Accumulated Other Comprehensive Income (Loss) Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (32.8)		$ (32.8)		$ (33.1)
Other comprehensive loss	0.0	$ (1.6)	0.3	$ (3.8)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(30.2)		(30.2)		(30.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.3
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(2.6)		(2.6)		(2.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.0
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (32.8)		(32.8)		$ (33.1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0.3
Other comprehensive loss		$ (1.6)	$ 0.3	$ (3.8)