Basis of Presentation and Accounting Policies - Legacy Asbestos and Environmental Matters (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (expense) income	$ 123.0	$ (62.0)	$ 71.0
Net income	$ (749.0)	$ (948.0)	$ (1,278.0)
Basic (in dollars per share)	$ 7.69	$ 8.32	$ 12.03
Change in Accounting Method Accounted for as Change in Estimate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (expense) income	$ 136.0
Net income	$ 103.0
Basic (in dollars per share)	$ (0.91)
Change in accounting method, expense	$ 91.0
Loss contingency, accrual, current	45.0
Other liabilities	441.0
Receivables, current and other assets, noncurrent	$ 151.0