Reclassification From Accumulated Other Comprehensive Income (Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales	$ 457	$ 717	$ 1,082	$ 1,510
Provision (benefit) for income taxes	(493)	140	(444)	269
Net Income (Loss)	$ (788)	$ 207	(710)	$ 401
Reclassification from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)			(58)
Cash Flow Hedges [Member] | Reclassification from Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision (benefit) for income taxes			(37)
Net Income (Loss)			(58)
Cash Flow Hedges [Member] | Reclassification from Accumulated Other Comprehensive Income [Member] | Settlements [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales			$ (95)