Employee Benefit Plans - Stock Options (Details) - Share-based Payment Arrangement, Option [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Stock Options
Outstanding at beginning of year, shares	219,663	823,486	1,115,776
Exercised, shares	(219,663)	(603,823)	(292,290)
Canceled or expired, shares	0	0	0
Outstanding at end of year, shares	0	219,663	823,486
Exercisable at end of year, shares	0	219,663	823,486
Weighted Average Exercise Price
Outstanding at beginning of year, weighted average exercise price, per share	$ 23.86	$ 23.84	$ 23.84
Exercised, weighted average exercise price, per share	23.86	23.83	23.83
Canceled or expired, weighted average exercise price, per share	0	0	0
Outstanding at end of year, weighted average exercise price, per share	0	23.86	23.84
Exercisable at end of year, weighted average exercise price, per share	$ 0	$ 23.86	$ 23.84
Additional information - stock options
Total intrinsic value of options exercised	$ 26.5	$ 47.2	$ 23.0