Reclassification From Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales	$ 645		$ 617		$ 2,155		$ 1,736
Loss before income taxes	351		310		1,021		932
Benefit for income taxes	140	[1]	124	[1]	409	[1]	373	[1]
Net Income (Loss)	211		186		612		559
Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)					(28)
Gains (Losses) On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss before income taxes					(47)
Benefit for income taxes					(19)
Net Income (Loss)					(28)
Gains (Losses) On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member] | Settlements [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales					(48)
Gains (Losses) On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member] | Ineffectiveness [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales					$ 1

[1] Interest expense and the provision for income taxes by segment are allocated as they are incurred at the corporate level.