Derivative Instruments and Hedging Activities - Derivatives Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Total	$ (8)	$ 14	$ (2)
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	4	(8)	8
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	(12)	22	(10)
Foreign currency exchange derivatives | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges on foreign currency exchange derivatives	46	(2)	89
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	(8)	46	66
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	$ 0	$ 1	$ 0