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Deposits - Additional Information About Corporation's Deposits (Detail) - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
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Banking and Thrift [Abstract] |  |
Certificate Of Deposit Account Registry Service Cdars Deposits Held | $ 358 | $ 0
Deposits from foreign sources (primarily Mexico) | 776,490 | 752,658
Deposits not covered by deposit insurance | $ 12,681,664 | $ 13,111,210

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

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- Definition Uninsured Deposits + References No definition available. + Details
Name: | cfr_UninsuredDeposits
Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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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=6882215&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=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_DepositsForeign
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant