Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)				91,478,064
Beginning balance				$ 1,027,066
Balance at Beginning of Period		$ 1,810,454	$ 1,407,683	1,587,085	$ 1,191,175
Balance at Beginning of Period		(54,864)	(654,254)	(625,733)	(513,597)
Net Income Available for Common Stock		92,620	108,158	403,189	407,879
Dividends Declared on Common Stock		(45,444)	(43,446)	(132,644)	(126,659)
Other Comprehensive Income (Loss), Net of Tax		$ 5,480	71,386	$ 576,349	(69,271)
Ending balance (shares)		91,803,996		91,803,996
Ending balance		$ 1,035,852		$ 1,035,852
Balance at June 30		1,857,630	1,472,395	1,857,630	1,472,395
Balance at End of Period		$ (49,384)	$ (582,868)	$ (49,384)	$ (582,868)
Dividends per share		$ 0.495	$ 0.475	$ 1.445	$ 1.385
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance		$ 1,031,341	$ 1,018,784	$ 1,027,066	$ 1,017,446
Share-Based Payment Expense	[1]	4,009	4,094	14,327	13,826
Common Stock Issued Under Stock and Benefit Plans		502	76
Stock Repurchased under Stock and Benefit Plans				(5,541)	(8,318)
Ending balance		1,035,852	1,022,954	1,035,852	1,022,954
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		1,810,454	1,407,683	1,587,085	1,191,175
Net Income Available for Common Stock		92,620	108,158	403,189	407,879
Dividends Declared on Common Stock		(45,444)	(43,446)	(132,644)	(126,659)
Balance at June 30		1,857,630	1,472,395	1,857,630	1,472,395
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(54,864)	(654,254)	(625,733)	(513,597)
Other Comprehensive Income (Loss), Net of Tax		5,480	71,386	576,349	(69,271)
Balance at End of Period		$ (49,384)	$ (582,868)	$ (49,384)	$ (582,868)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		91,795,000	91,449,000	91,478,000	91,182,000
Beginning balance (value)		$ 91,795	$ 91,449	$ 91,478	$ 91,182
Common Stock Issued Under Stock and Benefit Plans (Shares)		9,000	17,000	326,000	284,000
Common Stock Issued Under Stock and Benefit Plans		$ 9	$ 17	$ 326	$ 284
Ending balance (shares)		91,804,000	91,466,000	91,804,000	91,466,000
Ending balance (value)		$ 91,804	$ 91,466	$ 91,804	$ 91,466

[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.