| Current Federal Tax Expense (Benefit) | 74.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost | 1.55B | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Liability for Future Policy Benefit, Loss, Claim and Loss Expense | 34.31B | as of 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Unearned Premium | 7.28B | as of 2025-12-31 |
| Current Foreign Tax Expense (Benefit) | 265.00M | 2025-01-01 → 2025-12-31 |
| Current Income Tax Expense (Benefit) | 339.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue | 15.56B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Net Investment Income | 2.12B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Benefit, Claim, Loss and Settlement Expenses | 10.86B | 2025-01-01 → 2025-12-31 |
| Deferred Federal Income Tax Expense (Benefit) | -9.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Cost | 3.46B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense | 1.03B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Written | 15.51B | 2025-01-01 → 2025-12-31 |
| Deferred Foreign Income Tax Expense (Benefit) | -34.00M | 2025-01-01 → 2025-12-31 |
| Asset-Backed Securities, at Carrying Value | 1.40B | as of 2025-12-31 |
| Translation Adjustment Functional to Reporting Currency, Net of Tax, Period Increase (Decrease) | 663.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost | 45.48B | as of 2025-12-31 |
| Deposits with Clearing Organizations and Others, Securities | 1.42B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Fair Value | 45.44B | as of 2025-12-31 |
| Dividends | 335.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Amount | 45.43B | as of 2025-12-31 |
| Undistributed Earnings, Basic | 1.26B | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount | 283.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount | 0 | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense, after Tax | 61.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense, Tax Benefit | 6.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Trading, Restricted | 739.00M | as of 2025-12-31 |
| Direct Premiums Earned | 4.92B | 2025-01-01 → 2025-12-31 |
| Assets Held-in-trust | 3.36B | as of 2025-12-31 |
| Ceded Premiums Earned | 2.43B | 2025-01-01 → 2025-12-31 |
| Assumed Premiums Earned | 13.07B | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Realized Gain | 0 | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Realized Loss | 1.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount | 4.00M | 2025-01-01 → 2025-12-31 |
| Line of Credit Facility, Maximum Borrowing Capacity | 1.60B | as of 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Contingency, Amount | 0 | 2025-01-01 → 2025-12-31 |
| Undistributed Earnings, Diluted | 1.26B | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount | 27.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Realized Gain | 48.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Realized Loss | 159.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount | -74.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount | -30.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount | 0 | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One | 1.44B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 10.75B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 6.72B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 | 1.83B | as of 2025-12-31 |
| Net Income (Loss) Available to Common Stockholders, Diluted | 1.57B | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | 1.41B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 10.82B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 6.78B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | 1.77B | as of 2025-12-31 |
| Reinsurance Recoverable for Paid Claims and Claims Adjustments | 142.00M | as of 2025-12-31 |
| Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 4.97B | as of 2025-12-31 |
| Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | 5.10B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 70.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 549.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 619.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 640.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 619.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 4.19B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 7.76B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position | 11.95B | as of 2025-12-31 |
| Deferred Tax Assets, Operating Loss Carryforwards | 24.00M | as of 2025-12-31 |
| Reinsurance Recoverables on Paid Losses, Allowance | 57.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Credit Carryforwards, Foreign | 7.00M | as of 2025-12-31 |
| Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss | 9.00M | as of 2025-12-31 |
| Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain | 18.00M | as of 2025-12-31 |
| Deferred Tax Assets, Capital Loss Carryforwards | 0 | as of 2025-12-31 |
| Funds Held under Reinsurance Agreements, Liability | 267.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits | 10.00M | as of 2025-12-31 |
| Lease, Cost | 36.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Amortized Cost | 573.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 152.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves | 342.00M | as of 2025-12-31 |
| DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateYearOne | 25.00M | as of 2025-12-31 |
| DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYearOneThroughFive | 68.00M | as of 2025-12-31 |
| DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear5Through10 | 4.00M | as of 2025-12-31 |
| DebtSecuritiesHeldToMaturityAmortizedCostExcludingAccruedInterestAfterAllowanceForCreditLossMaturityAllocatedAndSingleMaturityDateAfterYear10 | 148.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | 54.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | 25.00M | as of 2025-12-31 |
| Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 69.00M | as of 2025-12-31 |
| Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 4.00M | as of 2025-12-31 |
| Debt Securities, Held-to-Maturity, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | 155.00M | as of 2025-12-31 |
| Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, Fair Value | 576.00M | as of 2025-12-31 |
| Deferred Tax Assets, Unrealized Losses on Trading Securities | 6.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year One | 28.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Two | 27.00M | as of 2025-12-31 |
| Deferred Tax Assets, Unrealized Currency Losses | 0 | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Three | 24.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Four | 23.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Five | 21.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, after Year Five | 125.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid | 247.00M | as of 2025-12-31 |
| Deferred Tax Assets, Other | 25.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 1.21B | as of 2025-12-31 |
| Deferred Tax Assets, Valuation Allowance | 28.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Undiscounted Excess Amount | 51.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 306.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net | 872.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Investment in Noncontrolled Affiliates | 40.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Leasing Arrangements | 32.00M | as of 2025-12-31 |
| Debt Securities, Held-to-maturity, Sale | 11.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Tax Deferred Income | 20.00M | as of 2025-12-31 |
| AOCI Tax, Attributable to Parent | -23.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Other | 25.00M | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Benefit Obligation | 3.00M | as of 2025-12-31 |
| Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation | 3.00M | as of 2025-12-31 |
| Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Plan Assets | 0 | as of 2025-12-31 |
| Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation | 3.00M | as of 2025-12-31 |
| Defined Benefit Plan, Pension Plan with Projected Benefit Obligation in Excess of Plan Assets, Plan Assets | 0 | as of 2025-12-31 |
| Current Year Claims and Claims Adjustment Expense | 10.20B | 2025-01-01 → 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | 657.00M | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims | 10.86B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year | 1.25B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | 6.53B | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross | 209.00M | as of 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossNotPreviouslyRecorded | 42.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross, Incurred Loss | 2.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross, Payment for Claims | 52.00M | 2025-01-01 → 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossSecuritiesSold | 26.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net | 193.00M | as of 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net, Incurred Loss | 0 | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net, Payment for Claims | 49.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Period Increase (Decrease) | 0 | 2025-01-01 → 2025-12-31 |
| Income Taxes Receivable, Current | 43.00M | as of 2025-12-31 |
| Advances from Federal Home Loan Banks | 1.02B | as of 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net | 0 | 2025-01-01 → 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense | 360.00M | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item | 1.44B | as of 2025-12-31 |
| Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost | 176.00M | as of 2025-12-31 |