Derivative Instruments and Hedging Activities - Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022
Derivative assets:
Total derivative assets — gross	$ 422	$ 2,418	$ 2,035
Gross amounts offset in the balance sheet	(190)	(295)	(215)
Cash collateral received	(55)	(398)	(603)
Total derivative assets — net	177	1,725	1,217
Derivative liabilities:
Total derivative liabilities — gross	(457)	(515)	(324)
Gross amounts offset in the balance sheet	190	295	215
Cash collateral pledged	102	7	0
Total derivative liabilities — net	(165)	(213)	(109)
Commodity contracts
Derivative assets:
Total derivative assets — gross	19	31	38
Derivative liabilities:
Total derivative liabilities — gross	(36)	(26)	(17)
Derivatives designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	34	123	49
Derivatives designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	9	57	18
Derivatives designated as hedging instruments: | Interest rate contracts
Derivative assets:
Total derivative assets — gross	25	66	31
Derivative liabilities:
Total derivative liabilities — gross	(21)	0	(1)
Derivatives not designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	369	2,264	1,948
Derivative liabilities:
Total derivative liabilities — gross	(400)	(489)	(306)
Derivatives not designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	14	62	17
Derivative liabilities:
Total derivative liabilities — gross	(4)	(2)	(2)
Derivatives not designated as hedging instruments: | Commodity contracts
Derivative assets:
Total derivative assets — gross	355	2,202	1,931
Derivative liabilities:
Total derivative liabilities — gross	$ (396)	$ (487)	$ (304)