Income Taxes (Components of Income Tax Expense) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current:
Federal									$ 0	$ 0	$ 48
State									0	0	(44)
Total current									0	0	4
Deferred:
Federal									(33)	26	(389)
State									(60)	134	(56)
Total deferred									(93)	160	(445)
Provision (benefit) for income taxes from continuing operations									(93)	160	(441)
Discontinued operations									6	(73)	(411)
Total									(87)	87	(852)
Components of income (loss) before income taxes:
Continuing operations									(735)	(637)	(888)
Discontinued operations									7	(185)	(1,043)
Total									(728)	(822)	(1,931)
Midwest Generation LLC [Member]
Current:
Federal									0	0	2
State									0	0	12
Total current									0	0	14
Deferred:
Federal									(14)	(76)	(145)
State									(3)	14	(41)
Total deferred									(17)	(62)	(186)
Provision (benefit) for income taxes from continuing operations	(17)	(1)	1	0	(23)	(7)	(27)	(5)	(17)	(62)	(172)
Components of income (loss) before income taxes:
Continuing operations									$ (650)	$ (1,526)	$ (442)