Discontinued Operations And Held For Sale Businesses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Jun. 30, 2012 Red Oak [Member]	Mar. 31, 2012 Red Oak [Member] mw	Jun. 30, 2012 Ironwood [Member]	Mar. 31, 2012 Ironwood [Member] mw
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Generation Capacity (MW)				832		710
Divestiture Of Ownership In Subsidiary Percent				100.00%		100.00%
Sale Proceeds			$ 147		$ 87
Expected gain on sale (minimum)			60		65
Expected gain on sale (maximum)			70		75
Discontinued Operations Income Loss
Revenue	37	197
Income (loss) from operations of discontinued businesses	3	(10)
Income tax (expense) benefit	(2)	3
Income (loss) from operations of discontinued businesses	1	(7)
Net gain/(loss) on sale and impairments of discontinued operations, net of tax	$ (5)	$ 0