Plant, Property, and Equipment (Schedule of Capital Leased Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capital Leases, Assets, Rollforward [Roll Forward]
Additions	$ 2,081	$ 1,722	$ 1,633
Consumers Energy Company
Capital Leases, Assets, Rollforward [Roll Forward]
Additions	1,825	1,683	1,618
Accumulated amortization	212	193
Consumers Energy Company | Assets Held under Capital Leases
Capital Leases, Assets, Rollforward [Roll Forward]
Balance at beginning of period	312	310
Additions	0	3
Net retirements and other adjustments	(3)	(1)
Balance at end of period	$ 309	$ 312	$ 310