Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	705	521	1,410	1,041
Expected return on plan assets	(859)	(948)	(1,720)	(1,895)
Amortization of prior service credits	(21)	(21)	(41)	(41)
Recognized net actuarial gain (loss)	(41)	(227)	(83)	(454)
Net periodic benefit income	(133)	(220)	(266)	(439)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	18	24	36
Interest cost	37	25	74	49
Expected return on plan assets	(2)	(3)	(4)	(5)
Amortization of prior service credits	(5)	(8)	(11)	(17)
Recognized net actuarial gain (loss)	44	28	88	56
Net periodic benefit income	(2)	4	(5)	7
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	1	2	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	31	39
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)	(221)	(268)	(441)
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	(14)	(14)	(29)	(29)
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)	(220)	(266)	(439)
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	$ 2	$ 6	$ 2	$ 10