Loans and Leases - Net Charge-Offs (Recoveries) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	$ 144	$ 136
Comerica Incorporated
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	94
Commercial \| Commercial and industrial loans
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	69	52
Commercial \| Commercial mortgage loans
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	0	10
Commercial \| Commercial leases
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	0	2
Consumer \| Indirect secured consumer loans
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	24	21
Consumer \| Credit card
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	14	17
Consumer \| Solar energy installation loans
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	23	18
Consumer \| Other consumer loans
Assets that Continue to be Recognized, Securitized or Asset-backed Financing Arrangement Assets and any Other Financial Assets Managed Together
Net charge-offs (recoveries)	$ 14	$ 16