Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share - CMS Energy [Abstract]
Income From continuing operations	$ 81	$ 101	$ 225	$ 161
Income attributable to noncontrolling interests	1	1	1	1
Income from Continuing operations available to common stockholders basic and diluted	$ 80	$ 100	$ 224	$ 160
Weighted average shares - basic	264.5	261.2	264.1	258.4
Add dilutive contingently convertible securities	6.4	5.9	6.2	8.3
Add dilutive non-vested awards	1.3	1.1	1.2	1.0
Weighted average shares - diluted	272.2	268.2	271.5	267.7
Basic	$ 0.30	$ 0.38	$ 0.85	$ 0.61
Diluted	$ 0.29	$ 0.37	$ 0.83	$ 0.59