Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 07, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Document Annual Report	true
Entity Incorporation, State or Country Code	DE
City Area Code	(214)
Local Phone Number	462-6831
Title of 12(b) Security	Common Stock, $5 par value
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity File Number	1-10706
Amendment Flag	false
Entity Registrant Name	Comerica Incorporated
Entity Central Index Key	0000028412
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		141,346,049
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Public Float			$ 10,700,000,000
Document Transition Report	false
Trading Symbol	CMA
Security Exchange Name	NYSE
Entity Address, Address Line One	1717 Main Street, MC 6404
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75201
Entity Tax Identification Number	38-1998421