Pension and Other Postretirement Benefits - Net Periodic Pension and Other Postretirement Plan Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	28	32	32
Expected return on assets	(72)	(71)	(70)
Amortization of actuarial loss	6	0	0
Settlement loss	8	7	3
Total net periodic benefit cost	(30)	(32)	(35)
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	4	4	4
Interest cost	10	13	12
Expected return on assets	(15)	(18)	(20)
Amortization of actuarial loss	2	0	0
Settlement loss	0	0	0
Total net periodic benefit cost	$ 1	$ (1)	$ (4)