "Investment Securities",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R110": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AllocatedShareBasedCompensationExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240844052 - Disclosure - Share-Based Compensation (Summary of Components of Share-Based Compensation Expense) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationSummaryofComponentsofShareBasedCompensationExpenseDetails",
     "shortName": "Share-Based Compensation (Summary of Components of Share-Based Compensation Expense) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AllocatedShareBasedCompensationExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R111": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrecognizedCompensationCostNonvestedAwardsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240854053 - Disclosure - Share-Based Compensation (Unrecognized Compensation Expense) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationUnrecognizedCompensationExpenseDetails",
     "shortName": "Share-Based Compensation (Unrecognized Compensation Expense) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrecognizedCompensationCostNonvestedAwardsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R112": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "2",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usdPerShare",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240864054 - Disclosure - Share-Based Compensation (Estimated Weighted-Average Grant-Date Fair Value Per Option Share and the Underlying Binomial Option-Pricing Model Assumptions) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails",
     "shortName": "Share-Based Compensation (Estimated Weighted-Average Grant-Date Fair Value Per Option Share and the Underlying Binomial Option-Pricing Model Assumptions) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "2",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usdPerShare",
      "xsiNil": "false"
     }
    },
    "R113": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ib3d192b308da44289d1d1d335c09c1d6_I20201231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240874055 - Disclosure - Share-Based Compensation (Summary of the Corporation's Stock Option Activity and Related Information) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails",
     "shortName": "Share-Based Compensation (Summary of the Corporation's Stock Option Activity and Related Information) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ib3d192b308da44289d1d1d335c09c1d6_I20201231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R114": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:NonvestedRestrictedStockSharesActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ib8c4181b174d430a927bb8470da15f7f_I20201231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
      "reportCount": 1,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240884056 - Disclosure - Share-Based Compensation (Summary of the Corporation's Restricted Stock Activity and Related Information) (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
     "shortName": "Share-Based Compensation (Summary of the Corporation's Restricted Stock Activity and Related Information) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:NonvestedRestrictedStockSharesActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ide2a5b53842a4b1e842b318373b8bc44_D20210101-20211231",
      "decimals": "-3",
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R115": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i510884db1da8403dbb470068ed9f79b2_I20201231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240894057 - Disclosure - Share-Based Compensation Summary of the Corporation's Restricted Stock Unit Activity and Related Information (Details)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
     "shortName": "Share-Based Compensation Summary of the Corporation's Restricted Stock Unit Activity and Related Information (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i510884db1da8403dbb470068ed9f79b2_I20201231",
      "decimals": "-3",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R116": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAllocationOfPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanFairValueOfPlanAssets",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240924058 - Disclosure - Employee Benefit Plans (Narrative) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
     "shortName": "Employee Benefit Plans (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "us-gaap:ScheduleOfExpectedBenefitPaymentsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R117": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAllocationOfPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanFairValueOfPlanAssets",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240934059 - Disclosure - Employee Benefit Plans (Reconciliations of Plan assets and the Projected Benefit Obligation, the Weighted-Average Assumptions Used to Determine Year-End Benefit Obligations, and the Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
     "shortName": "Employee Benefit Plans (Reconciliations of Plan assets and the Projected Benefit Obligation, the Weighted-Average Assumptions Used to Determine Year-End Benefit Obligations, and the Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfDefinedBenefitPlansDisclosuresTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i52efaf1efbf94fb8864d4018bc811189_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanContributionsByEmployer",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R118": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAmountsRecognizedInOtherComprehensiveIncomeLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240944060 - Disclosure - Employee Benefit Plans (Schedule of Changes, Net of Tax, in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
     "shortName": "Employee Benefit Plans (Schedule of Changes, Net of Tax, in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAmountsRecognizedInOtherComprehensiveIncomeLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R119": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanNetPeriodicBenefitCost",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240954061 - Disclosure - Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
     "shortName": "Employee Benefit Plans Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfNetBenefitCostsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i52efaf1efbf94fb8864d4018bc811189_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanExpectedReturnOnPlanAssets",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R12": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivablesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210221004 - Disclosure - Credit Quality And Allowance For Credit Losses",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLosses",
     "shortName": "Credit Quality And Allowance For Credit Losses",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivablesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R120": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAllocationOfPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:AssetsFairValueDisclosureExcludingAssetsValuedatNAV",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240964062 - Disclosure - Employee Benefit Plans (Fair Values of the Corporation's Qualified Defined Benefit Pension Plan Investments Measured at Fair Value on a Recurring Basis) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
     "shortName": "Employee Benefit Plans (Fair Values of the Corporation's Qualified Defined Benefit Pension Plan Investments Measured at Fair Value on a Recurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAllocationOfPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:AssetsFairValueDisclosureExcludingAssetsValuedatNAV",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R121": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEffectOfSignificantUnobservableInputsChangesInPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i389e6b65b6014714bf80448ed3353ce4_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:BalanceAtBeginningAndEndOfPeriod",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240974063 - Disclosure - Employee Benefit Plans (Summary of Changes in the Corporation's Qualified Defined Benefit Pension Plan's Level 3 Investments Measured at Fair Value on a Recurring Basis) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails",
     "shortName": "Employee Benefit Plans (Summary of Changes in the Corporation's Qualified Defined Benefit Pension Plan's Level 3 Investments Measured at Fair Value on a Recurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEffectOfSignificantUnobservableInputsChangesInPlanAssetsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i8d92b1511e8b43378c16242c38536518_I20191231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "cma:BalanceAtBeginningAndEndOfPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R122": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfExpectedBenefitPaymentsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i46ab555c160b45348054ee98e43fef25_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240984064 - Disclosure - Employee Benefit Plans (Schedule of Estimated Future Employer Contributions) (Details)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails",
     "shortName": "Employee Benefit Plans (Schedule of Estimated Future Employer Contributions) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfExpectedBenefitPaymentsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i46ab555c160b45348054ee98e43fef25_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R123": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:IncomeLossFromContinuingOperationsBeforeIncomeTaxes",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241014065 - Disclosure - Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Narrative) (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
     "shortName": "Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:IncomeLossFromContinuingOperationsBeforeIncomeTaxes",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R124": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CurrentFederalTaxExpenseBenefit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241024066 - Disclosure - Income Taxes And Tax-Related Items Current and Deferred Components of the Provision for Income Taxes (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails",
     "shortName": "Income Taxes And Tax-Related Items Current and Deferred Components of the Provision for Income Taxes (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CurrentFederalTaxExpenseBenefit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R125": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241034067 - Disclosure - Income Taxes And Tax-Related Items Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Corporation's Provision for Income Taxes (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails",
     "shortName": "Income Taxes And Tax-Related Items Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Corporation's Provision for Income Taxes (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R126": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:UnrecognizedTaxBenefits",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241044068 - Disclosure - Income Taxes And Tax-Related Items Reconciliation of the Beginning and Ending Amounts of Unrecognized Tax Benefits (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails",
     "shortName": "Income Taxes And Tax-Related Items Reconciliation of the Beginning and Ending Amounts of Unrecognized Tax Benefits (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ife8ca6d914994af685183bf219d43e8c_I20181231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:UnrecognizedTaxBenefits",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R127": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:SummaryOfIncomeTaxExaminationsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i661d3720b0274148a24d933ee7a77942_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OpenTaxYear",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241054069 - Disclosure - Income Taxes And Tax-Related Items Tax Years for Significant Jurisdictions That Remain Subject to Examination (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
     "shortName": "Income Taxes And Tax-Related Items Tax Years for Significant Jurisdictions That Remain Subject to Examination (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:SummaryOfIncomeTaxExaminationsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i661d3720b0274148a24d933ee7a77942_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OpenTaxYear",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R128": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "ix:continuation",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DeferredTaxAssetsPropertyPlantAndEquipment",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241064070 - Disclosure - Income Taxes And Tax-Related Items Principal Components of Deferred Tax Assets and Liabilities (Details)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails",
     "shortName": "Income Taxes And Tax-Related Items Principal Components of Deferred Tax Assets and Liabilities (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "ix:continuation",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DeferredTaxAssetsPropertyPlantAndEquipment",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R129": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoansAndLeasesReceivableRelatedPartiesBeginningOfPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241084071 - Disclosure - Transactions with Related Parties Transactions with Related Parties (Narrative) (Details)",
     "role": "http://www.comerica.com/role/TransactionswithRelatedPartiesTransactionswithRelatedPartiesNarrativeDetails",
     "shortName": "Transactions with Related Parties Transactions with Related Parties (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoansAndLeasesReceivableRelatedPartiesBeginningOfPeriod",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R13": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ConcentrationRiskDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210311005 - Disclosure - Significant Group Concentrations of Credit Risk",
     "role": "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRisk",
     "shortName": "Significant Group Concentrations of Credit Risk",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ConcentrationRiskDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R130": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ia157f7c0fc8e4ce3af82ef67f535bb49_D20200101-20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:AverageReserveRequirement",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241114072 - Disclosure - Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Narrative) (Details)",
     "role": "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
     "shortName": "Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ia157f7c0fc8e4ce3af82ef67f535bb49_D20200101-20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:AverageReserveRequirement",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R131": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:TierOneRiskBasedCapital",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241124073 - Disclosure - Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Summary of Capital Position) (Details)",
     "role": "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails",
     "shortName": "Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Summary of Capital Position) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:TierOneRiskBasedCapital",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R132": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProceedsFromLegalSettlements",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241144074 - Disclosure - Contingent Liabilities (Narrative) (Details)",
     "role": "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
     "shortName": "Contingent Liabilities (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProceedsFromLegalSettlements",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R133": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "INF",
      "first": true,
      "lang": "en-US",
      "name": "cma:NumberOfMajorBusinessSegments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "segments",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241174075 - Disclosure - Business Segment Information (Narrative) (Details)",
     "role": "http://www.comerica.com/role/BusinessSegmentInformationNarrativeDetails",
     "shortName": "Business Segment Information (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "INF",
      "first": true,
      "lang": "en-US",
      "name": "cma:NumberOfMajorBusinessSegments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "segments",
      "xsiNil": "false"
     }
    },
    "R134": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestIncomeExpenseNet",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241184076 - Disclosure - Business Segment Information (Business Segment Financial Results) (Details)",
     "role": "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
     "shortName": "Business Segment Information (Business Segment Financial Results) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfSegmentReportingInformationBySegmentTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "cma:NetCreditRelatedChargeOffs",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R135": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CashAndDueFromBanks",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241214077 - Disclosure - Parent Company Financial Statements Parent Company Financial Statements (Balance Sheets) (Details)",
     "role": "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
     "shortName": "Parent Company Financial Statements Parent Company Financial Statements (Balance Sheets) (Details)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "srt:ScheduleOfCondensedBalanceSheetTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i2691c2d021ea4328969895325fa5022e_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:CashAndDueFromBanks",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R136": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OtherInterestAndDividendIncome",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241224078 - Disclosure - Parent Company Financial Statements Parent Company Financial Statements (Statements of Income) (Details)",
     "role": "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
     "shortName": "Parent Company Financial Statements Parent Company Financial Statements (Statements of Income) (Details)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "srt:ScheduleOfCondensedIncomeStatementTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i7314644407924f079045f9877ca62d0c_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R137": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241234079 - Disclosure - Parent Company Financial Statements Parent Company Financial Statements (Statements of Cash Flows) (Details)",
     "role": "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
     "shortName": "Parent Company Financial Statements Parent Company Financial Statements (Statements of Cash Flows) (Details)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "srt:ScheduleOfCondensedCashFlowStatementTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i7314644407924f079045f9877ca62d0c_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R138": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestAndDividendIncomeOperating",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241264080 - Disclosure - Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited) (Summary of Quarterly Financial Statements) (Details)",
     "role": "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails",
     "shortName": "Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited) (Summary of Quarterly Financial Statements) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestAndDividendIncomeOperating",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R139": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241294081 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts with Customers (Details)",
     "role": "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails",
     "shortName": "Revenue from Contracts with Customers Revenue from Contracts with Customers (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RevenueFromContractWithCustomerExcludingAssessedTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R14": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PropertyPlantAndEquipmentDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210361006 - Disclosure - Premises and Equipment",
     "role": "http://www.comerica.com/role/PremisesandEquipment",
     "shortName": "Premises and Equipment",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PropertyPlantAndEquipmentDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R140": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SalesTypeLeaseLeaseIncome",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241324082 - Disclosure - Leases (Narrative) (Details)",
     "role": "http://www.comerica.com/role/LeasesNarrativeDetails",
     "shortName": "Leases (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SalesTypeLeaseLeaseIncome",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R141": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OperatingLeaseExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241334083 - Disclosure - Leases (Lease Expenses) (Details)",
     "role": "http://www.comerica.com/role/LeasesLeaseExpensesDetails",
     "shortName": "Leases (Lease Expenses) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OperatingLeaseExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R142": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:LeasesSupplementalBalanceSheetTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:RightOfUseROUAssets",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241344084 - Disclosure - Leases (Supplemental balance sheet) (Details)",
     "role": "http://www.comerica.com/role/LeasesSupplementalbalancesheetDetails",
     "shortName": "Leases (Supplemental balance sheet) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:LeasesSupplementalBalanceSheetTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:RightOfUseROUAssets",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R143": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:LeasesSupplementalCashFlowTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OperatingLeasePayments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241354085 - Disclosure - Leases (Supplemental cash flow) (Details)",
     "role": "http://www.comerica.com/role/LeasesSupplementalcashflowDetails",
     "shortName": "Leases (Supplemental cash flow) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:LeasesSupplementalCashFlowTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OperatingLeasePayments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R144": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:SalesTypeAndDirectFinancingLeasesLeaseReceivableMaturityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241364086 - Disclosure - Leases (Contractual Maturities of Operating Lease Liabilities) (Details) (Details)",
     "role": "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails",
     "shortName": "Leases (Contractual Maturities of Operating Lease Liabilities) (Details) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:SalesTypeAndDirectFinancingLeasesLeaseReceivableMaturityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R145": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:LesseeOperatingLeaseLiabilityMaturityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "241374087 - Disclosure - Leases (Contractual Maturities of Sales-Type and Direct Financing Lease Receivables) (Details) (Details)",
     "role": "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails",
     "shortName": "Leases (Contractual Maturities of Sales-Type and Direct Financing Lease Receivables) (Details) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:LesseeOperatingLeaseLiabilityMaturityTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R15": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:GoodwillAndIntangibleAssetsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210391007 - Disclosure - Goodwill and Intangible Assets",
     "role": "http://www.comerica.com/role/GoodwillandIntangibleAssets",
     "shortName": "Goodwill and Intangible Assets",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:GoodwillAndIntangibleAssetsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R16": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210441008 - Disclosure - Derivative And Credit-Related Financial Instruments",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstruments",
     "shortName": "Derivative And Credit-Related Financial Instruments",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R17": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:VariableInterestEntityDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210541009 - Disclosure - Variable Interest Entities (VIEs)",
     "role": "http://www.comerica.com/role/VariableInterestEntitiesVIEs",
     "shortName": "Variable Interest Entities (VIEs)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:VariableInterestEntityDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R18": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DepositLiabilitiesDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210581010 - Disclosure - Deposits",
     "role": "http://www.comerica.com/role/Deposits",
     "shortName": "Deposits",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DepositLiabilitiesDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R19": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShortTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210631011 - Disclosure - Short-term Borrowings",
     "role": "http://www.comerica.com/role/ShorttermBorrowings",
     "shortName": "Short-term Borrowings",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ShortTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R2": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CashAndDueFromBanks",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100010002 - Statement - Consolidated Balance Sheets",
     "role": "http://www.comerica.com/role/ConsolidatedBalanceSheets",
     "shortName": "Consolidated Balance Sheets",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "cma:LoansReceivableCommercialFinancialAndAgriculturalNetOfDeferredIncome",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R20": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LongTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210671012 - Disclosure - Medium- And Long-Term Debt",
     "role": "http://www.comerica.com/role/MediumAndLongTermDebt",
     "shortName": "Medium- And Long-Term Debt",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LongTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R21": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:StockholdersEquityNoteDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210721013 - Disclosure - Shareholders' Equity",
     "role": "http://www.comerica.com/role/ShareholdersEquity",
     "shortName": "Shareholders' Equity",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:StockholdersEquityNoteDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R22": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ComprehensiveIncomeNoteTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210741014 - Disclosure - Accumulated Other Comprehensive Loss",
     "role": "http://www.comerica.com/role/AccumulatedOtherComprehensiveLoss",
     "shortName": "Accumulated Other Comprehensive Loss",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ComprehensiveIncomeNoteTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R23": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210771015 - Disclosure - Net Income Per Common Share",
     "role": "http://www.comerica.com/role/NetIncomePerCommonShare",
     "shortName": "Net Income Per Common Share",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:EarningsPerShareTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R24": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210811016 - Disclosure - Share-Based Compensation",
     "role": "http://www.comerica.com/role/ShareBasedCompensation",
     "shortName": "Share-Based Compensation",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R25": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PensionAndOtherPostretirementBenefitsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210901017 - Disclosure - Employee Benefit Plans",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlans",
     "shortName": "Employee Benefit Plans",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PensionAndOtherPostretirementBenefitsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R26": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:IncomeTaxDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210991018 - Disclosure - Income Taxes And Tax-Related Items",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItems",
     "shortName": "Income Taxes And Tax-Related Items",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:IncomeTaxDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R27": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RelatedPartyTransactionsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211071019 - Disclosure - Transactions with Related Parties",
     "role": "http://www.comerica.com/role/TransactionswithRelatedParties",
     "shortName": "Transactions with Related Parties",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RelatedPartyTransactionsDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R28": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211091020 - Disclosure - Regulatory Capital and Reserve Requirements",
     "role": "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirements",
     "shortName": "Regulatory Capital and Reserve Requirements",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R29": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211131021 - Disclosure - Contingent Liabilities",
     "role": "http://www.comerica.com/role/ContingentLiabilities",
     "shortName": "Contingent Liabilities",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommitmentsAndContingenciesDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R3": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "INF",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PreferredStockNoParValue",
      "reportCount": 1,
      "unitRef": "usdPerShare",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100020003 - Statement - Consolidated Balance Sheets (Parenthetical)",
     "role": "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
     "shortName": "Consolidated Balance Sheets (Parenthetical)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": null
    },
    "R30": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SegmentReportingDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211151022 - Disclosure - Business Segment Information",
     "role": "http://www.comerica.com/role/BusinessSegmentInformation",
     "shortName": "Business Segment Information",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:SegmentReportingDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R31": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211191023 - Disclosure - Parent Company Financial Statements",
     "role": "http://www.comerica.com/role/ParentCompanyFinancialStatements",
     "shortName": "Parent Company Financial Statements",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R32": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:QuarterlyFinancialInformationTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211241024 - Disclosure - Summary of Quarterly Financial Statements (Unaudited)",
     "role": "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnaudited",
     "shortName": "Summary of Quarterly Financial Statements (Unaudited)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:QuarterlyFinancialInformationTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R33": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RevenueFromContractWithCustomerTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211271025 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts with Customers",
     "role": "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomers",
     "shortName": "Revenue from Contracts with Customers Revenue from Contracts with Customers",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:RevenueFromContractWithCustomerTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R34": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:LeasesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "211301026 - Disclosure - Leases (Notes)",
     "role": "http://www.comerica.com/role/LeasesNotes",
     "shortName": "Leases (Notes)",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:LeasesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R35": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ConsolidationPolicyTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "220022001 - Disclosure - Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies",
     "shortName": "Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Policies)",
     "subGroupType": "policies",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ConsolidationPolicyTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R36": {
     "firstAnchor": {
      "ancestors": [
       "div",
       "us-gaap:PensionAndOtherPostretirementPlansPolicy",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230043001 - Disclosure - Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Tables)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesTables",
     "shortName": "Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "div",
       "us-gaap:PensionAndOtherPostretirementPlansPolicy",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R37": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230093002 - Disclosure - Fair Value Measurements (Tables)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsTables",
     "shortName": "Fair Value Measurements (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R38": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230163003 - Disclosure - Investment Securities (Tables)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesTables",
     "shortName": "Investment Securities (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R39": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PastDueFinancingReceivablesTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230233004 - Disclosure - Credit Quality And Allowance For Credit Losses (Tables)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables",
     "shortName": "Credit Quality And Allowance For Credit Losses (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PastDueFinancingReceivablesTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R4": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestAndFeeIncomeLoansAndLeasesHeldInPortfolio",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100030004 - Statement - Consolidated Statements Of Income",
     "role": "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
     "shortName": "Consolidated Statements Of Income",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestAndFeeIncomeLoansAndLeasesHeldInPortfolio",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R40": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:SchedulesOfConcentrationOfRiskOutstandingLoansAndUnusedCommitmentsFromCommercialRealEstateTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230323005 - Disclosure - Significant Group Concentrations of Credit Risk (Tables)",
     "role": "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskTables",
     "shortName": "Significant Group Concentrations of Credit Risk (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:SchedulesOfConcentrationOfRiskOutstandingLoansAndUnusedCommitmentsFromCommercialRealEstateTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R41": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PropertyPlantAndEquipmentTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230373006 - Disclosure - Premises and Equipment (Tables)",
     "role": "http://www.comerica.com/role/PremisesandEquipmentTables",
     "shortName": "Premises and Equipment (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:PropertyPlantAndEquipmentTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R42": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfGoodwillTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230403007 - Disclosure - Goodwill and Intangible Assets Goodwill and Intangible Assets (Tables)",
     "role": "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsTables",
     "shortName": "Goodwill and Intangible Assets Goodwill and Intangible Assets (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfGoodwillTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R43": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230453008 - Disclosure - Derivative And Credit-Related Financial Instruments (Tables)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables",
     "shortName": "Derivative And Credit-Related Financial Instruments (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R44": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfVariableInterestEntitiesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230553009 - Disclosure - Variable Interest Entities (VIEs) (Tables)",
     "role": "http://www.comerica.com/role/VariableInterestEntitiesVIEsTables",
     "shortName": "Variable Interest Entities (VIEs) (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfVariableInterestEntitiesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R45": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "srt:ContractualObligationFiscalYearMaturityScheduleTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230593010 - Disclosure - Deposits (Tables)",
     "role": "http://www.comerica.com/role/DepositsTables",
     "shortName": "Deposits (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "srt:ContractualObligationFiscalYearMaturityScheduleTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R46": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfShortTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230643011 - Disclosure - Short-term Borrowings Short-term Borrowings (Tables)",
     "role": "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsTables",
     "shortName": "Short-term Borrowings Short-term Borrowings (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfShortTermDebtTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R47": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDebtInstrumentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230683012 - Disclosure - Medium- And Long-Term Debt (Tables)",
     "role": "http://www.comerica.com/role/MediumAndLongTermDebtTables",
     "shortName": "Medium- And Long-Term Debt (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDebtInstrumentsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R48": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230753013 - Disclosure - Accumulated Other Comprehensive Loss (Tables)",
     "role": "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossTables",
     "shortName": "Accumulated Other Comprehensive Loss (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R49": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230783014 - Disclosure - Net Income Per Common Share (Tables)",
     "role": "http://www.comerica.com/role/NetIncomePerCommonShareTables",
     "shortName": "Net Income Per Common Share (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R5": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfSegmentReportingInformationBySegmentTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100040005 - Statement - Consolidated Statements of Comprehensive Income",
     "role": "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
     "shortName": "Consolidated Statements of Comprehensive Income",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R50": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230823015 - Disclosure - Share-Based Compensation Share-Based Compensation (Tables)",
     "role": "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables",
     "shortName": "Share-Based Compensation Share-Based Compensation (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R51": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDefinedBenefitPlansDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "230913016 - Disclosure - Employee Benefit Plans (Tables)",
     "role": "http://www.comerica.com/role/EmployeeBenefitPlansTables",
     "shortName": "Employee Benefit Plans (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfDefinedBenefitPlansDisclosuresTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R52": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231003017 - Disclosure - Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Tables)",
     "role": "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables",
     "shortName": "Income Taxes And Tax-Related Items Income Taxes And Tax-Related Items (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R53": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231103018 - Disclosure - Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Tables)",
     "role": "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsTables",
     "shortName": "Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R54": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfSegmentReportingInformationBySegmentTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231163019 - Disclosure - Business Segment Information (Tables)",
     "role": "http://www.comerica.com/role/BusinessSegmentInformationTables",
     "shortName": "Business Segment Information (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfSegmentReportingInformationBySegmentTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R55": {
     "firstAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "srt:ScheduleOfCondensedBalanceSheetTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231203020 - Disclosure - Parent Company Financial Statements Parent Company Financial Statements (Tables)",
     "role": "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsTables",
     "shortName": "Parent Company Financial Statements Parent Company Financial Statements (Tables)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": {
      "ancestors": [
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "srt:ScheduleOfCondensedBalanceSheetTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R56": {
     "firstAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231253021 - Disclosure - Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited ) (Tables)",
     "role": "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedTables",
     "shortName": "Summary of Quarterly Financial Statements (Unaudited) Summary of Quarterly Financial Statements (Unaudited ) (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R57": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisaggregationOfRevenueTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231283022 - Disclosure - Revenue from Contracts with Customers Revenue from Contracts wtih Customers (Tables)",
     "role": "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswtihCustomersTables",
     "shortName": "Revenue from Contracts with Customers Revenue from Contracts wtih Customers (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DisaggregationOfRevenueTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R58": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:LeaseExpenseTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "231313023 - Disclosure - Leases (Tables)",
     "role": "http://www.comerica.com/role/LeasesTables",
     "shortName": "Leases (Tables)",
     "subGroupType": "tables",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "cma:LeaseExpenseTableTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R59": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240034001 - Disclosure - Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
     "shortName": "Basis of Presentation and Accounting Policies Basis of Presentation and Accounting Policies (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R6": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i22c89302c55b4df69f01ad95cb30b010_I20181231",
      "decimals": "-5",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommonStockSharesOutstanding",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100050006 - Statement - Consolidated Statements Of Changes In Shareholders' Equity",
     "role": "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
     "shortName": "Consolidated Statements Of Changes In Shareholders' Equity",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i22c89302c55b4df69f01ad95cb30b010_I20181231",
      "decimals": "-5",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommonStockSharesOutstanding",
      "reportCount": 1,
      "unique": true,
      "unitRef": "shares",
      "xsiNil": "false"
     }
    },
    "R60": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240054002 - Disclosure - Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Balance Sheets)(Details)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
     "shortName": "Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Balance Sheets)(Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "us-gaap:ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock",
       "div",
       "us-gaap:PensionAndOtherPostretirementPlansPolicy",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "idbb75990153c48199599abab9714d6f4_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AccumulatedOtherComprehensiveIncomeLossNetOfTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R61": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:OtherNoninterestExpense",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240064003 - Disclosure - Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Statements of Comprehensive Income) (Details)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
     "shortName": "Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Statements of Comprehensive Income) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "cma:ScheduleOfConsolidatedStatementsOfComprehensiveIncomeWithChangeInAccountingPrincipleTableTextBlock",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i88c00371436447749c10e79a90ddabaa_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:OtherNoninterestExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R62": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i106f18272f7143ec851825323786ae45_D20211001-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240074004 - Disclosure - Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Statements of Cash Flows) (Details)",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
     "shortName": "Basis of Presentation and Accounting Policies (Change in Accounting Principle - Consolidated Statements of Cash Flows) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "cma:ScheduleOfConsolidatedStatementsOfCashFlowsWithChangeInAccountingPrincipleTableTextBlock",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i2ffb89ed1e8440efb4071e62f7d46f1c_D20200101-20201231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DeferredIncomeTaxExpenseBenefit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R63": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeFairValueOfDerivativeLiability",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240104005 - Disclosure - Fair Value Measurements (Narrative) (Details)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails",
     "shortName": "Fair Value Measurements (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i8d65f8c77e1842b5a511d119b6a8af6f_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "cma:TransfersIntoOrOutOfLevelOneOrLevelTwoOrLevelThree",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R64": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleSecuritiesDebtSecurities",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240114006 - Disclosure - Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Recurring Basis) (Details)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
     "shortName": "Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Recurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "icae6fac0f9bf4f8baae3e16da728cf36_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleSecuritiesDebtSecurities",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R65": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ia483db447c71469dbc63b583f2bd0704_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240124007 - Disclosure - Fair Value Measurements (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
     "shortName": "Fair Value Measurements (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i2c97baae1e1341b585c4240e6b032921_I20191231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R66": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnNonrecurringBasisTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ie19a199410024eca97cdd9824b9acf03_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AssetsFairValueDisclosure",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240134008 - Disclosure - Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
     "shortName": "Fair Value Measurements (Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueAssetsMeasuredOnNonrecurringBasisTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ie19a199410024eca97cdd9824b9acf03_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AssetsFairValueDisclosure",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R67": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CashAndDueFromBanks",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240144009 - Disclosure - Fair Value Measurements (Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis) (Details)",
     "role": "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
     "shortName": "Fair Value Measurements (Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FairValueByBalanceSheetGroupingTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i07fe20c4f7524693a43e82f283ba85f0_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:CashAndDueFromBanks",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R68": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "INF",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions",
      "reportCount": 1,
      "unique": true,
      "unitRef": "pure",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240174010 - Disclosure - Investment Securities (Narrative) (Details)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
     "shortName": "Investment Securities (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "INF",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions",
      "reportCount": 1,
      "unique": true,
      "unitRef": "pure",
      "xsiNil": "false"
     }
    },
    "R69": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240184011 - Disclosure - Investment Securities (Summary Of Investment Securities) (Details)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
     "shortName": "Investment Securities (Summary Of Investment Securities) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R7": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "2",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:CommonStockDividendsPerShareDeclared",
      "reportCount": 1,
      "unitRef": "usdPerShare",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100060007 - Statement - Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical)",
     "role": "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquityParenthetical",
     "shortName": "Consolidated Statements Of Changes In Shareholders' Equity (Parenthetical)",
     "subGroupType": "parenthetical",
     "uniqueAnchor": null
    },
    "R70": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240194012 - Disclosure - Investment Securities (Summary Of Investment Securities In Unrealized Loss Positions) (Details)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails",
     "shortName": "Investment Securities (Summary Of Investment Securities In Unrealized Loss Positions) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R71": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "us-gaap:ScheduleOfQuarterlyFinancialInformationTableTextBlock",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i3a7604464ca74bcf8c38fb697ea6a4d7_D20201001-20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DebtAndEquitySecuritiesGainLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240204013 - Disclosure - Investment Securities (Gains And Losses On Securities) (Details)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails",
     "shortName": "Investment Securities (Gains And Losses On Securities) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfRealizedGainLossTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ic5b06a3d64d94560a1b3e092360c5ad2_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DebtSecuritiesAvailableForSaleRealizedGain",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R72": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleDebtSecuritiesAmortizedCostBasis",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240214014 - Disclosure - Investment Securities (Contractual Maturity Distribution Of Debt Securities) (Details)",
     "role": "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
     "shortName": "Investment Securities (Contractual Maturity Distribution Of Debt Securities) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:InvestmentsClassifiedByContractualMaturityDateTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i789bc78347e2482da18b4543bcb8cc73_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R73": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoanInterestReceivable",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240244015 - Disclosure - Credit Quality And Allowance For Credit Losses (Narrative) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoanInterestReceivable",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R74": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PastDueFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoansPastDueAndStillAccruing",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240254016 - Disclosure - Credit Quality And Allowance For Credit Losses (Aging Analysis Of Loans) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Aging Analysis Of Loans) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PastDueFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:LoansPastDueAndStillAccruing",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R75": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PastDueFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LoansAndLeasesReceivableNetOfDeferredIncome",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240264017 - Disclosure - Credit Quality And Allowance For Credit Losses (Loans By Credit Quality Indicator and Vintage Year) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Loans By Credit Quality Indicator and Vintage Year) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:FinancingReceivableCreditQualityIndicatorsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableOriginatedInCurrentFiscalYear",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R76": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i89861982187449f5b120e4ddbc695618_I20201231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableAllowanceForCreditLosses",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240274018 - Disclosure - Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Loan Losses And Related Loan Amounts) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Changes In The Allowance For Loan Losses And Related Loan Amounts) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ife8ca6d914994af685183bf219d43e8c_I20181231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableAllowanceForCreditLosses",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R77": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ImpairedFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableNonaccrualNoAllowance",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240284019 - Disclosure - Credit Quality And Allowance For Credit Losses (Nonaccrual Loans) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Nonaccrual Loans) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ImpairedFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableNonaccrualNoAllowance",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R78": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ForeclosedAssets",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240294020 - Disclosure - Credit Quality And Allowance For Credit Losses Foreclosed Properties (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesForeclosedPropertiesDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses Foreclosed Properties (Details)",
     "subGroupType": "details",
     "uniqueAnchor": null
    },
    "R79": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableModificationsPostModificationRecordedInvestment2",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240304021 - Disclosure - Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings Subsequent Default) (Details)",
     "role": "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
     "shortName": "Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings Subsequent Default) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FinancingReceivableModificationsPostModificationRecordedInvestment2",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R8": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfSegmentReportingInformationBySegmentTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ProfitLoss",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "statement",
     "isDefault": "false",
     "longName": "100070008 - Statement - Consolidated Statements Of Cash Flows",
     "role": "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
     "shortName": "Consolidated Statements Of Cash Flows",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:AccretionAmortizationOfDiscountsAndPremiumsInvestments",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R80": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "2",
      "first": true,
      "lang": "en-US",
      "name": "cma:ConcentrationRiskThresholdPercentage",
      "reportCount": 1,
      "unique": true,
      "unitRef": "number",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240334022 - Disclosure - Significant Group Concentrations of Credit Risk (Narrative) (Details)",
     "role": "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskNarrativeDetails",
     "shortName": "Significant Group Concentrations of Credit Risk (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "2",
      "first": true,
      "lang": "en-US",
      "name": "cma:ConcentrationRiskThresholdPercentage",
      "reportCount": 1,
      "unique": true,
      "unitRef": "number",
      "xsiNil": "false"
     }
    },
    "R81": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PastDueFinancingReceivablesTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LoansAndLeasesReceivableNetOfDeferredIncome",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240344023 - Disclosure - Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Commercial Real Estate Exposure) (Details)",
     "role": "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails",
     "shortName": "Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Commercial Real Estate Exposure) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i68a130106a9844d2bb44c3accff68a02_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:LoansAndLeasesReceivableNetOfDeferredIncome",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R82": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:TotalAutomotiveLoans",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240354024 - Disclosure - Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Schedule of Automotive Industry Outstanding Loans and Total Exposure) (Details)",
     "role": "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails",
     "shortName": "Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Schedule of Automotive Industry Outstanding Loans and Total Exposure) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:TotalAutomotiveLoans",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R83": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PropertyPlantAndEquipmentTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:Land",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240384025 - Disclosure - Premises and Equipment Summary of Premises and Equipment (Details)",
     "role": "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails",
     "shortName": "Premises and Equipment Summary of Premises and Equipment (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:PropertyPlantAndEquipmentTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:Land",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R84": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ia117a5a96ec84b988e2099395e1762c0_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AmortizationOfIntangibleAssets",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240414026 - Disclosure - Goodwill and Intangible Assets Goodwill and Intangible Assets (Narrative) (Details)",
     "role": "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
     "shortName": "Goodwill and Intangible Assets Goodwill and Intangible Assets (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ia117a5a96ec84b988e2099395e1762c0_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:AmortizationOfIntangibleAssets",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R85": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfGoodwillTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:Goodwill",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240424027 - Disclosure - Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of Changes in Carrying Value of Goodwill) (Details)",
     "role": "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
     "shortName": "Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of Changes in Carrying Value of Goodwill) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfGoodwillTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:Goodwill",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R86": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAcquiredFiniteLivedIntangibleAssetsByMajorClassTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i17cbd5aa82c64d49b276934234b9e1f0_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FiniteLivedIntangibleAssetsGross",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240434028 - Disclosure - Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of CDI Carrying Value and Amortization) (Details)",
     "role": "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails",
     "shortName": "Goodwill and Intangible Assets Goodwill and Intangible Assets (Summary of CDI Carrying Value and Amortization) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfAcquiredFiniteLivedIntangibleAssetsByMajorClassTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i17cbd5aa82c64d49b276934234b9e1f0_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:FiniteLivedIntangibleAssetsGross",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R87": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:DerivativeAssetsCashCollateral",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240464029 - Disclosure - Derivative And Credit-Related Financial Instruments (Narrative) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:DerivativeAssetsCashCollateral",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R88": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeNotionalAmount",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240474030 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Derivative Instruments) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Schedule Of Derivative Instruments) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "ix:continuation",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:DerivativeAssetFairValueGrossLiability",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R89": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:EffectsOfFairValueHedgingOnTheConsolidatedStatementsOfComprehensiveIncomeTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:InterestExpenseLongTermDebt",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240484031 - Disclosure - Derivative And Credit-Related Financial Instruments Derivative And Credit-Related Financial Instruments (Schedule of Effects of Fair Value Hedging on the Consolidated Statements of Comprehensive Income) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments Derivative And Credit-Related Financial Instruments (Schedule of Effects of Fair Value Hedging on the Consolidated Statements of Comprehensive Income) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:EffectsOfFairValueHedgingOnTheConsolidatedStatementsOfComprehensiveIncomeTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i270b3f90b5b147739bf0dce0cce9bad8_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "cma:Interestexpenseonhedgedmediumandlongtermdebt",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R9": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:BasisOfPresentationAndSignificantAccountingPoliciesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "210011001 - Disclosure - Basis of Presentation and Accounting Policies",
     "role": "http://www.comerica.com/role/BasisofPresentationandAccountingPolicies",
     "shortName": "Basis of Presentation and Accounting Policies",
     "subGroupType": "",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": null,
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:BasisOfPresentationAndSignificantAccountingPoliciesTextBlock",
      "reportCount": 1,
      "unique": true,
      "unitRef": null,
      "xsiNil": "false"
     }
    },
    "R90": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ib9c89b25657c409ea88a7fe7a17bfc65_I20211231",
      "decimals": "4",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeAverageFixedInterestRate",
      "reportCount": 1,
      "unique": true,
      "unitRef": "number",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240494032 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ib9c89b25657c409ea88a7fe7a17bfc65_I20211231",
      "decimals": "4",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeAverageFixedInterestRate",
      "reportCount": 1,
      "unique": true,
      "unitRef": "number",
      "xsiNil": "false"
     }
    },
    "R91": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i76f5638eba164910ba164f811a5e7bec_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:Carryingvalueofhedgeditem",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240504033 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Fair Value Swaps) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Fair Value Swaps) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i76f5638eba164910ba164f811a5e7bec_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:Carryingvalueofhedgeditem",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R92": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "iae61f89c99824b0fad3ea12b82ad96cb_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeGainLossOnDerivativeNet",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240514034 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "iae61f89c99824b0fad3ea12b82ad96cb_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:DerivativeGainLossOnDerivativeNet",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R93": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i895b23db6c9a4c5c91a92a0f9c5bbae4_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LossContingencyEstimateOfPossibleLoss",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240524035 - Disclosure - Derivative And Credit-Related Financial Instruments (Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "ix:continuation",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i895b23db6c9a4c5c91a92a0f9c5bbae4_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:LossContingencyEstimateOfPossibleLoss",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R94": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfInternallyClassifiedWatchListLettersOfCreditTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:TotalInternallyClassifiedWatchListLettersOfCredit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240534036 - Disclosure - Derivative And Credit-Related Financial Instruments (Summary Of Criticized Letters Of Credit) (Details)",
     "role": "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsSummaryOfCriticizedLettersOfCreditDetails",
     "shortName": "Derivative And Credit-Related Financial Instruments (Summary Of Criticized Letters Of Credit) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfInternallyClassifiedWatchListLettersOfCreditTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:TotalInternallyClassifiedWatchListLettersOfCredit",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R95": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:VariableInterestEntityActivityBetweenVIEAndEntityExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240564037 - Disclosure - Variable Interest Entities (VIEs) (Narrative) (Details)",
     "role": "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails",
     "shortName": "Variable Interest Entities (VIEs) (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:VariableInterestEntityActivityBetweenVIEAndEntityExpense",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R96": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ibb993871bb244a2b9329865516a2d152_D20210101-20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:NoninterestIncomeOtherOperatingIncome",
      "reportCount": 1,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240574038 - Disclosure - Variable Interest Entities (VIEs) (Impact Of VIEs On The Consolidated Statements Of Comprehensive Income) (Details)",
     "role": "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails",
     "shortName": "Variable Interest Entities (VIEs) (Impact Of VIEs On The Consolidated Statements Of Comprehensive Income) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "us-gaap:ScheduleOfVariableInterestEntitiesTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i1c67ae58dfd34b719645c11ccdc31453_D20210101-20211231",
      "decimals": "-6",
      "lang": "en-US",
      "name": "us-gaap:NoninterestIncomeOtherOperatingIncome",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R97": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:DomesticTimeDeposits250000orMore",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240604039 - Disclosure - Deposits Deposits (Narrative) (Details)",
     "role": "http://www.comerica.com/role/DepositsDepositsNarrativeDetails",
     "shortName": "Deposits Deposits (Narrative) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "div",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "cma:DomesticTimeDeposits250000orMore",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R98": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "srt:ContractualObligationFiscalYearMaturityScheduleTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:TimeDepositMaturitiesNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240614040 - Disclosure - Deposits Deposits (Schedule of Maturities of Certificates of Deposit and Other Deposits with a Stated Maturity) (Details)",
     "role": "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails",
     "shortName": "Deposits Deposits (Schedule of Maturities of Certificates of Deposit and Other Deposits with a Stated Maturity) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "srt:ContractualObligationFiscalYearMaturityScheduleTableTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "ica8f9c6ab1974ac295dd4703d633a5e2_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:TimeDepositMaturitiesNextRollingTwelveMonths",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    },
    "R99": {
     "firstAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfContractualMaturitiesOfTimeDepositsOfOneHundredThousandOrMoreTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i6949e44d04704fa9970faf0ad4d6ac4c_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsOrLess",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     },
     "groupType": "disclosure",
     "isDefault": "false",
     "longName": "240624041 - Disclosure - Deposits Deposits (Schedule of Maturities of Domestic Deposits of One Hundred Thousand or More) (Details)",
     "role": "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails",
     "shortName": "Deposits Deposits (Schedule of Maturities of Domestic Deposits of One Hundred Thousand or More) (Details)",
     "subGroupType": "details",
     "uniqueAnchor": {
      "ancestors": [
       "span",
       "td",
       "tr",
       "table",
       "div",
       "cma:ScheduleOfContractualMaturitiesOfTimeDepositsOfOneHundredThousandOrMoreTextBlock",
       "ix:continuation",
       "body",
       "html"
      ],
      "baseRef": "cma-20211231.htm",
      "contextRef": "i6949e44d04704fa9970faf0ad4d6ac4c_I20211231",
      "decimals": "-6",
      "first": true,
      "lang": "en-US",
      "name": "us-gaap:ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsOrLess",
      "reportCount": 1,
      "unique": true,
      "unitRef": "usd",
      "xsiNil": "false"
     }
    }
   },
   "segmentCount": 146,
   "tag": {
    "cma_A3.70NotesDue2023Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "3.70% Notes Due 2023 [Member]",
        "label": "3.70% Notes Due 2023 [Member]",
        "terseLabel": "3.70% notes due 2023"
       }
      }
     },
     "localname": "A3.70NotesDue2023Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_A4.00NotesDue2029Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "4.00% Notes Due 2029 [Member]",
        "label": "4.00% Notes Due 2029 [Member]",
        "terseLabel": "4.00% notes due 2029"
       }
      }
     },
     "localname": "A4.00NotesDue2029Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_AdvanceToSubsidiaryBank": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Advance to subsidiary bank",
        "label": "Advance to subsidiary bank",
        "terseLabel": "Advance to subsidiary bank"
       }
      }
     },
     "localname": "AdvanceToSubsidiaryBank",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AllowanceForCreditLossesPolicyTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy and method for estimating the allowance for losses on loans and lease receivables. The description may include (a) how the entity determines each element of the allowance, (b) which loans are evaluated individually and which loans are evaluated as a group, (c) how the entity determines both the allocated and unallocated portions of the allowance, (d) how the entity determines the loss factors applied to graded loans in order to develop a general allowance, and (e) what self-correcting mechanism the entity uses to reduce differences between estimated and actual losses. Also describes the policy and method for estimating the allowance for credit losses inherent in lending-related commitments, including unused commitments to extend credit, letters of credit and financial guarantees.",
        "label": "Allowance For Credit Losses [Policy Text Block]",
        "terseLabel": "Allowance for Credit Losses"
       }
      }
     },
     "localname": "AllowanceForCreditLossesPolicyTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_AllowanceForOffBalanceSheetCreditLosses": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Allowance For Off Balance Sheet Credit Losses",
        "label": "Allowance For Off Balance Sheet Credit Losses",
        "terseLabel": "Allowance for credit losses on lending-related commitments"
       }
      }
     },
     "localname": "AllowanceForOffBalanceSheetCreditLosses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AssetsFairValueDisclosureExcludingAssetsValuedatNAV": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total assets at fair value in the fair value hierarchy valued on a nonrecurring basis.",
        "label": "Assets, Fair Value Disclosure, Excluding Assets Valued at NAV",
        "terseLabel": "Fair value of plan assets in qualified defined benefit pension plan, Excluding assets valued at net asset value"
       }
      }
     },
     "localname": "AssetsFairValueDisclosureExcludingAssetsValuedatNAV",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AutomotiveDealerMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Automotive Dealer [Member]",
        "label": "Automotive Dealer [Member]",
        "terseLabel": "Automotive Dealer"
       }
      }
     },
     "localname": "AutomotiveDealerMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_AutomotiveProductionMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Automotive Production [Member]",
        "label": "Automotive Production [Member]",
        "terseLabel": "Automotive Production"
       }
      }
     },
     "localname": "AutomotiveProductionMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_AverageAssetsForLeverage": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average total assets for leverage ratio as defined in the regulations.",
        "label": "Average Assets For Leverage",
        "terseLabel": "Average assets (fourth quarter)"
       }
      }
     },
     "localname": "AverageAssetsForLeverage",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AverageBalanceDuringPeriodDeposits": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate average balances of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.",
        "label": "Average Balance During Period Deposits",
        "terseLabel": "Deposits, average"
       }
      }
     },
     "localname": "AverageBalanceDuringPeriodDeposits",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AverageBalanceDuringPeriodLoansAndLeasesReceivableNetOfDeferredIncome": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the average aggregate gross carrying amount of all categories of loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on loans and leases.",
        "label": "Average Balance During Period Loans And Leases Receivable Net Of Deferred Income",
        "verboseLabel": "Loans, average"
       }
      }
     },
     "localname": "AverageBalanceDuringPeriodLoansAndLeasesReceivableNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_AverageReserveRequirement": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The average amount of reserves required to be maintained at the Federal Reserve based on the level of customer deposits in banking subsidiaries during the period.",
        "label": "Average Reserve Requirement",
        "terseLabel": "Federal Reserve Bank average reserve requirement"
       }
      }
     },
     "localname": "AverageReserveRequirement",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_BalanceAtBeginningAndEndOfPeriod": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Balance at beginning and end of period",
        "label": "Balance at beginning and end of period",
        "periodEndLabel": "Balance at end of period",
        "periodStartLabel": "Balance at beginning of period"
       }
      }
     },
     "localname": "BalanceAtBeginningAndEndOfPeriod",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_BankcardHomeEquityAndOtherMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Bankcard, home equity and other similar lines of credit.",
        "label": "Bankcard Home Equity And Other Member",
        "terseLabel": "Bankcard, Revolving Check Credit And Home Equity Loan Commitments"
       }
      }
     },
     "localname": "BankcardHomeEquityAndOtherMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_BrokerageCommissionsRevenueMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Brokerage Commissions Revenue [Member]",
        "label": "Brokerage Commissions Revenue [Member]",
        "terseLabel": "Brokerage fees"
       }
      }
     },
     "localname": "BrokerageCommissionsRevenueMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_BusinessBankMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Business Bank",
        "label": "Business Bank [Member]",
        "terseLabel": "Commercial Bank"
       }
      }
     },
     "localname": "BusinessBankMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_BusinessLoansMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Portfolio segment of financing receivables related to business financing receivables.",
        "label": "Business Loans Member",
        "terseLabel": "Business Loans"
       }
      }
     },
     "localname": "BusinessLoansMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CET1CapitalToRiskWeightedAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "CET1 capital to risk-weighted assets",
        "label": "CET1 capital to risk-weighted assets",
        "terseLabel": "CET1 capital to risk-weighted assets"
       }
      }
     },
     "localname": "CET1CapitalToRiskWeightedAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_CardFees": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 4.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Card Fees",
        "label": "Card Fees",
        "terseLabel": "Card fees"
       }
      }
     },
     "localname": "CardFees",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CarryingValueOfStandbyAndCommercialLettersOfCredit": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value of standby and commercial letters of credit included in accrued expenses and other liabilities on the consolidated balance sheet.",
        "label": "Carrying Value Of Standby And Commercial Letters Of Credit",
        "terseLabel": "Carrying value of standby and commercial letters of credit included in accrued expenses and other liabilities"
       }
      }
     },
     "localname": "CarryingValueOfStandbyAndCommercialLettersOfCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CarryingValueOfStandbyAndCommercialLettersOfCreditIncludedInAllowanceForCreditLossesOnLendingRelatedCommitments": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value of standby and commercial letters of credit included in the allowance for lending-related commitments.",
        "label": "Carrying Value Of Standby And Commercial Letters Of Credit Included In Allowance For Credit Losses On Lending Related Commitments",
        "verboseLabel": "Allowance for credit losses on lending-related commitments, amount related to standby and commercial letters of credit"
       }
      }
     },
     "localname": "CarryingValueOfStandbyAndCommercialLettersOfCreditIncludedInAllowanceForCreditLossesOnLendingRelatedCommitments",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CarryingValueOfStandbyAndCommercialLettersOfCreditIncludedInDeferredFees": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value of standby and commercial letters of credit included in deferred fees.",
        "label": "Carrying Value Of Standby And Commercial Letters Of Credit Included In Deferred Fees",
        "verboseLabel": "Deferred fees on standby and commercial letters of credit included in accrued expenses and other liabilities"
       }
      }
     },
     "localname": "CarryingValueOfStandbyAndCommercialLettersOfCreditIncludedInDeferredFees",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CarryingValueOfUnusedCommitmentsToExtendCredit": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value of unused commitments to extend credit, included in the allowance for credit losses on lending-related commitments.",
        "label": "Carrying Value Of Unused Commitments To Extend Credit",
        "verboseLabel": "Allowance for credit losses on lending-related commitments, unused commitments to extend credit"
       }
      }
     },
     "localname": "CarryingValueOfUnusedCommitmentsToExtendCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Carryingvalueofhedgeditem": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying value of hedged debt",
        "label": "Carryingvalueofhedgeditem",
        "terseLabel": "Carrying Value of Hedged Item"
       }
      }
     },
     "localname": "Carryingvalueofhedgeditem",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CashCollateralPostedForDerivativesInLiabilityPosition": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cash Collateral Posted For Derivatives In Liability Position. Includes both the amount of cash offset against derivative liabilities under master netting arrangments and amounts not offset.",
        "label": "Cash Collateral Posted For Derivatives In Liability Position",
        "terseLabel": "Cash posted as collateral for derivative liabilities"
       }
      }
     },
     "localname": "CashCollateralPostedForDerivativesInLiabilityPosition",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CashDividendsPaidToParentCompanyByBankSubsidiaries": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents disclosure of the aggregate cash dividends paid to the entity by bank subsidiaries.",
        "label": "Cash Dividends Paid To Parent Company By Bank Subsidiaries",
        "terseLabel": "Dividends from bank subsidiaries"
       }
      }
     },
     "localname": "CashDividendsPaidToParentCompanyByBankSubsidiaries",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CertificatesOfDepositAndOtherDepositsWithStatedMaturityAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Certificates of Deposit and Other Deposits with a Stated Maturity [Axis]",
        "label": "Certificates of Deposit and Other Deposits with a Stated Maturity [Axis]",
        "terseLabel": "Certificates of Deposit and Other Deposits with a Stated Maturity [Axis]"
       }
      }
     },
     "localname": "CertificatesOfDepositAndOtherDepositsWithStatedMaturityAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_CertificatesOfDepositAndOtherDepositsWithStatedMaturityDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Certificates of Deposit and Other Deposits with a Stated Maturity [Domain]",
        "label": "Certificates of Deposit and Other Deposits with a Stated Maturity [Domain]",
        "terseLabel": "Certificates of Deposit and Other Deposits with a Stated Maturity [Domain]"
       }
      }
     },
     "localname": "CertificatesOfDepositAndOtherDepositsWithStatedMaturityDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ChangeInAccountingPrincipleConsolidatedBalanceSheetsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Change in Accounting Principle - Consolidated Balance Sheets [Line Items]",
        "label": "Change in Accounting Principle - Consolidated Balance Sheets [Line Items]",
        "terseLabel": "Change in Accounting Principle - Consolidated Balance Sheets [Line Items]"
       }
      }
     },
     "localname": "ChangeInAccountingPrincipleConsolidatedBalanceSheetsLineItems",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_ChangeInAccountingPrincipleConsolidatedBalanceSheetsTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Change in Accounting Principle - Consolidated Balance Sheets",
        "label": "Change in Accounting Principle - Consolidated Balance Sheets [Table]",
