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Derivatives - Additional Information (Detail) - Cross Currency Swaps [Member] - USD ($)
9 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Sep. 30, 2017
Prepaid Expenses And Other Asset Current And Other Liabilities [Member]      
Derivative [Line Items]      
Fair value of swaps, net liability $ 17,000,000   $ 13,000,000
Net Investment [Member]      
Derivative [Line Items]      
Notional amount 250,000,000    
Cumulative gain (loss) related to swaps (15,000,000)   $ (9,000,000)
Net cash interest received $ 2,000,000 $ 2,000,000  
Net Investment [Member] | Fixed Rate Debt [Member]      
Derivative [Line Items]      
Derivative Instruments Frequency of Cash Settlements semi-annually