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Deposits - Additional Information About Corporation's Deposits (Detail) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
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Disclosure Text Block [Abstract] |  |
Deposits from the Certificate of Deposit Account Registry Service (CDARS) deposits | $ 0 | $ 372
Deposits from foreign sources (primarily Mexico) | 906,220 | 884,169
Total deposits not covered by deposit insurance | 21,265,105 | 18,694,320
Time deposits not covered by deposit insurance | $ 250,437 | $ 237,298

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- Definition This element represents Certificate Of Deposit Account Registry Service (CDARS) deposits + References No definition available. + Details
Name: | cfr_CertificateOfDepositAccountRegistryServiceCdarsDeposits
Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Total Deposits Above FDIC Insurance Limit + References No definition available. + Details
Name: | cfr_TotalDepositsAboveFDICInsuranceLimit
Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The aggregate of all foreign interest-bearing and noninterest-bearing deposit liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-05(a)) -URI http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884 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 210.9-03.12(a)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
Name: | us-gaap_DepositsForeign
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_DisclosureTextBlockAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of time deposit liabilities, including certificates of deposit, in denominations that meet or exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 405 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818 + Details
Name: | us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant