Consolidated Statements Of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net Income (Loss)	$ 148	$ 94	$ 418	$ 382
Retirement Benefits Liability
Amortization of net actuarial loss (gain), net of tax	2	1	4	2
Amortization of prior service credit, net of tax	(1)	(1)	(1)	(1)
Investments
Unrealized gain (loss) on investments, net of tax	(2)		(3)
Derivative Instruments
Reclassification adjustments included in net income, net of tax				1
Other Comprehensive Income (Loss)	(1)			2
Comprehensive Income (Loss)	147	94	418	384
Comprehensive Income Attributable to Noncontrolling Interest			1	1
Comprehensive Income Attributable to CMS Energy	147	94	417	383
Consumers Energy Company [Member]
Net Income (Loss)	160	119	459	449
Retirement Benefits Liability
Amortization of net actuarial loss (gain), net of tax	1	1	3	2
Investments
Unrealized gain (loss) on investments, net of tax		(1)	(2)	2
Reclassification adjustments included in net income, net of tax			(5)
Derivative Instruments
Other Comprehensive Income (Loss)	1		(4)	4
Comprehensive Income Attributable to CMS Energy	$ 161	$ 119	$ 455	$ 453