Leases - Supplemental Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 108.5	$ 103.6
Operating cash flows from finance leases	0.4	0.4
Financing cash flows from finance leases	1.8	1.2
Right-Of-Use Asset Obtained In Exchange For Lease Liability [Abstract]
Operating leases	90.6	131.2
Financing leases	$ 0.9	$ 0.0