        "terseLabel": "Change in Accounting Principle - Consolidated Balance Sheets [Table]"
       }
      }
     },
     "localname": "ChangeInAccountingPrincipleConsolidatedBalanceSheetsTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_ChangeInAccountingPrincipleConsolidatedStatementsOfCashFlowsTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Change in Accounting Principle - Consolidated Statements of Cash Flows",
        "label": "Change in Accounting Principle - Consolidated Statements of Cash Flows [Table]",
        "terseLabel": "Change in Accounting Principle - Consolidated Statements of Cash Flows [Table]"
       }
      }
     },
     "localname": "ChangeInAccountingPrincipleConsolidatedStatementsOfCashFlowsTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_ChangeInAccountingPrincipleConsolidatedStatementsOfComprehensiveIncomeTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Change in Accounting Principle - Consolidated Statements of Comprehensive Income",
        "label": "Change in Accounting Principle - Consolidated Statements of Comprehensive Income [Table]",
        "terseLabel": "Change in Accounting Principle - Consolidated Statements of Comprehensive Income [Table]"
       }
      }
     },
     "localname": "ChangeInAccountingPrincipleConsolidatedStatementsOfComprehensiveIncomeTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_CollectiveInvestmentFundsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Collective Investment Funds [Member]",
        "label": "Collective Investment Funds [Member]",
        "terseLabel": "Collective investments funds"
       }
      }
     },
     "localname": "CollectiveInvestmentFundsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ComericaBankMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Subsidiary Bank[Member]",
        "label": "Comerica Bank [Member]",
        "terseLabel": "Comerica Bank"
       }
      }
     },
     "localname": "ComericaBankMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ComericaIncorporatedMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Comerica Incorporated [Member]",
        "label": "Comerica Incorporated [Member]",
        "terseLabel": "Comerica Incorporated"
       }
      }
     },
     "localname": "ComericaIncorporatedMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CommercialAndOtherMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Commercial and other loans.",
        "label": "Commercial And Other Member",
        "terseLabel": "Commercial And Other"
       }
      }
     },
     "localname": "CommercialAndOtherMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CommercialLendingFees": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 3.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The noninterest fee income derived from Commercial Lending activities (fees and commissions).",
        "label": "Commercial Lending Fees",
        "terseLabel": "Commercial lending fees"
       }
      }
     },
     "localname": "CommercialLendingFees",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CommercialRealEstateBusinessLineMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financing receivables included in the Commercial Real Estate line of business.",
        "label": "Commercial Real Estate business line [Member]",
        "terseLabel": "Commercial Real Estate business line"
       }
      }
     },
     "localname": "CommercialRealEstateBusinessLineMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CommercialRealEstateLineOfBusinessClassificationAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Determination of whether a commercial real estate financing receivable is in the Commercial Real Estate business line or in an other business line.",
        "label": "Commercial Real Estate Line of Business Classification [Axis]",
        "terseLabel": "Commercial Real Estate Line of Business Classification [Axis]"
       }
      }
     },
     "localname": "CommercialRealEstateLineOfBusinessClassificationAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_CommercialRealEstateLineOfBusinessClassificationDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Domain] for Commercial Real Estate Line of Business Classification",
        "label": "Commercial Real Estate Line of Business Classification [Domain]",
        "terseLabel": "Commercial Real Estate Line of Business Classification [Domain]"
       }
      }
     },
     "localname": "CommercialRealEstateLineOfBusinessClassificationDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Common Equity Tier One Capital Required To Be Well Capitalized To Risk Weighted Assets",
        "label": "CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets",
        "terseLabel": "CET1 risk-based capital"
       }
      }
     },
     "localname": "CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_CommonEquityTierOneRiskedBasedCapital": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Common Equity Tier One Risked Based as defined in the regulations.",
        "label": "Common Equity Tier One Risked Based Capital",
        "terseLabel": "CET 1 capital"
       }
      }
     },
     "localname": "CommonEquityTierOneRiskedBasedCapital",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_ConcentrationRiskThresholdPercentage": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Concentration risk threshold percentage",
        "label": "Concentration risk threshold percentage",
        "terseLabel": "Concentration risk threshold percentage"
       }
      }
     },
     "localname": "ConcentrationRiskThresholdPercentage",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_ConservationBuffer": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Conservation buffer",
        "label": "Conservation buffer",
        "terseLabel": "Conservation buffer"
       }
      }
     },
     "localname": "ConservationBuffer",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_ConsumerFinancingReceivableMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Class of financing receivables related to total consumer financing receivables.",
        "label": "Consumer Financing Receivable Member",
        "terseLabel": "Other consumer"
       }
      }
     },
     "localname": "ConsumerFinancingReceivableMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CorporateAndMunicipalBondsAndNotesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Corporate and Municipal Bonds and Notes [Member]",
        "label": "Corporate and Municipal Bonds and Notes [Member]",
        "terseLabel": "Corporate and municipal bonds and notes"
       }
      }
     },
     "localname": "CorporateAndMunicipalBondsAndNotesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CreditQualityAndAllowanceForCreditLossesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "-- None. No documentation exists for this element. --",
        "label": "Credit Quality And Allowance For Credit Losses [Abstract]",
        "terseLabel": "Credit Quality And Allowance For Credit Losses [Abstract]"
       }
      }
     },
     "localname": "CreditQualityAndAllowanceForCreditLossesAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_CreditRelatedFinancialInstruments": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value of credit-related financial instruments included in accrued expenses and other liabilities, including unused commitments to extend credit, letters of credit and financial guarantees. Includes the allowance for credit losses on lending-related commitments and the current amortized value of the guarantee liability recognized at fair value at inception of the commitment.",
        "label": "Credit Related Financial Instruments",
        "negatedTerseLabel": "Credit-related financial instruments"
       }
      }
     },
     "localname": "CreditRelatedFinancialInstruments",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CreditRelatedFinancialInstrumentsAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Credit related financial instruments.",
        "label": "Credit Related Financial Instruments [Axis]",
        "terseLabel": "Credit Related Financial Instruments [Axis]"
       }
      }
     },
     "localname": "CreditRelatedFinancialInstrumentsAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_CreditRelatedFinancialInstrumentsDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Credit related financial instruments.",
        "label": "Credit Related Financial Instruments [Domain]",
        "terseLabel": "Credit Related Financial Instruments [Domain]"
       }
      }
     },
     "localname": "CreditRelatedFinancialInstrumentsDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_CreditRelatedFinancialInstrumentsTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Credit Related Financial Instruments [Table]",
        "label": "Credit Related Financial Instruments [Table]",
        "terseLabel": "Credit Related Financial Instruments Axis [Table]"
       }
      }
     },
     "localname": "CreditRelatedFinancialInstrumentsTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_CreditRiskFinancialInstrumentsOffBalanceSheetRiskTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of financial instruments, excluding certain derivatives, with off-balance sheet credit risk (for example, unused commitments, standby letters of credit or financial guarantees).",
        "label": "Credit Risk Financial Instruments Off Balance Sheet Risk [Table Text Block]",
        "terseLabel": "Schedule Of Financial Instruments With Off-Balance Sheet Credit Risk"
       }
      }
     },
     "localname": "CreditRiskFinancialInstrumentsOffBalanceSheetRiskTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_CumulativeEffectOfChangeInAccountingPrinciple": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cumulative effect of change in accounting principle",
        "label": "Cumulative effect of change in accounting principle",
        "terseLabel": "Cumulative effect of change in accounting principle"
       }
      }
     },
     "localname": "CumulativeEffectOfChangeInAccountingPrinciple",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CurrentLoans": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Current loans",
        "label": "Current loans",
        "terseLabel": "Current loans"
       }
      }
     },
     "localname": "CurrentLoans",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_CustomerInitiatedAndOtherActivitiesDerivativesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative contracts entered into to meet the financing needs of customers (i.e., not designated as hedging instruments), including any offsetting positions taken by the company to mitigate associated market risk.",
        "label": "Customer Initiated And Other Activities Derivatives Member",
        "terseLabel": "Customer-initiated and other activities"
       }
      }
     },
     "localname": "CustomerInitiatedAndOtherActivitiesDerivativesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_Dayonedecreaseintheoverallallowanceforcreditlosses": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Day-one decrease in the overall allowance for credit losses",
        "label": "Day-one decrease in the overall allowance for credit losses",
        "terseLabel": "Day-one decrease in the overall allowance for credit losses"
       }
      }
     },
     "localname": "Dayonedecreaseintheoverallallowanceforcreditlosses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Dayspastduedefinedassubsequentdefault": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Days that a principal or interest payment is past due to be defined as a subsequent default",
        "label": "Days past due defined as subsequent default",
        "terseLabel": "Minimum period loan terms were extended"
       }
      }
     },
     "localname": "Dayspastduedefinedassubsequentdefault",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_DebtInstrumentMaturityYear": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Debt Instrument, Maturity Year",
        "label": "Debt Instrument, Maturity Year",
        "terseLabel": "Maturity year"
       }
      }
     },
     "localname": "DebtInstrumentMaturityYear",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "gYearItemType"
    },
    "cma_DeferredCompensationPlanAssetsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred compensation plan assets",
        "label": "Deferred Compensation Plan Assets Member",
        "terseLabel": "Deferred compensation plan assets"
       }
      }
     },
     "localname": "DeferredCompensationPlanAssetsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_DeferredTaxAssetsDeferredLoanOrginationFeesAndCosts": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from deferred loan origination fees and costs which can only be deducted for tax purposes when the loan has matured or been sold, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken.",
        "label": "Deferred Tax Assets Deferred Loan Orgination Fees And Costs",
        "terseLabel": "Deferred loan origination fees and costs"
       }
      }
     },
     "localname": "DeferredTaxAssetsDeferredLoanOrginationFeesAndCosts",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsFederalValuationAllowance": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred tax assets, federal valuation allowance",
        "label": "Deferred tax assets, federal valuation allowance",
        "terseLabel": "Deferred tax assets, federal valuation allowance"
       }
      }
     },
     "localname": "DeferredTaxAssetsFederalValuationAllowance",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsNetUnrealizedGainsOnInvestmentSecuritiesAvailableForSale": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Assets, net unrealized gains on investment securities available-for-sale",
        "label": "Deferred Tax Assets, net unrealized gains on investment securities available-for-sale",
        "terseLabel": "Net unrealized gains on investment securities available-for-sale"
       }
      }
     },
     "localname": "DeferredTaxAssetsNetUnrealizedGainsOnInvestmentSecuritiesAvailableForSale",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsOperatingLeaseLiability": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Assets, Operating Lease Liability",
        "label": "Deferred Tax Assets, Operating Lease Liability",
        "terseLabel": "Operating lease liabilities"
       }
      }
     },
     "localname": "DeferredTaxAssetsOperatingLeaseLiability",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsOperatingLossCarryforwardsFederal": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Assets, Operating Loss Carryforwards, Federal",
        "label": "Deferred Tax Assets, Operating Loss Carryforwards, Federal",
        "terseLabel": "Deferred Tax Assets, Operating Loss Carryforwards, Federal"
       }
      }
     },
     "localname": "DeferredTaxAssetsOperatingLossCarryforwardsFederal",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsOperatingLossCarryforwardsState": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Assets, Operating Loss Carryforwards, State",
        "label": "Deferred Tax Assets, Operating Loss Carryforwards, State",
        "terseLabel": "Deferred Tax Assets, Operating Loss Carryforwards, State"
       }
      }
     },
     "localname": "DeferredTaxAssetsOperatingLossCarryforwardsState",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxAssetsStateValuationAllowance": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred tax assets, state valuation allowance",
        "label": "Deferred tax assets, state valuation allowance",
        "terseLabel": "Deferred tax assets, state valuation allowance"
       }
      }
     },
     "localname": "DeferredTaxAssetsStateValuationAllowance",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxLiabilitiesTaxDeferredIncomeCompensationandBenefitsPensions": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Liabilities, Tax Deferred Income, Compensation and Benefits, Pensions",
        "label": "Deferred Tax Liabilities, Tax Deferred Income, Compensation and Benefits, Pensions",
        "negatedLabel": "Defined benefit plans"
       }
      }
     },
     "localname": "DeferredTaxLiabilitiesTaxDeferredIncomeCompensationandBenefitsPensions",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxLiabilityHedginggainsandlosses": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Liability, Hedging gains and losses",
        "label": "Deferred Tax Liability, Hedging gains and losses",
        "negatedLabel": "Net hedging gains"
       }
      }
     },
     "localname": "DeferredTaxLiabilityHedginggainsandlosses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxLiabilityLeaseRightofUseAsset": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Liability, Lease Right of Use Asset",
        "label": "Deferred Tax Liability, Lease Right of Use Asset",
        "negatedLabel": "Leasing right of use assets"
       }
      }
     },
     "localname": "DeferredTaxLiabilityLeaseRightofUseAsset",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DeferredTaxLiabilitynetunrealizedgainsoninvestmentsecuritiesavailableforsale": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Deferred Tax Liability, net unrealized gains on investment securities available-for-sale",
        "label": "Deferred Tax Liability, net unrealized gains on investment securities available-for-sale",
        "negatedLabel": "Net unrealized gains on investment securities available-for-sale"
       }
      }
     },
     "localname": "DeferredTaxLiabilitynetunrealizedgainsoninvestmentsecuritiesavailableforsale",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DefinedBenefitPlanActualRateOfReturnOnPlanAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The rate of return on plan assets reflecting the average rate of earnings on the funds invested during the period.",
        "label": "Defined Benefit Plan Actual Rate Of Return On Plan Assets",
        "terseLabel": "Actual rate of return on plan assets, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanActualRateOfReturnOnPlanAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_DefinedBenefitPlanActuarialGainLossAmortizationAdjustmentAllowablePercentage": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Minimum percentage by which the actuarial net gain/loss amortization adjustment included in net periodic defined benefit pension expense must exceeds the greater of the projected benefit obligation or the market-related value of plan assets to be included as a component of net periodic defined benefit pension cost.",
        "label": "Defined Benefit Plan Actuarial Gain Loss Amortization Adjustment, Allowable Percentage",
        "terseLabel": "Defined Benefit Plan Actuarial Gain Loss Amortization Adjustment, Allowable Percentage"
       }
      }
     },
     "localname": "DefinedBenefitPlanActuarialGainLossAmortizationAdjustmentAllowablePercentage",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_DefinedBenefitPlanHealthCareCostTrendRateInCurrentYearExpense": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The assumed health care cost trend rate reflected in net periodic defined benefit cost for the period.",
        "label": "Defined Benefit Plan, Health Care Cost Trend Rate In Current Year Expense",
        "terseLabel": "Health care cost trend rate assumed"
       }
      }
     },
     "localname": "DefinedBenefitPlanHealthCareCostTrendRateInCurrentYearExpense",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_DefinedBenefitPlanInvestmentGainLossAmortizationAdjustmentAllowablePercentage": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Maximum allowable percentage by which the investement gain/loss amortization adjustment included in net periodic defined benefit pension expense is allowed to exceed the fair value of plan assets.",
        "label": "Defined Benefit Plan Investment Gain Loss Amortization Adjustment, Allowable Percentage",
        "terseLabel": "Defined Benefit Plan Investment Gain Loss Amortization Adjustment, Allowable Percentage"
       }
      }
     },
     "localname": "DefinedBenefitPlanInvestmentGainLossAmortizationAdjustmentAllowablePercentage",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_DefinedBenefitPlanMarketRelatedValuePlanAssetsAmortizationPeriod": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Period over which the current year's investment gains and losses (actual investment return net of expected investment return) are amortized to determine market-related value of plan assets for the defined benefit pension.",
        "label": "Defined benefit plan market-related value plan assets amortization period",
        "terseLabel": "Defined Benefit Plan Market-related Value Plan Assets, Amortization Period"
       }
      }
     },
     "localname": "DefinedBenefitPlanMarketRelatedValuePlanAssetsAmortizationPeriod",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_DefinedBenefitPlanYearThatReachesUltimateTrendRateInCurrentExpense": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense",
        "label": "Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense",
        "terseLabel": "Defined Benefit Plan Year That Reaches Ultimate Trend Rate In Current Expense"
       }
      }
     },
     "localname": "DefinedBenefitPlanYearThatReachesUltimateTrendRateInCurrentExpense",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "gYearItemType"
    },
    "cma_DelinquencyStatusUnpaidScheduledMonthlyPayment": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Delinquency Status, Unpaid Scheduled Monthly Payment",
        "label": "Delinquency Status, Unpaid Scheduled Monthly Payment",
        "terseLabel": "Delinquency Status, Period of Unpaid Scheduled Monthly Payment"
       }
      }
     },
     "localname": "DelinquencyStatusUnpaidScheduledMonthlyPayment",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_DepositorySharesIssued": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Depository Shares, Issued",
        "label": "Depository Shares, Issued",
        "terseLabel": "Depository Shares, Issued"
       }
      }
     },
     "localname": "DepositorySharesIssued",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "cma_DepositsCustomerCertificatesDeposits": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 3.0,
       "parentTag": "us-gaap_InterestBearingDepositLiabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Certificates of deposit, including individual retirement accounts, other than those issued to local and national institutional depositors or acquired from brokers.",
        "label": "Deposits, Customer Certificates Deposits",
        "terseLabel": "Customer certificates of deposit"
       }
      }
     },
     "localname": "DepositsCustomerCertificatesDeposits",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DerivativeAssetsCashCollateral": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The total value of cash collateral received from counterparties to secure the fair value of derivative contracts in an unrealized gain position. Includes both the amount offset against derivative assets under master netting arrangements as well as cash collateral that has not been offset.",
        "label": "Derivative Assets Cash Collateral",
        "terseLabel": "Cash received as collateral for derivative assets"
       }
      }
     },
     "localname": "DerivativeAssetsCashCollateral",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_DerivativePurposeAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative Purpose [Axis]",
        "label": "Derivative Purpose [Axis]",
        "terseLabel": "Derivative Purpose [Axis]"
       }
      }
     },
     "localname": "DerivativePurposeAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_DerivativePurposeDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Domain] for Derivative Purpose [Axis]",
        "label": "Derivative Purpose [Domain]",
        "terseLabel": "Derivative Purpose [Domain]"
       }
      }
     },
     "localname": "DerivativePurposeDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_DocumentAndEntityInformationAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "-- None. No documentation exists for this element. --",
        "label": "Document And Entity Information [Abstract]",
        "terseLabel": "Document And Entity Information [Abstract]"
       }
      }
     },
     "localname": "DocumentAndEntityInformationAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_DomesticCertificatesOfDepositAndOtherDepositsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Domestic Certificates of Deposit and Other Deposits [Member]",
        "label": "Domestic Certificates of Deposit and Other Deposits [Member]",
        "terseLabel": "Domestic certificates of deposit and other deposits"
       }
      }
     },
     "localname": "DomesticCertificatesOfDepositAndOtherDepositsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_DomesticTimeDeposits250000orMore": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate amount of time deposit accounts (including certificates of deposit) in denominations that meet or exceed the FDIC insurance limit at the balance sheet date.",
        "label": "Domestic Time Deposits $250,000 or More",
        "terseLabel": "Domestic certificates of deposit of $250,000 or more"
       }
      }
     },
     "localname": "DomesticTimeDeposits250000orMore",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_EffectiveIncomeTaxRateReconciliationInterestOnIncomeTaxLiabilities": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the interest on income tax liabilities.",
        "label": "Effective Income Tax Rate Reconciliation Interest On Income Tax Liabilities",
        "terseLabel": "Tax-related interest and penalties, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationInterestOnIncomeTaxLiabilities",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_EffectsOfFairValueHedgingOnTheConsolidatedStatementsOfComprehensiveIncomeTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Table Text Block] for Effects of fair value hedging of the derivative instruments used for managing interest rate risk on the Consolidated Statements o Comprehensive Income [Table]",
        "label": "Effects of fair value hedging on the Consolidated Statements of Comprehensive Income [Table Text Block]",
        "terseLabel": "Schedule of Effects of Fair Value Hedging on the Consolidated Statements of Comprehensive Income"
       }
      }
     },
     "localname": "EffectsOfFairValueHedgingOnTheConsolidatedStatementsOfComprehensiveIncomeTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_EffectsoffairvaluehedgingontheConsolidatedStatementsoComprehensiveIncomeLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Line Items] for Effects of fair value hedging of the derivative instruments used for managing interest rate risk on the Consolidated Statements o Comprehensive Income [Table]",
        "label": "Effects of fair value hedging on the Consolidated Statements o Comprehensive Income [Line Items]",
        "terseLabel": "Statement [Line Items]"
       }
      }
     },
     "localname": "EffectsoffairvaluehedgingontheConsolidatedStatementsoComprehensiveIncomeLineItems",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_EffectsoffairvaluehedgingontheConsolidatedStatementsoComprehensiveIncomeTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Effects of fair value hedging of the derivative instruments used for managing interest rate risk on the Consolidated Statements o Comprehensive Income [Table]",
        "label": "Effects of fair value hedging on the Consolidated Statements o Comprehensive Income [Table]",
        "terseLabel": "Effects of fair value hedging on the Consolidated Statements o Comprehensive Income [Table]"
       }
      }
     },
     "localname": "EffectsoffairvaluehedgingontheConsolidatedStatementsoComprehensiveIncomeTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_EfficiencyRatio": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Noninterest expense for the period as a percent of the sum of net interest income (expense) FTE and noninterest income (excluding net securities gains(losses)) for the period.",
        "label": "Efficiency ratio",
        "terseLabel": "Efficiency ratio"
       }
      }
     },
     "localname": "EfficiencyRatio",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_EnergyCapsAndFloorsPurchasedMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Energy Caps and Floors Purchased [Member]",
        "label": "Energy Caps and Floors Purchased [Member]",
        "terseLabel": "Energy caps and floors purchased"
       }
      }
     },
     "localname": "EnergyCapsAndFloorsPurchasedMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_EnergyCapsAndFloorsWrittenMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Energy Caps and Floors Written [Member]",
        "label": "Energy Caps and Floors Written [Member]",
        "terseLabel": "Energy caps and floors written"
       }
      }
     },
     "localname": "EnergyCapsAndFloorsWrittenMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_EnergySwapsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Energy Swaps [Member]",
        "label": "Energy Swaps [Member]",
        "terseLabel": "Energy swaps"
       }
      }
     },
     "localname": "EnergySwapsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_EstimatedAverageLifeOfFund": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The estimated average life of plan used to calculate the expected long-term rate of return of plan assets.",
        "label": "Estimated Average Life Of Fund",
        "terseLabel": "Estimated average life of pension plan in years"
       }
      }
     },
     "localname": "EstimatedAverageLifeOfFund",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "decimalItemType"
    },
    "cma_FairValueAmountOfDerivativeCreditRiskParticipationAgreements": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair Value Amount of Derivative Credit Risk Participation Agreements",
        "label": "Fair Value Amount of Derivative Credit Risk Participation Agreements",
        "terseLabel": "Fair Value Amount of Derivative Credit Risk Participation Agreements"
       }
      }
     },
     "localname": "FairValueAmountOfDerivativeCreditRiskParticipationAgreements",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRealizedGainLossIncludedInEarnings": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents total realized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.",
        "label": "Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Realized Gain Loss Included In Earnings",
        "terseLabel": "Realized gains (losses) recorded in earnings",
        "verboseLabel": "Net Gains (Losses) Realized"
       }
      }
     },
     "localname": "FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRealizedGainLossIncludedInEarnings",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetUnrealizedGainLossIncludedInEarnings": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents total unrealized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.",
        "label": "Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Unrealized Gain Loss Included In Earnings",
        "terseLabel": "Unrealized gains (losses) recorded in earnings",
        "verboseLabel": "Net Gains (Losses) Unrealized"
       }
      }
     },
     "localname": "FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetUnrealizedGainLossIncludedInEarnings",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Fiduciaryincome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fiduciary income",
        "label": "Fiduciary income",
        "terseLabel": "Fiduciary income"
       }
      }
     },
     "localname": "Fiduciaryincome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_FinanceMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Finance [Member]",
        "label": "Finance Member",
        "terseLabel": "Finance"
       }
      }
     },
     "localname": "FinanceMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_FinanceOtherMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Finance Other [Member]",
        "label": "Finance Other [Member]",
        "terseLabel": "Finance &amp; Other"
       }
      }
     },
     "localname": "FinanceOtherMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_FinancingReceivableRatioOfAllowanceForCreditLossesToAllLoans": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The ratio of Allowance for Credit Losses to All Loans.",
        "label": "Financing Receivable, Ratio of Allowance for Credit Losses to All Loans",
        "verboseLabel": "As a percentage of total loans"
       }
      }
     },
     "localname": "FinancingReceivableRatioOfAllowanceForCreditLossesToAllLoans",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_FinancingReceivableRatioOfAllowanceForLoanLossesToAllLoansExcludingPPPLoans": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financing Receivable, Ratio of Allowance for Loan Losses to All Loans excluding PPP Loans",
        "label": "Financing Receivable, Ratio of Allowance for Loan Losses to All Loans excluding PPP Loans",
        "terseLabel": "As a percentage of total loans excluding PPP Loans"
       }
      }
     },
     "localname": "FinancingReceivableRatioOfAllowanceForLoanLossesToAllLoansExcludingPPPLoans",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_FixedInterestRateSwaps": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fixed interest rate swaps",
        "label": "Fixed interest rate swaps",
        "terseLabel": "Fixed interest rate swaps"
       }
      }
     },
     "localname": "FixedInterestRateSwaps",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_FloatingRateBasedonFHLBAuctionDue2026Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "FHLB floating rate advances priced based on FHLB auction due 2026",
        "label": "Floating Rate Based on FHLB Auction Due2026 [Member]",
        "terseLabel": "Floating-rate based on FHLB auction rate due 2026",
        "verboseLabel": "Floating-rate based on FHLB auction rate due 2026"
       }
      }
     },
     "localname": "FloatingRateBasedonFHLBAuctionDue2026Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ForeignExchangeSpotForwardAndSwapsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Foreign Exchange Spot Forward And Swaps [Member]",
        "label": "Foreign Exchange Spot Forward And Swaps [Member]",
        "terseLabel": "Foreign exchange spot, forwards and swaps"
       }
      }
     },
     "localname": "ForeignExchangeSpotForwardAndSwapsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ForeignExchangeSpotForwardsOptionsAndSwapsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Foreign Exchange Spot Forwards Options and Swaps [Member]",
        "label": "Foreign Exchange Spot, Forwards, Options and Swaps [Member]",
        "terseLabel": "Foreign exchange spot, options and swaps"
       }
      }
     },
     "localname": "ForeignExchangeSpotForwardsOptionsAndSwapsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_FourPercentagesubordinatedNotesDue2025Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Four Percentage Subordinated Notes Due 2025",
        "label": "Four Percentage subordinated Notes Due 2025 [Member]",
        "terseLabel": "4.00% subordinated notes due 2025"
       }
      }
     },
     "localname": "FourPercentagesubordinatedNotesDue2025Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_IncomeLossFromContinuingOperationsBeforeIncomeTaxes": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Income (loss) from continuing operations, minority interest, and income (loss) from equity method investments before income taxes.",
        "label": "Income (Loss) from Continuing Operations, before Income Taxes",
        "terseLabel": "Income before income taxes"
       }
      }
     },
     "localname": "IncomeLossFromContinuingOperationsBeforeIncomeTaxes",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_IncomeLossFromContinuingOperationsBeforeMinorityInterestsAndIncomeLossFromEquityMethodInvestments": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of operating profit and nonoperating income (expense) before income (loss) from equity method investments, extraordinary items, cumulative effects of changes in accounting principles, but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests, if any.",
        "label": "Income Loss From Continuing Operations Before Minority Interests And Income Loss From Equity Method Investments",
        "totalLabel": "Income before equity in undistributed earnings (losses) of subsidiaries"
       }
      }
     },
     "localname": "IncomeLossFromContinuingOperationsBeforeMinorityInterestsAndIncomeLossFromEquityMethodInvestments",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_IncomeTaxEffectsAllocatedDirectlytoEquityEmployeeStockOptionsPercentage": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The tax effects percentage of employee stock option transactions that are recognized differently for financial reporting and tax purposes, occurring during the period and charged or credited directly to shareholders' equity.",
        "label": "Income Tax Effects Allocated Directly to Equity, Employee Stock Options, Percentage",
        "terseLabel": "Employee Stock Transactions, percent"
       }
      }
     },
     "localname": "IncomeTaxEffectsAllocatedDirectlytoEquityEmployeeStockOptionsPercentage",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_IncomeTaxReconciliationInterestOnIncomeTaxLiabilities": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The portion of the difference between total income tax expense (benefit) as reported in the Income Statement for the period and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to interest on income tax liabilities.",
        "label": "Income Tax Reconciliation Interest On Income Tax Liabilities",
        "terseLabel": "Tax-related interest and penalties, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationInterestOnIncomeTaxLiabilities",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_IncreaseDecreaseInOtherFinancingAssetsAndLiabilitiesNet": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase (Decrease) in Other Financing Assets and Liabilities, Net",
        "label": "Increase (Decrease) in Other Financing Assets and Liabilities, Net",
        "negatedTerseLabel": "Other, net"
       }
      }
     },
     "localname": "IncreaseDecreaseInOtherFinancingAssetsAndLiabilitiesNet",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_IncreaseDecreaseInOtherInvestingAssetsAndLiabilitiesNet": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase (Decrease) in Other Investing Assets and Liabilities, Net",
        "label": "Increase (Decrease) in Other Investing Assets and Liabilities, Net",
        "negatedTerseLabel": "Other, net"
       }
      }
     },
     "localname": "IncreaseDecreaseInOtherInvestingAssetsAndLiabilitiesNet",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Increaseinretailloansallowanceforcreditlosses": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Increase in retail loans allowance for credit losses",
        "label": "Increase in retail loans allowance for credit losses",
        "terseLabel": "Increase in retail loans allowance for credit losses"
       }
      }
     },
     "localname": "Increaseinretailloansallowanceforcreditlosses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_IntercompanyManagementFee": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_Revenues",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Intercompany Management Fee. Revenue, comprised of base and incentive revenue derived from the management of joint ventures, managing third-party properties, or another entity's operations.",
        "label": "Intercompany Management Fee",
        "terseLabel": "Intercompany management fee"
       }
      }
     },
     "localname": "IntercompanyManagementFee",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_InterestAndDividendIncomeSecuritiesAFSAndHTM": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_InterestAndDividendIncomeOperating",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale and held-to-maturity securities.",
        "label": "Interest And Dividend Income Securities AFS And HTM",
        "terseLabel": "Interest on investment securities"
       }
      }
     },
     "localname": "InterestAndDividendIncomeSecuritiesAFSAndHTM",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_InterestBearingDepositLiabilitiesOtherTimeDeposit": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "All interest-bearing deposit liabilities except for customer certificates of deposit.",
        "label": "Interest-bearing Deposit Liabilities, Other Time Deposit",
        "terseLabel": "Interest-bearing deposits"
       }
      }
     },
     "localname": "InterestBearingDepositLiabilitiesOtherTimeDeposit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_InterestRateCapsAndFloorsPurchasedMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Interest Rate Caps and Floors Purchased [Member]",
        "label": "Interest Rate Caps and Floors Purchased [Member]",
        "terseLabel": "Interest rate caps and floors purchased"
       }
      }
     },
     "localname": "InterestRateCapsAndFloorsPurchasedMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_InterestRateCapsAndFloorsWrittenMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Interest Rate Caps And Floors Written [Member]",
        "label": "Interest Rate Caps And Floors Written [Member]",
        "terseLabel": "Interest rate caps and floors written"
       }
      }
     },
     "localname": "InterestRateCapsAndFloorsWrittenMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_InterestRateSwapAgreementMaturity": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Interest rate swap agreement maturity",
        "label": "Interest rate swap agreement maturity",
        "terseLabel": "Interest rate swap agreement maturity"
       }
      }
     },
     "localname": "InterestRateSwapAgreementMaturity",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Interestexpenseonhedgedmediumandlongtermdebt": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Interest expense on hedged medium- and long-term debt",
        "label": "Interest expense on hedged medium- and long-term debt",
        "terseLabel": "Interest rate contracts: Hedged items"
       }
      }
     },
     "localname": "Interestexpenseonhedgedmediumandlongtermdebt",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_InvestmentsInMajorityOwnedConsolidatedSubsidiaries": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Parent company only investment in majority-owned, fully consolidated entities.",
        "label": "Investments In Majority Owned Consolidated Subsidiaries",
        "terseLabel": "Investments in subsidiaries, principally banks"
       }
      }
     },
     "localname": "InvestmentsInMajorityOwnedConsolidatedSubsidiaries",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LeaseExpenseTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Lease expense",
        "label": "Lease expense [Table Text Block]",
        "terseLabel": "Lease expense"
       }
      }
     },
     "localname": "LeaseExpenseTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_LeaseFinancingMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Lease Financing Class of Financing Receivable",
        "label": "LeaseFinancing [Member]",
        "terseLabel": "Lease financing"
       }
      }
     },
     "localname": "LeaseFinancingMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_LeasesReceivableCommercialLeaseFinancingNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 6.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the gross carrying amount, after deducting net deferred income, of unpaid loans to commercial entities (rather than consumer) made in the form of direct lease financing and lease financing arising from involvement with leveraged leases where the entity is the long-term creditor.",
        "label": "Leases Receivable Commercial Lease Financing Net of Deferred Income",
        "terseLabel": "Lease financing"
       }
      }
     },
     "localname": "LeasesReceivableCommercialLeaseFinancingNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LeasesSupplementalBalanceSheetTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Leases - Supplemental balance sheet",
        "label": "Leases - Supplemental balance sheet [Table Text Block]",
        "terseLabel": "Leases - Supplemental balance sheet"
       }
      }
     },
     "localname": "LeasesSupplementalBalanceSheetTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_LeasesSupplementalCashFlowTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Leases - Supplemental cash flow",
        "label": "Leases - Supplemental cash flow [Table Text Block]",
        "terseLabel": "Leases - Supplemental cash flow"
       }
      }
     },
     "localname": "LeasesSupplementalCashFlowTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_LeasesTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Leases [Text Block]",
        "label": "Leases [Text Block]",
        "terseLabel": "Leases [Text Block]"
       }
      }
     },
     "localname": "LeasesTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesNotes"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_LesseeOperatingLeaseLiabilityToBePaidLessInterest": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Lessee, operating lease, liability, to be paid less interest",
        "label": "Lessee, operating lease, liability, to be paid less interest",
        "terseLabel": "Operating lease liabilities",
        "totalLabel": "Total operating lease liabilities"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityToBePaidLessInterest",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails",
      "http://www.comerica.com/role/LeasesSupplementalbalancesheetDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LetterOfCreditFees": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 5.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The noninterest income derived from Letter of Credit activities at the time of recognition.",
        "label": "Letter of Credit Fees",
        "terseLabel": "Letter of credit fees"
       }
      }
     },
     "localname": "LetterOfCreditFees",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LeverageRatio": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Leverage ratio",
        "label": "Leverage ratio",
        "terseLabel": "Leverage ratio"
       }
      }
     },
     "localname": "LeverageRatio",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_LiabilitiesSecuredByPledgedSecurities": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Liabilities, primarily public and other deposits of state and local government agencies and derivative instruments, secured by pledged securities.",
        "label": "Liabilities Secured By Pledged Securities",
        "terseLabel": "Liabilities secured by pledged collateral"
       }
      }
     },
     "localname": "LiabilitiesSecuredByPledgedSecurities",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoanClassificationAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Determination of whether a loan is a business loan or a retail loan.",
        "label": "Loan Classification [Axis]",
        "terseLabel": "Loan Classification [Axis]"
       }
      }
     },
     "localname": "LoanClassificationAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_LoanClassificationDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan Classification [Domain]",
        "label": "Loan Classification [Domain]",
        "terseLabel": "Loan Classification [Domain]"
       }
      }
     },
     "localname": "LoanClassificationDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_LoanInterestReceivable": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan interest receivable",
        "label": "Loan interest receivable",
        "terseLabel": "Loan interest receivable"
       }
      }
     },
     "localname": "LoanInterestReceivable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansAndLeasesReceivableConsumerLoansNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 5.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The gross amount, after deducting net deferred income, under revolving lines of credit outstanding extended to a homeowner and collateralized by the equity in the home and loans and leases to individuals not otherwise specified in the existing taxonomy.",
        "label": "Loans and Leases Receivable Consumer Loans Net of Deferred Income",
        "terseLabel": "Consumer loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableConsumerLoansNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansAndLeasesReceivableConsumerMortgageNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 4.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the gross carrying amount, after deducting net deferred income, of unpaid loans issued to individuals to acquire or improve land or a building or to provide cash to the borrower, and which are secured by the acquired or improved realty. Loans secured by one to four-family residential property of the borrower are generally referred to as residential mortgage loans. Repayment terms for residential mortgage loans may vary considerably. Such loans may be structured to provide for full amortization of principal, partial amortization with a balloon payment at a specified date, or negative amortization. Interest rates may be fixed or variable. This item excludes subordinated loans such as home equity lines of credit.",
        "label": "Loans and Leases Receivable Consumer Mortgage Net of Deferred Income",
        "terseLabel": "Residential mortgage loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableConsumerMortgageNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansAndLeasesReceivableForeignNetOfDeferredIncomeOther": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 7.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the sum of the gross carrying amounts, after deducting net deferred income, of the various categories of loans and leases made to borrowers outside the entity's country of domicile.",
        "label": "Loans and Leases Receivable Foreign Net of Deferred Income Other",
        "terseLabel": "International loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableForeignNetOfDeferredIncomeOther",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansAndLeasesReceivableRelatedPartiesBeginningOfPeriod": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loans and leases receivable, related parties beginning of period",
        "label": "Loans and leases receivable, related parties beginning of period",
        "terseLabel": "Loans and leases receivable, related parties beginning of period"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableRelatedPartiesBeginningOfPeriod",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/TransactionswithRelatedPartiesTransactionswithRelatedPartiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansAndLeasesReceivableRelatedPartiesEndOfPeriod": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loans and leases receivable, related parties end of period",
        "label": "Loans and leases receivable, related parties end of period",
        "terseLabel": "Loans and leases receivable, related parties end of period"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableRelatedPartiesEndOfPeriod",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/TransactionswithRelatedPartiesTransactionswithRelatedPartiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansPastDueAndStillAccruing": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loans past due and still accruing",
        "label": "Loans past due and still accruing",
        "terseLabel": "Loans past due and still accruing"
       }
      }
     },
     "localname": "LoansPastDueAndStillAccruing",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansReceivableCommercialFinancialAndAgriculturalNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the sum of the gross carrying amounts, after deducting net deferred income, of unpaid loans issued to businesses to provide financing for cash needs, financial asset purchases, or farm-related purposes. Includes all loans not included in another category. This category shall include, but not be limited to, loans to real estate investment trusts, mortgage companies, banks, and other financial institutions; loans for carrying securities; and loans for agricultural purposes. Do not include loans secured primarily by developed real estate.",
        "label": "Loans Receivable Commercial Financial and Agricultural Net of Deferred Income",
        "terseLabel": "Commercial loans"
       }
      }
     },
     "localname": "LoansReceivableCommercialFinancialAndAgriculturalNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansReceivableCommercialMortgageNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 3.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the carrying amount, after deducting net deferred income, of unpaid loans issued to businesses to provide financing on existing land or a building, which, pursuant to terms of the underlying debt instrument, are secured at a minimum but possibly exclusively by that real property. Mortgages represent permanent financing, and are issued to replace previously existing mortgages or pay off acquisition, development and construction loans, or to provide cash to the borrower.",
        "label": "Loans Receivable Commercial Mortgage Net of Deferred Income",
        "terseLabel": "Commercial mortgage loans"
       }
      }
     },
     "localname": "LoansReceivableCommercialMortgageNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansReceivableUnusedCommitment": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects unused commitments that have been issued to businesses to acquire real property, develop land for sale or construction thereon, to construct a facility and to provide financing on existing land or a building, which, pursuant to terms of the underlying debt instrument, are secured at a minimum but possibly exclusively by that real property.",
        "label": "Loans Receivable, Unused Commitment",
        "terseLabel": "Total unused commitments"
       }
      }
     },
     "localname": "LoansReceivableUnusedCommitment",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LoansWithTermsExtendedInAccordanceWithCARESAct": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loans with terms extended in accordance with CARES Act",
        "label": "Loans with terms extended in accordance with CARES Act",
        "terseLabel": "Loans with terms extended in accordance with CARES Act"
       }
      }
     },
     "localname": "LoansWithTermsExtendedInAccordanceWithCARESAct",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_LongestExpirationYearLettersOfCredit": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Longest Expiration Year Letters Of Credit",
        "label": "Longest Expiration Year Letters Of Credit",
        "terseLabel": "Final year of expiration for outstanding letters of credit"
       }
      }
     },
     "localname": "LongestExpirationYearLettersOfCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "gYearItemType"
    },
    "cma_LowIncomeHousingTaxCreditEntitiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Low Income Housing Tax Credit Entities [Member]",
        "label": "Low Income Housing Tax Credit Entities [Member]",
        "terseLabel": "Low Income Housing Tax Credit Entities"
       }
      }
     },
     "localname": "LowIncomeHousingTaxCreditEntitiesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_LowIncomeHousingTaxCreditsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Low Income Housing Tax Credits [Member]",
        "label": "Low Income Housing Tax Credits [Member]",
        "terseLabel": "Low income housing tax credits"
       }
      }
     },
     "localname": "LowIncomeHousingTaxCreditsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_Maximumpastduestatusjuniorlienhomeequityplacedonnonaccrualstatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The maximum number of days principal or interest payments past due at which junior lien home equity loans are placed on nonaccrual status when full collection is in doubt, such as when senior lien position is seriously delinquent.",
        "label": "MaximumPastDueStatusJuniorLienHomeEquityPlacedOnNonaccrualStatus",
        "terseLabel": "Maximum Past Due Status Junior Lien Home Equity Placed On Nonaccrual Status"
       }
      }
     },
     "localname": "Maximumpastduestatusjuniorlienhomeequityplacedonnonaccrualstatus",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_MethodofAssessingEffectivenessAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Method of Assessing Effectiveness [Axis]",
        "label": "Method of Assessing Effectiveness [Axis]",
        "terseLabel": "Method of Assessing Effectiveness [Axis]"
       }
      }
     },
     "localname": "MethodofAssessingEffectivenessAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_MethodofAssessingEffectivenessDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Domain] for Method of Assessing Effectiveness [Axis]",
        "label": "Method of Assessing Effectiveness [Domain]",
        "terseLabel": "Method of Assessing Effectiveness [Domain]"
       }
      }
     },
     "localname": "MethodofAssessingEffectivenessDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_NetCreditRelatedChargeOffs": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The sum of net loan and lease charge-offs and charge-offs associated with lending-related commitments.",
        "label": "Net credit-related charge-offs",
        "verboseLabel": "Net credit-related (recoveries) charge-offs"
       }
      }
     },
     "localname": "NetCreditRelatedChargeOffs",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_NetFeesFromPPPLoans": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Net fees from PPP loans",
        "label": "Net fees from PPP loans",
        "terseLabel": "Net fees from PPP loans"
       }
      }
     },
     "localname": "NetFeesFromPPPLoans",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_NetIncreaseInFixedAssets": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 8.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net cash inflow (outflow) from purchases, sales and disposals of property, plant, and equipment.",
        "label": "Net Increase in Fixed Assets",
        "negatedLabel": "Other, net",
        "terseLabel": "Other, net"
       }
      }
     },
     "localname": "NetIncreaseInFixedAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_NonInterestIncomeExcludingNetSecuritiesGains": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified, excluding net securities gains.",
        "label": "Non-interest Income (Excluding Net Securities Gains)",
        "terseLabel": "Noninterest income excluding net securities gains (losses)"
       }
      }
     },
     "localname": "NonInterestIncomeExcludingNetSecuritiesGains",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_NonaccrualLoansAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Nonaccrual Loans",
        "label": "Nonaccrual Loans [Abstract]"
       }
      }
     },
     "localname": "NonaccrualLoansAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_NoninterestDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "noninterest [Domain]",
        "label": "noninterest [Domain]",
        "terseLabel": "Other noninterest income"
       }
      }
     },
     "localname": "NoninterestDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_NotionalAmountOfDerivativeCreditRiskParticipationAgreements": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Notional amount of derivative credit risk participation agreements under which the participant assumes counterparty credit exposure associated with a borrower's performance related to certain derivative contracts.",
        "label": "Notional Amount of Derivative Credit Risk Participation Agreements",
        "terseLabel": "Notional Amount of Derivative Credit Risk Participation Agreements"
       }
      }
     },
     "localname": "NotionalAmountOfDerivativeCreditRiskParticipationAgreements",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_NumberOfMajorBusinessSegments": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of Major Business Segments",
        "label": "Number of Major Business Segments",
        "terseLabel": "Number of Major Business Segments"
       }
      }
     },
     "localname": "NumberOfMajorBusinessSegments",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationNarrativeDetails"
     ],
     "xbrltype": "integerItemType"
    },
    "cma_OpenTaxYearsSecondGrouping": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Open tax years - second grouping",
        "label": "Open tax years - second grouping",
        "terseLabel": "Open tax years - second grouping"
       }
      }
     },
     "localname": "OpenTaxYearsSecondGrouping",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "gYearListItemType"
    },
    "cma_OperatingLossCarryforwardsExpirationDateFederal": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Operating Loss Carryforwards, Expiration Date - Federal",
        "label": "Operating Loss Carryforwards, Expiration Date - Federal",
        "terseLabel": "Operating Loss Carryforwards, Expiration Date - Federal"
       }
      }
     },
     "localname": "OperatingLossCarryforwardsExpirationDateFederal",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "gYearItemType"
    },
    "cma_OperatingLossCarryforwardsExpirationDateState": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Operating Loss Carryforwards, Expiration Date - State",
        "label": "Operating Loss Carryforwards, Expiration Date - State",
        "terseLabel": "Operating Loss Carryforwards, Expiration Date - State"
       }
      }
     },
     "localname": "OperatingLossCarryforwardsExpirationDateState",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "gYearItemType"
    },
    "cma_OptionsExercisedPolicy": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Options exercised policy",
        "label": "Options exercised policy",
        "terseLabel": "Options exercised policy"
       }
      }
     },
     "localname": "OptionsExercisedPolicy",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_Other1Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Other1 [Member]",
        "label": "Other1 [Member]",
        "terseLabel": "Other"
       }
      }
     },
     "localname": "Other1Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_OtherBusinessLineMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Other Business Line",
        "label": "Other Business Line [Member]",
        "terseLabel": "Other Business Lines Member"
       }
      }
     },
     "localname": "OtherBusinessLineMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostBeforeTax": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostNetOfTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Before tax amount of the income statement impact of the reclassification adjustment for pension and other postretirement benefit plans recognized in net periodic defined benefit cost.",
        "label": "Other Comprehensive Income Loss Reclassification Adjustment Pension and Other Postretirement Benefit Plans Recognized In Net Periodic Defined Benefit Cost, Before Tax",
        "totalLabel": "Benefit plans, Total amounts recognized in other noninterest expenses"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostBeforeTax",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostNetOfTax": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Net of tax amount of the income statement impact of the reclassification adjustment for pension and other postretirement benefit plans recognized in net periodic defined benefit cost.",
        "label": "Other Comprehensive Income Loss Reclassification Adjustment Pension and Other Postretirement Benefit Plans Recognized In Net Periodic Defined Benefit Cost, Net of Tax",
        "totalLabel": "Benefit plans, Adjustment for amounts recognized as components of net periodic benefit cost during the period, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostNetOfTax",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostTax": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tax effect of the income statement impact of the reclassification adjustment for pension and other postretirement benefit plans recognized in net periodic defined benefit cost.",
        "label": "Other Comprehensive Income Loss Reclassification Adjustment Pension and Other Postretirement Benefit Plans Recognized In Net Periodic Defined Benefit Cost, Tax",
        "terseLabel": "Benefit plans, Less: Provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostTax",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_OtherShortTermInvestmentsPolicyTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element defines the items included in other short-term investments for the entity and describes the entity's accounting policy for such items.",
        "label": "Other Short-Term Investments [Policy Text Block]",
        "terseLabel": "Other Short-Term Investments"
       }
      }
     },
     "localname": "OtherShortTermInvestmentsPolicyTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_OtherTaxBenefitsRelatedToTaxCreditEntitiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Other Tax Benefits Related To Tax Credit Entities [Member]",
        "label": "Other Tax Benefits Related To Tax Credit Entities [Member]",
        "terseLabel": "Other tax benefits related to tax credit entities"
       }
      }
     },
     "localname": "OtherTaxBenefitsRelatedToTaxCreditEntitiesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_OtherTaxCreditEntitiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Other Tax Credit Entities [Member]",
        "label": "Other Tax Credit Entities [Member]",
        "terseLabel": "Other Tax Credit Entities"
       }
      }
     },
     "localname": "OtherTaxCreditEntitiesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_Othersourcesofnoninterestincome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 8.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Other sources of noninterest income not derived from contracts with customers",
        "label": "Other sources of noninterest income",
        "terseLabel": "Other sources of noninterest income"
       }
      }
     },
     "localname": "Othersourcesofnoninterestincome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_OutsideProcessingFeeExpense": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 4.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of expense incurred during the period from fees for services performed by outside vendors.",
        "label": "Outside Processing Fee Expense",
        "terseLabel": "Outside processing fee expense"
       }
      }
     },
     "localname": "OutsideProcessingFeeExpense",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_PastDuePeriodBusinessLoansPlacedOnNonaccrualStatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of days principal or interest payments are past due at which business loans are generally placed on nonaccrual status.",
        "label": "Past Due Period Business Loans Placed On Nonaccrual Status",
        "terseLabel": "Past Due Period Business Loans Placed On Nonaccrual Status"
       }
      }
     },
     "localname": "PastDuePeriodBusinessLoansPlacedOnNonaccrualStatus",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_PastDuePeriodResidentialMortgageAndHomeEquityLoansPlacedOnNonaccrualStatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of days principal or interest payments are past due at which residential mortgage and home equity loans are generally placed on nonaccrual status.",
        "label": "Past Due Period Residential Mortgage And Home Equity Loans Placed On Nonaccrual Status",
        "terseLabel": "Past Due Period Residential Mortgage And Home Equity Loans Placed On Nonaccrual Status"
       }
      }
     },
     "localname": "PastDuePeriodResidentialMortgageAndHomeEquityLoansPlacedOnNonaccrualStatus",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_PerformanceConditionsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Performance Conditions [Member]",
        "label": "Performance Conditions [Member]",
        "terseLabel": "Performance-Based Units"
       }
      }
     },
     "localname": "PerformanceConditionsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_PremisesandEquipmentsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Premises and Equipments [Abstract]",
        "label": "Premises and Equipments [Abstract]",
        "terseLabel": "Premises and Equipments [Abstract]"
       }
      }
     },
     "localname": "PremisesandEquipmentsAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_Purchases": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Purchases",
        "label": "Purchases",
        "terseLabel": "Purchases"
       }
      }
     },
     "localname": "Purchases",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_RealEstateConstructionLoansNetOfDeferredIncome": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the carrying amounts, after deducting net deferred income, of unpaid loans that had been issued to businesses to acquire real property, develop land for sale or construction thereon, to construct a facility and to provide financing on existing land or a building, which, pursuant to terms of the underlying debt instrument, are secured at a minimum but possibly exclusively by that real property.",
        "label": "Real Estate Construction Loans Net of Deferred Income",
        "terseLabel": "Real estate construction loans"
       }
      }
     },
     "localname": "RealEstateConstructionLoansNetOfDeferredIncome",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Reductioninbusinessloansallowanceforcreditlosses": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reduction in business loans allowance for credit losses",
        "label": "Reduction in business loans allowance for credit losses",
        "terseLabel": "Reduction in business loans allowance for credit losses"
       }
      }
     },
     "localname": "Reductioninbusinessloansallowanceforcreditlosses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Repositioningloweryieldingtreasurysecurities": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Repositioning lower-yielding treasury securities",
        "label": "Repositioning lower-yielding treasury securities",
        "terseLabel": "Repositioning lower-yielding treasury securities"
       }
      }
     },
     "localname": "Repositioningloweryieldingtreasurysecurities",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_RetailBankMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Retail Bank",
        "label": "Retail Bank [Member]",
        "terseLabel": "Retail Bank"
       }
      }
     },
     "localname": "RetailBankMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ReturnOnAverageAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Net income for the period as a percent of average assets for the period.",
        "label": "Return on average assets",
        "terseLabel": "Return on average assets"
       }
      }
     },
     "localname": "ReturnOnAverageAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_RevenuefromContractswithCustomersAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Revenue from Contracts with Customers [Abstract]",
        "label": "Revenue from Contracts with Customers [Abstract]",
        "terseLabel": "Revenue from Contracts with Customers [Abstract]"
       }
      }
     },
     "localname": "RevenuefromContractswithCustomersAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_RightOfUseROUAssets": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Right-of -use (ROU) assets",
        "label": "Right-of -use (ROU) assets",
        "terseLabel": "Right-of-use (ROU) assets"
       }
      }
     },
     "localname": "RightOfUseROUAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/LeasesSupplementalbalancesheetDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_RiskManagementDerivativesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instruments entered into for risk management purposes.",
        "label": "Risk Management Derivatives Member",
        "terseLabel": "Risk management purposes"
       }
      }
     },
     "localname": "RiskManagementDerivativesMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_RiskParticipationsCoveringStandbyAndCommercialLettersOfCredit": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total risk participations with third parties covering standby and commercial letters of credit outstanding.",
        "label": "Risk Participations Covering Standby And Commercial Letters Of Credit",
        "terseLabel": "Risk participation agreements covering standby and commercial letters of credit"
       }
      }
     },
     "localname": "RiskParticipationsCoveringStandbyAndCommercialLettersOfCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_Sales": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sales",
        "label": "Sales",
        "negatedTerseLabel": "Sales"
       }
      }
     },
     "localname": "Sales",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_ScheduleOfConsolidatedStatementsOfCashFlowsWithChangeInAccountingPrincipleTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of Consolidated Statements of Cash Flows with Change in Accounting Principle",
        "label": "Schedule of Consolidated Statements of Cash Flows with Change in Accounting Principle [Table Text Block]",
        "terseLabel": "Schedule of Consolidated Statements of Cash Flows with Change in Accounting Principle"
       }
      }
     },
     "localname": "ScheduleOfConsolidatedStatementsOfCashFlowsWithChangeInAccountingPrincipleTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfConsolidatedStatementsOfComprehensiveIncomeWithChangeInAccountingPrincipleTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of Consolidated Statements of Comprehensive Income with Change in Accounting Principle",
        "label": "Schedule of Consolidated Statements of Comprehensive Income with Change in Accounting Principle [Table Text Block]",
        "terseLabel": "Schedule of Consolidated Statements of Comprehensive Income with Change in Accounting Principle"
       }
      }
     },
     "localname": "ScheduleOfConsolidatedStatementsOfComprehensiveIncomeWithChangeInAccountingPrincipleTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfContractualMaturitiesOfTimeDepositsOfOneHundredThousandOrMoreTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of contractual maturities of domestic time deposits (which include certificates of deposits, individual retirement accounts and open accounts in domestic offices), in denominations of $100,000 or more.",
        "label": "Schedule Of Contractual Maturities Of Time Deposits Of One Hundred Thousand Or More [Text Block]",
        "terseLabel": "Schedule Of Maturities Of Domestic Deposits Of $100,000 Or More"
       }
      }
     },
     "localname": "ScheduleOfContractualMaturitiesOfTimeDepositsOfOneHundredThousandOrMoreTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DepositsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfCustomerInitiatedDerivativesGainsLossesRecognizedInIncomeLocationTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Location and amount of gains (losses) recognized in income related to customer-initiated derivative instruments, net of the impact of offsetting positions.",
        "label": "Schedule Of Customer Initiated Derivatives Gains Losses Recognized In Income Location [Table Text Block]",
        "terseLabel": "Schedule Of Net Gains Recognized In Income On Customer-Initiated Derivatives"
       }
      }
     },
     "localname": "ScheduleOfCustomerInitiatedDerivativesGainsLossesRecognizedInIncomeLocationTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfInternallyClassifiedWatchListLettersOfCreditTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total internally classified watch list standby and commercial letters of credit (generally consistent with regulatory defined special mention, substandard and doubtful).",
        "label": "Schedule Of Internally Classified Watch List Letters Of Credit [Text Block]",
        "terseLabel": "Summary Of Criticized Letters Of Credit"
       }
      }
     },
     "localname": "ScheduleOfInternallyClassifiedWatchListLettersOfCreditTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps",
        "label": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps [Table]",
        "terseLabel": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps [Table]"
       }
      }
     },
     "localname": "ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps",
        "label": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps [Table Text Block]",
        "terseLabel": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Cash Flow Swaps"
       }
      }
     },
     "localname": "ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining maturity of the notional amount of risk management interest rate swaps and weighted average interest rates.",
        "label": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Fair Value Swaps [Table Text Block]",
        "terseLabel": "Schedule Of Weighted Average Maturity And Interest Rates On Risk Management Fair Value Swaps"
       }
      }
     },
     "localname": "ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementInterestRateSwapsTable": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps [Table]",
        "label": "Schedule of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps [Table]",
        "terseLabel": "Schedule of Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps [Table]"
       }
      }
     },
     "localname": "ScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementInterestRateSwapsTable",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_SchedulesOfConcentrationOfRiskOutstandingLoansAndTotalExposureFromLoansAutomotiveTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Outstanding loans and total exposure from Automotive industry.",
        "label": "Schedules of Concentration of Risk, Outstanding Loans and Total Exposure From Loans, Automotive [Table Text Block]",
        "terseLabel": "Schedule of Automotive Industry Outstanding Loans and Total Exposure"
       }
      }
     },
     "localname": "SchedulesOfConcentrationOfRiskOutstandingLoansAndTotalExposureFromLoansAutomotiveTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_SchedulesOfConcentrationOfRiskOutstandingLoansAndUnusedCommitmentsFromCommercialRealEstateTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Outstanding loans and unused commitments from Commercial Real Estate.",
        "label": "Schedules of Concentration of Risk, Outstanding Loans and Unused Commitments From Commercial Real Estate [Table Text Block]",
        "terseLabel": "Schedule of Commercial Real Estate Loans and Unused Commitments"
       }
      }
     },
     "localname": "SchedulesOfConcentrationOfRiskOutstandingLoansAndUnusedCommitmentsFromCommercialRealEstateTableTextBlock",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "cma_SegmentReportingAverageAssets": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of average assets attributed to the reportable segment.",
        "label": "Segment Reporting Average Assets",
        "terseLabel": "Assets, average"
       }
      }
     },
     "localname": "SegmentReportingAverageAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_ServiceConditionsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Service Conditions [Member]",
        "label": "Service Conditions [Member]",
        "terseLabel": "Service-Based Units"
       }
      }
     },
     "localname": "ServiceConditionsMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_Servicechargesondepositaccounts": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Service charges on deposit accounts",
        "label": "Service charges on deposit accounts",
        "terseLabel": "Service charges on deposit accounts"
       }
      }
     },
     "localname": "Servicechargesondepositaccounts",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_SevenPointEightSevenFivePercentageSubordinatedNoteDue2026Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Seven Point Eight Seven Five Percentage Subordinated Note Due 2026 [Member]",
        "label": "Seven Point Eight Seven Five Percentage Subordinated Note Due2026 Member",
        "terseLabel": "7.875% subordinated notes due 2026"
       }
      }
     },
     "localname": "SevenPointEightSevenFivePercentageSubordinatedNoteDue2026Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ShareRepurchaseProgramMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Share Repurchase Program [Member]",
        "label": "Share Repurchase Program [Member]",
        "terseLabel": "Equity Repurchase Program"
       }
      }
     },
     "localname": "ShareRepurchaseProgramMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ShortCutMethodMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Short-Cut Method [Member]",
        "label": "Short-Cut Method [Member]",
        "terseLabel": "Short-Cut Method"
       }
      }
     },
     "localname": "ShortCutMethodMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_SignificantGroupConcentrationsOfCreditRiskAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Significant Group Concentrations of Credit Risk [Abstract]",
        "label": "Significant Group Concentrations of Credit Risk [Abstract]",
        "terseLabel": "Statement [Line Items]"
       }
      }
     },
     "localname": "SignificantGroupConcentrationsOfCreditRiskAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_SoftwareExpenses": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 5.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of expense incurred during the period from amortization of computer software and fees for software maintenance and rental.",
        "label": "Software Expenses",
        "terseLabel": "Software expense"
       }
      }
     },
     "localname": "SoftwareExpenses",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_StatementofChangesinEquityParentheticalAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Statement of Changes in Equity Parenthetical [Abstract]",
        "label": "Statement of Changes in Equity Parenthetical [Abstract]",
        "terseLabel": "Statement of Changes in Equity Parenthetical [Abstract]"
       }
      }
     },
     "localname": "StatementofChangesinEquityParentheticalAbstract",
     "nsuri": "http://www.comerica.com/20211231",
     "xbrltype": "stringItemType"
    },
    "cma_Stockoptionsexcludedbecauseexercisepricesweregreaterthanaveragemarketpriceofshares": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Stock options excluded because exercise prices were greater than average market price of shares",
        "label": "Stock options excluded because exercise prices were greater than average market price of shares",
        "terseLabel": "Average outstanding options"
       }
      }
     },
     "localname": "Stockoptionsexcludedbecauseexercisepricesweregreaterthanaveragemarketpriceofshares",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "cma_TaxCreditsandBenefitsRelatedToTaxCreditEntitiesAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tax Credits and Benefits Related To Tax Credit Entities [Axis]",
        "label": "Tax Credits and Benefits Related To Tax Credit Entities [Axis]",
        "terseLabel": "Tax Credits and Benefits Related To Tax Credit Entities [Axis]"
       }
      }
     },
     "localname": "TaxCreditsandBenefitsRelatedToTaxCreditEntitiesAxis",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "cma_TaxCreditsandBenefitsRelatedToTaxCreditEntitiesDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "[Domain] for Tax Credits and Benefits Related To Tax Credit Entities [Axis]",
        "label": "Tax Credits and Benefits Related To Tax Credit Entities [Domain]",
        "terseLabel": "Tax Credits and Benefits Related To Tax Credit Entities [Domain]"
       }
      }
     },
     "localname": "TaxCreditsandBenefitsRelatedToTaxCreditEntitiesDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_Taxbenefitsfromemployeestocktransactions": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tax benefits from employee stock transactions from the adoption of ASU 2016-09",
        "label": "Tax benefits from employee stock transactions",
        "verboseLabel": "Employee Stock Transactions, amount"
       }
      }
     },
     "localname": "Taxbenefitsfromemployeestocktransactions",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_ThreePointEightZeroPercentSubNotesDue2026Member": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Three Point Eight Zero Percent Sub Notes Due 2026 [Member]",
        "label": "Three Point Eight Zero Percent Sub Notes Due 2026 [Member]",
        "terseLabel": "3.80% subordinated notes due 2026"
       }
      }
     },
     "localname": "ThreePointEightZeroPercentSubNotesDue2026Member",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_ThresholdDaysPastDueOtherConsumerPlacedOnNonaccrualStatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of days principal or interest payments are past due at which other consumer loans are generally placed on nonaccrual status.",
        "label": "Threshold, Days Past Due, Other Consumer Placed On Nonaccrual Status",
        "terseLabel": "Threshold, Days Past Due, Other Consumer Placed On Nonaccrual Status"
       }
      }
     },
     "localname": "ThresholdDaysPastDueOtherConsumerPlacedOnNonaccrualStatus",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "cma_Tier1CapitalToRiskWeightedAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tier1 capital to risk-weighted assets",
        "label": "Tier1 capital to risk-weighted assets",
        "terseLabel": "Tier1 capital to risk-weighted assets"
       }
      }
     },
     "localname": "Tier1CapitalToRiskWeightedAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_Tier1RiskBasedCapital": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tier 1 risk-based capital",
        "label": "Tier 1 risk-based capital",
        "terseLabel": "Tier 1 risk-based capital"
       }
      }
     },
     "localname": "Tier1RiskBasedCapital",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_TotalAutomotiveExposure": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total automotive exposure including loans and other credit commitments to automotive dealers and to borrowers involved with automotive production.",
        "label": "Total Automotive Exposure",
        "terseLabel": "Total automotive exposure"
       }
      }
     },
     "localname": "TotalAutomotiveExposure",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_TotalAutomotiveLoans": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total automotive loans including loans to automotive dealers and to borrowers involved with automotive production.",
        "label": "Total Automotive Loans",
        "terseLabel": "Total automotive loans"
       }
      }
     },
     "localname": "TotalAutomotiveLoans",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_TotalCapitalToRiskWeightedAssets": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total capital to risk-weighted assets",
        "label": "Total capital to risk-weighted assets",
        "terseLabel": "Total capital to risk-weighted assets"
       }
      }
     },
     "localname": "TotalCapitalToRiskWeightedAssets",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_TotalInternallyClassifiedWatchListLettersOfCredit": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total internally classified watch list standby and commercial letters of credit (generally consistent with regulatory defined special mention, substandard and doubtful).",
        "label": "Total Internally Classified Watch List Letters of Credit",
        "terseLabel": "Total criticized standby and commercial letters of credit"
       }
      }
     },
