Reclassifications From Accumulated Other Comprehensive Income (Amounts Reclassified From AOCI Into Earnings) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Gas sales	$ 614,178		$ 435,392		$ 1,118,674		$ 897,526
General and administrative expenses	47,570		44,932		84,785		93,758
Loss before income taxes	409,842		(658,178)		622,454		(479,756)
Provision for income taxes	164,211	[1]	(253,046)	[1]	249,308	[1]	(182,328)	[1]
Net loss	245,631		(405,132)		373,146		(297,428)
Parent [Member]
Loss before income taxes	245,631		(405,132)		373,146		(297,428)
Net loss	245,631		(405,132)		373,146		(297,428)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Net loss					74,002
Reclassification out of Accumulated Other Comprehensive Income [Member] | Gains and Losses on Cash Flow Hedges [Member]
Loss before income taxes					124,225
Provision for income taxes					49,689
Net loss					74,536
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and Other Postretirement [Member]
General and administrative expenses					(890)	[2]
Loss before income taxes					(890)
Provision for income taxes					(356)
Net loss					(534)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Settlements [Member] | Gains and Losses on Cash Flow Hedges [Member]
Gas sales					124,956
Reclassification out of Accumulated Other Comprehensive Income [Member] | Ineffectiveness [Member] | Gains and Losses on Cash Flow Hedges [Member]
Gas sales					$ (731)

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

[2] This accumulated other comprehensive income component is included in the computation of net periodic pension cost (see footnote 13 for additional details.)