Other (Expense) Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Components of other income (expense)
Interest income	$ 9.7	$ 4.4	$ 1.6
Royalty income	13.2	10.9	10.2
Legacy product liability and environmental charges	(18.1)	(15.6)	(10.6)
Non-operating pension and postretirement benefit cost	(82.7)	(4.7)	(63.8)
Legal settlement (Note 17)	0.0	0.0	70.0
Other	6.6	3.4	(1.7)
Other (expense) income	$ (71.3)	$ (1.6)	$ 5.7