Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 844	$ 818	$ 1,665	$ 1,538
Income (loss) from continuing operations before income taxes	49	(171)	119	(79)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	795	794	1,567	1,486
Income (loss) from continuing operations before income taxes	112	127	217	240
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	49	24	98	52
Income (loss) from continuing operations before income taxes	(63)	(298)	(98)	(319)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	445	454	902	841
Income (loss) from continuing operations before income taxes	61	79	123	141
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	254	268	485	497
Income (loss) from continuing operations before income taxes	38	57	74	104
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	72	66	137	136
Income (loss) from continuing operations before income taxes	1	(6)	(2)
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	24	6	43	12
Income (loss) from continuing operations before income taxes	$ 12	$ (3)	$ 22	$ (5)