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Employee Benefit Plans (Summary of Changes in the Corporation's Qualified Defined Benefit Pension Plan's Level 3 Investments Measured at Fair Value on a Recurring Basis) (Details) - Private placements - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021
Balance at beginning of period | $ 50 | $ 58
Gains (Losses) Realized | (3) | 2
Gains (Losses) Unrealized | (12) | (4)
Purchases | 38 | 44
Sales | (34) | (50)
Balance at end of period | $ 39 | $ 50

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- Definition This element represents total realized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value. + References No definition available. + Details
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- Definition This element represents total unrealized gains or losses for the period, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value. + References No definition available. + Details
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Namespace Prefix: | cma_
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- Definition Purchases + 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 Sales + References No definition available. + Details
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Balance Type: | debit
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |