Fair Value Measurements - Financial Assets and Liabilities that are Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	$ 162	$ 298	$ 305
Liabilities:	(176)	(276)	(474)
Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	4	6	11
Liabilities:	(5)	(8)	(18)
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	42	39	40
Recurring | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	137	232	257
Liabilities:	(174)	(274)	(466)
Recurring | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	18	38	18
Liabilities:	(2)	(2)	(4)
Recurring | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	7	28	30
Liabilities:			(4)
Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	42	39	40
Recurring | Level 1 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	92	117	146
Liabilities:	(148)	(193)	(242)
Recurring | Level 1 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	0	0	0
Liabilities:	0	0	0
Recurring | Level 1 | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	0	0	0
Liabilities:			0
Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	0	0	0
Recurring | Level 2 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	45	115	111
Liabilities:	(26)	(81)	(224)
Recurring | Level 2 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	18	38	18
Liabilities:	(2)	(2)	(4)
Recurring | Level 2 | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	7	28	30
Liabilities:			(4)
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Non-qualified supplemental postretirement grantor trust investments	0	0	0
Recurring | Level 3 | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	0	0	0
Liabilities:	0	0	0
Recurring | Level 3 | Foreign currency contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	0	0	0
Liabilities:	0	0	0
Recurring | Level 3 | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets:	$ 0	$ 0	0
Liabilities:			$ 0