Benefit Plans - Schedule of Components of Net Cost (Benefit) for Pension and Other Postretirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of net periodic cost
Service cost	$ 133	$ 102	$ 104
Interest cost	249	229	199
Expected return on plan assets	(306)	(371)	(445)
Amortization of prior service credit	(21)	(52)	(75)
Costs and expenses	55	(92)	(217)
Remeasurement of projected benefit obligation	121	(1,444)	(325)
Remeasurement of plan assets	(112)	1,560	(319)
Remeasurement (gains) losses	9	116	(644)
Total net (benefit) cost	$ 64	$ 24	$ (861)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability, Property-Liability net investment income, Operating costs and expenses, Restructuring and related charges	Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability, Property-Liability net investment income, Operating costs and expenses, Restructuring and related charges	Policyholder Benefits and Claims Incurred, Net, Property, Casualty and Liability, Property-Liability net investment income, Operating costs and expenses, Restructuring and related charges
Pension benefits
Components of net periodic cost
Service cost	$ 132	$ 101	$ 103
Interest cost	239	219	191
Expected return on plan assets	(306)	(371)	(445)
Amortization of prior service credit	0	(27)	(50)
Costs and expenses	65	(78)	(201)
Remeasurement of projected benefit obligation	125	(1,382)	(309)
Remeasurement of plan assets	(112)	1,560	(319)
Remeasurement (gains) losses	13	178	(628)
Total net (benefit) cost	78	100	(829)
Postretirement benefits
Components of net periodic cost
Service cost	1	1	1
Interest cost	10	10	8
Expected return on plan assets	0	0	0
Amortization of prior service credit	(21)	(25)	(25)
Costs and expenses	(10)	(14)	(16)
Remeasurement of projected benefit obligation	(4)	(62)	(16)
Remeasurement of plan assets	0	0	0
Remeasurement (gains) losses	(4)	(62)	(16)
Total net (benefit) cost	$ (14)	$ (76)	$ (32)