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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share - CMS Energy [Abstract]
Income From continuing operations	$ 127	$ 149	$ 352	$ 310
Income attributable to noncontrolling interests	1	1	2	2
Income from Continuing operations available to common stockholders basic and diluted	$ 126	$ 148	$ 350	$ 308
Weighted average shares - basic	264.8	262.9	264.3	259.9
Add dilutive contingently convertible securities	6.2	5.1	6.2	7.2
Add dilutive non-vested awards	1.0	1.0	1.1	1.0
Weighted average shares - diluted	272.0	269.0	271.6	268.1
Basic	$ 0.48	$ 0.56	$ 1.32	$ 1.18
Diluted	$ 0.46	$ 0.55	$ 1.29	$ 1.14