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		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	$ (13.6)		$ (13.6)		$ (1.2)
(Loss)/Gain Recognized in OCI	(2.5)	$ (5.4)	(10.9)	$ (8.0)
Loss Reclassified From OCI into Income(Effective Portion)	(0.1)	2.1	1.2	7.1
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(1.2)		(1.2)		4.5
(Loss)/Gain Recognized in OCI	(4.5)	(0.4)	(1.2)	3.7
Loss Reclassified From OCI into Income(Effective Portion)	1.8	1.9	4.5	6.7
Interest rate swaps (2017 and 2018)
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(8.9)		(8.9)		(4.7)
(Loss)/Gain Recognized in OCI	(1.2)	(4.1)	(6.6)	(11.0)
Loss Reclassified From OCI into Income(Effective Portion)	(1.6)	0.2	(2.7)	0.4
Zinc contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(3.5)		(3.5)		$ (1.0)
(Loss)/Gain Recognized in OCI	3.2	(0.9)	(3.1)	(0.7)
Loss Reclassified From OCI into Income(Effective Portion)	$ (0.3)	$ 0.0	$ (0.6)	$ 0.0