Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 746	$ 727
Income (loss) before income taxes	99	50
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	701	680
Income (loss) before income taxes	140	86
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	45	47
Income (loss) before income taxes	(41)	(36)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	375	379
Income (loss) before income taxes	88	47
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	267	242
Income (loss) before income taxes	54	41
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	59	59
Income (loss) before income taxes	$ (2)	$ (2)