Leases - Schedule of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 3	$ 6
Finance lease costs
Amortization of right-of-use assets	2	4
Interest on lease liabilities	5	9
Variable lease costs	24	55
Total lease costs	34	74
Consumers Energy Company
Lessee, Lease, Description [Line Items]
Operating lease costs	3	5
Finance lease costs
Amortization of right-of-use assets	2	4
Interest on lease liabilities	5	9
Variable lease costs	24	55
Total lease costs	$ 34	$ 73