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Regulatory Capital and Reserve Requirements Regulatory Capital and Reserve Requirements (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Federal Reserve Bank average reserve requirement |  | $ 135 |
Dividends available to be paid to parent company without obtaining prior approval from bank regulatory agencies | $ 347 |  |
Dividends from bank subsidiaries | $ 852 | $ 498 | $ 1,200
Total risk-based capital | 10.00% | 10.00% |
Tier 1 risk-based capital | 6.00% | 6.00% |
U.S. Banking Subsidiaries |  |  |
Total risk-based capital | 10.00% |  |
Tier 1 risk-based capital | 8.00% |  |
CET1 risk-based capital | 6.50% |  |
Leverage ratio | 5.00% |  |

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- Definition The average amount of reserves required to be maintained at the Federal Reserve based on the level of customer deposits in banking subsidiaries during the period. + References No definition available. + Details
Name: | cma_AverageReserveRequirement
Namespace Prefix: | cma_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition This element represents disclosure of the aggregate cash dividends paid to the entity by bank subsidiaries. + References No definition available. + Details
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Namespace Prefix: | cma_
Data Type: | xbrli:monetaryItemType
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- Definition Common Equity Tier One Capital Required To Be Well Capitalized To Risk Weighted Assets + References No definition available. + Details
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Namespace Prefix: | cma_
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- Definition Leverage ratio + References No definition available. + Details
Name: | cma_LeverageRatio
Namespace Prefix: | cma_
Data Type: | dtr-types:percentItemType
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- Definition Tier 1 risk-based capital + References No definition available. + Details
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Data Type: | dtr-types:percentItemType
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- Definition Total risk-based capital + References No definition available. + Details
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Namespace Prefix: | cma_
Data Type: | dtr-types:percentItemType
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- Definition Amount of dividends that can be declared or paid with approval of regulatory agency. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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