Capitalization and Short-Term Borrowings - Summary of Changes in Common Stock Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		91,005,993
Beginning balance		$ 2,848,343
Net Income Available for Common Stock		518,504	$ 77,513	$ 476,866
Dividends Declared on Common Stock		(189,919)	(185,220)	(178,095)
Other Comprehensive Income (Loss), Net of Tax		$ (43,746)	$ 39,584	$ 570,673
Ending balance (in shares)		90,379,095	91,005,993
Ending balance		$ 3,094,604	$ 2,848,343
Dividend per share (in dollars per share)		$ 2.10	$ 2.02	$ 1.94
Stock And Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases under repurchase plan (in shares)		(71,394)
Share Repurchase Plan
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases under repurchase plan (in shares)		(828,720)
Share Repurchases Under Repurchase Plan		$ (53,800)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		91,006,000	91,819,000	91,478,000
Beginning balance		$ 91,006	$ 91,819	$ 91,478
Common stock issued under stock and benefit plans (in shares)		202,000	333,000	341,000
Common Stock Issued Under Stock and Benefit Plans		$ 202	$ 333	$ 341
Ending balance (in shares)		90,379,000	91,006,000	91,819,000
Ending balance		$ 90,379	$ 91,006	$ 91,819
Common Stock | Share Repurchase Plan
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share repurchases under repurchase plan (in shares)		(829,000)	(1,146,000)
Share Repurchases Under Repurchase Plan		$ (829)	$ (1,146)
Paid In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		1,045,487	1,040,761	1,027,066
Share-Based Payment Expense	[1]	17,306	19,868	18,746
Ending balance		1,050,918	1,045,487	1,040,761
Paid In Capital | Stock And Benefit Plans
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share Repurchases Under Repurchase Plan		(2,262)	(1,955)	(5,051)
Paid In Capital | Share Repurchase Plan
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share Repurchases Under Repurchase Plan		(9,613)	(13,187)
Earnings Reinvested in the Business
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		1,727,326	1,885,856	1,587,085
Net Income Available for Common Stock		518,504	77,513	476,866
Dividends Declared on Common Stock		(189,919)	(185,220)	(178,095)
Share Repurchases Under Repurchase Plan		(43,382)	(50,823)	0
Ending balance		2,012,529	1,727,326	1,885,856
Earnings Reinvested in the Business | Share Repurchase Plan
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share Repurchases Under Repurchase Plan		(43,382)	(50,823)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance		(15,476)	(55,060)	(625,733)
Other Comprehensive Income (Loss), Net of Tax		(43,746)	39,584	570,673
Ending balance		$ (59,222)	$ (15,476)	$ (55,060)

[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.