Income Taxes (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
Income Tax Disclosure [Abstract]
Effective income tax rate	14.00%	24.10%	18.50%	101.50%
U.S. statutory rate		24.50%
Effective income tax rate reconciliation, effect of tax cuts and jobs act of 2017, amount		$ 11.5		$ 491.2
Effective income tax rate reconciliation, effect of tax cuts and jobs act of 2017, percent		3.80%		81.80%
Gross unrecognized tax benefits	$ 20.1		$ 20.1		$ 20.1
Accrued interest and penalties related to unrecognized tax benefits	2.9		2.9		$ 2.5
Reasonably possible amount of reduction in gross unrecognized tax benefits for the next twelve months	6.0		6.0
Reasonably possible amount of net reduction to income tax provision if unrecognized tax benefits were recognized	$ 5.6		$ 5.6