     "localname": "TotalInternallyClassifiedWatchListLettersOfCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsSummaryOfCriticizedLettersOfCreditDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_TotalRiskBasedCapital": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total risk-based capital",
        "label": "Total risk-based capital",
        "terseLabel": "Total risk-based capital"
       }
      }
     },
     "localname": "TotalRiskBasedCapital",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_Totalothercomponentsofnetbenefitcreditorcost": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total other components of net benefit credit or cost",
        "label": "Total other components of net benefit credit or cost",
        "totalLabel": "Total other components of net benefit (credit) cost"
       }
      }
     },
     "localname": "Totalothercomponentsofnetbenefitcreditorcost",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_TransfersIntoOrOutOfLevelOneOrLevelTwoOrLevelThree": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Transfers between Level 1, Level 2 and Level three of the fair value hierarchy that have taken place during the period.",
        "label": "Transfers Into Or Out Of Level One Or Level Two Or Level Three",
        "terseLabel": "Transfers into or out of Level 1 or Level 2 or Level 3"
       }
      }
     },
     "localname": "TransfersIntoOrOutOfLevelOneOrLevelTwoOrLevelThree",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_TwoPointFivePercentageNotesDue2024MemberDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Two Point Five Percentage Notes Due2024 Member [Domain]",
        "label": "Two Point Five Percentage Notes Due2024 Member [Domain]",
        "terseLabel": "2.50% notes due 2024"
       }
      }
     },
     "localname": "TwoPointFivePercentageNotesDue2024MemberDomain",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "cma_UnrecognizedTaxBenefitsDecreaseResultingfromOtherTaxPositionChanges": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of decrease in unrecognized tax benefits resulting from other tax position changes.",
        "label": "Unrecognized Tax Benefits, Decrease Resulting from Other Tax Position Changes",
        "terseLabel": "Reduction as a result of expiration of statute of limitations"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsDecreaseResultingfromOtherTaxPositionChanges",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "cma_WatchListLettersOfCreditAsPercentageOfTotalLettersOfCredit": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total internally classified watch list standby and commercial letters of credit as a percentage of total standby and commercial letters of credit.",
        "label": "Watch List Letters of Credit As Percentage Of Total Letters of Credit",
        "terseLabel": "As a percentage of total outstanding standby and commercial letters of credit"
       }
      }
     },
     "localname": "WatchListLettersOfCreditAsPercentageOfTotalLettersOfCredit",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsSummaryOfCriticizedLettersOfCreditDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "cma_WealthManagementMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Wealth Management [Member]",
        "label": "Wealth Management [Member]",
        "terseLabel": "Wealth Management"
       }
      }
     },
     "localname": "WealthManagementMember",
     "nsuri": "http://www.comerica.com/20211231",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "dei_AmendmentFlag": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the XBRL content amends previously-filed or accepted submission.",
        "label": "Amendment Flag",
        "terseLabel": "Amendment Flag"
       }
      }
     },
     "localname": "AmendmentFlag",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_AuditorFirmId": {
     "auth_ref": [
      "r989",
      "r990",
      "r991"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "PCAOB issued Audit Firm Identifier",
        "label": "Auditor Firm ID",
        "terseLabel": "Auditor Firm ID"
       }
      }
     },
     "localname": "AuditorFirmId",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "nonemptySequenceNumberItemType"
    },
    "dei_AuditorLocation": {
     "auth_ref": [
      "r989",
      "r990",
      "r991"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Auditor Location",
        "terseLabel": "Auditor Location"
       }
      }
     },
     "localname": "AuditorLocation",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "internationalNameItemType"
    },
    "dei_AuditorName": {
     "auth_ref": [
      "r989",
      "r990",
      "r991"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "Auditor Name",
        "terseLabel": "Auditor Name"
       }
      }
     },
     "localname": "AuditorName",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "internationalNameItemType"
    },
    "dei_CityAreaCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Area code of city",
        "label": "City Area Code",
        "terseLabel": "City Area Code"
       }
      }
     },
     "localname": "CityAreaCode",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_CurrentFiscalYearEndDate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "End date of current fiscal year in the format --MM-DD.",
        "label": "Current Fiscal Year End Date",
        "terseLabel": "Current Fiscal Year End Date"
       }
      }
     },
     "localname": "CurrentFiscalYearEndDate",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "gMonthDayItemType"
    },
    "dei_DocumentAnnualReport": {
     "auth_ref": [
      "r989",
      "r990",
      "r991"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true only for a form used as an annual report.",
        "label": "Document Annual Report",
        "terseLabel": "Document Annual Report"
       }
      }
     },
     "localname": "DocumentAnnualReport",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_DocumentFiscalPeriodFocus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fiscal period values are FY, Q1, Q2, and Q3.  1st, 2nd and 3rd quarter 10-Q or 10-QT statements have value Q1, Q2, and Q3 respectively, with 10-K, 10-KT or other fiscal year statements having FY.",
        "label": "Document Fiscal Period Focus",
        "terseLabel": "Document Fiscal Period Focus"
       }
      }
     },
     "localname": "DocumentFiscalPeriodFocus",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "fiscalPeriodItemType"
    },
    "dei_DocumentFiscalYearFocus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This is focus fiscal year of the document report in YYYY format. For a 2006 annual report, which may also provide financial information from prior periods, fiscal 2006 should be given as the fiscal year focus. Example: 2006.",
        "label": "Document Fiscal Year Focus",
        "terseLabel": "Document Fiscal Year Focus"
       }
      }
     },
     "localname": "DocumentFiscalYearFocus",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "gYearItemType"
    },
    "dei_DocumentPeriodEndDate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period.  The format of the date is YYYY-MM-DD.",
        "label": "Document Period End Date",
        "terseLabel": "Document Period End Date"
       }
      }
     },
     "localname": "DocumentPeriodEndDate",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "dateItemType"
    },
    "dei_DocumentTransitionReport": {
     "auth_ref": [
      "r992"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true only for a form used as a transition report.",
        "label": "Document Transition Report",
        "terseLabel": "Document Transition Report"
       }
      }
     },
     "localname": "DocumentTransitionReport",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_DocumentType": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'.",
        "label": "Document Type",
        "terseLabel": "Document Type"
       }
      }
     },
     "localname": "DocumentType",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "submissionTypeItemType"
    },
    "dei_EntityAddressAddressLine1": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Address Line 1 such as Attn, Building Name, Street Name",
        "label": "Entity Address, Address Line One",
        "terseLabel": "Entity Address, Address Line One"
       }
      }
     },
     "localname": "EntityAddressAddressLine1",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressCityOrTown": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the City or Town",
        "label": "Entity Address, City or Town",
        "terseLabel": "Entity Address, City or Town"
       }
      }
     },
     "localname": "EntityAddressCityOrTown",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressPostalZipCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Code for the postal or zip code",
        "label": "Entity Address, Postal Zip Code",
        "terseLabel": "Entity Address, Postal Zip Code"
       }
      }
     },
     "localname": "EntityAddressPostalZipCode",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityAddressStateOrProvince": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the state or province.",
        "label": "Entity Address, State or Province",
        "terseLabel": "Entity Address, State or Province"
       }
      }
     },
     "localname": "EntityAddressStateOrProvince",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "stateOrProvinceItemType"
    },
    "dei_EntityCentralIndexKey": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.",
        "label": "Entity Central Index Key",
        "terseLabel": "Entity Central Index Key"
       }
      }
     },
     "localname": "EntityCentralIndexKey",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "centralIndexKeyItemType"
    },
    "dei_EntityCommonStockSharesOutstanding": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate number of shares or other units outstanding of each of registrant's classes of capital or common stock or other ownership interests, if and as stated on cover of related periodic report. Where multiple classes or units exist define each class/interest by adding class of stock items such as Common Class A [Member], Common Class B [Member] or Partnership Interest [Member] onto the Instrument [Domain] of the Entity Listings, Instrument.",
        "label": "Entity Common Stock, Shares Outstanding",
        "terseLabel": "Entity Common Stock, Shares Outstanding"
       }
      }
     },
     "localname": "EntityCommonStockSharesOutstanding",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "sharesItemType"
    },
    "dei_EntityCurrentReportingStatus": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate 'Yes' or 'No' whether registrants (1) have filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that registrants were required to file such reports), and (2) have been subject to such filing requirements for the past 90 days. This information should be based on the registrant's current or most recent filing containing the related disclosure.",
        "label": "Entity Current Reporting Status",
        "terseLabel": "Entity Current Reporting Status"
       }
      }
     },
     "localname": "EntityCurrentReportingStatus",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_EntityDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "All the names of the entities being reported upon in a document. Any legal structure used to conduct activities or to hold assets. Some examples of such structures are corporations, partnerships, limited liability companies, grantor trusts, and other trusts. This item does not include business and geographical segments which are included in the geographical or business segments domains.",
        "label": "Entity [Domain]",
        "terseLabel": "Entity [Domain]"
       }
      }
     },
     "localname": "EntityDomain",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "dei_EntityEmergingGrowthCompany": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate if registrant meets the emerging growth company criteria.",
        "label": "Entity Emerging Growth Company",
        "terseLabel": "Entity Emerging Growth Company"
       }
      }
     },
     "localname": "EntityEmergingGrowthCompany",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntityFileNumber": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Commission file number. The field allows up to 17 characters. The prefix may contain 1-3 digits, the sequence number may contain 1-8 digits, the optional suffix may contain 1-4 characters, and the fields are separated with a hyphen.",
        "label": "Entity File Number",
        "terseLabel": "Entity File Number"
       }
      }
     },
     "localname": "EntityFileNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "fileNumberItemType"
    },
    "dei_EntityFilerCategory": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate whether the registrant is one of the following: Large Accelerated Filer, Accelerated Filer, Non-accelerated Filer. Definitions of these categories are stated in Rule 12b-2 of the Exchange Act. This information should be based on the registrant's current or most recent filing containing the related disclosure.",
        "label": "Entity Filer Category",
        "terseLabel": "Entity Filer Category"
       }
      }
     },
     "localname": "EntityFilerCategory",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "filerCategoryItemType"
    },
    "dei_EntityIncorporationStateCountryCode": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Two-character EDGAR code representing the state or country of incorporation.",
        "label": "Entity Incorporation, State or Country Code",
        "terseLabel": "Entity Incorporation, State or Country Code"
       }
      }
     },
     "localname": "EntityIncorporationStateCountryCode",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "edgarStateCountryItemType"
    },
    "dei_EntityInteractiveDataCurrent": {
     "auth_ref": [
      "r1023"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).",
        "label": "Entity Interactive Data Current",
        "terseLabel": "Entity Interactive Data Current"
       }
      }
     },
     "localname": "EntityInteractiveDataCurrent",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_EntityPublicFloat": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate market value of the voting and non-voting common equity held by non-affiliates computed by reference to the price at which the common equity was last sold, or the average bid and asked price of such common equity, as of the last business day of the registrant's most recently completed second fiscal quarter.",
        "label": "Entity Public Float",
        "terseLabel": "Entity Public Float"
       }
      }
     },
     "localname": "EntityPublicFloat",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "monetaryItemType"
    },
    "dei_EntityRegistrantName": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.",
        "label": "Entity Registrant Name",
        "terseLabel": "Entity Registrant Name"
       }
      }
     },
     "localname": "EntityRegistrantName",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_EntityShellCompany": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Boolean flag that is true when the registrant is a shell company as defined in Rule 12b-2 of the Exchange Act.",
        "label": "Entity Shell Company",
        "terseLabel": "Entity Shell Company"
       }
      }
     },
     "localname": "EntityShellCompany",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntitySmallBusiness": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicates that the company is a Smaller Reporting Company (SRC).",
        "label": "Entity Small Business",
        "terseLabel": "Entity Small Business"
       }
      }
     },
     "localname": "EntitySmallBusiness",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_EntityTaxIdentificationNumber": {
     "auth_ref": [
      "r987"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS.",
        "label": "Entity Tax Identification Number",
        "terseLabel": "Entity Tax Identification Number"
       }
      }
     },
     "localname": "EntityTaxIdentificationNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "employerIdItemType"
    },
    "dei_EntityVoluntaryFilers": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate 'Yes' or 'No' if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.",
        "label": "Entity Voluntary Filers",
        "terseLabel": "Entity Voluntary Filers"
       }
      }
     },
     "localname": "EntityVoluntaryFilers",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_EntityWellKnownSeasonedIssuer": {
     "auth_ref": [
      "r1041"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Indicate 'Yes' or 'No' if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Is used on Form Type: 10-K, 10-Q, 8-K, 20-F, 6-K, 10-K/A, 10-Q/A, 20-F/A, 6-K/A, N-CSR, N-Q, N-1A.",
        "label": "Entity Well-known Seasoned Issuer",
        "terseLabel": "Entity Well-known Seasoned Issuer"
       }
      }
     },
     "localname": "EntityWellKnownSeasonedIssuer",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "yesNoItemType"
    },
    "dei_IcfrAuditorAttestationFlag": {
     "auth_ref": [
      "r989",
      "r990",
      "r991"
     ],
     "lang": {
      "en-us": {
       "role": {
        "label": "ICFR Auditor Attestation Flag",
        "terseLabel": "ICFR Auditor Attestation Flag"
       }
      }
     },
     "localname": "IcfrAuditorAttestationFlag",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "booleanItemType"
    },
    "dei_LegalEntityAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The set of legal entities associated with a report.",
        "label": "Legal Entity [Axis]",
        "terseLabel": "Legal Entity [Axis]"
       }
      }
     },
     "localname": "LegalEntityAxis",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "dei_LocalPhoneNumber": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Local phone number for entity.",
        "label": "Local Phone Number",
        "terseLabel": "Local Phone Number"
       }
      }
     },
     "localname": "LocalPhoneNumber",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "normalizedStringItemType"
    },
    "dei_Security12bTitle": {
     "auth_ref": [
      "r986"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Title of a 12(b) registered security.",
        "label": "Title of 12(b) Security",
        "terseLabel": "Title of 12(b) Security"
       }
      }
     },
     "localname": "Security12bTitle",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "securityTitleItemType"
    },
    "dei_SecurityExchangeName": {
     "auth_ref": [
      "r988"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the Exchange on which a security is registered.",
        "label": "Security Exchange Name",
        "terseLabel": "Security Exchange Name"
       }
      }
     },
     "localname": "SecurityExchangeName",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "edgarExchangeCodeItemType"
    },
    "dei_TradingSymbol": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Trading symbol of an instrument as listed on an exchange.",
        "label": "Trading Symbol",
        "terseLabel": "Trading Symbol"
       }
      }
     },
     "localname": "TradingSymbol",
     "nsuri": "http://xbrl.sec.gov/dei/2021q4",
     "presentation": [
      "http://www.comerica.com/role/DocumentAndEntityInformation"
     ],
     "xbrltype": "tradingSymbolItemType"
    },
    "srt_CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Condensed Financial Information Disclosure [Abstract]",
        "terseLabel": "Condensed Financial Information Disclosure [Abstract]"
       }
      }
     },
     "localname": "CondensedFinancialInformationOfParentCompanyOnlyDisclosureAbstract",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "srt_CondensedFinancialStatementsCaptionsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Condensed Financial Statements, Captions [Line Items]",
        "terseLabel": "Condensed Financial Statements, Captions [Line Items]"
       }
      }
     },
     "localname": "CondensedFinancialStatementsCaptionsLineItems",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_ConsolidatedEntitiesAxis": {
     "auth_ref": [
      "r136",
      "r386",
      "r391",
      "r399",
      "r664",
      "r665",
      "r670",
      "r671",
      "r810",
      "r983",
      "r1024",
      "r1026",
      "r1035",
      "r1036"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by consolidated entity or group of entities.",
        "label": "Consolidated Entities [Axis]",
        "terseLabel": "Consolidated Entities [Axis]"
       }
      }
     },
     "localname": "ConsolidatedEntitiesAxis",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_ConsolidatedEntitiesDomain": {
     "auth_ref": [
      "r136",
      "r386",
      "r391",
      "r399",
      "r664",
      "r665",
      "r670",
      "r671",
      "r810",
      "r983",
      "r1024",
      "r1026",
      "r1035",
      "r1036"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Entity or group of entities consolidated into reporting entity.",
        "label": "Consolidated Entities [Domain]",
        "terseLabel": "Consolidated Entities [Domain]",
        "verboseLabel": "Consolidated Entities [Domain]"
       }
      }
     },
     "localname": "ConsolidatedEntitiesDomain",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ConsolidationItemsAxis": {
     "auth_ref": [
      "r136",
      "r194",
      "r207",
      "r208",
      "r209",
      "r210",
      "r212",
      "r214",
      "r218",
      "r386",
      "r387",
      "r388",
      "r389",
      "r390",
      "r391",
      "r393",
      "r394",
      "r396",
      "r398",
      "r399",
      "r1026",
      "r1027",
      "r1028",
      "r1029",
      "r1030",
      "r1031",
      "r1032",
      "r1033",
      "r1034",
      "r1035",
      "r1036"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by components, eliminations, non-segment corporate-level activity and reconciling items used in consolidating a parent entity and its subsidiaries or its operating segments.",
        "label": "Consolidation Items [Axis]",
        "terseLabel": "Consolidation Items [Axis]"
       }
      }
     },
     "localname": "ConsolidationItemsAxis",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_ConsolidationItemsDomain": {
     "auth_ref": [
      "r136",
      "r194",
      "r207",
      "r208",
      "r209",
      "r210",
      "r212",
      "r214",
      "r218",
      "r386",
      "r387",
      "r388",
      "r389",
      "r390",
      "r391",
      "r393",
      "r394",
      "r396",
      "r398",
      "r399",
      "r1026",
      "r1027",
      "r1028",
      "r1029",
      "r1030",
      "r1031",
      "r1032",
      "r1033",
      "r1034",
      "r1035",
      "r1036"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Components, elimination, non-segment corporate-level activity and reconciling items used in consolidating a parent entity and its subsidiaries or its operating segments.",
        "label": "Consolidation Items [Domain]",
        "terseLabel": "Consolidation Items [Domain]"
       }
      }
     },
     "localname": "ConsolidationItemsDomain",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ContractualObligationFiscalYearMaturityScheduleTableTextBlock": {
     "auth_ref": [
      "r1022"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of contractual obligation by timing of payment due. Includes, but is not limited to, long-term debt obligation, lease obligation, and purchase obligation.",
        "label": "Contractual Obligation, Fiscal Year Maturity [Table Text Block]",
        "terseLabel": "Schedule Of Maturities Of Certificates of Deposit and Other Deposits with a Stated Maturity"
       }
      }
     },
     "localname": "ContractualObligationFiscalYearMaturityScheduleTableTextBlock",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "srt_MaximumMember": {
     "auth_ref": [
      "r404",
      "r428",
      "r551",
      "r556",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r848",
      "r952",
      "r954",
      "r984",
      "r985"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Upper limit of the provided range.",
        "label": "Maximum [Member]",
        "terseLabel": "Maximum"
       }
      }
     },
     "localname": "MaximumMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_MinimumMember": {
     "auth_ref": [
      "r404",
      "r428",
      "r551",
      "r556",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r848",
      "r952",
      "r954",
      "r984",
      "r985"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Lower limit of the provided range.",
        "label": "Minimum [Member]",
        "terseLabel": "Minimum",
        "verboseLabel": "Minimum"
       }
      }
     },
     "localname": "MinimumMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ParentCompanyMember": {
     "auth_ref": [
      "r136"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The registrant that controls, directly or indirectly, another entity (or entities). The usual condition for control is ownership of a majority (over 50%) of the outstanding voting stock. The power to control may also exist with a lesser percentage of ownership, for example, by contract, lease, agreement with other stockholders or by court decree.",
        "label": "Parent Company [Member]",
        "terseLabel": "Parent Company",
        "verboseLabel": "Comerica Incorporated"
       }
      }
     },
     "localname": "ParentCompanyMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ProductOrServiceAxis": {
     "auth_ref": [
      "r220",
      "r460",
      "r462",
      "r849",
      "r951",
      "r953"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by product and service, or group of similar products and similar services.",
        "label": "Product and Service [Axis]",
        "terseLabel": "Product and Service [Axis]"
       }
      }
     },
     "localname": "ProductOrServiceAxis",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_ProductsAndServicesDomain": {
     "auth_ref": [
      "r220",
      "r460",
      "r462",
      "r849",
      "r951",
      "r953"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Product or service, or a group of similar products or similar services.",
        "label": "Product and Service [Domain]",
        "terseLabel": "Product and Service [Domain]"
       }
      }
     },
     "localname": "ProductsAndServicesDomain",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_RangeAxis": {
     "auth_ref": [
      "r404",
      "r428",
      "r490",
      "r551",
      "r556",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r848",
      "r952",
      "r954",
      "r984",
      "r985"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by statistical measurement. Includes, but is not limited to, minimum, maximum, weighted average, arithmetic average, and median.",
        "label": "Statistical Measurement [Axis]",
        "terseLabel": "Statistical Measurement [Axis]"
       }
      }
     },
     "localname": "RangeAxis",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_RangeMember": {
     "auth_ref": [
      "r404",
      "r428",
      "r490",
      "r551",
      "r556",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r848",
      "r952",
      "r954",
      "r984",
      "r985"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Statistical measurement. Includes, but is not limited to, minimum, maximum, weighted average, arithmetic average, and median.",
        "label": "Statistical Measurement [Domain]",
        "terseLabel": "Statistical Measurement [Domain]"
       }
      }
     },
     "localname": "RangeMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_RegulatoryCapitalRequirementsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]",
        "terseLabel": "Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]"
       }
      }
     },
     "localname": "RegulatoryCapitalRequirementsAbstract",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "srt_ReportableLegalEntitiesMember": {
     "auth_ref": [
      "r136",
      "r386",
      "r391",
      "r399",
      "r1026",
      "r1035",
      "r1036"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Legal entities of the consolidated entity reporting separate financial information in the entity's financial statements.",
        "label": "Reportable Legal Entities [Member]",
        "terseLabel": "Subsidiaries"
       }
      }
     },
     "localname": "ReportableLegalEntitiesMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_RevisionOfPriorPeriodChangeInAccountingPrincipleAdjustmentMember": {
     "auth_ref": [
      "r142",
      "r143"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cumulative increase (decrease) to previously issued financial statements for change in accounting principle. Excludes adjustment for amendment to accounting standards.",
        "label": "Revision of Prior Period, Change in Accounting Principle, Adjustment [Member]",
        "terseLabel": "Accounting change impact"
       }
      }
     },
     "localname": "RevisionOfPriorPeriodChangeInAccountingPrincipleAdjustmentMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ScenarioPreviouslyReportedMember": {
     "auth_ref": [
      "r3",
      "r139",
      "r141",
      "r142",
      "r143",
      "r147",
      "r148",
      "r149",
      "r150",
      "r152",
      "r153",
      "r154",
      "r155",
      "r175",
      "r297",
      "r298",
      "r604",
      "r643",
      "r726",
      "r730",
      "r731",
      "r732",
      "r957",
      "r958",
      "r959",
      "r960",
      "r961",
      "r962",
      "r963",
      "r964",
      "r965",
      "r966",
      "r1045",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Represents amount as previously reported before adjustment for retrospective application of amendment to accounting standards, other change in accounting principle, correction of error, and other revision.",
        "label": "Previously Reported [Member]",
        "terseLabel": "Previously Reported"
       }
      }
     },
     "localname": "ScenarioPreviouslyReportedMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "srt_ScheduleOfCondensedBalanceSheetTableTextBlock": {
     "auth_ref": [
      "r1037"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of condensed balance sheet, including, but not limited to, balance sheets of consolidated entities and consolidation eliminations.",
        "label": "Condensed Balance Sheet [Table Text Block]",
        "terseLabel": "Balance Sheets - Comerica Incorporated"
       }
      }
     },
     "localname": "ScheduleOfCondensedBalanceSheetTableTextBlock",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "srt_ScheduleOfCondensedCashFlowStatementTableTextBlock": {
     "auth_ref": [
      "r1037"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of condensed cash flow statement, including, but not limited to, cash flow statements of consolidated entities and consolidation eliminations.",
        "label": "Condensed Cash Flow Statement [Table Text Block]",
        "terseLabel": "Statements of Cash Flows - Comerica Incorporated"
       }
      }
     },
     "localname": "ScheduleOfCondensedCashFlowStatementTableTextBlock",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "srt_ScheduleOfCondensedFinancialStatementsTable": {
     "auth_ref": [
      "r136",
      "r660",
      "r1025",
      "r1038",
      "r1039",
      "r1040"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about condensed financial statements, including, but not limited to, the balance sheet, income statement, and statement of cash flows.",
        "label": "Condensed Financial Statements [Table]",
        "terseLabel": "Schedule of Condensed Financial Statements [Table]"
       }
      }
     },
     "localname": "ScheduleOfCondensedFinancialStatementsTable",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "srt_ScheduleOfCondensedIncomeStatementTableTextBlock": {
     "auth_ref": [
      "r1037"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of condensed income statement, including, but not limited to, income statements of consolidated entities and consolidation eliminations.",
        "label": "Condensed Income Statement [Table Text Block]",
        "terseLabel": "Statements of Income - Comerica Incorporated"
       }
      }
     },
     "localname": "ScheduleOfCondensedIncomeStatementTableTextBlock",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "srt_SubsidiariesMember": {
     "auth_ref": [
      "r517",
      "r804",
      "r805",
      "r807"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Entity owned or controlled by another entity.",
        "label": "Subsidiaries [Member]",
        "verboseLabel": "U.S. Banking Subsidiaries"
       }
      }
     },
     "localname": "SubsidiariesMember",
     "nsuri": "http://fasb.org/srt/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AccountingPoliciesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Accounting Policies [Abstract]",
        "terseLabel": "Accounting Policies [Abstract]"
       }
      }
     },
     "localname": "AccountingPoliciesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccountingStandardsUpdate201613Member": {
     "auth_ref": [
      "r292"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accounting Standards Update 2016-13 Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.",
        "label": "Accounting Standards Update 2016-13 [Member]",
        "terseLabel": "Accounting Standards Update 2016-13 [Member]"
       }
      }
     },
     "localname": "AccountingStandardsUpdate201613Member",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AccountsNotesAndLoansReceivableLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Accounts, Notes, Loans and Financing Receivable [Line Items]",
        "terseLabel": "Accounts, Notes, Loans and Financing Receivable [Line Items]"
       }
      }
     },
     "localname": "AccountsNotesAndLoansReceivableLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis": {
     "auth_ref": [
      "r47"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of receivable.",
        "label": "Receivable Type [Axis]",
        "terseLabel": "Receivable Type [Axis]"
       }
      }
     },
     "localname": "AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccountsNotesLoansAndFinancingReceivablesByIndustryOfCounterpartyTypeAxis": {
     "auth_ref": [
      "r47"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by industry of counterparty. A counterparty is the other party that participates in a financial transaction.",
        "label": "Industry of Counterparty, Type [Axis]",
        "terseLabel": "Industry of Counterparty, Type [Axis]"
       }
      }
     },
     "localname": "AccountsNotesLoansAndFinancingReceivablesByIndustryOfCounterpartyTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments": {
     "auth_ref": [
      "r115"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 7.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.",
        "label": "Accretion (Amortization) of Discounts and Premiums, Investments",
        "negatedLabel": "Net amortization of securities"
       }
      }
     },
     "localname": "AccretionAmortizationOfDiscountsAndPremiumsInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment": {
     "auth_ref": [
      "r33",
      "r355"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.",
        "label": "Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment",
        "negatedTerseLabel": "Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment"
       }
      }
     },
     "localname": "AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax": {
     "auth_ref": [
      "r69"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "AOCI, Debt Securities, Available-for-sale, Adjustment, after Tax",
        "periodEndLabel": "Investment securities, Balance at end of period, net of tax",
        "periodStartLabel": "Investment securities, Balance at beginning of period, net of tax"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax": {
     "auth_ref": [
      "r64",
      "r70",
      "r511"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).",
        "label": "Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax",
        "periodEndLabel": "Benefit plans, Balance at end of period, net of tax",
        "periodStartLabel": "Benefit plans, Balance at beginning of period, net of tax"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax": {
     "auth_ref": [
      "r27",
      "r67",
      "r69",
      "r70",
      "r938",
      "r962",
      "r966"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 3.0,
       "parentTag": "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.",
        "label": "Accumulated Other Comprehensive Income (Loss), Net of Tax",
        "terseLabel": "Accumulated other comprehensive (loss) income",
        "verboseLabel": "Total accumulated other comprehensive (loss) income at end of period, net of tax"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeLossNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]",
        "terseLabel": "Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_AccumulatedOtherComprehensiveIncomeMember": {
     "auth_ref": [
      "r66",
      "r70",
      "r79",
      "r80",
      "r81",
      "r139",
      "r140",
      "r141",
      "r669",
      "r957",
      "r958",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accumulated increase (decrease) in equity from transactions and other events and circumstances from non-owner sources, attributable to the parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners.",
        "label": "AOCI Attributable to Parent [Member]",
        "terseLabel": "Accumulated Other Comprehensive (Loss) Income"
       }
      }
     },
     "localname": "AccumulatedOtherComprehensiveIncomeMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Acquired Finite-Lived Intangible Assets [Line Items]",
        "terseLabel": "Acquired Finite-Lived Intangible Assets [Line Items]"
       }
      }
     },
     "localname": "AcquiredFiniteLivedIntangibleAssetsLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AdditionalPaidInCapitalCommonStock": {
     "auth_ref": [
      "r25"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value received from shareholders in common stock-related transactions that are in excess of par value or stated value and amounts received from other stock-related transactions. Includes only common stock transactions (excludes preferred stock transactions). May be called contributed capital, capital in excess of par, capital surplus, or paid-in capital.",
        "label": "Additional Paid in Capital, Common Stock",
        "terseLabel": "Capital surplus"
       }
      }
     },
     "localname": "AdditionalPaidInCapitalCommonStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AdditionalPaidInCapitalMember": {
     "auth_ref": [
      "r139",
      "r140",
      "r141",
      "r601",
      "r602",
      "r603",
      "r730"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders.",
        "label": "Additional Paid-in Capital [Member]",
        "terseLabel": "Capital Surplus"
       }
      }
     },
     "localname": "AdditionalPaidInCapitalMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis": {
     "auth_ref": [
      "r142",
      "r143",
      "r144",
      "r145"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of change in accounting principle. Excludes change from amendment to accounting standards.",
        "label": "Change in Accounting Principle, Type [Axis]",
        "terseLabel": "Change in Accounting Principle, Type [Axis]"
       }
      }
     },
     "localname": "AdjustmentsForChangeInAccountingPrincipleAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AdjustmentsForNewAccountingPronouncementsAxis": {
     "auth_ref": [
      "r0",
      "r1",
      "r2",
      "r3",
      "r4",
      "r142",
      "r143",
      "r144",
      "r145",
      "r156",
      "r258",
      "r259",
      "r293",
      "r294",
      "r295",
      "r296",
      "r297",
      "r298",
      "r385",
      "r597",
      "r598",
      "r599",
      "r600",
      "r601",
      "r602",
      "r603",
      "r604",
      "r640",
      "r641",
      "r642",
      "r643",
      "r722",
      "r723",
      "r724",
      "r725",
      "r726",
      "r727",
      "r728",
      "r729",
      "r730",
      "r731",
      "r732",
      "r761",
      "r762",
      "r763",
      "r764",
      "r765",
      "r766",
      "r767",
      "r768",
      "r801",
      "r851",
      "r852",
      "r853",
      "r955",
      "r956",
      "r957",
      "r958",
      "r959",
      "r960",
      "r961",
      "r962",
      "r963",
      "r964",
      "r965",
      "r966",
      "r1042",
      "r1043",
      "r1044",
      "r1045",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by amendment to accounting standards.",
        "label": "Accounting Standards Update [Axis]",
        "terseLabel": "Adjustments for New Accounting Pronouncements [Axis]"
       }
      }
     },
     "localname": "AdjustmentsForNewAccountingPronouncementsAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue": {
     "auth_ref": [
      "r558",
      "r560",
      "r607",
      "r608"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase to additional paid-in capital (APIC) for recognition of cost for award under share-based payment arrangement.",
        "label": "APIC, Share-based Payment Arrangement, Increase for Cost Recognition",
        "terseLabel": "Share-based compensation"
       }
      }
     },
     "localname": "AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]",
        "terseLabel": "Adjustments to reconcile net income to net cash provided by operating activities:"
       }
      }
     },
     "localname": "AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AdvertisingExpense": {
     "auth_ref": [
      "r610"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 7.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.",
        "label": "Advertising Expense",
        "terseLabel": "Advertising expense"
       }
      }
     },
     "localname": "AdvertisingExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AffordableHousingTaxCreditsAndOtherTaxBenefitsAmount": {
     "auth_ref": [
      "r290"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of affordable housing tax credits and other tax benefits recognized.",
        "label": "Affordable Housing Tax Credits and Other Tax Benefits, Amount",
        "negatedTerseLabel": "Provision for income taxes, affordable housing tax credits and other tax benefits"
       }
      }
     },
     "localname": "AffordableHousingTaxCreditsAndOtherTaxBenefitsAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AllocatedShareBasedCompensationExpense": {
     "auth_ref": [
      "r560",
      "r593",
      "r606"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.",
        "label": "Share-based Payment Arrangement, Expense",
        "terseLabel": "Total share-based compensation expense"
       }
      }
     },
     "localname": "AllocatedShareBasedCompensationExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryofComponentsofShareBasedCompensationExpenseDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock": {
     "auth_ref": [
      "r235",
      "r305"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of allowance for credit loss on financing receivable.",
        "label": "Financing Receivable, Allowance for Credit Loss [Table Text Block]",
        "terseLabel": "Changes In The Allowance For Loan Losses"
       }
      }
     },
     "localname": "AllowanceForCreditLossesOnFinancingReceivablesTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after recoveries, of loans and leases that have been written-off.",
        "label": "Allowance for Loan and Lease Losses Write-offs, Net",
        "negatedTotalLabel": "Net loan (charge-offs) recoveries"
       }
      }
     },
     "localname": "AllowanceForLoanAndLeaseLossesWriteoffsNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AlternativeInvestment": {
     "auth_ref": [
      "r734",
      "r746"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.",
        "label": "Alternative Investment",
        "terseLabel": "Nonmarketable equity securities"
       }
      }
     },
     "localname": "AlternativeInvestment",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization": {
     "auth_ref": [
      "r291"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of amortization expense of investment in qualified affordable housing projects.",
        "label": "Amortization Method Qualified Affordable Housing Project Investments, Amortization",
        "terseLabel": "Provision for income taxes, amortization of LIHTC investments"
       }
      }
     },
     "localname": "AmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AmortizationOfIntangibleAssets": {
     "auth_ref": [
      "r114",
      "r342",
      "r347"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.",
        "label": "Amortization of Intangible Assets",
        "terseLabel": "Amortization expense of core deposit intangible"
       }
      }
     },
     "localname": "AmortizationOfIntangibleAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of antidilutive security.",
        "label": "Antidilutive Securities [Axis]",
        "terseLabel": "Antidilutive Securities [Axis]"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]",
        "terseLabel": "Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfNetIncomePerOutstandingUnitAmount": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic net Income or Loss per outstanding limited partnership unit in the future and that were not included in the computation of diluted net income per limited partnership unit, because to do so would increase net income per unit amounts or decrease loss per unit amounts for the period presented.",
        "label": "Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, Amount",
        "terseLabel": "Range of exercise prices"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesExcludedFromComputationOfNetIncomePerOutstandingUnitAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_AntidilutiveSecuritiesNameDomain": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Incremental common shares attributable to securities that were not included in diluted earnings per share (EPS) because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.",
        "label": "Antidilutive Securities, Name [Domain]",
        "terseLabel": "Antidilutive Securities, Name [Domain]"
       }
      }
     },
     "localname": "AntidilutiveSecuritiesNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_AociLossCashFlowHedgeCumulativeGainLossAfterTax": {
     "auth_ref": [
      "r67"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax",
        "terseLabel": "AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax"
       }
      }
     },
     "localname": "AociLossCashFlowHedgeCumulativeGainLossAfterTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_Assets": {
     "auth_ref": [
      "r129",
      "r202",
      "r209",
      "r216",
      "r289",
      "r386",
      "r387",
      "r388",
      "r390",
      "r391",
      "r392",
      "r393",
      "r395",
      "r397",
      "r399",
      "r400",
      "r664",
      "r670",
      "r759",
      "r811",
      "r813",
      "r861",
      "r935"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.",
        "label": "Assets",
        "totalLabel": "Total assets"
       }
      }
     },
     "localname": "Assets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AssetsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Assets [Abstract]",
        "terseLabel": "ASSETS"
       }
      }
     },
     "localname": "AssetsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_AssetsFairValueDisclosure": {
     "auth_ref": [
      "r735"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.",
        "label": "Assets, Fair Value Disclosure",
        "terseLabel": "Total assets at fair value"
       }
      }
     },
     "localname": "AssetsFairValueDisclosure",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax": {
     "auth_ref": [
      "r268"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax",
        "terseLabel": "Investment securities available-for-sale, Gross Unrealized Gains"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax": {
     "auth_ref": [
      "r269"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax",
        "verboseLabel": "Investment securities available-for-sale, Gross Unrealized Losses"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis": {
     "auth_ref": [
      "r266",
      "r329"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Amortized Cost",
        "terseLabel": "Investment securities available-for-sale, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleDebtSecuritiesAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost",
        "terseLabel": "Available-for-sale, Within one year, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesNextRollingTwelveMonthsAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenAmortizedCostBasis": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost",
        "terseLabel": "Available-for-sale, After ten years, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after rolling tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value",
        "terseLabel": "Available-for-sale, After ten years, Fair Value"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingAfterYearTenFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in rolling sixth through tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost",
        "terseLabel": "Available-for-sale, After five years through ten years, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in rolling sixth through tenth fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value",
        "terseLabel": "Available-for-sale, After five years through ten years, Fair Value"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost",
        "terseLabel": "Available-for-sale, After one year through five years, Amortized Cost"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveAmortizedCostBasis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment in debt security, measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next rolling fiscal year through fifth year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.",
        "label": "Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value",
        "terseLabel": "Available-for-sale, After one year through five years, Fair Value"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue": {
     "auth_ref": [
      "r270",
      "r271",
      "r909"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One",
        "terseLabel": "Available-for-sale, Within one year, Fair Value"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AvailableForSaleSecuritiesDebtSecurities": {
     "auth_ref": [
      "r263",
      "r267",
      "r329",
      "r868"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 4.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale",
        "terseLabel": "Investment Securities, Available-for-sale",
        "verboseLabel": "Investment securities available-for-sale, Fair Value"
       }
      }
     },
     "localname": "AvailableForSaleSecuritiesDebtSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_AverageTermOfCreditRiskDerivatives1": {
     "auth_ref": [
      "r713"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average period covered by credit risk derivative contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Average Term of Credit Risk Derivatives",
        "terseLabel": "Weighted average remaining maturity of credit risk participation agreements, in years"
       }
      }
     },
     "localname": "AverageTermOfCreditRiskDerivatives1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_AwardTypeAxis": {
     "auth_ref": [
      "r562",
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of award under share-based payment arrangement.",
        "label": "Award Type [Axis]",
        "terseLabel": "Award Type [Axis]"
       }
      }
     },
     "localname": "AwardTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_BalanceSheetLocationAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by location on balance sheet (statement of financial position).",
        "label": "Balance Sheet Location [Axis]",
        "terseLabel": "Balance Sheet Location [Axis]"
       }
      }
     },
     "localname": "BalanceSheetLocationAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_BalanceSheetLocationDomain": {
     "auth_ref": [
      "r695",
      "r700"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Location in the balance sheet (statement of financial position).",
        "label": "Balance Sheet Location [Domain]",
        "terseLabel": "Balance Sheet Location [Domain]"
       }
      }
     },
     "localname": "BalanceSheetLocationDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_BankAcceptancesExecutedAndOutstanding": {
     "auth_ref": [
      "r873"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying amount as of the balance sheet date of drafts and bills of exchange that have been accepted by the reporting bank, or by others for its own account, as its liability to holders of the drafts.",
        "label": "Bank Acceptances Executed and Outstanding",
        "terseLabel": "Acceptances outstanding"
       }
      }
     },
     "localname": "BankAcceptancesExecutedAndOutstanding",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_BankOwnedLifeInsuranceIncome": {
     "auth_ref": [
      "r894"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 6.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 6.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Earnings on or other increases in the value of the cash surrender value of bank owned life insurance policies.",
        "label": "Bank Owned Life Insurance Income",
        "terseLabel": "Bank-owned life insurance"
       }
      }
     },
     "localname": "BankOwnedLifeInsuranceIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock": {
     "auth_ref": [
      "r138"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for the basis of presentation and significant accounting policies concepts. Basis of presentation describes the underlying basis used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS).  Accounting policies describe all significant accounting policies of the reporting entity.",
        "label": "Basis of Presentation and Significant Accounting Policies [Text Block]",
        "terseLabel": "Basis of Presentation and Accounting Policies"
       }
      }
     },
     "localname": "BasisOfPresentationAndSignificantAccountingPoliciesTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_BorrowingsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Obligations to pay to another in accordance with an expressed or implied agreement.",
        "label": "Borrowings [Member]",
        "terseLabel": "Other Short-term Borrowings"
       }
      }
     },
     "localname": "BorrowingsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_BrokerageCommissionsRevenue": {
     "auth_ref": [
      "r855",
      "r893"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 7.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 7.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of commission revenue from buying and selling securities on behalf of customers.",
        "label": "Brokerage Commissions Revenue",
        "terseLabel": "Brokerage fees"
       }
      }
     },
     "localname": "BrokerageCommissionsRevenue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_BuildingAndBuildingImprovementsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Facility held for productive use including, but not limited to, office, production, storage and distribution facilities and any addition, improvement, or renovation to the structure, for example, but not limited to, interior masonry, interior flooring, electrical, and plumbing.",
        "label": "Building and Building Improvements [Member]",
        "terseLabel": "Premises the Corporation owns"
       }
      }
     },
     "localname": "BuildingAndBuildingImprovementsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_BuildingsAndImprovementsGross": {
     "auth_ref": [
      "r10",
      "r354"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.",
        "label": "Buildings and Improvements, Gross",
        "terseLabel": "Buildings and improvements"
       }
      }
     },
     "localname": "BuildingsAndImprovementsGross",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_Capital": {
     "auth_ref": [
      "r923"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of total capital as defined by regulatory framework.",
        "label": "Banking Regulation, Total Capital, Actual",
        "terseLabel": "Total capital"
       }
      }
     },
     "localname": "Capital",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CarryingReportedAmountFairValueDisclosureMember": {
     "auth_ref": [
      "r755",
      "r756"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measured as reported on the statement of financial position (balance sheet).",
        "label": "Reported Value Measurement [Member]",
        "terseLabel": "Carrying Amount"
       }
      }
     },
     "localname": "CarryingReportedAmountFairValueDisclosureMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CashAndCashEquivalentsAtCarryingValue": {
     "auth_ref": [
      "r8",
      "r29",
      "r116"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.",
        "label": "Cash and Cash Equivalents, at Carrying Value",
        "periodEndLabel": "Cash and cash equivalents at end of period",
        "periodStartLabel": "Cash and cash equivalents at beginning of period"
       }
      }
     },
     "localname": "CashAndCashEquivalentsAtCarryingValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.",
        "label": "Cash and Cash Equivalents, Period Increase (Decrease)",
        "terseLabel": "Net increase (decrease) in cash and cash equivalents",
        "totalLabel": "Net increase (decrease) in cash and cash equivalents"
       }
      }
     },
     "localname": "CashAndCashEquivalentsPeriodIncreaseDecrease",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashAndCashEquivalentsPolicyTextBlock": {
     "auth_ref": [
      "r11",
      "r118"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for cash and cash equivalents, including the policy for determining which items are treated as cash equivalents. Other information that may be disclosed includes (1) the nature of any restrictions on the entity's use of its cash and cash equivalents, (2) whether the entity's cash and cash equivalents are insured or expose the entity to credit risk, (3) the classification of any negative balance accounts (overdrafts), and (4) the carrying basis of cash equivalents (for example, at cost) and whether the carrying amount of cash equivalents approximates fair value.",
        "label": "Cash and Cash Equivalents, Policy [Policy Text Block]",
        "terseLabel": "Statements Of Cash Flows"
       }
      }
     },
     "localname": "CashAndCashEquivalentsPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_CashAndDueFromBanks": {
     "auth_ref": [
      "r858"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For banks and other depository institutions: Includes cash on hand (currency and coin), cash items in process of collection, noninterest bearing deposits due from other financial institutions (including corporate credit unions), and noninterest bearing balances with the Federal Reserve Banks, Federal Home Loan Banks and central banks.",
        "label": "Cash and Due from Banks",
        "terseLabel": "Cash and due from banks",
        "verboseLabel": "Cash and due from subsidiary bank"
       }
      }
     },
     "localname": "CashAndDueFromBanks",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries": {
     "auth_ref": [
      "r137"
     ],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_Revenues",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.",
        "label": "SEC Schedule, 12-04, Cash Dividends Paid to Registrant, Consolidated Subsidiaries",
        "terseLabel": "Dividends from subsidiaries"
       }
      }
     },
     "localname": "CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CashFlowHedgingMember": {
     "auth_ref": [
      "r692"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Hedge of the exposure to variability in the cash flows of a recognized asset or liability, or of a forecasted transaction, that is attributable to a particular risk.",
        "label": "Cash Flow Hedging [Member]",
        "terseLabel": "Swaps - cash flow - receive fixed/pay floating rate"
       }
      }
     },
     "localname": "CashFlowHedgingMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]",
        "terseLabel": "Noncash investing and financing activities:"
       }
      }
     },
     "localname": "CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ChangeInAccountingPrincipleMember": {
     "auth_ref": [
      "r142",
      "r143",
      "r144",
      "r145"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Change in accounting principle. Excludes change from amendment to accounting standards.",
        "label": "Change in Accounting Principle, Type [Domain]",
        "terseLabel": "Change in Accounting Principle, Type [Domain]"
       }
      }
     },
     "localname": "ChangeInAccountingPrincipleMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1": {
     "auth_ref": [
      "r719"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement.",
        "label": "Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments",
        "terseLabel": "Interest rate contracts: Derivatives designated as hedging instruments"
       }
      }
     },
     "localname": "ChangeInUnrealizedGainLossOnFairValueHedgingInstruments1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis": {
     "auth_ref": [
      "r316"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of borrower determined on the basis of initial measurement attribute, risk characteristics and method of monitoring and assessing credit risk.",
        "label": "Type of Borrower [Axis]",
        "terseLabel": "Type of Borrower [Axis]"
       }
      }
     },
     "localname": "ClassOfFinancingReceivableTypeOfBorrowerAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ClassOfFinancingReceivableTypeOfBorrowerDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Category of entity or individual who borrows funds.",
        "label": "Class of Financing Receivable, Type of Borrower [Domain]",
        "terseLabel": "Class of Financing Receivable, Type of Borrower [Domain]"
       }
      }
     },
     "localname": "ClassOfFinancingReceivableTypeOfBorrowerDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CollateralizedMortgageObligationsMember": {
     "auth_ref": [
      "r383"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The category includes multiclass, pay-through securitizations collateralized by mortgages secured by assets, such as automobiles and boats, which are generally structured so that the collections of principal and interest due from the underlying debtors are paid to the holders of the CMO.",
        "label": "Collateralized Mortgage Obligations [Member]",
        "terseLabel": "Mortgage-backed secutities"
       }
      }
     },
     "localname": "CollateralizedMortgageObligationsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialAndIndustrialSectorMember": {
     "auth_ref": [
      "r320"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sector of the economy consisting of companies engaged in commercial and industrial business activities.",
        "label": "Commercial and Industrial Sector [Member]",
        "terseLabel": "Other business lines"
       }
      }
     },
     "localname": "CommercialAndIndustrialSectorMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialBorrowerMember": {
     "auth_ref": [
      "r317"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Business which borrows funds.",
        "label": "Commercial Borrower [Member]",
        "terseLabel": "Commercial borrower"
       }
      }
     },
     "localname": "CommercialBorrowerMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialLoanMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A loan, whether secured or unsecured, to a company for purposes such as seasonal working capital needs, inventory financing, equipment purchases and acquisitions.",
        "label": "Commercial Loan [Member]",
        "terseLabel": "Commercial loan servicing fees"
       }
      }
     },
     "localname": "CommercialLoanMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialMortgageBackedSecuritiesMember": {
     "auth_ref": [
      "r272",
      "r491"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Securities collateralized by commercial real estate mortgage loans.",
        "label": "Commercial Mortgage Backed Securities [Member]",
        "terseLabel": "Commercial Mortgage Backed Securities"
       }
      }
     },
     "localname": "CommercialMortgageBackedSecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialPortfolioSegmentMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Portfolio segment of the company's total financing receivables related to commercial receivables.",
        "label": "Commercial Portfolio Segment [Member]",
        "terseLabel": "Business loans"
       }
      }
     },
     "localname": "CommercialPortfolioSegmentMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommercialRealEstateMember": {
     "auth_ref": [
      "r322",
      "r491"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Property that is solely used for business purposes.",
        "label": "Commercial Real Estate [Member]",
        "terseLabel": "Total commercial real estate"
       }
      }
     },
     "localname": "CommercialRealEstateMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommitmentsAndContingenciesDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Commitments and Contingencies Disclosure [Abstract]",
        "terseLabel": "Commitments and Contingencies Disclosure [Abstract]"
       }
      }
     },
     "localname": "CommitmentsAndContingenciesDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_CommitmentsAndContingenciesDisclosureTextBlock": {
     "auth_ref": [
      "r364",
      "r365",
      "r366",
      "r376",
      "r979"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for commitments and contingencies.",
        "label": "Commitments and Contingencies Disclosure [Text Block]",
        "terseLabel": "Contingent Liabilities"
       }
      }
     },
     "localname": "CommitmentsAndContingenciesDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilities"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_CommitmentsToExtendCreditMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan commitments are legally binding commitments to extend credit to a counterparty under certain terms and conditions.",
        "label": "Commitments to Extend Credit [Member]",
        "terseLabel": "Unused Commitments to Extend Credit"
       }
      }
     },
     "localname": "CommitmentsToExtendCreditMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommodityContractMember": {
     "auth_ref": [
      "r491",
      "r708"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument whose primary underlying risk is tied to commodity prices.",
        "label": "Commodity Contract [Member]",
        "terseLabel": "Energy derivative contracts",
        "verboseLabel": "Energy contracts"
       }
      }
     },
     "localname": "CommodityContractMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommonStockCapitalSharesReservedForFutureIssuance": {
     "auth_ref": [
      "r44"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate number of common shares reserved for future issuance.",
        "label": "Common Stock, Capital Shares Reserved for Future Issuance",
        "terseLabel": "Common stock shares reserved for future issuance"
       }
      }
     },
     "localname": "CommonStockCapitalSharesReservedForFutureIssuance",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockDividendsPerShareDeclared": {
     "auth_ref": [
      "r447"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate dividends declared during the period for each share of common stock outstanding.",
        "label": "Common Stock, Dividends, Per Share, Declared",
        "terseLabel": "Cash dividends declared per common share"
       }
      }
     },
     "localname": "CommonStockDividendsPerShareDeclared",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquityParenthetical",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_CommonStockMember": {
     "auth_ref": [
      "r139",
      "r140",
      "r730"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Stock that is subordinate to all other stock of the issuer.",
        "label": "Common Stock [Member]",
        "terseLabel": "Common Stock",
        "verboseLabel": "Common stock"
       }
      }
     },
     "localname": "CommonStockMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CommonStockParOrStatedValuePerShare": {
     "auth_ref": [
      "r24"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Face amount or stated value per share of common stock.",
        "label": "Common Stock, Par or Stated Value Per Share",
        "terseLabel": "Common stock, par value"
       }
      }
     },
     "localname": "CommonStockParOrStatedValuePerShare",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_CommonStockSharesAuthorized": {
     "auth_ref": [
      "r24"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The maximum number of common shares permitted to be issued by an entity's charter and bylaws.",
        "label": "Common Stock, Shares Authorized",
        "terseLabel": "Common stock, authorized shares"
       }
      }
     },
     "localname": "CommonStockSharesAuthorized",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockSharesIssued": {
     "auth_ref": [
      "r24"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.",
        "label": "Common Stock, Shares, Issued",
        "terseLabel": "Common stock, issued shares"
       }
      }
     },
     "localname": "CommonStockSharesIssued",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockSharesOutstanding": {
     "auth_ref": [
      "r24",
      "r441"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.",
        "label": "Common Stock, Shares, Outstanding",
        "terseLabel": "BALANCE (in shares)"
       }
      }
     },
     "localname": "CommonStockSharesOutstanding",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_CommonStockValue": {
     "auth_ref": [
      "r24",
      "r813"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity.",
        "label": "Common Stock, Value, Issued",
        "terseLabel": "Common stock - $5 par value: Authorized - 325,000,000 shares; Issued - 228,164,824 shares"
       }
      }
     },
     "localname": "CommonStockValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]",
        "terseLabel": "Summary of Capital Position [Line Items]"
       }
      }
     },
     "localname": "ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest": {
     "auth_ref": [
      "r75",
      "r77",
      "r88",
      "r663",
      "r683",
      "r886",
      "r947"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.",
        "label": "Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest",
        "terseLabel": "Comprehensive income",
        "totalLabel": "Comprehensive Income"
       }
      }
     },
     "localname": "ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ComprehensiveIncomeNoteTextBlock": {
     "auth_ref": [
      "r87",
      "r96",
      "r885",
      "r946"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.",
        "label": "Comprehensive Income (Loss) Note [Text Block]",
        "terseLabel": "Accumulated Other Comprehensive Income (Loss)"
       }
      }
     },
     "localname": "ComprehensiveIncomeNoteTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLoss"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ComprehensiveIncomePolicyPolicyTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for comprehensive income.",
        "label": "Comprehensive Income, Policy [Policy Text Block]",
        "terseLabel": "Comprehensive Income (Loss)"
       }
      }
     },
     "localname": "ComprehensiveIncomePolicyPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ComputerSoftwareIntangibleAssetMember": {
     "auth_ref": [
      "r343",
      "r345",
      "r658"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Collection of computer programs and related data that provide instructions to a computer, for example, but not limited to, application program, control module or operating system, that perform one or more particular functions or tasks.",
        "label": "Computer Software, Intangible Asset [Member]",
        "terseLabel": "Software"
       }
      }
     },
     "localname": "ComputerSoftwareIntangibleAssetMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ConcentrationRiskDisclosureTextBlock": {
     "auth_ref": [
      "r189"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for any concentrations existing at the date of the financial statements that make an entity vulnerable to a reasonably possible, near-term, severe impact. This disclosure informs financial statement users about the general nature of the risk associated with the concentration, and may indicate the percentage of concentration risk as of the balance sheet date.",
        "label": "Concentration Risk Disclosure [Text Block]",
        "terseLabel": "Significant Group Concentrations of Credit Risk"
       }
      }
     },
     "localname": "ConcentrationRiskDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRisk"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ConcentrationRiskLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Concentration Risk [Line Items]",
        "terseLabel": "Concentration Risk [Line Items]"
       }
      }
     },
     "localname": "ConcentrationRiskLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ConcentrationRiskTable": {
     "auth_ref": [
      "r185",
      "r186",
      "r187",
      "r188",
      "r757",
      "r758",
      "r978"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Describes the nature of a concentration, a benchmark to which it is compared, and the percentage that the risk is to the benchmark.",
        "label": "Concentration Risk [Table]",
        "terseLabel": "Concentration Risk [Table]"
       }
      }
     },
     "localname": "ConcentrationRiskTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock": {
     "auth_ref": [
      "r5",
      "r136",
      "r660"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for condensed financial information, including the financial position, cash flows, and the results of operations of the registrant (parent company) as of the same dates or for the same periods for which audited consolidated financial statements are being presented. Alternatively, the details of this disclosure can be reported by the specific parent company taxonomy elements, indicating the appropriate date and period contexts in an instance document.",
        "label": "Condensed Financial Information of Parent Company Only Disclosure [Text Block]",
        "terseLabel": "Parent Company Financial Statments"
       }
      }
     },
     "localname": "CondensedFinancialInformationOfParentCompanyOnlyDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatements"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ConsolidationPolicyTextBlock": {
     "auth_ref": [
      "r123",
      "r666"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy regarding (1) the principles it follows in consolidating or combining the separate financial statements, including the principles followed in determining the inclusion or exclusion of subsidiaries or other entities in the consolidated or combined financial statements and (2) its treatment of interests (for example, common stock, a partnership interest or other means of exerting influence) in other entities, for example consolidation or use of the equity or cost methods of accounting.  The accounting policy may also address the accounting treatment for intercompany accounts and transactions, noncontrolling interest, and the income statement treatment in consolidation for issuances of stock by a subsidiary.",
        "label": "Consolidation, Policy [Policy Text Block]",
        "terseLabel": "Principles of Consolidation"
       }
      }
     },
     "localname": "ConsolidationPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ConstructionLoansMember": {
     "auth_ref": [
      "r975"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A borrowing arrangement which provides the entity constructing a facility (such as a building and a landfill) with funds to effect construction, generally on a draw down, or as needed, basis.",
        "label": "Construction Loans [Member]",
        "terseLabel": "Real estate construction",
        "verboseLabel": "Real estate construction loans"
       }
      }
     },
     "localname": "ConstructionLoansMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ConstructionMember": {
     "auth_ref": [
      "r462"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Building or developing real estate. Includes, but is not limited to, improvement to land for drainage, utilities, grading and subdividing.",
        "label": "Construction [Member]",
        "terseLabel": "Construction"
       }
      }
     },
     "localname": "ConstructionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ConsumerBorrowerMember": {
     "auth_ref": [
      "r318"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Individual who borrows funds.",
        "label": "Consumer Borrower [Member]",
        "terseLabel": "Home equity"
       }
      }
     },
     "localname": "ConsumerBorrowerMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ConsumerPortfolioSegmentMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Portfolio segment of the company's total financing receivables related to consumer receivables.",
        "label": "Consumer Portfolio Segment [Member]",
        "terseLabel": "Retail loans"
       }
      }
     },
     "localname": "ConsumerPortfolioSegmentMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ContractualInterestRateReductionMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan modification for a reduction of contractual interest rate.",
        "label": "Contractual Interest Rate Reduction [Member]",
        "terseLabel": "Interest Rate Reductions",
        "verboseLabel": "Interest Rate Reductions"
       }
      }
     },
     "localname": "ContractualInterestRateReductionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ContractualMaturitiesTimeDeposits100000OrMoreAfter12Months": {
     "auth_ref": [
      "r993"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more, maturing after twelve months from the balance sheet date.",
        "label": "Contractual Maturities, Time Deposits, $100,000 or More, after 12 Months",
        "terseLabel": "Over twelve months"
       }
      }
     },
     "localname": "ContractualMaturitiesTimeDeposits100000OrMoreAfter12Months",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractualMaturitiesTimeDeposits100000OrMoreSixMonthsThrough12Months": {
     "auth_ref": [
      "r993"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more, maturing within six to twelve months after the balance sheet date.",
        "label": "Contractual Maturities, Time Deposits, $100,000 or More, Six Months Through 12 Months",
        "terseLabel": "Over six months to twelve months"
       }
      }
     },
     "localname": "ContractualMaturitiesTimeDeposits100000OrMoreSixMonthsThrough12Months",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsOrLess": {
     "auth_ref": [
      "r993"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more, maturing within three months or fewer from the balance sheet date.",
        "label": "Contractual Maturities, Time Deposits, $100,000 or More, Three Months or Less",
        "terseLabel": "Three Months or Less"
       }
      }
     },
     "localname": "ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsOrLess",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsThroughSixMonths": {
     "auth_ref": [
      "r993"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more, maturing within three to six months after the balance sheet date.",
        "label": "Contractual Maturities, Time Deposits, $100,000 or More, Three Months Through Six Months",
        "terseLabel": "Over three months to six months"
       }
      }
     },
     "localname": "ContractualMaturitiesTimeDeposits100000OrMoreThreeMonthsThroughSixMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CoreDepositsMember": {
     "auth_ref": [
      "r917"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Entity's long-term relationships with depositors, commonly known as core deposit intangibles, which are separate from the financial instruments themselves.",
        "label": "Core Deposits [Member]",
        "terseLabel": "Core deposit intangible"
       }
      }
     },
     "localname": "CoreDepositsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CostsAndExpenses": {
     "auth_ref": [
      "r93"
     ],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total costs of sales and operating expenses for the period.",
        "label": "Costs and Expenses",
        "totalLabel": "Total expenses"
       }
      }
     },
     "localname": "CostsAndExpenses",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CreditAndDebitCardMember": {
     "auth_ref": [
      "r462"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Card issued to user to facilitate payment for purchase of product and service paid directly to merchant by issuer, or from user's checking account.",
        "label": "Credit and Debit Card [Member]",
        "terseLabel": "Card fees"
       }
      }
     },
     "localname": "CreditAndDebitCardMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CreditDerivativeMaximumExposureUndiscounted": {
     "auth_ref": [
      "r715"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.",
        "label": "Credit Derivative, Maximum Exposure, Undiscounted",
        "terseLabel": "Maximum estimated exposure to credit risk participation agreements assuming 100% default"
       }
      }
     },
     "localname": "CreditDerivativeMaximumExposureUndiscounted",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CriticizedMember": {
     "auth_ref": [
      "r311"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Credit rating classification which identifies weaknesses related to credit risk. Includes, but is not limited to, special mention, substandard and doubtful classifications. Excludes noncriticized classification.",
        "label": "Criticized [Member]",
        "terseLabel": "Criticized"
       }
      }
     },
     "localname": "CriticizedMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_CurrentFederalTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r636",
      "r646"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Current Federal Tax Expense (Benefit)",
        "terseLabel": "Current federal income tax"
       }
      }
     },
     "localname": "CurrentFederalTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CurrentForeignTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r636"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current foreign income tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Current Foreign Tax Expense (Benefit)",
        "terseLabel": "Current foreign income tax"
       }
      }
     },
     "localname": "CurrentForeignTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CurrentIncomeTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r636",
      "r646",
      "r648"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.",
        "label": "Current Income Tax Expense (Benefit)",
        "terseLabel": "Total current income tax"
       }
      }
     },
     "localname": "CurrentIncomeTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_CurrentStateAndLocalTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r636",
      "r646"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current state and local tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Current State and Local Tax Expense (Benefit)",
        "terseLabel": "Current state and local income tax"
       }
      }
     },
     "localname": "CurrentStateAndLocalTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtAndEquitySecuritiesGainLoss": {
     "auth_ref": [
      "r90",
      "r91"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 8.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unrealized and realized gain (loss) on investment in debt and equity securities.",
        "label": "Debt and Equity Securities, Gain (Loss)",
        "negatedTerseLabel": "Net securities losses",
        "terseLabel": "Net securities losses",
        "verboseLabel": "Net securities gains (losses)"
       }
      }
     },
     "localname": "DebtAndEquitySecuritiesGainLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Debt Disclosure [Abstract]",
        "terseLabel": "Debt Disclosure [Abstract]"
       }
      }
     },
     "localname": "DebtDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_DebtInstrumentAxis": {
     "auth_ref": [
      "r17",
      "r19",
      "r20",
      "r128",
      "r136",
      "r401",
      "r402",
      "r403",
      "r404",
      "r405",
      "r406",
      "r407",
      "r408",
      "r409",
      "r410",
      "r411",
      "r412",
      "r413",
      "r414",
      "r415",
      "r416",
      "r417",
      "r421",
      "r422",
      "r423",
      "r424",
      "r782",
      "r862",
      "r864",
      "r931"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of debt instrument, including, but not limited to, draws against credit facilities.",
        "label": "Debt Instrument [Axis]",
        "terseLabel": "Debt Instrument [Axis]"
       }
      }
     },
     "localname": "DebtInstrumentAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DebtInstrumentCarryingAmount": {
     "auth_ref": [
      "r20",
      "r419",
      "r864",
      "r931"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.",
        "label": "Long-term Debt, Gross",
        "terseLabel": "Total"
       }
      }
     },
     "localname": "DebtInstrumentCarryingAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtInstrumentInterestRateDuringPeriod": {
     "auth_ref": [
      "r40",
      "r414",
      "r780"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The average effective interest rate during the reporting period.",
        "label": "Debt Instrument, Interest Rate During Period",
        "terseLabel": "Weighted average interest rate during the year"
       }
      }
     },
     "localname": "DebtInstrumentInterestRateDuringPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DebtInstrumentInterestRateStatedPercentage": {
     "auth_ref": [
      "r40",
      "r402"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Contractual interest rate for funds borrowed, under the debt agreement.",
        "label": "Debt Instrument, Interest Rate, Stated Percentage",
        "terseLabel": "Stated interest rate"
       }
      }
     },
     "localname": "DebtInstrumentInterestRateStatedPercentage",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DebtInstrumentLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Debt Instrument [Line Items]",
        "terseLabel": "Debt Instrument [Line Items]"
       }
      }
     },
     "localname": "DebtInstrumentLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DebtInstrumentNameDomain": {
     "auth_ref": [
      "r42",
      "r128",
      "r136",
      "r401",
      "r402",
      "r403",
      "r404",
      "r405",
      "r406",
      "r407",
      "r408",
      "r409",
      "r410",
