Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	5	4	4
Expected return on plan assets	(10)	(9)	(10)
Net periodic (benefit) cost	(4)	(4)	(5)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	10	8
Interest cost	7	6	8
Expected return on plan assets	(15)	(14)	(14)
Net losses	3	5	3
Settlements or Curtailments cost			1
Net periodic (benefit) cost	4	7	6
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	(3)	(3)	(3)
Net losses	(1)
Settlements or Curtailments cost			(1)
Net periodic (benefit) cost	(3)	(2)	(3)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Net periodic (benefit) cost	$ 1	$ 1	$ 1