Leases (Schedule of Lease Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 6	$ 6
Finance lease costs
Amortization of right-of-use assets	6	9
Interest on lease liabilities	16	15
Variable lease costs	107	107
Short-term lease costs	13	14
Total lease costs	148	151
Consumers Energy Company
Lessee, Lease, Description [Line Items]
Operating lease costs	5	5
Finance lease costs
Amortization of right-of-use assets	5	8
Interest on lease liabilities	13	13
Variable lease costs	107	107
Short-term lease costs	12	14
Total lease costs	$ 142	$ 147