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Significant Group Concentrations of Credit Risk Significant Group Concentrations of Credit Risk (Schedule of Automotive Industry Outstanding Loans and Total Exposure) (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Concentration Risk [Line Items] |  |  |
Total automotive loans |  | $ 5,274 | $ 6,785
Total automotive exposure |  | 12,706 | 11,920
Automotive Production |  |  |
Concentration Risk [Line Items] |  |  |
Total automotive loans | [1] | 1,112 | 1,093
Total automotive exposure | [1] | 2,041 | 2,267
Automotive Dealer |  |  |
Concentration Risk [Line Items] |  |  |
Total automotive loans |  | 4,162 | 5,692
Total automotive exposure |  | $ 10,665 | $ 9,653
[1] | Excludes PPP loans.

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- Definition Total automotive exposure including loans and other credit commitments to automotive dealers and to borrowers involved with automotive production. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Total automotive loans including loans to automotive dealers and to borrowers involved with automotive production. + References No definition available. + Details
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Namespace Prefix: | cma_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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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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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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