Leases - Summary of Components of Lease Cost for Operating and Finance Leases (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Leases [Abstract]
Operating lease cost	$ 6.2	$ 20.6
Finance lease cost:
Amortization of right-of-use asset	2.4	4.8
Interest on lease liabilities	0.1	0.2
Total finance lease cost	2.5	5.0
Short-term lease cost	5.7	19.7
Variable lease costs not included in lease liability	0.4	1.2
Sublease income	(0.1)	(0.4)
Total lease cost	$ 14.7	$ 46.1