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Variable Interest Entities (VIEs) (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Variable Interest Entity [Line Items] |  |  |
Unfunded commitments to fund tax credit entities | $ 169 |  |
Amount of financial or other support not contractually required provided by the Corporation to VIEs | 0 | $ 0 | $ 0
Low Income Housing Tax Credit Entities |  |  |
Variable Interest Entity [Line Items] |  |  |
Exposure to loss as a result of involvement with VIEs | 451 |  |
Other Tax Credit Entities |  |  |
Variable Interest Entity [Line Items] |  |  |
Exposure to loss as a result of involvement with VIEs | $ 20 |  |

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- Definition The amount of expense between the reporting entity and the Variable Interest Entity (VIE). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph d -URI http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123419778&loc=d3e5747-111685 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=123419778&loc=d3e5728-111685 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | instant

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- Definition The amount of financial or other support the reporting entity has provided (explicitly or implicitly) to the Variable Interest Entity (VIE) that it was not previously contractually required to provide or that the reporting entity intends to provide, including, for example, situations in which the reporting entity assisted the VIE in obtaining another type of support. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123419778&loc=SL6759159-111685 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_ConsolidatedEntitiesAxis=cma_OtherTaxCreditEntitiesMember
Namespace Prefix: |
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Balance Type: |
Period Type: |