Capitalization And Short-Term Borrowings (Summary Of Changes In Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended															12 Months Ended
		Sep. 30, 2016		Jun. 30, 2016	[2]	Mar. 31, 2016	[3]	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015	[6]	Mar. 31, 2015	[7]	Dec. 31, 2014	Sep. 30, 2016		Sep. 30, 2015	Sep. 30, 2014
Schedule of Capitalization [Line Items]
Beginning balance (shares)								84,594,383									84,594,383
Beginning balance								$ 744,274									$ 744,274
Balance at Beginning of Year								1,103,200								$ 1,614,361	1,103,200		$ 1,614,361	$ 1,442,617
Beginning balance								93,372								(3,979)	93,372		(3,979)
Net Income (Loss) Available for Common Stock		$ 37,553	[1]	$ 8,286		$ (147,688)		$ (189,109)	[4]	$ (187,703)	[5]	$ (293,134)		$ 16,669		$ 84,741	(290,958)		(379,427)	299,413
Dividends Declared on Common Stock																	(135,881)		(131,734)	(127,669)
Other Comprehensive Income (Loss), Net of Tax																	(99,012)		97,351	15,255
Share-Based Payment Expense																	$ 4,800		$ 2,100	10,500
Ending balance (Shares)		85,118,886								84,594,383							85,118,886		84,594,383
Ending balance		$ 771,164								$ 744,274							$ 771,164		$ 744,274
Balance at End of Year		676,361								1,103,200							676,361		1,103,200	1,614,361
Ending balance		(5,640)								$ 93,372							(5,640)		93,372	(3,979)
Tax benefits related to stock-based compensation																	$ 1,868		$ 9,064	$ 4,641
Dividend per share																	$ 1.60		$ 1.56	$ 1.52
Accumulated earnings free from limitations		$ 532,200															$ 532,200
Common Stock [Member]
Schedule of Capitalization [Line Items]
Beginning balance (shares)								84,594,000								84,157,000	84,594,000		84,157,000	83,662,000
Beginning balance (value)								$ 84,594								$ 84,157	$ 84,594		$ 84,157	$ 83,662
Common Stock Issued Under Stock and Benefit Plans (Shares)	[8]																525,000		437,000	495,000
Common Stock Issued Under Stock and Benefit Plans (Value)	[8]																$ 525		$ 437	$ 495
Ending balance (Shares)		85,119,000								84,594,000							85,119,000		84,594,000	84,157,000
Ending balance (Value)		$ 85,119								$ 84,594							$ 85,119		$ 84,594	$ 84,157
Paid In Capital [Member]
Schedule of Capitalization [Line Items]
Beginning balance								744,274								716,144	744,274		716,144	687,684
Share-Based Payment Expense	[9]																4,843		2,207	10,654
Common Stock Issued Under Stock and Benefit Plans (Value)	[8]																22,047		25,923	17,806
Ending balance		771,164								744,274							771,164		744,274	716,144
Earnings Reinvested In The Business [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year								1,103,200								1,614,361	1,103,200		1,614,361	1,442,617
Net Income (Loss) Available for Common Stock																	(290,958)		(379,427)	299,413
Dividends Declared on Common Stock																	(135,881)		(131,734)	(127,669)
Balance at End of Year		676,361	[10]							1,103,200							676,361	[10]	1,103,200	1,614,361
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization [Line Items]
Beginning balance								$ 93,372								$ (3,979)	93,372		(3,979)	(19,234)
Other Comprehensive Income (Loss), Net of Tax																	(99,012)		97,351	15,255
Ending balance		$ (5,640)								$ 93,372							$ (5,640)		$ 93,372	$ (3,979)

[1] Includes a non-cash $32.7 million impairment charge ($19.0 million after tax) associated with the Exploration and Production segment's oil and gas producing properties

[2] Includes a non-cash $82.7 million impairment charge ($47.9 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $397.4 million impairment charge ($230.5 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[4] Includes a non-cash $435.5 million impairment charge ($252.6 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[5] 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 ($4.7 million after tax) related to performance based restricted stock units.

[6] 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.

[7] 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.

[8] Paid in Capital includes tax benefits of $1.9 million, $9.1 million and $4.6 million for September 30, 2016, 2015 and 2014, respectively, related to stock-based compensation.

[9] Paid in Capital includes compensation costs associated with stock option, SARs, performance share and/or restricted stock awards. The expense is included within Net Income Available For Common Stock, net of tax benefits.

[10] The availability of consolidated earnings reinvested in the business for dividends payable in cash is limited under terms of the indentures covering long-term debt. At September 30, 2016, $532.2 million of accumulated earnings was free of such limitations.