Derivative Instruments and Hedging Activities - Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022
Derivative assets:
Total derivative assets — gross	$ 305	$ 2,418	$ 2,068
Gross amounts offset in the balance sheet	(134)	(295)	(226)
Cash collateral received	(36)	(398)	(659)
Total derivative assets — net	135	1,725	1,183
Derivative liabilities:
Total derivative liabilities — gross	(474)	(515)	(363)
Gross amounts offset in the balance sheet	134	295	226
Cash collateral pledged	137	7	13
Total derivative liabilities — net	(203)	(213)	(124)
Commodity contracts
Derivative assets:
Total derivative assets — gross	11	31	30
Derivative liabilities:
Total derivative liabilities — gross	(18)	(26)	(23)
Derivatives designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	36	123	72
Derivatives designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	6	57	28
Derivatives designated as hedging instruments: | Interest rate contracts
Derivative assets:
Total derivative assets — gross	30	66	44
Derivative liabilities:
Total derivative liabilities — gross	(4)	0	0
Derivatives not designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	258	2,264	1,966
Derivative liabilities:
Total derivative liabilities — gross	(452)	(489)	(340)
Derivatives not designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	12	62	31
Derivative liabilities:
Total derivative liabilities — gross	(4)	(2)	(2)
Derivatives not designated as hedging instruments: | Commodity contracts
Derivative assets:
Total derivative assets — gross	246	2,202	1,935
Derivative liabilities:
Total derivative liabilities — gross	$ (448)	$ (487)	$ (338)