Pension and Postretirement Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 0	$ 1	$ 1
Interest cost	1	2	3	5
Expected return on plan assets	(3)	(2)	(7)	(7)
Amortization of prior service cost (credit)	0	0	(1)	0
Net periodic benefit credit	(1)	0	(4)	(1)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	18	25	55	75
Expected return on plan assets	(46)	(46)	(136)	(138)
Net actuarial loss	157	0	157	0
Settlement (gain) loss	6	0	6	0
Net periodic benefit credit	135	(21)	82	(63)
Foreign Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6	5	19	16
Interest cost	9	14	27	40
Expected return on plan assets	(27)	(26)	(83)	(78)
Amortization of prior service cost (credit)	0	0	1	0
Settlement (gain) loss	0	0	0	1
Net periodic benefit credit	$ (12)	$ (7)	$ (36)	$ (21)