| Current Federal Tax Expense (Benefit) | 314.00M | 2025-01-01 → 2025-12-31 |
| Securities Segregated under Securities Exchange Commission Regulation | 3.40B | as of 2025-12-31 |
| Cash and Securities Segregated under Securities Exchange Commission Regulation | 600.00M | as of 2025-12-31 |
| Current State and Local Tax Expense (Benefit) | 37.00M | 2025-01-01 → 2025-12-31 |
| Current Foreign Tax Expense (Benefit) | 48.00M | 2025-01-01 → 2025-12-31 |
| Current Income Tax Expense (Benefit) | 399.00M | 2025-01-01 → 2025-12-31 |
| Deferred Federal Income Tax Expense (Benefit) | 81.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Deferred Policy Acquisition Cost | 986.00M | as of 2025-12-31 |
| Deferred State and Local Income Tax Expense (Benefit) | 10.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Reserve for Unpaid Claim and Claim Adjustment Expense | 26.60B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Discount Deducted from Reserve | 583.00M | as of 2025-12-31 |
| Deferred Foreign Income Tax Expense (Benefit) | 21.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Unearned Premium | 7.63B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Earned Premium | 10.90B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Net Investment Income | 2.47B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Amortization of Deferred Policy Acquisition Cost | 1.90B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Paid Claim and Claim Adjustment Expense | 5.77B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Premium Written | 11.10B | 2025-01-01 → 2025-12-31 |
| Federal Income Tax Expense (Benefit), Continuing Operations | 395.00M | 2025-01-01 → 2025-12-31 |
| State and Local Income Tax Expense (Benefit), Continuing Operations | 47.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense | 41.00M | 2025-01-01 → 2025-12-31 |
| Foreign Income Tax Expense (Benefit), Continuing Operations | 69.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount | 479.00M | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Cost | 1.20B | as of 2025-12-31 |
| Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount | 38.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount | 25.00M | 2025-01-01 → 2025-12-31 |
| Direct Premiums Earned | 15.36B | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount | 6.00M | 2025-01-01 → 2025-12-31 |
| Ceded Premiums Earned | 4.75B | 2025-01-01 → 2025-12-31 |
| Assumed Premiums Earned | 293.00M | 2025-01-01 → 2025-12-31 |
| Guaranty Liabilities | 89.00M | as of 2025-12-31 |
| Contract with Customer, Liability, Revenue Recognized | 1.40B | 2025-01-01 → 2025-12-31 |
| Property, Plant and Equipment, Additions | 602.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount | 14.00M | 2025-01-01 → 2025-12-31 |
| SegmentReportingOtherItemAmount | 807.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount | 30.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Gain (Loss) | 1.10B | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Other Adjustments, Amount | 10.00M | 2025-01-01 → 2025-12-31 |
| Revenue, Remaining Performance Obligation, Amount | 23.60B | as of 2025-12-31 |
| Treasury Stock, Value, Acquired, Cost Method | 789.00M | 2025-01-01 → 2025-12-31 |
| Treasury Stock, Retired, Cost Method, Amount | 0 | 2025-01-01 → 2025-12-31 |
| Capitalized Contract Cost, Amortization | 1.20B | 2025-01-01 → 2025-12-31 |
| Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 5.98B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 2.29B | as of 2025-12-31 |
| Stockholders' Equity before Treasury Stock | 18.69B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1.09B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 2.29B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position | 20.64B | as of 2025-12-31 |
| Reinsurance Recoverables on Paid Losses, Gross | 426.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits | 81.00M | as of 2025-12-31 |
| Operating Lease, Cost | 53.00M | 2025-01-01 → 2025-12-31 |
| Short-term Lease, Cost | 4.00M | 2025-01-01 → 2025-12-31 |
| Variable Lease, Cost | 20.00M | 2025-01-01 → 2025-12-31 |
| Lease, Cost | 77.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 227.00M | as of 2025-12-31 |
| Right-of-Use Asset Obtained in Exchange for Operating Lease Liability | 27.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross | 258.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year One | 55.00M | as of 2025-12-31 |
| Deferred Tax Assets, Deferred Income | 84.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Two | 55.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Three | 50.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Four | 51.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Five | 47.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, after Year Five | 255.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid | 513.00M | as of 2025-12-31 |
