Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 1	$ 5	$ 3
Interest cost	658	705	1,976	2,115
Expected return on plan assets	(827)	(861)	(2,483)	(2,581)
Amortization of prior service credits	(20)	(20)	(61)	(61)
Recognized net actuarial loss	66	42	200	125
Net periodic benefit income	(121)	(133)	(363)	(399)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	13	12	38	36
Interest cost	31	37	93	111
Expected return on plan assets	(2)	(2)	(8)	(6)
Amortization of prior service credits	(3)	(6)	(8)	(17)
Recognized net actuarial loss	(44)	(44)	(132)	(132)
Net periodic benefit income	(5)	(3)	(17)	(8)
Operating Income (Loss) | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	2	1	5	3
Operating Income (Loss) | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	12	16	35	47
Other Income | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	(123)	(134)	(368)	(402)
Other Income | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	(18)	(15)	(55)	(44)
Operating Income (Loss) Before Taxes | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	(121)	(133)	(363)	(399)
Operating Income (Loss) Before Taxes | Postretirement
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earnings from operations, other income, and loss before income taxes	$ (6)	$ 1	$ (20)	$ 3