Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 917	$ 518	$ 2,505	$ 1,955
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	851	480	2,343	1,824
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	66	38	162	131
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	302	141	812	643
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	324	212	922	695
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	225	127	609	486
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	479	197	1,288	931
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	189	59	501	354
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	197	106	537	398
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	93	32	250	179
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	303	220	864	707
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	85	54	232	206
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	118	98	358	271
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	100	68	274	230
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	69	63	191	186
Purification Solutions [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	28	28	79	83
Purification Solutions [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	9	8	27	26
Purification Solutions [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 32	$ 27	$ 85	$ 77