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, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	$ 21.2		$ 21.2		$ (7.8)
(Loss)/Gain Recognized in OCI	23.4	$ (3.9)	15.2	$ (8.4)
Loss Reclassified From OCI into Income(Effective Portion)	(4.7)	0.2	(9.4)	1.3
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	(4.2)		(4.2)		(4.9)
(Loss)/Gain Recognized in OCI	2.6	7.3	(5.3)	3.3
Loss Reclassified From OCI into Income(Effective Portion)	(3.4)	0.8	(6.0)	2.7
Interest rate swaps contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	16.9		16.9		(7.3)
(Loss)/Gain Recognized in OCI	21.5	(5.9)	16.7	(5.4)
Loss Reclassified From OCI into Income(Effective Portion)	(1.8)	(0.6)	(3.1)	(1.1)
Zinc contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives - Foreign Currency contracts	8.5		8.5		$ 4.4
(Loss)/Gain Recognized in OCI	(0.7)	(5.3)	3.8	(6.3)
Loss Reclassified From OCI into Income(Effective Portion)	$ 0.5	$ 0.0	$ (0.3)	$ (0.3)