Supplemental Information (Related Party Transactions) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2025	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Related Party Transaction [Line Items]
Trade receivables, net		$ 1,901.2	$ 1,821.6
Related Party
Related Party Transaction [Line Items]
Related party transaction income (expense)		355.0	350.0	$ 380.0
Trade receivables, net		105.0	$ 120.0
Affiliated Entity | Mantle Ridge LP and Affiliates Transaction
Related Party Transaction [Line Items]
Related party transaction income (expense)	$ (24.7)	$ (24.7)