Stock-Based Compensation (Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 13.89	[1]
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 14.17	[1]
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 13.89		$ 16.22	$ 13.49
Restricted Stock [Member] | Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 14.17		$ 16.27	$ 13.44

[1] During 2011, CMS Energy granted 310,100 TSR shares, 215,400 time-lapse shares, 25,329 shares from dividends paid on TSR shares, and 236,320 shares granted as a result of the outcome of the TSR awards' market condition. During 2011, Consumers granted 295,035 TSR shares, 207,613 time-lapse shares, 23,328 shares from dividends paid on TSR shares, and 211,528 shares granted as a result of the outcome of the TSR awards' market condition.