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		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	$ 4.3		$ 4.3		$ 12.0
(Loss)/Gain Recognized in OCI	(1.1)	$ 6.6	(2.6)	$ 3.7
Loss Reclassified From OCI into Income(Effective Portion)	2.3	(2.2)	5.0	(5.1)
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	3.6		3.6		4.3
(Loss)/Gain Recognized in OCI	0.9	1.6	4.1	(0.8)
Loss Reclassified From OCI into Income(Effective Portion)	2.0	(1.9)	4.8	(4.3)
Derivatives - 2017 Interest Rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	0.9		0.9
(Loss)/Gain Recognized in OCI	(1.7)		(5.1)
Loss Reclassified From OCI into Income(Effective Portion)	0.2		0.2
Derivatives - 2018 Interest Rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(0.4)		(0.4)
(Loss)/Gain Recognized in OCI	(0.5)		(1.8)
Loss Reclassified From OCI into Income(Effective Portion)	0.1		0.0
2018 Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts					$ 7.7
(Loss)/Gain Recognized in OCI		5.0		4.5
Loss Reclassified From OCI into Income(Effective Portion)		$ (0.3)		$ (0.8)
Zinc contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	0.2		0.2
(Loss)/Gain Recognized in OCI	0.2		0.2
Loss Reclassified From OCI into Income(Effective Portion)	$ 0.0		$ 0.0