Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 844	$ 818	$ 1,665	$ 1,538
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	795	794	1,567	1,486
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	49	24	98	52
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	283		553
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	262		559
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	250		455
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	445	454	902	841
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	169		336
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	180		382
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	96		184
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	254	268	485	497
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	81		153
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	75		160
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	98		172
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	72	66	137	136
Purification Solutions [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	31		60
Purification Solutions [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	7		16
Purification Solutions [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	34		61
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	24	$ 6	43	$ 12
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