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, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares that vested during the year	$ 31	$ 29	$ 16
Compensation expense recognized	16	20	14
Income tax benefit recognized	7	8	5
Unrecognized compensation cost	$ 15
Unrecognized compensation cost recognition period	1 year 9 months 18 days
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares that vested during the year	$ 30	28	15
Compensation expense recognized	16	19	13
Income tax benefit recognized	6	$ 7	$ 5
Unrecognized compensation cost	$ 14
Unrecognized compensation cost recognition period	1 year 9 months 18 days