Capitalization and Short-Term Borrowings (Summary of Changes in Common Stock Equity) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
		Dec. 31, 2023	Dec. 31, 2022
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		91,819,405
Beginning balance		$ 2,963,376
Net Income Available for Common Stock		133,020	$ 169,689
Dividends Declared on Common Stock		(45,597)	(43,598)
Other Comprehensive Income, Net of Tax		$ 122,441	$ 331,987
Ending balance (in shares)		92,115,581
Ending balance		$ 3,174,002
Dividends per share (in dollars per share)		$ 0.495	$ 0.475
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		91,819,000	91,478,000
Beginning balance		$ 91,819	$ 91,478
Common Stock Issued Under Stock and Benefit Plans (Shares)		297,000	309,000
Common Stock Issued Under Stock and Benefit Plans		$ 297	$ 309
Ending balance (in shares)		92,116,000	91,787,000
Ending balance		$ 92,116	$ 91,787
Paid In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		1,040,761	1,027,066
Share-Based Payment Expense	[1]	4,135	5,118
Stock Repurchased under Stock and Benefit Plans		(3,670)	(6,545)
Ending balance		1,041,226	1,025,639
Earnings Reinvested in the Business
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		1,885,856	1,587,085
Net Income Available for Common Stock		133,020	169,689
Dividends Declared on Common Stock		(45,597)	(43,598)
Ending balance		1,973,279	1,713,176
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(55,060)	(625,733)
Other Comprehensive Income, Net of Tax		122,441	331,987
Ending balance		$ 67,381	$ (293,746)

[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.