Benefit Plans - Net Pension and Other Postretirement Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Net pension cost	$ 98	$ 17	$ 1
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	91	134	150
Interest cost	129	77	71
Expected return on plan assets	(141)	(187)	(174)
Amortization of prior service credit	(7)	(15)	(16)
Amortization of loss	58	61	97
Curtailments/settlement loss	44	73	9
Net pension cost	174	143	137
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension cost	$ 25	$ 20	$ 41