Financial Instruments and Risk Management - Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss) (Details) - Designated as Hedging Instrument - Cash Flow Hedging - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	$ (5.8)		$ (7.8)
(Loss)/Gain Recognized in OCI	(8.2)	$ (4.5)
Loss Reclassified From OCI into Income(Effective Portion)	(4.7)	1.1
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(10.2)		(4.9)
(Loss)/Gain Recognized in OCI	(7.9)	(4.0)
Loss Reclassified From OCI into Income(Effective Portion)	(2.6)	1.9
Interest rate swaps contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(5.3)		(7.3)
(Loss)/Gain Recognized in OCI	(4.8)	0.5
Loss Reclassified From OCI into Income(Effective Portion)	(1.3)	(0.5)
Zinc contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	9.7		$ 4.4
(Loss)/Gain Recognized in OCI	4.5	(1.0)
Loss Reclassified From OCI into Income(Effective Portion)	$ (0.8)	$ (0.3)