Derivative Instruments - Pre-tax Amount of Gains (Losses) on Forward Exchange Contracts Not Designated as Hedging Instruments (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax amount of gains (losses) from forward exchange contracts not designated as hedging instruments recognized in the Consolidated Statement of Operations	$ (17.6)	$ 39.1	$ (8.3)
Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax amount of gains (losses) from forward exchange contracts not designated as hedging instruments recognized in the Consolidated Statement of Operations	1.6	0.5	(0.2)
Other (expense) income
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax amount of gains (losses) from forward exchange contracts not designated as hedging instruments recognized in the Consolidated Statement of Operations	$ (19.2)	$ 38.6	$ (8.1)