Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues from external customers	$ 1,016	$ 968	$ 2,993	$ 2,966
Income (loss) before income taxes	158	130	394	324
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	981	931	2,894	2,858
Income (loss) before income taxes	191	164	534	437
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	35	37	99	108
Income (loss) before income taxes	(33)	(34)	(140)	(113)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	649	624	1,966	1,939
Income (loss) before income taxes	136	132	414	348
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	332	307	928	919
Income (loss) before income taxes	$ 55	$ 32	$ 120	$ 89