Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		6 Months Ended											1 Months Ended	12 Months Ended	1 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Consumers Energy Company [Member]	Dec. 31, 2012 Consumers Energy Company [Member]	May 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member]	Jan. 31, 2013 Electric Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Electric Rate Case [Member] 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]	Jun. 30, 2013 Gas Revenue Decoupling Mechanism [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]	Jan. 31, 2013 Renewable Energy Grant [Member] Consumers Energy Company [Member]	Jun. 30, 2013 Renewable Energy Grant [Member] Consumers Energy Company [Member]
Annual rate increase requested							$ 145	$ 148
Annual rate increase self-implemented						110
Annual rate increase authorized					89				118
Rate of return on equity authorized					10.30%				10.30%
Rate of return on equity requested								10.50%
Regulatory assets, noncurrent	2,202	2,287	2,202	2,287									85
Amount paid to transfer ownership and responsibility													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												5					68
Energy Optimization Incentive Requested for Exceeding 2012 Savings Targets				17
Authorized Recovery										16
Regulatory asset												17
Requested recovery											$ 17