Leases and Palisades Financing - Schedule of Lease Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 10	$ 11
Finance lease costs
Amortization of right-of-use assets	6	6
Interest on lease liabilities	17	18
Variable lease costs	94	95
Short-term lease costs	17	16
Total lease costs	144	146
Consumers Energy Company
Lessee, Lease, Description [Line Items]
Operating lease costs	9	9
Finance lease costs
Amortization of right-of-use assets	6	6
Interest on lease liabilities	17	18
Variable lease costs	94	95
Short-term lease costs	16	16
Total lease costs	$ 142	$ 144