Benefit Plans - Net Pension and Other Postretirement Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 110	$ 81	$ 77
Interest cost	61	72	87
Expected return on plan assets	(112)	(109)	(123)
Amortization of prior service credit	(14)	(15)	(15)
Amortization of loss	92	77	68
Settlements	0	(7)	0
Net pension and postretirement cost	138	113	93
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	3
Interest cost	4	5	7
Expected return on plan assets	0	0	0
Amortization of prior service credit	(5)	(5)	(5)
Amortization of loss	2	2	3
Settlements	0	0	0
Net pension and postretirement cost	4	5	9
Foreign Plans | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension and postretirement cost	$ 43	$ 35	$ 32