Consolidated Statements Of Changes In Equity (USD $) In Millions	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]	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]	Noncontrolling Interest [Member]	Total
Total Equity, beginning at Jun. 30, 2011	$ 841	$ 2,957		$ (15)	$ 15	$ 511	$ 44	$ 4,353	$ 3	$ 4,621	$ (38)	$ (38)	$ 1	$ (1)	$ (1,628)	$ 44	$ 3,002
Common stock issued										7
Common stock reissued
Common stock repurchased										(6)
Stockholder contribution
Retirement benefits liability adjustments, net of tax
Unrealized gain (loss) on investments, net of tax													(2)				(2)
Net income						155		155									140
Net income attributable to CMS Energy															139		139
Common stock dividends declared						(96)									(53)
Preferred stock dividends declared						(1)
Income attributable to noncontrolling interests																1	1
Distributions and other changes in noncontrolling interests																(1)
Total Equity, end at Sep. 30, 2011	841	2,957		(15)	15	569	44	4,411	3	4,622	(40)	(38)	(1)	(1)	(1,542)	44	3,087
Total Equity, beginning at Dec. 31, 2010	841	2,832		(16)	16	463	44	4,180	2	4,588	(40)	(39)		(1)	(1,757)	44	2,837
Common stock issued									1	35
Common stock reissued										5
Common stock repurchased										(6)
Stockholder contribution		125						125
Retirement benefits liability adjustments, net of tax				1				1				1					1
Unrealized gain (loss) on investments, net of tax					(1)			(1)					(1)				(1)
Net income						400		400									376
Net income attributable to CMS Energy															374		374
Common stock dividends declared						(292)									(159)
Preferred stock dividends declared						(2)
Income attributable to noncontrolling interests																2	2
Distributions and other changes in noncontrolling interests																(2)
Total Equity, end at Sep. 30, 2011	841	2,957		(15)	15	569	44	4,411	3	4,622	(40)	(38)	(1)	(1)	(1,542)	44	3,087
Total Equity, beginning at Dec. 31, 2011	841	2,957	(2)	(19)	17	554	44	4,394	3	4,627	(49)	(48)		(1)	(1,553)	44	3,072
Common stock issued										38
Common stock reissued										6
Common stock repurchased										(9)
Stockholder contribution		150						150
Retirement benefits liability adjustments, net of tax				2				2				3					3
Unrealized gain (loss) on investments, net of tax													3				3
Net income						361		361									317
Net income attributable to CMS Energy															315		315
Common stock dividends declared						(302)									(188)
Preferred stock dividends declared						(2)
Income attributable to noncontrolling interests																2	2
Distributions and other changes in noncontrolling interests																(2)
Total Equity, end at Sep. 30, 2012	841	3,107		(17)	17	611	44	4,603	3	4,662	(43)	(45)	3	(1)	(1,426)	44	3,240
Total Equity, beginning at Jun. 30, 2012	841	3,107	(1)	(18)	17	593	44	4,584	3	4,664	(45)	(46)	2	(1)	(1,511)	44	3,155
Common stock issued										7
Common stock reissued
Common stock repurchased										(9)
Stockholder contribution
Retirement benefits liability adjustments, net of tax				1				1				1					1
Unrealized gain (loss) on investments, net of tax													1				1
Net income						163		163									149
Net income attributable to CMS Energy															148		148
Common stock dividends declared						(144)									(63)
Preferred stock dividends declared						(1)
Income attributable to noncontrolling interests																1	1
Distributions and other changes in noncontrolling interests																(1)
Total Equity, end at Sep. 30, 2012	$ 841	$ 3,107		$ (17)	$ 17	$ 611	$ 44	$ 4,603	$ 3	$ 4,662	$ (43)	$ (45)	$ 3	$ (1)	$ (1,426)	$ 44	$ 3,240