v3.26.1
Financial Information by Segment - Schedule of Details of Segment EBIT Including Segment Revenue and Significant Segment Expenses (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting Information [Line Items]        
Segment revenues from external customers $ 982 $ 923 $ 2,735 $ 2,814
Segment cost of sales 798 679 2,130 2,094
Operating Segments [Member]        
Segment Reporting Information [Line Items]        
Segment revenues from external customers 950 893 2,642 2,720
Segment cost of sales (716) (644) (1,970) (1,981)
Segment operating expenses (71) (65) (210) (203)
Other Segment Items 2 1 5 5
Segment EBIT 165 185 467 541
Reinforcement Materials [Member] | Operating Segments [Member]        
Segment Reporting Information [Line Items]        
Segment revenues from external customers 599 573 1,663 1,778
Segment cost of sales (468) (415) (1,271) (1,292)
Segment operating expenses (35) (31) (102) (99)
Other Segment Items 1 1 2 2
Segment EBIT 97 128 292 389
Performance Chemicals [Member] | Operating Segments [Member]        
Segment Reporting Information [Line Items]        
Segment revenues from external customers 351 320 979 942
Segment cost of sales (248) (229) (699) (689)
Segment operating expenses (36) (34) (108) (104)
Other Segment Items 1 0 3 3
Segment EBIT $ 68 $ 57 $ 175 $ 152