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Stock-Based Compensation (Schedule of Share-based Compensation, Stock Options, Activity) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance 437,080    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (127,500)    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period (244,000)    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance 65,580 437,080  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period $ 22.34    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price $ 11.87    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price $ 27.85    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period $ 22.20 $ 22.34  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term 0.2 1.1  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value   $ (2)  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value, less than for 2009 1 1 1
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options 2    
Unrealized Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation 31    
Consumers Energy Company [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Beginning Balance 267,468    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period (92,968)    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period (113,000)    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance 61,500 267,468  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Beginning of Period $ 20.64    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price $ 10.25    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price $ 28.34    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, End of Period $ 22.20 $ 20.64  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term 0.2 1.2  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value   (1)  
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value, less than for 2009 1 1 1
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options $ 1