Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified			12 Months Ended				1 Months Ended																	1 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010 Consumers Energy Company [Member]	Sep. 30, 2012 Consumers Energy Company [Member]	May 31, 2012 Consumers Energy Company [Member]	Dec. 31, 2011 Consumers Energy Company [Member]	Jun. 30, 2012 Electric Rate Case 2011 [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Electric Rate Case 2011 [Member] Consumers Energy Company [Member]	Jun. 30, 2011 Electric Rate Case 2011 [Member] Consumers Energy Company [Member]	Mar. 31, 2011 2009-2010 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Mar. 31, 2012 2010-2011 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Mar. 31, 2012 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Sep. 30, 2012 2011 Gas Rate Case [Member] Consumers Energy Company [Member]	Jun. 30, 2012 2011 Gas Rate Case [Member] Consumers Energy Company [Member]	Mar. 31, 2012 2011 Gas Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2011 2011 Gas Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2011 2010-2011 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Sep. 30, 2012 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member]	Sep. 30, 2011 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member]	Apr. 30, 2010 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member]	Aug. 31, 2012 Gas Revenue Decoupling Mechanism 2011-2012 [Member] Consumers Energy Company [Member]	Sep. 30, 2012 DOE Settlement [Member] Consumers Energy Company [Member]	Jul. 31, 2011 Nuclear Fuel Disposal Cost [Member] Consumers Energy Company [Member]
Annual rate increase requested									$ 195							$ 49
Rate of return on equity requested									10.70%							10.70%
Annual rate increase self-implemented								118							23
Annual rate increase authorized							118							16
Rate of return on equity authorized							10.30%							10.30%
Increase in annual depreciation expense authorized							20
Public utilities, property, plant and equipment, amount of loss (recovery) on plant abandonment			22				(14)
Regulatory asset							14											33
Revenue collected in excess of the costs incurred to decommission Big Rock, plus interest, and ordered refund																					85
Regulatory assets, noncurrent	2,273	2,466		2,273		2,466													85
Amount paid to transfer ownership and responsibility																			30
Regulatory liabilities	122	125		122		125																	120
Nuclear fuel storage costs incurred as a result of the DOE's failure to accept spent nuclear fuel																			55
Litigation settlement, gross																								120
Regulatory liability, noncurrent	1,939	1,875		1,939		1,875
Proposed recovery of regulatory asset																				85
Proposed refund of spent nuclear fuel disposal costs collected																				23
Recommended refund of spent nuclear fuel disposal costs collected																			44
Recommended recovery of regulatory asset																			76
Requested recovery										27	32						16					17
Amount of rates to be refunded to customers													2
Write-off of regulatory asset												59
Annual amount of reduction of renewable energy plan surcharge billed to customers					3
Amended annual renewable energy plan surcharge billed to customers					20
Energy optimization incentive authorized for exceeding 2011 savings targets				$ 15