Derivative Instruments and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Debt | Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 1,056	$ 2,140
Foreign Exchange Contract [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	3,146	2,766
Currency Swap | Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	2,119	910
Fixed To Floating | Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	700	700
Interest Rate Swap [Member] | Cash Flow Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount	$ 500	$ 500