Consolidated Statements of Changes in Equity (USD $) In Millions, except Share data	Consumers Energy Company [Member] CMS Energy Common Stock [Member]	Consumers Energy Company [Member] Other Paid-in Capital [Member]	Consumers Energy Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Consumers Energy Company [Member] Retirement benefits liability [Member]	Consumers Energy Company [Member] Investments [Member]	Consumers Energy Company [Member] Retained Earnings (Accumulated Deficit) [Member]	Consumers Energy Company [Member] Preferred Stock [Member]	Consumers Energy Company [Member] Comprehensive Income [Member]	Consumers Energy Company [Member]	CMS Energy Common Stock [Member]	Other Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retirement benefits liability [Member]	Investments [Member]	Derivative instruments [Member]	Retained Earnings (Accumulated Deficit) [Member]	Preferred Stock [Member]	Noncontrolling Interest [Member]	Comprehensive Income [Member]	Total
Total Equity, beginning at Dec. 31, 2008	$ 841	$ 2,482	$ (1)	$ (7)	$ 6	$ 383	$ 44		$ 3,749	$ 2	$ 4,533	$ (28)	$ (27)		$ (1)	$ (2,031)	$ 243	$ 96		$ 2,815
Beginning of period, shares at Dec. 31, 2008											226,414,000
Shares of common stock issued											1,793,000
Common stock issued											17
Common stock reissued, shares											0
Common stock reissued, value											0
Common stock repurchased, shares											(78,000)
Common stock repurchased											(1)
Common stock reacquired, shares											(238,000)
Common stock reacquired, value											0
Conversion option on convertible debt											11
Charge for deferred issuance costs											0					0
Stockholder's contribution		100							100
Income attributable to noncontrolling interests																		11	11	11
Net gain (loss) arising during the period				(4)				(4)					(6)						(6)
Amortization of net actuarial loss				0				0					1						1
Prior service credit adjustment													0						0
Unrealized gain (loss) on investments, net of tax					10			10						5					5
Reclassification adjustments included in net income (loss), net of tax					(3)			(3)	3					(5)					(5)	5
Net income						293		293	293										240	240
Common stock dividends declared						(285)										(114)
Preferred stock dividends declared						(2)										(11)
Distributions and other changes in noncontrolling interests																		(10)
Net Income Attributable to CMS Energy																229			229	229
Total Comprehensive Income								296											224
Conversion of preferred stock																	(4)
Total Equity, end at Dec. 31, 2009	841	2,582	2	(11)	13	389	44		3,858	2	4,560	(33)	(32)	0	(1)	(1,927)	239	97		2,938
End of period, shares at Dec. 31, 2009											227,891,000
Net income									107											88
Net Income Attributable to CMS Energy																				88
Total Equity, end at Mar. 31, 2010
Total Equity, beginning at Dec. 31, 2009	841	2,582	2	(11)	13	389	44		3,858	2	4,560	(33)	(32)	0	(1)	(1,927)	239	97		2,938
Beginning of period, shares at Dec. 31, 2009											227,891,000
Shares of common stock issued											22,090,000
Common stock issued											22
Common stock reissued, shares											0
Common stock reissued, value											0
Common stock repurchased, shares											(148,000)
Common stock repurchased											(2)
Common stock reacquired, shares											(205,000)
Common stock reacquired, value											0
Conversion option on convertible debt											0
Charge for deferred issuance costs											8					(8)
Stockholder's contribution		250							250
Income attributable to noncontrolling interests																		3	3	3
Net gain (loss) arising during the period				(5)				(5)					(9)						(9)
Amortization of net actuarial loss				0				0					1						1
Prior service credit adjustment													1						1
Unrealized gain (loss) on investments, net of tax					3			3						0					0
Reclassification adjustments included in net income (loss), net of tax					0			0						0					0
Net income						434		434	434										343	343
Common stock dividends declared						(358)										(154)
Preferred stock dividends declared						(2)										(8)
Distributions and other changes in noncontrolling interests																		(56)
Net Income Attributable to CMS Energy																340			340	340
Total Comprehensive Income								432											333
Conversion of preferred stock																	(239)
Total Equity, end at Dec. 31, 2010	841	2,832	0	(16)	16	463	44		4,180	2	4,588	(40)	(39)	0	(1)	(1,757)	0	44		2,837
End of period, shares at Dec. 31, 2010											249,628,000
Total Equity, beginning at Mar. 31, 2010
Income attributable to noncontrolling interests																				2
Net income									88											84
Net Income Attributable to CMS Energy																				82
Total Equity, end at Jun. 30, 2010														0
Income attributable to noncontrolling interests																				1
Net income									160											146
Net Income Attributable to CMS Energy																				145
Total Equity, end at Sep. 30, 2010
Net income									79											25
Net Income Attributable to CMS Energy																				25
Total Equity, end at Dec. 31, 2010			0				44		4,180			(40)			(1)					2,837
Net income									153											135
Net Income Attributable to CMS Energy																				135
Total Equity, end at Mar. 31, 2011
Total Equity, beginning at Dec. 31, 2010	841	2,832	0	(16)	16	463	44		4,180	2	4,588	(40)	(39)	0	(1)	(1,757)	0	44		2,837
Beginning of period, shares at Dec. 31, 2010											249,628,000
Shares of common stock issued											4,541,000
Common stock issued										1	40
Common stock reissued, shares											269,000
Common stock reissued, value											5
Common stock repurchased, shares											(323,000)
Common stock repurchased											(6)
Common stock reacquired, shares											(15,000)
Common stock reacquired, value											0
Conversion option on convertible debt											0
Charge for deferred issuance costs											0					0
Stockholder's contribution		125							125
Income attributable to noncontrolling interests																		2	2	2
Net gain (loss) arising during the period				(4)				(4)					(11)						(11)
Amortization of net actuarial loss				1				1					2						2
Prior service credit adjustment																			0
Unrealized gain (loss) on investments, net of tax					1			1						0					0
Reclassification adjustments included in net income (loss), net of tax					0			0						0					0
Net income						467		467	467										417	417
Common stock dividends declared						(374)										(211)
Preferred stock dividends declared						(2)										0
Distributions and other changes in noncontrolling interests																		(2)
Net Income Attributable to CMS Energy																415			415	415
Total Comprehensive Income								465											406
Conversion of preferred stock																	0
Total Equity, end at Dec. 31, 2011	841	2,957	(2)	(19)	17	554	44		4,394	3	4,627	(49)	(48)	0	(1)	(1,553)	0	44		3,072
End of period, shares at Dec. 31, 2011											254,100,000
Total Equity, beginning at Mar. 31, 2011
Income attributable to noncontrolling interests																				1
Net income									92											101
Net Income Attributable to CMS Energy																				100
Total Equity, end at Jun. 30, 2011														0
Income attributable to noncontrolling interests																				1
Net income									155											140
Net Income Attributable to CMS Energy																				139
Total Equity, end at Sep. 30, 2011
Net income									67											41
Net Income Attributable to CMS Energy																				41
Total Equity, end at Dec. 31, 2011			$ (2)				$ 44		$ 4,394			$ (49)			$ (1)					$ 3,072