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Asset Retirement Obligations (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Asset Retirement Obligations Assumed Market Risk Premium 5.00%  
Hypothetical Asset Retirement Obligations Liability Increase $ 16 $ 13
Asset Retirement Obligation, Beginning Balance 254 245
Asset Retirement Obligation, Liabilities Incurred 7 (2)
Asset Retirement Obligation, Liabilities Settled (8) [1] (7) [1]
Asset Retirement Obligation, Accretion Expense 19 18
Asset Retirement Obligation, Revision of Estimate 40   
Asset Retirement Obligation, Ending Balance 312 254
Consumers Energy Company [Member]
   
Asset Retirement Obligations Assumed Market Risk Premium 5.00%  
Hypothetical Asset Retirement Obligations Liability Increase 16 13
Asset Retirement Obligation, Beginning Balance 253 244
Asset Retirement Obligation, Liabilities Incurred 7 (2)
Asset Retirement Obligation, Liabilities Settled (8) [1] (7) [1]
Asset Retirement Obligation, Accretion Expense 19 18
Asset Retirement Obligation, Revision of Estimate 40   
Asset Retirement Obligation, Ending Balance 311 253
Close Gas Treating Plant and Gas Wells [Member]
   
Asset Retirement Obligation, Beginning Balance 1 1
Asset Retirement Obligation, Liabilities Incurred     
Asset Retirement Obligation, Liabilities Settled    [1]  
Asset Retirement Obligation, Accretion Expense     
Asset Retirement Obligation, Revision of Estimate      
Asset Retirement Obligation, Ending Balance 1 1
Coal Ash Disposal Areas [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Beginning Balance 70 66
Asset Retirement Obligation, Liabilities Settled (3) [1] (2) [1]
Asset Retirement Obligation, Accretion Expense 7 6
Asset Retirement Obligation, Revision of Estimate 40   
Asset Retirement Obligation, Ending Balance 114 70
Wells at Gas Storage Fields [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Beginning Balance 1 1
Asset Retirement Obligation, Liabilities Settled (1) [1]  
Asset Retirement Obligation, Revision of Estimate     
Asset Retirement Obligation, Ending Balance   1
Indoor Gas Services Relocations [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Beginning Balance   1
Asset Retirement Obligation, Liabilities Settled   (1) [1]
Asset Retirement Obligation, Revision of Estimate     
Asbestos Abatement [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Beginning Balance 42 40
Asset Retirement Obligation, Liabilities Settled (1) [1] (1) [1]
Asset Retirement Obligation, Accretion Expense 2 3
Asset Retirement Obligation, Revision of Estimate     
Asset Retirement Obligation, Ending Balance 43 42
Gas Distribution Cut, Purge, Cap [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Beginning Balance 140 136
Asset Retirement Obligation, Liabilities Incurred 4 (2)
Asset Retirement Obligation, Liabilities Settled (3) [1] (3) [1]
Asset Retirement Obligation, Accretion Expense 10 9
Asset Retirement Obligation, Revision of Estimate     
Asset Retirement Obligation, Ending Balance 151 140
Wind Farm [Member] | Consumers Energy Company [Member]
   
Asset Retirement Obligation, Liabilities Incurred 3  
Asset Retirement Obligation, Ending Balance $ 3  
[1] Cash payments of $8 million in 2012 and $7 million in 2011 were included in other current and non-current assets and liabilities as a component of net cash provided by operating activities in CMS Energy’s and Consumers’ consolidated statements of cash flow.