Maximum percentage of premiums written per year to be considered for Assessment under Guaranty Fund.

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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The amount of insurance-related assessment liability that is expected to be recovered through a premium tax offset based on current laws applied to in-force policies.

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The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

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Amount per policy of risk ceded to reinsurer in excess of risk undertaken originally by insurer that is not ceded to reinsurer.

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Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts for accident years not separately presented in claim development information. Excludes unallocated claim adjustment expense.

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Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs.

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Commitments and Contingencies - Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2017	Dec. 31, 2021
Loss Contingencies [Line Items]
Other Commitment	$ 3,800
Loss Contingency, Undiscounted Amount of Insurance-related Assessment Liability	70	$ 77
Premium tax offsets	0	0
Fair value of derivative instrument in a net liability position	33
Collateral already posted	31
Additional Collateral, Aggregate Fair Value	0
Other liabilities \| Retained Earnings
Loss Contingencies [Line Items]
Off-Balance Sheet, Credit Loss, Liability	$ 7	9	$ 22		$ 25
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	$ 2,100
Private Placement Securities
Loss Contingencies [Line Items]
Other Commitment	1,000
Mortgage loans
Loss Contingencies [Line Items]
Other Commitment	636
Cancelable mortgage loan [Member]
Loss Contingencies [Line Items]
Other Commitment	53
Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group
Loss Contingencies [Line Items]
Deferred Revenue	64	209
Adverse development from comprehensive annual review	300
Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group \| Remaining [Member]
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	0
Reinsurance Policy, Type [Axis]: Adverse Development Cover Navigators Group \| Maximum
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	300
Reinsurance Policy, Type [Axis]: Retroactive Reinsurance [Member] \| Other liabilities
Loss Contingencies [Line Items]
Deferred Revenue	914	997
Asbestos and Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	224
Asbestos and Environmental \| Segment Reconciling Items
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	315
Prior accident year development [1]	141	$ 0	$ 0
Asbestos and Environmental \| Reinsurance Policy, Type [Axis]: Asbestos and Environmental
Loss Contingencies [Line Items]
Deferred Revenue	850
Reinsurance, Amount Retained, Per Policy				$ 1,700
Adverse development from comprehensive annual review	1,500
Asbestos and Environmental \| Reinsurance Policy, Type [Axis]: Asbestos and Environmental \| Remaining [Member]
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	0
Asbestos and Environmental \| Reinsurance Policy, Type [Axis]: Asbestos and Environmental \| Maximum
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	$ 1,500