Related Party Transactions - Consumers (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Purchased power - related parties	$ 82	$ 85
Other income	16	32	80
Accounts payable - related parties	9	9
Investments	50	49
CMS Energy Corporation [Member]
Accounts payable - related parties	163	156
Investments	5,096	4,941
Consumers Energy Company [Member]
Purchased power - related parties	81	84	81
Other income	19	31	47
Accounts payable - related parties	11	11	11
Investment Owned, Balance, Shares	1.6
Investments	$ 35	$ 34