Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues from external customers	$ 1,092	$ 842	$ 2,060	$ 1,588
Income (loss) before income taxes	147	118	54	217
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	1,023	791	1,927	1,492
Income (loss) before income taxes	171	149	308	289
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	69	51	133	96
Income (loss) before income taxes	(24)	(31)	(254)	(72)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	627	434	1,168	809
Income (loss) before income taxes	101	89	186	177
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	360	294	662	561
Income (loss) before income taxes	70	58	122	112
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 36	63	$ 97	$ 122
Income (loss) before income taxes		$ 2