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Loans (Narrative) (Detail) (USD $) | 12 Months Ended |
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Dec. 31, 2014 Item | Dec. 31, 2013 | Dec. 31, 2012 | Nov. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Concentration of loans in a single industry in excess of ten percent | 0.00%cfr_Concentrationofloansinasingleindustryinexcessoftenpercent | 0.00%cfr_Concentrationofloansinasingleindustryinexcessoftenpercent |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | $ 8,916,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 | $ 14,833,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 | $ 2,316,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 |
Maximum loan-to-value percentage on home equity loans | 80.00%cfr_MaximumLoanToValuePercentageOnHomeEquityLoans |  |  |
Maximum percentage loan related to single industry | 10.00%cfr_MaximumPercentageOfLoanRelatedToSingleIndustry | 10.00%cfr_MaximumPercentageOfLoanRelatedToSingleIndustry |  |
Commercial and industrial loans related to overdraft for correspondent bank customer | 7,700,000 us-gaap_BankOverdrafts | 6,800,000 us-gaap_BankOverdrafts |  |
Minimum number of days to be considered past due | 90 days |  |  |
Troubled debt restructurings | 8,339,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 | 11,215,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 | 2,188,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 |
Previously restructured loans past due | 0 cfr_PreviouslyRestructuredLoansPastDue |  |  |
Number of days past due for payment of interest on loans, minimum | 120 days |  |  |
Number of loans with calculated risk of 10 or higher greater than $5 million | 6 cfr_NumberOfLoansWithCalculatedRiskOfTenOrHigher |  |  |
Loan amount threshold | 5,000,000 cfr_LoanAmountThreshold |  |  |
Loan value with weighted-average loan-to-value | 44,400,000 cfr_LoanValueWithWeightedAverageLoanToValue |  |  |
Weighted-average loan-to-value ratio | 53.70%cfr_WeightedAverageLoanToValueRatioPercentage |  |  |
Texas Leading Index economic condition indicator |  | 129.1 cfr_TexasLeadingIndexEconomicConditionIndicator |  | 131.4 cfr_TexasLeadingIndexEconomicConditionIndicator
Maximum origination value of loans which were subject to further refinement of valuation methodology | 1,000,000 cfr_MaximumOriginationValueOfLoansWhichWereSubjectToFurtherRefinementOfValuationMethodology |  |  |
Commercial And Industrial Energy Financing Receivable [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | 0 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember | 528,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember |
Percentage of loans related to a single industry | 16.10%cfr_Percentageofloansrelatedtoasingleindustry / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember | 11.70%cfr_Percentageofloansrelatedtoasingleindustry / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember |  |
Troubled debt restructurings | 0 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember | 531,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember |
Commercial Real Estate Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Percentage of owner-occupied commercial real estate loans | 55.00%cfr_PercentageOfOwnerOccupiedCommercialRealEstateLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateLoansMember |  |  |
Non Accrual Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Troubled debt restructurings | 8,300,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_NonAccrualLoansMember | 10,100,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_NonAccrualLoansMember |  |
Additional interest that would have been recognized on non-accrual loans, net of tax | 1,500,000 us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_NonAccrualLoansMember | 2,200,000 us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_NonAccrualLoansMember | 2,600,000 us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_NonAccrualLoansMember |
Consumer Real Estate Financing Receivable [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | 0 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember |
Troubled debt restructurings | 0 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember | 0 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_ConsumerRealEstateFinancingReceivableMember |
Grade 12 [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
General percentage of valuation allowance in excess of principal balance, maximum | 30.00%cfr_PercentOfValuationAllowanceInExcessOfPrincipalBalanceMaximum / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_GradeTwelveMember |  |  |
Grade 13 [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
General percentage of valuation allowance in excess of principal balance, minimum | 30.00%cfr_PercentOfValuationAllowanceInExcessOfPrincipalBalanceMinimum / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_GradeThirteenMember |  |  |
Commercial and Industrial, Other Commercial [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | 5,795,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember | 6,334,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember | 1,602,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember |
Troubled debt restructurings | 5,391,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember | 4,937,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember | 1,478,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember |
Amount charged off related to loans restructured | 627,000 cfr_ChargeOffOfPreviouslyRestructuresLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember |  |  |
Number of days past due for payment of interest on loans, minimum | 180 days |  |  |
Commercial and Industrial, Other Commercial [Member] | Commercial Portfolio Segment [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | 2,700,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember / us-gaap_FinancingReceivableTroubledDebtRestructuringAxis = us-gaap_CommercialPortfolioSegmentMember |  |  |
Commercial Real Estate Buildings Land And Other Financing Receivable [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | 3,121,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember | 7,964,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember | 714,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember |
Troubled debt restructurings | 2,948,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember | 5,747,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember | 710,000 us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember |
Amount charged off related to loans restructured | 0 cfr_ChargeOffOfPreviouslyRestructuresLoans / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember |  |  |
Previously Restructured Loans Moved to OREO | 500,000 cfr_PreviouslyRestructuredLoansMovedtoOREO / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember |  |  |
Commercial Real Estate Buildings Land And Other Financing Receivable [Member] | Commercial Real Estate Portfolio Segment [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing Receivable, Modifications, Pre-Modification Recorded Investment | $ 2,900,000 us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember / us-gaap_FinancingReceivableTroubledDebtRestructuringAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |  |

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- Definition Carrying value as of the balance sheet date of payments made in excess of existing cash balances, which will be honored by the bank but reflected as a loan to the entity. Overdrafts generally have a very short time frame for correction or repayment and are therefore more similar to short-term bank financing than trade financing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Current Liabilities -URI http://asc.fasb.org/extlink&oid=6509677 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=28361426&loc=d3e1243-112600 + Details
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