Stock-Based Compensation (Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 7	$ 7	$ 4
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost	10	9	9
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	4	4	3
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	10
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2.0
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	7	6	4
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost	10	9	8
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	4	3	3
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 10
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	2.0