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, 2019	Dec. 31, 2018	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	$ (6.8)		$ (1.2)
(Loss)/Gain Recognized in OCI	(4.5)	$ (1.6)
Loss Reclassified From OCI into Income(Effective Portion)	1.1	2.7
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(1.4)		4.5
(Loss)/Gain Recognized in OCI	(4.0)	3.2
Loss Reclassified From OCI into Income(Effective Portion)	1.9	2.8
Interest rate swaps (2017 and 2018)
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(3.7)		(4.7)
(Loss)/Gain Recognized in OCI	0.5	(4.8)
Loss Reclassified From OCI into Income(Effective Portion)	(0.5)	$ (0.1)
Zinc contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(1.7)		$ (1.0)
(Loss)/Gain Recognized in OCI	(1.0)
Loss Reclassified From OCI into Income(Effective Portion)	$ (0.3)