Income Taxes - Consolidated Income (Loss) Before Income Taxes and Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	$ (88)	$ 133	$ 295
Foreign tax authority | Ireland
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	(24)	(13)	(1)
Foreign tax authority | Other Foreign
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	34	507	474
United States
Income Tax Contingency [Line Items]
Income before income taxes and noncontrolling interests	$ (98)	$ (361)	$ (178)