Schedule of Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	6 Months Ended
	Mar. 31, 2019 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	$ (241.8)
OCI before reclassifications	14.7
Reclassifications to earnings	(1.7)
Activity related to discontinued operations	1.3
Balance at March 31, 2019	(227.5)
Foreign Currency Translation Adjustments (1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	(113.6)
OCI before reclassifications	16.6
Reclassifications to earnings	0.0
Activity related to discontinued operations	0.0
Balance at March 31, 2019	(97.0)
Pension Activity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	(136.4)
OCI before reclassifications	0.0
Reclassifications to earnings	2.1
Activity related to discontinued operations	0.0
Balance at March 31, 2019	(134.3)
Foreign Currency Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	3.3
OCI before reclassifications	3.2
Reclassifications to earnings	(3.7)
Activity related to discontinued operations	0.0
Balance at March 31, 2019	2.8
Zinc contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	0.0
OCI before reclassifications	0.2
Reclassifications to earnings	0.0
Activity related to discontinued operations	1.3
Balance at March 31, 2019	1.5
Interest Rate Contracts | Foreign Currency Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at September 30, 2018	4.9
OCI before reclassifications	(5.3)
Reclassifications to earnings	(0.1)
Activity related to discontinued operations	0.0
Balance at March 31, 2019	$ (0.5)