Fair Value Measurements and Derivative Instruments - Summary of Effects on Consolidated Financial Statements of Designated As Cash Flow Hedges (Details) - Cash Flow Hedges - Designated - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Interest Rate Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	$ 6.1	$ (13.3)	$ 36.1
Net gain (loss) reclassified from Accumulated other comprehensive income (loss) into Interest expense, net	5.7	11.1	15.2
Fuel Swap Contracts
Derivative Instruments Gain Loss [Line Items]
(Loss) income recognized in Other comprehensive income (loss)	0.1	(0.5)	0.0
Net gain (loss) reclassified from Accumulated other comprehensive income (loss) into Interest expense, net	$ (0.3)	$ 0.0	$ 0.0