Earnings Per Share - CMS Energy (Basic and Diluted EPS Computation) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share - CMS Energy [Abstract]
Income from Continuing Operations	$ 101	$ 101	$ 161	$ 234
Less Income Attributable to Noncontrolling Interest	1	1	1	1
Income from Continuing operations available to common stockholders basic and diluted	$ 100	$ 100	$ 160	$ 233
Weighted average shares basic	261.2	250.3	258.4	250.2
Add dilutive contingently convertible securities	5.9	11.3	8.3	11.0
Add dilutive Non vested awards and options	1.1	0.3	1.0	0.3
Weighted average shares - diluted	268.2	261.9	267.7	261.5
Basic	$ 0.38	$ 0.40	$ 0.61	$ 0.93
Diluted	$ 0.37	$ 0.38	$ 0.59	$ 0.89