Commitments and Contingencies - Schedule of Raw Material Purchased under Long Term Purchase Agreements (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 258	$ 466	$ 441
Reinforcement Materials [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	198	393	375
Performance Chemicals [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	58	65	55
Purification Solutions [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 2	$ 8	$ 11