Derivative Counter Party [Line Items]

No definition available.

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Namespace Prefix:	cfr_
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Balance Type:	na
Period Type:	duration

- 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=64837297&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: 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=64837297&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=64837297&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Notional Amount
-URI http://asc.fasb.org/extlink&oid=6519104

Reference 3: 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=64837297&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=64837297&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

Name:	us-gaap_CounterpartyNameAxis=cfr_FinancialInstitutionCounterpartiesMember
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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
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Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
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Data Type:	na
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- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
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Balance Type:
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- Details

Name:	us-gaap_CounterpartyNameAxis=cfr_CustomerCounterpartiesMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cfr_GBPForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cfr_AUDForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_EurodollarFutureMember
Namespace Prefix:
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Derivative Financial Instruments - Notional Amount and Fair Value of Foreign Currency Forward Contract (Detail) € in Thousands, £ in Thousands, CAD in Thousands, AUD in Thousands, $ in Thousands	Sep. 30, 2017 USD ($)	Sep. 30, 2017 CAD	Sep. 30, 2017 AUD	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 GBP (£)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2016 AUD	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 GBP (£)
Financial Institution Counterparties [Member] \| Other Assets [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount		CAD 7,234	AUD 60	€ 135	£ 547		CAD 0	AUD 0	€ 0	£ 0
Financial Institution Counterparties [Member] \| Other Liabilities [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Notional Amount		0		4,693	1,075		2,214		870	419
Customer Counterparties [Member] \| Other Assets [Member] \| Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount		CAD 7,205		€ 3,867	£ 192		CAD 2,205		€ 0	£ 0
Foreign Exchange Forward [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	$ 15					$ 0
Forward Contracts – Liability Estimated Fair Value	0					(21)
Foreign Exchange Forward [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	15					29
GBP 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	(24)					(3)
GBP Foreign Exchange Forward [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	2					0
AUD Foreign Exchange Forward [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	1					0
Eurodollar Future [Member] \| Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	1					0
Forward Contracts – Liability Estimated Fair Value	(80)					(9)
Eurodollar Future [Member] \| Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	$ 104					$ 0