Consolidated Statements Of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net gain (loss) arising during the period, tax	$ (7)	$ (7)	$ (6)
Amortization of net actuarial loss, tax	1	1
Tax on prior service credit adjustment			1
Unrealized gain (loss) on investments, tax expense (tax benefit)	1
Consumers Energy Company [Member]
Net gain (loss) arising during the period, tax	(5)	(3)	(3)
Amortization of net actuarial loss, tax	1	1
Unrealized gain (loss) on investments, tax expense (tax benefit)	2		2
Reclassification adjustments included in net income, tax	$ (2)