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Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]      
Cash flow hedges $ 27 $ 85 $ 81
Interest Rate Swap [Member] | Cash Flow Hedging      
Derivative Instruments and Hedging Activities Disclosures [Line Items]      
Cash flow hedges 23 92 $ 72
Net after-tax gain upon termination of contract   41  
Derivative, Notional Amount $ 500 $ 500