Earnings Per Share - CMS Energy (Basic And Diluted EPS Computations) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share - CMS Energy [Abstract]
Income From Continuing Operations	$ 67	$ 149	$ 101	$ 60	$ 41		$ 140		$ 101		$ 133		$ 377	$ 415	$ 366
Less income attributable to noncontrolling interest													2	2	3
Less charge for deferred issuance cost of preferred stock															8
Less Preferred Stock Dividends															8
Income from Continuing Operations Available to Common Stockholders - Basic and Diluted													$ 375	$ 413	$ 347
Weighted average shares - basic													260.7	250.8	231.5
Add dilutive contingently convertible securities													6.8	12.2	21.3
Add dilutive non-vested awards and options													1.1	0.4	0.1
Weighted average shares - diluted													268.6	263.4	252.9
Basic	$ 0.26	$ 0.56	$ 0.38	$ 0.23	$ 0.16	[1]	$ 0.55	[1]	$ 0.40	[1]	$ 0.53	[1]	$ 1.43	$ 1.65	$ 1.50
Diluted	$ 0.25	$ 0.55	$ 0.37	$ 0.22	$ 0.15	[1]	$ 0.53	[1]	$ 0.38	[1]	$ 0.51	[1]	$ 1.39	$ 1.57	$ 1.36

[1] The sum of the quarters may not equal annual EPS due to changes in the number of shares outstanding.