Plant, Property, and Equipment (Schedule of Capital Leased Asssets) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross, Additions	[1]	$ 1,741	$ 1,616	$ 1,408
Consumers Energy Company [Member]
Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross, Additions	[1]	1,694	1,612	1,403
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation		152	143
Consumers Energy Company [Member] | Assets Held under Capital Leases [Member]
Property, Plant and Equipment [Line Items]
Balance at beginning of period		295	291
Capital Leased Assets, Gross, Additions		17	7
Capital Leased Assets, Gross, Net retirements and other adjustments		(12)	(3)
Balance at end of period		$ 300	$ 295	$ 291

[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.