Postretirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 3	$ 3
Interest cost	2,820	2,080	1,988
Expected return on plan assets	(3,441)	(3,789)	(3,848)
Amortization of prior service credits	(81)	(81)	(80)
Recognized net actuarial loss/(gain)	173	913	1,219
Settlement/curtailment (gain)/loss		(4)	193
Net periodic benefit (income)/cost	(527)	(878)	(525)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	49	72	87
Interest cost	148	98	97
Expected return on plan assets	(9)	(10)	(7)
Amortization of prior service credits	(22)	(35)	(35)
Recognized net actuarial loss/(gain)	(175)	(111)	(56)
Settlement/curtailment (gain)/loss
Net periodic benefit (income)/cost	(9)	14	86
Operating Income (Loss) | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	2	3	3
Operating Income (Loss) | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	62	79	90
Other Income | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	(529)	(881)	(528)
Other Income | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	(58)	(58)	(1)
Operating Income (Loss) Before Taxes | Pension
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	(527)	(878)	(525)
Operating Income (Loss) Before Taxes | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit (income)/cost included in (loss)/earning from operations, other income, and loss before income taxes	$ 4	$ 21	$ 89