Benefit Plans - Net Pension and Other Postretirement Cost (Detail) - Pension Plans - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 150	$ 153	$ 134
Interest cost	71	84	107
Expected return on plan assets	(174)	(188)	(180)
Amortization of prior service credit	(16)	(13)	(13)
Amortization of loss	97	97	78
Curtailment/settlement loss	9	4	10
Net pension cost	137	137	135
Foreign Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension cost	$ 41	$ 41	$ 32