Pension and Postretirement Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ (49)	$ 157	$ (252)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	1	$ 1
Interest cost	0	1	1	3
Expected return on plan assets	(2)	(3)	(6)	(7)
Amortization of prior service credit	(1)	0	(3)	(1)
Net periodic benefit credit	(3)	(1)	(7)	(4)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	14	18	36	55
Expected return on plan assets	(42)	(46)	(126)	(136)
Net actuarial (gain) loss	(49)	157	(252)	157
Settlement (gain) loss	(1)	6	(5)	6
Net periodic benefit credit	(78)	135	(347)	82
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	6	20	19
Interest cost	8	9	24	27
Expected return on plan assets	(29)	(27)	(84)	(83)
Amortization of prior service credit	1	0	1	1
Net periodic benefit credit	$ (13)	$ (12)	$ (39)	$ (36)