Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Leases [Abstract]
Operating lease expense	$ 100.2	$ 103.6	$ 109.8
Variable lease expense	18.8	16.6	15.8
Finance Leases
Amortization of right-of-use assets	5.2	6.9	1.7
Interest on lease liabilities	0.3	0.6	0.4
Total lease expense	$ 124.5	$ 127.7	$ 127.7