Discontinued Operations (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	Dec. 31, 2010
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges									$ 464
Write down of assets held for sale to net realizable value, net of tax									297
Summarized results of discontinued operations:
Total operating revenues									0	395	527
Total operating expenses									29	(496)	(538)
Asset impairment and other charges									0	(89)	(1,032)
Other income (expense)									0	5	0
Income (loss) before income taxes									29	(185)	(1,043)
Discontinued Operations, Reorganization Items									22	0	0
Provision (benefit) for income taxes									6	(73)	(411)
Income (loss) from operations of discontinued operations	(15)	(1)	18	(1)	17	(76)	(29)	(24)	1	(112)	(632)
Major components of asset and liabilities of discontinued operations:
Cash and cash equivalents	0				2				0	2	79	127
Other current assets	0				7				0	7
Carrying value adjustment	0				(9)				0	(9)
Assets of discontinued operations	0				0				0	0
Homer City
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges										89	1,032
Write down of assets held for sale to net realizable value, net of tax										$ 53	$ 623