CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net gain (loss) adjustment, tax expense (benefit)	$ 22	$ 4	$ (10)
Unrealized holding losses arising during period, income tax expense (benefit)	19	(6)	(7)
Reclassification adjustments included in net loss, income tax benefit	(3)	16	25
Midwest Generation LLC [Member]
Net gain (loss) adjustment, tax expense (benefit)	17	0	(8)
Unrealized holding losses arising during period, income tax expense (benefit)	(1)	3	15
Reclassification adjustments included in net loss, income tax benefit	$ (2)	$ 17	$ 16