Consolidated Statements Of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income	$ 479	$ 454	$ 384
Retirement Benefits Liability
Net gain (loss) arising during the period, net of tax	(29)	26	(10)
Prior service credit adjustment, net of tax		5
Amortization of net actuarial loss, net of tax	3	4	2
Amortization of prior service credit, net of tax	(1)
Investments
Unrealized gain (loss) on investments, net of tax	(1)	(2)	2
Derivative Instruments
Reclassification adjustments included in net income, net of tax	1
Other Comprehensive Income (Loss)	(27)	33	(6)
Comprehensive Income	452	487	378
Comprehensive Income Attributable to Noncontrolling Interest	2	2	2
Comprehensive Income Attributable to CMS Energy	450	485	376
Consumers Energy Company [Member]
Net Income	567	534	439
Retirement Benefits Liability
Net gain (loss) arising during the period, net of tax	(11)	5	(8)
Amortization of net actuarial loss, net of tax	2	3	2
Investments
Unrealized gain (loss) on investments, net of tax	4	1	3
Reclassification adjustments included in net income, net of tax		(3)	(3)
Derivative Instruments
Other Comprehensive Income (Loss)	(5)	6	(6)
Comprehensive Income	$ 562	$ 540	$ 433