Restructuring - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	$ 19	$ 16	$ (30)
Proceeds from the sale of land			39
2020 Reorganization [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	17
Restructuring charges expected in fiscal 2021 related to site demolition and clearing costs	1
Restructuring charges expected thereafter fiscal year related to site demolition and clearing costs	3
Restructuring cash payments of fiscal year	13
Restructuring cash payments in fiscal 2021	4
Restructuring future cash payments thereafter fiscal year	4
Accrued severance charges	4
Purification Solutions Transformation Plan [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	2	8
Restructuring charges expected in fiscal 2021 related to site demolition and clearing costs	1
Restructuring cash payments of fiscal year	2	8
Restructuring cash payments in fiscal 2021	2
Restructuring future cash payments thereafter fiscal year	2
Accrued severance charges	1
Restructuring Charges		9
Professional fees and other charges		$ 1
Restructuring charges expected thereafter fiscal 2021 related to site demolition and clearing costs	$ 1
Operational Restructuring [Member] | Thane, India [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land			28
Net benefit to earnings			28
Operational Restructuring [Member] | Merak, Indonesia [Member] | Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land			13
Net benefit to earnings			$ 11