Commitments and Contingencies - Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended			84 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2016	Dec. 31, 2023	Dec. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Other Commitment	$ 2,600			$ 2,600
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	77	$ 82
Premium tax offsets	0	1		0
Fair value of derivative instrument in a net liability position	43			43
Collateral already posted	39			39
Asbestos and Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	248			248
Adverse development from comprehensive annual review				1,438
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	62
Reinsurance, Amount Retained, Per Policy			$ 1,700
Other liabilities | Retained Earnings
Loss Contingencies [Line Items]
Off-Balance Sheet, Credit Loss, Liability	$ 9	$ 22		9	$ 25	$ 26
Insurance-related Assessments [Member]
Loss Contingencies [Line Items]
Minimum Percentage of Premiums Written Per Year to be Considered for Assessment Under Guaranty Fund	1.00%
Maximum Percentage of Premiums Written Per Year to be Considered for Assessment Under Guaranty Fund	2.00%
Limited partnerships and other alternative investments
Loss Contingencies [Line Items]
Other Commitment	$ 1,900			1,900
Private Placement Securities
Loss Contingencies [Line Items]
Other Commitment	313			313
Mortgage loans
Loss Contingencies [Line Items]
Other Commitment	376			376
Cancelable mortgage loan [Member]
Loss Contingencies [Line Items]
Other Commitment	$ 84			$ 84