Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Current Tax Provision
Federal									$ 2.4	$ 0.0	$ 0.0
State									0.6	0.6	0.5
Foreign									47.0	58.3	31.6
Current Income Tax Provision									50.0	58.9	32.1
Deferred Tax Provision
Federal									1.1	1.3	1.4
State									0.1	0.1	0.1
Foreign									1.6	(1.5)	(1.9)
Deferred Income Tax Provision									2.8	(0.1)	(0.4)
Income Tax Expense	$ 11.6	$ 14.4	$ 11.5	$ 15.3	$ 15.6	$ 17.6	$ 12.2	$ 13.4	$ 52.8	$ 58.8	$ 31.7