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Deposits (Additional Information About Corporation's Deposits) (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Deposits [Abstract] |  |
Deposits from foreign sources (primarily Mexico) | $ 716,339 | $ 776,003
Deposits not covered by deposit insurance | 13,281,040 | 12,889,047
Deposits from certain directors, executive officers and their affiliates | $ 196,686 | $ 199,969

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

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- References No definition available. + Details
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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://www.xbrl.org/2003/role/presentationRef -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://www.xbrl.org/2003/role/presentationRef -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
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- Definition Amount of deposits held by the entity for a related party (entity, shareholder, employee). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(k)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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Period Type: | instant