Derivative Instruments and Hedging Activities - Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020
Derivative assets:
Total derivative assets — gross	$ 661	$ 139	$ 117
Gross amounts offset in the balance sheet	(77)	(57)	(42)
Cash collateral received	(105)	0	0
Total derivative assets — net	479	82	75
Derivative liabilities:
Total derivative liabilities — gross	(193)	(187)	(238)
Gross amounts offset in the balance sheet	77	57	42
Cash collateral pledged	0	7	21
Total derivative liabilities — net	(116)	(123)	(175)
Commodity contracts
Derivative assets:
Total derivative assets — gross	14	7	3
Derivative liabilities:
Total derivative liabilities — gross	(6)	0	(2)
Derivatives designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	15	17	25
Derivatives designated as hedging instruments: | Interest rate contracts
Derivative liabilities:
Total derivative liabilities — gross	(35)	(55)	(59)
Derivatives not designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	632	115	89
Derivative liabilities:
Total derivative liabilities — gross	(152)	(132)	(177)
Derivatives not designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	9	15	24
Derivative liabilities:
Total derivative liabilities — gross	(13)	(14)	(7)
Derivatives not designated as hedging instruments: | Commodity contracts
Derivative assets:
Total derivative assets — gross	623	100	65
Derivative liabilities:
Total derivative liabilities — gross	$ (139)	$ (118)	$ (170)