Financial Information by Segment - Schedule of Performance Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 818	$ 678	$ 1,538	$ 1,289
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	794	654	1,486	1,234
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	268	228	497	433
Performance Chemicals [Member] | Specialty Carbons and Formulations [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	193	162	353	300
Performance Chemicals [Member] | Metal Oxides [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	$ 75	$ 66	$ 144	$ 133