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, 2012		Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 12.32	[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	$ 12.28	[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	$ 12.32		$ 13.89	$ 16.22
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	$ 12.28		$ 14.17	$ 16.27

[1] During 2012, CMS Energy granted 306,917 TSR shares, 176,809 time-lapse shares, 38,401 shares from dividends paid on TSR shares, and 407,000 shares granted as a result of the outcome of the TSR awards’ market condition. During 2012, Consumers granted 291,722 TSR shares, 169,754 time-lapse shares, 37,109 shares from dividends paid on TSR shares, and 390,485 shares granted as a result of the outcome of the TSR awards’ market condition.