Deposits (Additional Information About Corporation's Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deposit Liability [Line Items]
Deposits from foreign sources (primarily Mexico)	$ 1,219,463	$ 1,061,701
Non-interest-bearing public funds deposits	14,441,820	14,926,094
Interest-bearing public funds deposits	28,280,928	26,994,474
Total deposits not covered by deposit insurance	22,972,618	22,393,786
Time deposits not covered by deposit insurance	2,744,112	2,339,716
Deposits from certain directors, executive officers and their affiliates	121,113	115,798
Public Funds [Member]
Deposit Liability [Line Items]
Non-interest-bearing public funds deposits	759,819	675,016
Interest-bearing public funds deposits	$ 625,104	$ 630,455

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (1)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (5)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph c
-Publisher SEC

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph a
-Subparagraph (4)
-Publisher SEC

+ Details

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

- Definition

Amount of uninsured deposit liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph e
-Publisher SEC

+ Details

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

- Definition

The aggregate of all foreign interest-bearing and noninterest-bearing deposit liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(12)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-1

+ Details

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

- Definition

The aggregate of all domestic and foreign interest-bearing deposit liabilities.

+ References

+ Details

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

- Definition

The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.

+ References

+ Details

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

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1

+ Details

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

- Definition

Amount of uninsured time deposit liability in excess of Federal Deposit Insurance Corporation (FDIC) insurance limit or similar state deposit insurance regime in United States of America (US). Excludes time deposit that is otherwise uninsured.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1406
-Paragraph f
-Subparagraph (1)
-Publisher SEC

+ Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=cfr_PublicFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: