Earnings Per Share - CMS Energy (Basic and Diluted EPS Computation) (Details) (USD $) In Millions, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share - CMS Energy [Abstract]
Income from Continuing Operations	$ 140	$ 146	$ 374	$ 335
Less Income Attributable to Noncontrolling Interest	1	1	2	3
Less charge for deferred issuance cost of preferred stock	0	8	0	8
Less Preferred Stock Dividends		3		8
Income from Continuing operations available to common stockholders basic and diluted	$ 139	$ 134	$ 372	$ 316
Weighted average shares basic	251.3	229.0	250.5	228.4
Add dilutive contingently convertible securities	11.3	24.9	11.4	21.3
Add dilutive Non vested awards and options	0.6	0.2	0.4	0.1
Add dilutive convertible debentures	0.7	0.6
Weighted average shares - diluted	263.9	254.7	262.3	249.8
Basic	$ 0.55	$ 0.58	$ 1.48	$ 1.38
Diluted	$ 0.53	$ 0.53	$ 1.42	$ 1.26