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, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share - CMS Energy [Abstract]
Income from continuing operations	$ 68	$ 84	$ 270	$ 288
Less income attributable to noncontrolling interest	1	1	1	1
Income from continuing operations available to common stockholders - basic and diluted	$ 67	$ 83	$ 269	$ 287
Weighted average shares - basic	275.4	268.0	275.1	267.1
Add dilutive contingently convertible securities		6.0		6.2
Add dilutive non-vested stock awards	0.8	0.6	0.8	0.6
Weighted average shares - diluted	276.2	274.6	275.9	273.9
Basic	$ 0.25	$ 0.31	$ 0.98	$ 1.07
Diluted	$ 0.25	$ 0.30	$ 0.98	$ 1.05