Restructuring - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2015 Employees	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Restructuring Cost And Reserve [Line Items]
Site demolition, clearing and environmental remediation costs			$ 1	$ 1	$ 1
Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Accrued severance charges			1
Maximum [Member] | Severance Costs [Member]
Restructuring Cost And Reserve [Line Items]
Accrued severance charges			1
Operational Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Number of employees termination | Employees	300
Restructuring expected charges				30
Pre-tax charge to earnings			1	29
Expected cumulative net cash outlays related to plan			30
Cash payments			30	27
Operational Restructuring [Member] | Maximum [Member] | Scenario, Forecast [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax charge to earnings		$ 1
Closure of Carbon Black Facility [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expected charges			27
Pre-tax charge to earnings				25
Expected cumulative net cash outlays related to plan			6
Cash payments			3
Site demolition and clearing and environmental remediation charges expected in fiscal 2018			2
Severance charges			3
Site demolition, clearing and environmental remediation costs			3
Restructuring future cash payments in fiscal 2018			3
Closure of Carbon Black Facility [Member] | Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax charge to earnings				22
Closure of Carbon Black Facility [Member] | Severance and Other Transition Costs [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax charge to earnings				3
Closure of Carbon Black Facility [Member] | Maximum [Member] | Transition Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax charge to earnings			1
Previous Actions and Sites Pending Sale [Member]
Restructuring Cost And Reserve [Line Items]
Pre-tax charge to earnings			2
Severance charges			2
Net benefit to earnings				$ 8
Previous Actions and Sites Pending Sale [Member] | Severance Costs [Member] | Restructuring Activities Other [Member]
Restructuring Cost And Reserve [Line Items]
Accrued severance charges			2
Restructuring cash payments in fiscal 2018 and thereafter			$ 3