Loans - Troubled Debt Restructuring (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans modified as troubled debt restructurings	$ 1,155	$ 7,017
Balance at period end	1,083	6,678
Commercial Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans modified as troubled debt restructurings	0	1,312
Balance at period end	0	1,237
Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans modified as troubled debt restructurings	0	3,817
Balance at period end	0	3,566
Commercial Real Estate Buildings Land And Other Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans modified as troubled debt restructurings	1,155	1,888
Balance at period end	$ 1,083	$ 1,875

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.

No definition available.

+ Details

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

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfr_CommercialandIndustrialTotalEnergyLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cfr_CommercialRealEstateBuildingsLandAndOtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: