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Employee Benefit Plans (Narrative) (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Expense related to benefit plans $ 10,800,000us-gaap_PensionAndOtherPostretirementBenefitExpense $ 11,400,000us-gaap_PensionAndOtherPostretirementBenefitExpense $ 9,200,000us-gaap_PensionAndOtherPostretirementBenefitExpense
Net actuarial loss expected to be recognized 7,000,000cfr_OtherComprehensiveIncomeNetActuarialGainLossExpectedToBeRecognized    
Modeling process confidence ratio 90.00%cfr_ModelingProcessConfidenceRatio    
Percentage of equity investments in mutual fund 71.00%cfr_PercentageOfEquityInvestmentsInMutualFund    
Assumed long-term rate of return 7.75%cfr_AssumedLongTermRateOfReturnInDeterminationOfNetPeriodicBenefitCost    
Expected defined benefit plans contribution within a year 1,100,000cfr_ExpectedDefinedBenefitPlansContributionWithinOneYear    
Target percentage of pay at age 55 45.00%cfr_TargetPercentageOfPayAtAgeOfFiftyFive    
Target percentage of pay at age 60 60.00%cfr_TargetPercentageOfPayAtAgeOfSixty    
Stock purchase plan expense 9,142,000us-gaap_StockOptionPlanExpense 8,814,000us-gaap_StockOptionPlanExpense 9,663,000us-gaap_StockOptionPlanExpense
Maximum exercise period of options granted, years 10 years    
Awards other than in the form of stock options 281,840cfr_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsNumberofAdditionalSharesAuthorized    
Intrinsic value of outstanding in-the-money stock options 66,500,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue    
Outstanding in-the-money exercisable stock options 56,400,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1    
Weighted-average period, unrecognized expense related to stock options, years 3 years 1 month 6 days    
Weighted-average period, unrecognized expense related to non-vested stock awards, years 2 years 6 months    
Weighted-average fair value of stock options granted $ 16.97us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue $ 13.74us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue $ 11.07us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue
401(k) Plan [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Contribution match by employer 100.00%cfr_DefinedBenefitPlanContributionEmployerMatchPercentage
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember		    
Participants contribution eligible for match 6.00%cfr_ParticipantsContributionEligibleForMatch
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember		    
Stock purchase plan expense $ 12,300,000us-gaap_StockOptionPlanExpense
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember		 $ 11,500,000us-gaap_StockOptionPlanExpense
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember		 $ 10,800,000us-gaap_StockOptionPlanExpense
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember
Equity Securities [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Target asset allocation percentage 65.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember		    
Fixed Income Securities [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Target asset allocation percentage 32.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
2005 Plan [Member] | Stock Options [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Life period of options awarded, years 10 years 10 years 10 years
Vesting period of options awarded, years 4 years 4 years 4 years
2005 Plan [Member] | Non Vested Stock Awards and Stock Units [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Life period of options awarded, years 10 years 10 years 10 years
Cliff vesting period, years 4 years 4 years 4 years
2007 Directors Plan [Member] | Stock Options [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Options awarded during period 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_StockOptionMember
/ us-gaap_PlanNameAxis
= cfr_TwoThousandSevenDirectorPlanMember		 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_StockOptionMember
/ us-gaap_PlanNameAxis
= cfr_TwoThousandSevenDirectorPlanMember		 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_StockOptionMember
/ us-gaap_PlanNameAxis
= cfr_TwoThousandSevenDirectorPlanMember
Minimum [Member] | 401(k) Plan [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Contribution percentage of eligible compensation 2.00%cfr_DefinedBenefitPlanContributionsByPlanParticipantsPercentage
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		    
Maximum [Member] | 401(k) Plan [Member]      
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Contribution percentage of eligible compensation 50.00%cfr_DefinedBenefitPlanContributionsByPlanParticipantsPercentage
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= cfr_FourZeroOneKPlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember