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Deposits Deposits (Narrative) (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Deposits [Abstract] |  |
Domestic certificates of deposit of $250,000 or more | $ 627 | $ 632
Foreign office time deposits in denominations of $250,000 or more | $ 50 | $ 66

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- Definition The aggregate amount of time deposit accounts (including certificates of deposit) in denominations that meet or exceed the FDIC insurance limit at the balance sheet date. + References No definition available. + Details
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Namespace Prefix: | cma_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

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- Definition Amount of interest-bearing time deposits in foreign banking offices. Time deposits bear interest for a fixed, stated period of time and include certificate of deposits and individual retirement accounts. + 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) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant