Regulatory Matters (Schedule of GCR Reconciliation Filing Pending with the MPSC) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]	Dec. 31, 2009 Consumers Energy Company [Member]	Mar. 31, 2011 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member]	Mar. 31, 2010 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member]
Date Of Filing							June 2011	June 2010
Net Over/(Under) Recovery, Including Interest, Requested by Consumers							$ 6	$ 1
Cost of gas sold	$ 1,512	$ 1,590	$ 1,866	$ 1,438	$ 1,516	$ 1,778	$ 1,200	$ 1,300