Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)				91,181,549
Beginning balance				$ 1,017,446
Balance at Beginning of Period		$ 1,281,963	$ 1,028,844	1,191,175	$ 991,630
Balance at Beginning of Period		(277,026)	(79,741)	(513,597)	(114,757)
Net Income Available for Common Stock		167,328	112,436	299,720	190,210
Dividends Declared on Common Stock		(41,608)	(40,562)	(83,212)	(81,122)
Other Comprehensive Income (Loss), Net of Tax		$ (377,228)	(22,247)	$ (140,657)	12,769
Ending balance (shares)		91,449,226		91,449,226
Ending balance		$ 1,018,784		$ 1,018,784
Balance at March 31		1,407,683	1,100,718	1,407,683	1,100,718
Balance at End of Period		$ (654,254)	$ (101,988)	$ (654,254)	$ (101,988)
Dividends per share		$ 0.455	$ 0.445	$ 0.91	$ 0.89
Paid-in Capital [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance		$ 1,013,821	$ 1,004,369	$ 1,017,446	$ 1,004,158
Share-Based Payment Expense	[1]	4,692	4,283	9,732	7,779
Common Stock Issued Under Stock and Benefit Plans		271	423
Stock Repurchased under Stock and Benefit Plans				(8,394)	(2,862)
Ending balance		1,018,784	1,009,075	1,018,784	1,009,075
Earnings Reinvested in The Business [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		1,281,963	1,028,844	1,191,175	991,630
Net Income Available for Common Stock		167,328	112,436	299,720	190,210
Dividends Declared on Common Stock		(41,608)	(40,562)	(83,212)	(81,122)
Balance at March 31		1,407,683	1,100,718	1,407,683	1,100,718
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Capitalization, Equity [Line Items]
Balance at Beginning of Period		(277,026)	(79,741)	(513,597)	(114,757)
Other Comprehensive Income (Loss), Net of Tax		(377,228)	(22,247)	(140,657)	12,769
Balance at End of Period		$ (654,254)	$ (101,988)	$ (654,254)	$ (101,988)
Common Stock [Member]
Schedule of Capitalization, Equity [Line Items]
Beginning balance (shares)		91,437,000	91,153,000	91,182,000	90,955,000
Beginning balance (value)		$ 91,437	$ 91,153	$ 91,182	$ 90,955
Common Stock Issued Under Stock and Benefit Plans (Shares)		12,000	11,000	267,000	209,000
Common Stock Issued Under Stock and Benefit Plans		$ 12	$ 11	$ 267	$ 209
Ending balance (shares)		91,449,000	91,164,000	91,449,000	91,164,000
Ending balance (value)		$ 91,449	$ 91,164	$ 91,449	$ 91,164

[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.