Leases - Summary of Components of Lease Cost for Operating and Finance Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating lease cost	$ 31.5	$ 32.1
Finance lease cost:
Amortization of right-of-use asset	34.7	27.0
Interest on lease liabilities	3.2	1.6
Total finance lease cost	37.9	28.6
Short-term lease cost	22.1	23.7
Variable lease costs not included in lease liability	3.8	3.3
Sublease income	(0.7)	(0.7)
Total lease cost	$ 94.6	$ 87.0