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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2023
Goodwill And Intangible Assets [Line Items]      
Amortization expense estimated for year one $ 7    
Amortization expense estimated for year two 7    
Amortization expense estimated for year three 7    
Amortization expense estimated for year four 7    
Amortization expense estimated for year five 7    
Cost of Sales, Selling and Administrative Expenses and Research and Technical Expenses [Member]      
Goodwill And Intangible Assets [Line Items]      
Amortization of intangible assets $ 6 $ 6 $ 6
Minimum [Member]      
Goodwill And Intangible Assets [Line Items]      
Useful life of intangible assets 10 years    
Maximum [Member]      
Goodwill And Intangible Assets [Line Items]      
Useful life of intangible assets 25 years    
Weighted Average [Member]      
Goodwill And Intangible Assets [Line Items]      
Useful life of intangible assets 16 years