Leases - Schedule of Lease Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 3
Finance lease costs
Amortization of right-of-use assets	2
Interest on lease liabilities	4
Short-term lease costs	3
Variable lease costs	31
Total lease costs	43
Consumers Energy Company
Lessee, Lease, Description [Line Items]
Operating lease costs	2
Finance lease costs
Amortization of right-of-use assets	2
Interest on lease liabilities	4
Short-term lease costs	3
Variable lease costs	31
Total lease costs	$ 42