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Strategic Lines of Business (Narrative) (Details)	9 Months Ended
	Sep. 30, 2023 segment
Segment Reporting [Abstract]
Number of Major Business Segments	3

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- 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

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- References

No definition available.

+ Details

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