Regulatory Matters (Narrative) (Details) (USD $) In Millions, unless otherwise specified																						12 Months Ended							1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Consumers Energy Company [Member]	Oct. 31, 2011 Consumers Energy Company [Member]	May 31, 2011 Consumers Energy Company [Member]	Dec. 31, 2010 Consumers Energy Company [Member]	Jun. 30, 2011 2010 Electric Rate Case [Member] Consumers Energy Company [Member]	Dec. 31, 2010 2010 Electric Rate Case [Member] Consumers Energy Company [Member]	Jun. 30, 2011 Power Supply Cost Recover (PSCR) [Member] Consumers Energy Company [Member]	Nov. 30, 2011 Gas Cost Recover (GCR) [Member] Consumers Energy Company [Member]	Mar. 31, 2011 Electric Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Nov. 30, 2011 Uncollectible Expense Tracking Mechanism [Member] Consumers Energy Company [Member]	Mar. 31, 2011 Uncollectible Expense Tracking Mechanism [Member] Consumers Energy Company [Member]	May 31, 2011 2010 Gas Rate Case [Member] Consumers Energy Company [Member]	Aug. 31, 2010 2010 Gas Rate Case [Member] Consumers Energy Company [Member]	Sep. 30, 2011 Gas Revenue Decoupling Mechanism [Member] Consumers Energy Company [Member]	Dec. 31, 2011 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]	Feb. 28, 2010 Big Rock Decommissioning And Related Costs [Member] Consumers Energy Company [Member]	Dec. 31, 2010 Refund Of Revenue In Excess Of Nuclear Decommissioning Costs [Member] Consumers Energy Company [Member]	Apr. 30, 2010 Refund Of Revenue In Excess Of Nuclear Decommissioning Costs [Member] Consumers Energy Company [Member]	Dec. 31, 2011 2011 Electric Energy Optimization Plan [Member] Consumers Energy Company [Member]	Dec. 31, 2011 2011 Gas Energy Optimization Plan [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Big Rock Nuclear Decommissioning And Related Costs [Member] Consumers Energy Company [Member]		Sep. 30, 2011 Big Rock Nuclear Decommissioning And Related Costs [Member] Consumers Energy Company [Member]	Dec. 31, 2010 Big Rock Nuclear Decommissioning And Related Costs [Member] Consumers Energy Company [Member]		Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]	Dec. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]
Annual Rate Increase Authorized by the MPSC								$ 146						$ 31
Annual Rate Increase Requested by Consumers															55
Difference Between the Annual Rate Increase Authorized by MPSC and the Annual Rate Increase Self-implemented by Consumers								4
Amount of rates to be refunded to customers							0
Requested Recovery											27		3			16
Regulatory assets	2,466	2,093	2,466			2,093											85							85	[1]		85	[1]
Amount Paid to Transfer Ownership and Responsibility																	30
Regulatory liabilities	125	22	125			22														7										120
Amended Annual Renewable Energy Plan Surcharge Billed To Customers					23
Proposed Amended Annual Renewable Energy Plan Surcharge Billed To Customers				20
Litigation Settlement, Gross																													120
Proposed Recovery Of Regulatory Asset																										85
Proposed Refund Of Spent Nuclear Fuel Disposal Costs Collected																		23
Remaining Portion of Litigation Settlement																		12
Percentage of Difference Between Rate Base Expense and Actual Expense To Collect/Refund													80.00%
Authorized Recovery												3
Contributions to Fund Decommissioning Costs																			44
Revenue Collected in Excess of the Costs Incurred to Decommission Big Rock, Plus Interest, and Ordered for Refund																					85
Nuclear Fuel Storage Costs Incurred as a Result of the DOE's Failure to Accept Spent Nuclear Fuel																	55
Annual Amount Of Reduction Of Renewable Energy Plan Surcharge Billed To Customers					54
Proposed Annual Amount Of Reduction Of Renewable Energy Plan Surcharge Billed To Customers				3
Authorized Energy Optimization Incentive for Exceeding Savings Targets			8		6
Percent of Savings Target Achieved																						138.00%	129.00%
Energy Optimization Incentive to be Requested for Exceeding 2011 Savings Targets			15
Rate of Return on Equity Requested by Consumers															11.00%
Rate of Return On Equity Authorized by the MPSC														10.50%
Net Over/(Under) Recovery, Including Interest, Authorized by the MPSC									$ (31)	$ 1

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