Financial Information by Segment & Geographic Area - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 3,409	$ 2,614	$ 3,337
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	3,186	2,442	3,144
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	223	172	193
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	1,781	1,256	1,815
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	1,148	933	995
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	257	253	278
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues			56
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	1,119	868	1,114
Americas [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	699	490	688
Americas [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	310	266	294
Americas [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	110	112	126
Americas [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues			6
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	1,264	931	1,158
Asia Pacific [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	745	529	769
Asia Pacific [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	485	368	353
Asia Pacific [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	34	34	35
Asia Pacific [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues			1
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	803	643	872
Europe, Middle East and Africa [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	337	237	358
Europe, Middle East and Africa [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	353	299	348
Europe, Middle East and Africa [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 113	$ 107	117
Europe, Middle East and Africa [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues			$ 49