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Derivative Financial Instruments - Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding (Detail)	Mar. 31, 2015
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair value hedge loan/lease interest rate swaps	2.70%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	0.17%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	4.04%cfr_NonHedgingInterestRateSwaps / us-gaap_CounterpartyNameAxis = cfr_FinancialInstitutionCounterpartiesMember / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRatePaidMember
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – financial institution counterparties	1.74%cfr_NonHedgingInterestRateSwaps / us-gaap_CounterpartyNameAxis = cfr_FinancialInstitutionCounterpartiesMember / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRateReceivedMember
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – customer counterparties	1.74%cfr_NonHedgingInterestRateSwaps2 / us-gaap_CounterpartyNameAxis = cfr_CustomerCounterpartiesMember / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRatePaidMember
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – customer counterparties	4.04%cfr_NonHedgingInterestRateSwaps2 / us-gaap_CounterpartyNameAxis = cfr_CustomerCounterpartiesMember / us-gaap_DerivativeByNatureAxis = cfr_WeightedAverageInterestRateReceivedMember

X

- Definition

Fair Value Hedge Loan Lease Interest Rate Swaps

+ References

No definition available.

+ Details

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Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Non-hedging interest rate swaps

+ References

No definition available.

+ Details

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Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Non-hedging interest rate swaps (2)

+ References

No definition available.

+ Details

Name:	cfr_NonHedgingInterestRateSwaps2
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_WeightedAverageDiscountRateLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CounterpartyNameAxis=cfr_FinancialInstitutionCounterpartiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeByNatureAxis=cfr_WeightedAverageInterestRatePaidMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeByNatureAxis=cfr_WeightedAverageInterestRateReceivedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: