Name:	cma_ReducedRateLoans
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects the carrying amount of nonaccrual loans, reduced-rate loans and real estate acquired through foreclosure.

No definition available.

Name:	cma_TotalNonperformingAssets
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects the carrying amount of nonaccrual loans and reduced-rate loans.

No definition available.

Name:	cma_TotalNonperformingLoans
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5162-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4437-111522

Name:	us-gaap_ForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524