Derivative Instruments and Hedging Activities - Additional Information (Detail) - Cash flow hedges - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other comprehensive income (loss), cash flow hedge, gain (loss), before reclassification and tax	$ (10)	$ 23	$ 92
Net after-tax gain upon termination of contract	67		$ 41
Foreign currency-denominated debt
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other comprehensive income (loss), cash flow hedge, gain (loss), after reclassification and tax	$ 0