Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 710	$ 844	$ 1,437	$ 1,665
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	664	795	1,344	1,567
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	46	49	93	98
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	259	283	502	553
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	210	262	483	559
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	195	250	359	455
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	355	445	734	902
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	154	169	295	336
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	122	180	292	382
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	79	96	147	184
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	245	254	487	485
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	76	81	152	153
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	79	75	173	160
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	90	98	162	172
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	64	72	123	137
Purification Solutions [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	29	31	55	60
Purification Solutions [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	9	7	18	16
Purification Solutions [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 26	34	$ 50	61
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues		24		43
Specialty Fluids [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues		2		4
Specialty Fluids [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues				1
Specialty Fluids [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues		$ 22		$ 38