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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share - CMS Energy [Abstract]
Income from continuing operations	$ 148	$ 94	$ 418	$ 382
Less income attributable to noncontrolling interest			1	1
Income from continuing operations available to common stockholders - basic and diluted	$ 148	$ 94	$ 417	$ 381
Weighted average shares - basic	276.0	274.0	275.4	269.4
Add dilutive contingently convertible securities				4.1
Add dilutive non-vested stock awards	0.9	0.7	0.9	0.7
Weighted average shares - diluted	276.9	274.7	276.3	274.2
Basic	$ 0.53	$ 0.34	$ 1.51	$ 1.41
Diluted	$ 0.53	$ 0.34	$ 1.51	$ 1.39