      "r411",
      "r412",
      "r413",
      "r414",
      "r415",
      "r416",
      "r417",
      "r421",
      "r422",
      "r423",
      "r424",
      "r782"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The name for the particular debt instrument or borrowing that distinguishes it from other debt instruments or borrowings, including draws against credit facilities.",
        "label": "Debt Instrument, Name [Domain]",
        "terseLabel": "Debt Instrument [Domain]"
       }
      }
     },
     "localname": "DebtInstrumentNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DebtInstrumentTable": {
     "auth_ref": [
      "r42",
      "r128",
      "r136",
      "r401",
      "r402",
      "r403",
      "r404",
      "r405",
      "r406",
      "r407",
      "r408",
      "r409",
      "r410",
      "r411",
      "r412",
      "r413",
      "r414",
      "r415",
      "r416",
      "r417",
      "r418",
      "r421",
      "r422",
      "r423",
      "r424",
      "r442",
      "r444",
      "r445",
      "r446",
      "r779",
      "r780",
      "r782",
      "r783",
      "r919"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A table or schedule providing information pertaining to long-term debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the company, if longer.",
        "label": "Schedule of Long-term Debt Instruments [Table]",
        "terseLabel": "Schedule of Long-term Debt Instruments [Table]"
       }
      }
     },
     "localname": "DebtInstrumentTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount": {
     "auth_ref": [
      "r41"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.",
        "label": "Debt Instrument, Unused Borrowing Capacity, Amount",
        "terseLabel": "Debt Instrument, Unused Borrowing Capacity, Amount"
       }
      }
     },
     "localname": "DebtInstrumentUnusedBorrowingCapacityAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecurities": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading).",
        "label": "Debt Securities",
        "terseLabel": "Debt Securities"
       }
      }
     },
     "localname": "DebtSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger": {
     "auth_ref": [
      "r279",
      "r334",
      "r337"
     ],
     "calculation": {
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer",
        "terseLabel": "12 Months or more, Fair Value"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss": {
     "auth_ref": [
      "r279",
      "r334"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss",
        "terseLabel": "12 Months or more, Unrealized Losses"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months": {
     "auth_ref": [
      "r279",
      "r334",
      "r337"
     ],
     "calculation": {
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months",
        "terseLabel": "Less than 12 Months, Fair Value"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss": {
     "auth_ref": [
      "r279",
      "r334"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss",
        "terseLabel": "Less than 12 Months, Unrealized Losses"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleRealizedGain": {
     "auth_ref": [
      "r280"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Realized Gain",
        "terseLabel": "Securities gains"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleRealizedGain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleRealizedLoss": {
     "auth_ref": [
      "r280"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Realized Loss",
        "negatedLabel": "Securities losses"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleRealizedLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleRestricted": {
     "auth_ref": [
      "r829",
      "r976",
      "r977"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Debt Securities, Available-for-sale, Restricted",
        "terseLabel": "Carrying value of securities pledged"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleRestricted",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition": {
     "auth_ref": [
      "r275",
      "r330",
      "r337"
     ],
     "calculation": {
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.",
        "label": "Debt Securities, Available-for-sale, Unrealized Loss Position",
        "totalLabel": "Total, Fair Value"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleUnrealizedLossPosition",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss": {
     "auth_ref": [
      "r276",
      "r331"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss",
        "terseLabel": "Total, Unrealized Losses"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions": {
     "auth_ref": [
      "r277",
      "r332"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.",
        "label": "Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions",
        "terseLabel": "Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions"
       }
      }
     },
     "localname": "DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "integerItemType"
    },
    "us-gaap_DebtSecuritiesMember": {
     "auth_ref": [
      "r282"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Debt instrument issued by corporations, governments and governmental agencies, municipalities, and other institutions.",
        "label": "Debt Securities [Member]",
        "terseLabel": "Debt securities"
       }
      }
     },
     "localname": "DebtSecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.",
        "label": "Deferred Compensation Liability, Current and Noncurrent",
        "terseLabel": "Deferred compensation plan liabilities"
       }
      }
     },
     "localname": "DeferredCompensationLiabilityCurrentAndNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredDiscountsFinanceChargesAndInterestIncludedInReceivables": {
     "auth_ref": [
      "r227"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Unearned discounts (other than cash or quantity discounts and the like), finance charges, and interest included in the face amount of receivables, that are shown as a deduction from the related receivables. For example, 1) finance charges booked as a receivable when a loan is made and recognized as income at a later date; and 2) interest charges deducted from the face loan amount, resulting in a discounted amount actually advanced to the borrower (wherein the receivable includes the amount actually advanced to the borrower and the as yet unearned interest income).",
        "label": "Deferred Discounts, Finance Charges and Interest Included in Receivables",
        "negatedLabel": "Less: Deferred interest income"
       }
      }
     },
     "localname": "DeferredDiscountsFinanceChargesAndInterestIncludedInReceivables",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredFederalIncomeTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r637",
      "r646"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred federal income tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Deferred Federal Income Tax Expense (Benefit)",
        "terseLabel": "Deferred federal income tax"
       }
      }
     },
     "localname": "DeferredFederalIncomeTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredIncomeTaxExpenseBenefit": {
     "auth_ref": [
      "r114",
      "r130",
      "r637",
      "r646",
      "r647",
      "r648"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 3.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Deferred Income Tax Expense (Benefit)",
        "netLabel": "Total deferred income tax",
        "terseLabel": "Provision (benefit) for deferred income taxes",
        "verboseLabel": "Benefit for deferred income taxes"
       }
      }
     },
     "localname": "DeferredIncomeTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredIncomeTaxLiabilities": {
     "auth_ref": [
      "r21",
      "r22",
      "r628",
      "r863",
      "r930"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred tax liability attributable to taxable temporary differences.",
        "label": "Deferred Tax Liabilities, Gross",
        "negatedTerseLabel": "Total deferred tax liabilities"
       }
      }
     },
     "localname": "DeferredIncomeTaxLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredStateAndLocalIncomeTaxExpenseBenefit": {
     "auth_ref": [
      "r130",
      "r637",
      "r646"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred state and local tax expense (benefit) pertaining to income (loss) from continuing operations.",
        "label": "Deferred State and Local Income Tax Expense (Benefit)",
        "terseLabel": "Deferred state and local income tax"
       }
      }
     },
     "localname": "DeferredStateAndLocalIncomeTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsGross": {
     "auth_ref": [
      "r629"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.",
        "label": "Deferred Tax Assets, Gross",
        "terseLabel": "Total deferred tax asset before valuation allowance"
       }
      }
     },
     "localname": "DeferredTaxAssetsGross",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsGrossAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Deferred Tax Assets, Gross [Abstract]",
        "terseLabel": "Deferred tax assets:"
       }
      }
     },
     "localname": "DeferredTaxAssetsGrossAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DeferredTaxAssetsLiabilitiesNet": {
     "auth_ref": [
      "r631"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.",
        "label": "Deferred Tax Assets, Net",
        "verboseLabel": "Net deferred tax asset"
       }
      }
     },
     "localname": "DeferredTaxAssetsLiabilitiesNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsNet": {
     "auth_ref": [
      "r631"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.",
        "label": "Deferred Tax Assets, Net of Valuation Allowance",
        "terseLabel": "Total deferred tax assets"
       }
      }
     },
     "localname": "DeferredTaxAssetsNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsOther": {
     "auth_ref": [
      "r634",
      "r635"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.",
        "label": "Deferred Tax Assets, Other",
        "terseLabel": "Other temporary differences, net"
       }
      }
     },
     "localname": "DeferredTaxAssetsOther",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment.",
        "label": "Deferred Tax Assets, Property, Plant and Equipment",
        "terseLabel": "Allowance for depreciation"
       }
      }
     },
     "localname": "DeferredTaxAssetsPropertyPlantAndEquipment",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation": {
     "auth_ref": [
      "r634",
      "r635"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from employee compensation.",
        "label": "Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation",
        "terseLabel": "Deferred compensation"
       }
      }
     },
     "localname": "DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses": {
     "auth_ref": [
      "r634",
      "r635"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary difference from allowance for credit loss on financing receivable.",
        "label": "Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Financing Receivable, Allowance for Credit Loss",
        "terseLabel": "Allowance for loan losses"
       }
      }
     },
     "localname": "DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxAssetsValuationAllowance": {
     "auth_ref": [
      "r630"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.",
        "label": "Deferred Tax Assets, Valuation Allowance",
        "negatedLabel": "Valuation allowance"
       }
      }
     },
     "localname": "DeferredTaxAssetsValuationAllowance",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxLiabilitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Deferred Tax Liabilities, Gross [Abstract]",
        "terseLabel": "Deferred tax liabilities:"
       }
      }
     },
     "localname": "DeferredTaxLiabilitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DeferredTaxLiabilitiesLeasingArrangements": {
     "auth_ref": [
      "r634",
      "r635"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred tax liability attributable to taxable temporary differences from leasing arrangements.",
        "label": "Deferred Tax Liabilities, Leasing Arrangements",
        "negatedLabel": "Lease financing transactions"
       }
      }
     },
     "localname": "DeferredTaxLiabilitiesLeasingArrangements",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment": {
     "auth_ref": [
      "r634",
      "r635"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.",
        "label": "Deferred Tax Liabilities, Property, Plant and Equipment",
        "negatedLabel": "Allowance for depreciation"
       }
      }
     },
     "localname": "DeferredTaxLiabilitiesPropertyPlantAndEquipment",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsPrincipalComponentsofDeferredTaxAssetsandLiabilitiesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation": {
     "auth_ref": [
      "r499"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.",
        "label": "Defined Benefit Plan, Accumulated Benefit Obligation",
        "terseLabel": "Accumulated benefit obligation"
       }
      }
     },
     "localname": "DefinedBenefitPlanAccumulatedBenefitObligation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax": {
     "auth_ref": [
      "r64",
      "r70",
      "r511"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).",
        "label": "Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax",
        "negatedTotalLabel": "Balance at December 31"
       }
      }
     },
     "localname": "DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax": {
     "auth_ref": [
      "r70",
      "r511"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.",
        "label": "Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax",
        "terseLabel": "Actuarial net loss"
       }
      }
     },
     "localname": "DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax": {
     "auth_ref": [
      "r70",
      "r511"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).",
        "label": "Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax",
        "terseLabel": "Prior service credit"
       }
      }
     },
     "localname": "DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod": {
     "auth_ref": [
      "r495",
      "r537"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.",
        "label": "Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Sold",
        "terseLabel": "Actual return on plan assets"
       }
      }
     },
     "localname": "DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanActuarialGainLoss": {
     "auth_ref": [
      "r473"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.",
        "label": "Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)",
        "terseLabel": "Actuarial (gain) loss"
       }
      }
     },
     "localname": "DefinedBenefitPlanActuarialGainLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit": {
     "auth_ref": [
      "r467",
      "r506",
      "r531"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss), recognized immediately as component of net periodic benefit (cost) credit, for change in value of benefit obligation or plan assets from experience different from that assumed, change in actuarial assumption, or consequence of temporarily deviating from substantive plan. Includes, but is not limited to, amount in excess of ten percent of greater of fair value of plan assets or benefit obligation.",
        "label": "Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit",
        "terseLabel": "Actuarial gain (loss) arising during the period"
       }
      }
     },
     "localname": "DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses": {
     "auth_ref": [
      "r467",
      "r506",
      "r531",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": 4.0,
       "parentTag": "cma_Totalothercomponentsofnetbenefitcreditorcost",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.",
        "label": "Defined Benefit Plan, Amortization of Gain (Loss)",
        "terseLabel": "Amortization of actuarial net loss"
       }
      }
     },
     "localname": "DefinedBenefitPlanAmortizationOfGainsLosses",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit": {
     "auth_ref": [
      "r467",
      "r507",
      "r532",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": 3.0,
       "parentTag": "cma_Totalothercomponentsofnetbenefitcreditorcost",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.",
        "label": "Defined Benefit Plan, Amortization of Prior Service Cost (Credit)",
        "terseLabel": "Amortization of prior service credit"
       }
      }
     },
     "localname": "DefinedBenefitPlanAmortizationOfPriorServiceCostCredit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate": {
     "auth_ref": [
      "r512"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate",
        "terseLabel": "Weighted-average assumptions, discount rate, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease": {
     "auth_ref": [
      "r513"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase",
        "terseLabel": "Weighted-average assumptions, rate of compensation increase, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate": {
     "auth_ref": [
      "r515"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted-average interest crediting rate used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, cash balance and other defined benefit plans with promised interest crediting rate.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate",
        "terseLabel": "Weighted-average assumptions, interest credit rating"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationWeightedAverageInterestCreditingRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate": {
     "auth_ref": [
      "r512"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate",
        "terseLabel": "Weighted-average assumptions, discount rate, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets": {
     "auth_ref": [
      "r514",
      "r536"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets",
        "terseLabel": "Weighted-average assumptions, expected long-term return on plan assets, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease": {
     "auth_ref": [
      "r513"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.",
        "label": "Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase",
        "terseLabel": "Weighted-average assumptions, rate of compensation increase, percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanBenefitObligation": {
     "auth_ref": [
      "r468"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.",
        "label": "Defined Benefit Plan, Benefit Obligation",
        "periodEndLabel": "Projected benefit obligation at December 31",
        "periodStartLabel": "Projected benefit obligation at January 1"
       }
      }
     },
     "localname": "DefinedBenefitPlanBenefitObligation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanBenefitObligationBenefitsPaid": {
     "auth_ref": [
      "r475",
      "r543"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.",
        "label": "Defined Benefit Plan, Benefit Obligation, Benefits Paid",
        "negatedTerseLabel": "Benefits paid"
       }
      }
     },
     "localname": "DefinedBenefitPlanBenefitObligationBenefitsPaid",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant": {
     "auth_ref": [
      "r472"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of contributions received by defined benefit plan from participant which increase benefit obligation.",
        "label": "Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant",
        "terseLabel": "Plan participants' contributions"
       }
      }
     },
     "localname": "DefinedBenefitPlanBenefitObligationContributionsByPlanParticipant",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis": {
     "auth_ref": [
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r517",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by defined benefit plan asset investment.",
        "label": "Defined Benefit Plan, Plan Assets, Category [Axis]",
        "terseLabel": "Defined Benefit Plan, Plan Assets, Category [Axis]"
       }
      }
     },
     "localname": "DefinedBenefitPlanByPlanAssetCategoriesAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DefinedBenefitPlanContributionsByEmployer": {
     "auth_ref": [
      "r482",
      "r491",
      "r493",
      "r535",
      "r537",
      "r538"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of contribution received by defined benefit plan from employer which increases plan assets.",
        "label": "Defined Benefit Plan, Plan Assets, Contributions by Employer",
        "terseLabel": "Plan participants' contributions"
       }
      }
     },
     "localname": "DefinedBenefitPlanContributionsByEmployer",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanDisclosureLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Defined Benefit Plan Disclosure [Line Items]",
        "terseLabel": "Defined Benefit Plan Disclosure [Line Items]"
       }
      }
     },
     "localname": "DefinedBenefitPlanDisclosureLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years",
        "terseLabel": "2027 - 2031"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, Year One",
        "terseLabel": "2022"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in fifth fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, Year Five",
        "terseLabel": "2026"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in fourth fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, Year Four",
        "terseLabel": "2025"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in third fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, Year Three",
        "terseLabel": "2024"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo": {
     "auth_ref": [
      "r500"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of benefit for defined benefit plan expected to be paid in second fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Benefit Payment, Year Two",
        "terseLabel": "2023"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear": {
     "auth_ref": [
      "r501",
      "r538"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.",
        "label": "Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year",
        "terseLabel": "Estimated employer contributions for defined benefit plans for the next year"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets": {
     "auth_ref": [
      "r467",
      "r505",
      "r530",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.",
        "label": "Defined Benefit Plan, Expected Return (Loss) on Plan Assets",
        "negatedTerseLabel": "Expected return on plan assets"
       }
      }
     },
     "localname": "DefinedBenefitPlanExpectedReturnOnPlanAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanFairValueOfPlanAssets": {
     "auth_ref": [
      "r479",
      "r491",
      "r493",
      "r494",
      "r537"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.",
        "label": "Defined Benefit Plan, Plan Assets, Amount",
        "periodEndLabel": "Fair value of plan assets at December 31",
        "periodStartLabel": "Fair value of plan assets at January 1",
        "terseLabel": "Fair value of plan assets in defined benefit pension plan",
        "verboseLabel": "Fair value of plan assets in qualified defined benefit pension plan"
       }
      }
     },
     "localname": "DefinedBenefitPlanFairValueOfPlanAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanFundedStatusOfPlan": {
     "auth_ref": [
      "r466",
      "r488",
      "r537"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.",
        "label": "Defined Benefit Plan, Funded (Unfunded) Status of Plan",
        "terseLabel": "Funded Status at December 31"
       }
      }
     },
     "localname": "DefinedBenefitPlanFundedStatusOfPlan",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear": {
     "auth_ref": [
      "r516"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.",
        "label": "Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year",
        "verboseLabel": "Healthcare cost trend rate assumed for next year"
       }
      }
     },
     "localname": "DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanInterestCost": {
     "auth_ref": [
      "r467",
      "r471",
      "r504",
      "r529",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost recognized for passage of time related to defined benefit plan.",
        "label": "Defined Benefit Plan, Interest Cost",
        "terseLabel": "Interest cost"
       }
      }
     },
     "localname": "DefinedBenefitPlanInterestCost",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost": {
     "auth_ref": [
      "r502",
      "r527",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 5.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      },
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of net periodic benefit cost (credit) for defined benefit plan.",
        "label": "Defined Benefit Plan, Net Periodic Benefit Cost (Credit)",
        "terseLabel": "Net periodic defined benefit credit",
        "totalLabel": "Net periodic defined benefit (credit) cost",
        "verboseLabel": "Net periodic defined benefit credit"
       }
      }
     },
     "localname": "DefinedBenefitPlanNetPeriodicBenefitCost",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanPlanAmendments": {
     "auth_ref": [
      "r476"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in benefit obligation of defined benefit plan from change in terms of existing plan or initiation of new plan.",
        "label": "Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment",
        "negatedTerseLabel": "Plan amendments"
       }
      }
     },
     "localname": "DefinedBenefitPlanPlanAmendments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage": {
     "auth_ref": [
      "r490",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.",
        "label": "Defined Benefit Plan, Plan Assets, Target Allocation, Percentage",
        "terseLabel": "Defined Benefit Plan, Plan Assets, Target Allocation, Percentage"
       }
      }
     },
     "localname": "DefinedBenefitPlanPlanAssetsTargetAllocationPercentage",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanServiceCost": {
     "auth_ref": [
      "r469",
      "r503",
      "r528",
      "r537",
      "r538"
     ],
     "calculation": {
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.",
        "label": "Defined Benefit Plan, Service Cost",
        "terseLabel": "Service cost"
       }
      }
     },
     "localname": "DefinedBenefitPlanServiceCost",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate1": {
     "auth_ref": [
      "r516"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Ultimate trend rate for health care cost for defined benefit postretirement plan.",
        "label": "Defined Benefit Plan, Ultimate Health Care Cost Trend Rate",
        "terseLabel": "Rate to which the healthcare cost trend rate is assumed to decline (the ultimate trend rate), percent"
       }
      }
     },
     "localname": "DefinedBenefitPlanUltimateHealthCareCostTrendRate1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedBenefitPlanYearHealthCareCostTrendRateReachesUltimateTrendRate": {
     "auth_ref": [
      "r516"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Year ultimate health care cost trend rate is expected to be reached, in YYYY format.",
        "label": "Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate",
        "terseLabel": "Year when healthcare cost trend rate reaches the ultimate trend rate"
       }
      }
     },
     "localname": "DefinedBenefitPlanYearHealthCareCostTrendRateReachesUltimateTrendRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "gYearListItemType"
    },
    "us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]",
        "terseLabel": "Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]"
       }
      }
     },
     "localname": "DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable": {
     "auth_ref": [
      "r523",
      "r524",
      "r525",
      "r526",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosures and provisions pertaining to defined benefit pension plans or other postretirement defined benefit plans. The arrangements are generally based on terms and conditions stipulated by the entity, and which contain a promise by the employer to pay certain amounts or awards at designated future dates, including a period after retirement, upon compliance with stipulated requirements. Excludes disclosures pertaining to defined contribution plans.",
        "label": "Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table]",
        "terseLabel": "Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table]"
       }
      }
     },
     "localname": "DefinedBenefitPlansAndOtherPostretirementBenefitPlansDisclosuresTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]",
        "terseLabel": "Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]"
       }
      }
     },
     "localname": "DefinedBenefitPlansAndOtherPostretirementBenefitPlansTableTextBlockLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DefinedContributionPlanCostRecognized": {
     "auth_ref": [
      "r544"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost for defined contribution plan.",
        "label": "Defined Contribution Plan, Cost",
        "terseLabel": "Defined contribution plan expense"
       }
      }
     },
     "localname": "DefinedContributionPlanCostRecognized",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.",
        "label": "Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay",
        "terseLabel": "Percent of qualified earnings contributed by employee matched by the Corporation"
       }
      }
     },
     "localname": "DefinedContributionPlanEmployerMatchingContributionPercent",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage employer matches of the employee's percentage contribution matched.",
        "label": "Defined Contribution Plan, Employer Matching Contribution, Percent of Match",
        "terseLabel": "Defined Contribution Plan, Employer Matching Contribution, Percent of Match"
       }
      }
     },
     "localname": "DefinedContributionPlanEmployerMatchingContributionPercentOfMatch",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DepositAccountMember": {
     "auth_ref": [
      "r462"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Bank account at depository institution allowing money to be withdrawn or deposited by account holder.",
        "label": "Deposit Account [Member]",
        "terseLabel": "Service charges on deposit accounts"
       }
      }
     },
     "localname": "DepositAccountMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DepositLiabilitiesDisclosuresTextBlock": {
     "auth_ref": [
      "r871",
      "r915",
      "r1014",
      "r1021"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for deposit liabilities including data and tables. It may include a description of the entity's deposit liabilities, the aggregate amount of time deposits (including certificates of deposit) in denominations of $100,000 or more at the balance sheet date; the aggregate amount of any demand deposits that have been reclassified as loan balances, such as overdrafts, at the balance sheet date; deposits that are received on terms other than those in the normal course of business, the amount of accrued interest on deposit liabilities; securities, mortgage loans or other financial instruments that serve as collateral for deposits; for time deposits having a remaining term of more than one year, the aggregate amount of maturities for each of the five years following the balance sheet date; and the weighted average interest rate for all deposit liabilities held by the entity.",
        "label": "Deposit Liabilities Disclosures [Text Block]",
        "terseLabel": "Deposits"
       }
      }
     },
     "localname": "DepositLiabilitiesDisclosuresTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/Deposits"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_Deposits": {
     "auth_ref": [
      "r871"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.",
        "label": "Deposits",
        "terseLabel": "Total deposits",
        "totalLabel": "Total deposits"
       }
      }
     },
     "localname": "Deposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DepositsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Deposits [Abstract]",
        "terseLabel": "Deposits [Abstract]"
       }
      }
     },
     "localname": "DepositsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_DepositsMoneyMarketDepositsAndNegotiableOrderOfWithdrawalNOW": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_InterestBearingDepositLiabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts. Also includes amount of deposits in interest-bearing transaction accounts at banks or savings and loans, that are restricted in regard to ownership and can usually only be held by individuals, nonprofit entities and governments. Negotiable order of withdrawal accounts differ from money market demand accounts as they typically have higher reserve requirements and no limit on the number of checks that can be written.",
        "label": "Deposits, Money Market Deposits and Negotiable Order of Withdrawal (NOW)",
        "terseLabel": "Money market and interest-bearing checking deposits"
       }
      }
     },
     "localname": "DepositsMoneyMarketDepositsAndNegotiableOrderOfWithdrawalNOW",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DepositsSavingsDeposits": {
     "auth_ref": [
      "r871"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_InterestBearingDepositLiabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).",
        "label": "Deposits, Savings Deposits",
        "terseLabel": "Savings deposits"
       }
      }
     },
     "localname": "DepositsSavingsDeposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DepreciationAndAmortization": {
     "auth_ref": [
      "r114",
      "r353"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 4.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.",
        "label": "Depreciation, Depletion and Amortization, Nonproduction",
        "terseLabel": "Depreciation and amortization",
        "verboseLabel": "Depreciation and amortization"
       }
      }
     },
     "localname": "DepreciationAndAmortization",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset": {
     "auth_ref": [
      "r50",
      "r686"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.",
        "label": "Derivative Asset, Collateral, Obligation to Return Cash, Offset",
        "negatedTerseLabel": "Derivative assets, Netting adjustment - Cash collateral received"
       }
      }
     },
     "localname": "DerivativeAssetCollateralObligationToReturnCashOffset",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeAssetFairValueGrossLiability": {
     "auth_ref": [
      "r50",
      "r59",
      "r698"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.",
        "label": "Derivative Asset, Fair Value, Gross Liability",
        "negatedLabel": "Derivative assets, Netting adjustment - Offsetting derivative liabilities"
       }
      }
     },
     "localname": "DerivativeAssetFairValueGrossLiability",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeAssetFairValueOfCollateral": {
     "auth_ref": [
      "r54"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of securities received as collateral against derivative assets.",
        "label": "Derivative Asset, Fair Value of Collateral",
        "terseLabel": "Fair value of securities pledged as collateral for derivative assets"
       }
      }
     },
     "localname": "DerivativeAssetFairValueOfCollateral",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeAssets": {
     "auth_ref": [
      "r51",
      "r53",
      "r57",
      "r754"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.",
        "label": "Derivative Asset",
        "verboseLabel": "Net derivative assets included in consolidated balance sheets"
       }
      }
     },
     "localname": "DerivativeAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeAverageFixedInterestRate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average fixed interest rate related to the group of interest rate derivatives.",
        "label": "Derivative, Average Fixed Interest Rate",
        "terseLabel": "Weighted Average Receive Rate"
       }
      }
     },
     "localname": "DerivativeAverageFixedInterestRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DerivativeAverageRemainingMaturity1": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Derivative, Average Remaining Maturity",
        "terseLabel": "Weighted Average Remaining Maturity"
       }
      }
     },
     "localname": "DerivativeAverageRemainingMaturity1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_DerivativeAverageVariableInterestRate": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Average variable interest rate related to the group of interest rate derivatives.",
        "label": "Derivative, Average Variable Interest Rate",
        "terseLabel": "Weighted Average Pay Rate"
       }
      }
     },
     "localname": "DerivativeAverageVariableInterestRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_DerivativeCollateralObligationToReturnSecurities": {
     "auth_ref": [
      "r52",
      "r55",
      "r56"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of obligation to return securities collateral under master netting arrangements that have not been offset against derivative assets.",
        "label": "Derivative, Collateral, Obligation to Return Securities",
        "negatedTerseLabel": "Derivative assets, securities pledged as collateral"
       }
      }
     },
     "localname": "DerivativeCollateralObligationToReturnSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeCollateralRightToReclaimSecurities": {
     "auth_ref": [
      "r52",
      "r55",
      "r56"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of right to receive securities collateral under master netting arrangements that have not been offset against derivative liabilities.",
        "label": "Derivative, Collateral, Right to Reclaim Securities",
        "negatedTerseLabel": "Derivative liabilities, securities pledged as collateral"
       }
      }
     },
     "localname": "DerivativeCollateralRightToReclaimSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeContractTypeDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financial instrument or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.",
        "label": "Derivative Contract [Domain]",
        "terseLabel": "Derivative Contract [Domain]",
        "verboseLabel": "Derivative Contract Type [Domain]"
       }
      }
     },
     "localname": "DerivativeContractTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DerivativeCreditRiskValuationAdjustmentDerivativeAssets": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties.",
        "label": "Derivative Credit Risk Valuation Adjustment, Derivative Assets",
        "terseLabel": "Credit valuation adjustments for counterparty credit risk"
       }
      }
     },
     "localname": "DerivativeCreditRiskValuationAdjustmentDerivativeAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeFairValueOfDerivativeAsset": {
     "auth_ref": [
      "r49",
      "r57",
      "r58",
      "r698",
      "r827"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.",
        "label": "Derivative Asset, Fair Value, Gross Asset",
        "terseLabel": "Fair Value of Gross Derivative Assets",
        "verboseLabel": "Derivative assets"
       }
      }
     },
     "localname": "DerivativeFairValueOfDerivativeAsset",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral": {
     "auth_ref": [
      "r55",
      "r717"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, after effects of master netting arrangements, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset offset against an obligation to return collateral. Includes assets not subject to a master netting arrangement and not elected to be offset.",
        "label": "Derivative Asset, Fair Value, Amount Offset Against Collateral",
        "terseLabel": "Net derivative assets after deducting amounts not offset in the consolidated balance sheets"
       }
      }
     },
     "localname": "DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeFairValueOfDerivativeLiability": {
     "auth_ref": [
      "r49",
      "r57",
      "r58",
      "r698",
      "r827"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.",
        "label": "Derivative Liability, Fair Value, Gross Liability",
        "terseLabel": "Derivative liabilities",
        "verboseLabel": "Fair Value of Gross Derivative Liabilities"
       }
      }
     },
     "localname": "DerivativeFairValueOfDerivativeLiability",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral": {
     "auth_ref": [
      "r55",
      "r717"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, after effects of master netting arrangements, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset offset against the right to receive collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.",
        "label": "Derivative Liability, Fair Value, Amount Offset Against Collateral",
        "terseLabel": "Net derivative liabilities after deducting amounts not offset in the consolidated balance sheets"
       }
      }
     },
     "localname": "DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This item represents derivative instrument obligations meeting the definition of a liability which are reported as of the balance sheet date. Derivative instrument obligations are generally measured at fair value, and adjustments to the carrying amount of hedged items reflect changes in their fair value (that is, losses) that are attributable to the risk being hedged and that arise while the hedge is in effect.",
        "label": "Derivative Financial Instruments, Liabilities [Member]",
        "terseLabel": "Derivative Financial Instruments, Liabilities"
       }
      }
     },
     "localname": "DerivativeFinancialInstrumentsLiabilitiesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DerivativeGainLossOnDerivativeNet": {
     "auth_ref": [
      "r697"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.",
        "label": "Derivative, Gain (Loss) on Derivative, Net",
        "verboseLabel": "Net derivative gain recognized in income"
       }
      }
     },
     "localname": "DerivativeGainLossOnDerivativeNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeInstrumentRiskAxis": {
     "auth_ref": [
      "r57",
      "r696",
      "r699",
      "r705",
      "r710"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of derivative contract.",
        "label": "Derivative Instrument [Axis]",
        "terseLabel": "Derivative Instrument [Axis]",
        "verboseLabel": "Derivative, by Nature [Axis]"
       }
      }
     },
     "localname": "DerivativeInstrumentRiskAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Derivative Instruments and Hedging Activities Disclosure [Abstract]",
        "terseLabel": "Derivative Instruments and Hedging Activities Disclosure [Abstract]"
       }
      }
     },
     "localname": "DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock": {
     "auth_ref": [
      "r721",
      "r733"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for derivative instruments and hedging activities including, but not limited to, risk management strategies, non-hedging derivative instruments, assets, liabilities, revenue and expenses, and methodologies and assumptions used in determining the amounts.",
        "label": "Derivative Instruments and Hedging Activities Disclosure [Text Block]",
        "terseLabel": "Schedule of Derivative Instruments"
       }
      }
     },
     "localname": "DerivativeInstrumentsAndHedgingActivitiesDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstruments"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis": {
     "auth_ref": [
      "r693",
      "r696",
      "r705"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of hedging relationship.",
        "label": "Hedging Relationship [Axis]",
        "terseLabel": "Derivative Instruments, Gain (Loss) by Hedging Relationship [Axis]"
       }
      }
     },
     "localname": "DerivativeInstrumentsGainLossByHedgingRelationshipAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable": {
     "auth_ref": [
      "r693",
      "r696",
      "r705",
      "r710",
      "r711",
      "r718",
      "r720"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about the location and amount of derivative instruments and nonderivative instruments designated as hedging instruments reported before netting adjustments, and the amount of gain (loss) on derivative instruments and nonderivative instruments designated and qualified as hedging instruments.",
        "label": "Derivative Instruments, Gain (Loss) [Table]",
        "terseLabel": "Derivative Instruments, Gain (Loss) [Table]"
       }
      }
     },
     "localname": "DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativeInstrumentsGainLossLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Derivative Instruments, Gain (Loss) [Line Items]",
        "terseLabel": "Derivative Instruments, Gain (Loss) [Line Items]"
       }
      }
     },
     "localname": "DerivativeInstrumentsGainLossLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativeLiabilities": {
     "auth_ref": [
      "r51",
      "r53",
      "r57",
      "r754"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.",
        "label": "Derivative Liability",
        "verboseLabel": "Net derivative liabilities included in the consolidated balance sheet"
       }
      }
     },
     "localname": "DerivativeLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeLiabilityCollateralRightToReclaimCashOffset": {
     "auth_ref": [
      "r50",
      "r686"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.",
        "label": "Derivative Liability, Collateral, Right to Reclaim Cash, Offset",
        "negatedTerseLabel": "Derivative liabilities, Netting adjustment - Cash collateral posted"
       }
      }
     },
     "localname": "DerivativeLiabilityCollateralRightToReclaimCashOffset",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeLiabilityFairValueGrossAsset": {
     "auth_ref": [
      "r50",
      "r56",
      "r59",
      "r698"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.",
        "label": "Derivative Liability, Fair Value, Gross Asset",
        "negatedTerseLabel": "Derivative liabilities, Netting adjustment - Offsetting derivative assets"
       }
      }
     },
     "localname": "DerivativeLiabilityFairValueGrossAsset",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativeNotionalAmount": {
     "auth_ref": [
      "r688",
      "r690"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Nominal or face amount used to calculate payment on derivative.",
        "label": "Derivative, Notional Amount",
        "terseLabel": "Derivative, Notional Amount"
       }
      }
     },
     "localname": "DerivativeNotionalAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DerivativesFairValueLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Derivatives, Fair Value [Line Items]",
        "terseLabel": "Derivatives, Fair Value [Line Items]"
       }
      }
     },
     "localname": "DerivativesFairValueLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_DerivativesPolicyTextBlock": {
     "auth_ref": [
      "r135",
      "r687",
      "r689",
      "r693",
      "r694",
      "r716"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for its derivative instruments and hedging activities.",
        "label": "Derivatives, Policy [Policy Text Block]",
        "terseLabel": "Derivative Instruments and Hedging Activities"
       }
      }
     },
     "localname": "DerivativesPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_DesignatedAsHedgingInstrumentMember": {
     "auth_ref": [
      "r693"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument designated as hedging instrument under Generally Accepted Accounting Principles (GAAP).",
        "label": "Designated as Hedging Instrument [Member]",
        "verboseLabel": "Derivatives designated as hedging instruments"
       }
      }
     },
     "localname": "DesignatedAsHedgingInstrumentMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_DisaggregationOfRevenueTableTextBlock": {
     "auth_ref": [
      "r460"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of disaggregation of revenue into categories depicting how nature, amount, timing, and uncertainty of revenue and cash flows are affected by economic factor.",
        "label": "Disaggregation of Revenue [Table Text Block]",
        "terseLabel": "Composition of Revenue from Contracts with Customers"
       }
      }
     },
     "localname": "DisaggregationOfRevenueTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswtihCustomersTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock": {
     "auth_ref": [
      "r609"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for share-based payment arrangement.",
        "label": "Share-based Payment Arrangement [Text Block]",
        "terseLabel": "Share-based Compensation"
       }
      }
     },
     "localname": "DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensation"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_DividendsCommonStockCash": {
     "auth_ref": [
      "r447"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.",
        "label": "Dividends, Common Stock, Cash",
        "negatedTerseLabel": "Cash dividends declared on common stock",
        "terseLabel": "Cash dividends declared on common stock"
       }
      }
     },
     "localname": "DividendsCommonStockCash",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DividendsPreferredStock": {
     "auth_ref": [
      "r447",
      "r914"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).",
        "label": "Dividends, Preferred Stock",
        "terseLabel": "Less preferred stock dividends"
       }
      }
     },
     "localname": "DividendsPreferredStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DividendsPreferredStockCash": {
     "auth_ref": [
      "r447",
      "r914"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of paid and unpaid preferred stock dividends declared with the form of settlement in cash.",
        "label": "Dividends, Preferred Stock, Cash",
        "negatedTerseLabel": "Dividends, Preferred Stock, Cash"
       }
      }
     },
     "localname": "DividendsPreferredStockCash",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DividendsPreferredStockStock": {
     "auth_ref": [
      "r447",
      "r914"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of paid and unpaid preferred stock dividends declared with the form of settlement in stock.",
        "label": "Dividends, Preferred Stock, Stock",
        "terseLabel": "Preferred stock dividends"
       }
      }
     },
     "localname": "DividendsPreferredStockStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DueFromAffiliates": {
     "auth_ref": [
      "r805",
      "r806",
      "r944"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For an unclassified balance sheet, amount of receivables due from an entity that is affiliated with the reporting entity by means of direct or indirect ownership.",
        "label": "Due from Affiliates",
        "terseLabel": "Due from Affiliates"
       }
      }
     },
     "localname": "DueFromAffiliates",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_DueFromCustomerAcceptances": {
     "auth_ref": [
      "r882"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amounts receivable from customers on short-term negotiable time drafts drawn on and accepted by the institution (also known as banker's acceptance transactions) that are outstanding on the reporting date.",
        "label": "Due from Customer Acceptances",
        "terseLabel": "Customers' liability on acceptances outstanding"
       }
      }
     },
     "localname": "DueFromCustomerAcceptances",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EarningsPerShareAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Earnings Per Share [Abstract]",
        "terseLabel": "Earnings Per Share [Abstract]"
       }
      }
     },
     "localname": "EarningsPerShareAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_EarningsPerShareBasic": {
     "auth_ref": [
      "r89",
      "r147",
      "r148",
      "r150",
      "r151",
      "r152",
      "r157",
      "r160",
      "r167",
      "r170",
      "r171",
      "r175",
      "r176",
      "r731",
      "r732",
      "r887",
      "r948"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.",
        "label": "Earnings Per Share, Basic",
        "terseLabel": "Basic earnings per common share",
        "verboseLabel": "Basic net income per common share"
       }
      }
     },
     "localname": "EarningsPerShareBasic",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_EarningsPerShareDiluted": {
     "auth_ref": [
      "r89",
      "r147",
      "r148",
      "r150",
      "r151",
      "r152",
      "r160",
      "r167",
      "r170",
      "r171",
      "r175",
      "r176",
      "r731",
      "r732",
      "r887",
      "r948"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.",
        "label": "Earnings Per Share, Diluted",
        "terseLabel": "Diluted earnings per common share",
        "verboseLabel": "Diluted net income per common share"
       }
      }
     },
     "localname": "EarningsPerShareDiluted",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_EarningsPerSharePolicyTextBlock": {
     "auth_ref": [
      "r172",
      "r173"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for computing basic and diluted earnings or loss per share for each class of common stock and participating security. Addresses all significant policy factors, including any antidilutive items that have been excluded from the computation and takes into account stock dividends, splits and reverse splits that occur after the balance sheet date of the latest reporting period but before the issuance of the financial statements.",
        "label": "Earnings Per Share, Policy [Policy Text Block]",
        "terseLabel": "Earnings Per Share"
       }
      }
     },
     "localname": "EarningsPerSharePolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_EarningsPerShareTextBlock": {
     "auth_ref": [
      "r172",
      "r173",
      "r174",
      "r177"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for earnings per share.",
        "label": "Earnings Per Share [Text Block]",
        "terseLabel": "Net Income Per Common Share"
       }
      }
     },
     "localname": "EarningsPerShareTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShare"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateContinuingOperations": {
     "auth_ref": [
      "r615"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.",
        "label": "Effective Income Tax Rate Reconciliation, Percent",
        "terseLabel": "Provision for income taxes, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateContinuingOperations",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate": {
     "auth_ref": [
      "r132",
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of domestic federal statutory tax rate applicable to pretax income (loss).",
        "label": "Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent",
        "terseLabel": "Tax based on federal statutory rate, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther": {
     "auth_ref": [
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other nondeductible expenses.",
        "label": "Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Percent",
        "verboseLabel": "FDIC insurance expense, rate"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments": {
     "auth_ref": [
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments.",
        "label": "Effective Income Tax Rate Reconciliation, Other Adjustments, Percent",
        "terseLabel": "Other, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationOtherAdjustments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes": {
     "auth_ref": [
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).",
        "label": "Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent",
        "terseLabel": "State income tax, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsOther": {
     "auth_ref": [
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other tax credits.",
        "label": "Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent",
        "verboseLabel": "Affordable housing and historic credits, amount, rate"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationTaxCreditsOther",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EffectiveIncomeTaxRateReconciliationTaxExemptIncome": {
     "auth_ref": [
      "r615",
      "r650"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes.",
        "label": "Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent",
        "negatedTerseLabel": "Bank-owned life insurance, percent"
       }
      }
     },
     "localname": "EffectiveIncomeTaxRateReconciliationTaxExemptIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized": {
     "auth_ref": [
      "r594"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cost not yet recognized for nonvested award under share-based payment arrangement.",
        "label": "Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount",
        "terseLabel": "Total unrecognized share-based compensation expense"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationUnrecognizedCompensationExpenseDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1": {
     "auth_ref": [
      "r594"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.",
        "label": "Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition",
        "terseLabel": "Weighted-average expected recognition period (in years)"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationUnrecognizedCompensationExpenseDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense": {
     "auth_ref": [
      "r593"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax benefit for recognition of expense of award under share-based payment arrangement.",
        "label": "Share-based Payment Arrangement, Expense, Tax Benefit",
        "terseLabel": "Related tax benefits recognized in net income"
       }
      }
     },
     "localname": "EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryofComponentsofShareBasedCompensationExpenseDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EmployeeStockOptionMember": {
     "auth_ref": [
      "r591"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Share-based payment arrangement granting right, subject to vesting and other restrictions, to purchase or sell certain number of shares at predetermined price for specified period of time.",
        "label": "Share-based Payment Arrangement, Option [Member]",
        "terseLabel": "Stock Options"
       }
      }
     },
     "localname": "EmployeeStockOptionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EnergyRelatedDerivativeMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument whose primary underlying risk is tied to energy, for example, but not limited to, crude oil, electricity and natural gas.",
        "label": "Energy Related Derivative [Member]",
        "terseLabel": "Energy contracts"
       }
      }
     },
     "localname": "EnergyRelatedDerivativeMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EquipmentExpense": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 3.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents equipment expense including depreciation, repairs, rentals, and service contract costs. This item also includes equipment purchases which do not qualify for capitalization in accordance with the entity's accounting policy. This item may also include furniture expenses.",
        "label": "Equipment Expense",
        "terseLabel": "Equipment expense"
       }
      }
     },
     "localname": "EquipmentExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EquityComponentDomain": {
     "auth_ref": [
      "r2",
      "r79",
      "r80",
      "r81",
      "r139",
      "r140",
      "r141",
      "r143",
      "r153",
      "r155",
      "r184",
      "r296",
      "r441",
      "r447",
      "r601",
      "r602",
      "r603",
      "r642",
      "r643",
      "r730",
      "r771",
      "r772",
      "r773",
      "r774",
      "r775",
      "r777",
      "r957",
      "r958",
      "r959",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Components of equity are the parts of the total Equity balance including that which is allocated to common, preferred, treasury stock, retained earnings, etc.",
        "label": "Equity Component [Domain]",
        "terseLabel": "Equity Component [Domain]"
       }
      }
     },
     "localname": "EquityComponentDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EquityFundsMember": {
     "auth_ref": [
      "r491"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "An investment that pools funds from many investors to invest in a combination of underlying investments, primarily equity investments.",
        "label": "Equity Funds [Member]",
        "terseLabel": "Mutual funds"
       }
      }
     },
     "localname": "EquityFundsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EquityMethodInvestmentsPolicy": {
     "auth_ref": [
      "r30",
      "r109",
      "r288",
      "r759"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for equity method of accounting for investments and other interests. Investment includes, but is not limited to, unconsolidated subsidiary, corporate joint venture, noncontrolling interest in real estate venture, limited partnership, and limited liability company. Information includes, but is not limited to, ownership percentage, reason equity method is or is not considered appropriate, and accounting policy election for distribution received.",
        "label": "Equity Method Investments [Policy Text Block]",
        "terseLabel": "Nonmarketable Equity Securities"
       }
      }
     },
     "localname": "EquityMethodInvestmentsPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_EquitySecuritiesByIndustryAxis": {
     "auth_ref": [
      "r320"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by industry sector, examples include but are not limited to, commercial, industrial, agricultural, financial services, technology, healthcare and real estate.",
        "label": "Industry Sector [Axis]",
        "terseLabel": "Industry Sector [Axis]"
       }
      }
     },
     "localname": "EquitySecuritiesByIndustryAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_EquitySecuritiesFvNi": {
     "auth_ref": [
      "r751"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.",
        "label": "Equity Securities, FV-NI, Current",
        "terseLabel": "Equity Securities, FV-NI"
       }
      }
     },
     "localname": "EquitySecuritiesFvNi",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_EquitySecuritiesIndustryMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Industry sector consisting of government, private and corporate entities engaged in business activities, including but not limited to, commercial, industrial, agricultural, financial services, technology, healthcare and real estate.",
        "label": "Industry Sector [Domain]",
        "terseLabel": "Industry Sector [Domain]"
       }
      }
     },
     "localname": "EquitySecuritiesIndustryMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EquitySecuritiesMember": {
     "auth_ref": [
      "r12",
      "r18",
      "r282",
      "r932",
      "r970",
      "r971",
      "r972"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Ownership interest or right to acquire or dispose of ownership interest in corporations and other legal entities for which ownership interest is represented by shares of common or preferred stock, convertible securities, stock rights, or stock warrants.",
        "label": "Equity Securities [Member]",
        "terseLabel": "Equity and other non-debt securities",
        "verboseLabel": "Equity securities"
       }
      }
     },
     "localname": "EquitySecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_EstimateOfFairValueFairValueDisclosureMember": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r754"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measured as an estimate of fair value.",
        "label": "Estimate of Fair Value Measurement [Member]",
        "terseLabel": "Estimated Fair Value"
       }
      }
     },
     "localname": "EstimateOfFairValueFairValueDisclosureMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]",
        "terseLabel": "Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis [Line Items]",
        "verboseLabel": "Assets and Liabilities Measured at Fair Value on a Recurring Basis [Line Items]"
       }
      }
     },
     "localname": "FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable": {
     "auth_ref": [
      "r735",
      "r736",
      "r737",
      "r745"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about asset and liability measured at fair value on recurring and nonrecurring basis.",
        "label": "Fair Value, Recurring and Nonrecurring [Table]",
        "terseLabel": "Fair Value, Recurring and Nonrecurring [Table]",
        "verboseLabel": "Fair Value, Recurring and Nonrecurring [Table]"
       }
      }
     },
     "localname": "FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisTextBlock": {
     "auth_ref": [
      "r735",
      "r736",
      "r738"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of assets and liabilities by class, including financial instruments measured at fair value that are classified in shareholders' equity, if any, that are measured at fair value on a nonrecurring basis in periods after initial recognition (for example, impaired assets). Disclosures may include, but are not limited to: (a) the fair value measurements recorded and the reasons for the measurements and (b) the level within the fair value hierarchy in which the fair value measurements are categorized in their entirety (levels 1, 2, 3).",
        "label": "Fair Value Measurements, Nonrecurring [Table Text Block]",
        "terseLabel": "Assets And Liabilities Recorded At Fair Value On A Nonrecurring Basis"
       }
      }
     },
     "localname": "FairValueAssetsMeasuredOnNonrecurringBasisTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain": {
     "auth_ref": [
      "r741"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Class of asset.",
        "label": "Asset Class [Domain]",
        "terseLabel": "Asset Class [Domain]"
       }
      }
     },
     "localname": "FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock": {
     "auth_ref": [
      "r741",
      "r745"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset.",
        "label": "Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]",
        "terseLabel": "Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis"
       }
      }
     },
     "localname": "FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueByAssetClassAxis": {
     "auth_ref": [
      "r735",
      "r745"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by class of asset.",
        "label": "Asset Class [Axis]",
        "terseLabel": "Asset Class [Axis]"
       }
      }
     },
     "localname": "FairValueByAssetClassAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByBalanceSheetGroupingTable": {
     "auth_ref": [
      "r735",
      "r755",
      "r756"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities.",
        "label": "Fair Value, by Balance Sheet Grouping [Table]",
        "terseLabel": "Fair Value, by Balance Sheet Grouping [Table]"
       }
      }
     },
     "localname": "FairValueByBalanceSheetGroupingTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByBalanceSheetGroupingTextBlock": {
     "auth_ref": [
      "r735",
      "r755"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities.",
        "label": "Fair Value, by Balance Sheet Grouping [Table Text Block]",
        "terseLabel": "Estimated Fair Values Of Financial Instruments Not Recorded At Fair Value In Their Entirety On A Recurring Basis"
       }
      }
     },
     "localname": "FairValueByBalanceSheetGroupingTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueByFairValueHierarchyLevelAxis": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r537",
      "r736",
      "r817",
      "r818",
      "r819"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by level within fair value hierarchy and fair value measured at net asset value per share as practical expedient.",
        "label": "Fair Value Hierarchy and NAV [Axis]",
        "terseLabel": "Fair Value Hierarchy and NAV [Axis]"
       }
      }
     },
     "localname": "FairValueByFairValueHierarchyLevelAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByMeasurementBasisAxis": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r735",
      "r746"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by measurement basis.",
        "label": "Measurement Basis [Axis]",
        "terseLabel": "Measurement Basis [Axis]"
       }
      }
     },
     "localname": "FairValueByMeasurementBasisAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueByMeasurementFrequencyAxis": {
     "auth_ref": [
      "r735",
      "r736",
      "r739",
      "r740",
      "r748"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by measurement frequency.",
        "label": "Measurement Frequency [Axis]",
        "terseLabel": "Fair Value by Measurement Frequency [Axis]"
       }
      }
     },
     "localname": "FairValueByMeasurementFrequencyAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueDisclosureItemAmountsDomain": {
     "auth_ref": [
      "r410",
      "r421",
      "r422"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measurement basis, for example, but not limited to, reported value, fair value, portion at fair value, portion at other than fair value.",
        "label": "Fair Value Measurement [Domain]",
        "terseLabel": "Fair Value Measurement [Domain]"
       }
      }
     },
     "localname": "FairValueDisclosureItemAmountsDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueDisclosuresAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Fair Value Disclosures [Abstract]",
        "terseLabel": "Fair Value Disclosures [Abstract]"
       }
      }
     },
     "localname": "FairValueDisclosuresAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_FairValueDisclosuresTextBlock": {
     "auth_ref": [
      "r744"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.",
        "label": "Fair Value Disclosures [Text Block]",
        "terseLabel": "Fair Value Measurements"
       }
      }
     },
     "localname": "FairValueDisclosuresTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurements"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValueHedgingMember": {
     "auth_ref": [
      "r691"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A hedge of the exposure to changes in the fair value of a recognized asset or liability, or of an unrecognized firm commitment, that are attributable to a particular risk.",
        "label": "Fair Value Hedging [Member]",
        "terseLabel": "Swaps - fair value - receive fixed/pay floating",
        "verboseLabel": "Swaps - fair value - receive fixed/pay floating"
       }
      }
     },
     "localname": "FairValueHedgingMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueInputsLevel1Member": {
     "auth_ref": [
      "r410",
      "r491",
      "r493",
      "r498",
      "r537",
      "r736",
      "r817"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Quoted prices in active markets for identical assets or liabilities that the reporting entity can access at the measurement date.",
        "label": "Fair Value, Inputs, Level 1 [Member]",
        "terseLabel": "Level 1",
        "verboseLabel": "Level 1"
       }
      }
     },
     "localname": "FairValueInputsLevel1Member",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueInputsLevel2Member": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r491",
      "r493",
      "r498",
      "r537",
      "r736",
      "r818"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Inputs other than quoted prices included within level 1 that are observable for an asset or liability, either directly or indirectly, including, but not limited to, quoted prices for similar assets or liabilities in active markets, or quoted prices for identical or similar assets or liabilities in inactive markets.",
        "label": "Fair Value, Inputs, Level 2 [Member]",
        "terseLabel": "Level 2"
       }
      }
     },
     "localname": "FairValueInputsLevel2Member",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueInputsLevel3Member": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r537",
      "r736",
      "r819"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.",
        "label": "Fair Value, Inputs, Level 3 [Member]",
        "terseLabel": "Level 3"
       }
      }
     },
     "localname": "FairValueInputsLevel3Member",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments": {
     "auth_ref": [
      "r747"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).",
        "label": "Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments",
        "terseLabel": "Commitments to fund additional investments in nonmarketable equity securities"
       }
      }
     },
     "localname": "FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FairValueMeasurementFrequencyDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measurement frequency.",
        "label": "Measurement Frequency [Domain]",
        "terseLabel": "Measurement Frequency [Domain]"
       }
      }
     },
     "localname": "FairValueMeasurementFrequencyDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements": {
     "auth_ref": [
      "r742"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.",
        "label": "Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements",
        "terseLabel": "Sales"
       }
      }
     },
     "localname": "FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue": {
     "auth_ref": [
      "r741"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.",
        "label": "Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value",
        "periodEndLabel": "Balance at end of period",
        "periodStartLabel": "Balance at beginning of period"
       }
      }
     },
     "localname": "FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FairValueMeasurementsFairValueHierarchyDomain": {
     "auth_ref": [
      "r410",
      "r421",
      "r422",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r537",
      "r817",
      "r818",
      "r819"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Categories used to prioritize the inputs to valuation techniques to measure fair value.",
        "label": "Fair Value Hierarchy and NAV [Domain]",
        "terseLabel": "Fair Value Hierarchy and NAV [Domain]"
       }
      }
     },
     "localname": "FairValueMeasurementsFairValueHierarchyDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementsNonrecurringMember": {
     "auth_ref": [
      "r735",
      "r736",
      "r739",
      "r740",
      "r743",
      "r748"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Infrequent fair value measurement. Includes, but is not limited to, fair value adjustment for impairment of asset, liability or equity, not frequently measured at fair value.",
        "label": "Fair Value, Nonrecurring [Member]",
        "terseLabel": "Nonrecurring"
       }
      }
     },
     "localname": "FairValueMeasurementsNonrecurringMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueMeasurementsRecurringMember": {
     "auth_ref": [
      "r744",
      "r748"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Frequent fair value measurement. Includes, but is not limited to, fair value adjustment for impairment of asset, liability or equity, frequently measured at fair value.",
        "label": "Fair Value, Recurring [Member]",
        "terseLabel": "Recurring"
       }
      }
     },
     "localname": "FairValueMeasurementsRecurringMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FairValueOfFinancialInstrumentsPolicy": {
     "auth_ref": [
      "r749",
      "r753"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for determining the fair value of financial instruments.",
        "label": "Fair Value of Financial Instruments, Policy [Policy Text Block]",
        "terseLabel": "Fair Value Measurements"
       }
      }
     },
     "localname": "FairValueOfFinancialInstrumentsPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable": {
     "auth_ref": [
      "r695",
      "r701",
      "r718"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule that discloses the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position.",
        "label": "Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]",
        "terseLabel": "Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]"
       }
      }
     },
     "localname": "FairValuesDerivativesBalanceSheetLocationByDerivativeContractTypeByHedgingDesignationTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FederalDepositInsuranceCorporationPremiumExpense": {
     "auth_ref": [
      "r897"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 6.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expense for Federal Deposit Insurance Corporation (FDIC) insurance.",
        "label": "Federal Deposit Insurance Corporation Premium Expense",
        "terseLabel": "FDIC insurance expense"
       }
      }
     },
     "localname": "FederalDepositInsuranceCorporationPremiumExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseMember": {
     "auth_ref": [
      "r872"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Short term borrowing where a bank borrows, at the federal funds rate, from another bank and securities that an entity sells and agrees to repurchase at a specified date for a specified price.",
        "label": "Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member]",
        "terseLabel": "Federal Funds Purchased and Securities Sold Under Agreements to Repurchase"
       }
      }
     },
     "localname": "FederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FederalHomeLoanBankAdvancesLongTerm": {
     "auth_ref": [
      "r876",
      "r916",
      "r918"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Including both current and noncurrent portions, Federal Home Loan Bank borrowings initially due beyond one year or beyond the normal operating cycle if longer.",
        "label": "Long-term Federal Home Loan Bank Advances",
        "terseLabel": "Long-term Federal Home Loan Bank advances"
       }
      }
     },
     "localname": "FederalHomeLoanBankAdvancesLongTerm",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FederalHomeLoanBankStock": {
     "auth_ref": [
      "r912"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).",
        "label": "Federal Home Loan Bank Stock",
        "terseLabel": "Federal Home Loan Bank Stock"
       }
      }
     },
     "localname": "FederalHomeLoanBankStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FederalHomeLoanBankStockAndFederalReserveBankStock": {
     "auth_ref": [],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of Federal Home Loan Bank (FHLB) and Federal Reserve Bank stock.",
        "label": "Federal Home Loan Bank Stock and Federal Reserve Bank Stock",
        "terseLabel": "Restricted equity investments"
       }
      }
     },
     "localname": "FederalHomeLoanBankStockAndFederalReserveBankStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FederalReserveBankStock": {
     "auth_ref": [
      "r912"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).",
        "label": "Federal Reserve Bank Stock",
        "terseLabel": "Federal Reserve Bank Stock"
       }
      }
     },
     "localname": "FederalReserveBankStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FiduciaryAndTrustMember": {
     "auth_ref": [
      "r462"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Person or entity with legal duty to act in best interest of client or beneficiary of trust and fiduciary relationship in which one party gives another party right to hold title to asset for benefit of beneficiary.",
        "label": "Fiduciary and Trust [Member]",
        "terseLabel": "Fiduciary income"
       }
      }
     },
     "localname": "FiduciaryAndTrustMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinanceLeaseLiabilityPaymentsDueAfterYearFive": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Finance Lease, Liability, to be Paid, after Year Five",
        "terseLabel": "Thereafter"
       }
      }
     },
     "localname": "FinanceLeaseLiabilityPaymentsDueAfterYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinanceLeasesPortfolioSegmentMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Portfolio segment of the company's total financing receivables related to finance leases.",
        "label": "Finance Leases Portfolio Segment [Member]",
        "terseLabel": "Lease financing"
       }
      }
     },
     "localname": "FinanceLeasesPortfolioSegmentMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinanceLoanAndLeaseReceivablesHeldForInvestmentAllowanceAndNonperformingLoansNonperformingLoansPolicy": {
     "auth_ref": [
      "r229",
      "r247"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for (1) placing loans on nonaccrual status (or discontinuing accrual of interest) and recording payments received on nonaccrual loans, and the policy for resuming accrual of interest, (2) charging-off uncollectible loans, and (3) determining past due or delinquency status (that is, whether past due status is based on how recently payments have been received or contractual terms).",
        "label": "Finance, Loan and Lease Receivables, Held-for-investment, Allowance and Nonperforming Loans, Nonperforming Loans Policy [Policy Text Block]",
        "terseLabel": "Nonperforming Assets"
       }
      }
     },
     "localname": "FinanceLoanAndLeaseReceivablesHeldForInvestmentAllowanceAndNonperformingLoansNonperformingLoansPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FinanceLoansAndLeasesReceivablePolicy": {
     "auth_ref": [
      "r229",
      "r236",
      "r239",
      "r247",
      "r251",
      "r254",
      "r255",
      "r257"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for financing receivable.",
        "label": "Financing Receivable [Policy Text Block]",
        "terseLabel": "Loans"
       }
      }
     },
     "localname": "FinanceLoansAndLeasesReceivablePolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FinanceReceivablesMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amounts due the Company from customers, clients, lessees, borrowers, or others under the terms of its agreements therewith. Such amount may include accrued interest receivable in accordance with the terms of the agreements. The agreements also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among myriad other features and characteristics.",
        "label": "Financing Receivable [Member]",
        "terseLabel": "Financing Receivable"
       }
      }
     },
     "localname": "FinanceReceivablesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancialInstrumentAxis": {
     "auth_ref": [
      "r273",
      "r274",
      "r283",
      "r284",
      "r285",
      "r300",
      "r305",
      "r306",
      "r310",
      "r311",
      "r333",
      "r335",
      "r336",
      "r337",
      "r418",
      "r439",
      "r721",
      "r814",
      "r815",
      "r816",
      "r817",
      "r818",
      "r819",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r826",
      "r828",
      "r831",
      "r833",
      "r834",
      "r835",
      "r836",
      "r837",
      "r838",
      "r839",
      "r840",
      "r841",
      "r842",
      "r843",
      "r844",
      "r845",
      "r846",
      "r847",
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of financial instrument.",
        "label": "Financial Instrument [Axis]",
        "terseLabel": "Financial Instrument [Axis]",
        "verboseLabel": "Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis]"
       }
      }
     },
     "localname": "FinancialInstrumentAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralAtFairValue": {
     "auth_ref": [
      "r828",
      "r830"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The fair value as of the balance sheet date of financial instruments and other positions owned by the entity and pledged to counterparties as collateral, including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities.",
        "label": "Financial Instruments, Owned and Pledged as Collateral, at Fair Value",
        "terseLabel": "Pledged to the FHLB as collateral for potential future borrowings"
       }
      }
     },
     "localname": "FinancialInstrumentsOwnedAndPledgedAsCollateralAtFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableAllowanceForCreditLosses": {
     "auth_ref": [
      "r230",
      "r299",
      "r301",
      "r304",
      "r869",
      "r1009",
      "r1011",
      "r1013"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.",
        "label": "Financing Receivable, Allowance for Credit Loss",
        "periodEndLabel": "Balance at end of period",
        "periodStartLabel": "Balance at beginning of period"
       }
      }
     },
     "localname": "FinancingReceivableAllowanceForCreditLosses",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Financing Receivable, Allowance for Credit Loss [Line Items]",
        "terseLabel": "Financing Receivable, Allowance for Credit Loss [Line Items]"
       }
      }
     },
     "localname": "FinancingReceivableAllowanceForCreditLossesLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery": {
     "auth_ref": [
      "r233",
      "r303",
      "r327"
     ],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase in allowance for credit loss on financing receivable from recovery.",
        "label": "Financing Receivable, Allowance for Credit Loss, Recovery",
        "terseLabel": "Recoveries on loans previously charged-off"
       }
      }
     },
     "localname": "FinancingReceivableAllowanceForCreditLossesRecovery",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs": {
     "auth_ref": [
      "r232",
      "r302",
      "r327"
     ],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_AllowanceForLoanAndLeaseLossesWriteoffsNet",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of writeoff of financing receivable, charged against allowance for credit loss.",
        "label": "Financing Receivable, Allowance for Credit Loss, Writeoff",
        "negatedLabel": "Loan charge-offs"
       }
      }
     },
     "localname": "FinancingReceivableAllowanceForCreditLossesWriteOffs",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableCreditQualityIndicatorsTableTextBlock": {
     "auth_ref": [
      "r240",
      "r311"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of financing receivables by credit quality indicator. The credit quality indicator is a statistic about the credit quality of financing receivables. Examples include, but not limited to, consumer credit risk scores, credit-rating-agency ratings, an entity's internal credit risk grades, loan-to-value ratios, collateral, collection experience and other internal metrics.",
        "label": "Financing Receivable Credit Quality Indicators [Table Text Block]",
        "terseLabel": "Loans By Credit Quality Indicator and Vintage Year"
       }
      }
     },
     "localname": "FinancingReceivableCreditQualityIndicatorsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FinancingReceivableImpairedLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Financing Receivable, Impaired [Line Items]",
