| Cover Document | Apr. 20, 2021 |
| Cover [Abstract] | |
| Entity Central Index Key | 0000028412 |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Entity Incorporation, State or Country Code | DE |
| Document Type | 8-K |
| Title of 12(b) Security | Common Stock, $5 par value |
| Trading Symbol | CMA |
| Security Exchange Name | NYSE |
| Document Period End Date | Apr. 20, 2021 |
| Entity Registrant Name | COMERICA INCORPORATED |
| 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 |
| City Area Code | (214) |
| Local Phone Number | 462-6831 |
| Entity File Number | 1-10706 |
| Entity Tax Identification Number | 38-1998421 |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Amendment Flag | false |
