Consolidated Statements Of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 384	$ 417	$ 343
Net loss arising during the period, net of tax	(10)	(11)	(9)
Amortization of net actuarial loss, net of tax	2	2	1
Prior service credit adjustment			1
Unrealized gain on investments, net of tax	2
Other Comprehensive Loss	(6)	(9)	(7)
Comprehensive Income	378	408	336
Comprehensive Income Attributable to Noncontrolling Interest	2	2	3
Comprehensive Income Attributable to CMS Energy	376	406	333
Consumers Energy Company [Member]
Net Income	439	467	434
Net loss arising during the period, net of tax	(8)	(4)	(5)
Amortization of net actuarial loss, net of tax	2	1
Unrealized gain on investments, net of tax	3	1	3
Reclassification adjustments included in net income	(3)
Other Comprehensive Loss	(6)	(2)	(2)
Comprehensive Income	$ 433	$ 465	$ 432