Reclassification From Accumulated Other Comprehensive Income (Amounts Reclassified From Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Gas sales	$ 2,381,478		$ 1,956,311		$ 2,078,151
General and administrative expenses	191,310		175,147		158,041
Income (loss) before income taxes	1,190,377		(1,150,203)		1,050,990
Provision (benefit) for income taxes	486,874	[1]	(443,139)	[1]	413,221	[1]
Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Net income (loss)	171,762
Parent [Member]
Income (loss) before income taxes			(707,064)		637,769
Gains And Losses On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Income (loss) before income taxes	307,525
Provision (benefit) for income taxes	123,010
Net income (loss)	184,515
Gains And Losses On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Settlements [Member]
Gas sales	309,177
Gains And Losses On Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Ineffectiveness [Member]
Gas sales	(1,652)
Pension And Other Postretirement [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
General and administrative expenses	(21,009)	[2]
Income (loss) before income taxes	(21,009)
Provision (benefit) for income taxes	(8,256)
Net income (loss)	$ (12,753)

[1] Interest expense and the provision (benefit) for income taxes by segment are an allocation of corporate amounts as they are incurred at the corporate level.

[2] Included in the computation of net periodic pension cost (see Note 12 for additional details).