Earnings Per Share - CMS Energy (Basic and Diluted EPS Computation) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income from Continuing Operations	$ 41	$ 140	$ 101	$ 133	$ 31		$ 146		$ 100		$ 89		$ 415	$ 366	$ 220
Less Income Attributable to Noncontrolling Interest													2	3	11
Less charge for deferred issuance cost of preferred stock							8						0	8	0
Less Preferred Stock Dividends														8	11
Income from Continuing operations available to common stockholders basic and diluted													413	347	198
Weighted average shares basic													250.8	231.5	227.2
Add dilutive contingently convertible securities													12.2	21.3	10.6
Add dilutive Non vested awards and options													0.4	0.1	0.1
Weighted average shares - diluted													263.4	252.9	237.9
Basic	$ 0.16	$ 0.55	$ 0.40	$ 0.53	$ 0.13	[1]	$ 0.58	[1]	$ 0.42	[1]	$ 0.38	[1]	$ 1.65	$ 1.50	$ 0.87
Diluted	$ 0.15	$ 0.53	$ 0.38	$ 0.51	$ 0.11	[1]	$ 0.53	[1]	$ 0.39	[1]	$ 0.35	[1]	$ 1.57	$ 1.36	$ 0.83
CMS Energy Corporation [Member]
Income from Continuing Operations													415	350	229
Less charge for deferred issuance cost of preferred stock														$ 8

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