Consolidated Statements Of Changes In Equity - USD ($) shares in Millions, $ 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 Dec. 31, 2013		$ 3,257	$ (2)	$ (17)	$ 15	$ 724		$ 4,857		$ 4,715	$ (22)	$ (21)		$ (1)	$ (1,242)	$ 37	$ 3,491
Common stock issued										52
Common stock repurchased										(7)
Conversion option on convertible debt										7
Stockholder contribution		495
Return of stockholder contribution		(178)
Amortization of net actuarial loss (gain)				2				2				2					2
Amortization of prior service credit												(1)					(1)
Unrealized gain (loss) on investments, net of tax					$ 2			2
Reclassification adjustments included in net income, net of tax
Reclassification adjustments included in net income														$ 1			(1)
Net income (loss) attributable to CMS Energy																	381
Net income						449		449							381		382
Dividends declared on common stock						(375)									(219)
Preferred stock dividends and distributions declared						(1)
Income Attributable to Noncontrolling Interests																1	1
Distributions, redemptions, and other changes in noncontrolling interests																(1)
Total Equity, end at Sep. 30, 2014	$ 841	3,574	2	(15)	$ 17	797	$ 37	5,251	$ 3	4,767	(20)	(20)			(1,080)	37	3,707
Total Equity, beginning at Jun. 30, 2014		3,572	2	(16)	18	798		5,250		4,761	(20)	(20)			(1,099)	37	3,682
Common stock issued										7
Common stock repurchased										(1)
Stockholder contribution		180
Return of stockholder contribution		(178)
Amortization of net actuarial loss (gain)				1				1				1					1
Amortization of prior service credit												(1)					(1)
Unrealized gain (loss) on investments, net of tax					$ (1)			(1)
Reclassification adjustments included in net income, net of tax
Reclassification adjustments included in net income
Net income (loss) attributable to CMS Energy																	94
Net income						119		119							94		94
Dividends declared on common stock						(120)									(75)
Total Equity, end at Sep. 30, 2014	841	3,574	2	(15)	$ 17	797	37	5,251	3	4,767	(20)	(20)			(1,080)	37	3,707
Total Equity, beginning at Dec. 31, 2014		3,574	(7)	(26)	19	832		$ 5,277		4,774	(49)	(48)	$ (1)		(1,058)	37	$ 3,707
Beginning of period, shares at Dec. 31, 2014								84.1									275.2
Common stock issued										56
Common stock repurchased										(11)
Common stock reissued										10
Stockholder contribution		150
Amortization of net actuarial loss (gain)				3				$ 3				4					$ 4
Amortization of prior service credit												(1)					(1)
Unrealized gain (loss) on investments, net of tax					(2)			(2)					(3)				(3)
Reclassification adjustments included in net income, net of tax					(5)			5
Reclassification adjustments included in net income
Net income (loss) attributable to CMS Energy																	417
Net income						459		$ 459							417		418
Dividends declared on common stock						(359)									(240)
Preferred stock dividends and distributions declared						(1)
Income Attributable to Noncontrolling Interests																1	$ 1
Distributions, redemptions, and other changes in noncontrolling interests																(1)
End of period, shares at Sep. 30, 2015								84.1									277.1
Total Equity, end at Sep. 30, 2015	841	3,724	(11)	(23)	12	931	37	$ 5,522	3	4,829	(49)	(45)	(4)		(881)	37	$ 3,939
Total Equity, beginning at Jun. 30, 2015		$ 3,724	(12)	(24)	$ 12	876		5,466		4,812	(48)	(46)	(2)		(949)	37	3,855
Common stock issued										$ 17
Common stock repurchased
Stockholder contribution
Amortization of net actuarial loss (gain)				1				1				2					2
Amortization of prior service credit												(1)					(1)
Unrealized gain (loss) on investments, net of tax													(2)				(2)
Reclassification adjustments included in net income, net of tax
Reclassification adjustments included in net income
Net income (loss) attributable to CMS Energy																	148
Net income						160		$ 160							148		$ 148
Dividends declared on common stock						(105)									(80)
End of period, shares at Sep. 30, 2015								84.1									277.1
Total Equity, end at Sep. 30, 2015	$ 841	$ 3,724	$ (11)	$ (23)	$ 12	$ 931	$ 37	$ 5,522	$ 3	$ 4,829	$ (49)	$ (45)	$ (4)		$ (881)	$ 37	$ 3,939