Reclassification From Accumulated Other Comprehensive Income (Amounts Reclassified From Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gas sales									$ 2,827	$ 2,381	$ 1,956
Net actuarial loss									25
Gain (loss) before income taxes									1,449	1,190	(1,150)
Provision (benefit) for income taxes									525	486	(443)
Net Income (Loss)	312	211	207	194	144	186	246	128	924	704	(707)
Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)									1
Gains (Losses) To Other Comprehensive Income On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gain (loss) before income taxes									26
Provision (benefit) for income taxes									10
Net Income (Loss)									16
Gains (Losses) To Other Comprehensive Income 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									26
Pension And Other Postretirement [Member] | Reclassification Out Of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net actuarial loss									(25)
Gain (loss) before income taxes									(25)
Provision (benefit) for income taxes									(10)
Net Income (Loss)									$ (15)