Other Income (Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Other Income and Expenses [Abstract]
Interest income	$ 0.3	$ 2.4
Royalty income	2.1	2.5
Legacy product liability and environmental charges	(4.6)	(2.7)
Non-operating pension and postretirement benefit cost	(7.0)	(8.7)
Legal settlement (Note 13)	70.0	0.0
Other	0.2	(3.2)
Other income (expense)	$ 61.0	$ (9.7)