Derivative Instruments and Hedging Activities - Derivatives Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Total	$ (34)	$ (3)	$ (10)
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)	(4)	(2)
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	(30)	1	5
Foreign currency exchange derivatives | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges on foreign currency exchange derivatives	29	(37)	(5)
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	2	(16)	(4)
Equity swaps | Selling, general and administrative
Derivative Instruments, Gain (Loss) [Line Items]
Pre-tax gain (loss) on equity swap derivatives not designated as hedging instrument	$ 0	$ 0	$ (13)