        "terseLabel": "Financing Receivable, Impaired [Line Items]"
       }
      }
     },
     "localname": "FinancingReceivableImpairedLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableModificationsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Financing Receivable, Troubled Debt Restructuring [Line Items]",
        "terseLabel": "Financing Receivable, Troubled Debt Restructuring [Line Items]"
       }
      }
     },
     "localname": "FinancingReceivableModificationsLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2": {
     "auth_ref": [
      "r242"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after troubled debt restructuring, of modified financing receivable.",
        "label": "Financing Receivable, Troubled Debt Restructuring, Postmodification",
        "terseLabel": "Financing Receivable, Troubled Debt Restructuring, Postmodification"
       }
      }
     },
     "localname": "FinancingReceivableModificationsPostModificationRecordedInvestment2",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1": {
     "auth_ref": [
      "r243"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.",
        "label": "Financing Receivable, Troubled Debt Restructuring, Subsequent Default",
        "terseLabel": "Subsequent default during period"
       }
      }
     },
     "localname": "FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableNonaccrualInterestIncome": {
     "auth_ref": [
      "r308"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of interest income on financing receivable on nonaccrual status.",
        "label": "Financing Receivable, Nonaccrual, Interest Income",
        "terseLabel": "Financing Receivable, Nonaccrual, Interest Income"
       }
      }
     },
     "localname": "FinancingReceivableNonaccrualInterestIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableNonaccrualNoAllowance": {
     "auth_ref": [
      "r309"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable on nonaccrual status with no allowance for credit loss.",
        "label": "Financing Receivable, Nonaccrual, No Allowance",
        "terseLabel": "Nonaccrual loans with no related allowance"
       }
      }
     },
     "localname": "FinancingReceivableNonaccrualNoAllowance",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated more than five years prior to current fiscal year.",
        "label": "Financing Receivable, Originated, More than Five Years before Current Fiscal Year",
        "terseLabel": "Financing Receivable, Originated, More than Five Years before Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated four years prior to current fiscal year.",
        "label": "Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year",
        "terseLabel": "Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedInCurrentFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated in current fiscal year.",
        "label": "Financing Receivable, Year One, Originated, Current Fiscal Year",
        "terseLabel": "Financing Receivable, Year One, Originated, Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedInCurrentFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated in fiscal year prior to current fiscal year.",
        "label": "Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year",
        "terseLabel": "Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated three years prior to current fiscal year.",
        "label": "Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year",
        "terseLabel": "Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable originated two years prior to current fiscal year.",
        "label": "Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year",
        "terseLabel": "Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year"
       }
      }
     },
     "localname": "FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivablePortfolioSegmentAxis": {
     "auth_ref": [
      "r300",
      "r305",
      "r314",
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004",
      "r1007",
      "r1008",
      "r1009",
      "r1010",
      "r1011",
      "r1012",
      "r1013"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by the level at which an entity develops and documents a systematic methodology to determine its allowance for credit losses.",
        "label": "Financing Receivable Portfolio Segment [Axis]",
        "terseLabel": "Financing Receivable Portfolio Segment [Axis]"
       }
      }
     },
     "localname": "FinancingReceivablePortfolioSegmentAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivablePortfolioSegmentDomain": {
     "auth_ref": [
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004",
      "r1007",
      "r1008",
      "r1009",
      "r1010",
      "r1011",
      "r1012",
      "r1013"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Level at which an entity develops and documents a systematic methodology to determine its allowance for credit losses.",
        "label": "Financing Receivable Portfolio Segment [Domain]",
        "terseLabel": "Financing Receivable Portfolio Segment [Domain]"
       }
      }
     },
     "localname": "FinancingReceivablePortfolioSegmentDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis": {
     "auth_ref": [
      "r241",
      "r249",
      "r250",
      "r306",
      "r310",
      "r311",
      "r315",
      "r319",
      "r327",
      "r328",
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004",
      "r1007",
      "r1008",
      "r1009",
      "r1010",
      "r1011",
      "r1012",
      "r1013"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by class of financing receivable determined on the basis of initial measurement attribute, risk characteristics and method of monitoring and assessing credit risk.",
        "label": "Class of Financing Receivable [Axis]",
        "terseLabel": "Class of Financing Receivable [Axis]"
       }
      }
     },
     "localname": "FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain": {
     "auth_ref": [
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004",
      "r1007",
      "r1008",
      "r1009",
      "r1010",
      "r1011",
      "r1012",
      "r1013"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financing receivables determined on the basis of initial measurement attribute, risk characteristics and method of monitoring and assessing credit risk.",
        "label": "Class of Financing Receivable [Domain]",
        "terseLabel": "Class of Financing Receivable [Domain]"
       }
      }
     },
     "localname": "FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivableRecordedInvestmentLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Financing Receivable, Credit Quality Indicator [Line Items]",
        "terseLabel": "Financing Receivable, Credit Quality Indicator [Line Items]"
       }
      }
     },
     "localname": "FinancingReceivableRecordedInvestmentLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus": {
     "auth_ref": [
      "r248",
      "r307",
      "r1010",
      "r1011"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable on nonaccrual status.",
        "label": "Financing Receivable, Nonaccrual",
        "terseLabel": "Nonaccrual loans with related allowance"
       }
      }
     },
     "localname": "FinancingReceivableRecordedInvestmentNonaccrualStatus",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Financing Receivable, Past Due [Line Items]",
        "terseLabel": "Financing Receivable, Past Due [Line Items]"
       }
      }
     },
     "localname": "FinancingReceivableRecordedInvestmentPastDueLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivableRevolving": {
     "auth_ref": [
      "r312",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of financing receivable that can be withdrawn, repaid and redrawn.",
        "label": "Financing Receivable, Revolving",
        "terseLabel": "Financing Receivable, Revolving"
       }
      }
     },
     "localname": "FinancingReceivableRevolving",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableRevolvingConvertedToTermLoan": {
     "auth_ref": [
      "r313",
      "r327"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of revolving financing receivable converted to term loan.",
        "label": "Financing Receivable, Revolving, Converted to Term Loan",
        "terseLabel": "Financing Receivable, Revolving, Converted to Term Loan"
       }
      }
     },
     "localname": "FinancingReceivableRevolvingConvertedToTermLoan",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff": {
     "auth_ref": [
      "r306"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Financing Receivable, Threshold Period Past Due, Writeoff",
        "terseLabel": "Past Due Threshold For Charge-Off"
       }
      }
     },
     "localname": "FinancingReceivableThresholdPeriodPastDueWriteoff",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_FinancingReceivables30To59DaysPastDueMember": {
     "auth_ref": [
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financial asset more than 29 days past due but fewer than 60 days past due.",
        "label": "Financial Asset, 30 to 59 Days Past Due [Member]",
        "terseLabel": "30 to 59 days past due and still accruing"
       }
      }
     },
     "localname": "FinancingReceivables30To59DaysPastDueMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivables60To89DaysPastDueMember": {
     "auth_ref": [
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financial asset more than 59 days past due but fewer than 90 days past due.",
        "label": "Financial Asset, 60 to 89 Days Past Due [Member]",
        "terseLabel": "60 to 89 days past due and still accruing"
       }
      }
     },
     "localname": "FinancingReceivables60To89DaysPastDueMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember": {
     "auth_ref": [
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financial asset equal to or greater than 90 days past due.",
        "label": "Financial Asset, Equal to or Greater than 90 Days Past Due [Member]",
        "terseLabel": "90 days or more past due and still accruing"
       }
      }
     },
     "localname": "FinancingReceivablesEqualToGreaterThan90DaysPastDueMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivablesPeriodPastDueAxis": {
     "auth_ref": [
      "r250",
      "r306",
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by period in which financial asset is past due or not past due.",
        "label": "Financial Asset, Aging [Axis]",
        "terseLabel": "Financial Asset, Period Past Due [Axis]"
       }
      }
     },
     "localname": "FinancingReceivablesPeriodPastDueAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FinancingReceivablesPeriodPastDueDomain": {
     "auth_ref": [
      "r250",
      "r306",
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Period in which financial asset is past due or not past due. For past due, element name and standard label in Financial Asset, [numeric lower end] to [numeric higher end] [date measure] Past Due [Member] or Financial Asset, Greater than [low end numeric value] [date measure] Past Due [Member] or Financial Asset, Less than [high end numeric value] [date measure] Past Due [Member] formats.",
        "label": "Financial Asset, Aging [Domain]",
        "terseLabel": "Financial Asset, Period Past Due [Domain]"
       }
      }
     },
     "localname": "FinancingReceivablesPeriodPastDueDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FinancingReceivablesTextBlock": {
     "auth_ref": [
      "r253",
      "r260"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for financing receivable.",
        "label": "Financing Receivables [Text Block]",
        "terseLabel": "Credit Quality And Allowance For Credit Losses"
       }
      }
     },
     "localname": "FinancingReceivablesTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLosses"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization": {
     "auth_ref": [
      "r346"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.",
        "label": "Finite-Lived Intangible Assets, Accumulated Amortization",
        "negatedTerseLabel": "Accumulated amortization"
       }
      }
     },
     "localname": "FiniteLivedIntangibleAssetsAccumulatedAmortization",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis": {
     "auth_ref": [
      "r343",
      "r344",
      "r346",
      "r348",
      "r850",
      "r854"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by major type or class of finite-lived intangible assets.",
        "label": "Finite-Lived Intangible Assets by Major Class [Axis]",
        "terseLabel": "Finite-Lived Intangible Assets by Major Class [Axis]"
       }
      }
     },
     "localname": "FiniteLivedIntangibleAssetsByMajorClassAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_FiniteLivedIntangibleAssetsGross": {
     "auth_ref": [
      "r346",
      "r854"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.",
        "label": "Finite-Lived Intangible Assets, Gross",
        "terseLabel": "Gross carrying amount"
       }
      }
     },
     "localname": "FiniteLivedIntangibleAssetsGross",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain": {
     "auth_ref": [
      "r343",
      "r345"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The major class of finite-lived intangible asset (for example, patents, trademarks, copyrights, etc.) A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.",
        "label": "Finite-Lived Intangible Assets, Major Class Name [Domain]",
        "terseLabel": "Finite-Lived Intangible Assets, Major Class Name [Domain]"
       }
      }
     },
     "localname": "FiniteLivedIntangibleAssetsMajorClassNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FiniteLivedIntangibleAssetsNet": {
     "auth_ref": [
      "r346",
      "r850"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.",
        "label": "Finite-Lived Intangible Assets, Net",
        "terseLabel": "Net carrying amount"
       }
      }
     },
     "localname": "FiniteLivedIntangibleAssetsNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ForeclosedAssets": {
     "auth_ref": [
      "r226",
      "r228"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.",
        "label": "Repossessed Assets",
        "terseLabel": "Foreclosed property"
       }
      }
     },
     "localname": "ForeclosedAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesForeclosedPropertiesDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ForeignCurrencyGainLossMember": {
     "auth_ref": [
      "r709"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Primary financial statement caption encompassing foreign currency gain (loss).",
        "label": "Foreign Currency Gain (Loss) [Member]",
        "terseLabel": "Foreign exchange income"
       }
      }
     },
     "localname": "ForeignCurrencyGainLossMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ForeignCurrencyTransactionGainBeforeTax": {
     "auth_ref": [
      "r769",
      "r770"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before tax of foreign currency transaction realized and unrealized gain recognized in the income statement.",
        "label": "Foreign Currency Transaction Gain, before Tax",
        "terseLabel": "Derivative income"
       }
      }
     },
     "localname": "ForeignCurrencyTransactionGainBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ForeignExchangeContractMember": {
     "auth_ref": [
      "r57",
      "r491",
      "r707"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument whose primary underlying risk is tied to foreign exchange rates.",
        "label": "Foreign Exchange Contract [Member]",
        "terseLabel": "Foreign exchange contracts"
       }
      }
     },
     "localname": "ForeignExchangeContractMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_FurnitureAndFixturesGross": {
     "auth_ref": [
      "r354"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.",
        "label": "Furniture and Fixtures, Gross",
        "terseLabel": "Furniture and equipment"
       }
      }
     },
     "localname": "FurnitureAndFixturesGross",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GainLossOnCashFlowHedgeIneffectivenessNet": {
     "auth_ref": [
      "r703"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.",
        "label": "Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net",
        "terseLabel": "Cash flow hedges, Net (losses) gains arising during the period"
       }
      }
     },
     "localname": "GainLossOnCashFlowHedgeIneffectivenessNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GainLossOnForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstruments": {
     "auth_ref": [
      "r696",
      "r704"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of foreign currency derivatives not designated as hedging instruments.",
        "label": "Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments",
        "terseLabel": "Net gain on open foreign currency positions"
       }
      }
     },
     "localname": "GainLossOnForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstruments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GainsLossesOnSalesOfOtherRealEstate": {
     "auth_ref": [
      "r896"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net gain (loss) resulting from sales and other disposals of other real estate owned, increases (decreases) in the valuation allowance for foreclosed real estate, and write-downs of other real estate owned after acquisition or physical possession.",
        "label": "Gains (Losses) on Sales of Other Real Estate",
        "negatedTerseLabel": "Net gains (losses) on sales of foreclosed property"
       }
      }
     },
     "localname": "GainsLossesOnSalesOfOtherRealEstate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GeographicDistributionAxis": {
     "auth_ref": [
      "r323",
      "r906",
      "r907",
      "r994",
      "r995",
      "r996",
      "r997",
      "r998",
      "r999",
      "r1000",
      "r1001",
      "r1002",
      "r1003",
      "r1004",
      "r1005",
      "r1015",
      "r1016",
      "r1017",
      "r1018",
      "r1019",
      "r1020"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by geographic distribution of business activity identified as either domestic or foreign. Excludes names of countries, states and provinces, and cities.",
        "label": "Geographic Distribution [Axis]",
        "terseLabel": "Geographic Distribution [Axis]"
       }
      }
     },
     "localname": "GeographicDistributionAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_GeographicDistributionDomain": {
     "auth_ref": [
      "r906",
      "r907",
      "r994",
      "r995",
      "r996",
      "r997",
      "r998",
      "r999",
      "r1000",
      "r1001",
      "r1002",
      "r1003",
      "r1004",
      "r1005",
      "r1015",
      "r1016",
      "r1017",
      "r1018",
      "r1019",
      "r1020"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Allocation of business activity identified as domestic or foreign. Excludes names of countries, states and provinces, and cities.",
        "label": "Geographic Distribution [Domain]",
        "terseLabel": "Geographic Distribution [Domain]"
       }
      }
     },
     "localname": "GeographicDistributionDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_GeographicDistributionDomesticMember": {
     "auth_ref": [
      "r324",
      "r994",
      "r995",
      "r996",
      "r997",
      "r998",
      "r999",
      "r1000",
      "r1001",
      "r1002",
      "r1003",
      "r1004",
      "r1005",
      "r1015",
      "r1016",
      "r1017",
      "r1018",
      "r1019",
      "r1020"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Allocation of business activity identified as domestic.",
        "label": "Geographic Distribution, Domestic [Member]",
        "terseLabel": "Domestic loans"
       }
      }
     },
     "localname": "GeographicDistributionDomesticMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_GeographicDistributionForeignMember": {
     "auth_ref": [
      "r325",
      "r906",
      "r907",
      "r994",
      "r995",
      "r996",
      "r997",
      "r998",
      "r999",
      "r1000",
      "r1001",
      "r1002",
      "r1003",
      "r1004",
      "r1005",
      "r1015",
      "r1016",
      "r1017",
      "r1018",
      "r1019",
      "r1020"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Allocation of business activity identified as foreign.",
        "label": "Geographic Distribution, Foreign [Member]",
        "terseLabel": "International loans"
       }
      }
     },
     "localname": "GeographicDistributionForeignMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_Goodwill": {
     "auth_ref": [
      "r338",
      "r339",
      "r813",
      "r859"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.",
        "label": "Goodwill",
        "terseLabel": "Balance"
       }
      }
     },
     "localname": "Goodwill",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Goodwill and Intangible Assets Disclosure [Abstract]",
        "terseLabel": "Goodwill and Intangible Assets Disclosure [Abstract]"
       }
      }
     },
     "localname": "GoodwillAndIntangibleAssetsDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock": {
     "auth_ref": [
      "r352"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for goodwill and intangible assets.",
        "label": "Goodwill and Intangible Assets Disclosure [Text Block]",
        "terseLabel": "Goodwill and Core Deposit Intangibles"
       }
      }
     },
     "localname": "GoodwillAndIntangibleAssetsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssets"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_GoodwillAndIntangibleAssetsGoodwillPolicy": {
     "auth_ref": [
      "r340"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for goodwill. This accounting policy also may address how an entity assesses and measures impairment of goodwill, how reporting units are determined, how goodwill is allocated to such units, and how the fair values of the reporting units are determined.",
        "label": "Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block]",
        "terseLabel": "Goodwill and Core Deposit Intangibles"
       }
      }
     },
     "localname": "GoodwillAndIntangibleAssetsGoodwillPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_GoodwillLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Goodwill [Line Items]",
        "terseLabel": "Goodwill [Line Items]"
       }
      }
     },
     "localname": "GoodwillLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_GuaranteesIndemnificationsAndWarrantiesPolicies": {
     "auth_ref": [
      "r381"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for guarantees, indemnifications and product warranties, and methodologies used in determining the amount of such liabilities.",
        "label": "Guarantees, Indemnifications and Warranties Policies [Policy Text Block]",
        "terseLabel": "Financial Guarantees"
       }
      }
     },
     "localname": "GuaranteesIndemnificationsAndWarrantiesPolicies",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_HedgingDesignationAxis": {
     "auth_ref": [
      "r693",
      "r711"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by designation of purpose of derivative instrument.",
        "label": "Hedging Designation [Axis]",
        "terseLabel": "Hedging Designation [Axis]"
       }
      }
     },
     "localname": "HedgingDesignationAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_HedgingDesignationDomain": {
     "auth_ref": [
      "r693"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Designation of purpose of derivative instrument.",
        "label": "Hedging Designation [Domain]",
        "terseLabel": "Hedging Designation [Domain]"
       }
      }
     },
     "localname": "HedgingDesignationDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_HedgingRelationshipDomain": {
     "auth_ref": [
      "r693"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Nature or intent of a hedge.",
        "label": "Hedging Relationship [Domain]",
        "terseLabel": "Hedging Relationship [Domain]"
       }
      }
     },
     "localname": "HedgingRelationshipDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_HomeEquityLoanMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan based on the equity of the borrower's residential property in which the borrower receives the loan amount upfront. Excludes home equity lines of credit.",
        "label": "Home Equity Loan [Member]",
        "terseLabel": "Home equity"
       }
      }
     },
     "localname": "HomeEquityLoanMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_HostingArrangementServiceContractImplementationCostCapitalizedAccumulatedAmortization": {
     "auth_ref": [
      "r350",
      "r355"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated amortization of capitalized implementation cost from hosting arrangement that is service contract.",
        "label": "Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, Accumulated Amortization",
        "terseLabel": "Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, Accumulated Amortization"
       }
      }
     },
     "localname": "HostingArrangementServiceContractImplementationCostCapitalizedAccumulatedAmortization",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_HostingArrangementServiceContractImplementationCostCapitalizedAfterAccumulatedAmortization": {
     "auth_ref": [
      "r350",
      "r354"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after accumulated amortization, of capitalized implementation cost from hosting arrangement that is service contract.",
        "label": "Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, after Accumulated Amortization",
        "terseLabel": "Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, after Accumulated Amortization"
       }
      }
     },
     "localname": "HostingArrangementServiceContractImplementationCostCapitalizedAfterAccumulatedAmortization",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ImpairedFinancingReceivablesTableTextBlock": {
     "auth_ref": [
      "r237"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of impaired financing receivables.",
        "label": "Impaired Financing Receivables [Table Text Block]",
        "terseLabel": "Nonaccrual Loans"
       }
      }
     },
     "localname": "ImpairedFinancingReceivablesTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic": {
     "auth_ref": [
      "r131",
      "r649"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The portion of earnings or loss from continuing operations before income taxes that is attributable to domestic operations.",
        "label": "Income (Loss) from Continuing Operations before Income Taxes, Domestic",
        "negatedTotalLabel": "Income before income taxes"
       }
      }
     },
     "localname": "IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign": {
     "auth_ref": [
      "r131",
      "r649"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The portion of earnings or loss from continuing operations before income taxes that is attributable to foreign operations, which is defined as Income or Loss generated from operations located outside the entity's country of domicile.",
        "label": "Income (Loss) from Continuing Operations before Income Taxes, Foreign",
        "terseLabel": "Foreign-source income"
       }
      }
     },
     "localname": "IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments": {
     "auth_ref": [
      "r202",
      "r208",
      "r212",
      "r215",
      "r218"
     ],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 1.0,
       "parentTag": "cma_IncomeLossFromContinuingOperationsBeforeMinorityInterestsAndIncomeLossFromEquityMethodInvestments",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.",
        "label": "Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest",
        "totalLabel": "Income before benefit for income taxes and equity in undistributed earnings (losses) of subsidiaries"
       }
      }
     },
     "localname": "IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeLossFromEquityMethodInvestments": {
     "auth_ref": [
      "r86",
      "r114",
      "r199",
      "r286",
      "r883",
      "r945"
     ],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of income (loss) for proportionate share of equity method investee's income (loss).",
        "label": "Income (Loss) from Equity Method Investments",
        "terseLabel": "Equity in undistributed earnings of subsidiaries, principally banks"
       }
      }
     },
     "localname": "IncomeLossFromEquityMethodInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions": {
     "auth_ref": [
      "r114"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This element represents the undistributed income (or loss) of equity method investments, net of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations; such investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.",
        "label": "Income (Loss) from Equity Method Investments, Net of Dividends or Distributions",
        "terseLabel": "Undistributed (losses) earnings of subsidiaries, principally banks"
       }
      }
     },
     "localname": "IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeStatementAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Income Statement [Abstract]",
        "terseLabel": "Income Statement [Abstract]"
       }
      }
     },
     "localname": "IncomeStatementAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncomeStatementLocationAxis": {
     "auth_ref": [
      "r358",
      "r361"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by location in the income statement.",
        "label": "Income Statement Location [Axis]",
        "terseLabel": "Derivative Instrument Gain (Loss) by Income Statement Location [Axis]"
       }
      }
     },
     "localname": "IncomeStatementLocationAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncomeStatementLocationDomain": {
     "auth_ref": [
      "r361"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Location in the income statement.",
        "label": "Income Statement Location [Domain]",
        "terseLabel": "Income Statement Location [Domain]"
       }
      }
     },
     "localname": "IncomeStatementLocationDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_IncomeTaxAuthorityAxis": {
     "auth_ref": [
      "r618"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by tax jurisdiction.",
        "label": "Income Tax Authority [Axis]",
        "terseLabel": "Income Tax Authority [Axis]"
       }
      }
     },
     "localname": "IncomeTaxAuthorityAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncomeTaxAuthorityDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Agency, division or body classification that levies income taxes, examines tax returns for compliance, or grants exemptions from or makes other decisions pertaining to income taxes.",
        "label": "Income Tax Authority [Domain]",
        "terseLabel": "Income Tax Authority [Domain]"
       }
      }
     },
     "localname": "IncomeTaxAuthorityDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_IncomeTaxDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Income Tax Disclosure [Abstract]",
        "terseLabel": "Income Tax Disclosure [Abstract]"
       }
      }
     },
     "localname": "IncomeTaxDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_IncomeTaxDisclosureTextBlock": {
     "auth_ref": [
      "r132",
      "r616",
      "r626",
      "r633",
      "r644",
      "r651",
      "r655",
      "r656",
      "r657"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.",
        "label": "Income Tax Disclosure [Text Block]",
        "terseLabel": "Income Taxes and Tax-Related Items"
       }
      }
     },
     "localname": "IncomeTaxDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItems"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_IncomeTaxExpenseBenefit": {
     "auth_ref": [
      "r133",
      "r154",
      "r155",
      "r200",
      "r614",
      "r645",
      "r653",
      "r950"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": -1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 2.0,
       "parentTag": "cma_IncomeLossFromContinuingOperationsBeforeMinorityInterestsAndIncomeLossFromEquityMethodInvestments",
       "weight": -1.0
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 6.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.",
        "label": "Income Tax Expense (Benefit)",
        "netLabel": "Benefit for income taxes",
        "terseLabel": "Provision (benefit) for income taxes",
        "verboseLabel": "Provision (benefit) for income taxes"
       }
      }
     },
     "localname": "IncomeTaxExpenseBenefit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsCurrentandDeferredComponentsoftheProvisionforIncomeTaxesDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxPolicyTextBlock": {
     "auth_ref": [
      "r78",
      "r612",
      "r613",
      "r626",
      "r627",
      "r632",
      "r638"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.",
        "label": "Income Tax, Policy [Policy Text Block]",
        "terseLabel": "Income Taxes"
       }
      }
     },
     "localname": "IncomeTaxPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.",
        "label": "Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount",
        "terseLabel": "Tax based on federal statutory rate, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other nondeductible expenses.",
        "label": "Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount",
        "verboseLabel": "FDIC insurance expense, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationNondeductibleExpenseOther",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxReconciliationOtherAdjustments": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments.",
        "label": "Effective Income Tax Rate Reconciliation, Other Adjustments, Amount",
        "terseLabel": "Other, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationOtherAdjustments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to state and local income tax expense (benefit).",
        "label": "Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount",
        "terseLabel": "State income tax, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationStateAndLocalIncomeTaxes",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxReconciliationTaxCreditsOther": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other tax credits.",
        "label": "Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount",
        "negatedLabel": "Affordable housing and historic credits, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationTaxCreditsOther",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxReconciliationTaxExemptIncome": {
     "auth_ref": [
      "r615"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes.",
        "label": "Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount",
        "negatedTerseLabel": "Bank-owned life insurance, amount"
       }
      }
     },
     "localname": "IncomeTaxReconciliationTaxExemptIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationofExpectedIncomeTaxExpenseattheFederalStatutoryRatetotheCorporationsProvisionforIncomeTaxesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncomeTaxesPaidNet": {
     "auth_ref": [
      "r119"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.",
        "label": "Income Taxes Paid, Net",
        "terseLabel": "Income taxes paid"
       }
      }
     },
     "localname": "IncomeTaxesPaidNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInAccruedLiabilities": {
     "auth_ref": [
      "r113"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 8.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The increase (decrease) during the reporting period in the aggregate amount of expenses incurred but not yet paid.",
        "label": "Increase (Decrease) in Accrued Liabilities",
        "terseLabel": "Net change in accrued expenses payable"
       }
      }
     },
     "localname": "IncreaseDecreaseInAccruedLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInDeposits": {
     "auth_ref": [
      "r117",
      "r903"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 1.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net cash inflow or outflow for the increase (decrease) in the beginning and end of period deposits balances.",
        "label": "Increase (Decrease) in Deposits",
        "terseLabel": "Net change in deposits"
       }
      }
     },
     "localname": "IncreaseDecreaseInDeposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInInterestAndDividendsReceivable": {
     "auth_ref": [
      "r113"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The increase (decrease) during the reporting period in the aggregate amount due to the entity in the form of unpaid interest and dividends.",
        "label": "Increase (Decrease) in Interest and Dividends Receivable",
        "negatedTerseLabel": "Net change in accrued income receivable"
       }
      }
     },
     "localname": "IncreaseDecreaseInInterestAndDividendsReceivable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet": {
     "auth_ref": [
      "r113"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 9.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) in operating assets after deduction of operating liabilities classified as other.",
        "label": "Increase (Decrease) in Other Operating Assets and Liabilities, Net",
        "negatedLabel": "Other, net",
        "terseLabel": "Other, net"
       }
      }
     },
     "localname": "IncreaseDecreaseInOtherOperatingCapitalNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements": {
     "auth_ref": [
      "r161",
      "r162",
      "r163",
      "r171"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.",
        "label": "Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements",
        "terseLabel": "Net effect of the assumed exercise of stock awards"
       }
      }
     },
     "localname": "IncrementalCommonSharesAttributableToShareBasedPaymentArrangements",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_IndustryOfCounterpartyDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The industry of the party or parties having primary responsibility to meet the obligations of the arrangement with the entity.",
        "label": "Industry of Counterparty [Domain]",
        "terseLabel": "Industry of Counterparty [Domain]"
       }
      }
     },
     "localname": "IndustryOfCounterpartyDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskScheduleofAutomotiveIndustryOutstandingLoansandTotalExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_InterestAndDividendIncomeOperating": {
     "auth_ref": [
      "r889"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_InterestIncomeExpenseNet",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.",
        "label": "Interest and Dividend Income, Operating",
        "terseLabel": "Interest income",
        "totalLabel": "Total interest income"
       }
      }
     },
     "localname": "InterestAndDividendIncomeOperating",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestAndDividendIncomeOperatingAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Interest and Dividend Income, Operating [Abstract]",
        "terseLabel": "INTEREST INCOME"
       }
      }
     },
     "localname": "InterestAndDividendIncomeOperatingAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_InterestAndFeeIncomeLoansAndLeasesHeldInPortfolio": {
     "auth_ref": [
      "r888"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_InterestAndDividendIncomeOperating",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Interest and fee income generated by loans the Entity intends and has the ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (1) industrial and agricultural; (2) real estate; and (3) real estate construction loans; (4) trade financing; (5) lease financing; (6) home equity lines-of-credit; (7) automobile and other vehicle loans; and (8) credit card and other revolving-type loans. Also includes interest income for leases held by the Entity.",
        "label": "Interest and Fee Income, Loans and Leases Held-in-portfolio",
        "terseLabel": "Interest and fees on loans"
       }
      }
     },
     "localname": "InterestAndFeeIncomeLoansAndLeasesHeldInPortfolio",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestBearingDepositLiabilities": {
     "auth_ref": [
      "r871"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_Deposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate of all domestic and foreign interest-bearing deposit liabilities.",
        "label": "Interest-bearing Deposit Liabilities",
        "totalLabel": "Total interest-bearing deposits"
       }
      }
     },
     "localname": "InterestBearingDepositLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestBearingDepositsInBanks": {
     "auth_ref": [
      "r857",
      "r877"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For banks and other depository institutions (including Federal Reserve Banks, if applicable): Interest-bearing deposits in other financial institutions for relatively short periods of time including, for example, certificates of deposits, which are presented separately from cash on the balance sheet.",
        "label": "Interest-bearing Deposits in Banks and Other Financial Institutions",
        "terseLabel": "Interest-bearing deposits with banks"
       }
      }
     },
     "localname": "InterestBearingDepositsInBanks",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestBearingForeignDepositTimeDeposits": {
     "auth_ref": [
      "r871",
      "r905"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 4.0,
       "parentTag": "us-gaap_InterestBearingDepositLiabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of interest-bearing time deposits in foreign banking offices. Time deposits bear interest for a fixed, stated period of time and include certificate of deposits and individual retirement accounts.",
        "label": "Interest-bearing Foreign Deposit, Time Deposits",
        "terseLabel": "Foreign office time deposits",
        "verboseLabel": "Foreign office time deposits in denominations of $250,000 or more"
       }
      }
     },
     "localname": "InterestBearingForeignDepositTimeDeposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/DepositsDepositsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestExpense": {
     "auth_ref": [
      "r84",
      "r196",
      "r778",
      "r781",
      "r902"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_InterestIncomeExpenseNet",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of the cost of borrowed funds accounted for as interest expense.",
        "label": "Interest Expense",
        "terseLabel": "Interest expense",
        "totalLabel": "Total interest expense"
       }
      }
     },
     "localname": "InterestExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestExpenseAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Interest Expense [Abstract]",
        "terseLabel": "INTEREST EXPENSE"
       }
      }
     },
     "localname": "InterestExpenseAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_InterestExpenseDeposits": {
     "auth_ref": [
      "r899"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_InterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate amount of interest expense on all deposits.",
        "label": "Interest Expense, Deposits",
        "terseLabel": "Interest on deposits"
       }
      }
     },
     "localname": "InterestExpenseDeposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestExpenseLongTermDebt": {
     "auth_ref": [
      "r901",
      "r994",
      "r995"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 3.0,
       "parentTag": "us-gaap_InterestExpense",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_CostsAndExpenses",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate amount of interest paid or due on all long-term debt.",
        "label": "Interest Expense, Long-term Debt",
        "terseLabel": "Interest on medium- and long-term debt"
       }
      }
     },
     "localname": "InterestExpenseLongTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestExpenseShortTermBorrowings": {
     "auth_ref": [
      "r900",
      "r994",
      "r995"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_InterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate interest expense incurred on short-term borrowings including commercial paper and Federal funds purchased and securities sold under agreements to repurchase.",
        "label": "Interest Expense, Short-term Borrowings",
        "terseLabel": "Interest on short-term borrowings"
       }
      }
     },
     "localname": "InterestExpenseShortTermBorrowings",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss": {
     "auth_ref": [
      "r892"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of interest income or expense, including any amortization and accretion (as applicable) of discounts and premiums, including consideration of the provisions for loan, lease, credit, and other related losses.",
        "label": "Interest Income (Expense), after Provision for Loan Loss",
        "totalLabel": "Net interest income after provision for credit losses"
       }
      }
     },
     "localname": "InterestIncomeExpenseAfterProvisionForLoanLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestIncomeExpenseNet": {
     "auth_ref": [
      "r890"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss",
       "weight": 1.0
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net amount of operating interest income (expense).",
        "label": "Interest Income (Expense), Net",
        "terseLabel": "Net interest income",
        "totalLabel": "Net interest income",
        "verboseLabel": "Net interest income (expense)"
       }
      }
     },
     "localname": "InterestIncomeExpenseNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestPaid": {
     "auth_ref": [
      "r119"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities.",
        "label": "Interest Paid, Including Capitalized Interest, Operating and Investing Activities",
        "terseLabel": "Interest paid"
       }
      }
     },
     "localname": "InterestPaid",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestPayableCurrentAndNoncurrent": {
     "auth_ref": [
      "r874",
      "r943"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 2.0,
       "parentTag": "cma_LesseeOperatingLeaseLiabilityToBePaidLessInterest",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of interest payable on debt, including, but not limited to, trade payables.",
        "label": "Interest Payable",
        "terseLabel": "Less: Imputed interest"
       }
      }
     },
     "localname": "InterestPayableCurrentAndNoncurrent",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InterestRateContractMember": {
     "auth_ref": [
      "r57",
      "r491",
      "r706"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument whose primary underlying risk is tied to the right to receive or pay a sum of money at a given interest rate.",
        "label": "Interest Rate Contract [Member]",
        "terseLabel": "Interest rate contracts"
       }
      }
     },
     "localname": "InterestRateContractMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_InterestRateSwapMember": {
     "auth_ref": [
      "r706"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Forward based contracts in which two parties agree to swap periodic payments that are fixed at the outset of the swap contract with variable payments based on a market interest rate (index rate) over a specified period.",
        "label": "Interest Rate Swap [Member]",
        "terseLabel": "Interest Rate Swap [Member]",
        "verboseLabel": "Interest rate swap"
       }
      }
     },
     "localname": "InterestRateSwapMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsDerivativeAndCreditRelatedFinancialInstrumentsScheduleofEffectsofFairValueHedgingontheConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_InterestReceivable": {
     "auth_ref": [
      "r48"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.",
        "label": "Interest Receivable",
        "terseLabel": "Loan interest receivable"
       }
      }
     },
     "localname": "InterestReceivable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_InternalCreditAssessmentAxis": {
     "auth_ref": [
      "r240",
      "r311",
      "r326",
      "r327",
      "r380",
      "r714"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by entity-defined rating.",
        "label": "Internal Credit Assessment [Axis]",
        "terseLabel": "Internal Credit Assessment [Axis]"
       }
      }
     },
     "localname": "InternalCreditAssessmentAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_InternalCreditAssessmentDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Entity defined credit risk rating.",
        "label": "Internal Credit Assessment [Domain]",
        "terseLabel": "Internal Credit Assessment [Domain]"
       }
      }
     },
     "localname": "InternalCreditAssessmentDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_InternalRevenueServiceIRSMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Designated tax department of the United States of America government entitled to levy and collect income taxes from the entity.",
        "label": "Internal Revenue Service (IRS) [Member]",
        "terseLabel": "Federal"
       }
      }
     },
     "localname": "InternalRevenueServiceIRSMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_InternalUseSoftwarePolicy": {
     "auth_ref": [
      "r349",
      "r351"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for costs incurred when both (1) the software is acquired, internally developed, or modified solely to meet the entity's internal needs, and (2) during the software's development or modification, no substantive plan exists or is being developed to market the software externally.",
        "label": "Internal Use Software, Policy [Policy Text Block]",
        "terseLabel": "Software"
       }
      }
     },
     "localname": "InternalUseSoftwarePolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments.",
        "label": "Investments Classified by Contractual Maturity Date [Table Text Block]",
        "terseLabel": "Contractual Maturity Distribution Of Debt Securities"
       }
      }
     },
     "localname": "InvestmentsClassifiedByContractualMaturityDateTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Investments, Debt and Equity Securities [Abstract]",
        "terseLabel": "Investments, Debt and Equity Securities [Abstract]"
       }
      }
     },
     "localname": "InvestmentsDebtAndEquitySecuritiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock": {
     "auth_ref": [
      "r282",
      "r856",
      "r911",
      "r973",
      "r1006"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for  investments in certain debt and equity securities.",
        "label": "Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]",
        "terseLabel": "Investment Securities"
       }
      }
     },
     "localname": "InvestmentsInDebtAndMarketableEquitySecuritiesAndCertainTradingAssetsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecurities"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_LaborAndRelatedExpense": {
     "auth_ref": [
      "r92"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_CostsAndExpenses",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expense for salary, wage, profit sharing; incentive and equity-based compensation; and other employee benefit.",
        "label": "Labor and Related Expense",
        "terseLabel": "Salaries and benefits expense"
       }
      }
     },
     "localname": "LaborAndRelatedExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_Land": {
     "auth_ref": [
      "r9",
      "r32"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.",
        "label": "Land",
        "terseLabel": "Land"
       }
      }
     },
     "localname": "Land",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LeaseCost": {
     "auth_ref": [
      "r794",
      "r796"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lease cost recognized by lessee for lease contract.",
        "label": "Lease, Cost",
        "terseLabel": "Total lease expense"
       }
      }
     },
     "localname": "LeaseCost",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesLeaseExpensesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LeasesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Leases [Abstract]",
        "terseLabel": "Leases [Abstract]"
       }
      }
     },
     "localname": "LeasesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_LegalFees": {
     "auth_ref": [
      "r94"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.",
        "label": "Legal Fees",
        "terseLabel": "Legal fees"
       }
      }
     },
     "localname": "LegalFees",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseDiscountRate": {
     "auth_ref": [
      "r789"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Discount rate used by lessee to determine present value of operating lease payments.",
        "label": "Lessee, Operating Lease, Discount Rate",
        "terseLabel": "Weighted average discount rate"
       }
      }
     },
     "localname": "LesseeOperatingLeaseDiscountRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesSupplementalbalancesheetDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityMaturityTableTextBlock": {
     "auth_ref": [
      "r795"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of undiscounted cash flows of lessee's operating lease liability. Includes, but is not limited to, reconciliation of undiscounted cash flows to operating lease liability recognized in statement of financial position.",
        "label": "Lessee, Operating Lease, Liability, Maturity [Table Text Block]",
        "terseLabel": "Contractual maturities of sales-type and direct financing lease receivables"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityMaturityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 1.0,
       "parentTag": "cma_LesseeOperatingLeaseLiabilityToBePaidLessInterest",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease.",
        "label": "Lessee, Operating Lease, Liability, to be Paid",
        "totalLabel": "Total contractual maturities"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Lessee, Operating Lease, Liability, to be Paid, Year One",
        "terseLabel": "2022"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Lessee, Operating Lease, Liability, to be Paid, Year Five",
        "terseLabel": "2026"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDueYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 6.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Lessee, Operating Lease, Liability, to be Paid, Year Four",
        "terseLabel": "2025"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDueYearFour",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Lessee, Operating Lease, Liability, to be Paid, Year Three",
        "terseLabel": "2024"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDueYearThree",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo": {
     "auth_ref": [
      "r795"
     ],
     "calculation": {
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Lessee, Operating Lease, Liability, to be Paid, Year Two",
        "terseLabel": "2023"
       }
      }
     },
     "localname": "LesseeOperatingLeaseLiabilityPaymentsDueYearTwo",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofOperatingLeaseLiabilitiesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LesseeOperatingLeaseTermOfContract": {
     "auth_ref": [
      "r788"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.",
        "label": "Lessee, Operating Lease, Term of Contract",
        "terseLabel": "Weighted average lease term in years"
       }
      }
     },
     "localname": "LesseeOperatingLeaseTermOfContract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesSupplementalbalancesheetDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_LetterOfCreditMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A document typically issued by a financial institution which acts as a guarantee of payment to a beneficiary, or as the source of payment for a specific transaction (for example, wiring funds to a foreign exporter if and when specified merchandise is accepted pursuant to the terms of the letter of credit).",
        "label": "Letter of Credit [Member]",
        "terseLabel": "Commercial Letters Of Credit"
       }
      }
     },
     "localname": "LetterOfCreditMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_LettersOfCreditOutstandingAmount": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.",
        "label": "Letters of Credit Outstanding, Amount",
        "terseLabel": "Standby and commercial letters of credit outstanding"
       }
      }
     },
     "localname": "LettersOfCreditOutstandingAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_Liabilities": {
     "auth_ref": [
      "r39",
      "r129",
      "r210",
      "r289",
      "r386",
      "r387",
      "r388",
      "r391",
      "r392",
      "r393",
      "r395",
      "r397",
      "r399",
      "r400",
      "r665",
      "r670",
      "r671",
      "r759",
      "r811",
      "r812"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.",
        "label": "Liabilities",
        "totalLabel": "Total liabilities"
       }
      }
     },
     "localname": "Liabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LiabilitiesAndStockholdersEquity": {
     "auth_ref": [
      "r28",
      "r129",
      "r289",
      "r759",
      "r813",
      "r865",
      "r940"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of liabilities and equity items, including the portion of equity attributable to noncontrolling interests, if any.",
        "label": "Liabilities and Equity",
        "totalLabel": "Total liabilities and shareholders' equity"
       }
      }
     },
     "localname": "LiabilitiesAndStockholdersEquity",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LiabilitiesAndStockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Liabilities and Equity [Abstract]",
        "terseLabel": "LIABILITIES AND SHAREHOLDERS' EQUITY"
       }
      }
     },
     "localname": "LiabilitiesAndStockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LiabilitiesFairValueDisclosure": {
     "auth_ref": [
      "r735"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of financial and nonfinancial obligations.",
        "label": "Financial and Nonfinancial Liabilities, Fair Value Disclosure",
        "terseLabel": "Total liabilities at fair value",
        "verboseLabel": "Total liabilities at fair value"
       }
      }
     },
     "localname": "LiabilitiesFairValueDisclosure",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity": {
     "auth_ref": [
      "r37"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.",
        "label": "Line of Credit Facility, Current Borrowing Capacity",
        "terseLabel": "Available collateralized borrowing with the FRB"
       }
      }
     },
     "localname": "LineOfCreditFacilityCurrentBorrowingCapacity",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity": {
     "auth_ref": [
      "r37"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).",
        "label": "Line of Credit Facility, Remaining Borrowing Capacity",
        "terseLabel": "Potential future borrowings"
       }
      }
     },
     "localname": "LineOfCreditFacilityRemainingBorrowingCapacity",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LitigationReserve": {
     "auth_ref": [
      "r43",
      "r367"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.",
        "label": "Estimated Litigation Liability",
        "terseLabel": "Estimated Litigation Liability"
       }
      }
     },
     "localname": "LitigationReserve",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LitigationStatusAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by status of pending, threatened, or settled litigation.",
        "label": "Litigation Status [Axis]",
        "terseLabel": "Litigation Status [Axis]"
       }
      }
     },
     "localname": "LitigationStatusAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LitigationStatusDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Status of pending, threatened, or settled litigation.",
        "label": "Litigation Status [Domain]",
        "terseLabel": "Litigation Status [Domain]"
       }
      }
     },
     "localname": "LitigationStatusDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_LoanRestructuringModificationAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by concessions made to the terms of loan contracts.",
        "label": "Loan Restructuring Modification [Axis]",
        "terseLabel": "Loan Restructuring Modification [Axis]"
       }
      }
     },
     "localname": "LoanRestructuringModificationAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LoanRestructuringModificationDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Concessions made to the terms of loan contracts, including but not limited to, interest rate reductions, maturity extensions, principal forgiveness, and payment deferral.",
        "label": "Loan Restructuring Modification [Domain]",
        "terseLabel": "Loan Restructuring Modification [Domain]"
       }
      }
     },
     "localname": "LoanRestructuringModificationDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_LoansAndLeasesReceivableAllowance": {
     "auth_ref": [
      "r230",
      "r234",
      "r252",
      "r261"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetReportedAmount",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.",
        "label": "Loans and Leases Receivable, Allowance",
        "negatedLabel": "Less allowance for loan losses"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableAllowance",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableDeferredIncome": {
     "auth_ref": [
      "r246",
      "r256",
      "r785",
      "r881"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for loans and leases covered under loss sharing agreements.",
        "label": "Loans and Leases Receivable, Deferred Income",
        "terseLabel": "Net Deferred Income on Originated Loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableDeferredIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend": {
     "auth_ref": [
      "r262"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.",
        "label": "Financing Receivable, Troubled Debt Restructuring, Commitment to Lend",
        "terseLabel": "Commitments to lend additional funds to TDR borrowers"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableImpairedCommitmentToLend",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest": {
     "auth_ref": [
      "r248"
     ],
     "calculation": {
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.",
        "label": "Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest",
        "terseLabel": "Nonaccrual loans",
        "verboseLabel": "Nonaccrual loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome": {
     "auth_ref": [
      "r225",
      "r246"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_LoansAndLeasesReceivableNetReportedAmount",
       "weight": 1.0
      },
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.",
        "label": "Loans and Leases Receivable, Net of Deferred Income",
        "terseLabel": "Total loans",
        "totalLabel": "Total loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableNetOfDeferredIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableNetReportedAmount": {
     "auth_ref": [
      "r225",
      "r881"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 5.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.",
        "label": "Loans and Leases Receivable, Net Amount",
        "terseLabel": "Total loans, net of allowance for loan losses",
        "totalLabel": "Net loans"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableNetReportedAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableOriginationFeesDiscountsOrPremiumsAndDirectCostsToAcquireLoansPolicy": {
     "auth_ref": [
      "r238"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for method for recognizing interest income and amortizing deferred fee or cost of financing receivable. Includes, but is not limited to, treatment of fee, cost, premium and discount.",
        "label": "Financing Receivable, Fee and Interest Income [Policy Text Block]",
        "terseLabel": "Loan Origination Fees and Costs"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableOriginationFeesDiscountsOrPremiumsAndDirectCostsToAcquireLoansPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_LoansAndLeasesReceivableRelatedPartiesAdditions": {
     "auth_ref": [
      "r805",
      "r880"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the amount of new advances made to related parties in the form of loan and lease receivables.",
        "label": "Loans and Leases Receivable, Related Parties, Additions",
        "terseLabel": "New loans to related parties"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableRelatedPartiesAdditions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/TransactionswithRelatedPartiesTransactionswithRelatedPartiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansAndLeasesReceivableRelatedPartiesProceeds": {
     "auth_ref": [
      "r98",
      "r870"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from related parties which reduce the amount of loans and leases receivable due from related parties.",
        "label": "Loans and Leases Receivable, Related Parties, Proceeds",
        "terseLabel": "Repayments on loans to related parties"
       }
      }
     },
     "localname": "LoansAndLeasesReceivableRelatedPartiesProceeds",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/TransactionswithRelatedPartiesTransactionswithRelatedPartiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansMember": {
     "auth_ref": [
      "r134",
      "r253"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "When a lender gives money or property over other debt securities sold by the issuer. In the event the issuer goes bankrupt, senior debt holders receive priority for [must receive] repayment [prior] relative to junior and unsecured (general) creditors.",
        "label": "Loans [Member]",
        "terseLabel": "Variable rate loans"
       }
      }
     },
     "localname": "LoansMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_LoansReceivableFairValueDisclosure": {
     "auth_ref": [
      "r253"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.",
        "label": "Loans Receivable, Fair Value Disclosure",
        "terseLabel": "Loans"
       }
      }
     },
     "localname": "LoansReceivableFairValueDisclosure",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup": {
     "auth_ref": [
      "r225",
      "r974"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.",
        "label": "Financing Receivable, Held-for-Sale, Not Part of Disposal Group, after Valuation Allowance",
        "terseLabel": "Loans held-for-sale"
       }
      }
     },
     "localname": "LoansReceivableHeldForSaleNetNotPartOfDisposalGroup",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebt": {
     "auth_ref": [
      "r20",
      "r409",
      "r420",
      "r421",
      "r422",
      "r864",
      "r937"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 3.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.",
        "label": "Long-term Debt",
        "terseLabel": "Medium- and long-term debt",
        "verboseLabel": "Long-term Debt"
       }
      }
     },
     "localname": "LongTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Next Rolling Twelve Months",
        "terseLabel": "2022"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFive": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Rolling after Year Five",
        "terseLabel": "Therafter"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFive": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Rolling Year Five",
        "terseLabel": "2026"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Rolling Year Four",
        "terseLabel": "2025"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Rolling Year Three",
        "terseLabel": "2024"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo": {
     "auth_ref": [
      "r136"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Long-term Debt, Maturities, Repayments of Principal in Rolling Year Two",
        "terseLabel": "2023"
       }
      }
     },
     "localname": "LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleofMaturitiesofMediumandLongtermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_LongTermDebtMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Debt arrangement having an initial term longer than one year or beyond the normal operating cycle, if longer.",
        "label": "Long-term Debt [Member]",
        "terseLabel": "Long-term Debt [Member]"
       }
      }
     },
     "localname": "LongTermDebtMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_LongTermDebtTextBlock": {
     "auth_ref": [
      "r425"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for long-term debt.",
        "label": "Long-term Debt [Text Block]",
        "terseLabel": "Medium- And Long-Term Debt"
       }
      }
     },
     "localname": "LongTermDebtTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebt"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_LossContingenciesLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Loss Contingencies [Line Items]",
        "terseLabel": "Loss Contingencies [Line Items]"
       }
      }
     },
     "localname": "LossContingenciesLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LossContingenciesTable": {
     "auth_ref": [
      "r367",
      "r368",
      "r369",
      "r371",
      "r372",
      "r373",
      "r375",
      "r378",
      "r379"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Discloses the specific components (such as the nature, name, and date) of the loss contingency and gives an estimate of the possible loss or range of loss, or states that a reasonable estimate cannot be made. Excludes environmental contingencies, warranties and unconditional purchase obligations.",
        "label": "Loss Contingencies [Table]",
        "terseLabel": "Loss Contingencies [Table]"
       }
      }
     },
     "localname": "LossContingenciesTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_LossContingencyEstimateOfPossibleLoss": {
     "auth_ref": [
      "r370",
      "r374",
      "r378"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.",
        "label": "Loss Contingency, Estimate of Possible Loss",
        "terseLabel": "Loss contingency, estimate of possible loss, maximum",
        "verboseLabel": "Loss contingency, estimate of possible loss"
       }
      }
     },
     "localname": "LossContingencyEstimateOfPossibleLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ManagingRisksInherentInServicingAssetsAndServicingLiabilitiesByTypeOfRiskAxis": {
     "auth_ref": [
      "r832"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of risks inherent in servicing assets and servicing liabilities.",
        "label": "Servicing Assets and Servicing Liabilities Risk [Axis]",
        "terseLabel": "Servicing Assets and Servicing Liabilities Risk [Axis]"
       }
      }
     },
     "localname": "ManagingRisksInherentInServicingAssetsAndServicingLiabilitiesByTypeOfRiskAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_MarketableSecuritiesPolicy": {
     "auth_ref": [
      "r910"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for investment classified as marketable security.",
        "label": "Marketable Securities, Policy [Policy Text Block]",
        "terseLabel": "Investment Securities"
       }
      }
     },
     "localname": "MarketableSecuritiesPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_MortgageLoansInProcessOfForeclosureAmount": {
     "auth_ref": [
      "r245"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.",
        "label": "Mortgage Loans in Process of Foreclosure, Amount",
        "terseLabel": "Retail loans secured by residential real estate in process of foreclosure"
       }
      }
     },
     "localname": "MortgageLoansInProcessOfForeclosureAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInFinancingActivities": {
     "auth_ref": [
      "r110"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 3.0,
       "parentTag": "us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.",
        "label": "Net Cash Provided by (Used in) Financing Activities",
        "terseLabel": "Net cash provided by (used in) financing activities",
        "totalLabel": "Net cash provided by (used in) financing activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInFinancingActivities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided by (Used in) Financing Activities [Abstract]",
        "terseLabel": "FINANCING ACTIVITIES"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInFinancingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetCashProvidedByUsedInInvestingActivities": {
     "auth_ref": [
      "r110"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 2.0,
       "parentTag": "us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.",
        "label": "Net Cash Provided by (Used in) Investing Activities",
        "terseLabel": "Net cash used in investing activities",
        "totalLabel": "Net cash used in investing activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInInvestingActivities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided by (Used in) Investing Activities [Abstract]",
        "terseLabel": "INVESTING ACTIVITIES"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInInvestingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetCashProvidedByUsedInOperatingActivities": {
     "auth_ref": [
      "r110",
      "r112",
      "r115"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 1.0,
       "parentTag": "us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease",
       "weight": 1.0
      }
     },
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.",
        "label": "Net Cash Provided by (Used in) Operating Activities",
        "terseLabel": "Net cash provided by operating activities",
        "totalLabel": "Net cash provided by operating activities"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInOperatingActivities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Net Cash Provided by (Used in) Operating Activities [Abstract]",
        "terseLabel": "OPERATING ACTIVITIES"
       }
      }
     },
     "localname": "NetCashProvidedByUsedInOperatingActivitiesAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic": {
     "auth_ref": [
      "r147",
      "r148",
      "r150",
      "r151",
      "r157",
      "r158",
      "r166",
      "r171",
      "r202",
      "r208",
      "r212",
      "r215",
      "r218"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.",
        "label": "Net Income (Loss) Available to Common Stockholders, Basic",
        "terseLabel": "Net income attributable to common shares",
        "totalLabel": "Net income attributable to common shares"
       }
      }
     },
     "localname": "NetIncomeLossAvailableToCommonStockholdersBasic",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NonUsMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Countries excluding the United States of America (US).",
        "label": "Non-US [Member]",
        "terseLabel": "Non-US"
       }
      }
     },
     "localname": "NonUsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_NondesignatedMember": {
     "auth_ref": [
      "r693"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Derivative instrument not designated as hedging instrument under Generally Accepted Accounting Principles (GAAP).",
        "label": "Not Designated as Hedging Instrument [Member]",
        "terseLabel": "Not Designated as Hedging Instrument [Member]",
        "verboseLabel": "Derivatives used as economic hedges"
       }
      }
     },
     "localname": "NondesignatedMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfDerivativeInstrumentsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_NoninterestBearingDepositLiabilities": {
     "auth_ref": [
      "r871"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 1.0,
       "parentTag": "us-gaap_Deposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.",
        "label": "Noninterest-bearing Deposit Liabilities",
        "terseLabel": "Noninterest-bearing deposits",
        "verboseLabel": "Demand deposits (noninterest-bearing)"
       }
      }
     },
     "localname": "NoninterestBearingDepositLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NoninterestExpense": {
     "auth_ref": [
      "r897"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 3.0,
       "parentTag": "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic",
       "weight": -1.0
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total aggregate amount of all noninterest expense.",
        "label": "Noninterest Expense",
        "terseLabel": "Noninterest expenses",
        "totalLabel": "Total noninterest expenses",
        "verboseLabel": "Noninterest expenses"
       }
      }
     },
     "localname": "NoninterestExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NoninterestExpenseAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Noninterest Expense [Abstract]",
        "terseLabel": "NONINTEREST EXPENSES"
       }
      }
     },
     "localname": "NoninterestExpenseAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NoninterestIncome": {
     "auth_ref": [
      "r894"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic",
       "weight": 1.0
      },
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.",
        "label": "Noninterest Income",
        "terseLabel": "Noninterest income",
        "totalLabel": "Total noninterest income"
       }
      }
     },
     "localname": "NoninterestIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NoninterestIncomeAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Noninterest Income [Abstract]",
        "terseLabel": "NONINTEREST INCOME"
       }
      }
     },
     "localname": "NoninterestIncomeAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_NoninterestIncomeOtherOperatingIncome": {
     "auth_ref": [
      "r83",
      "r884",
      "r949"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 9.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of revenue earned, classified as other, excluding interest income.",
        "label": "Noninterest Income, Other Operating Income",
        "terseLabel": "Other noninterest income"
       }
      }
     },
     "localname": "NoninterestIncomeOtherOperatingIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock": {
     "auth_ref": [
      "r567"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the changes in outstanding nonvested restricted stock shares.",
        "label": "Nonvested Restricted Stock Shares Activity [Table Text Block]",
        "terseLabel": "Summary of Restricted Stock Activity and Related Information"
       }
      }
     },
     "localname": "NonvestedRestrictedStockSharesActivityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_NumberOfReportingUnits": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.",
        "label": "Number of Reporting Units",
        "verboseLabel": "Number of Reporting Units"
       }
      }
     },
     "localname": "NumberOfReportingUnits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "integerItemType"
    },
    "us-gaap_OccupancyNet": {
     "auth_ref": [
      "r95",
      "r784",
      "r895"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of net occupancy expense that may include items, such as depreciation of facilities and equipment, lease expenses, property taxes and property and casualty insurance expense.",
        "label": "Occupancy, Net",
        "terseLabel": "Occupancy expense"
       }
      }
     },
     "localname": "OccupancyNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OpenTaxYear": {
     "auth_ref": [
      "r618"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tax year that remains open to examination under enacted tax laws, in YYYY format.",
        "label": "Open Tax Year",
        "terseLabel": "Open Tax Year"
       }
      }
     },
     "localname": "OpenTaxYear",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "gYearListItemType"
    },
    "us-gaap_OperatingLeaseExpense": {
     "auth_ref": [
      "r786"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of operating lease expense. Excludes sublease income.",
        "label": "Operating Lease, Expense",
        "terseLabel": "Operating lease expense"
       }
      }
     },
     "localname": "OperatingLeaseExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesLeaseExpensesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingLeaseLeaseIncomeTableTextBlock": {
     "auth_ref": [
      "r182",
      "r799"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of components of income from operating lease.",
        "label": "Operating Lease, Lease Income [Table Text Block]",
        "terseLabel": "Operating Leases"
       }
      }
     },
     "localname": "OperatingLeaseLeaseIncomeTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_OperatingLeasePayments": {
     "auth_ref": [
      "r787",
      "r792"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.",
        "label": "Operating Lease, Payments",
        "terseLabel": "Operating cash flows from operating activities"
       }
      }
     },
     "localname": "OperatingLeasePayments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesSupplementalcashflowDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OperatingSegmentsMember": {
     "auth_ref": [
      "r207",
      "r208",
      "r209",
      "r210",
      "r212",
      "r218"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Identifies components of an entity that engage in business activities from which they may earn revenue and incur expenses, including transactions with other components of the same entity.",
        "label": "Operating Segments [Member]",
        "terseLabel": "Parent Company"
       }
      }
     },
     "localname": "OperatingSegmentsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_OtherAssets": {
     "auth_ref": [
      "r15",
      "r860",
      "r934"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 7.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of assets classified as other.",
        "label": "Other Assets",
        "terseLabel": "Accrued income and other assets"
       }
      }
     },
     "localname": "OtherAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostCreditArisingDuringPeriodBeforeTax": {
     "auth_ref": [
      "r65",
      "r67",
      "r510"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).",
        "label": "Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax",
        "terseLabel": "Prior service (cost) credit arising during the period"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostCreditArisingDuringPeriodBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax": {
     "auth_ref": [
      "r63",
      "r67",
      "r510"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.",
        "label": "Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, after Tax",
        "totalLabel": "Benefit plans, Net defined benefit pension and other postretirement adjustment arising during the period, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax": {
     "auth_ref": [
      "r68"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.",
        "label": "Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax",
        "terseLabel": "Benefit plans, Less: Provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax": {
     "auth_ref": [
      "r67",
      "r71",
      "r72",
      "r510"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostBeforeTax",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) of defined benefit plan.",
        "label": "Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax",
        "netLabel": "Amortization of prior service credit",
        "terseLabel": "Amortization of prior service credit",
        "verboseLabel": "Benefit plans, Amortization of prior service credit"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax": {
     "auth_ref": [
      "r61",
      "r62",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossBeforeTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax and after adjustment, of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.",
        "label": "OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, before Tax",
        "totalLabel": "Change in net unrealized (losses) gains before income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax": {
     "auth_ref": [
      "r61",
      "r62",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and adjustment, of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.",
        "label": "OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax",
        "totalLabel": "Investment securities, Change in net unrealized (losses) gains on investment securities, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax": {
     "auth_ref": [
      "r70",
      "r79",
      "r80",
      "r771",
      "r773",
      "r777"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before tax and reclassification adjustments of other comprehensive income (loss).",
        "label": "Other Comprehensive Income (Loss), before Reclassifications, before Tax",
        "terseLabel": "Net cash flow hedge gains included in interest and fees on loans"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossBeforeTax": {
     "auth_ref": [
      "r79",
      "r80",
      "r87",
      "r287",
      "r771",
      "r776",
      "r777",
      "r885",
      "r946"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossNetOfTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before tax, after reclassification adjustments of other comprehensive income (loss).",
        "label": "Other Comprehensive Income (Loss), before Tax",
        "totalLabel": "Total other comprehensive (loss) income before income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax": {
     "auth_ref": [
      "r60",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax",
        "totalLabel": "Change in net cash flow hedges gains, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax": {
     "auth_ref": [
      "r60",
      "r67"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax and after reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax",
        "terseLabel": "Change in net cash flow hedge gains arising during the period, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax": {
     "auth_ref": [
      "r60",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and before reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax",
        "terseLabel": "Change in net cash flow hedge gains arising during the period, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax": {
     "auth_ref": [
      "r68"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, Tax",
        "terseLabel": "Net cash flow hedge gains included in interest and fees on loans"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax": {
     "auth_ref": [
      "r67",
      "r71"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax",
        "terseLabel": "Cash flow hedges, reclassification adjustment for net cash flow hedge gains included in net income, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax": {
     "auth_ref": [
      "r68"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax expense (benefit) for reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.",
        "label": "Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax",
