Reclassification From Accumulated Other Comprehensive Income (Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales	$ 625	$ 793
Provision (benefit) for income taxes	49	129
Net Income	78	194
Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(25)
Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision (benefit) for income taxes	17
Net Income	(25)
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	$ (42)