Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenues from external customers	$ 917	$ 518	$ 2,505	$ 1,955
Income (loss) before income taxes	123	(11)	340	51
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	851	480	2,343	1,824
Income (loss) before income taxes	145	18	434	199
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	66	38	162	131
Income (loss) before income taxes	(22)	(29)	(94)	(148)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	479	197	1,288	931
Income (loss) before income taxes	85	(5)	262	103
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	303	220	864	707
Income (loss) before income taxes	54	21	166	93
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	69	63	191	186
Income (loss) before income taxes	$ 6	$ 2	$ 6	$ 3