Earnings Per Share - CMS Energy (Basic and Diluted EPS Computation) (Details) (USD $) In Millions, except Per Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share - CMS Energy
Income from Continuing Operations	$ 101	$ 100	$ 234	$ 189
Less Income Attributable to Noncontrolling Interest	1	2	1	2
Less Preferred Stock Dividends		2		5
Income from Continuing operations available to common stockholders basic and diluted	$ 100	$ 96	$ 233	$ 182
Weighted average shares basic	250.3	228.2	250.2	228.1
Add dilutive contingently convertible securities	11.3	19.3	11.0	19.5
Add dilutive Non vested awards and options	0.3	0.1	0.3	0.1
Weighted average shares - diluted	261.9	247.6	261.5	247.7
Basic	$ 0.40	$ 0.42	$ 0.93	$ 0.80
Diluted	$ 0.38	$ 0.39	$ 0.89	$ 0.74

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