Pension Benefit Obligations - Schedule of Reconciliation of Amounts In the Consolidated Statements of Stockholder's Equity (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
U.S.
Reconciliation of amounts in consolidated statements of stockholders’ equity:
Prior service cost	$ (0.1)	$ (0.1)	$ (0.1)
Net loss	(75.4)	(77.6)	(77.5)
Total recognized in accumulated other comprehensive loss	(75.5)	(77.7)	(77.6)
Int’l
Reconciliation of amounts in consolidated statements of stockholders’ equity:
Prior service cost	(1.2)	(1.3)	(1.2)
Net loss	(235.5)	(234.9)	(207.1)
Total recognized in accumulated other comprehensive loss	$ (236.7)	$ (236.2)	$ (208.3)