Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 845	$ 854	$ 2,510	$ 2,392
Income (loss) from continuing operations before income taxes	69	95	188	16
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	798	822	2,365	2,308
Income (loss) from continuing operations before income taxes	112	127	329	367
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	47	32	145	84
Income (loss) from continuing operations before income taxes	(43)	(32)	(141)	(351)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	461	466	1,363	1,307
Income (loss) from continuing operations before income taxes	72	74	195	215
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	251	274	736	771
Income (loss) from continuing operations before income taxes	37	56	111	160
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	73	70	210	206
Income (loss) from continuing operations before income taxes	1	(6)	(1)	(6)
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	13	12	56	24
Income (loss) from continuing operations before income taxes	$ 2	$ 3	$ 24	$ (2)