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Premises and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Premises and Equipment [Abstract]
Capitalized Computer Software, Amortization	$ 28	$ 26	$ 25
Capitalized Computer Software, Unamoritize	$ 137	$ 106

X

- Definition

Capitalized Computer Software, Unamoritize

+ References

No definition available.

+ Details

Name:	cma_CapitalizedComputerSoftwareUnamoritize
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Premises and Equipment [Abstract]

+ References

No definition available.

+ Details

Name:	cma_PremisesandEquipmentAbstract
Namespace Prefix:	cma_
Data Type:	xbrli:stringItemType
Balance Type:	na
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X

- Definition

Amount of expense for amortization of capitalized computer software costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-1

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	duration