Quarterly Financial and Common Stock Information (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
Operating Revenue	$ 1,670	$ 1,507	$ 1,333	$ 1,743	$ 1,620		$ 1,464		$ 1,364		$ 2,055		$ 6,253		$ 6,503		$ 6,432
Operating Income (Loss)	212	343	260	188	174		316		207		306		1,003		1,003		978
Income From Continuing Operations	67	149	101	60	41		140		101		133		377		415		366
Income (Loss) From Discontinued Operations				7							2		7	[1]	2	[2]	(23)	[3]
Net Income	67	149	101	67	41		140		101		135		384		417		343
Income Attributable to Noncontrolling Interests		1	1				1		1				2		2		3
Net Income Attributable to CMS Energy	67	148	100	67	41		139		100		135		382		415		340
Net Income Available to Common Stockholders	67	148	100	67	41		139		100		135		382		415		324
Earnings from continuing operations per average common share - basic	$ 0.26	$ 0.56	$ 0.38	$ 0.23	$ 0.16	[4]	$ 0.55	[4]	$ 0.40	[4]	$ 0.53	[4]	$ 1.43		$ 1.65		$ 1.50
Earnings from continuing operations per average common share - diluted	$ 0.25	$ 0.55	$ 0.37	$ 0.22	$ 0.15	[4]	$ 0.53	[4]	$ 0.38	[4]	$ 0.51	[4]	$ 1.39		$ 1.57		$ 1.36
Basic earnings per average common share	$ 0.26	$ 0.56	$ 0.38	$ 0.26	$ 0.16	[4]	$ 0.55	[4]	$ 0.40	[4]	$ 0.54	[4]	$ 1.46		$ 1.66		$ 1.40
Diluted earnings per average common share	$ 0.25	$ 0.55	$ 0.37	$ 0.25	$ 0.15	[4]	$ 0.53	[4]	$ 0.38	[4]	$ 0.52	[4]	$ 1.42		$ 1.58		$ 1.28
CMS Energy [Member]
Operating Income (Loss)													(8)		(3)		(6)
Income From Continuing Operations													382		415		350
Income (Loss) From Discontinued Operations																	(10)
Net Income													382		415		340
Net Income Available to Common Stockholders													382		415		324
Consumers Energy Company [Member]
Operating Revenue	1,608	1,448	1,282	1,675	1,565		1,397		1,303		1,988		6,013		6,253		6,156
Operating Income (Loss)	207	334	260	183	173		305		207		300		984		985		926
Net Income	78	163	122	76	67		155		92		153		439		467		434
Preferred Stock Dividends		1	1				1		1
Net Income Available to Common Stockholders	$ 78	$ 162	$ 121	$ 76	$ 67		$ 154		$ 91		$ 153		$ 437		$ 465		$ 432
Maximum [Member] | CMS Energy Common Stock [Member]
Share price	$ 24.70	$ 24.81	$ 23.87	$ 22.31	$ 22.35		$ 20.47		$ 20.39		$ 19.78		$ 24.70		$ 22.35
Minimum [Member] | CMS Energy Common Stock [Member]
Share price	$ 22.79	$ 22.70	$ 21.52	$ 21.33	$ 19.18		$ 17.16		$ 18.90		$ 18.60		$ 22.79		$ 19.18

[1] Includes an $11 million ($7 million net of tax) reversal of a loss on disposal due to the elimination of a liability associated with the 2003 sale of Panhandle.

[2] Includes an operating gain of $3 million related to a litigation settlement at CMS Viron.

[3] Includes an operating loss of $2 million ($1 million net of tax) at Exeter, whose assets and liabilities were reclassified as held for sale in 2009.

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