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Derivatives - Additional Information (Detail) - Cross Currency Swaps [Member] - USD ($)
6 Months Ended
Mar. 31, 2019
Sep. 30, 2018
Prepaid Expenses And Other Asset Current And Other Liabilities [Member]    
Derivative [Line Items]    
Fair value of swaps, net liability $ 7,000,000 $ 18,000,000
Net Investment Hedge [Member]    
Derivative [Line Items]    
Notional Amount 250,000,000  
Cumulative gain (loss) related to swaps $ (4,000,000) $ (14,000,000)
Net Investment Hedge [Member] | Fixed Rate Debt [Member]    
Derivative [Line Items]    
Derivative Instruments Frequency of Cash Settlements semi-annually