Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1		$ 3	$ 2
Interest cost	705	520	2,115	1,561
Expected return on plan assets	(861)	(948)	(2,581)	(2,843)
Amortization of prior service credits	(20)	(20)	(61)	(61)
Recognized net actuarial loss	42	227	125	681
Settlement/curtailment gain		(4)		(4)
Net periodic benefit income	(133)	(225)	(399)	(664)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	18	36	54
Interest cost	37	24	111	73
Expected return on plan assets	(2)	(3)	(6)	(8)
Amortization of prior service credits	(6)	(9)	(17)	(26)
Recognized net actuarial loss	(44)	(27)	(132)	(83)
Net periodic benefit income	(3)	3	(8)	10
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	1		3	2
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	16	20	47	59
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	(134)	(225)	(402)	(666)
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	(15)	(15)	(44)	(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	(133)	(225)	(399)	(664)
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	$ 1	$ 5	$ 3	$ 15