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Derivative Financial Instruments - Additional Information (Detail) (USD $)
3 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Oct. 31, 2007
Derivative [Line Items]      
Deferred accumulated gain   $ 21,300,000us-gaap_DerivativeInstrumentsGainRecognizedInOtherComprehensiveIncomeEffectivePortion  
Deferred accumulated after-tax gain   13,800,000us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet  
Weighted-average strike rate for outstanding interest rate caps 2.98%cfr_WeightedAverageStrikeRateOutstandingInterestRateCaps    
Approximate credit exposure related to swaps with bank customers 47,000,000us-gaap_CreditDerivativeMaximumExposureUndiscounted    
Aggregate fair value of securities posted as collateral for derivative contracts 23,600,000us-gaap_PledgedAssetsSeparatelyReportedSecuritiesPledgedAsCollateralAtFairValue    
Cash collateral for borrowed securities 19,400,000us-gaap_CashCollateralForBorrowedSecurities    
Interest Rate Swaps With Upstream Financial Institution Counterparties [Member]      
Derivative [Line Items]      
Approximate credit exposure related to swaps with bank customers 9,200,000us-gaap_CreditDerivativeMaximumExposureUndiscounted
/ us-gaap_DerivativeByNatureAxis
= cfr_InterestRateSwapsWithUpstreamFinancialInstitutionCounterpartiesMember
   
Variable-Rate Loans Outstanding [Member]      
Derivative [Line Items]      
Notional amount of interest rate swap contracts     1,200,000,000invest_DerivativeNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
Principal amount outstanding of variable-rate loans     $ 1,200,000,000us-gaap_PrincipalAmountOutstandingOfLoansHeldInPortfolio
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
Period for which cash flow hedges were used to hedge monthly interest receipts     84 months