Goodwill and Intangible Assets - Schedule of Changes in Balances (Detail) $ in Millions	6 Months Ended
	Mar. 31, 2024 USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 134
Foreign currency impact	3
Ending balance	137
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	51
Foreign currency impact	2
Ending balance	53
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	83
Foreign currency impact	1
Ending balance	$ 84