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	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 29	$ 16	$ 10
Allocated Share-based Compensation Expense	20	14	14
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	8	5	5
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 15
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 9 months 18 days
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	$ 28	15	9
Allocated Share-based Compensation Expense	19	13	14
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	7	$ 5	$ 5
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 15
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 9 months 18 days