Income Taxes - Current and Deferred Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)									$ 0.8	$ 0.7	$ 1.3
Current State and Local Tax Expense (Benefit)									0.5	1.2	0.8
Current Foreign Tax Expense (Benefit)									22.4	16.7	16.8
Current Income Tax Expense (Benefit)									23.7	18.6	18.9
Deferred Income Tax Expense (Benefit)									22.3	(9.8)	(0.8)
Other Tax Expense (Benefit)									0.0	0.0	(0.1)
Income tax expense	$ 4.8	$ 8.9	$ 6.8	$ 25.5	$ 1.1	$ 2.3	$ 3.3	$ 2.1	$ 46.0	$ 8.8	$ 18.0