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, 2017		Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016		Jun. 30, 2016	[2]	Mar. 31, 2016	[3]	Dec. 31, 2015		Sep. 30, 2017		Sep. 30, 2016	Sep. 30, 2015
Schedule of Capitalization [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term															0 years
Beginning balance (shares)						85,118,886									85,118,886
Beginning balance						$ 771,164									$ 771,164
Balance at Beginning of Year						676,361							$ 1,103,200		676,361		$ 1,103,200	$ 1,614,361
Beginning balance						(5,640)							93,372		(5,640)		93,372
Net Income (Loss) Available for Common Stock		$ 45,577		$ 59,714	$ 89,283	$ 88,908	$ 37,553	[1]	$ 8,286		$ (147,688)		$ (189,109)	[4]	283,482		(290,958)	(379,427)
Dividends Declared on Common Stock															(140,090)		(135,881)	(131,734)
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation		$ 31,900													31,900
Other Comprehensive Income (Loss), Net of Tax															(24,483)		(99,012)	97,351
Share-Based Payment Expense															$ 10,800		$ 4,800	2,100
Ending balance (Shares)		85,543,125					85,118,886								85,543,125		85,118,886
Ending balance		$ 796,646					$ 771,164								$ 796,646		$ 771,164
Balance at End of Year		851,669					676,361								851,669		676,361	1,103,200
Ending balance		(30,123)					$ (5,640)								$ (30,123)		$ (5,640)	$ 93,372
Dividend per share															$ 1.64		$ 1.60	$ 1.56
Tax benefit related to stock-based compensation recorded to Paid in Capital																	$ 1,868	$ 9,064
Accumulated earnings free from limitations		$ 707,500													$ 707,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term															0 years
Common Stock [Member]
Schedule of Capitalization [Line Items]
Beginning balance (shares)						85,119,000							84,594,000		85,119,000		84,594,000	84,157,000
Beginning balance (value)						$ 85,119							$ 84,594		$ 85,119		$ 84,594	$ 84,157
Common Stock Issued Under Stock and Benefit Plans (Shares)	[5]														424,000		525,000	437,000
Common Stock Issued Under Stock and Benefit Plans (Value)	[5]														$ 424		$ 525	$ 437
Ending balance (Shares)		85,543,000					85,119,000								85,543,000		85,119,000	84,594,000
Ending balance (Value)		$ 85,543					$ 85,119								$ 85,543		$ 85,119	$ 84,594
Paid In Capital [Member]
Schedule of Capitalization [Line Items]
Beginning balance						771,164							744,274		771,164		744,274	716,144
Share-Based Payment Expense	[6]														10,902		4,843	2,207
Common Stock Issued Under Stock and Benefit Plans (Value)	[5]														14,580		22,047	25,923
Ending balance		796,646					771,164								796,646		771,164	744,274
Earnings Reinvested In The Business [Member]
Schedule of Capitalization [Line Items]
Balance at Beginning of Year						676,361							1,103,200		676,361		1,103,200	1,614,361
Net Income (Loss) Available for Common Stock															283,482		(290,958)	(379,427)
Dividends Declared on Common Stock															(140,090)		(135,881)	(131,734)
Cumulative Effect of Adoption of Authoritative Guidance for Stock-Based Compensation		31,916													31,916
Balance at End of Year		851,669	[7]				676,361								851,669	[7]	676,361	1,103,200
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization [Line Items]
Beginning balance						$ (5,640)							$ 93,372		(5,640)		93,372	(3,979)
Other Comprehensive Income (Loss), Net of Tax															(24,483)		(99,012)	97,351
Ending balance		$ (30,123)					$ (5,640)								$ (30,123)		$ (5,640)	$ 93,372

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

[6] 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.

[7] 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, 2017, $707.5 million of accumulated earnings was free of such limitations.