Consolidated Statements Of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Income	$ 462	$ 553	$ 525
Retirement Benefits Liability
Net gain (loss) arising during the period, net of tax	(5)	(8)	1
Prior service credit adjustment, net of tax	4
Amortization of net actuarial loss, net of tax	2	2	5
Amortization of prior service credit, net of tax	(1)	(1)	(1)
Investments
Unrealized gain (loss) on investments, net of tax		1	(3)
Other-than-temporary impairment included in net income, net of tax		3
Other Comprehensive Income (Loss)		(3)	2
Comprehensive Income	462	550	527
Comprehensive Income Attributable to Noncontrolling Interest	2	2	2
Comprehensive Income Attributable to CMS Energy	460	548	525
Consumers Energy Company [Member]
Net Income	632	616	594
Retirement Benefits Liability
Net gain (loss) arising during the period, net of tax	(4)	(3)	3
Amortization of net actuarial loss, net of tax	1	1	4
Investments
Unrealized gain (loss) on investments, net of tax	3	3	(1)
Reclassification adjustments included in net income, net of tax	(9)		(5)
Other-than-temporary impairment included in net income, net of tax		2
Other Comprehensive Income (Loss)	(9)	3	1
Comprehensive Income Attributable to CMS Energy	$ 623	$ 619	$ 595