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Derivatives - Additional Information (Detail)
12 Months Ended
Sep. 30, 2022
USD ($)
Derivative
Sep. 30, 2021
USD ($)
Derivative
Sep. 30, 2020
USD ($)
Derivative [Line Items]      
Significant concentration of credit risk associated with our derivative instruments $ 0 $ 0  
Maximum [Member]      
Derivative [Line Items]      
Fair value of derivative instruments not designated as hedges, liability 1,000,000 1,000,000  
Fair value of derivative instruments not designated as hedges, asset   1,000,000  
Cross Currency Swaps [Member]      
Derivative [Line Items]      
Fair value of swaps, net asset $ 29,000,000 $ 3,000,000  
Fair Value Hedging [Member] | Interest Rate Swap-Fixed to Variable [Member] | Interest Rate Risk [Member]      
Derivative [Line Items]      
Derivatives held to manage interest rate risk | Derivative 0 0  
Net Investment Hedge [Member] | Cross Currency Swaps [Member]      
Derivative [Line Items]      
Notional Amount $ 250,000,000    
Net cash interest received 4,000,000 $ 3,000,000 $ 4,000,000
Cumulative gain related to swaps $ 32,000,000 $ 6,000,000  
Net Investment Hedge [Member] | Cross Currency Swaps [Member] | Fixed Rate Debt [Member]      
Derivative [Line Items]      
Derivative Instruments Frequency of Cash Settlements semi-annually