Consolidated Statements of Changes in Equity (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net gain (loss) arising during the period, tax	$ (7)	$ (6)	$ (3)
Amortization of net actuarial loss, tax	1	0	0
Tax on prior service credit adjustment	0	1	0
Unrealized gain (loss) on investments, tax expense (tax benefit)	0	0	3
Reclassification adjustments included in net income, tax	0	0	(3)
Consumers Energy Company [Member]
Net gain (loss) arising during the period, tax	(3)	(3)	(2)
Amortization of net actuarial loss, tax	1	0	0
Unrealized gain (loss) on investments, tax expense (tax benefit)	0	2	6
Reclassification adjustments included in net income, tax	$ 0	$ 0	$ (2)