Concentration of loans in a single industry in excess of ten percent

No definition available.

Name:	cfr_Concentrationofloansinasingleindustryinexcessoftenpercent
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Interest income recognized subsequent to classification as impaired

+ References

No definition available.

+ Details

Name:	cfr_Interestincomerecognizedsubsequenttoclassificationasimpaired
Namespace Prefix:	cfr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum Percentage of Loan Related To Single Industry

+ References

No definition available.

+ Details

Name:	cfr_MaximumPercentageOfLoanRelatedToSingleIndustry
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of total energy loans to total loans

+ References

No definition available.

+ Details

Name:	cfr_Percentageoftotalenergyloanstototalloans
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Texas Leading Index economic condition indicator

+ References

No definition available.

+ Details

Name:	cfr_TexasLeadingIndexEconomicConditionIndicator
Namespace Prefix:	cfr_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Unfunded balances

+ References

No definition available.

+ Details

Name:	cfr_Unfundedbalances
Namespace Prefix:	cfr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(e))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommitmentsToExtendCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration of loans in a single industry in excess of ten percent	0.00%
Maximum percentage loan related to single industry	10.00%
Percentage of total energy loans to total loans	10.80%		11.40%
Loans and Leases Receivable, Related Parties	$ 272.4		$ 256.1
Interest income recognized subsequent to classification as impaired	$ 0.0		$ 0.0
Texas Leading Index economic condition indicator	127.3		125.6
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional interest that would have been recognized on non-accrual loans, net of tax	$ 1.0	$ 1.5
Commitments to Extend Credit [Member] \| Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	1,200.0
Standby Letters of Credit [Member] \| Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	$ 53.4