Income Taxes (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Effective Tax Rate
Loss from continuing operations before income taxes	$ (203,000,000)	$ (88,000,000)	$ (375,000,000)	$ (151,000,000)
Benefit for income taxes at federal statutory rate of 35%	(71,000,000)	(30,000,000)	(131,000,000)	(53,000,000)
Increase (decrease) in income tax from
State tax - net of federal benefit	(6,000,000)	(4,000,000)	(21,000,000)	(9,000,000)
Production tax credits, net	(17,000,000)	(18,000,000)	(36,000,000)	(36,000,000)
Taxes on income allocated to noncontrolling interests	(5,000,000)	(1,000,000)	(4,000,000)	(1,000,000)
Other	0	(4,000,000)	2,000,000	(3,000,000)
Total benefit for income taxes from continuing operations	(99,000,000)	(57,000,000)	(190,000,000)	(102,000,000)
Effective tax rate (as a percent)	49.00%	65.00%	51.00%	68.00%
Federal statutory rate (as a percent)	35.00%	35.00%	35.00%	35.00%
Tax benefits related tax credit carryforwards and operating loss carryforwards	961,000,000		961,000,000
IRS Examination
Increase (decrease) in income tax from
Estimated potential future federal tax payment as of the balance sheet date, including interest and penalties, based on a proposed adjustment	196,000,000		196,000,000
Penalty for understatement of tax liability (as a percent)			40.00%
Homer City
Income Tax Disclosures:
Tax deduction due to change in tax treatment of entity			$ 1,000,000,000