Regulatory Matters (Schedule of GCR Reconciliation Filing Pending with the MPSC) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]	Mar. 31, 2012 Gas Cost Recover (GCR) [Member] 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 2012
Net Over/(Under) Recovery, Including Interest, Requested by Consumers							$ 2
Cost of gas sold	$ 1,150	$ 1,512	$ 1,590	$ 1,110	$ 1,438	$ 1,516	$ 900	$ 1,200	$ 1,300