Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 154	$ 152
Amortization expense estimated for year one	8
Amortization expense estimated for year two	8
Amortization expense estimated for year three	8
Amortization expense estimated for year four	8
Amortization expense estimated for year five	8
Cost of Sales and Selling and Administrative Expenses [Member]
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 8	$ 7	$ 14
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	14 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	19 years