Consolidated Statements Of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net gain (loss) arising during the period, tax	$ 6		$ 6
Tax on prior service credit adjustment	3		3
Amortization of net actuarial loss, tax			2
Unrealized gain (loss) on investments, tax expense (tax benefit)	(1)	1	(1)	1
Consumers Energy Company [Member]
Amortization of net actuarial loss, tax	1		1
Reclassification adjustments included in net income, tax			$ (1)