Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 25, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Entity Registrant Name	Comerica INC /NEW/
Entity Central Index Key	0000028412
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		161,698,314
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Current Reporting Status	Yes