Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	4	5	5
Expected return on plan assets	(3)	(9)	(10)
Settlements or Curtailments cost	3
Net periodic (benefit) cost	5	(3)	(4)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	7	9
Interest cost	3	5	7
Expected return on plan assets	(9)	(10)	(15)
Amortization of prior service cost		2
Net losses	3	2	3
Settlements or Curtailments cost	1	(7)
Net periodic (benefit) cost	3	(1)	4
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Amortization of prior service cost		(2)	(3)
Net losses	(1)	(1)	(1)
Net periodic (benefit) cost		(2)	(3)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost		1	1
Net losses	1
Net periodic (benefit) cost	$ 1	$ 1	$ 1