Leases - Components of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease Cost [Abstract]
Operating lease cost	$ 13.8	$ 13.8
Variable lease cost	9.5	3.8
Short-term lease cost	$ 2.2	$ 1.1