Derivative Financial Instruments - Summary of Amounts Recorded in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Other current assets
Derivatives, Fair Value [Line Items]
Other assets	$ 0	$ 0
Other current liabilities
Derivatives, Fair Value [Line Items]
Other liabilities	3	0
Other noncurrent assets
Derivatives, Fair Value [Line Items]
Other assets	4	2
Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Other liabilities	$ 11	$ 13