        "terseLabel": "Cash flow hedges, Less: (Benefit) provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossNetOfTax": {
     "auth_ref": [
      "r74",
      "r77",
      "r79",
      "r80",
      "r82",
      "r87",
      "r441",
      "r771",
      "r776",
      "r777",
      "r885",
      "r946"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after tax and reclassification adjustments of other comprehensive income (loss).",
        "label": "Other Comprehensive Income (Loss), Net of Tax",
        "terseLabel": "Other comprehensive income (loss), net of tax",
        "totalLabel": "Total other comprehensive (loss) income, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax": {
     "auth_ref": [
      "r64",
      "r67",
      "r510",
      "r537"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossBeforeTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.",
        "label": "Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax",
        "negatedLabel": "Total recognized in other comprehensive loss",
        "negatedTotalLabel": "Change in defined benefit pension and other postretirement plans adjustment before income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax": {
     "auth_ref": [
      "r64",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.",
        "label": "Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax",
        "totalLabel": "Benefit plans, Change in defined benefit pension and other postretirement plans adjustment, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax": {
     "auth_ref": [
      "r63",
      "r67",
      "r510"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of gain (loss) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.",
        "label": "Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax",
        "verboseLabel": "Benefit plans, Net defined benefit pension and other postretirement plans adjustment arising during the period"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax": {
     "auth_ref": [
      "r67",
      "r71",
      "r72",
      "r281"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.",
        "label": "Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax",
        "terseLabel": "Less reclassification adjustment for net securities losses included in net income",
        "verboseLabel": "Investment securities, Net realized losses included in net securities losses"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax": {
     "auth_ref": [
      "r67",
      "r71",
      "r72",
      "r281"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.",
        "label": "Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax",
        "totalLabel": "Investment securities, Reclassification adjustment for net securities losses included in net income, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax": {
     "auth_ref": [
      "r68",
      "r281"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.",
        "label": "Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax",
        "terseLabel": "Investment securities, Less: Benefit for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax": {
     "auth_ref": [
      "r67",
      "r71",
      "r72",
      "r702"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).",
        "label": "Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax",
        "terseLabel": "Net cash flow hedge gains included in interest and fees on loans"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax": {
     "auth_ref": [
      "r67",
      "r71",
      "r72",
      "r510"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "cma_OtherComprehensiveIncomeLossReclassificationAdjustmentPensionAndOtherPostretirementBenefitPlansRecognizedInNetPeriodicDefinedBenefitCostBeforeTax",
       "weight": -1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.",
        "label": "Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax",
        "terseLabel": "Benefit plans, Amortization of actuarial net loss",
        "verboseLabel": "Amortization of net actuarial loss"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax": {
     "auth_ref": [
      "r68",
      "r663"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax (expense) benefit for reclassification adjustment from accumulated other comprehensive (income) loss of defined benefit plan.",
        "label": "Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax",
        "terseLabel": "Cash flow hedges, Less: Provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeLossTax": {
     "auth_ref": [
      "r68",
      "r79",
      "r87",
      "r614",
      "r652",
      "r654",
      "r771",
      "r774",
      "r777",
      "r885",
      "r946"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of tax expense (benefit) allocated to other comprehensive income (loss).",
        "label": "Other Comprehensive Income (Loss), Tax",
        "terseLabel": "(Benefit) provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeLossTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax": {
     "auth_ref": [
      "r61",
      "r67"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentNetOfTax",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after tax and before adjustment, of unrealized holding gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Excludes unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.",
        "label": "OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax",
        "totalLabel": "Investment securities, Net unrealized holding (losses) gains arising during period, net of tax"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax": {
     "auth_ref": [
      "r62",
      "r68"
     ],
     "calculation": {
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, before adjustment, of tax expense (benefit) for unrealized holding gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Excludes tax expense (benefit) for unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.",
        "label": "OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax",
        "terseLabel": "Investment securities, Less: (Benefit) provision for income taxes"
       }
      }
     },
     "localname": "OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherIncomeMember": {
     "auth_ref": [
      "r712"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Primary financial statement caption encompassing other revenue.",
        "label": "Other Income [Member]",
        "terseLabel": "Other noninterest income"
       }
      }
     },
     "localname": "OtherIncomeMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfNetGainsRecognizedInIncomeOnCustomerInitiatedDerivativesDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_OtherInterestAndDividendIncome": {
     "auth_ref": [
      "r898"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 3.0,
       "parentTag": "us-gaap_InterestAndDividendIncomeOperating",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_Revenues",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, after discount, accretion and premium amortization, of interest income and dividend income classified as other.",
        "label": "Other Interest and Dividend Income",
        "terseLabel": "Interest on short-term investments",
        "verboseLabel": "Other interest income"
       }
      }
     },
     "localname": "OtherInterestAndDividendIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherLiabilities": {
     "auth_ref": [
      "r875"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_Liabilities",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of liabilities classified as other.",
        "label": "Other Liabilities",
        "terseLabel": "Accrued expenses and other liabilities",
        "verboseLabel": "Accrued expenses and other liabilities"
       }
      }
     },
     "localname": "OtherLiabilities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherLongTermDebt": {
     "auth_ref": [
      "r20",
      "r864",
      "r937"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of long-term debt classified as other.",
        "label": "Other Long-term Debt",
        "terseLabel": "Medium- and long-term notes"
       }
      }
     },
     "localname": "OtherLongTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherNoninterestExpense": {
     "auth_ref": [
      "r897"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 8.0,
       "parentTag": "us-gaap_NoninterestExpense",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_CostsAndExpenses",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of noninterest expense classified as other.",
        "label": "Other Noninterest Expense",
        "terseLabel": "Other noninterest expenses"
       }
      }
     },
     "localname": "OtherNoninterestExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_OtherPensionPlansDefinedBenefitMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Plan designed to provide retirement benefits, classified as other. Includes, but is not limited to, defined benefit and defined contribution plans.",
        "label": "Other Pension Plan [Member]",
        "terseLabel": "Non-Qualified Plan"
       }
      }
     },
     "localname": "OtherPensionPlansDefinedBenefitMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember": {
     "auth_ref": [
      "r465",
      "r466",
      "r468",
      "r469",
      "r470",
      "r471",
      "r472",
      "r473",
      "r474",
      "r475",
      "r476",
      "r477",
      "r478",
      "r479",
      "r480",
      "r481",
      "r482",
      "r483",
      "r484",
      "r485",
      "r486",
      "r487",
      "r488",
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r500",
      "r501",
      "r502",
      "r503",
      "r504",
      "r505",
      "r506",
      "r507",
      "r508",
      "r509",
      "r510",
      "r511",
      "r512",
      "r514",
      "r515",
      "r517",
      "r520",
      "r524",
      "r527",
      "r528",
      "r529",
      "r530",
      "r531",
      "r532",
      "r533",
      "r534",
      "r535",
      "r536",
      "r537",
      "r538",
      "r544",
      "r545",
      "r546",
      "r547",
      "r548",
      "r549"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Plan designed to provide other postretirement benefits. Includes, but is not limited to, defined benefit and defined contribution plans. Excludes pension benefits.",
        "label": "Other Postretirement Benefits Plan [Member]",
        "terseLabel": "Postretirement Benefit Plan"
       }
      }
     },
     "localname": "OtherPostretirementBenefitPlansDefinedBenefitMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_OtherShortTermInvestments": {
     "auth_ref": [
      "r48",
      "r879",
      "r942"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 3.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of short-term investments classified as other.",
        "label": "Other Short-term Investments",
        "terseLabel": "Other short-term investments",
        "verboseLabel": "Other short-term investments"
       }
      }
     },
     "localname": "OtherShortTermInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PassMember": {
     "auth_ref": [
      "r240",
      "r311"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A category of financing receivables not considered to be special mention, substandard, doubtful, and loss receivables.",
        "label": "Pass [Member]",
        "terseLabel": "Pass"
       }
      }
     },
     "localname": "PassMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PastDueFinancingReceivablesTableTextBlock": {
     "auth_ref": [
      "r249",
      "r250",
      "r306",
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of aging analysis for financing receivable.",
        "label": "Financing Receivable, Past Due [Table Text Block]",
        "terseLabel": "Aging Analysis Of Loans"
       }
      }
     },
     "localname": "PastDueFinancingReceivablesTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PaymentDeferralMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan modification for a temporary postponement of loan payments.",
        "label": "Payment Deferral [Member]",
        "terseLabel": "Principal deferrals"
       }
      }
     },
     "localname": "PaymentDeferralMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PaymentsForProceedsFromLoansAndLeases": {
     "auth_ref": [
      "r904"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 6.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net cash outflow or inflow for the increase (decrease) in the beginning and end of period of loan and lease balances which are not originated or purchased specifically for resale. Includes cash payments and proceeds associated with (a) loans held-for-investment, (b) leases held-for-investment, and (c) both.",
        "label": "Payments for (Proceeds from) Loans and Leases",
        "negatedLabel": "Net change in loans"
       }
      }
     },
     "localname": "PaymentsForProceedsFromLoansAndLeases",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsForRepurchaseOfCommonStock": {
     "auth_ref": [
      "r105"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 5.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash outflow to reacquire common stock during the period.",
        "label": "Payments for Repurchase of Common Stock",
        "negatedLabel": "Repurchases of common stock",
        "terseLabel": "Repurchases of common stock"
       }
      }
     },
     "localname": "PaymentsForRepurchaseOfCommonStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsOfDividendsCommonStock": {
     "auth_ref": [
      "r105"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 6.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.",
        "label": "Payments of Ordinary Dividends, Common Stock",
        "negatedLabel": "Cash dividends paid on common stock",
        "terseLabel": "Cash dividends paid on common stock"
       }
      }
     },
     "localname": "PaymentsOfDividendsCommonStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock": {
     "auth_ref": [
      "r105"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow in the form of ordinary dividends to preferred shareholders of the parent entity.",
        "label": "Payments of Ordinary Dividends, Preferred Stock and Preference Stock",
        "negatedTerseLabel": "Preferred stock cash dividends paid",
        "terseLabel": "Cash dividends paid on preferred stock"
       }
      }
     },
     "localname": "PaymentsOfDividendsPreferredStockAndPreferenceStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt": {
     "auth_ref": [
      "r97",
      "r101",
      "r264"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 5.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow to acquire investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Payments to Acquire Debt Securities, Available-for-sale",
        "negatedLabel": "Purchases of investment securities available-for-sale"
       }
      }
     },
     "localname": "PaymentsToAcquireAvailableForSaleSecuritiesDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PaymentsToAcquireFederalHomeLoanBankStock": {
     "auth_ref": [
      "r102"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 2.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash outflow to acquire Federal Home Loan Bank (FHLB) stock.",
        "label": "Payments to Acquire Federal Home Loan Bank Stock",
        "negatedTerseLabel": "Purchases of Federal Home Loan Bank stock"
       }
      }
     },
     "localname": "PaymentsToAcquireFederalHomeLoanBankStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PendingLitigationMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Risk of loss associated with the outcome of pending litigation against the entity, for example, but not limited to, litigation in arbitration or within the trial process.",
        "label": "Pending Litigation [Member]",
        "terseLabel": "Pending Litigation"
       }
      }
     },
     "localname": "PendingLitigationMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock": {
     "auth_ref": [
      "r490",
      "r492",
      "r498",
      "r516",
      "r518",
      "r519",
      "r520",
      "r521",
      "r522",
      "r537",
      "r539",
      "r542",
      "r544",
      "r557"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for retirement benefits.",
        "label": "Retirement Benefits [Text Block]",
        "terseLabel": "Employee Benefit Plans"
       }
      }
     },
     "localname": "PensionAndOtherPostretirementBenefitsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlans"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PensionAndOtherPostretirementPlansPolicy": {
     "auth_ref": [
      "r523",
      "r540",
      "r541",
      "r544",
      "r550"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for pension and other postretirement benefit plans. This accounting policy may address (1) the types of plans sponsored by the entity, and the benefits provided by each plan (2) groups that participate in (or are covered by) each plan (3) how plan assets, liabilities and expenses are measured, including the use of any actuaries and (4) significant assumptions used by the entity to value plan assets and liabilities and how such assumptions are derived.",
        "label": "Pension and Other Postretirement Plans, Policy [Policy Text Block]",
        "terseLabel": "Defined Benefit Pension and Other Postretirement Costs"
       }
      }
     },
     "localname": "PensionAndOtherPostretirementPlansPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PensionPlansDefinedBenefitMember": {
     "auth_ref": [
      "r464",
      "r466",
      "r468",
      "r469",
      "r470",
      "r471",
      "r472",
      "r473",
      "r474",
      "r475",
      "r476",
      "r477",
      "r478",
      "r479",
      "r480",
      "r481",
      "r482",
      "r483",
      "r484",
      "r485",
      "r486",
      "r487",
      "r488",
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r499",
      "r500",
      "r501",
      "r502",
      "r503",
      "r504",
      "r505",
      "r506",
      "r507",
      "r508",
      "r509",
      "r510",
      "r511",
      "r512",
      "r514",
      "r515",
      "r517",
      "r520",
      "r524",
      "r527",
      "r528",
      "r529",
      "r530",
      "r531",
      "r532",
      "r533",
      "r534",
      "r535",
      "r536",
      "r537",
      "r538",
      "r544",
      "r545",
      "r552",
      "r553",
      "r554",
      "r555"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Plan designed to provide participant with pension benefits. Includes, but is not limited to, defined benefit and defined contribution plans. Excludes other postretirement benefits.",
        "label": "Pension Plan [Member]",
        "terseLabel": "Qualified Plan"
       }
      }
     },
     "localname": "PensionPlansDefinedBenefitMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PlanAssetCategoriesDomain": {
     "auth_ref": [
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r517",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Defined benefit plan asset investment.",
        "label": "Defined Benefit Plan, Plan Assets, Category [Domain]",
        "terseLabel": "Defined Benefit Plan, Plan Assets, Category [Domain]"
       }
      }
     },
     "localname": "PlanAssetCategoriesDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalHomeLoanBankDebt": {
     "auth_ref": [
      "r829"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.",
        "label": "Pledged Financial Instruments, Not Separately Reported, Loans Receivable, for Federal Home Loan Bank Debt",
        "terseLabel": "Real estate-related loans securing FHLB advances"
       }
      }
     },
     "localname": "PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalHomeLoanBankDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForOtherArrangements": {
     "auth_ref": [
      "r829"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of other debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.",
        "label": "Pledged Financial Instruments, Not Separately Reported, Loans Receivable, for Other Arrangements",
        "terseLabel": "Pledged loans to provide collateralized borrowing with the FRB"
       }
      }
     },
     "localname": "PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForOtherArrangements",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PortionAtFairValueFairValueDisclosureMember": {
     "auth_ref": [
      "r752"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Measured at fair value for financial reporting purposes.",
        "label": "Portion at Fair Value Measurement [Member]",
        "terseLabel": "Portion at Fair Value Measurement [Member]"
       }
      }
     },
     "localname": "PortionAtFairValueFairValueDisclosureMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PreferredStockDividendRatePercentage": {
     "auth_ref": [
      "r427"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The percentage rate used to calculate dividend payments on preferred stock.",
        "label": "Preferred Stock, Dividend Rate, Percentage",
        "terseLabel": "Preferred Stock, Dividend Rate, Percentage"
       }
      }
     },
     "localname": "PreferredStockDividendRatePercentage",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_PreferredStockLiquidationPreference": {
     "auth_ref": [
      "r23",
      "r126",
      "r430",
      "r442",
      "r443"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The per share liquidation preference (or restrictions) of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) that has a preference in involuntary liquidation considerably in excess of the par or stated value of the shares. The liquidation preference is the difference between the preference in liquidation and the par or stated values of the share.",
        "label": "Preferred Stock, Liquidation Preference Per Share",
        "terseLabel": "Preferred Stock, Liquidation Preference Per Share"
       }
      }
     },
     "localname": "PreferredStockLiquidationPreference",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_PreferredStockLiquidationPreferenceValue": {
     "auth_ref": [
      "r126",
      "r430"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value of the difference between preference in liquidation and the par or stated values of the preferred shares.",
        "label": "Preferred Stock, Liquidation Preference, Value",
        "terseLabel": "Preferred Stock, Liquidation Preference, Value"
       }
      }
     },
     "localname": "PreferredStockLiquidationPreferenceValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PreferredStockMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Preferred shares may provide a preferential dividend to the dividend on common stock and may take precedence over common stock in the event of a liquidation. Preferred shares typically represent an ownership interest in the company.",
        "label": "Preferred Stock [Member]",
        "terseLabel": "Nonredeemable Preferred Stock"
       }
      }
     },
     "localname": "PreferredStockMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PreferredStockNoParValue": {
     "auth_ref": [
      "r23",
      "r426"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Face amount per share of no-par value preferred stock nonredeemable or redeemable solely at the option of the issuer.",
        "label": "Preferred Stock, No Par Value",
        "terseLabel": "Preferred Stock, No Par Value"
       }
      }
     },
     "localname": "PreferredStockNoParValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_PreferredStockSharesAuthorized": {
     "auth_ref": [
      "r23"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.",
        "label": "Preferred Stock, Shares Authorized",
        "terseLabel": "Preferred Stock, Shares Authorized"
       }
      }
     },
     "localname": "PreferredStockSharesAuthorized",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_PreferredStockSharesIssued": {
     "auth_ref": [
      "r23",
      "r426"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.",
        "label": "Preferred Stock, Shares Issued",
        "terseLabel": "Preferred Stock, Shares Issued"
       }
      }
     },
     "localname": "PreferredStockSharesIssued",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_PreferredStockValue": {
     "auth_ref": [
      "r23",
      "r813"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity.",
        "label": "Preferred Stock, Value, Issued",
        "terseLabel": "Fixed rate reset non-cumulative perpetual preferred stock, series A, no par value, $100,000 liquidation preference per share: Authorized - 4,000 shares, Issued - 4,000 shares at 12/31/2021 and 12/31/2020"
       }
      }
     },
     "localname": "PreferredStockValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PrepaymentRiskMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The risk associated with the early unscheduled return of principal on a loan or debt security.",
        "label": "Prepayment Risk [Member]",
        "terseLabel": "Prepayment options"
       }
      }
     },
     "localname": "PrepaymentRiskMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PrivatePlacementMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A private placement is a direct offering of securities to a limited number of sophisticated investors such as insurance companies, pension funds, mezzanine funds, stock funds and trusts.",
        "label": "Private Placement [Member]",
        "terseLabel": "Private placements"
       }
      }
     },
     "localname": "PrivatePlacementMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ProceedsFromIssuanceOfCommonStock": {
     "auth_ref": [
      "r103"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash inflow from the additional capital contribution to the entity.",
        "label": "Proceeds from Issuance of Common Stock",
        "terseLabel": "Issuances of common stock under employee stock plans"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfCommonStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromIssuanceOfLongTermDebt": {
     "auth_ref": [
      "r104"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 4.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.",
        "label": "Proceeds from Issuance of Long-term Debt",
        "terseLabel": "Issuances and advances of medium- and long-term debt"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfLongTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromIssuanceOfPreferredStockAndPreferenceStock": {
     "auth_ref": [
      "r103"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholders and which takes precedence over common stockholders in the event of liquidation.",
        "label": "Proceeds from Issuance of Preferred Stock and Preference Stock",
        "terseLabel": "Issuances of preferred stock"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfPreferredStockAndPreferenceStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromIssuanceOfPreferredStockPreferenceStockAndWarrants": {
     "auth_ref": [
      "r103"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholder, which takes precedence over common stockholders in the event of liquidation and from issuance of rights to purchase common shares at a predetermined price.",
        "label": "Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants",
        "terseLabel": "Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfPreferredStockPreferenceStockAndWarrants",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions": {
     "auth_ref": [
      "r103",
      "r596"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 7.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from issuance of shares under share-based payment arrangement. Includes, but is not limited to, option exercised.",
        "label": "Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised",
        "terseLabel": "Issuances of common stock under employee stock plans"
       }
      }
     },
     "localname": "ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromLegalSettlements": {
     "auth_ref": [
      "r111"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Cash received for the settlement of litigation during the current period.",
        "label": "Proceeds from Legal Settlements",
        "terseLabel": "Proceeds from Legal Settlements"
       }
      }
     },
     "localname": "ProceedsFromLegalSettlements",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ContingentLiabilitiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromLifeInsurancePolicies": {
     "auth_ref": [
      "r100",
      "r108"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 9.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow for proceeds from settlement of corporate-owned life insurance policy, classified as investing activities. Includes, but is not limited to, bank-owned life insurance policy.",
        "label": "Proceeds from Life Insurance Policy",
        "terseLabel": "Proceeds from bank-owned life insurance settlements"
       }
      }
     },
     "localname": "ProceedsFromLifeInsurancePolicies",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities": {
     "auth_ref": [
      "r97",
      "r98",
      "r264"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 4.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from maturity, prepayment and call of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-sale",
        "terseLabel": "Maturities and redemptions of investment securities available-for-sale"
       }
      }
     },
     "localname": "ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromRepaymentsOfShortTermDebt": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 2.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The net cash inflow or outflow for borrowing having initial term of repayment within one year or the normal operating cycle, if longer.",
        "label": "Proceeds from (Repayments of) Short-term Debt",
        "terseLabel": "Net change in short-term borrowings"
       }
      }
     },
     "localname": "ProceedsFromRepaymentsOfShortTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt": {
     "auth_ref": [
      "r97",
      "r98",
      "r264"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 1.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).",
        "label": "Proceeds from Sale of Debt Securities, Available-for-sale",
        "terseLabel": "Sales of investment securities available-for-sale"
       }
      }
     },
     "localname": "ProceedsFromSaleOfAvailableForSaleSecuritiesDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromSaleOfFederalHomeLoanBankStock": {
     "auth_ref": [
      "r99"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 3.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of cash inflow from sale of Federal Home Loan Bank (FHLB) stock.",
        "label": "Proceeds from Sale of Federal Home Loan Bank Stock",
        "terseLabel": "Redemptions of Federal Home Loan Bank stock"
       }
      }
     },
     "localname": "ProceedsFromSaleOfFederalHomeLoanBankStock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProceedsFromSaleOfForeclosedAssets": {
     "auth_ref": [
      "r100"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 7.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInInvestingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash inflow from the sale assets received in full or partial satisfaction of a receivable including real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts. Foreclosed assets also include loans that are treated as if the underlying collateral had been foreclosed because the institution has taken possession of the collateral, even though legal foreclosure or repossession proceedings have not taken place.",
        "label": "Proceeds from Sale of Foreclosed Assets",
        "terseLabel": "Proceeds from sales of foreclosed property"
       }
      }
     },
     "localname": "ProceedsFromSaleOfForeclosedAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ProfitLoss": {
     "auth_ref": [
      "r7",
      "r73",
      "r76",
      "r81",
      "r107",
      "r129",
      "r142",
      "r154",
      "r155",
      "r202",
      "r208",
      "r212",
      "r215",
      "r218",
      "r289",
      "r386",
      "r387",
      "r388",
      "r391",
      "r392",
      "r393",
      "r395",
      "r397",
      "r399",
      "r400",
      "r663",
      "r667",
      "r668",
      "r682",
      "r683",
      "r732",
      "r759",
      "r907"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 1.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome": {
       "order": 1.0,
       "parentTag": "us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.",
        "label": "Net Income (Loss), Including Portion Attributable to Noncontrolling Interest",
        "terseLabel": "Net income (loss)",
        "totalLabel": "Net Income"
       }
      }
     },
     "localname": "ProfitLoss",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentByTypeAxis": {
     "auth_ref": [
      "r33",
      "r356"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of long-lived, physical assets used to produce goods and services and not intended for resale.",
        "label": "Long-Lived Tangible Asset [Axis]",
        "terseLabel": "Property, Plant and Equipment, Type [Axis]"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentByTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock": {
     "auth_ref": [
      "r360",
      "r980",
      "r981",
      "r982"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for long-lived, physical asset used in normal conduct of business and not intended for resale. Includes, but is not limited to, work of art, historical treasure, and similar asset classified as collections.",
        "label": "Property, Plant and Equipment Disclosure [Text Block]",
        "terseLabel": "Premises and Equipment"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipment"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentGross": {
     "auth_ref": [
      "r32",
      "r354"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.",
        "label": "Property, Plant and Equipment, Gross",
        "terseLabel": "Total cost"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentGross",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Property, Plant and Equipment [Line Items]",
        "terseLabel": "Property, Plant and Equipment [Line Items]"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentNet": {
     "auth_ref": [
      "r13",
      "r14",
      "r356",
      "r813",
      "r913",
      "r941"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 6.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_Assets",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.",
        "label": "Property, Plant and Equipment, Net",
        "terseLabel": "Premises and equipment"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentNet",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentPolicyTextBlock": {
     "auth_ref": [
      "r31",
      "r356",
      "r980",
      "r981"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for long-lived, physical asset used in normal conduct of business and not intended for resale. Includes, but is not limited to, work of art, historical treasure, and similar asset classified as collections.",
        "label": "Property, Plant and Equipment, Policy [Policy Text Block]",
        "terseLabel": "Premises and Equipment"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentTextBlock": {
     "auth_ref": [
      "r13",
      "r356"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation.",
        "label": "Property, Plant and Equipment [Table Text Block]",
        "terseLabel": "Premises and Equipment"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/PremisesandEquipmentTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentTransfersAndChanges": {
     "auth_ref": [
      "r357"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase (decrease) of physical assets used in the normal conduct of business and not intended for resale, from reclassification, impairment, donation, or changes classified as other. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.",
        "label": "Property, Plant and Equipment, Transfers and Changes",
        "terseLabel": "Capital transactions with subsidiaries"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentTransfersAndChanges",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentTypeDomain": {
     "auth_ref": [
      "r13",
      "r354"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Listing of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.",
        "label": "Long-Lived Tangible Asset [Domain]",
        "terseLabel": "Property, Plant and Equipment, Type [Domain]"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/PremisesandEquipmentSummaryofPremisesandEquipmentDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_PropertyPlantAndEquipmentUsefulLife": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.",
        "label": "Property, Plant and Equipment, Useful Life",
        "terseLabel": "Premises and Equipment, Useful Life"
       }
      }
     },
     "localname": "PropertyPlantAndEquipmentUsefulLife",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_ProvisionForLoanLeaseAndOtherLosses": {
     "auth_ref": [
      "r113",
      "r231",
      "r891"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 2.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss",
       "weight": -1.0
      },
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_ProfitLoss",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.",
        "label": "Provision for Loan, Lease, and Other Losses",
        "terseLabel": "Provision for credit losses",
        "verboseLabel": "Provision for loan losses"
       }
      }
     },
     "localname": "ProvisionForLoanLeaseAndOtherLosses",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_QuarterlyFinancialInformationDisclosureAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Quarterly Financial Information Disclosure [Abstract]",
        "terseLabel": "Quarterly Financial Information Disclosure [Abstract]"
       }
      }
     },
     "localname": "QuarterlyFinancialInformationDisclosureAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_QuarterlyFinancialInformationTextBlock": {
     "auth_ref": [
      "r181",
      "r183"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for quarterly financial data. Includes, but is not limited to, tabular presentation of financial information for fiscal quarters, effect of year-end adjustments, and an explanation of matters or transactions that affect comparability of the information.",
        "label": "Quarterly Financial Information [Text Block]",
        "terseLabel": "Summary of Quarterly Financial Statements (Unaudited)"
       }
      }
     },
     "localname": "QuarterlyFinancialInformationTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnaudited"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_RealEstateLoanMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan to finance the purchase of real estate, including but not limited to, land or building.",
        "label": "Real Estate Loan [Member]",
        "terseLabel": "Commercial mortgage",
        "verboseLabel": "Commercial mortgage"
       }
      }
     },
     "localname": "RealEstateLoanMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnANonrecurringBasisDetails",
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RealEstateSectorMember": {
     "auth_ref": [
      "r321"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Sector of the economy consisting of companies engaged in real estate business activities.",
        "label": "Real Estate Sector [Member]",
        "terseLabel": "Commercial Real Estate business line"
       }
      }
     },
     "localname": "RealEstateSectorMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ReceivableTypeDomain": {
     "auth_ref": [
      "r47"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Financing arrangement representing a contractual right to receive money either on demand or on fixed and determinable dates.",
        "label": "Receivable [Domain]",
        "terseLabel": "Receivable Type [Domain]"
       }
      }
     },
     "localname": "ReceivableTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTable": {
     "auth_ref": [
      "r207",
      "r212"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Identification, description, and amounts of all significant reconciling items in the reconciliation of total revenues from reportable segments to the entity's consolidated revenues.",
        "label": "Reconciliation of Revenue from Segments to Consolidated [Table]",
        "terseLabel": "Reconciliation of Revenue from Segments to Consolidated [Table]"
       }
      }
     },
     "localname": "ReconciliationOfRevenueFromSegmentsToConsolidatedTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock": {
     "auth_ref": [
      "r920",
      "r921",
      "r922",
      "r924",
      "r925",
      "r926",
      "r928",
      "r929"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for regulatory capital requirement for depository and lending institutions. Institutions include, but not are not limited to, finance company, insured depository institution, bank holding company, savings and loan association holding company, bank and savings institution not federally insured, mortgage company, foreign financial institution and credit union.",
        "label": "Regulatory Capital Requirements under Banking Regulations [Text Block]",
        "terseLabel": "Regulatory Capital and Reserve Requirements"
       }
      }
     },
     "localname": "RegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirements"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_RelatedPartyTransactionsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Related Party Transactions [Abstract]",
        "terseLabel": "Related Party Transactions [Abstract]"
       }
      }
     },
     "localname": "RelatedPartyTransactionsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_RelatedPartyTransactionsDisclosureTextBlock": {
     "auth_ref": [
      "r802",
      "r803",
      "r805",
      "r808",
      "r809"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.",
        "label": "Related Party Transactions Disclosure [Text Block]",
        "terseLabel": "Transactions with Related Parties"
       }
      }
     },
     "localname": "RelatedPartyTransactionsDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/TransactionswithRelatedParties"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_RepaymentsOfDebt": {
     "auth_ref": [
      "r106"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.",
        "label": "Repayments of Debt",
        "negatedTerseLabel": "Maturities of medium- and long-term debt"
       }
      }
     },
     "localname": "RepaymentsOfDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RepaymentsOfLongTermDebt": {
     "auth_ref": [
      "r106"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 3.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInFinancingActivities",
       "weight": -1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.",
        "label": "Repayments of Long-term Debt",
        "terseLabel": "Maturities of medium- and long-term debt"
       }
      }
     },
     "localname": "RepaymentsOfLongTermDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RepurchaseAgreementsValuationPolicy": {
     "auth_ref": [
      "r750",
      "r760"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of the accounting policy for determining which carrying amount is used for securities sold under repurchase agreements and the method used to determine that amount.",
        "label": "Repurchase Agreements, Valuation, Policy [Policy Text Block]",
        "terseLabel": "Short-Term Borrowings"
       }
      }
     },
     "localname": "RepurchaseAgreementsValuationPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ResidentialMortgageBackedSecuritiesMember": {
     "auth_ref": [
      "r265",
      "r491"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Securities collateralized by residential real estate mortgage loans.",
        "label": "Residential Mortgage Backed Securities [Member]",
        "terseLabel": "Residential mortgage-backed securities"
       }
      }
     },
     "localname": "ResidentialMortgageBackedSecuritiesMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ResidentialMortgageMember": {
     "auth_ref": [
      "r327"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Loan to purchase or refinance residential real estate for example, but not limited to, a home, in which the real estate itself serves as collateral for the loan.",
        "label": "Residential Mortgage [Member]",
        "terseLabel": "Residential mortgage"
       }
      }
     },
     "localname": "ResidentialMortgageMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RestrictedStockMember": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Stock including a provision that prohibits sale or substantive sale of an equity instrument for a specified period of time or until specified performance conditions are met.",
        "label": "Restricted Stock [Member]",
        "terseLabel": "Restricted Stock"
       }
      }
     },
     "localname": "RestrictedStockMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RestrictedStockUnitsRSUMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Share instrument which is convertible to stock or an equivalent amount of cash, after a specified period of time or when specified performance conditions are met.",
        "label": "Restricted Stock Units (RSUs) [Member]",
        "terseLabel": "Restricted Stock Units (RSUs)"
       }
      }
     },
     "localname": "RestrictedStockUnitsRSUMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RetainedEarningsAccumulatedDeficit": {
     "auth_ref": [
      "r26",
      "r447",
      "r604",
      "r813",
      "r939",
      "r961",
      "r966"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 4.0,
       "parentTag": "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
       "weight": 1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cumulative amount of the reporting entity's undistributed earnings or deficit.",
        "label": "Retained Earnings (Accumulated Deficit)",
        "terseLabel": "Retained earnings"
       }
      }
     },
     "localname": "RetainedEarningsAccumulatedDeficit",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedBalanceSheetsDetails",
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RetainedEarningsMember": {
     "auth_ref": [
      "r2",
      "r139",
      "r140",
      "r141",
      "r143",
      "r153",
      "r155",
      "r296",
      "r601",
      "r602",
      "r603",
      "r642",
      "r643",
      "r730",
      "r957",
      "r959"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The cumulative amount of the reporting entity's undistributed earnings or deficit.",
        "label": "Retained Earnings [Member]",
        "terseLabel": "Retained Earnings"
       }
      }
     },
     "localname": "RetainedEarningsMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RetirementPlanTypeAxis": {
     "auth_ref": [
      "r464",
      "r465",
      "r466",
      "r468",
      "r469",
      "r470",
      "r471",
      "r472",
      "r473",
      "r474",
      "r475",
      "r476",
      "r477",
      "r478",
      "r479",
      "r480",
      "r481",
      "r482",
      "r483",
      "r484",
      "r485",
      "r486",
      "r487",
      "r488",
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r499",
      "r500",
      "r501",
      "r502",
      "r503",
      "r504",
      "r505",
      "r506",
      "r507",
      "r508",
      "r509",
      "r510",
      "r511",
      "r512",
      "r514",
      "r515",
      "r517",
      "r520",
      "r524",
      "r527",
      "r528",
      "r529",
      "r530",
      "r531",
      "r532",
      "r533",
      "r534",
      "r535",
      "r536",
      "r537",
      "r538",
      "r544",
      "r545",
      "r546",
      "r547",
      "r548",
      "r549",
      "r552",
      "r553",
      "r554",
      "r555"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of retirement benefit plan. Includes, but is not limited to, retirement benefit arrangement for defined benefit pension and other postretirement plans, retirement benefit arrangement for defined contribution pension and other postretirement plans, and special and contractual termination benefits payable upon retirement.",
        "label": "Retirement Plan Type [Axis]",
        "terseLabel": "Retirement Plan Type [Axis]"
       }
      }
     },
     "localname": "RetirementPlanTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_RetirementPlanTypeDomain": {
     "auth_ref": [
      "r464",
      "r465",
      "r466",
      "r468",
      "r469",
      "r470",
      "r471",
      "r472",
      "r473",
      "r474",
      "r475",
      "r476",
      "r477",
      "r478",
      "r479",
      "r480",
      "r481",
      "r482",
      "r483",
      "r484",
      "r485",
      "r486",
      "r487",
      "r488",
      "r490",
      "r491",
      "r493",
      "r494",
      "r495",
      "r496",
      "r497",
      "r498",
      "r499",
      "r500",
      "r501",
      "r502",
      "r503",
      "r504",
      "r505",
      "r506",
      "r507",
      "r508",
      "r509",
      "r510",
      "r511",
      "r512",
      "r514",
      "r515",
      "r517",
      "r520",
      "r524",
      "r527",
      "r528",
      "r529",
      "r530",
      "r531",
      "r532",
      "r533",
      "r534",
      "r535",
      "r536",
      "r537",
      "r538",
      "r544",
      "r545",
      "r546",
      "r547",
      "r548",
      "r549",
      "r552",
      "r553",
      "r554",
      "r555"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Type of plan designed to provide participants with retirement benefits. Includes, but is not limited to, retirement benefit arrangement for defined benefit pension and other postretirement plans, retirement benefit arrangement for defined contribution pension and other postretirement plans, and special and contractual termination benefits payable upon retirement.",
        "label": "Retirement Plan Type [Domain]",
        "terseLabel": "Retirement Plan Type [Domain]"
       }
      }
     },
     "localname": "RetirementPlanTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax": {
     "auth_ref": [
      "r193",
      "r194",
      "r207",
      "r213",
      "r214",
      "r220",
      "r221",
      "r223",
      "r459",
      "r460",
      "r849"
     ],
     "calculation": {
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails": {
       "order": 9.0,
       "parentTag": "us-gaap_NoninterestIncome",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.",
        "label": "Revenue from Contract with Customer, Excluding Assessed Tax",
        "verboseLabel": "Total revenue from contracts with customers"
       }
      }
     },
     "localname": "RevenueFromContractWithCustomerExcludingAssessedTax",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RevenueFromContractWithCustomerTextBlock": {
     "auth_ref": [
      "r451",
      "r452",
      "r453",
      "r454",
      "r455",
      "r456",
      "r457",
      "r458",
      "r461",
      "r463"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.",
        "label": "Revenue from Contract with Customer [Text Block]",
        "terseLabel": "Revenue from Contract with Customer"
       }
      }
     },
     "localname": "RevenueFromContractWithCustomerTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomers"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_RevenueRecognitionPolicyTextBlock": {
     "auth_ref": [
      "r124",
      "r125"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for revenue. Includes revenue from contract with customer and from other sources.",
        "label": "Revenue [Policy Text Block]",
        "terseLabel": "Revenue Recognition"
       }
      }
     },
     "localname": "RevenueRecognitionPolicyTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_Revenues": {
     "auth_ref": [
      "r85",
      "r129",
      "r193",
      "r194",
      "r207",
      "r213",
      "r214",
      "r220",
      "r221",
      "r223",
      "r289",
      "r386",
      "r387",
      "r388",
      "r391",
      "r392",
      "r393",
      "r395",
      "r397",
      "r399",
      "r400",
      "r759",
      "r907"
     ],
     "calculation": {
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).",
        "label": "Revenues",
        "totalLabel": "Total income"
       }
      }
     },
     "localname": "Revenues",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability": {
     "auth_ref": [
      "r793",
      "r796"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase in right-of-use asset obtained in exchange for operating lease liability.",
        "label": "Right-of-Use Asset Obtained in Exchange for Operating Lease Liability",
        "terseLabel": "ROU assets obtained in exchange for new lease liabilities"
       }
      }
     },
     "localname": "RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesSupplementalcashflowDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RiskWeightedAssets": {
     "auth_ref": [
      "r923"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of risk-weighted assets as defined by regulatory framework.",
        "label": "Banking Regulation, Risk-Weighted Assets, Actual",
        "terseLabel": "Risk-weighted assets"
       }
      }
     },
     "localname": "RiskWeightedAssets",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_RisksInherentInServicingAssetsAndServicingLiabilitiesTypeDomain": {
     "auth_ref": [
      "r832"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The nature of risks inherent in servicing assets and servicing liabilities.",
        "label": "Risks Inherent in Servicing Assets and Servicing Liabilities, Type [Domain]",
        "terseLabel": "Risks Inherent in Servicing Assets and Servicing Liabilities, Type [Domain]"
       }
      }
     },
     "localname": "RisksInherentInServicingAssetsAndServicingLiabilitiesTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivable": {
     "auth_ref": [
      "r798",
      "r800"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Present value of lease payments not yet received by lessor and amount expected to be derived from underlying asset, following end of lease term guaranteed by lessee or other third party unrelated to lessor, from sales-type and direct financing leases.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable",
        "terseLabel": "Total lease receivables"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails",
      "http://www.comerica.com/role/LeasesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedAfterRollingYearFive": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases after fifth rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Lease Payments to be Received, after Rolling Year Five",
        "terseLabel": "Thereafter"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedAfterRollingYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearFive": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases in fifth rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Lease Payments to be Received, Rolling Year Five",
        "terseLabel": "2026"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearThree": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases in third rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Lease Payments to be Received, Rolling Year Three",
        "terseLabel": "2024"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearThree",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearTwo": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases in second rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Lease Payments to be Received, Rolling Year Two",
        "terseLabel": "2023"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivableLeasePaymentsToBeReceivedRollingYearTwo",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableMaturityTableTextBlock": {
     "auth_ref": [
      "r798"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of maturity of undiscounted cash flows to be received on annual basis for sales-type and direct financing leases receivable. Includes, but is not limited to, reconciliation to lease receivable recognized in statement of financial position.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Maturity [Table Text Block]",
        "terseLabel": "Contractual maturities of operating lease liabilities"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivableMaturityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceived": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received",
        "terseLabel": "Total lease payments receivable"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceived",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextRollingTwelveMonths": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases in next rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Next Rolling Twelve Months",
        "terseLabel": "2022"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedNextRollingTwelveMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedRollingYearFour": {
     "auth_ref": [
      "r798"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases in fourth rolling twelve months following latest statement of financial position date. For interim and annual periods when interim periods are reported on rolling approach, from latest statement of financial position date.",
        "label": "Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Rolling Year Four",
        "terseLabel": "2025"
       }
      }
     },
     "localname": "SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceivedRollingYearFour",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeLeaseLeaseIncome": {
     "auth_ref": [
      "r182",
      "r797",
      "r799"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of lease income from variable lease payments, interest income from net investment on sales-type lease, and profit (loss) recognized at commencement.",
        "label": "Sales-type Lease, Lease Income",
        "terseLabel": "Sales-type Lease, Lease Income"
       }
      }
     },
     "localname": "SalesTypeLeaseLeaseIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SalesTypeLeaseUnguaranteedResidualAsset": {
     "auth_ref": [
      "r800"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Present value expected to be derived from underlying asset following end of lease term not guaranteed by lessee or other third party unrelated to lessor.",
        "label": "Sales-type Lease, Unguaranteed Residual Asset",
        "terseLabel": "Unguaranteed residual values"
       }
      }
     },
     "localname": "SalesTypeLeaseUnguaranteedResidualAsset",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesContractualMaturitiesofSalesTypeandDirectFinancingLeaseReceivablesDetailsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable": {
     "auth_ref": [
      "r47"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule itemizing specific types of trade accounts and notes receivable, and for each the gross carrying value, allowance, and net carrying value as of the balance sheet date. Presentation is categorized by current, noncurrent and unclassified receivables.",
        "label": "Schedule of Accounts, Notes, Loans and Financing Receivable [Table]",
        "terseLabel": "Schedule of Accounts, Notes, Loans and Financing Receivable [Table]"
       }
      }
     },
     "localname": "ScheduleOfAccountsNotesLoansAndFinancingReceivableTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SignificantGroupConcentrationsofCreditRiskSignificantGroupConcentrationsofCreditRiskCommercialRealEstateExposureDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock": {
     "auth_ref": [
      "r70",
      "r776",
      "r777"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the components of accumulated other comprehensive income (loss).",
        "label": "Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]",
        "terseLabel": "Schedule Of Accumulated Other Comprehensive Income (Loss)"
       }
      }
     },
     "localname": "ScheduleOfAccumulatedOtherComprehensiveIncomeLossTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable": {
     "auth_ref": [
      "r343"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the major classes of acquired finite-lived intangible assets showing the amount, any significant residual value, weighted average amortization period, and other characteristics. A major class is composed of intangible assets that can be grouped together because they are similar, either by nature or by their use in the operations of the company.",
        "label": "Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table]",
        "terseLabel": "Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table]"
       }
      }
     },
     "localname": "ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofCDICarryingValueandAmortizationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetsByMajorClassTextBlock": {
     "auth_ref": [
      "r343"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the characteristics, including initial carrying value, residual amount, weighted average useful life, of finite-lived intangible assets acquired during the period by major class. A major class is composed of intangible assets that can be grouped together because they are similar, either by nature or by their use in the operations of the company.",
        "label": "Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block]",
        "terseLabel": "Summary of Core Deposit Intangible Carrying Value and Amortization"
       }
      }
     },
     "localname": "ScheduleOfAcquiredFiniteLivedIntangibleAssetsByMajorClassTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfAllocationOfPlanAssetsTableTextBlock": {
     "auth_ref": [
      "r489"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the major categories of plan assets of pension plans and/or other employee benefit plans.  This information may include, but is not limited to, the target allocation of plan assets, the fair value of each major category of plan assets, and the level within the fair value hierarchy in which the fair value measurements fall.",
        "label": "Schedule of Allocation of Plan Assets [Table Text Block]",
        "terseLabel": "Fair Value of Defined Benefit Plan Investments"
       }
      }
     },
     "localname": "ScheduleOfAllocationOfPlanAssetsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfAmountsRecognizedInOtherComprehensiveIncomeLossTableTextBlock": {
     "auth_ref": [
      "r510"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the net gain (loss) and net prior service cost or credit recognized in other comprehensive income (loss) for the period for pension plans and/or other employee benefit plans, and reclassification adjustments of other comprehensive income (loss) for the period, as those amounts, including amortization of the net transition asset or obligation, are recognized as components of net periodic benefit cost.",
        "label": "Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]",
        "terseLabel": "Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss)"
       }
      }
     },
     "localname": "ScheduleOfAmountsRecognizedInOtherComprehensiveIncomeLossTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule for securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by Antidilutive Securities.",
        "label": "Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]",
        "terseLabel": "Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table]"
       }
      }
     },
     "localname": "ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareScheduleofAverageSharesExcludedFromDilutedNetIncomePerCommonShareComputationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock": {
     "auth_ref": [
      "r172"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented, by antidilutive securities.",
        "label": "Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]",
        "terseLabel": "Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation"
       }
      }
     },
     "localname": "ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value.",
        "label": "Schedule of Available-for-sale Securities Reconciliation [Table Text Block]",
        "terseLabel": "Summary Of Investment Securities"
       }
      }
     },
     "localname": "ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable": {
     "auth_ref": [
      "r923",
      "r927"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A table disclosing the capital amounts and ratios as of the balance sheet date indicating whether the entity or entities are in compliance with regulatory capital requirements, by entity.",
        "label": "Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table]",
        "terseLabel": "Summary of Capital Position [Table]"
       }
      }
     },
     "localname": "ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock": {
     "auth_ref": [
      "r923",
      "r927"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the capital amounts and ratios as of the balance sheet date, indicating whether the entity or entities are in compliance with regulatory capital requirements, by entity.",
        "label": "Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]",
        "terseLabel": "Summary of Capital Position"
       }
      }
     },
     "localname": "ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock": {
     "auth_ref": [
      "r638"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years.",
        "label": "Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]",
        "terseLabel": "Current and Deferred Components of the Provision for Income Taxes"
       }
      }
     },
     "localname": "ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfDebtInstrumentsTextBlock": {
     "auth_ref": [
      "r42",
      "r136",
      "r421",
      "r423",
      "r442",
      "r444",
      "r445",
      "r446",
      "r779",
      "r780",
      "r783",
      "r919"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.",
        "label": "Schedule of Long-term Debt Instruments [Table Text Block]",
        "terseLabel": "Schedule Of Medium- And Long-Term Debt"
       }
      }
     },
     "localname": "ScheduleOfDebtInstrumentsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock": {
     "auth_ref": [
      "r631"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets.",
        "label": "Schedule of Deferred Tax Assets and Liabilities [Table Text Block]",
        "terseLabel": "Principal Components of Deferred Tax Assets and Liabilities"
       }
      }
     },
     "localname": "ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable": {
     "auth_ref": [
      "r523",
      "r524",
      "r525",
      "r526",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosures about an individual defined benefit pension plan or an other postretirement defined benefit plan. It may be appropriate to group certain similar plans.  Also includes schedule for fair value of plan assets by major categories of plan assets by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets or liabilities (Level 1), Significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).",
        "label": "Schedule of Defined Benefit Plans Disclosures [Table]",
        "terseLabel": "Schedule of Defined Benefit Plans Disclosures [Table]"
       }
      }
     },
     "localname": "ScheduleOfDefinedBenefitPlansDisclosuresTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansEmployeeBenefitPlansNetPeriodicDefinedBenefitCostDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTextBlock": {
     "auth_ref": [
      "r523",
      "r524",
      "r525",
      "r526",
      "r537"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans.",
        "label": "Schedule of Defined Benefit Plans Disclosures [Table Text Block]",
        "terseLabel": "Schedule of Defined Benefit Plans Disclosures"
       }
      }
     },
     "localname": "ScheduleOfDefinedBenefitPlansDisclosuresTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock": {
     "auth_ref": [
      "r701"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position.",
        "label": "Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]",
        "terseLabel": "Schedule Of Derivative Instruments"
       }
      }
     },
     "localname": "ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock": {
     "auth_ref": [
      "r171"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations.",
        "label": "Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]",
        "terseLabel": "Basic And Diluted Net Income Per Common Share"
       }
      }
     },
     "localname": "ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfEffectOfSignificantUnobservableInputsChangesInPlanAssetsTableTextBlock": {
     "auth_ref": [
      "r494"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the effect of fair value measurements using significant unobservable inputs (Level 3) on changes in plan assets of pension plans and/or other employee benefit plans for the period.",
        "label": "Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]",
        "terseLabel": "Changes in Level 3 Defined Benefit Plan Investments"
       }
      }
     },
     "localname": "ScheduleOfEffectOfSignificantUnobservableInputsChangesInPlanAssetsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock": {
     "auth_ref": [
      "r615"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations.",
        "label": "Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]",
        "terseLabel": "Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Provision for Income Taxes"
       }
      }
     },
     "localname": "ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock": {
     "auth_ref": [
      "r560",
      "r592",
      "r606"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement.",
        "label": "Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]",
        "terseLabel": "Summary of Components of Share-Based Compensation Expense"
       }
      }
     },
     "localname": "ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock": {
     "auth_ref": [
      "r500"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of benefits expected to be paid by pension plans and/or other employee benefit plans in each of the next five fiscal years and in the aggregate for the five fiscal years thereafter.",
        "label": "Schedule of Expected Benefit Payments [Table Text Block]",
        "terseLabel": "Estimated Future Benefit Payments"
       }
      }
     },
     "localname": "ScheduleOfExpectedBenefitPaymentsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock": {
     "auth_ref": [
      "r735",
      "r736"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3).",
        "label": "Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]",
        "terseLabel": "Assets And Liabilities Recorded At Fair Value On A Recurring Basis"
       }
      }
     },
     "localname": "ScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable": {
     "auth_ref": [
      "r305",
      "r1013"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about allowance for credit loss on financing receivable.",
        "label": "Financing Receivable, Allowance for Credit Loss [Table]",
        "terseLabel": "Financing Receivable, Allowance for Credit Loss [Table]"
       }
      }
     },
     "localname": "ScheduleOfFinancingReceivableAllowanceForCreditLossesTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable": {
     "auth_ref": [
      "r311",
      "r327"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about credit quality indicator for financing receivable.",
        "label": "Financing Receivable, Credit Quality Indicator [Table]",
        "terseLabel": "Financing Receivable, Credit Quality Indicator [Table]"
       }
      }
     },
     "localname": "ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesLoansByCreditQualityIndicatorandVintageYearDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable": {
     "auth_ref": [
      "r242",
      "r244"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about financing receivable modified as troubled debt restructuring.",
        "label": "Financing Receivable, Troubled Debt Restructuring [Table]",
        "terseLabel": "Financing Receivable, Troubled Debt Restructuring [Table]"
       }
      }
     },
     "localname": "ScheduleOfFinancingReceivableTroubledDebtRestructuringsTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTroubledDebtRestructuringsSubsequentDefaultDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfFinancingReceivablesPastDueTable": {
     "auth_ref": [
      "r306",
      "r328"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about aging analysis for financing receivable.",
        "label": "Financing Receivable, Past Due [Table]",
        "terseLabel": "Financing Receivable, Past Due [Table]"
       }
      }
     },
     "localname": "ScheduleOfFinancingReceivablesPastDueTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesAgingAnalysisOfLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfGoodwillTable": {
     "auth_ref": [
      "r340",
      "r341"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of goodwill and the changes during the year due to acquisition, sale, impairment or for other reasons.",
        "label": "Schedule of Goodwill [Table]",
        "terseLabel": "Schedule of Goodwill [Table]"
       }
      }
     },
     "localname": "ScheduleOfGoodwillTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfGoodwillTextBlock": {
     "auth_ref": [
      "r340",
      "r341"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.",
        "label": "Schedule of Goodwill [Table Text Block]",
        "terseLabel": "Summary of Changes in Carrying Value of Goodwill"
       }
      }
     },
     "localname": "ScheduleOfGoodwillTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfImpairedFinancingReceivableTable": {
     "auth_ref": [
      "r237"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule of the recorded investment, unpaid principal balance, associated allowance, average recorded investment, accounting policies, and interest income recognized on the accrual and cash basis for impaired financing receivables by class of financing receivable.",
        "label": "Schedule of Impaired Financing Receivable [Table]",
        "terseLabel": "Financing Receivable, Nonaccrual [Table]"
       }
      }
     },
     "localname": "ScheduleOfImpairedFinancingReceivableTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNonaccrualLoansDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfInvestmentsLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Schedule of Investments [Line Items]",
        "terseLabel": "Schedule of Investments [Line Items]"
       }
      }
     },
     "localname": "ScheduleOfInvestmentsLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfInvestmentsTable": {
     "auth_ref": [
      "r969"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A container table for all schedule of investment items. It ties in the \"Legal Entity [Axis]\" to all of its contained line items.",
        "label": "Schedule of Investments [Table]",
        "terseLabel": "Schedule of Gain (Loss) on Securities [Table]"
       }
      }
     },
     "localname": "ScheduleOfInvestmentsTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfMaturitiesOfLongTermDebtTableTextBlock": {
     "auth_ref": [
      "r384"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of maturity and sinking fund requirement for long-term debt.",
        "label": "Schedule of Maturities of Long-term Debt [Table Text Block]",
        "terseLabel": "Schedule of Maturities of Medium- and Long-term Debt"
       }
      }
     },
     "localname": "ScheduleOfMaturitiesOfLongTermDebtTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfNetBenefitCostsTableTextBlock": {
     "auth_ref": [
      "r502"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments.",
        "label": "Schedule of Net Benefit Costs [Table Text Block]",
        "terseLabel": "Components of Net Periodic Defined Benefit Cost"
       }
      }
     },
     "localname": "ScheduleOfNetBenefitCostsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock": {
     "auth_ref": [
      "r146",
      "r150",
      "r178",
      "r179"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of changes in accounting principles, including adoption of new accounting pronouncements, that describes the new methods, amount and effects on financial statement line items.",
        "label": "Accounting Standards Update and Change in Accounting Principle [Table Text Block]",
        "terseLabel": "Schedule of Consolidated Balance Sheets with Change in Accounting Principle"
       }
      }
     },
     "localname": "ScheduleOfNewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock": {
     "auth_ref": [
      "r576"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the changes in outstanding nonvested restricted stock units.",
        "label": "Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]",
        "terseLabel": "Summary of Restricted Stock Unit Activity and Related Information"
       }
      }
     },
     "localname": "ScheduleOfNonvestedRestrictedStockUnitsActivityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfPropertyPlantAndEquipmentTable": {
     "auth_ref": [
      "r33",
      "r356"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of information about physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation.",
        "label": "Property, Plant and Equipment [Table]",
        "terseLabel": "Property, Plant and Equipment [Table]"
       }
      }
     },
     "localname": "ScheduleOfPropertyPlantAndEquipmentTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfQuarterlyFinancialInformationTableTextBlock": {
     "auth_ref": [
      "r180"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of quarterly financial data. Includes, but is not limited to, financial information for fiscal quarters, cumulative effect of a change in accounting principle and earnings per share data.",
        "label": "Quarterly Financial Information [Table Text Block]",
        "terseLabel": "Summary of Quarterly Financial Statements"
       }
      }
     },
     "localname": "ScheduleOfQuarterlyFinancialInformationTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfRealizedGainLossTableTextBlock": {
     "auth_ref": [
      "r280"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales.",
        "label": "Schedule of Realized Gain (Loss) [Table Text Block]",
        "terseLabel": "Summary of Net Securities Gains (Losses)"
       }
      }
     },
     "localname": "ScheduleOfRealizedGainLossTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable": {
     "auth_ref": [
      "r202",
      "r205",
      "r211",
      "r340"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A table disclosing the profit or loss and total assets for each reportable segment of the entity. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.",
        "label": "Schedule of Segment Reporting Information, by Segment [Table]",
        "terseLabel": "Schedule of Segment Reporting Information, By Segment [Table]"
       }
      }
     },
     "localname": "ScheduleOfSegmentReportingInformationBySegmentTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock": {
     "auth_ref": [
      "r202",
      "r205",
      "r211",
      "r340"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.",
        "label": "Schedule of Segment Reporting Information, by Segment [Table Text Block]",
        "terseLabel": "Business Segment Financial Results"
       }
      }
     },
     "localname": "ScheduleOfSegmentReportingInformationBySegmentTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock": {
     "auth_ref": [
      "r568",
      "r581",
      "r584"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value.",
        "label": "Share-based Payment Arrangement, Option, Activity [Table Text Block]",
        "terseLabel": "Summary of Stock Option Activity and Related Information"
       }
      }
     },
     "localname": "ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock": {
     "auth_ref": [
      "r586"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions.",
        "label": "Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]",
        "terseLabel": "Estimated Weighted-Average Grant-Date Fair Value per Option and the Underlying Model Assumptions"
       }
      }
     },
     "localname": "ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfShortTermDebtTable": {
     "auth_ref": [
      "r38"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A table or schedule providing information pertaining to borrowings under which repayment was required in less than twelve months (or normal operating cycle, if longer) after its issuance. It may include: (1) description of the short-term debt arrangement; (2) identification of the lender or type of lender; (3) repayment terms; (4) weighted average interest rate; (5) carrying amount of funds borrowed under the specified short-term debt arrangement as of the balance sheet date and measures of the maximum and average amount outstanding during the period; (6) description of the refinancing of a short-term obligation when that obligation is excluded from current liabilities in the balance sheet; and (7) amount of a short-term obligation that has been excluded from current liabilities in the balance sheet because of a refinancing of the obligation.",
        "label": "Schedule of Short-term Debt [Table]",
        "terseLabel": "Schedule of Short-term Debt [Table]"
       }
      }
     },
     "localname": "ScheduleOfShortTermDebtTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfShortTermDebtTextBlock": {
     "auth_ref": [
      "r38"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of short-term debt arrangements (having initial terms of repayment within one year or the normal operating cycle, if longer) including: (1) description of the short-term debt arrangement; (2) identification of the lender or type of lender; (3) repayment terms; (4) weighted average interest rate; (5) carrying amount of funds borrowed under the specified short-term debt arrangement as of the balance sheet date; (6) description of the refinancing of a short-term obligation when that obligation is excluded from current liabilities in the balance sheet; and (7) amount of a short-term obligation that has been excluded from current liabilities in the balance sheet because of a refinancing of the obligation.",
        "label": "Schedule of Short-term Debt [Table Text Block]",
        "terseLabel": "Summary of Short-term Borrowings"
       }
      }
     },
     "localname": "ScheduleOfShortTermDebtTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock": {
     "auth_ref": [
      "r278"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).",
        "label": "Schedule of Unrealized Loss on Investments [Table Text Block]",
        "terseLabel": "Summary Of Investment Securities In Unrealized Loss Positions"
       }
      }
     },
     "localname": "ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfUnrecognizedCompensationCostNonvestedAwardsTableTextBlock": {
     "auth_ref": [
      "r594"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of cost not yet recognized and weighted-average period over which cost is expected to be recognized for nonvested award under share-based payment arrangement.",
        "label": "Share-based Payment Arrangement, Nonvested Award, Cost [Table Text Block]",
        "terseLabel": "Schedule of Unrecognized Compensation Expense"
       }
      }
     },
     "localname": "ScheduleOfUnrecognizedCompensationCostNonvestedAwardsTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock": {
     "auth_ref": [
      "r625",
      "r639"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the change in unrecognized tax benefits.",
        "label": "Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]",
        "terseLabel": "Reconciliation of Beginning and Ending Unrecognized Tax Benefits"
       }
      }
     },
     "localname": "ScheduleOfUnrecognizedTaxBenefitsRollForwardTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ScheduleOfVariableInterestEntitiesTable": {
     "auth_ref": [
      "r664",
      "r665",
      "r670",
      "r671",
      "r672",
      "r674",
      "r676",
      "r679",
      "r680"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of qualitative and quantitative information related to variable interests the entity holds, whether or not such variable interest entity (VIE) is included in the reporting entity's consolidated financial statements. Includes, but is not limited to, description of the significant judgments and assumptions made in determining whether a variable interest (as defined) held by the entity requires the variable interest entity (VIE) (as defined) to be consolidated and (or) disclose information about its involvement with the VIE, individually or in aggregate (as applicable); the nature of restrictions, if any, on the consolidated VIE's assets and on the settlement of its liabilities reported by an entity in its statement of financial position, including the carrying amounts of such assets and liabilities; the nature of, and changes in, the risks associated with involvement in the VIE; how involvement with the VIE affects the entity's financial position, financial performance, and cash flows; the lack of recourse if creditors (or beneficial interest holders) of the consolidated VIE have no recourse to the general credit of the primary beneficiary (if applicable); the terms of arrangements, giving consideration to both explicit arrangements and implicit variable interests, if any, that could require the entity to provide financial support to the VIE, including events or circumstances that could expose the entity to a loss; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; the significant factors considered and judgments made in determining that the power to direct the activities of a VIE that most significantly impact the VIE's economic performance are shared (as defined); the carrying amounts and classification of assets and liabilities of the VIE included in the statement of financial position; the entity's maximum exposure to loss, if any, as a result of its involvement with the VIE, including how the maximum exposure is determined and significant sources of the entity's exposure to the VIE; a tabular comparison of the carrying amounts of the assets and liabilities and the entity's maximum exposure to loss; information about any liquidity arrangements, guarantees, and (or) other commitments by third parties that may affect the fair value or risk of the entity's variable interest in the VIE; whether or not the entity has provided financial support or other support (explicitly or implicitly) to the VIE that it was not previously contractually required to provide or whether the entity intends to provide that support, including the type and amount of the support and the primary reasons for providing the support; and supplemental information the entity determines necessary to provide.",
        "label": "Schedule of Variable Interest Entities [Table]",
        "terseLabel": "Schedule of Variable Interest Entities [Table]"
       }
      }
     },
     "localname": "ScheduleOfVariableInterestEntitiesTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ScheduleOfVariableInterestEntitiesTextBlock": {
     "auth_ref": [
      "r672",
      "r674",
      "r676",
      "r679",
