Derivative Counter Party [Line Items]

No definition available.

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- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeLiabilityNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value as of the balance sheet date of all foreign currency derivative assets not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

+ Details

Name:	us-gaap_ForeignCurrencyDerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value as of the balance sheet date of all foreign currency derivative liabilities not designated as hedging instruments.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
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- Details

Name:	us-gaap_CounterpartyNameAxis=cfr_CustomerCounterpartiesMember
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cfr_GBPForeignExchangeForwardMember
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cfr_AUDForeignExchangeForwardMember
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EurodollarFutureMember
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Derivative Financial Instruments - Notional Amount and Fair Value of Foreign Currency Forward Contract (Detail) € in Thousands, £ in Thousands, $ in Thousands, $ in Thousands, $ in Thousands	Mar. 31, 2018 USD ($)	Mar. 31, 2018 CAD ($)	Mar. 31, 2018 AUD ($)	Mar. 31, 2018 EUR (€)	Mar. 31, 2018 GBP (£)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 AUD ($)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 GBP (£)
Financial Institution Counterparties [Member] \| Other Assets [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount			$ 59	€ 5,110	£ 832			$ 0	€ 4,014	£ 127
Financial Institution Counterparties [Member] \| Other Liabilities [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Notional Amount	$ 58	$ 23,228		0	453		$ 25,413	$ 0	4,846	1,178
Customer Counterparties [Member] \| Other Assets [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount		$ 23,170		0	88		$ 25,282		3,867	0
Customer Counterparties [Member] \| Other Liabilities [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Notional Amount				€ 4,041	£ 0				€ 4,041	£ 127
Foreign Exchange Forward [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Estimated Fair Value	(68)					$ (142)
Foreign Exchange Forward [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	136					279
GBP Foreign Exchange Forward [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	8					1
Forward Contracts – Liability Estimated Fair Value	(5)					(9)
GBP Foreign Exchange Forward [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	1					0
Forward Contracts – Liability Estimated Fair Value	0					0
AUD Foreign Exchange Forward [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	1					0
Forward Contracts – Liability Estimated Fair Value	0					0
Eurodollar Future [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	167					77
Forward Contracts – Liability Estimated Fair Value	0					(37)
Eurodollar Future [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	0					58
Forward Contracts – Liability Estimated Fair Value	$ (135)					$ (51)