Derivative Instruments and Hedging Activities - Gains (Losses) on Net Investment Hedges (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	$ (41)	$ (21)	$ (1)	$ (101)
Foreign currency-denominated debt
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	4	(22)	(25)	(164)
Cross-currency swaps (a)
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	21	$ (21)	(34)	$ (101)
Terminated Currency Swap
Derivative Instruments, Gain (Loss) [Line Items]
Net gains (losses) recorded to Accumulated other comprehensive income (loss), net of tax	$ 13		$ 13