Asset Sales, Discontinued Operations, and Impairment Charges (Asset Sales) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Proceeds From Sale Of Assets	$ 1		$ 1
Gains (Losses) on Sales of Assets	0	6	13
CMS Generation San Nicolas Company [Member]
Gains (Losses) on Sales of Assets		3
Cost-method investment [Member]
Gains (Losses) on Sales of Assets		3
Cost Method Investment Sold Carrying Amount		0
Consumers Energy Company [Member]
Proceeds From Sale Of Assets	1		1
Gains (Losses) on Sales of Assets	$ 0		$ 9