XML 95 R79.htm IDEA: XBRL DOCUMENT
v3.20.4

Investment Securities (Summary Of Available For Sale Investment Securities By Maturity Groupings) (Details) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 12,097,533,000 | $ 8,435,531,000
Debt Securities, Available-for-sale, Fair Value |  | 12,449,264,000 | 8,571,626,000
U.S. Government And Federal Agency Obligations [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 775,592,000 | 827,861,000
Debt Securities, Available-for-sale, Fair Value |  | $ 838,059,000 | 851,776,000
Weighted Average Yield | [1] | 1.66% |
U.S. Government And Federal Agency Obligations [Member] | Maturity Within 1 Year [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 59,627,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 59,641,000 |
Weighted Average Yield | [1] | 0.90% |
U.S. Government And Federal Agency Obligations [Member] | Maturity After 1 But Within 5 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 490,333,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 521,540,000 |
Weighted Average Yield | [1] | 2.22% |
U.S. Government And Federal Agency Obligations [Member] | Maturity After 5 But Within 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 225,632,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 256,878,000 |
Weighted Average Yield | [1] | 0.65% |
US Government-sponsored Enterprise Debt Securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 50,803,000 | 138,734,000
Debt Securities, Available-for-sale, Fair Value |  | $ 54,485,000 | 139,277,000
Weighted Average Yield |  | 2.32% |
US Government-sponsored Enterprise Debt Securities [Member] | Maturity Within 1 Year [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 14,993,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 14,916,000 |
Weighted Average Yield |  | 2.15% |
US Government-sponsored Enterprise Debt Securities [Member] | Maturity After 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 35,810,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 39,569,000 |
Weighted Average Yield |  | 2.39% |
State and municipal obligations [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 1,968,006,000 | 1,225,532,000
Debt Securities, Available-for-sale, Fair Value |  | $ 2,045,099,000 | 1,267,927,000
Weighted Average Yield |  | 2.06% |
State and municipal obligations [Member] | Maturity Within 1 Year [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 34,694,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 34,866,000 |
Weighted Average Yield |  | 2.35% |
State and municipal obligations [Member] | Maturity After 1 But Within 5 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 865,165,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 901,201,000 |
Weighted Average Yield |  | 2.20% |
State and municipal obligations [Member] | Maturity After 5 But Within 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 595,510,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 627,063,000 |
Weighted Average Yield |  | 2.01% |
State and municipal obligations [Member] | Maturity After 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 472,637,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 481,969,000 |
Weighted Average Yield |  | 1.84% |
Agency mortgage-backed securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 6,557,098,000 | 3,893,247,000
Debt Securities, Available-for-sale, Fair Value |  | $ 6,712,085,000 | 3,937,964,000
Weighted Average Yield |  | 2.00% |
Non-agency mortgage-backed securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 358,074,000 | 796,451,000
Debt Securities, Available-for-sale, Fair Value |  | $ 361,074,000 | 809,782,000
Weighted Average Yield |  | 2.39% |
Asset-backed Securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 1,853,791,000 | 1,228,151,000
Debt Securities, Available-for-sale, Fair Value |  | $ 1,882,243,000 | 1,233,489,000
Weighted Average Yield |  | 1.53% |
Total mortgage and asset-backed securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 8,768,963,000 | 5,917,849,000
Debt Securities, Available-for-sale, Fair Value |  | $ 8,955,402,000 | 5,981,235,000
Weighted Average Yield |  | 1.92% |
Other Debt Securities [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | $ 534,169,000 | 325,555,000
Debt Securities, Available-for-sale, Fair Value |  | 556,219,000 | $ 331,411,000
Other Debt Securities [Member] | Maturity Within 1 Year [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 8,041,000 |
Debt Securities, Available-for-sale, Fair Value |  | 8,118,000 |
Other Debt Securities [Member] | Maturity After 1 But Within 5 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 254,173,000 |
Debt Securities, Available-for-sale, Fair Value |  | 265,486,000 |
Other Debt Securities [Member] | Maturity After 5 But Within 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 240,759,000 |
Debt Securities, Available-for-sale, Fair Value |  | 250,036,000 |
Other Debt Securities [Member] | Maturity After 10 Years [Member] |  |  |
Investment [Line Items] |  |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 31,196,000 |
Debt Securities, Available-for-sale, Fair Value |  | $ 32,579,000 |
[1] | Rate does not reflect inflation adjustment on inflation-protected securities

X
- Definition Available-for-sale securities, weighted average yield, percentage + References No definition available. + Details
Name: | cbsh_AvailableForSaleSecuritiesWeightedAverageYieldPercentage
Namespace Prefix: | cbsh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition 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. + References No definition available. + Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cbsh_InvestmentMaturityAxis=cbsh_AvailableForSaleSecuritiesMaturityWithin1YearMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cbsh_InvestmentMaturityAxis=cbsh_AvailableForSaleSecuritiesMaturityAfter1ButWithin5YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cbsh_InvestmentMaturityAxis=cbsh_AvailableForSaleSecuritiesMaturityAfter5ButWithin10YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cbsh_InvestmentMaturityAxis=cbsh_AvailableForSaleMaturityAfter10YearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=cbsh_AgencyMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=cbsh_NonAgencyMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=cbsh_TotalMortgageAndAssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |