Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
U.S. federal tax	35.00%
Foreign statutory tax rate, minimum (as percent)	17.00%
Income Tax Holiday [Line Items]
Deferred Tax Liabilities, Net	$ 19.2	$ 32.0
Accrued income taxes	31.4	12.7
Cash taxes paid	42.9
Tax credit carryforwards	0.9	64.2
Decrease in valuation allowance	54.7
Cumulative undistributed earnings	1,070.8
U.S. income and foreign withholding taxes estimate	196.2
Unrecognized tax benefits	19.9	12.9	$ 10.3	$ 16.0
Unrecognized tax benefits that would impact effective tax rate	$ 19.9	12.6
Foreign Tax Authority
Income Tax Holiday [Line Items]
Tax benefit of holidays, reduction	50.00%
Net benefit of tax holidays	$ 8.0	$ 7.1	$ 9.6
Loss carryforwards	1.5
Change From Separate Return Method [Member]
Income Tax Holiday [Line Items]
Deferred Tax Liabilities, Net	(17.5)
Accrued income taxes	$ 13.0