Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues from external customers	$ 4,321	$ 3,409	$ 2,614
Depreciation and amortization	146	160	158
Equity in earnings of affiliated companies	10	3	3
Income (loss) from continuing operations before income taxes	335	406	(33)
Assets	3,525	3,306	2,781
Total expenditures for additions to long-lived assets	221	198	169
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	4,044	3,186	2,442
Depreciation and amortization	145	159	156
Equity in earnings of affiliated companies	10	4	4
Income (loss) from continuing operations before income taxes	642	550	283
Assets	3,149	3,029	2,518
Total expenditures for additions to long-lived assets	217	193	166
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	277	223	172
Depreciation and amortization	1	1	2
Equity in earnings of affiliated companies		(1)	(1)
Income (loss) from continuing operations before income taxes	(307)	(144)	(316)
Assets	376	277	263
Total expenditures for additions to long-lived assets	4	5	3
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	2,575	1,781	1,256
Depreciation and amortization	70	70	68
Equity in earnings of affiliated companies	4
Income (loss) from continuing operations before income taxes	408	329	162
Assets	1,691	1,421	1,077
Total expenditures for additions to long-lived assets	114	104	66
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	1,372	1,148	933
Depreciation and amortization	72	73	64
Equity in earnings of affiliated companies	5	2	1
Income (loss) from continuing operations before income taxes	234	211	118
Assets	1,458	1,325	1,145
Total expenditures for additions to long-lived assets	100	80	92
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	97	257	253
Depreciation and amortization	3	16	24
Equity in earnings of affiliated companies	1	2	3
Income (loss) from continuing operations before income taxes		10	3
Assets		283	296
Total expenditures for additions to long-lived assets	$ 3	$ 9	$ 8