Regulatory Matters (Narrative) (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended				12 Months Ended			12 Months Ended												12 Months Ended							1 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]	Jun. 30, 2012 Electric Rate Case [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Power Supply Cost Recover (PSCR) [Member] Consumers Energy Company [Member]	Dec. 31, 2010 Power Supply Cost Recover (PSCR) [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Power Supply Cost Recover (PSCR) [Member] 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]	Sep. 30, 2012 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Gas Rate Case [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Gas Rate Case [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Gas Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2011 Gas Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2011 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]	Dec. 31, 2012 Electric Energy Optimization Plan [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Gas Energy Optimization Plan [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Cancelled Coal-Fueled Plant Costs [Member] Consumers Energy Company [Member]	Dec. 31, 2012 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member]		Sep. 30, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Dec. 31, 2012 DOE Settlement [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]	Dec. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]
Requested recovery																						$ 16,000,000	$ 17,000,000
Energy optimization incentive authorized for exceeding 2011 savings targets				15,000,000	15,000,000
Percent of Savings Target Achieved																								123.00%	132.00%
Energy Optimization Incentive Requested for Exceeding 2012 Savings Targets				17,000,000	17,000,000
Authorized Recovery																										14,000,000
Regulatory assets, noncurrent	2,287,000,000	2,466,000,000		2,287,000,000	2,287,000,000	2,466,000,000																						85,000,000	[1]
Regulatory asset				2,322,000,000	2,322,000,000	2,467,000,000											59,000,000
Amount paid to transfer ownership and responsibility																											30,000,000	30,000,000
Nuclear fuel storage costs incurred as a result of the DOE's failure to accept spent nuclear fuel																												55,000,000
Litigation settlement, gross																																120,000,000
Proposed recovery of regulatory asset																														85,000,000
Proposed refund of spent nuclear fuel disposal costs collected																														23,000,000
Authorized Refund Of Spent Nuclear Fuel Disposal Costs Collected																															23,000,000
Remaining Portion Of Litigation Settlement																																	12,000,000
Trust assets assigned for future prescription drug costs				792,000,000	792,000,000
Increase in regulatory liabilities				151,000,000
Write-off of regulatory asset																59,000,000
Annual rate increase requested																					49,000,000
Rate of return on equity authorized								10.30%											10.30%
Annual rate increase self-implemented																				23,000,000
Annual rate increase authorized								118,000,000											16,000,000
Increase in annual depreciation expense authorized								20,000,000
Cost of Goods Sold, Electric									1,800,000,000	1,700,000,000
Cost of Goods Sold, Electric									1,800,000,000	1,700,000,000
Cost of Natural Gas Purchases	1,150,000,000	1,512,000,000	1,590,000,000		1,110,000,000	1,438,000,000	1,516,000,000					900,000,000	1,200,000,000	1,300,000,000
Net Over/(Under) Recovery, Including Interest, Authorized by the MPSC											(11,000,000)	1,000,000			6,000,000
Rate of return on equity requested																					10.70%
Regulatory liabilities, current	25,000,000	125,000,000		25,000,000	25,000,000	125,000,000																									23,000,000		23,000,000	120,000,000
Amount of rates to be refunded to customers																		$ 2,000,000

[1] These regulatory assets represent expenditures for which the MPSC has provided, or Consumers expects, recovery without a return on investment.