Financial Information by Segment - Revenue from External Customers by Geographic Region (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]
Net sales and other operating revenues	$ 1,016	$ 968	$ 2,993	$ 2,966
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	981	931	2,894	2,858
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	35	37	99	108
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	368	354	1,077	1,064
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	377	353	1,132	1,120
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	236	224	685	674
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	649	624	1,966	1,939
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	265	260	793	781
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	245	234	760	752
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	139	130	413	406
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	332	307	928	919
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	103	94	284	283
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	132	119	372	368
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 97	$ 94	$ 272	$ 268