Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenues from external customers	$ 958	$ 965
Income (loss) before income taxes	94	84
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	926	929
Income (loss) before income taxes	163	123
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	32	36
Income (loss) before income taxes	(69)	(39)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	641	643
Income (loss) before income taxes	129	94
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	285	286
Income (loss) before income taxes	$ 34	$ 29