Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Financial Transmission Right [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Other Assets [Member] Commodity Contracts [Member]	Dec. 31, 2011 Other Assets [Member] Commodity Contracts [Member]	Mar. 31, 2012 Other Assets [Member] Commodity Contracts [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Other Assets [Member] Commodity Contracts [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Other Liabilities [Member] Commodity Contracts [Member]	Dec. 31, 2011 Other Liabilities [Member] Commodity Contracts [Member]
Derivative Assets				$ 3	$ 3	$ 1	$ 2
Derivative Liabilities								7	7
Gain Or Loss Deferred In Regulatory Accounts			2
Derivative Liabilities Subject to Credit-Related-Contingent Features	$ 3	$ 4