Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	5	5	4
Expected return on plan assets	(9)	(10)	(9)
Net periodic (benefit) cost	(3)	(4)	(4)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	9	10
Interest cost	5	7	6
Expected return on plan assets	(10)	(15)	(14)
Amortization of prior service cost	2
Net losses	2	3	5
Settlements or Curtailments cost	(7)
Net periodic (benefit) cost	(1)	4	7
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)	(3)
Net losses	(1)	(1)
Net periodic (benefit) cost	(2)	(3)	(2)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Net periodic (benefit) cost	$ 1	$ 1	$ 1