| Document and Entity Information | Feb. 25, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | COMERICA INC /NEW/ |
| Amendment Flag | false |
| Entity Central Index Key | 0000028412 |
| Document Type | 8-K |
| Document Period End Date | Feb. 25, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-10706 |
| Entity Tax Identification Number | 38-1998421 |
| Entity Address, Address Line One | Comerica Bank Tower |
| Entity Address, Address Line Two | 1717 Main Street |
| Entity Address, Address Line Three | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $5 par value |
| Trading Symbol | CMA |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
