Summary Of Significant Accounting Policies Summary Of Significant Accounting Policies (Reclassification Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		3 Months Ended													12 Months Ended
		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014	Sep. 30, 2014		Jun. 30, 2014	Mar. 31, 2014		Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues		$ 301,062		$ 339,815		$ 596,127		$ 523,909	$ 366,623		$ 440,144	$ 756,242		$ 550,072	$ 1,760,913	$ 2,113,081	$ 1,829,551
Purchased Gas															(349,984)	(605,838)	(460,432)
Other Income															8,039	9,461	4,697
Income Before Income Taxes															(698,563)	489,027	432,759
Income Tax Expense															319,136	(189,614)	(172,758)
Net Income (Loss) Available for Common Stock		$ (187,703)	[1]	$ (293,134)	[2]	$ 16,669	[3]	$ 84,741	$ 57,431	[2]	$ 64,520	$ 95,210	[4]	$ 82,252	(379,427)	299,413	$ 260,001
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income Before Income Taxes															176,327	(26,188)
Income Tax Expense															(75,187)	12,643
Net Income (Loss) Available for Common Stock															101,140	(13,545)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Gains and Losses on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Income															591	662
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Amortization of Prior Year Funded Status of Pension and Other Post-Retirement Benefit Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of Prior Service Credit	[5]														109	131
Recognition of Net Actuarial Loss	[5]														(9,326)	(9,334)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Commodity Contract [Member] | Gains and Losses on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues															180,069	(14,880)
Purchased Gas															$ 4,884	$ (2,767)

[1] Includes a non-cash $417.2 million impairment charge ($240.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $8.0 million reversal of stock-based compensation expense ($5.2 million after tax) related to performance based restricted stock units.

[2] Includes a non-cash $588.7 million impairment charge ($339.8 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $120.3 million impairment charge ($69.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[4] Includes $3.6 million of income associated with a death benefit gain on life insurance proceeds recorded in the Corporate category.

[5] These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note H — Retirement Plan and Other Post-Retirement Benefits for additional details.