Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)				86,315,287
Beginning balance				$ 832,264
Balance at Beginning of Period		$ 1,176,870	$ 1,236,657	1,272,601	$ 1,098,900
Balance at Beginning of Period		(18,917)	(54,286)	(52,155)	(67,750)
Net Income Available for Common Stock		41,250	63,753	21,773	257,009
Dividends Declared on Common Stock		(40,470)	(37,543)	(115,774)	(110,885)
Other Comprehensive Income (Loss), Net of Tax		$ (22,877)	21,620	$ 10,361	35,084
Ending balance (shares)		90,943,652		90,943,652
Ending balance		$ 999,057		$ 999,057
Balance at June 30		1,177,650	1,262,867	1,177,650	1,262,867
Balance at End of Period		(41,794)	(32,666)	(41,794)	(32,666)
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Common Stock Issued from Sale of Common Stock (Value)		161,488		161,488
Common Stock Issued Under Stock and Benefit Plans (Value)		426	352
Beginning balance		835,444	821,837	832,264	820,223
Share-Based Payment Expense	[1]	1,699	5,054	8,403	15,008
Common Stock Repurchased under Stock and Benefit Plans				(3,098)	(7,988)
Ending balance		999,057	827,243	999,057	827,243
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		1,176,870	1,236,657	1,272,601	1,098,900
Net Income Available for Common Stock		41,250	63,753	21,773	257,009
Dividends Declared on Common Stock		(40,470)	(37,543)	(115,774)	(110,885)
Balance at June 30		1,177,650	1,262,867	1,177,650	1,262,867
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(18,917)	(54,286)	(52,155)	(67,750)
Other Comprehensive Income (Loss), Net of Tax		(22,877)	21,620	10,361	35,084
Balance at End of Period		$ (41,794)	$ (32,666)	$ (41,794)	$ (32,666)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		86,562,000	86,301,000	86,315,000	85,957,000
Beginning balance (value)		$ 86,562	$ 86,301	$ 86,315	$ 85,957
Common Stock Issued from Sale of Common Stock (Shares)		4,370,000		4,370,000
Common Stock Issued from Sale of Common Stock (Value)		$ 4,370		$ 4,370
Common Stock Issued Under Stock and Benefit Plans (Shares)		12,000	6,000	259,000	350,000
Common Stock Issued Under Stock and Benefit Plans (Value)		$ 12	$ 6	$ 259	$ 350
Ending balance (shares)		90,944,000	86,307,000	90,944,000	86,307,000
Ending balance (value)		$ 90,944	$ 86,307	$ 90,944	$ 86,307
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		0	0	(950)	0
Guidance for Hedging [Member] | Earnings Reinvested in The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period				(950)
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		0	0	0	7,437
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Earnings Reinvested in The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period					7,437
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		$ 0	$ 0	$ 0	10,406
Guidance for Reclassification of Stranded Tax Effects [Member] | Earnings Reinvested in The Business [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period					$ 10,406

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