Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	6 Months Ended
	Mar. 31, 2021 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	$ (307.7)
OCI before reclassifications	36.5
Reclassifications to earnings	10.5
Balance at March 31, 2021	(260.7)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	(137.4)
OCI before reclassifications	26.2
Reclassifications to earnings	0.0
Balance at March 31, 2021	(111.2)
Pension Activity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	(163.5)
OCI before reclassifications	(1.4)
Reclassifications to earnings	3.4
Balance at March 31, 2021	(161.5)
Foreign Currency Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	(4.1)
OCI before reclassifications	(3.9)
Reclassifications to earnings	4.5
Balance at March 31, 2021	(3.5)
Zinc contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	3.4
OCI before reclassifications	2.9
Reclassifications to earnings	0.2
Balance at March 31, 2021	6.5
Interest Rate Contracts | Foreign Currency Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2020	(6.1)
OCI before reclassifications	12.7
Reclassifications to earnings	2.4
Balance at March 31, 2021	$ 9.0