Financial Information by Segment & Geographic Area - Schedule of Performance Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net sales	$ 723	$ 705	$ 678	$ 611	$ 619	$ 621	$ 568	$ 603	$ 2,717	$ 2,411	$ 2,871
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									2,611	2,310	2,772
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									908	865	927
Performance Chemicals [Member] | Specialty Carbons and Formulations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									623	578	630
Performance Chemicals [Member] | Metal Oxides [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales									$ 285	$ 287	$ 297