Leases - Summary of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 25.3
Operating cash flows from finance leases	(0.3)
Repayments of finance lease obligations	(9.9)	$ (5.8)	$ (6.3)
Non-cash items:
Right-of-use Assets Obtained In Exchange For New Operating Liabilities	17.1
Right-of-use Assets Obtained In Exchange For New Finance Liabilities	$ 20.2