Leases - Supplemental Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 101.7	$ 102.9	$ 108.5
Operating cash flows from finance leases	0.3	0.6	0.4
Financing cash flows from finance leases	5.5	8.8	1.8
Right-Of-Use Asset Obtained In Exchange For Lease Liability [Abstract]
Operating leases	93.3	63.4	90.6
Financing leases	$ 0.0	$ 11.8	$ 0.9