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Strategic Lines of Business (Narrative) (Details)	3 Months Ended
	Mar. 31, 2025 segment
Segment Reporting [Abstract]
Number of Major Business Segments	3

X

- Definition

Number of Major Business Segments

+ References

No definition available.

+ Details

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Namespace Prefix:	cma_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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