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Loans - Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 709us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2	$ 819us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Balance at period end	613us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2	793us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember	0us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember
Balance at period end	0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember	0us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialEnergyFinancingReceivableMember
Commercial and industrial, Other commercial [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	709us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember	819us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember
Balance at period end	$ 613us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember	$ 793us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2 / us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis = cfr_CommercialAndIndustrialOtherCommercialFinancingReceivableMember

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- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

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