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Derivative Financial Instruments (Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding) (Detail)	Dec. 31, 2014
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	2.80%cfr_FairValueHedgeLoanLeaseInterestRateSwaps / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRatePaidMember
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	0.16%cfr_FairValueHedgeLoanLeaseInterestRateSwaps / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRateReceivedMember
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	4.05%cfr_NonHedgingInterestRateSwaps / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRatePaidMember / us-gaap_HedgingDesignationAxis = cfr_FinancialInstitutionCounterpartiesMember
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	1.67%cfr_NonHedgingInterestRateSwaps / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRateReceivedMember / us-gaap_HedgingDesignationAxis = cfr_FinancialInstitutionCounterpartiesMember
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	1.67%cfr_NonHedgingInterestRateSwaps2 / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRatePaidMember / us-gaap_HedgingDesignationAxis = cfr_CustomerCounterpartiesMember
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	4.05%cfr_NonHedgingInterestRateSwaps2 / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRateReceivedMember / us-gaap_HedgingDesignationAxis = cfr_CustomerCounterpartiesMember

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- Definition

Fair Value Hedge Loan Lease Interest Rate Swaps

+ References

No definition available.

+ Details

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Period Type:	instant

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- Definition

Non-hedging interest rate swaps

+ References

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- Definition

Non-hedging interest rate swaps (2)

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	instant

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- Details

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Balance Type:	na
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- Details

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Data Type:	na
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- Details

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X

- Details

Name:	us-gaap_HedgingDesignationAxis=cfr_CustomerCounterpartiesMember
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