| Deferred Tax Assets, Other | 179.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 1.20B | as of 2025-12-31 |
| Deferred Tax Assets, Valuation Allowance | 25.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net of Valuation Allowance | 1.18B | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Undiscounted Excess Amount | 138.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 2.00B | as of 2025-12-31 |
| Deferred Tax Liabilities, Property, Plant and Equipment | 1.06B | as of 2025-12-31 |
| Other Comprehensive Income (Loss), before Reclassifications, Net of Tax | 808.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Investments | 218.00M | as of 2025-12-31 |
| Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax | -67.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Other | 87.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Net | 823.00M | as of 2025-12-31 |
| Defined Benefit Plan, Accumulated Benefit Obligation | 856.00M | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Reported Claims, Amount | 9.06B | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount | 17.54B | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss) | 176.00M | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year One | 1.10B | as of 2025-12-31 |
| Current Year Claims and Claims Adjustment Expense | 6.72B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Two | 1.10B | as of 2025-12-31 |
| Long-Term Debt, Maturity, Year Three | 56.00M | as of 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | 189.00M | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims | 6.95B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year | 1.09B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Four | 1.20B | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | 4.68B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Five | 1.10B | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) | 185.00M | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, after Year Five | 5.10B | as of 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossNotPreviouslyRecorded | 6.00M | 2025-01-01 → 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate | 4.00M | 2025-01-01 → 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossSecuritiesSold | 6.00M | 2025-01-01 → 2025-12-31 |
| DebtSecuritiesAvailableForSaleExcludingAccruedInterestAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal | 20.00M | 2025-01-01 → 2025-12-31 |
| Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net | 72.00M | as of 2025-12-31 |
| Unrecognized Tax Benefits | 0 | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedNetPremiumOriginalDiscountRateBeforeCashFlowAndReinsurance | 3.29B | as of 2025-12-31 |
| AociLiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeTax | 71.00M | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedNetPremiumInterestIncome | 176.00M | 2025-01-01 → 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedNetPremiumNetPremiumCollected | 406.00M | 2025-01-01 → 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedNetPremiumBeforeReinsuranceAfterDiscountRateChange | 3.36B | as of 2025-12-31 |
| Unrecognized Tax Benefits, Interest on Income Taxes Expense | 0 | 2025-01-01 → 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitOriginalDiscountRateBeforeCashFlowAndReinsurance | 16.98B | as of 2025-12-31 |
| AociLiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeTax | -173.00M | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitInterestExpense | 918.00M | 2025-01-01 → 2025-12-31 |
| Other Comprehensive Income, Other, Net of Tax | -1.00M | 2025-01-01 → 2025-12-31 |
| Liability for Future Policy Benefit, Expected Future Policy Benefit, Benefit Payment | 1.17B | 2025-01-01 → 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitBeforeReinsuranceAfterDiscountRateChange | 16.81B | as of 2025-12-31 |
| Liability for Future Policy Benefit, before Reinsurance | 13.45B | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFuturePolicyBenefitUndiscountedBeforeReinsurance | 31.32B | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumUndiscountedBeforeReinsurance | 4.93B | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitExpectedFutureGrossPremiumDiscountedBeforeReinsurance | 3.50B | as of 2025-12-31 |
| Liability for Future Policy Benefit, Adverse Development, Expense | 135.00M | 2025-01-01 → 2025-12-31 |
| Liability for Future Policy Benefit, Gross Premium Income | 423.00M | 2025-01-01 → 2025-12-31 |
| Liability for Future Policy Benefit, Interest Expense | 742.00M | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Domestic | 2.00B | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Foreign | 284.00M | 2025-01-01 → 2025-12-31 |
| Other Receivables | 318.00M | as of 2025-12-31 |
| Interest Costs Capitalized | 11.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost | 143.00M | as of 2025-12-31 |
| APIC, Share-based Payment Arrangement, Increase for Cost Recognition | 8.00M | 2025-01-01 → 2025-12-31 |