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v3.19.3.a.u2

Off-Balance Sheet Arrangements Commitments Guarantees and Contingencies (Narrative) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Commitments And Guarantees [Line Items] |  |
Credit card guarantees | $ 8.5 | $ 8.1
Fully collateralized credit card guarantees | $ 1.3 | $ 1.4

X
- Definition Collateralized Credit Card Guarantees + References No definition available. + Details
Name: | cfr_CollateralizedCreditCardGuarantees
Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Commitments And Guarantees [Line Items] + References No definition available. + Details
Name: | cfr_CommitmentsAndGuaranteesLineItems
Namespace Prefix: | cfr_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Credit Card Guarantees + References No definition available. + Details
Name: | cfr_CreditCardGuarantees
Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration