Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Effective income tax rate	17.70%	22.60%	17.20%	22.10%
U.S. statutory rate	35.00%	35.00%	35.00%	35.00%
Gross unrecognized tax benefits	$ 41.6		$ 41.6		$ 32.4
Accrued interest and penalties related to unrecognized tax benefits	5.7		5.7		$ 5.2
Reasonably possible amount of reduction in gross unrecognized tax benefits for the next twelve months	20.1		20.1
Reasonably possible amount of net reduction to income tax provision if unrecognized tax benefits were recognized	$ 5.8		$ 5.8
Earliest open year for income tax examinations, U.S. federal			2014
Earliest open tax year for income tax examinations, state, local and non-U.S.			2003