Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	$ 298	$ 2,418
Derivative instruments, Liabilities	(276)	(515)
Non-qualified supplemental postretirement grantor trust investments	39	43
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	39	43
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-qualified supplemental postretirement grantor trust investments	0	0
Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	232	2,233
Derivative instruments, Liabilities	(274)	(513)
Commodity contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	117	938
Derivative instruments, Liabilities	(193)	(377)
Commodity contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	115	1,268
Derivative instruments, Liabilities	(81)	(136)
Commodity contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	0	27
Derivative instruments, Liabilities	0	0
Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	38	119
Derivative instruments, Liabilities	(2)	(2)
Foreign currency contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	0	0
Derivative instruments, Liabilities	0	0
Foreign currency contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	38	119
Derivative instruments, Liabilities	(2)	(2)
Foreign currency contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	0	0
Derivative instruments, Liabilities	0	0
Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	28	66
Interest rate contracts | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	0	0
Interest rate contracts | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	28	66
Interest rate contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, Assets	$ 0	$ 0