Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		1 Months Ended	3 Months Ended								1 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Jan. 31, 2013 Consumers Energy Company [Member]	Mar. 31, 2013 Consumers Energy Company [Member]	Dec. 31, 2012 Consumers Energy Company [Member]	Jun. 30, 2012 Electric Rate Case [Member] Consumers Energy Company [Member]	Dec. 31, 2012 2010-2011 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Aug. 31, 2012 2011-2012 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]	Dec. 31, 2012 DOE Settlement [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Renewable Energy Grant [Member] Consumers Energy Company [Member]
Annual rate increase authorized						$ 118
Rate of return on equity authorized						10.30%
Regulatory assets, noncurrent	2,223	2,287		2,223	2,287						85
Amount paid to transfer ownership and responsibility										30	30
Nuclear fuel storage costs incurred as a result of the DOE's failure to accept spent nuclear fuel											55
Litigation settlement, gross												120
Proposed recovery of regulatory asset											85
Proposed refund of spent nuclear fuel disposal costs collected											23
Authorized Refund Of Spent Nuclear Fuel Disposal Costs Collected													23
Remaining Portion Of Litigation Settlement													12
Renewable energy grant received	69		69	69
Recorded liability														69
Energy Optimization Incentive Requested for Exceeding 2012 Savings Targets					17
Authorized Recovery							16
Regulatory asset									18
Requested recovery								$ 17