Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2020 USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 90	[1]
Goodwill acquired	45	[1],[2]
Foreign currency impact	(1)	[1]
Ending balance	134	[1]
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	50
Foreign currency impact	(4)
Ending balance	46
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	40
Goodwill acquired	45	[2]
Foreign currency impact	3
Ending balance	$ 88

[1] ^{The Company incurred $444 million accumulated impairment losses associated with the goodwill of the Purification Solutions segment as of both September 30, 2020 and 2019. There were no accumulated impairment losses associated with the goodwill of the Reinforcement Materials or Performance Chemicals segments.}

[2] ^{Consists of goodwill acquired in the acquisition of SUSN as described in Note C.}