Consolidated Statements Of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net Income	$ 144	$ 67
Retirement benefits liability adjustments, net of tax	1	1
Unrealized gain (loss) on investments		1
Other Comprehensive Income (Loss)	1	2
Comprehensive Income	145	69
Comprehensive Income Attributable to CMS Energy	145	69
Consumers Energy Company [Member]
Net Income	162	76
Retirement benefits liability adjustments, net of tax	1	1
Unrealized gain (loss) on investments	4	(3)
Reclassification adjustments included in net income, net of tax	(3)
Other Comprehensive Income (Loss)	2	(2)
Comprehensive Income	$ 164	$ 74