Pension and Other Postretirement Benefits - Employer Contributions (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	$ 0	$ 1
Expected employer contributions
Expected employer contributions	1
Expected benefit payments
Expected benefit payments 2020	127
Expected benefit payments 2021	92
Expected benefit payments 2022	86
Expected benefit payments 2023	82
Expected benefit payments 2024	74
Expected benefit payments 2025-2029	293
Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	10	$ 11
Expected employer contributions
Expected employer contributions	10
Expected benefit payments
Expected benefit payments 2020	6
Expected benefit payments 2021	6
Expected benefit payments 2022	6
Expected benefit payments 2023	6
Expected benefit payments 2024	6
Expected benefit payments 2025-2029	$ 34