Income Taxes - Temporary Differences and Carryforwards (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Deferred tax assets:
Accrued expenses and reserves	$ 137	$ 123
Employee and retiree benefits	31	24
Net operating loss and other carryforwards	2,227	1,400
Property, plant and equipment	106	114
Intangible assets	97	112
Operating lease liabilities	60	57
Research and development	129	102
Deferred tax assets, gross	2,787	1,932
Valuation allowances	(2,614)	(1,769)
Deferred tax assets, net	173	163
Deferred tax liabilities:
Unremitted earnings of foreign subsidiaries	33	39
Operating lease right-of-use assets	60	57
Other	6	13
Deferred tax liabilities, gross	99	109
Net deferred tax asset	$ 74	$ 54