Financial Information by Segment - Schedule of Performance Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 720	$ 611
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	692	580
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	229	205
Performance Chemicals [Member] | Specialty Carbons and Formulations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	160	138
Performance Chemicals [Member] | Metal Oxides [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	$ 69	$ 67