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Derivative And Credit-Related Financial Instruments (Summary Of Criticized Letters Of Credit) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Total criticized standby and commercial letters of credit	$ 37	$ 50
As a percentage of total outstanding standby and commercial letters of credit	0.90%	1.40%

X

- Definition

Total internally classified watch list standby and commercial letters of credit (generally consistent with regulatory defined special mention, substandard and doubtful).

+ References

No definition available.

+ Details

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Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Total internally classified watch list standby and commercial letters of credit as a percentage of total standby and commercial letters of credit.

+ References

No definition available.

+ Details

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Namespace Prefix:	cma_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration