Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Liabilities Subject to Credit-Related-Contingent Features	$ 4	$ 1
Financial Transmission Right [Member] | Consumers Energy Company [Member]
Gain Or Loss Deferred In Regulatory Accounts	2	3	9
Other Assets [Member] | Commodity Contracts [Member]
Derivative Assets	3	1
Other Assets [Member] | Commodity Contracts [Member] | Consumers Energy Company [Member]
Derivative Assets	2	1
Other Liabilities [Member] | Commodity Contracts [Member]
Derivative Liabilities	7	4
Other Liabilities [Member] | Commodity Contracts [Member] | Consumers Energy Company [Member]
Derivative Liabilities	$ 0	$ 0