Plant, Property, and Equipment (Schedule of Capital Leased Asssets) (Details) (Consumers Energy Company [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Consumers Energy Company [Member]
Balance at beginning of period	$ 280	$ 278
Capital Leased Assets, Gross, Additions	9	4
Capital Leased Assets, Gross, Disposals and Transfers	(4)	(2)
Balance at end of period	285	280
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	$ 108	$ 87