      "r680"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of the significant judgments and assumptions made in determining whether a variable interest (as defined) held by the entity requires the variable interest entity (VIE) (as defined) to be consolidated and (or) disclose information about its involvement with the VIE, individually or in aggregate (as applicable); the nature of restrictions, if any, on the consolidated VIE's assets and on the settlement of its liabilities reported by an entity in its statement of financial position, including the carrying amounts of such assets and liabilities; the nature of, and changes in, the risks associated with involvement in the VIE; how involvement with the VIE affects the entity's financial position, financial performance, and cash flows; the lack of recourse if creditors (or beneficial interest holders) of the consolidated VIE have no recourse to the general credit of the primary beneficiary (if applicable); the terms of arrangements, giving consideration to both explicit arrangements and implicit variable interests, if any, that could require the entity to provide financial support to the VIE, including events or circumstances that could expose the entity to a loss; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; the significant factors considered and judgments made in determining that the power to direct the activities of a VIE that most significantly impact the VIE's economic performance are shared (as defined); the carrying amounts and classification of assets and liabilities of the VIE included in the statement of financial position; the entity's maximum exposure to loss, if any, as a result of its involvement with the VIE, including how the maximum exposure is determined and significant sources of the entity's exposure to the VIE; a comparison of the carrying amounts of the assets and liabilities and the entity's maximum exposure to loss; information about any liquidity arrangements, guarantees, and (or) other commitments by third parties that may affect the fair value or risk of the entity's variable interest in the VIE; whether or not the entity has provided financial support or other support (explicitly or implicitly) to the VIE that it was not previously contractually required to provide or whether the entity intends to provide that support, including the type and amount of the support and the primary reasons for providing the support; and supplemental information the entity determines necessary to provide.",
        "label": "Schedule of Variable Interest Entities [Table Text Block]",
        "terseLabel": "Impact of VIEs on the Consolidated Statements of Income"
       }
      }
     },
     "localname": "ScheduleOfVariableInterestEntitiesTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SecuritiesBorrowedLiability": {
     "auth_ref": [
      "r50",
      "r59"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of liability associated with securities borrowed from entities in exchange for collateral.",
        "label": "Securities Borrowed, Liability",
        "terseLabel": "Securities Borrowed, Liability"
       }
      }
     },
     "localname": "SecuritiesBorrowedLiability",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SegmentDomain": {
     "auth_ref": [
      "r190",
      "r193",
      "r194",
      "r195",
      "r196",
      "r197",
      "r198",
      "r199",
      "r200",
      "r201",
      "r202",
      "r203",
      "r204",
      "r207",
      "r208",
      "r209",
      "r210",
      "r212",
      "r213",
      "r214",
      "r215",
      "r216",
      "r218",
      "r223",
      "r362",
      "r363",
      "r951"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Components of an entity that engage in business activities from which they may earn revenue and incur expenses, including transactions with other components of the same entity.",
        "label": "Segments [Domain]",
        "terseLabel": "Segment [Domain]"
       }
      }
     },
     "localname": "SegmentDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_SegmentReportingAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Segment Reporting [Abstract]",
        "terseLabel": "Segment Reporting [Abstract]"
       }
      }
     },
     "localname": "SegmentReportingAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_SegmentReportingDisclosureTextBlock": {
     "auth_ref": [
      "r190",
      "r191",
      "r192",
      "r202",
      "r206",
      "r212",
      "r216",
      "r217",
      "r218",
      "r219",
      "r220",
      "r222",
      "r223",
      "r224"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.",
        "label": "Segment Reporting Disclosure [Text Block]",
        "terseLabel": "Business Segment Information"
       }
      }
     },
     "localname": "SegmentReportingDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformation"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SegmentReportingRevenueReconcilingItemLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Segment Reporting, Revenue Reconciling Item [Line Items]",
        "terseLabel": "Segment Reporting, Revenue Reconciling Item [Line Items]"
       }
      }
     },
     "localname": "SegmentReportingRevenueReconcilingItemLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareBasedCompensation": {
     "auth_ref": [
      "r113"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows": {
       "order": 6.0,
       "parentTag": "us-gaap_NetCashProvidedByUsedInOperatingActivities",
       "weight": 1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of noncash expense for share-based payment arrangement.",
        "label": "Share-based Payment Arrangement, Noncash Expense",
        "terseLabel": "Share-based compensation expense",
        "verboseLabel": "Share-based compensation expense"
       }
      }
     },
     "localname": "ShareBasedCompensation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofCashFlowsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Share-based Payment Arrangement, Noncash Expense [Abstract]",
        "terseLabel": "Share-based Payment Arrangement, Noncash Expense [Abstract]"
       }
      }
     },
     "localname": "ShareBasedCompensationAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1": {
     "auth_ref": [
      "r563"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period",
        "terseLabel": "Share-based compensation vesting period"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod": {
     "auth_ref": [
      "r574"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period",
        "negatedLabel": "Restricted shares forfeited",
        "negatedTerseLabel": "Restricted shares forfeited"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r580"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value",
        "terseLabel": "Restricted shares forfeited (Weighted-average grant-date fair value)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod": {
     "auth_ref": [
      "r578"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period",
        "terseLabel": "Non-vested shares granted"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r578"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value",
        "terseLabel": "Non-vested shares granted (Weighted-average grant-date fair value)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber": {
     "auth_ref": [
      "r577"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number",
        "periodEndLabel": "Restricted shares outstanding at December 31, 2021",
        "periodStartLabel": "Restricted shares outstanding at January 1, 2021",
        "terseLabel": "Shares of restricted stock outstanding"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r577"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value",
        "periodEndLabel": "Restricted shares outstanding at December 31, 2021 (Weighted-average grant-date fair value)",
        "periodStartLabel": "Restricted shares outstanding at January 1, 2021 (Weighted-average grant-date fair value)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod": {
     "auth_ref": [
      "r579"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period",
        "negatedTerseLabel": "Restricted shares vested"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue": {
     "auth_ref": [
      "r583"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value",
        "terseLabel": "Total fair value of restricted stock awards that fully vested"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r579"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value",
        "terseLabel": "Restricted shares vested (Weighted-average grant-date fair value)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate": {
     "auth_ref": [
      "r589"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate",
        "terseLabel": "Expected dividend yield"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate": {
     "auth_ref": [
      "r588"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate",
        "terseLabel": "Expected volatility factors of the market price of Comerica common stock"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate": {
     "auth_ref": [
      "r590"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The risk-free interest rate assumption that is used in valuing an option on its own shares.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate",
        "terseLabel": "Risk-free interest rates"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized": {
     "auth_ref": [
      "r564"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of shares authorized for issuance under share-based payment arrangement.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized",
        "terseLabel": "Number of shares originally available for grant"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant": {
     "auth_ref": [
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant",
        "terseLabel": "Shares available for grant"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber": {
     "auth_ref": [
      "r571"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number",
        "terseLabel": "Number of options exercisable at December 31, 2021"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice": {
     "auth_ref": [
      "r571"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price",
        "terseLabel": "Options exercisable at December 31, 2021 (Weighted-average exercise price)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue": {
     "auth_ref": [
      "r583"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value",
        "terseLabel": "Total intrinsic value of stock options exercised"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod": {
     "auth_ref": [
      "r575"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period",
        "negatedTerseLabel": "Options forfeited or expired"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [
      "r575"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price of options that were either forfeited or expired.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price",
        "terseLabel": "Options forfeited or expired (Weighted-average exercise price)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresAndExpirationsInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod": {
     "auth_ref": [
      "r572"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Net number of share options (or share units) granted during the period.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures",
        "terseLabel": "Options granted"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue": {
     "auth_ref": [
      "r582"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value",
        "terseLabel": "Weighted-average grant-date fair value per option"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue": {
     "auth_ref": [
      "r595"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value",
        "verboseLabel": "Aggregate intrinsic value outstanding at December 31, 2021"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber": {
     "auth_ref": [
      "r570",
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of options outstanding, including both vested and non-vested options.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number",
        "periodEndLabel": "Number of options outstanding at December 31, 2021",
        "periodStartLabel": "Number of options outstanding at January 1, 2021"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice": {
     "auth_ref": [
      "r569"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price",
        "periodEndLabel": "Options outstanding at December 31, 2021 Weighted-average exercise price)",
        "periodStartLabel": "Options outstanding at January 1, 2021 (Weighted-average exercise price)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain": {
     "auth_ref": [
      "r559",
      "r565"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Award under share-based payment arrangement.",
        "label": "Award Type [Domain]",
        "terseLabel": "Award Type [Domain]",
        "verboseLabel": "Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain]"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average price at which option holders acquired shares when converting their stock options into shares.",
        "label": "Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price",
        "terseLabel": "Options exercised (Weighted-average exercise price)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.",
        "label": "Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price",
        "terseLabel": "Options granted (Weighted-average exercise price)"
       }
      }
     },
     "localname": "ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicy": {
     "auth_ref": [
      "r562",
      "r566"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Disclosure of accounting policy for award under share-based payment arrangement. Includes, but is not limited to, methodology and assumption used in measuring cost.",
        "label": "Share-based Payment Arrangement [Policy Text Block]",
        "terseLabel": "Share-Based Compensation"
       }
      }
     },
     "localname": "ShareBasedCompensationOptionAndIncentivePlansPolicy",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesPolicies"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SharePrice": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Price of a single share of a number of saleable stocks of a company.",
        "label": "Share Price",
        "terseLabel": "Closing stock price per share"
       }
      }
     },
     "localname": "SharePrice",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_ShareRepurchaseProgramAxis": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by share repurchase program.",
        "label": "Share Repurchase Program [Axis]",
        "terseLabel": "Share Repurchase Program [Axis]"
       }
      }
     },
     "localname": "ShareRepurchaseProgramAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShareRepurchaseProgramDomain": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Name of the share repurchase program.",
        "label": "Share Repurchase Program [Domain]",
        "terseLabel": "Share Repurchase Program [Domain]"
       }
      }
     },
     "localname": "ShareRepurchaseProgramDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1": {
     "auth_ref": [
      "r587",
      "r605"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term",
        "terseLabel": "Expected option life (in years)"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationEstimatedWeightedAverageGrantDateFairValuePerOptionShareandtheUnderlyingBinomialOptionPricingModelAssumptionsDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1": {
     "auth_ref": [
      "r595"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value",
        "terseLabel": "Aggregate intrinsic value exercisable at December 31, 2021"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1": {
     "auth_ref": [
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term",
        "terseLabel": "Weighted-average remaining contractual term in years exercisable at December 31, 2021"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2": {
     "auth_ref": [
      "r585"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term",
        "terseLabel": "Weighted-average remaining contractual term in years at December 31, 2021"
       }
      }
     },
     "localname": "SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "durationItemType"
    },
    "us-gaap_ShortTermBorrowings": {
     "auth_ref": [
      "r16",
      "r813",
      "r862",
      "r936"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.",
        "label": "Short-term Debt",
        "verboseLabel": "Amount outstanding at year-end"
       }
      }
     },
     "localname": "ShortTermBorrowings",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShortTermBorrowingsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Short-term Debt [Abstract]",
        "terseLabel": "Short-term Debt [Abstract]"
       }
      }
     },
     "localname": "ShortTermBorrowingsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShortTermDebtLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Short-term Debt [Line Items]",
        "terseLabel": "Short-term Debt [Line Items]"
       }
      }
     },
     "localname": "ShortTermDebtLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShortTermDebtTextBlock": {
     "auth_ref": [
      "r425"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for short-term debt.",
        "label": "Short-term Debt [Text Block]",
        "terseLabel": "Short-term Borrowings"
       }
      }
     },
     "localname": "ShortTermDebtTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowings"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_ShortTermDebtTypeAxis": {
     "auth_ref": [
      "r38"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by type of short-term debt arrangement.",
        "label": "Short-term Debt, Type [Axis]",
        "terseLabel": "Short-term Debt, Type [Axis]"
       }
      }
     },
     "localname": "ShortTermDebtTypeAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_ShortTermDebtTypeDomain": {
     "auth_ref": [
      "r35"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Type of short-term debt arrangement, such as notes, line of credit, commercial paper, asset-based financing, project financing, letter of credit financing.",
        "label": "Short-term Debt, Type [Domain]",
        "terseLabel": "Short-term Debt, Type [Domain]"
       }
      }
     },
     "localname": "ShortTermDebtTypeDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_ShortTermDebtWeightedAverageInterestRate": {
     "auth_ref": [
      "r36"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Weighted average interest rate of short-term debt outstanding calculated at point in time.",
        "label": "Short-term Debt, Weighted Average Interest Rate, at Point in Time",
        "terseLabel": "Weighted average interest rate at year-end"
       }
      }
     },
     "localname": "ShortTermDebtWeightedAverageInterestRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "percentItemType"
    },
    "us-gaap_ShortTermInvestments": {
     "auth_ref": [
      "r18",
      "r866",
      "r867",
      "r933"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.",
        "label": "Short-term Investments",
        "terseLabel": "Other short-term investments"
       }
      }
     },
     "localname": "ShortTermInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShorttermDebtAverageOutstandingAmount": {
     "auth_ref": [
      "r994",
      "r995"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.",
        "label": "Short-term Debt, Average Outstanding Amount",
        "terseLabel": "Average balance outstanding during the year"
       }
      }
     },
     "localname": "ShorttermDebtAverageOutstandingAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_ShorttermDebtMaximumMonthendOutstandingAmount": {
     "auth_ref": [
      "r17"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.",
        "label": "Short-term Debt, Maximum Month-end Outstanding Amount",
        "terseLabel": "Maximum month-end balance during the year"
       }
      }
     },
     "localname": "ShorttermDebtMaximumMonthendOutstandingAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShorttermBorrowingsShorttermBorrowingsSummaryofShorttermBorrowingsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StandbyLettersOfCreditMember": {
     "auth_ref": [
      "r377",
      "r382",
      "r659",
      "r968"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "An irrevocable undertaking (typically by a financial institution) to guarantee payment of a specified financial obligation.",
        "label": "Standby Letters of Credit [Member]",
        "terseLabel": "Standby Letters Of Credit"
       }
      }
     },
     "localname": "StandbyLettersOfCreditMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_StateAndLocalJurisdictionMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Designated tax department of a state or local government entitled to levy and collect income taxes from the entity.",
        "label": "State and Local Jurisdiction [Member]",
        "terseLabel": "California"
       }
      }
     },
     "localname": "StateAndLocalJurisdictionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_StatementBusinessSegmentsAxis": {
     "auth_ref": [
      "r6",
      "r190",
      "r193",
      "r194",
      "r195",
      "r196",
      "r197",
      "r198",
      "r199",
      "r200",
      "r201",
      "r202",
      "r203",
      "r204",
      "r207",
      "r208",
      "r209",
      "r210",
      "r212",
      "r213",
      "r214",
      "r215",
      "r216",
      "r218",
      "r223",
      "r340",
      "r359",
      "r362",
      "r363",
      "r951"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by business segments.",
        "label": "Segments [Axis]",
        "terseLabel": "Segments [Axis]",
        "verboseLabel": "Business Segments [Axis]"
       }
      }
     },
     "localname": "StatementBusinessSegmentsAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsSummaryofChangesinCarryingValueofGoodwillDetails",
      "http://www.comerica.com/role/RevenuefromContractswithCustomersRevenuefromContractswithCustomersDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementEquityComponentsAxis": {
     "auth_ref": [
      "r2",
      "r46",
      "r79",
      "r80",
      "r81",
      "r139",
      "r140",
      "r141",
      "r143",
      "r153",
      "r155",
      "r184",
      "r296",
      "r441",
      "r447",
      "r601",
      "r602",
      "r603",
      "r642",
      "r643",
      "r730",
      "r771",
      "r772",
      "r773",
      "r774",
      "r775",
      "r777",
      "r957",
      "r958",
      "r959",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by component of equity.",
        "label": "Equity Components [Axis]",
        "terseLabel": "Equity Components [Axis]"
       }
      }
     },
     "localname": "StatementEquityComponentsAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Statement [Line Items]",
        "terseLabel": "Statement [Line Items]"
       }
      }
     },
     "localname": "StatementLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofCashFlowsDetails",
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesChangeinAccountingPrincipleConsolidatedStatementsofComprehensiveIncomeDetails",
      "http://www.comerica.com/role/BusinessSegmentInformationBusinessSegmentFinancialResultsDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementFairValueSwapsDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsEstimatedFairValuesOfFinancialInstrumentsNotRecordedAtFairValueInTheirEntiretyOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfCashFlowsAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement of Cash Flows [Abstract]",
        "terseLabel": "Statement of Cash Flows [Abstract]"
       }
      }
     },
     "localname": "StatementOfCashFlowsAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfFinancialPositionAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement of Financial Position [Abstract]",
        "terseLabel": "Statement of Financial Position [Abstract]"
       }
      }
     },
     "localname": "StatementOfFinancialPositionAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfIncomeAndComprehensiveIncomeAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement of Comprehensive Income [Abstract]",
        "terseLabel": "Statement of Comprehensive Income [Abstract]"
       }
      }
     },
     "localname": "StatementOfIncomeAndComprehensiveIncomeAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementOfStockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Statement of Stockholders' Equity [Abstract]",
        "terseLabel": "Statement of Stockholders' Equity [Abstract]"
       }
      }
     },
     "localname": "StatementOfStockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatementTable": {
     "auth_ref": [
      "r139",
      "r140",
      "r141",
      "r184",
      "r849"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Schedule reflecting a Statement of Income, Statement of Cash Flows, Statement of Financial Position, Statement of Shareholders' Equity and Other Comprehensive Income, or other statement as needed.",
        "label": "Statement [Table]",
        "terseLabel": "Statement [Table]"
       }
      }
     },
     "localname": "StatementTable",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/BasisofPresentationandAccountingPoliciesBasisofPresentationandAccountingPoliciesNarrativeDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesNarrativeDetails",
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails",
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsNarrativeDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansReconciliationsofPlanassetsandtheProjectedBenefitObligationtheWeightedAverageAssumptionsUsedtoDetermineYearEndBenefitObligationsandtheAmountsRecognizedinAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofChangesNetofTaxinPlanAssetsandBenefitObligationsRecognizedinOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansScheduleofEstimatedFutureEmployerContributionsDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansSummaryofChangesintheCorporationsQualifiedDefinedBenefitPensionPlansLevel3InvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsChangesInLevel3AssetsAndLiabilitiesMeasuredAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsNarrativeDetails",
      "http://www.comerica.com/role/GoodwillandIntangibleAssetsGoodwillandIntangibleAssetsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails",
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsTaxYearsforSignificantJurisdictionsThatRemainSubjecttoExaminationDetails",
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithRegulatoryApproval": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of dividends that can be declared or paid with approval of regulatory agency.",
        "label": "Statutory Accounting Practices, Statutory Amount Available for Dividend Payments with Regulatory Approval",
        "terseLabel": "Dividends available to be paid to parent company without obtaining prior approval from bank regulatory agencies"
       }
      }
     },
     "localname": "StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithRegulatoryApproval",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants": {
     "auth_ref": [],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value of preferred stock and warrants for common stock issued.",
        "label": "Stock and Warrants Issued During Period, Value, Preferred Stock and Warrants",
        "terseLabel": "Issuance of preferred stock"
       }
      }
     },
     "localname": "StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows",
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation": {
     "auth_ref": [
      "r23",
      "r24",
      "r441",
      "r447"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number, after forfeiture, of shares or units issued under share-based payment arrangement. Excludes shares or units issued under employee stock ownership plan (ESOP).",
        "label": "Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture",
        "terseLabel": "Net issuance of common stock under employee stock plans (in shares)"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodSharesShareBasedCompensation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised": {
     "auth_ref": [
      "r23",
      "r24",
      "r441",
      "r447",
      "r573"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of share options (or share units) exercised during the current period.",
        "label": "Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period",
        "negatedTerseLabel": "Options exercised"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodSharesStockOptionsExercised",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsStockOptionActivityandRelatedInformationDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation": {
     "auth_ref": [
      "r23",
      "r24",
      "r447",
      "r561",
      "r582"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value, after forfeiture, of shares issued under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).",
        "label": "Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture",
        "terseLabel": "Net issuance of common stock under employee stock plans"
       }
      }
     },
     "localname": "StockIssuedDuringPeriodValueShareBasedCompensation",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockOptionMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Contracts conveying rights, but not obligations, to buy or sell a specific quantity of stock at a specified price during a specified period (an American option) or at a specified date (a European option).",
        "label": "Equity Option [Member]",
        "terseLabel": "Stock Option"
       }
      }
     },
     "localname": "StockOptionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_StockRepurchasedDuringPeriodValue": {
     "auth_ref": [
      "r23",
      "r24",
      "r441",
      "r447"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.",
        "label": "Stock Repurchased During Period, Value",
        "terseLabel": "Stock repurchased during the period"
       }
      }
     },
     "localname": "StockRepurchasedDuringPeriodValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockholdersEquityAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Stockholders' Equity Attributable to Parent [Abstract]",
        "terseLabel": "Stockholders' Equity Attributable to Parent [Abstract]"
       }
      }
     },
     "localname": "StockholdersEquityAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest": {
     "auth_ref": [
      "r2",
      "r3",
      "r80",
      "r129",
      "r139",
      "r140",
      "r141",
      "r143",
      "r153",
      "r289",
      "r296",
      "r447",
      "r601",
      "r602",
      "r603",
      "r642",
      "r643",
      "r661",
      "r662",
      "r681",
      "r730",
      "r759",
      "r771",
      "r772",
      "r777",
      "r958",
      "r959",
      "r1046"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 2.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.",
        "label": "Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest",
        "periodEndLabel": "BALANCE",
        "periodStartLabel": "BALANCE",
        "terseLabel": "Total shareholders' equity",
        "totalLabel": "Total shareholders' equity"
       }
      }
     },
     "localname": "StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_StockholdersEquityNoteAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Stockholders' Equity Note [Abstract]",
        "terseLabel": "Stockholders' Equity Note [Abstract]"
       }
      }
     },
     "localname": "StockholdersEquityNoteAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_StockholdersEquityNoteDisclosureTextBlock": {
     "auth_ref": [
      "r127",
      "r427",
      "r429",
      "r430",
      "r431",
      "r432",
      "r433",
      "r434",
      "r435",
      "r436",
      "r437",
      "r438",
      "r440",
      "r447",
      "r450"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.",
        "label": "Stockholders' Equity Note Disclosure [Text Block]",
        "terseLabel": "Stockholders' Equity"
       }
      }
     },
     "localname": "StockholdersEquityNoteDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquity"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SubleaseIncome": {
     "auth_ref": [
      "r791",
      "r796"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of sublease income excluding finance and operating lease expense.",
        "label": "Sublease Income",
        "negatedTerseLabel": "Sublease Income"
       }
      }
     },
     "localname": "SubleaseIncome",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesLeaseExpensesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SubordinatedDebt": {
     "auth_ref": [
      "r17",
      "r20",
      "r864",
      "r937"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.",
        "label": "Subordinated Debt",
        "terseLabel": "Subordinated notes"
       }
      }
     },
     "localname": "SubordinatedDebt",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtScheduleOfMediumAndLongTermDebtDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_SummaryOfIncomeTaxExaminationsTextBlock": {
     "auth_ref": [
      "r619",
      "r639"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of income tax examinations that an enterprise is currently subject to or that have been completed in the current period typically including a description of the examination, the jurisdiction conducting the examination, the tax year(s) under examination, the likelihood of an unfavorable settlement, the range of possible losses, the liability recorded, the increase or decrease in the liability from the prior period, and any penalties and interest that have been recorded.",
        "label": "Summary of Income Tax Examinations [Table Text Block]",
        "terseLabel": "Tax Years Remaining Open for Examination for Significant Tax Jurisdictions"
       }
      }
     },
     "localname": "SummaryOfIncomeTaxExaminationsTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_SwapMember": {
     "auth_ref": [
      "r685"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "A forward-based contract in which two parties agree to swap streams of payments over a specified period. The payment streams are based on an agreed-upon (or notional) principal amount. The term notional is used because swap contracts generally involve no exchange of principal at either inception or maturity. Rather, the notional amount serves as a basis for calculation of the payment streams to be exchanged.",
        "label": "Swap [Member]",
        "terseLabel": "Cash flow swap"
       }
      }
     },
     "localname": "SwapMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfWeightedAverageMaturityAndInterestRatesOnRiskManagementCashFlowSwapsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_TierOneRiskBasedCapital": {
     "auth_ref": [
      "r923"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of Tier 1 risk-based capital as defined by regulatory framework.",
        "label": "Banking Regulation, Tier One Risk-Based Capital, Actual",
        "terseLabel": "Tier 1 capital"
       }
      }
     },
     "localname": "TierOneRiskBasedCapital",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/RegulatoryCapitalandReserveRequirementsRegulatoryCapitalandReserveRequirementsSummaryofCapitalPositionDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesAfterYearFive": {
     "auth_ref": [
      "r384"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 6.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit maturing after fifth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Time Deposit Maturities, after Year Five",
        "terseLabel": "Thereafter"
       }
      }
     },
     "localname": "TimeDepositMaturitiesAfterYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesNextRollingTwelveMonths": {
     "auth_ref": [],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 1.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposits maturing in the next rolling twelve months following the latest balance sheet. Time deposits include, but are not limited to, certificates of deposits. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.",
        "label": "Time Deposit Maturities, Next Rolling Twelve Months",
        "terseLabel": "2022"
       }
      }
     },
     "localname": "TimeDepositMaturitiesNextRollingTwelveMonths",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesYearFive": {
     "auth_ref": [
      "r384"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 5.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit maturing in fifth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Time Deposit Maturities, Year Five",
        "terseLabel": "2026"
       }
      }
     },
     "localname": "TimeDepositMaturitiesYearFive",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesYearFour": {
     "auth_ref": [
      "r384"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 4.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit maturing in fourth fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Time Deposit Maturities, Year Four",
        "terseLabel": "2025"
       }
      }
     },
     "localname": "TimeDepositMaturitiesYearFour",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesYearThree": {
     "auth_ref": [
      "r384"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 3.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit maturing in third fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Time Deposit Maturities, Year Three",
        "terseLabel": "2024"
       }
      }
     },
     "localname": "TimeDepositMaturitiesYearThree",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDepositMaturitiesYearTwo": {
     "auth_ref": [
      "r384"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": 2.0,
       "parentTag": "us-gaap_TimeDeposits",
       "weight": 1.0
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit maturing in second fiscal year following current fiscal year. Time deposit includes, but is not limited to, certificate of deposit. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).",
        "label": "Time Deposit Maturities, Year Two",
        "terseLabel": "2023"
       }
      }
     },
     "localname": "TimeDepositMaturitiesYearTwo",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDeposits": {
     "auth_ref": [
      "r871",
      "r915"
     ],
     "calculation": {
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails": {
       "order": null,
       "parentTag": null,
       "root": true,
       "weight": null
      }
     },
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit.",
        "label": "Time Deposits",
        "totalLabel": "Total"
       }
      }
     },
     "localname": "TimeDeposits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofCertificatesofDepositandOtherDepositswithaStatedMaturityDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TimeDeposits100000OrMore": {
     "auth_ref": [
      "r993"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more.",
        "label": "Time Deposits, $100,000 or More",
        "terseLabel": "Total"
       }
      }
     },
     "localname": "TimeDeposits100000OrMore",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DepositsDepositsScheduleofMaturitiesofDomesticDepositsofOneHundredThousandorMoreDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TradingSecurities": {
     "auth_ref": [
      "r878"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).",
        "label": "Debt Securities, Trading, and Equity Securities, FV-NI",
        "terseLabel": "Deferred compensation plan assets"
       }
      }
     },
     "localname": "TradingSecurities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TransferToOtherRealEstate": {
     "auth_ref": [
      "r120",
      "r121",
      "r122"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Value transferred from mortgage loans to real estate owned (REO) in noncash transactions.",
        "label": "Real Estate Owned, Transfer to Real Estate Owned",
        "terseLabel": "Loans transferred to other real estate"
       }
      }
     },
     "localname": "TransferToOtherRealEstate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfCashFlows"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain": {
     "auth_ref": [
      "r273",
      "r274",
      "r283",
      "r284",
      "r285",
      "r418",
      "r439",
      "r721",
      "r814",
      "r815",
      "r816",
      "r817",
      "r818",
      "r819",
      "r820",
      "r821",
      "r822",
      "r823",
      "r824",
      "r825",
      "r826",
      "r828",
      "r831",
      "r833",
      "r834",
      "r835",
      "r836",
      "r837",
      "r838",
      "r839",
      "r840",
      "r841",
      "r842",
      "r843",
      "r844",
      "r845",
      "r846",
      "r847",
      "r994",
      "r995",
      "r996",
      "r997",
      "r1002",
      "r1003",
      "r1004"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Instrument or contract that imposes a contractual obligation to deliver cash or another financial instrument or to exchange other financial instruments on potentially unfavorable terms and conveys a contractual right to receive cash or another financial instrument or to exchange other financial instruments on potentially favorable terms.",
        "label": "Financial Instruments [Domain]",
        "terseLabel": "Financial Instruments [Domain]",
        "verboseLabel": "Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Domain]"
       }
      }
     },
     "localname": "TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/DerivativeAndCreditRelatedFinancialInstrumentsScheduleOfFinancialInstrumentsWithOffBalanceSheetCreditRiskDetails",
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesContractualMaturityDistributionOfDebtSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesGainsAndLossesOnSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_TreasuryStockAcquiredAverageCostPerShare": {
     "auth_ref": [
      "r448"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Total cost of shares repurchased divided by the total number of shares repurchased.",
        "label": "Treasury Stock Acquired, Average Cost Per Share",
        "terseLabel": "Average cost per share of shares repurchased under equity repurchase program"
       }
      }
     },
     "localname": "TreasuryStockAcquiredAverageCostPerShare",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "perShareItemType"
    },
    "us-gaap_TreasuryStockMember": {
     "auth_ref": [
      "r45",
      "r448"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Shares of an entity that have been repurchased by the entity. This stock has no voting rights and receives no dividends. Note that treasury stock may be recorded at its total cost or separately as par (or stated) value and additional paid in capital. Classified within stockholders' equity if nonredeemable or redeemable solely at the option of the issuer. Classified within temporary equity if redemption is outside the control of the issuer.",
        "label": "Treasury Stock [Member]",
        "terseLabel": "Treasury Stock"
       }
      }
     },
     "localname": "TreasuryStockMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_TreasuryStockShares": {
     "auth_ref": [
      "r45",
      "r448"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.",
        "label": "Treasury Stock, Shares",
        "terseLabel": "Shares in treasury"
       }
      }
     },
     "localname": "TreasuryStockShares",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheetsParenthetical",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails",
      "http://www.comerica.com/role/ShareBasedCompensationShareBasedCompensationNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_TreasuryStockSharesAcquired": {
     "auth_ref": [
      "r24",
      "r441",
      "r447"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of shares that have been repurchased during the period and are being held in treasury.",
        "label": "Treasury Stock, Shares, Acquired",
        "terseLabel": "Purchase of common stock (in shares)",
        "verboseLabel": "Shares repurchased under equity repurchase program"
       }
      }
     },
     "localname": "TreasuryStockSharesAcquired",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity",
      "http://www.comerica.com/role/ShareholdersEquityShareholdersEquityNarrativeDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_TreasuryStockValue": {
     "auth_ref": [
      "r45",
      "r448",
      "r449"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedBalanceSheets": {
       "order": 5.0,
       "parentTag": "us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest",
       "weight": -1.0
      },
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails": {
       "order": 6.0,
       "parentTag": "us-gaap_LiabilitiesAndStockholdersEquity",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount allocated to treasury stock. Treasury stock is common and preferred shares of an entity that were issued, repurchased by the entity, and are held in its treasury.",
        "label": "Treasury Stock, Value",
        "negatedTerseLabel": "Less cost of common stock in treasury - 97,476,872 shares at 12/31/21 and 88,997,430 shares at 12/31/20",
        "terseLabel": "Less cost of common stock in treasury - 97,476,872 shares at 12/31/21 and 88,997,430 shares at 12/31/20"
       }
      }
     },
     "localname": "TreasuryStockValue",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedBalanceSheets",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsBalanceSheetsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TreasuryStockValueAcquiredCostMethod": {
     "auth_ref": [
      "r441",
      "r447",
      "r448"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.",
        "label": "Treasury Stock, Value, Acquired, Cost Method",
        "negatedLabel": "Purchase of common stock"
       }
      }
     },
     "localname": "TreasuryStockValueAcquiredCostMethod",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfChangesInShareholdersEquity"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock": {
     "auth_ref": [
      "r242",
      "r244"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Tabular disclosure of financing receivable modified as troubled debt restructuring.",
        "label": "Financing Receivable, Troubled Debt Restructuring [Table Text Block]",
        "verboseLabel": "Troubled Debt Restructurings By Type Of Modification"
       }
      }
     },
     "localname": "TroubledDebtRestructuringsOnFinancingReceivablesTableTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesTables"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_TypeOfAdoptionMember": {
     "auth_ref": [
      "r0",
      "r1",
      "r2",
      "r3",
      "r4",
      "r142",
      "r143",
      "r144",
      "r145",
      "r156",
      "r258",
      "r259",
      "r293",
      "r294",
      "r295",
      "r296",
      "r297",
      "r298",
      "r385",
      "r597",
      "r598",
      "r599",
      "r600",
      "r601",
      "r602",
      "r603",
      "r604",
      "r640",
      "r641",
      "r642",
      "r643",
      "r722",
      "r723",
      "r724",
      "r725",
      "r726",
      "r727",
      "r728",
      "r729",
      "r730",
      "r731",
      "r732",
      "r761",
      "r762",
      "r763",
      "r764",
      "r765",
      "r766",
      "r767",
      "r768",
      "r801",
      "r851",
      "r852",
      "r853",
      "r955",
      "r956",
      "r957",
      "r958",
      "r959",
      "r960",
      "r961",
      "r962",
      "r963",
      "r964",
      "r965",
      "r966",
      "r1042",
      "r1043",
      "r1044",
      "r1045",
      "r1046"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amendment to accounting standards.",
        "label": "Accounting Standards Update [Domain]",
        "terseLabel": "Type of Adoption [Domain]"
       }
      }
     },
     "localname": "TypeOfAdoptionMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/CreditQualityAndAllowanceForCreditLossesChangesInTheAllowanceForLoanLossesAndRelatedLoanAmountsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_USTreasuryAndGovernmentMember": {
     "auth_ref": [
      "r491",
      "r908",
      "r967"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "This category includes investments in debt securities issued by the United States Department of the Treasury, US Government Agencies and US Government-sponsored Enterprises. Such securities may include treasury bills (short-term maturities - one year or less), treasury notes (intermediate term maturities - two to ten years), and treasury bonds (long-term maturities - ten to thirty years), debt securities issued by the Government National Mortgage Association (Ginnie Mae) and debt securities issued by the Federal National Mortgage Association (Fannie Mae) or the Federal Home Loan Mortgage Corporation (Freddie Mac).",
        "label": "US Treasury and Government [Member]",
        "terseLabel": "U.S. Treasury and other U.S. government agency securities",
        "verboseLabel": "U.S. Treasury and other U.S. government agency securities"
       }
      }
     },
     "localname": "USTreasuryAndGovernmentMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/EmployeeBenefitPlansFairValuesoftheCorporationsQualifiedDefinedBenefitPensionPlanInvestmentsMeasuredatFairValueonaRecurringBasisDetails",
      "http://www.comerica.com/role/FairValueMeasurementsAssetsAndLiabilitiesRecordedAtFairValueOnARecurringBasisDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesNarrativeDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesDetails",
      "http://www.comerica.com/role/InvestmentSecuritiesSummaryOfInvestmentSecuritiesInUnrealizedLossPositionsDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_UnamortizedDebtIssuanceExpense": {
     "auth_ref": [
      "r34"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.",
        "label": "Unamortized Debt Issuance Expense",
        "terseLabel": "Unamortized debt issuance costs"
       }
      }
     },
     "localname": "UnamortizedDebtIssuanceExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/MediumAndLongTermDebtNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesDiluted": {
     "auth_ref": [
      "r164",
      "r165",
      "r168",
      "r169"
     ],
     "calculation": {
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome": {
       "order": 2.0,
       "parentTag": "us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic",
       "weight": -1.0
      }
     },
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of undistributed earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.",
        "label": "Undistributed Earnings (Loss) Allocated to Participating Securities, Diluted",
        "terseLabel": "Less income allocated to participating securities",
        "verboseLabel": "Less income allocated to participating securities"
       }
      }
     },
     "localname": "UndistributedEarningsLossAllocatedToParticipatingSecuritiesDiluted",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ConsolidatedStatementsOfIncome",
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails",
      "http://www.comerica.com/role/ParentCompanyFinancialStatementsParentCompanyFinancialStatementsStatementsofIncomeDetails",
      "http://www.comerica.com/role/SummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsUnauditedSummaryofQuarterlyFinancialStatementsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrealizedGainLossOnInvestments": {
     "auth_ref": [
      "r114"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unrealized gain (loss) on investment.",
        "label": "Unrealized Gain (Loss) on Investments",
        "terseLabel": "Net unrealized holding (losses) gains arising during the period"
       }
      }
     },
     "localname": "UnrealizedGainLossOnInvestments",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/AccumulatedOtherComprehensiveLossScheduleOfAccumulatedOtherComprehensiveIncomeLossDetails",
      "http://www.comerica.com/role/ConsolidatedStatementsofComprehensiveIncome"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefits": {
     "auth_ref": [
      "r611",
      "r620"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of unrecognized tax benefits.",
        "label": "Unrecognized Tax Benefits",
        "periodEndLabel": "Balance at December 31",
        "periodStartLabel": "Balance at January 1"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefits",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities": {
     "auth_ref": [
      "r623"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.",
        "label": "Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities",
        "negatedLabel": "Decreases related to settlements with tax authorities"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued": {
     "auth_ref": [
      "r617"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.",
        "label": "Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued",
        "terseLabel": "Liability for tax-related interest and penalties"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions": {
     "auth_ref": [
      "r622"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.",
        "label": "Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions",
        "terseLabel": "Increase as a result of tax positions taken during a current period"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions": {
     "auth_ref": [
      "r621"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.",
        "label": "Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions",
        "terseLabel": "Increase as a result of tax positions taken during a prior period"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsReconciliationoftheBeginningandEndingAmountsofUnrecognizedTaxBenefitsDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate": {
     "auth_ref": [
      "r624"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.",
        "label": "Unrecognized Tax Benefits that Would Impact Effective Tax Rate",
        "terseLabel": "Unrecognized tax benefits that would impact the effective tax rate"
       }
      }
     },
     "localname": "UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/IncomeTaxesAndTaxRelatedItemsIncomeTaxesAndTaxRelatedItemsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_VariableInterestEntityActivityBetweenVIEAndEntityExpense": {
     "auth_ref": [
      "r678"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of expense between the reporting entity and the Variable Interest Entity (VIE).",
        "label": "Variable Interest Entity, Measure of Activity, Expense",
        "terseLabel": "Unfunded commitments to fund tax credit entities"
       }
      }
     },
     "localname": "VariableInterestEntityActivityBetweenVIEAndEntityExpense",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_VariableInterestEntityDisclosureTextBlock": {
     "auth_ref": [
      "r684"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The entire disclosure for a variable interest entity (VIE), including but not limited to, judgments and assumptions in determining whether to consolidate and in identifying the primary beneficiary, gain (loss) recognized on the initial consolidation of the VIE, terms of arrangements, amounts and classification of the VIE's assets and liabilities, and the entity's maximum exposure to loss.",
        "label": "Variable Interest Entity Disclosure [Text Block]",
        "terseLabel": "Variable Interest Entities (VIEs)"
       }
      }
     },
     "localname": "VariableInterestEntityDisclosureTextBlock",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEs"
     ],
     "xbrltype": "textBlockItemType"
    },
    "us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount": {
     "auth_ref": [
      "r673",
      "r677"
     ],
     "crdr": "credit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).",
        "label": "Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount",
        "terseLabel": "Exposure to loss as a result of involvement with VIEs"
       }
      }
     },
     "localname": "VariableInterestEntityEntityMaximumLossExposureAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_VariableInterestEntityFinancialOrOtherSupportAmount": {
     "auth_ref": [
      "r675"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The amount of financial or other support the reporting entity has provided (explicitly or implicitly) to the Variable Interest Entity (VIE) that it was not previously contractually required to provide or that the reporting entity intends to provide, including, for example, situations in which the reporting entity assisted the VIE in obtaining another type of support.",
        "label": "Variable Interest Entity, Financial or Other Support, Amount",
        "terseLabel": "Amount of financial or other support not contractually required provided by the Corporation to VIEs"
       }
      }
     },
     "localname": "VariableInterestEntityFinancialOrOtherSupportAmount",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_VariableInterestEntityLineItems": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.",
        "label": "Variable Interest Entity [Line Items]",
        "terseLabel": "Variable Interest Entity [Line Items]"
       }
      }
     },
     "localname": "VariableInterestEntityLineItems",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails",
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsNarrativeDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_VariableInterestEntityNotPrimaryBeneficiaryDisclosuresAbstract": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "label": "Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]",
        "terseLabel": "Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]"
       }
      }
     },
     "localname": "VariableInterestEntityNotPrimaryBeneficiaryDisclosuresAbstract",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "xbrltype": "stringItemType"
    },
    "us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember": {
     "auth_ref": [],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Variable Interest Entities (VIE) in which the entity does not have a controlling financial interest (as defined) and of which it is therefore not the primary beneficiary. VIEs of which the entity is not the primary beneficiary because it does not have the power to direct the activities of the VIE that most significantly impact the VIE's economic performance and for which it does not have the obligation to absorb losses of the VIE that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE are not included in the consolidated financial statements of the entity.",
        "label": "Variable Interest Entity, Not Primary Beneficiary [Member]",
        "verboseLabel": "Variable Interest Entity"
       }
      }
     },
     "localname": "VariableInterestEntityNotPrimaryBeneficiaryMember",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/VariableInterestEntitiesVIEsImpactOfVIEsOnTheConsolidatedStatementsOfComprehensiveIncomeDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_VariableLeaseCost": {
     "auth_ref": [
      "r790",
      "r796"
     ],
     "crdr": "debit",
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Amount of variable lease cost, excluded from lease liability, recognized when obligation for payment is incurred for finance and operating leases.",
        "label": "Variable Lease, Cost",
        "terseLabel": "Variable lease expense"
       }
      }
     },
     "localname": "VariableLeaseCost",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/LeasesLeaseExpensesDetails"
     ],
     "xbrltype": "monetaryItemType"
    },
    "us-gaap_VestingAxis": {
     "auth_ref": [
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Information by vesting schedule of award under share-based payment arrangement.",
        "label": "Vesting [Axis]",
        "terseLabel": "Vesting [Axis]"
       }
      }
     },
     "localname": "VestingAxis",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "stringItemType"
    },
    "us-gaap_VestingDomain": {
     "auth_ref": [
      "r595"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Vesting schedule of award under share-based payment arrangement.",
        "label": "Vesting [Domain]",
        "terseLabel": "Vesting [Domain]"
       }
      }
     },
     "localname": "VestingDomain",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/ShareBasedCompensationSummaryoftheCorporationsRestrictedStockUnitActivityandRelatedInformationDetails"
     ],
     "xbrltype": "domainItemType"
    },
    "us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding": {
     "auth_ref": [
      "r159",
      "r171"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.",
        "label": "Weighted Average Number of Shares Outstanding, Diluted",
        "verboseLabel": "Diluted average common shares"
       }
      }
     },
     "localname": "WeightedAverageNumberOfDilutedSharesOutstanding",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails"
     ],
     "xbrltype": "sharesItemType"
    },
    "us-gaap_WeightedAverageNumberOfSharesOutstandingBasic": {
     "auth_ref": [
      "r157",
      "r171"
     ],
     "lang": {
      "en-us": {
       "role": {
        "documentation": "Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.",
        "label": "Weighted Average Number of Shares Outstanding, Basic",
        "terseLabel": "Basic average common shares"
       }
      }
     },
     "localname": "WeightedAverageNumberOfSharesOutstandingBasic",
     "nsuri": "http://fasb.org/us-gaap/2021-01-31",
     "presentation": [
      "http://www.comerica.com/role/NetIncomePerCommonShareBasicAndDilutedNetIncomePerCommonShareDetails"
     ],
     "xbrltype": "sharesItemType"
    }
   },
   "unitCount": 7
  }
 },
 "std_ref": {
  "r0": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "105",
   "URI": "http://asc.fasb.org/extlink&oid=124434974&loc=SL124442142-165695"
  },
  "r1": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "105",
   "URI": "http://asc.fasb.org/extlink&oid=124434974&loc=SL124442142-165695"
  },
  "r10": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=124098289&loc=d3e6812-107765"
  },
  "r100": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585"
  },
  "r1000": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(1)(i)"
  },
  "r1001": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(1)(ii)"
  },
  "r1002": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(2)(i)"
  },
  "r1003": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(2)(ii)"
  },
  "r1004": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(2)(iii)"
  },
  "r1005": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Publisher": "SEC",
   "Section": "1402",
   "Subsection": "Instruction 5"
  },
  "r1006": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1403"
  },
  "r1007": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1404"
  },
  "r1008": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1404"
  },
  "r1009": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1405",
   "Subparagraph": "(1)"
  },
  "r101": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585"
  },
  "r1010": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1405",
   "Subparagraph": "(2)"
  },
  "r1011": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1405",
   "Subparagraph": "(3)"
  },
  "r1012": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1405",
   "Subparagraph": "(4)"
  },
  "r1013": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1405"
  },
  "r1014": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Publisher": "SEC",
   "Section": "1406"
  },
  "r1015": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1406",
   "Subparagraph": "(1)"
  },
  "r1016": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1406",
   "Subparagraph": "(2)"
  },
  "r1017": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1406",
   "Subparagraph": "(3)"
  },
  "r1018": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1406",
   "Subparagraph": "(4)"
  },
  "r1019": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1406",
   "Subparagraph": "(5)"
  },
  "r102": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3213-108585"
  },
  "r1020": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(c)",
   "Publisher": "SEC",
   "Section": "1406"
  },
  "r1021": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(e)",
   "Publisher": "SEC",
   "Section": "1406"
  },
  "r1022": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "303",
   "Subparagraph": "(5)"
  },
  "r1023": {
   "Name": "Regulation S-T",
   "Number": "232",
   "Publisher": "SEC",
   "Section": "405"
  },
  "r1024": {
   "Footnote": "4",
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "28"
  },
  "r1025": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "a",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "04"
  },
  "r1026": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(i)",
   "Subsection": "01"
  },
  "r1027": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(i)",
   "Subsection": "02"
  },
  "r1028": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(ii)",
   "Subsection": "01"
  },
  "r1029": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)",
   "Subsection": "01"
  },
  "r103": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585"
  },
  "r1030": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)(A)",
   "Subsection": "01"
  },
  "r1031": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)(A)",
   "Subsection": "02"
  },
  "r1032": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)(B)",
   "Subsection": "01"
  },
  "r1033": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)(B)",
   "Subsection": "02"
  },
  "r1034": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iii)(C)",
   "Subsection": "02"
  },
  "r1035": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iv)",
   "Subsection": "01"
  },
  "r1036": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "13",
   "Subparagraph": "(4)(iv)",
   "Subsection": "02"
  },
  "r1037": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "i",
   "Publisher": "SEC",
   "Section": "3",
   "Subsection": "10"
  },
  "r1038": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "c",
   "Publisher": "SEC",
   "Section": "5",
   "Subparagraph": "Schedule I",
   "Subsection": "04"
  },
  "r1039": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Paragraph": "c",
   "Publisher": "SEC",
   "Section": "7",
   "Subparagraph": "Schedule II",
   "Subsection": "05"
  },
  "r104": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585"
  },
  "r1040": {
   "Name": "Regulation S-X (SX)",
   "Number": "210",
   "Publisher": "SEC",
   "Section": "9",
   "Subsection": "06"
  },
  "r1041": {
   "Name": "Securities Act",
   "Number": "230",
   "Publisher": "SEC",
   "Section": "405"
  },
  "r1042": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "848"
  },
  "r1043": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "848"
  },
  "r1044": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "848"
  },
  "r1045": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)(3)(iii)(01)",
   "Topic": "848"
  },
  "r1046": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)(3)(iii)(03)",
   "Topic": "848"
  },
  "r105": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3291-108585"
  },
  "r106": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3291-108585"
  },
  "r107": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3000-108585"
  },
  "r108": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21C",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=SL94080552-108585"
  },
  "r109": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21D",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=SL94080555-108585"
  },
  "r11": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(1))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r110": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "24",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3521-108585"
  },
  "r111": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3536-108585"
  },
  "r112": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3536-108585"
  },
  "r113": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585"
  },
  "r114": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585"
  },
  "r115": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585"
  },
  "r116": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3044-108585"
  },
  "r117": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3095-108585"
  },
  "r118": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123431023&loc=d3e4273-108586"
  },
  "r119": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123431023&loc=d3e4297-108586"
  },
  "r12": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(12))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r120": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123431023&loc=d3e4304-108586"
  },
  "r121": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123431023&loc=d3e4313-108586"
  },
  "r122": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123431023&loc=d3e4332-108586"
  },
  "r123": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=123372394&loc=d3e18823-107790"
  },
  "r124": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=123372394&loc=d3e18823-107790"
  },
  "r125": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=123372394&loc=d3e18823-107790"
  },
  "r126": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(d))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r127": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(e)(1))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r128": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(f))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r129": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(g)(1)(ii))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r13": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(13))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r130": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(h)(1)(Note 1))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r131": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(h)(1))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r132": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(h)(2))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r133": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(h))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r134": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(m)(1)(ii)(A))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r135": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.4-08(n))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690"
  },
  "r136": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.12-04(a))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690"
  },
  "r137": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.12-04(b))",
   "Topic": "235",
   "URI": "http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690"
  },
  "r138": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "235",
   "URI": "http://asc.fasb.org/topic&trid=2122369"
  },
  "r139": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "23",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124436220&loc=d3e21914-107793"
  },
  "r14": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(14))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r140": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "24",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124436220&loc=d3e21930-107793"
  },
  "r141": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124436220&loc=d3e21711-107793"
  },
  "r142": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(2)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794"
  },
  "r143": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(3)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794"
  },
  "r144": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(4)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794"
  },
  "r145": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794"
  },
  "r146": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22499-107794"
  },
  "r147": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22694-107794"
  },
  "r148": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22694-107794"
  },
  "r149": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=SL124452830-107794"
  },
  "r15": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(17))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r150": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22583-107794"
  },
  "r151": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22595-107794"
  },
  "r152": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22644-107794"
  },
  "r153": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22644-107794"
  },
  "r154": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22658-107794"
  },
  "r155": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=124431687&loc=d3e22663-107794"
  },
  "r156": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 11.M.Q2)",
   "Topic": "250",
   "URI": "http://asc.fasb.org/extlink&oid=122038215&loc=d3e31137-122693"
  },
  "r157": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1448-109256"
  },
  "r158": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1377-109256"
  },
  "r159": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1505-109256"
  },
  "r16": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(19)(a))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r160": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1252-109256"
  },
  "r161": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1707-109256"
  },
  "r162": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "23",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1757-109256"
  },
  "r163": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1500-109256"
  },
  "r164": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "60",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e2740-109256"
  },
  "r165": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "60B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=SL5780133-109256"
  },
  "r166": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "60B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=SL5780133-109256"
  },
  "r167": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "60B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=SL5780133-109256"
  },
  "r168": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "65",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e2793-109256"
  },
  "r169": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "66",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e2814-109256"
  },
  "r17": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(19))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r170": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125511455&loc=d3e1337-109256"
  },
  "r171": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257"
  },
  "r172": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257"
  },
  "r173": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=124432515&loc=d3e3630-109257"
  },
  "r174": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=109243012&loc=SL65017193-207537"
  },
  "r175": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125512782&loc=d3e3842-109258"
  },
  "r176": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "52",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "260",
   "URI": "http://asc.fasb.org/extlink&oid=125512782&loc=d3e4984-109258"
  },
  "r177": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "260",
   "URI": "http://asc.fasb.org/topic&trid=2144383"
  },
  "r178": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "270",
   "URI": "http://asc.fasb.org/extlink&oid=124437754&loc=d3e725-108305"
  },
  "r179": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "270",
   "URI": "http://asc.fasb.org/extlink&oid=124437754&loc=d3e765-108305"
  },
  "r18": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(2))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r180": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "270",
   "URI": "http://asc.fasb.org/extlink&oid=124502072&loc=d3e1280-108306"
  },
  "r181": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "270",
   "URI": "http://asc.fasb.org/extlink&oid=124502072&loc=SL124452896-108306"
  },
  "r182": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "270",
   "URI": "http://asc.fasb.org/extlink&oid=124502072&loc=SL77927221-108306"
  },
  "r183": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "270",
   "URI": "http://asc.fasb.org/topic&trid=2126967"
  },
  "r184": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "272",
   "URI": "http://asc.fasb.org/extlink&oid=125520817&loc=d3e70191-108054"
  },
  "r185": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6327-108592"
  },
  "r186": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592"
  },
  "r187": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592"
  },
  "r188": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "275",
   "URI": "http://asc.fasb.org/extlink&oid=99393423&loc=d3e6442-108592"
  },
  "r189": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "275",
   "URI": "http://asc.fasb.org/topic&trid=2134479"
  },
  "r19": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(20))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r190": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8657-108599"
  },
  "r191": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8721-108599"
  },
  "r192": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8721-108599"
  },
  "r193": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r194": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r195": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r196": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r197": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r198": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r199": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(g)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r2": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "105",
   "URI": "http://asc.fasb.org/extlink&oid=124434974&loc=SL124442142-165695"
  },
  "r20": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(22))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r200": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r201": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(j)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r202": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8736-108599"
  },
  "r203": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8813-108599"
  },
  "r204": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8813-108599"
  },
  "r205": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8813-108599"
  },
  "r206": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "26",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8844-108599"
  },
  "r207": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599"
  },
  "r208": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599"
  },
  "r209": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599"
  },
  "r21": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(26)(a))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r210": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599"
  },
  "r211": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "30",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8906-108599"
  },
  "r212": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "31",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8924-108599"
  },
  "r213": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r214": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r215": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r216": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r217": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r218": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "32",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8933-108599"
  },
  "r219": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "34",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e8981-108599"
  },
  "r22": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(26)(b))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r220": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "40",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e9031-108599"
  },
  "r221": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "41",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e9038-108599"
  },
  "r222": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "41",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e9038-108599"
  },
  "r223": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "42",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "280",
   "URI": "http://asc.fasb.org/extlink&oid=123359005&loc=d3e9054-108599"
  },
  "r224": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "280",
   "URI": "http://asc.fasb.org/topic&trid=2134510"
  },
  "r225": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522"
  },
  "r226": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=124259787&loc=d3e4437-111522"
  },
  "r227": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=124259787&loc=d3e4519-111522"
  },
  "r228": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5162-111524"
  },
  "r229": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r23": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(28))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r230": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r231": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r232": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(3)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r233": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(4)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r234": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(g)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r235": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524"
  },
  "r236": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b,d)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524"
  },
  "r237": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524"
  },
  "r238": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5033-111524"
  },
  "r239": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5033-111524"
  },
  "r24": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(29))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r240": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "29",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953659-111524"
  },
  "r241": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5066-111524"
  },
  "r242": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "33",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524"
  },
  "r243": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "34",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524"
  },
  "r244": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "34",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524"
  },
  "r245": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "35",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL49126937-111524"
  },
  "r246": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5074-111524"
  },
  "r247": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5093-111524"
  },
  "r248": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524"
  },
  "r249": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524"
  },
  "r25": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(1))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r250": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524"
  },
  "r251": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=123577603&loc=d3e5144-111524"
  },
  "r252": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.L.1)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=122038336&loc=d3e74567-122707"
  },
  "r253": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "SubTopic": "10",
   "Topic": "310",
   "URI": "http://asc.fasb.org/subtopic&trid=2196772"
  },
  "r254": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=84159169&loc=d3e10133-111534"
  },
  "r255": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=84159169&loc=d3e10149-111534"
  },
  "r256": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=84159169&loc=d3e10152-111534"
  },
  "r257": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=84159169&loc=d3e10178-111534"
  },
  "r258": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=124402435&loc=SL124402458-218513"
  },
  "r259": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=124402435&loc=SL124402458-218513"
  },
  "r26": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(3))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r260": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "SubTopic": "20",
   "Topic": "310",
   "URI": "http://asc.fasb.org/subtopic&trid=2196816"
  },
  "r261": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(b)(1)(ii)",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544"
  },
  "r262": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Topic": "310",
   "URI": "http://asc.fasb.org/extlink&oid=121585226&loc=d3e18794-111554"
  },
  "r263": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562"
  },
  "r264": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=124260329&loc=d3e26853-111562"
  },
  "r265": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=SL6283291-111563"
  },
  "r266": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563"
  },
  "r267": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(aa)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563"
  },
  "r268": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563"
  },
  "r269": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563"
  },
  "r27": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(30)(a)(4))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r270": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563"
  },
  "r271": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27198-111563"
  },
  "r272": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27198-111563"
  },
  "r273": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563"
  },
  "r274": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=SL120269820-111563"
  },
  "r275": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563"
  },
  "r276": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563"
  },
  "r277": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(3)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563"
  },
  "r278": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27290-111563"
  },
  "r279": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563"
  },
  "r28": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02(32))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r280": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27357-111563"
  },
  "r281": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "320",
   "URI": "http://asc.fasb.org/extlink&oid=123581744&loc=d3e27357-111563"
  },
  "r282": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "320",
   "URI": "http://asc.fasb.org/topic&trid=2196928"
  },
  "r283": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "321",
   "URI": "http://asc.fasb.org/extlink&oid=123583765&loc=SL75117539-209714"
  },
  "r284": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "321",
   "URI": "http://asc.fasb.org/extlink&oid=123583765&loc=SL75117539-209714"
  },
  "r285": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "321",
   "URI": "http://asc.fasb.org/extlink&oid=123583765&loc=SL75117539-209714"
  },
  "r286": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570"
