Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 1,019	$ 1,033	$ 1,977	$ 1,998
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	987	998	1,913	1,927
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	32	35	64	71
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	367	380	709	710
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	375	368	755	767
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	245	250	449	450
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	676	672	1,317	1,315
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	274	280	528	521
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	255	245	515	518
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	147	147	274	276
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	311	326	596	612
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	93	100	181	189
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	120	123	240	249
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 98	$ 103	$ 175	$ 174