Leases - Summary of Components of Lease Cost for Operating and Finance Leases (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 7.1	$ 14.4
Finance lease cost:
Amortization of right-of-use asset	1.3	2.4
Interest on lease liabilities		0.1
Total finance lease cost	1.3	2.5
Short-term lease cost	7.7	14.0
Variable lease costs not included in lease liability	0.6	0.8
Sublease income	(0.1)	(0.3)
Total lease cost	$ 16.6	$ 31.4