Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share - CMS Energy [Abstract]
Income from continuing operations	$ 94	$ 127	$ 382	$ 352
Less income attributable to noncontrolling interest		1	1	2
Income from continuing operations available to common stockholders - basic and diluted	$ 94	$ 126	$ 381	$ 350
Weighted average shares - basic	274.0	264.8	269.4	264.3
Add dilutive contingently convertible securities		6.2	4.1	6.2
Add dilutive non-vested stock awards	0.7	1.0	0.7	1.1
Weighted average shares - diluted	274.7	272.0	274.2	271.6
Basic	$ 0.34	$ 0.48	$ 1.41	$ 1.32
Diluted	$ 0.34	$ 0.46	$ 1.39	$ 1.29