| Current Federal Tax Expense (Benefit) | 296.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost | 1.34B | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Liability for Future Policy Benefit, Loss, Claim and Loss Expense | 14.46B | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Unearned Premium | 5.25B | as of 2025-12-31 |
| Current Foreign Tax Expense (Benefit) | 8.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Policy Claim and Benefit Payable | 35.00M | as of 2025-12-31 |
| Current Income Tax Expense (Benefit) | 304.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue | 9.98B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Net Investment Income | 1.06B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses | 6.64B | 2025-01-01 → 2025-12-31 |
| Cash and Cash Equivalents, Fair Value Disclosure | 1.43B | as of 2025-12-31 |
| Deferred Federal Income Tax Expense (Benefit) | 271.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Cost | 1.85B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Deferred Policy Acquisition Cost | 974.00M | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense | 1.07B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Reserve for Unpaid Claim and Claim Adjustment Expense | 11.45B | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Written | 10.08B | 2025-01-01 → 2025-12-31 |
| Deferred Foreign Income Tax Expense (Benefit) | 12.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Unearned Premium | 5.25B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Earned Premium | 9.65B | 2025-01-01 → 2025-12-31 |
| Loans Receivable, Fair Value Disclosure | 43.00M | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Net Investment Income | 854.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Amortization of Deferred Policy Acquisition Cost | 1.82B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Paid Claim and Claim Adjustment Expense | 4.99B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Premium Written | 10.08B | 2025-01-01 → 2025-12-31 |
| Investments, Fair Value Disclosure | 31.97B | as of 2025-12-31 |
| SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount | 76.00M | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Gross | 127.45B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Ceded | 40.14B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Assumed | 0 | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Net | 87.31B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost | 23.43B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Fair Value | 0 | as of 2025-12-31 |
| Notes Payable, Fair Value Disclosure | 25.00M | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Amount | 31.78B | as of 2025-12-31 |
| Debt Instrument, Fair Value Disclosure | 874.00M | as of 2025-12-31 |
| Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount | 626.00M | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Cost | 4.16B | as of 2025-12-31 |
| Share-based Payment Arrangement, Expense, after Tax | 37.00M | 2025-01-01 → 2025-12-31 |
| Liabilities Related to Investment Contracts, Fair Value Disclosure | 653.00M | as of 2025-12-31 |
| Share-based Payment Arrangement, Expense, Tax Benefit | 9.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | 44.00M | as of 2025-12-31 |
| Direct Premiums Earned | 9.89B | 2025-01-01 → 2025-12-31 |
| Ceded Premiums Earned | 576.00M | 2025-01-01 → 2025-12-31 |
| Assumed Premiums Earned | 673.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount | 10.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount | 21.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount | 23.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Other Adjustments, Amount | -5.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One | 993.00M | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 3.56B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 4.40B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 | 9.49B | as of 2025-12-31 |
| Defined Benefit Plan, Service Cost | 5.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Interest Cost | 14.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | 990.00M | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 3.58B | as of 2025-12-31 |
| Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment | 0 | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 4.43B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | 9.27B | as of 2025-12-31 |
| Defined Benefit Plan, Net Periodic Benefit Cost (Credit) | -7.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Plan Assets, Amount | 380.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 22.00M | as of 2025-12-31 |
| Defined Benefit Plan, Benefit Obligation | 263.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 375.00M | as of 2025-12-31 |
| Defined Benefit Plan, Funded (Unfunded) Status of Plan | 117.00M | as of 2025-12-31 |
| Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | -7.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Benefit Obligation, Benefits Paid | 21.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 216.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 397.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 2.21B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 5.67B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position | 7.88B | as of 2025-12-31 |
| Deferred Tax Assets, Operating Loss Carryforwards, Foreign | 13.00M | as of 2025-12-31 |
| Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) | 43.00M | 2025-01-01 → 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | 202.00M | as of 2025-12-31 |
| Defined Benefit Plan, Plan Assets, Benefits Paid | 21.00M | 2025-01-01 → 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | 26.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Credit Carryforwards, Foreign | 34.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | 173.00M | as of 2025-12-31 |
| Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position | 117.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 210.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves | 168.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, Year One | 18.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, Year Two | 15.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, Year Three | 13.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, Year Four | 10.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, Year Five | 6.00M | as of 2025-12-31 |
| Finance Lease, Liability, to be Paid, after Year Five | 3.00M | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax | 86.00M | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax | 1.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year One | 3.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Two | 3.00M | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax | -85.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Three | 2.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Four | 2.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Five | 2.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, after Year Five | 2.00M | as of 2025-12-31 |
| Defined Benefit Plan, Amount Recognized in Net Periodic Benefit Cost (Credit) and Other Comprehensive (Income) Loss, before Tax | -17.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Other | 62.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 487.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 2.32B | as of 2025-12-31 |
| Deferred Policy Acquisition Cost, Capitalization | 1.95B | 2025-01-01 → 2025-12-31 |
| Debt Instrument, Face Amount | 793.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Unrealized Gains on Trading Securities | 1.78B | as of 2025-12-31 |
| Insurance Commissions and Fees | 20.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, Year One | 40.00M | as of 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, Year Two | 31.00M | as of 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, Year Three | 32.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Investments | 56.00M | as of 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, Year Four | 31.00M | as of 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, Year Five | 29.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Undistributed Foreign Earnings | 77.00M | as of 2025-12-31 |
| Defined Benefit Plan, Expected Future Benefit Payment, after Year Five for Next Five Years | 105.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Other | 89.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Net | 1.83B | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Benefit Obligation | 252.00M | as of 2025-12-31 |
| Current Year Claims and Claims Adjustment Expense | 6.53B | 2025-01-01 → 2025-12-31 |
| Defined Contribution Plan, Employer Discretionary Contribution Amount | 32.00M | 2025-01-01 → 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | -196.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss | 54.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss, Securities Sold | 9.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net | 136.00M | as of 2025-12-31 |
| Income Tax Examination, Penalties Expense | 0 | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Domestic | 2.89B | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Foreign | 90.00M | 2025-01-01 → 2025-12-31 |
| Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 3.44B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 10.80B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense | 647.00M | as of 2025-12-31 |
| DebtSecuritiesAvailableForSaleAmortizedCostAfterAllowanceForCreditLoss | 18.30B | as of 2025-12-31 |
| Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost | 229.00M | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Amount Available for Dividend Payments | 975.00M | as of 2025-12-31 |
| Assets Held by Insurance Regulators | 115.00M | as of 2025-12-31 |