Pension and Other Postretirement Benefits - Net Periodic Pension and Other Postretirement Plan Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	32	32	36
Expected return on assets	(71)	(70)	(70)
Amortization of actuarial loss	0	0	15
Settlement loss	7	3	15
Total net periodic benefit cost	(32)	(35)	(4)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	4	4	6
Interest cost	13	12	11
Expected return on assets	(18)	(20)	(16)
Amortization of actuarial loss	0	0	2
Settlement loss	0	0	0
Total net periodic benefit cost	$ (1)	$ (4)	$ 3