| Current Federal Tax Expense (Benefit) | 2.51B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost | 6.16B | as of 2025-12-31 |
| Current State and Local Tax Expense (Benefit) | 122.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Unearned Premium | 29.08B | as of 2025-12-31 |
| Current Foreign Tax Expense (Benefit) | 99.00M | 2025-01-01 → 2025-12-31 |
| Current Income Tax Expense (Benefit) | 2.73B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Net Investment Income | 3.45B | 2025-01-01 → 2025-12-31 |
| Capitalized Computer Software, Net | 349.00M | as of 2025-12-31 |
| Deferred Federal Income Tax Expense (Benefit) | 103.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Cost | 8.39B | 2025-01-01 → 2025-12-31 |
| Deferred State and Local Income Tax Expense (Benefit) | 46.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense | 9.63B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Written | 63.42B | 2025-01-01 → 2025-12-31 |
| Deferred Foreign Income Tax Expense (Benefit) | 7.00M | 2025-01-01 → 2025-12-31 |
| Federal Income Tax Expense (Benefit), Continuing Operations | 2.62B | 2025-01-01 → 2025-12-31 |
| Investments, Fair Value Disclosure | 73.29B | as of 2025-12-31 |
| State and Local Income Tax Expense (Benefit), Continuing Operations | 168.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount | 310.00M | as of 2025-12-31 |
| Share-based Payment Arrangement, Expense | 123.00M | 2025-01-01 → 2025-12-31 |
| Foreign Income Tax Expense (Benefit), Continuing Operations | 106.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense | 525.00M | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account | 0 | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction | 518.00M | 2025-01-01 → 2025-12-31 |
| Margin Deposit Assets | 95.00M | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost | 82.48B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Amount | 83.24B | as of 2025-12-31 |
| Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset | 1.00M | as of 2025-12-31 |
| Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount | 2.76B | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Cost | 8.03B | as of 2025-12-31 |
| Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount | 134.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense, Tax Benefit | 17.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount | 15.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Exercise of Option, Tax Benefit | 24.00M | 2025-01-01 → 2025-12-31 |
| EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount | 8.00M | 2025-01-01 → 2025-12-31 |
| Preferred Stock, Including Additional Paid in Capital | 2.00B | as of 2025-12-31 |
| Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | 97.00M | as of 2025-12-31 |
| Direct Premiums Earned | 63.70B | 2025-01-01 → 2025-12-31 |
| Ceded Premiums Earned | 2.68B | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Credit, Amount | 55.00M | 2025-01-01 → 2025-12-31 |
| Assumed Premiums Earned | 431.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount | 47.00M | 2025-01-01 → 2025-12-31 |
| Restructuring Reserve, Accrual Adjustment | 3.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Contingency, Amount | -14.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount | 3.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Other Adjustments, Amount | -11.00M | 2025-01-01 → 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year One | 172.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Two | 125.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Three | 83.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Four | 38.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Five | 14.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost | 3.43B | as of 2025-12-31 |
| Net Income (Loss) Available to Common Stockholders, Diluted | 10.16B | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Amortized Cost | 1.46B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Amortized Cost | 22.58B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Amortized Cost | 21.54B | as of 2025-12-31 |
| Defined Benefit Plan, Interest Cost | 243.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Amortized Cost | 9.71B | as of 2025-12-31 |
| Defined Benefit Plan, Expected Return (Loss) on Plan Assets | 313.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Amortization of Prior Service Cost (Credit) | -1.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value | 3.48B | as of 2025-12-31 |
| Defined Benefit Plan, Actuarial Gain (Loss), Immediate Recognition as Component in Net Periodic Benefit (Cost) Credit | 35.00M | 2025-01-01 → 2025-12-31 |
| Defined Benefit Plan, Net Periodic Benefit Cost (Credit) | 1.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value | 1.46B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value | 22.71B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value | 21.78B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value | 9.69B | as of 2025-12-31 |
| Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) | -96.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 777.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 392.00M | as of 2025-12-31 |
| Deferred Tax Assets, Operating Loss Carryforwards | 222.00M | as of 2025-12-31 |
