Income Taxes - Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Current:
Federal	$ 1.0	$ 23.4	$ 2.6
State	1.5	2.0	(0.8)
Foreign	20.8	11.1	19.2
Current total	23.3	36.5	21.0
Deferred:
Federal	10.3	(44.1)	5.9
State	(3.0)	(4.6)	0.7
Foreign	10.3	(21.9)	7.7
Deferred total	17.6	(70.6)	14.3
Income tax provision (benefit)	$ 40.9	$ (34.1)	$ 35.3