Plant, Property, and Equipment (Schedule of Capital Leased Asssets) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross, Additions	[1]	$ 1,722	$ 1,633	$ 1,741
Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross, Additions	[1]	1,683	1,618	1,694
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		193	172
Consumers Energy Company [Member] | Assets Held under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Balance at beginning of period		310	300
Capital Leased Assets, Gross, Additions		3	13
Capital Leased Assets, Gross, Net retirements and other adjustments		(1)	(3)
Balance at end of period		$ 312	$ 310	$ 300

[1] Amounts include purchase of capital lease additions. Amounts also include a portion of Consumers' capital expenditures for plant and equipment attributable to both the electric and gas utility businesses.