Regulatory Matters (Schedule of the Components of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Regulatory Assets Current	$ 1		$ 19
Regulatory assets noncurrent	2,466		2,093
Regulatory liabilities	125		22
Regulatory Liability, Noncurrent	1,875		1,988
Consumers Energy Company [Member]
Regulatory Assets Current	1		19
Regulatory assets noncurrent	2,466		2,093
Total regulatory asset	2,467		2,112
Regulatory liabilities	125		22
Regulatory Liability, Noncurrent	1,875		1,988
Total regulatory liabilities	2,000		2,010
DOE Settlement [Member] | Consumers Energy Company [Member]
Current Regulatory Liability Recovery End Date	2012
Regulatory liabilities	120
Cost Of Removal [Member] | Consumers Energy Company [Member]
Regulatory Liability, Noncurrent	1,364		1,311
Income Taxes, Net [Member] | Consumers Energy Company [Member]
Regulatory Liability, Noncurrent	181		410
Renewable Energy Plan [Member] | Consumers Energy Company [Member]
Regulatory Liability, Noncurrent	161		101
ARO [Member] | Consumers Energy Company [Member]
Regulatory Liability, Noncurrent	113		122
Energy Optimization Plan [Member] | Consumers Energy Company [Member]
Regulatory Liability, Noncurrent	45		34
Other Regulatory Liabilities [Member] | Consumers Energy Company [Member]
Current Regulatory Liability Recovery End Date	2012
Regulatory liabilities	5		1
Regulatory Liability, Noncurrent	11		10
Postretirement Benefits [Member] | Consumers Energy Company [Member]
Regulatory Current Asset, End Date for Recovery	2011
Regulatory Assets Current			19	[1]
Regulatory assets noncurrent	1,665	[1]	1,364	[1]
Securitized Costs [Member] | Consumers Energy Company [Member]
Noncurrent Regulatory Asset Recovery End Date	2015
Regulatory assets noncurrent	252	[2]	310	[2]
ARO [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	114	[2]	107	[2]
Big Rock Nuclear Decommissioning And Related Costs [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	85	[2]	85	[2]
MGP Sites [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	156	[2]	58	[2]
Electric Revenue Decoupling Mechanism [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	59		28
Unamortized Debt Costs [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	44	[2]	52	[2]
Stranded Costs [Member] | Consumers Energy Company [Member]
Noncurrent Regulatory Asset Recovery End Date	2013
Regulatory assets noncurrent	23	[3]	46	[3]
Gas Revenue Decoupling Mechanism [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	21		11
Energy Optimization Plan Incentive [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	26		14
Uncollectible Expense Tracking Mechanism [Member] | Consumers Energy Company [Member]
Noncurrent Regulatory Asset Recovery End Date	2012
Regulatory assets noncurrent	2	[3]	3	[3]
Other Regulatory Assets [Member] | Consumers Energy Company [Member]
Regulatory Current Asset, End Date for Recovery	2012
Regulatory Assets Current	1	[3]
Regulatory assets noncurrent	19	[3]	15	[3]
Big Rock Decommissioning And Related Costs [Member] | Consumers Energy Company [Member]
Regulatory assets noncurrent	85
Refund Of Revenue In Excess Of Nuclear Decommissioning Costs [Member] | Consumers Energy Company [Member]
Current Regulatory Liability Recovery End Date	2011
Regulatory liabilities			7
Self-Implemented Rate Refunds [Member] | Consumers Energy Company [Member]
Current Regulatory Liability Recovery End Date	2011
Regulatory liabilities			$ 14

[1] The regulatory asset associated with postretirement benefits is offset partially by liabilities. The net amount is included in rate base, thereby providing a return.

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

[3] These regulatory assets either are included in rate base (or are expected to be included, for costs incurred subsequent to the most recently approved rate case), thereby providing a return on expenditures, or provide a specific return on investment authorized by the MPSC.