Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 2	$ 1	$ 3	$ 2
Expected return on plan assets	(3)	(3)	(5)	(5)
Net periodic benefit (credit) cost	(1)	(2)	(2)	(3)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	4	4
Interest cost	1	2	3	4
Expected return on plan assets	(2)	(3)	(6)	(7)
Amortization of actuarial loss			1	1
Settlement and curtailment gain			(6)
Net periodic benefit (credit) cost	1	$ 1	(4)	2
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1		1
Amortization of prior service credit	$ (1)		$ (1)	(1)
Net periodic benefit (credit) cost				$ (1)