Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share - CMS Energy [Abstract]
Net Income	$ 93	$ 125	$ 292	$ 289
Less income attributable to noncontrolling interest	1	1	1	1
Net Income Available to Common Stockholders	$ 92	$ 124	$ 291	$ 288
Weighted average shares - basic	279.5	278.2	279.2	277.4
Add dilutive nonvested stock awards	0.8	1.1	0.9	1.2
Weighted average shares - diluted	280.3	279.3	280.1	278.6
Basic	$ 0.33	$ 0.45	$ 1.04	$ 1.04
Diluted	$ 0.33	$ 0.45	$ 1.04	$ 1.04