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Loans - Unallocated Portion of Allowance for Loan Losses (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 | Dec. 31, 2013
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Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | $ 105,708 us-gaap_LoansAndLeasesReceivableAllowance | $ 99,542 us-gaap_LoansAndLeasesReceivableAllowance | $ 95,156 us-gaap_LoansAndLeasesReceivableAllowance | $ 92,438 us-gaap_LoansAndLeasesReceivableAllowance
Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 63,905 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember | 59,604 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember |  |
Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,475 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember | 1,680 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember |  |
Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 14,347 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember | 13,477 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember |  |
Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,996 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember | 3,093 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember |  |
Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 6,433 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember | 2,492 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember |  |
Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 4,545 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember | 3,807 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember |  |
Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 7,102 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember | 5,305 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember |  |
Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 3,002 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember | 2,782 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember |  |
Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 3,076 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember | 2,164 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember |  |
Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 7,846 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember | 7,906 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember |  |
Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | (13,684)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember | (15,837)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember |  |
General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 4,665 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember | 13,069 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember |  |
Commercial and Industrial [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 64,713 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 59,192 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 57,054 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 52,790 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember
Commercial and Industrial [Member] | Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 35,339 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 32,421 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,404 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 1,613 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 7,263 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 6,773 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,762 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 3,090 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 5,903 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 2,114 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,690 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 2,248 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 5,395 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 3,958 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,116 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 1,907 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,168 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 1,483 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,043 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 2,110 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | (5,199)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | (6,234)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial and Industrial [Member] | General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,829 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember | 7,709 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialPortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 27,105 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 27,163 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 21,020 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 22,590 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial Real Estate Portfolio Segment [Member] | Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 14,620 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 14,684 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 71 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 67 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 3,546 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 3,547 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 234 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 3 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 530 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 378 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,855 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 1,559 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,707 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 1,347 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 886 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 875 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 908 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 681 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,261 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 2,284 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | (698)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | (1,800)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Commercial Real Estate Portfolio Segment [Member] | General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,185 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember | 3,538 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_CommercialRealEstatePortfolioSegmentMember |  |
Consumer Real Estate [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 4,907 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 5,178 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 4,533 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 5,230 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember
Consumer Real Estate [Member] | Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,046 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 2,017 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 478 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 474 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 2,364 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 2,336 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | (211)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | (364)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer Real Estate [Member] | General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 230 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember | 715 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ResidentialPortfolioSegmentMember |  |
Consumer and Other [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 8,983 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 8,009 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 5,691 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 5,010 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember
Consumer and Other [Member] | Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 11,900 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 10,482 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 3,060 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 2,683 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 1,178 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 1,176 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | (7,576)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | (7,439)us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Consumer and Other [Member] | General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 421 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember | 1,107 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_ConsumerPortfolioSegmentMember |  |
Unallocated [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 6,858 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 6,818 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember
Unallocated [Member] | Historical Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HistoricalValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Specific Valuation Allowances [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_SpecificValuationAllowancesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Environmental Risk Adjustment [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_EnvironmentalRiskAdjustmentMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Distressed Industries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_DistressedIndustriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Excessive Industry Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_ExcessiveIndustryConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Large Relationship Concentrations [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LargeRelationshipConcentrationsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Highly-Leveraged Credit Relationships [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_HighlyLeveragedCreditRelationshipsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Policy Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_PolicyExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Credit and Collateral Exceptions [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_CreditAndCollateralExceptionsMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Loans Not Reviewed by Concurrence [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_LoansNotReviewedByConcurrenceMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | Adjustment for Recoveries [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_AdjustmentForRecoveriesMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |
Unallocated [Member] | General Macroeconomic Risk [Member] |  |  |  |
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items] |  |  |  |
Portion of allowance for loan losses | $ 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember | $ 0 us-gaap_LoansAndLeasesReceivableAllowance / us-gaap_FinancialInstrumentAxis = cfr_GeneralMacroeconomicRiskMember / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = us-gaap_UnallocatedFinancingReceivablesMember |  |

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953423-111524 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section L -Subsection 1 + Details
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