Derivative Instruments and Hedging Activities - Gains (Losses) on Net Investment Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	$ 40	$ (80)
Foreign currency-denominated debt
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	(29)	(142)
Cross-currency swaps
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	$ (55)	$ (80)