Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 821	$ 720
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	772	692
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	49	28
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	270
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	297
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	205
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	457	387
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	167
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	202
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	88
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	231	229
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	72
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	85
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	74
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	65	70
Purification Solutions [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	29
Purification Solutions [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	9
Purification Solutions [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	27
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	19	$ 6
Specialty Fluids [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	2
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	$ 16