Derivative Instruments (Effect of Derivative Instruments on Consolidated Statements of Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Gain/(Loss) Recognized in Income on Derivative Instruments		$ 10	$ (1)
Commodity Contracts [Member] | Operating Revenue [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments	2	4	7
Commodity Contracts [Member] | Fuel for Electric Generation [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments		4	(3)
Commodity Contracts [Member] | Cost of Gas Sold [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments	(2)		(2)
Commodity Contracts [Member] | Purchased And Interchange Power [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments		2
Commodity Contracts [Member] | Other Expense [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments			(1)
Commodity Contracts [Member] | Other Expense [Member] | Consumers Energy Company [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments			(1)
Interest Rate Contracts [Member] | Other Expense [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments			(1)
Foreign Exchange Contracts [Member] | Other Expense [Member]
Gain/(Loss) Recognized in Income on Derivative Instruments			$ (1)