Stock-Based Compensation (Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan) (Details) (Restricted Stock [Member], USD $) In Millions, unless otherwise specified	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, Vested in Period, Total Fair Value	$ 10	$ 7	$ 7
Allocated Share-based Compensation Expense	12	10	9
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	5	4	4
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	1 year 8 months 12 days
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	8	7	6
Allocated Share-based Compensation Expense	11	10	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	$ 9
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 8 months 12 days