Derivative Instruments and Hedging Activities - Derivatives Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Total	$ 14	$ (2)	$ (33)
Foreign currency exchange derivatives | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) on foreign currency exchange derivatives not designated as hedging instrument	(8)	8	0
Foreign currency exchange derivatives | Net financing charges
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) on foreign currency exchange derivatives not designated as hedging instrument	22	(10)	(33)
Foreign currency exchange derivatives | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges on foreign currency exchange derivatives	(2)	89	8
Foreign currency exchange derivatives | Cash flow hedging | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges on foreign currency exchange derivatives, reclassified from AOCI	46	66	6
Foreign currency exchange derivatives | Cash flow hedging | Net financing charges
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges on foreign currency exchange derivatives, reclassified from AOCI	$ 1	$ 0	$ 0