  },
  "r287": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=109237563&loc=d3e33775-111570"
  },
  "r288": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571"
  },
  "r289": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571"
  },
  "r29": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.1)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r290": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "740",
   "Subparagraph": "(a)",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=116633289&loc=SL49122993-202985"
  },
  "r291": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "740",
   "Subparagraph": "(c)",
   "Topic": "323",
   "URI": "http://asc.fasb.org/extlink&oid=116633289&loc=SL49122993-202985"
  },
  "r292": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL82887624-210437"
  },
  "r293": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r294": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r295": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r296": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r297": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(e)(3)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r298": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(e)(4)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=122640432&loc=SL121648383-210437"
  },
  "r299": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446"
  },
  "r3": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "105",
   "URI": "http://asc.fasb.org/extlink&oid=124434974&loc=SL124442142-165695"
  },
  "r30": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.12)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r300": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919244-210447"
  },
  "r301": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447"
  },
  "r302": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447"
  },
  "r303": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(e)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447"
  },
  "r304": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(f)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447"
  },
  "r305": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447"
  },
  "r306": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447"
  },
  "r307": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447"
  },
  "r308": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447"
  },
  "r309": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447"
  },
  "r31": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.13(a))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r310": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447"
  },
  "r311": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447"
  },
  "r312": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL82919232-210447"
  },
  "r313": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124255953&loc=SL120270059-210447"
  },
  "r314": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921830-210448"
  },
  "r315": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921833-210448"
  },
  "r316": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r317": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(a)(1)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r318": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(a)(2)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r319": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r32": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.13)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r320": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r321": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(c)(1)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r322": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(d)(2)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r323": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(e)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r324": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(e)(1)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r325": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(e)(2)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921835-210448"
  },
  "r326": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82921842-210448"
  },
  "r327": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "79",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82922352-210448"
  },
  "r328": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "80",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124267575&loc=SL82922355-210448"
  },
  "r329": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454"
  },
  "r33": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.14)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r330": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)(1)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455"
  },
  "r331": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)(2)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455"
  },
  "r332": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(b)(3)",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455"
  },
  "r333": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455"
  },
  "r334": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455"
  },
  "r335": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922895-210455"
  },
  "r336": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455"
  },
  "r337": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "30",
   "Topic": "326",
   "URI": "http://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456"
  },
  "r338": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266"
  },
  "r339": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975"
  },
  "r34": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.17)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r340": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267"
  },
  "r341": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=121556970&loc=d3e13854-109267"
  },
  "r342": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274"
  },
  "r343": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275"
  },
  "r344": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(d)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275"
  },
  "r345": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275"
  },
  "r346": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)(1)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275"
  },
  "r347": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)(2)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275"
  },
  "r348": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(d)",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275"
  },
  "r349": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "30",
   "SubTopic": "40",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=118172244&loc=d3e17916-109280"
  },
  "r35": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19(a))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r350": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=118198657&loc=SL118198666-228104"
  },
  "r351": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "25",
   "SubTopic": "50",
   "Topic": "350",
   "URI": "http://asc.fasb.org/extlink&oid=16397303&loc=d3e19379-109286"
  },
  "r352": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "350",
   "URI": "http://asc.fasb.org/topic&trid=2144416"
  },
  "r353": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r354": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r355": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r356": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229"
  },
  "r357": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=109226691&loc=d3e2921-110230"
  },
  "r358": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230"
  },
  "r359": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "360",
   "URI": "http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230"
  },
  "r36": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19(b))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r360": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "360",
   "URI": "http://asc.fasb.org/topic&trid=2155823"
  },
  "r361": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "420",
   "URI": "http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869"
  },
  "r362": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "420",
   "URI": "http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869"
  },
  "r363": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 5.P.4(d))",
   "Topic": "420",
   "URI": "http://asc.fasb.org/extlink&oid=115931487&loc=d3e140904-122747"
  },
  "r364": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "440",
   "URI": "http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308"
  },
  "r365": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "440",
   "URI": "http://asc.fasb.org/extlink&oid=123406679&loc=d3e25336-109308"
  },
  "r366": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "440",
   "URI": "http://asc.fasb.org/topic&trid=2144648"
  },
  "r367": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349"
  },
  "r368": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14615-108349"
  },
  "r369": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14394-108349"
  },
  "r37": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19(b),22(b))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r370": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349"
  },
  "r371": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14435-108349"
  },
  "r372": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14453-108349"
  },
  "r373": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14472-108349"
  },
  "r374": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349"
  },
  "r375": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "450",
   "URI": "http://asc.fasb.org/extlink&oid=121557415&loc=d3e14557-108349"
  },
  "r376": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "450",
   "URI": "http://asc.fasb.org/topic&trid=2127136"
  },
  "r377": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=124440162&loc=d3e12021-110248"
  },
  "r378": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=124440162&loc=d3e12021-110248"
  },
  "r379": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=124440162&loc=d3e12053-110248"
  },
  "r38": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r380": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(4)",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248"
  },
  "r381": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=123368208&loc=d3e12565-110249"
  },
  "r382": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "460",
   "URI": "http://asc.fasb.org/extlink&oid=123408193&loc=d3e12803-110250"
  },
  "r383": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "19",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=99376301&loc=d3e1398-112600"
  },
  "r384": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601"
  },
  "r385": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S65",
   "SubTopic": "10",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359872&loc=SL124427846-239511"
  },
  "r386": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(i))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r387": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(ii))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r388": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(iii)(A))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r389": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(iii)(B))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r39": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.19-26)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r390": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(iii))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r391": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(4)(iv))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r392": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-01(a)(5))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756"
  },
  "r393": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(i))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r394": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iii)(A)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r395": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iii)(A))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r396": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iii)(B)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r397": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iii)(B))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r398": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iii)(C))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r399": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(4)(iv))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r4": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "105",
   "URI": "http://asc.fasb.org/extlink&oid=124434974&loc=SL124442142-165695"
  },
  "r40": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.22(a)(1))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r400": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.13-02(a)(5))",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756"
  },
  "r401": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r402": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r403": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r404": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r405": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(e)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r406": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(f)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r407": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611"
  },
  "r408": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611"
  },
  "r409": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611"
  },
  "r41": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.22(b))",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r410": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611"
  },
  "r411": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1E",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611"
  },
  "r412": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1E",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611"
  },
  "r413": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1E",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611"
  },
  "r414": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611"
  },
  "r415": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611"
  },
  "r416": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(1)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611"
  },
  "r417": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611"
  },
  "r418": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1I",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611"
  },
  "r419": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(1)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870"
  },
  "r42": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.22)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r420": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(3)",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870"
  },
  "r421": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "69B",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612"
  },
  "r422": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "69C",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612"
  },
  "r423": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "69E",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466577&loc=SL123495743-112612"
  },
  "r424": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "69F",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "470",
   "URI": "http://asc.fasb.org/extlink&oid=123466577&loc=SL123495745-112612"
  },
  "r425": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "470",
   "URI": "http://asc.fasb.org/topic&trid=2208564"
  },
  "r426": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r427": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r428": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r429": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(g)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r43": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.25)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r430": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r431": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(i)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r432": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644"
  },
  "r433": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644"
  },
  "r434": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644"
  },
  "r435": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644"
  },
  "r436": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496180-112644"
  },
  "r437": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644"
  },
  "r438": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644"
  },
  "r439": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644"
  },
  "r44": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.29)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r440": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644"
  },
  "r441": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21463-112644"
  },
  "r442": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21475-112644"
  },
  "r443": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21484-112644"
  },
  "r444": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21506-112644"
  },
  "r445": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21521-112644"
  },
  "r446": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=123467817&loc=d3e21538-112644"
  },
  "r447": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.3-04)",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770"
  },
  "r448": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655"
  },
  "r449": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "505",
   "URI": "http://asc.fasb.org/extlink&oid=6405834&loc=d3e23315-112656"
  },
  "r45": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.29,30)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r450": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "505",
   "URI": "http://asc.fasb.org/topic&trid=2208762"
  },
  "r451": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130551-203045"
  },
  "r452": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045"
  },
  "r453": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045"
  },
  "r454": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045"
  },
  "r455": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045"
  },
  "r456": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130554-203045"
  },
  "r457": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(2)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130556-203045"
  },
  "r458": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130558-203045"
  },
  "r459": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130543-203045"
  },
  "r46": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.29-31)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r460": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130545-203045"
  },
  "r461": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123351226&loc=SL49130550-203045"
  },
  "r462": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "91",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "606",
   "URI": "http://asc.fasb.org/extlink&oid=123410239&loc=SL49130690-203046-203046"
  },
  "r463": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "606",
   "URI": "http://asc.fasb.org/topic&trid=49130388"
  },
  "r464": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "15",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "712",
   "URI": "http://asc.fasb.org/extlink&oid=6410066&loc=d3e79218-111664"
  },
  "r465": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "15",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "712",
   "URI": "http://asc.fasb.org/extlink&oid=6410066&loc=d3e79218-111664"
  },
  "r466": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123453770&loc=d3e1703-114919"
  },
  "r467": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123453770&loc=SL108413299-114919"
  },
  "r468": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r469": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r47": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.3,4)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r470": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(10)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r471": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r472": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(3)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r473": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(4)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r474": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(5)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r475": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(6)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r476": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(7)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r477": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(8)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r478": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(9)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r479": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r48": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-02.8)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682"
  },
  "r480": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r481": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r482": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(3)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r483": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(4)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r484": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(5)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r485": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(6)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r486": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(7)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r487": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(8)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r488": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r489": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(5)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r49": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312"
  },
  "r490": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(i)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r491": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(ii)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r492": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iii)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r493": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(01)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r494": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r495": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(A)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r496": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(B)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r497": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(02)(C)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r498": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(iv)(03)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r499": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(e)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r5": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-04(Schedule I))",
   "Topic": "205",
   "URI": "http://asc.fasb.org/extlink&oid=120391182&loc=d3e5864-122674"
  },
  "r50": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312"
  },
  "r500": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(f)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r501": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(g)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r502": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r503": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r504": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r505": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(3)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r506": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(4)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r507": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(5)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r508": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(6)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r509": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(h)(7)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r51": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312"
  },
  "r510": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(i)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r511": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(j)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r512": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(k)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r513": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(k)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r514": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(k)(3)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r515": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(k)(4)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r516": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(l)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r517": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(n)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r518": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(o)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r519": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(p)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r52": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)(2)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312"
  },
  "r520": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(q)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r521": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(r)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r522": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(r)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r523": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920"
  },
  "r524": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2410-114920"
  },
  "r525": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2417-114920"
  },
  "r526": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2439-114920"
  },
  "r527": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r528": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(1)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r529": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(2)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r53": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313"
  },
  "r530": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(3)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r531": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(4)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r532": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(5)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r533": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(6)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r534": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(7)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r535": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920"
  },
  "r536": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123447040&loc=d3e2919-114920"
  },
  "r537": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921"
  },
  "r538": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "18",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=123450688&loc=d3e4587-114921"
  },
  "r539": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "20",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=21916913&loc=d3e273930-122802"
  },
  "r54": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313"
  },
  "r540": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=6412939&loc=d3e15145-114933"
  },
  "r541": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "60",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=66047640&loc=d3e39622-114963"
  },
  "r542": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "60",
   "Subparagraph": "(c)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=6414203&loc=d3e39689-114964"
  },
  "r543": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "60",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964"
  },
  "r544": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "70",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942"
  },
  "r545": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "35",
   "SubTopic": "80",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=29639808&loc=d3e29008-114946"
  },
  "r546": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(a)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947"
  },
  "r547": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947"
  },
  "r548": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(c)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947"
  },
  "r549": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947"
  },
  "r55": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313"
  },
  "r550": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=d3e29149-114947"
  },
  "r551": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(d)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450657-114947"
  },
  "r552": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(a)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450673-114947"
  },
  "r553": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450673-114947"
  },
  "r554": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(c)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450673-114947"
  },
  "r555": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(b)",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947"
  },
  "r556": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "80",
   "Topic": "715",
   "URI": "http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948"
  },
  "r557": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "715",
   "URI": "http://asc.fasb.org/topic&trid=2235017"
  },
  "r558": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "35",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=123468992&loc=d3e4534-113899"
  },
  "r559": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r56": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226038-175313"
  },
  "r560": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r561": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r562": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901"
  },
  "r563": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r564": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(3)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r565": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a),(g)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r566": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b),(f)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r567": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r568": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r569": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r57": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "22",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313"
  },
  "r570": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(i)-(ii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r571": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r572": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r573": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r574": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(3)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r575": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)(iv)(3)-(4)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r576": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r577": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(i)-(ii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r578": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(iii)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r579": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(iii)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r58": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313"
  },
  "r580": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)(iii)(3)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r581": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r582": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r583": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r584": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r585": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r586": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r587": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r588": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)(ii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r589": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)(iii)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r59": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=99393222&loc=SL20226003-175313"
  },
  "r590": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)(iv)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r591": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(g)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r592": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r593": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)(1)(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r594": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(i)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r595": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901"
  },
  "r596": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=120381028&loc=SL79508275-113901"
  },
  "r597": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r598": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r599": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r6": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "205",
   "URI": "http://asc.fasb.org/extlink&oid=109222650&loc=d3e1361-107760"
  },
  "r60": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r600": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r601": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r602": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(f)(1)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r603": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r604": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(g)(2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333"
  },
  "r605": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 14.D.2)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809"
  },
  "r606": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 14.F)",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809"
  },
  "r607": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=122142933&loc=d3e11149-113907"
  },
  "r608": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "718",
   "URI": "http://asc.fasb.org/extlink&oid=122142933&loc=d3e11178-113907"
  },
  "r609": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "718",
   "URI": "http://asc.fasb.org/topic&trid=2228938"
  },
  "r61": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r610": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "35",
   "Subparagraph": "(b)",
   "Topic": "720",
   "URI": "http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848"
  },
  "r611": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123427490&loc=SL37586934-109318"
  },
  "r612": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123427490&loc=d3e32247-109318"
  },
  "r613": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123427490&loc=d3e32280-109318"
  },
  "r614": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32672-109319"
  },
  "r615": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319"
  },
  "r616": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319"
  },
  "r617": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32718-109319"
  },
  "r618": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32718-109319"
  },
  "r619": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32718-109319"
  },
  "r62": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r620": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r621": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r622": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r623": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(3)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r624": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r625": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319"
  },
  "r626": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319"
  },
  "r627": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "19",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32840-109319"
  },
  "r628": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319"
  },
  "r629": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319"
  },
  "r63": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(i)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r630": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319"
  },
  "r631": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319"
  },
  "r632": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32847-109319"
  },
  "r633": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319"
  },
  "r634": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32621-109319"
  },
  "r635": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32632-109319"
  },
  "r636": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32639-109319"
  },
  "r637": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32639-109319"
  },
  "r638": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=121826272&loc=d3e32639-109319"
  },
  "r639": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "217",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=124434304&loc=d3e36027-109320"
  },
  "r64": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(i-k)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r640": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123459177&loc=SL121830611-158277"
  },
  "r641": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123459177&loc=SL121830611-158277"
  },
  "r642": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)(2)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123459177&loc=SL121830611-158277"
  },
  "r643": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(d)(3)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123459177&loc=SL121830611-158277"
  },
  "r644": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB TOPIC 6.I.5.Q1)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r645": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB TOPIC 6.I.7)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r646": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.I.7)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r647": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.I.Fact.1)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r648": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.I.Fact.2)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r649": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.I.Fact.3)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r65": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(j)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r650": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 6.I.Fact.4)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817"
  },
  "r651": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 11.C)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817"
  },
  "r652": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123586238&loc=d3e39076-109324"
  },
  "r653": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123586238&loc=d3e38679-109324"
  },
  "r654": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=123586238&loc=d3e38679-109324"
  },
  "r655": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "270",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338"
  },
  "r656": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "740",
   "URI": "http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331"
  },
  "r657": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "740",
   "URI": "http://asc.fasb.org/topic&trid=2144680"
  },
  "r658": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "38",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "805",
   "URI": "http://asc.fasb.org/extlink&oid=123410050&loc=d3e5504-128473"
  },
  "r659": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "15",
   "SubTopic": "10",
   "Subparagraph": "(f)(2)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=116873149&loc=d3e923-111674"
  },
  "r66": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580"
  },
  "r660": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123454820&loc=d3e5283-111683"
  },
  "r661": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123454820&loc=SL4568447-111683"
  },
  "r662": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "16",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123454820&loc=SL4568740-111683"
  },
  "r663": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "19",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123454820&loc=SL4569616-111683"
  },
  "r664": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988"
  },
  "r665": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "25",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988"
  },
  "r666": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=d3e5614-111684"
  },
  "r667": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r668": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r669": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c),(3)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684"
  },
  "r67": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=d3e637-108580"
  },
  "r670": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bb)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5710-111685"
  },
  "r671": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5710-111685"
  },
  "r672": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5710-111685"
  },
  "r673": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "b",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5728-111685"
  },
  "r674": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5728-111685"
  },
  "r675": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=SL6759159-111685"
  },
  "r676": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=SL6759159-111685"
  },
  "r677": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685"
  },
  "r678": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "d",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685"
  },
  "r679": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685"
  },
  "r68": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=d3e640-108580"
  },
  "r680": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "9",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=123419778&loc=SL6228884-111685"
  },
  "r681": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4I",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=120409616&loc=SL4590271-111686"
  },
  "r682": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4J",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=120409616&loc=SL4591551-111686"
  },
  "r683": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4K",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "810",
   "URI": "http://asc.fasb.org/extlink&oid=120409616&loc=SL4591552-111686"
  },
  "r684": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "810",
   "URI": "http://asc.fasb.org/topic&trid=2197479"
  },
  "r685": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "83",
   "Publisher": "FASB",
   "Section": "15",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125514181&loc=d3e34841-113949"
  },
  "r686": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958"
  },
  "r687": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5579240-113959"
  },
  "r688": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959"
  },
  "r689": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959"
  },
  "r69": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=d3e681-108580"
  },
  "r690": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959"
  },
  "r691": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)(i)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41620-113959"
  },
  "r692": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)(ii)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41620-113959"
  },
  "r693": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41620-113959"
  },
  "r694": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41638-113959"
  },
  "r695": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959"
  },
  "r696": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959"
  },
  "r697": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959"
  },
  "r698": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a),(c)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959"
  },
  "r699": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959"
  },
  "r7": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "205",
   "URI": "http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760"
  },
  "r70": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580"
  },
  "r700": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959"
  },
  "r701": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959"
  },
  "r702": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4C",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959"
  },
  "r703": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4C",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959"
  },
  "r704": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4C",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959"
  },
  "r705": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4C",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959"
  },
  "r706": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959"
  },
  "r707": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(2)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959"
  },
  "r708": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(4)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959"
  },
  "r709": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959"
  },
  "r71": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=d3e689-108580"
  },
  "r710": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624177-113959"
  },
  "r711": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4E",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624181-113959"
  },
  "r712": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5624186-113959"
  },
  "r713": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4K",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5708775-113959"
  },
  "r714": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4K",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)(4)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5708775-113959"
  },
  "r715": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4K",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=SL5708775-113959"
  },
  "r716": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41675-113959"
  },
  "r717": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=125515794&loc=d3e41678-113959"
  },
  "r718": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "182",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123421605&loc=SL5629052-113961"
  },
  "r719": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "25",
   "Subparagraph": "(a)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986"
  },
  "r72": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL34724391-108580"
  },
  "r720": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "25",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986"
  },
  "r721": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Subparagraph": "(f)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123477628&loc=d3e90205-114008"
  },
  "r722": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(a)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r723": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(a)(2)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r724": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(a)(3)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r725": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(b)(1)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r726": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(b)(2)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r727": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(c)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r728": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(d)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r729": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(e)(2)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r73": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669619-108580"
  },
  "r730": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(e)(3)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r731": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(e)(4)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r732": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(f)",
   "Topic": "815",
   "URI": "http://asc.fasb.org/extlink&oid=123482062&loc=SL123482106-238011"
  },
  "r733": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "815",
   "URI": "http://asc.fasb.org/topic&trid=2229140"
  },
  "r734": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "54B",
   "Publisher": "FASB",
   "Section": "35",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=122636397&loc=SL7495116-110257"
  },
  "r735": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r736": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r737": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bb)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r738": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bbb)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r739": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bbb)(1)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r74": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669619-108580"
  },
  "r740": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(bbb)(2)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r741": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r742": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r743": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(h)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r744": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258"
  },
  "r745": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=d3e19279-110258"
  },
  "r746": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=SL6742756-110258"
  },
  "r747": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=SL6742756-110258"
  },
  "r748": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=123874694&loc=SL6742756-110258"
  },
  "r749": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "60",
   "SubTopic": "10",
   "Topic": "820",
   "URI": "http://asc.fasb.org/extlink&oid=7493716&loc=d3e21868-110260"
  },
  "r75": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669619-108580"
  },
  "r750": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "25",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594681&loc=d3e12762-108607"
  },
  "r751": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740"
  },
  "r752": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594809&loc=d3e13220-108610"
  },
  "r753": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13279-108611"
  },
  "r754": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611"
  },
  "r755": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13467-108611"
  },
  "r756": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13476-108611"
  },
  "r757": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13531-108611"
  },
  "r758": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "21",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123594938&loc=d3e13537-108611"
  },
  "r759": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(f)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612"
  },
  "r76": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669625-108580"
  },
  "r760": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "28",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612"
  },
  "r761": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL120254526-165497"
  },
  "r762": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL120254526-165497"
  },
  "r763": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL121967933-165497"
  },
  "r764": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL121967933-165497"
  },
  "r765": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)(1)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL121967933-165497"
  },
  "r766": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(c)(2)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL121967933-165497"
  },
  "r767": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL122642865-165497"
  },
  "r768": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "825",
   "URI": "http://asc.fasb.org/extlink&oid=123597120&loc=SL122642865-165497"
  },
  "r769": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=125521441&loc=d3e30690-110894"
  },
  "r77": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124509347&loc=SL7669625-108580"
  },
  "r770": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=124440516&loc=d3e30840-110895"
  },
  "r771": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "17",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900"
  },
  "r772": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r773": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(b)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r774": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(c)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r775": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Subparagraph": "(d)",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r776": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "20",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900"
  },
  "r777": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "830",
   "URI": "http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901"
  },
  "r778": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391"
  },
  "r779": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=124435984&loc=d3e28541-108399"
  },
  "r78": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124431353&loc=SL116659661-227067"
  },
  "r780": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=124435984&loc=d3e28551-108399"
  },
  "r781": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399"
  },
  "r782": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=124429444&loc=SL124452920-239629"
  },
  "r783": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "8",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "30",
   "Topic": "835",
   "URI": "http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400"
  },
  "r784": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "840",
   "URI": "http://asc.fasb.org/extlink&oid=123386454&loc=d3e45280-112737"
  },
  "r785": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)(4)",
   "Topic": "840",
   "URI": "http://asc.fasb.org/extlink&oid=123392090&loc=d3e45377-112738"
  },
  "r786": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123391704&loc=SL77918638-209977"
  },
  "r787": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123391704&loc=SL77918643-209977"
  },
  "r788": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)(3)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980"
  },
  "r789": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(3)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918673-209980"
  },
  "r79": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124431353&loc=SL124442407-227067"
  },
  "r790": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(d)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980"
  },
  "r791": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(e)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980"
  },
  "r792": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(g)(1)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980"
  },
  "r793": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(g)(2)",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980"
  },
  "r794": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918686-209980"
  },
  "r795": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123408670&loc=SL77918701-209980"
  },
  "r796": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "53",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "20",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123414884&loc=SL77918982-209971"
  },
  "r797": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=123420820&loc=SL77919311-209978"
  },
  "r798": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=124258985&loc=SL77919391-209981"
  },
  "r799": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=124258985&loc=SL77919372-209981"
  },
  "r8": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765"
  },
  "r80": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124431353&loc=SL124442411-227067"
  },
  "r800": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Topic": "842",
   "URI": "http://asc.fasb.org/extlink&oid=124258985&loc=SL77919379-209981"
  },
  "r801": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "848",
   "URI": "http://asc.fasb.org/extlink&oid=122150657&loc=SL122150809-237846"
  },
  "r802": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r803": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r804": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(c)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r805": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(d)",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864"
  },
  "r806": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39599-107864"
  },
  "r807": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864"
  },
  "r808": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "850",
   "URI": "http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864"
  },
  "r809": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "850",
   "URI": "http://asc.fasb.org/topic&trid=2122745"
  },
  "r81": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124431353&loc=SL124452729-227067"
  },
  "r810": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "14",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "852",
   "URI": "http://asc.fasb.org/extlink&oid=124437977&loc=d3e55792-112764"
  },
  "r811": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "852",
   "URI": "http://asc.fasb.org/extlink&oid=124433192&loc=SL2890621-112765"
  },
  "r812": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "852",
   "URI": "http://asc.fasb.org/extlink&oid=124433192&loc=SL2890621-112765"
  },
  "r813": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "10",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "852",
   "URI": "http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766"
  },
  "r814": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)(i)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r815": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)(ii)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r816": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r817": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r818": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r819": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(bb)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r82": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "10",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=124507222&loc=d3e1436-108581"
  },
  "r820": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r821": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r822": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719"
  },
  "r823": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r824": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r825": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(b)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r826": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719"
  },
  "r827": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(c)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719"
  },
  "r828": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "30",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728"
  },
  "r829": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(b)(1)(i)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729"
  },
  "r83": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(1)(e))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868656-224227"
  },
  "r830": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(c)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729"
  },
  "r831": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "30",
   "Subparagraph": "(a)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729"
  },
  "r832": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(b)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122596-111746"
  },
  "r833": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122625-111746"
  },
  "r834": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122625-111746"
  },
  "r835": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122625-111746"
  },
  "r836": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(4)(i)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122625-111746"
  },
  "r837": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r838": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r839": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r84": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(210.5-03(11))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r840": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(4)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r841": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(5)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r842": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(6)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r843": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(a)(7)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r844": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(b)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r845": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(e)(1)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r846": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(e)(2)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r847": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "50",
   "Subparagraph": "(e)(3)",
   "Topic": "860",
   "URI": "http://asc.fasb.org/extlink&oid=125521744&loc=d3e122739-111746"
  },
  "r848": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "910",
   "URI": "http://asc.fasb.org/extlink&oid=123353855&loc=SL119991595-234733"
  },
  "r849": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SAB Topic 11.L)",
   "Topic": "924",
   "URI": "http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856"
  },
  "r85": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(1))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r850": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Topic": "926",
   "URI": "http://asc.fasb.org/extlink&oid=120154696&loc=d3e54445-107959"
  },
  "r851": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "926",
   "URI": "http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079"
  },
  "r852": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "20",
   "Subparagraph": "(b)",
   "Topic": "926",
   "URI": "http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079"
  },
  "r853": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "20",
   "Subparagraph": "(c)",
   "Topic": "926",
   "URI": "http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079"
  },
  "r854": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "340",
   "Topic": "928",
   "URI": "http://asc.fasb.org/extlink&oid=6473545&loc=d3e61844-108004"
  },
  "r855": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "05",
   "SubTopic": "20",
   "Topic": "940",
   "URI": "http://asc.fasb.org/extlink&oid=123369997&loc=d3e40544-110947"
  },
  "r856": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "SubTopic": "320",
   "Topic": "940",
   "URI": "http://asc.fasb.org/subtopic&trid=2176304"
  },
  "r857": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "210",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117340910&loc=d3e59706-112781"
  },
  "r858": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(1))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r859": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(10)(1))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r86": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(12))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r860": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(10))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r861": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(11))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r862": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(13))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r863": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(15)(2))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r864": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(16))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r865": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(23))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r866": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(4))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r867": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(5))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r868": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(6))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r869": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(7)(2))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r87": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(21))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r870": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03(7)(e)(1)(i))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r871": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.12)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r872": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.13(1))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r873": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.14)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r874": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.15(5))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r875": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.15)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r876": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.16)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r877": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.2)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r878": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.4)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r879": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.5)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r88": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(22))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r880": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.7(e))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r881": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.7)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r882": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.9-03.9)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878"
  },
  "r883": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(13)(f))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r884": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(13))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r885": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(23))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r886": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(24))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r887": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04(27))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r888": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.1)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r889": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.1-5)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r89": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(25))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r890": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.10)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r891": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.11)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r892": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.12)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r893": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.13(a),(b))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r894": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.13)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r895": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.14(b))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r896": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.14(d))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r897": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.14)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r898": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.4)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r899": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.6)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r9": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(e)",
   "Topic": "210",
   "URI": "http://asc.fasb.org/extlink&oid=124098289&loc=d3e6812-107765"
  },
  "r90": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(7)(c))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r900": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.7)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r901": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.8)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r902": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.9-04.9)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260"
  },
  "r903": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "230",
   "Subparagraph": "(b)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123398031&loc=d3e60009-112784"
  },
  "r904": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "230",
   "Subparagraph": "(c)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123398031&loc=d3e60009-112784"
  },
  "r905": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "235",
   "Subparagraph": "(SX 210.9-05(a))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884"
  },
  "r906": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "235",
   "Subparagraph": "(SX 210.9-05(b)(1))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884"
  },
  "r907": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "235",
   "Subparagraph": "(SX 210.9-05(b)(2))",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884"
  },
  "r908": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "320",
   "Subparagraph": "(b)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599081&loc=d3e62557-112803"
  },
  "r909": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "320",
   "Subparagraph": "(a)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599081&loc=SL120269850-112803"
  },
  "r91": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(9)(a))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r910": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "5",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "320",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599081&loc=d3e62652-112803"
  },
  "r911": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "SubTopic": "320",
   "Topic": "942",
   "URI": "http://asc.fasb.org/subtopic&trid=2209399"
  },
  "r912": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "325",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599499&loc=d3e63345-112809"
  },
  "r913": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "360",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=124429447&loc=SL124453093-239630"
  },
  "r914": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "405",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817"
  },
  "r915": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "405",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818"
  },
  "r916": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "470",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822"
  },
  "r917": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "470",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599511&loc=d3e64684-112823"
  },
  "r918": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "470",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599511&loc=d3e64702-112823"
  },
  "r919": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "3",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "470",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823"
  },
  "r92": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03(b)(4))",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r920": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(a)(1)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r921": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(a)(2)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r922": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(b)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r923": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(c)(1)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r924": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(c)(2)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r925": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Subparagraph": "(e)",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826"
  },
  "r926": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958569-112826"
  },
  "r927": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1B",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826"
  },
  "r928": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1D",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958573-112826"
  },
  "r929": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1F",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "505",
   "Topic": "942",
   "URI": "http://asc.fasb.org/extlink&oid=117337116&loc=SL5958575-112826"
  },
  "r93": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r930": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(15)(b)(2))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r931": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(16))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r932": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(1)(b))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r933": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(1)(g))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r934": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(10))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r935": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(12))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r936": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(16)(a)(1))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r937": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(16))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r938": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(23)(a)(3))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r939": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(23)(a)(4))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r94": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03.3)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r940": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(25))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r941": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03(a)(8))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r942": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03.1(g))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r943": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03.15(a))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r944": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "210",
   "Subparagraph": "(SX 210.7-03.3)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910"
  },
  "r945": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(10))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r946": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(19))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r947": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(20))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r948": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(23))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r949": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(4))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r95": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "10",
   "Subparagraph": "(SX 210.5-03.6)",
   "Topic": "220",
   "URI": "http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227"
  },
  "r950": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "220",
   "Subparagraph": "(SX 210.7-04(9))",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263"
  },
  "r951": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4H",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=116884468&loc=SL65671331-158438"
  },
  "r952": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7A",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "40",
   "Subparagraph": "(d)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124506351&loc=SL117782755-158439"
  },
  "r953": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "13H",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "40",
   "Subparagraph": "(a)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124504033&loc=SL117783719-158441"
  },
  "r954": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "29F",
   "Publisher": "FASB",
   "Section": "55",
   "SubTopic": "40",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124504033&loc=SL117819544-158441"
  },
  "r955": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(a)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r956": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(b)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r957": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(e)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r958": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(f)(1)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r959": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(f)(2)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r96": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "Topic": "220",
   "URI": "http://asc.fasb.org/topic&trid=2134417"
  },
  "r960": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(1)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r961": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(i)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r962": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(ii)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r963": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(iii)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r964": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(g)(2)(iv)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r965": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(h)(1)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r966": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "65",
   "SubTopic": "40",
   "Subparagraph": "(h)(2)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641"
  },
  "r967": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "80",
   "Subparagraph": "(e)",
   "Topic": "944",
   "URI": "http://asc.fasb.org/extlink&oid=124508989&loc=d3e19393-158473"
  },
  "r968": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "15",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "20",
   "Subparagraph": "(a)",
   "Topic": "946",
   "URI": "http://asc.fasb.org/extlink&oid=66023616&loc=SL35737432-115832"
  },
  "r969": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "320",
   "Subparagraph": "(SX 210.12-12)",
   "Topic": "946",
   "URI": "http://asc.fasb.org/extlink&oid=122147990&loc=d3e611133-123010"
  },
  "r97": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "11",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3151-108585"
  },
  "r970": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "320",
   "Subparagraph": "(SX 210.12-15(Column B))",
   "Topic": "946",
   "URI": "http://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010"
  },
  "r971": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "320",
   "Subparagraph": "(SX 210.12-15(Column C))",
   "Topic": "946",
   "URI": "http://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010"
  },
  "r972": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "320",
   "Subparagraph": "(SX 210.12-15(Column D))",
   "Topic": "946",
   "URI": "http://asc.fasb.org/extlink&oid=122147990&loc=d3e611379-123010"
  },
  "r973": {
   "Name": "Accounting Standards Codification",
   "Publisher": "FASB",
   "SubTopic": "320",
   "Topic": "946",
   "URI": "http://asc.fasb.org/subtopic&trid=2324412"
  },
  "r974": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "310",
   "Topic": "948",
   "URI": "http://asc.fasb.org/extlink&oid=124265262&loc=d3e48678-111004"
  },
  "r975": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "310",
   "Subparagraph": "(SX 210.12-29(Footnote 4))",
   "Topic": "948",
   "URI": "http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014"
  },
  "r976": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "4",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "210",
   "Topic": "954",
   "URI": "http://asc.fasb.org/extlink&oid=120413173&loc=SL6242262-115580"
  },
  "r977": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "210",
   "Topic": "954",
   "URI": "http://asc.fasb.org/extlink&oid=120413209&loc=SL6242269-115581"
  },
  "r978": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "2",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "310",
   "Topic": "954",
   "URI": "http://asc.fasb.org/extlink&oid=123364037&loc=d3e3115-115594"
  },
  "r979": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "440",
   "Subparagraph": "(a)",
   "Topic": "954",
   "URI": "http://asc.fasb.org/extlink&oid=6491277&loc=d3e6429-115629"
  },
  "r98": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(a)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585"
  },
  "r980": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "360",
   "Subparagraph": "(d)",
   "Topic": "958",
   "URI": "http://asc.fasb.org/extlink&oid=120429125&loc=d3e99779-112916"
  },
  "r981": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "6",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "360",
   "Topic": "958",
   "URI": "http://asc.fasb.org/extlink&oid=120429125&loc=d3e99893-112916"
  },
  "r982": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "7",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "360",
   "Topic": "958",
   "URI": "http://asc.fasb.org/extlink&oid=120429125&loc=SL120174063-112916"
  },
  "r983": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "S99",
   "SubTopic": "360",
   "Subparagraph": "(SX 210.12-28(Footnote 4))",
   "Topic": "970",
   "URI": "http://asc.fasb.org/extlink&oid=120402810&loc=d3e638233-123024"
  },
  "r984": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "310",
   "Subparagraph": "(c)",
   "Topic": "976",
   "URI": "http://asc.fasb.org/extlink&oid=6497875&loc=d3e22274-108663"
  },
  "r985": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "1",
   "Publisher": "FASB",
   "Section": "50",
   "SubTopic": "310",
   "Subparagraph": "(b)",
   "Topic": "978",
   "URI": "http://asc.fasb.org/extlink&oid=123360121&loc=d3e27327-108691"
  },
  "r986": {
   "Name": "Exchange Act",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "b"
  },
  "r987": {
   "Name": "Exchange Act",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "b-2"
  },
  "r988": {
   "Name": "Exchange Act",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "12",
   "Subsection": "d1-1"
  },
  "r989": {
   "Name": "Form 10-K",
   "Number": "249",
   "Publisher": "SEC",
   "Section": "310"
  },
  "r99": {
   "Name": "Accounting Standards Codification",
   "Paragraph": "12",
   "Publisher": "FASB",
   "Section": "45",
   "SubTopic": "10",
   "Subparagraph": "(b)",
   "Topic": "230",
   "URI": "http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585"
  },
  "r990": {
   "Name": "Form 20-F",
   "Number": "249",
   "Publisher": "SEC",
   "Section": "220",
   "Subsection": "f"
  },
  "r991": {
   "Name": "Form 40-F",
   "Number": "249",
   "Publisher": "SEC",
   "Section": "240",
   "Subsection": "f"
  },
  "r992": {
   "Name": "Forms 10-K, 10-Q, 20-F",
   "Number": "240",
   "Publisher": "SEC",
   "Section": "13",
   "Subsection": "a-1"
  },
  "r993": {
   "Name": "Industry Guide",
   "Number": "3",
   "Paragraph": "D-E",
   "Publisher": "SEC",
   "Section": "V"
  },
  "r994": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(a)",
   "Publisher": "SEC",
   "Section": "1402"
  },
  "r995": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(1)"
  },
  "r996": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(2)"
  },
  "r997": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(3)"
  },
  "r998": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(4)"
  },
  "r999": {
   "Name": "Regulation S-K (SK)",
   "Number": "229",
   "Paragraph": "(b)",
   "Publisher": "SEC",
   "Section": "1402",
   "Subparagraph": "(5)"
  }
 },
 "version": "2.1"
}
