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Business Segment Information (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2021 segments
Segment Reporting [Abstract] |
Number of Major Business Segments | 3

X
- Definition Number of Major Business Segments + References No definition available. + Details
Name: | cma_NumberOfMajorBusinessSegments
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