Quarterly Financial Data (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
Quarterly Financial Information [Line Items]
Operating revenues	$ 324	$ 385		$ 315	$ 307	$ 280		$ 340	$ 324	$ 343	$ 1,331	$ 1,287	$ 1,653
Operating income (loss)	(38)	(431)	[1]	(63)	(47)	(111)		(71)	(98)	(48)	(579)	(328)	(698)
Provision (benefit) for income taxes											(93)	160	(441)
Income (loss) from continuing operations	(12)	(447)		(102)	(81)	(578)		(86)	(75)	(58)	(642)	(797)	(447)
Income (loss) from operations of discontinued subsidiaries, net of tax	(15)	(1)		18	(1)	17		(76)	(29)	(24)	1	(112)	(632)
Net Income (Loss)	(27)	(448)		(84)	(82)	(561)		(162)	(104)	(82)	(641)	(909)	(1,079)
Impairment charges											464
Impairment charges, after tax											297
Midwest Generation LLC [Member]
Quarterly Financial Information [Line Items]
Operating revenues	203	232		203	179	193		253	213	233	817	892	1,286
Operating income (loss)	(23)	(463)	[1]	(40)	(60)	(1,437)	[2]	(39)	(88)	(33)	(586)	(1,597)	(516)
Provision (benefit) for income taxes	(17)	(1)		1	0	(23)		(7)	(27)	(5)	(17)	(62)	(172)
Net Income (Loss)	(14)	(471)		(74)	(74)	(1,401)		(12)	(42)	(9)	(633)	(1,464)	(270)
Impairment charges											464		640
Impairment charges, after tax											297
Impairment of loan to affiliate											$ 0	$ 1,378	$ 0

[1] Reflects a $464 million pre-tax ($297 million, after tax) impairment charge related to Will County. For more information, see Note 13—Asset Impairments and Other Charges.

[2] Reflects a $1.4 billion pre-tax charge for a valuation allowance recorded by Midwest Generation on its note receivable from EME. For more information, see Note 15—Related Party Transactions.