Derivative Instruments and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021
Foreign Exchange Contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative	$ 1,486	$ 2,735
Cross-Currency Swaps | Net investment hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative	1,958	1,958
Interest Rate Swaps | Fair value hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative	700	700
Forward Starting Interest Rate Swaps | Cash flow hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative	1,000	1,000
Foreign Currency-Denominated Debt | Net investment hedges
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative	$ 2,419	$ 2,543