Leases - Schedule of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 2	$ 8
Finance lease costs
Amortization of right-of-use assets	2	6
Interest on lease liabilities	4	13
Variable lease costs	20	75
Total lease costs	28	102
Consumers Energy Company
Lessee, Lease, Description [Line Items]
Operating lease costs	2	7
Finance lease costs
Amortization of right-of-use assets	2	6
Interest on lease liabilities	4	13
Variable lease costs	20	75
Total lease costs	$ 28	$ 101