Goodwill and Intangible Assets - Schedule of Changes in Balances (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2024 USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 133
Foreign currency impact	(6)
Ending balance	127
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	48
Foreign currency impact	(2)
Ending balance	46
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	85
Foreign currency impact	(4)
Ending balance	$ 81