Name:	cma_AverageReserveRequirement
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

This element represents disclosure of the aggregate cash dividends paid to the entity by bank subsidiaries.

No definition available.

Name:	cma_CashDividendsPaidToParentCompanyByBankSubsidiaries
Namespace Prefix:	cma_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Common Equity Tier One Capital Required To Be Well Capitalized To Risk Weighted Assets

No definition available.

Name:	cma_CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	cma_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of dividends that can be declared or paid with approval of regulatory agency.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithRegulatoryApproval
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

Name:	us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.