| Securities Loaned, Not Subject to Master Netting Arrangement | 1.87B | as of 2025-12-31 |
| Deferred Tax Assets, Capital Loss Carryforwards | 0 | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Postretirement Benefits | 6.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions | 1.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation | 142.00M | as of 2025-12-31 |
| Variable Lease, Cost | 9.00M | 2025-01-01 → 2025-12-31 |
| Lease, Cost | 91.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 1.05B | as of 2025-12-31 |
| Right-of-Use Asset Obtained in Exchange for Operating Lease Liability | 54.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves | 312.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year One | 67.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Two | 54.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Three | 32.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Four | 22.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Five | 14.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, after Year Five | 11.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid | 200.00M | as of 2025-12-31 |
| Deferred Tax Assets, Other | 145.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 1.99B | as of 2025-12-31 |
| Deferred Tax Assets, Valuation Allowance | 68.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net of Valuation Allowance | 1.92B | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Undiscounted Excess Amount | 16.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 2.15B | as of 2025-12-31 |
| Long-term Debt, Gross | 7.54B | as of 2025-12-31 |
| Debt, Long-term and Short-term, Combined Amount | 7.49B | as of 2025-12-31 |
| Assets, Fair Value Disclosure | 72.03B | as of 2025-12-31 |
| Debt Securities, Gain (Loss) | -253.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Intangible Assets | 44.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Other | 206.00M | as of 2025-12-31 |
| Deferred Policy Acquisition Costs and Present Value of Future Insurance Profits, Addition | 8.78B | 2025-01-01 → 2025-12-31 |
| DeferredPolicyAcquisitionCostAndPresentValueOfFutureInsuranceProfitExperienceAdjustment | 5.00M | 2025-01-01 → 2025-12-31 |
| Premium Receivable, Credit Loss Expense (Reversal) | 487.00M | 2025-01-01 → 2025-12-31 |
| Premium Receivable, Allowance for Credit Loss, Writeoff | 485.00M | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year One | 550.00M | as of 2025-12-31 |
| Defined Contribution Plan, Cost | 132.00M | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Two | 0 | as of 2025-12-31 |
| Long-Term Debt, Maturity, Year Three | 0 | as of 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | -1.81B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Four | 500.00M | as of 2025-12-31 |
| Long-Term Debt, Maturity, Year Five | 600.00M | as of 2025-12-31 |
| Long-Term Debt, Maturity, after Year Five | 5.89B | as of 2025-12-31 |
| Off-Balance Sheet, Credit Loss, Liability | 15.00M | as of 2025-12-31 |
| Debt Issuance Costs, Net | 51.00M | as of 2025-12-31 |
| Unrecognized Tax Benefits | 27.00M | as of 2025-12-31 |
| Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions | 14.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions | 0 | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Income Tax Penalties Expense | 0 | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Interest on Income Taxes Expense | -3.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Income Tax Penalties Accrued | 3.00M | as of 2025-12-31 |
| Unrecognized Tax Benefits, Interest on Income Taxes Accrued | 12.00M | as of 2025-12-31 |
| Amount of Restricted Net Assets for Consolidated and Unconsolidated Subsidiaries | 29.06B | as of 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Domestic | 12.72B | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Foreign | 434.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 484.00M | as of 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | 36.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | 6.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 153.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 117.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 56.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 39.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 379.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) | 34.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value | 1.00M | as of 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings | -1.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss) | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 | 0 | 2025-01-01 → 2025-12-31 |
| Collateral Already Posted, Aggregate Fair Value | 14.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost | 1.27B | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Net Income Amount | 8.79B | 2025-01-01 → 2025-12-31 |
| Statutory Accounting Practices, Statutory Capital and Surplus, Balance | 22.95B | as of 2025-12-31 |
| Assets Held by Insurance Regulators | 202.00M | as of 2025-12-31 |
| Financial Guarantee Insurance Contract, Premium Revenue to be Recognized, Year One | 2.06B | as of 2025-12-31 |
| Financial Guarantee Insurance Contract, Premium Revenue to be Recognized, Year Two | 1.52B | as of 2025-12-31 |