Commitments and Contingencies - Schedule of Raw Material Purchased under Long Term Purchase Agreements (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 331	$ 268	$ 352
Reinforcement Materials [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	281	193	276
Performance Chemicals [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	43	68	62
Purification Solutions [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 7	$ 7	$ 14