Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 152
Foreign currency impact	2
Ending balance	154
Accumulated impairment losses	(352)	$ (352)
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	52
Foreign currency impact	1
Ending balance	53
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	9
Ending balance	9
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	91
Foreign currency impact	1
Ending balance	92
Accumulated impairment losses	$ (352)	$ (352)