Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share - CMS Energy [Abstract]
Net Income	$ 172	$ 186	$ 464	$ 475
Less income attributable to noncontrolling interest			1	1
Net Income Available to Common Stockholders	$ 172	$ 186	$ 463	$ 474
Weighted average shares - basic	280.8	278.2	279.8	277.7
Add dilutive nonvested stock awards	0.8	1.0	0.8	1.1
Weighted average shares - diluted	281.6	279.2	280.6	278.8
Basic	$ 0.61	$ 0.67	$ 1.65	$ 1.71
Diluted	$ 0.61	$ 0.67	$ 1.65	$ 1.70