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Loans (Narrative) (Detail) (USD $)
 12 Months Ended
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 $ 8,916,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 $ 14,833,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 $ 2,316,000us-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 7,700,000us-gaap_BankOverdrafts 6,800,000us-gaap_BankOverdrafts    
Minimum number of days to be considered past due 90 days      
Troubled debt restructurings 8,339,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 11,215,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 2,188,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2  
Previously restructured loans past due 0cfr_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 6cfr_NumberOfLoansWithCalculatedRiskOfTenOrHigher      
Loan amount threshold 5,000,000cfr_LoanAmountThreshold      
Loan value with weighted-average loan-to-value 44,400,000cfr_LoanValueWithWeightedAverageLoanToValue      
Weighted-average loan-to-value ratio 53.70%cfr_WeightedAverageLoanToValueRatioPercentage      
Texas Leading Index economic condition indicator   129.1cfr_TexasLeadingIndexEconomicConditionIndicator   131.4cfr_TexasLeadingIndexEconomicConditionIndicator
Maximum origination value of loans which were subject to further refinement of valuation methodology 1,000,000cfr_MaximumOriginationValueOfLoansWhichWereSubjectToFurtherRefinementOfValuationMethodology      
Commercial And Industrial Energy Financing Receivable [Member]        
Accounts, Notes, Loans and Financing Receivable [Line Items]        
Financing Receivable, Modifications, Pre-Modification Recorded Investment 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 528,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 0us-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 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 531,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialEnergyFinancingReceivableMember		 0us-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 8,300,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		 10,100,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		    
Additional interest that would have been recognized on non-accrual loans, net of tax 1,500,000us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		 2,200,000us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_NonAccrualLoansMember		 2,600,000us-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 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_ConsumerRealEstateFinancingReceivableMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_ConsumerRealEstateFinancingReceivableMember		 0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_ConsumerRealEstateFinancingReceivableMember		  
Troubled debt restructurings 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_ConsumerRealEstateFinancingReceivableMember		 0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_ConsumerRealEstateFinancingReceivableMember		 0us-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 5,795,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		 6,334,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		 1,602,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		  
Troubled debt restructurings 5,391,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		 4,937,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		 1,478,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember		  
Amount charged off related to loans restructured 627,000cfr_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 2,700,000us-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 3,121,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		 7,964,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		 714,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		  
Troubled debt restructurings 2,948,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		 5,747,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		 710,000us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		  
Amount charged off related to loans restructured 0cfr_ChargeOffOfPreviouslyRestructuresLoans
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember		      
Previously Restructured Loans Moved to OREO 500,000cfr_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 $ 2,900,000us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= cfr_CommercialRealEstateBuildingsLandAndOtherFinancingReceivableMember
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember