Derivative Instruments and Hedging Activities - Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023
Derivative assets:
Total derivative assets — gross	$ 162	$ 298	$ 305
Gross amounts offset in the balance sheet	(94)	(124)	(134)
Cash collateral received	(12)	(40)	(36)
Total derivative assets — net	56	134	135
Derivative liabilities:
Total derivative liabilities — gross	(176)	(276)	(474)
Gross amounts offset in the balance sheet	94	124	134
Cash collateral pledged	32	53	137
Total derivative liabilities — net	(50)	(99)	(203)
Commodity contracts
Derivative assets:
Total derivative assets — gross	4	6	11
Derivative liabilities:
Total derivative liabilities — gross	(5)	(8)	(18)
Derivatives designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	19	42	36
Derivatives designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	12	14	6
Derivatives designated as hedging instruments: | Interest rate contracts
Derivative assets:
Total derivative assets — gross	7	28	30
Derivative liabilities:
Total derivative liabilities — gross	0	0	(4)
Derivatives not designated as hedging instruments:
Derivative assets:
Total derivative assets — gross	139	250	258
Derivative liabilities:
Total derivative liabilities — gross	(171)	(268)	(452)
Derivatives not designated as hedging instruments: | Foreign currency contracts
Derivative assets:
Total derivative assets — gross	6	24	12
Derivative liabilities:
Total derivative liabilities — gross	(2)	(2)	(4)
Derivatives not designated as hedging instruments: | Commodity contracts
Derivative assets:
Total derivative assets — gross	133	226	246
Derivative liabilities:
Total derivative liabilities — gross	$ (169)	$ (266)	$ (448)