| Current Income Tax Expense (Benefit) | 2.08B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Deferred Policy Acquisition Cost | 4.21B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Reserve for Unpaid Claim and Claim Adjustment Expense | 69.67B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Unearned Premium | 26.28B | as of 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Earned Premium | 45.79B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Net Investment Income | 5.34B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property, Casualty Insurance Underwriters, Current Year Claim and Claim Adjustment Expense | 27.81B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property, Casualty Insurance Underwriters, Prior Year Claim and Claim Adjustment Expense | -1.11B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Amortization of Deferred Policy Acquisition Cost | 8.65B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Paid Claim and Claim Adjustment Expense | 24.29B | 2025-01-01 → 2025-12-31 |
| SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters, Premium Written | 47.56B | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense | -23.00M | 2025-01-01 → 2025-12-31 |
| Alternative Investment | 17.24B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Gross | 245.32B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Ceded | 40.07B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Assumed | 3.60B | as of 2025-12-31 |
| SEC Schedule, 12-17, Insurance Companies, Reinsurance, Life Insurance in Force, Net | 208.85B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Cost | 170.22B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Fair Value | 168.26B | as of 2025-12-31 |
| SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties, Amount | 168.23B | as of 2025-12-31 |
| Share-based Payment Arrangement, Expense, Tax Benefit | 36.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | 436.00M | as of 2025-12-31 |
| Direct Premiums Earned | 58.91B | 2025-01-01 → 2025-12-31 |
| Ceded Premiums Earned | 10.83B | 2025-01-01 → 2025-12-31 |
| Assumed Premiums Earned | 4.94B | 2025-01-01 → 2025-12-31 |
| Secured Debt, Repurchase Agreements | 3.32B | as of 2025-12-31 |
| Derivative, Gain (Loss) on Derivative, Net | -165.00M | 2025-01-01 → 2025-12-31 |
| Line of Credit Facility, Current Borrowing Capacity | 3.80B | as of 2025-12-31 |
| Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases | 3.00B | as of 2025-12-31 |
| SegmentReportingOtherItemAmount | 83.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Other Adjustments, Amount | 59.00M | 2025-01-01 → 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year One | 309.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Two | 284.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Three | 270.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Four | 238.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Five | 222.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost | 91.96B | as of 2025-12-31 |
| DerivativeLiabilityAfterOffsetSubjectToMasterNettingArrangement | -179.00M | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | 4.75B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 35.61B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 31.51B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | 20.08B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value | 91.96B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value | 30.72B | as of 2025-12-31 |
| Reinsurance Recoverable for Paid Claims and Claims Adjustments | 1.99B | as of 2025-12-31 |
| Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 18.35B | as of 2025-12-31 |
| Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | 20.34B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 237.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2.90B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 3.14B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 1.95B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 3.95B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 12.57B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 32.38B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position | 44.95B | as of 2025-12-31 |
| Reinsurance Recoverables on Unpaid Losses, Gross | 18.57B | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | 1.05B | as of 2025-12-31 |
| Financing Receivable, Allowance for Credit Loss, Recovery | 2.00M | 2025-01-01 → 2025-12-31 |
| Reinsurance Recoverables on Paid Losses, Allowance | 72.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | 232.00M | 2025-01-01 → 2025-12-31 |
| Reinsurance Recoverables on Unpaid Losses, Allowance | 248.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Credit Carryforwards, Foreign | 5.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | 934.00M | as of 2025-12-31 |
| Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) | 1.00M | 2025-01-01 → 2025-12-31 |
| Goodwill, Foreign Currency Translation Gain (Loss) | 445.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Capital Loss Carryforwards | 162.00M | as of 2025-12-31 |
| Operating Lease, Cost | 239.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 713.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves | 2.07B | as of 2025-12-31 |
| Deferred Tax Assets, Property, Plant and Equipment | 0 | as of 2025-12-31 |
| Deferred Tax Assets, Unrealized Losses on Trading Securities | 234.00M | as of 2025-12-31 |
| Deferred Tax Assets, Investments | 0 | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid | 1.89B | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months | 210.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two | 175.00M | as of 2025-12-31 |
| Deferred Tax Assets, Other | 498.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three | 142.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four | 120.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five | 103.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 3.55B | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five | 1.14B | as of 2025-12-31 |
| Deferred Tax Assets, Valuation Allowance | 637.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net of Valuation Allowance | 2.92B | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Undiscounted Excess Amount | 678.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 3.35B | as of 2025-12-31 |
| Deferred Tax Assets, Net | 429.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Property, Plant and Equipment | 112.00M | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Expected Amortization, Year One | 178.00M | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Expected Amortization, Year Two | 159.00M | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Expected Amortization, Year Three | 145.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Investments | 127.00M | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Expected Amortization, Year Four | 133.00M | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Expected Amortization, Year Five | 121.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Undistributed Foreign Earnings | 303.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Intangible Assets | 1.15B | as of 2025-12-31 |
| Present Value of Future Insurance Profits, Foreign Currency Translation Gain (Loss) | -24.00M | 2025-01-01 → 2025-12-31 |
| Reinsurance Recoverable, Credit Loss Expense (Reversal) | 25.00M | 2025-01-01 → 2025-12-31 |
| Reinsurance, Loss on Uncollectible Accounts in Period, Amount | 18.00M | 2025-01-01 → 2025-12-31 |
| Defined Contribution Plan, Cost | 317.00M | 2025-01-01 → 2025-12-31 |
| Current Year Claims and Claims Adjustment Expense | 27.81B | 2025-01-01 → 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | -1.13B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims | 26.70B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year | 8.78B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | 15.51B | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss | 52.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff | -2.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss, Recovery | -113.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease) | 97.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross | 1.23B | as of 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross, Incurred Loss | 279.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Gross, Payment for Claims | 392.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net | 824.00M | as of 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net, Incurred Loss | 197.00M | 2025-01-01 → 2025-12-31 |
| Liability for Asbestos and Environmental Claims, Net, Payment for Claims | 258.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits | 79.00M | as of 2025-12-31 |
| Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions | 20.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions | 26.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions | 5.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities | 50.00M | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations | 0 | 2025-01-01 → 2025-12-31 |
| Unrecognized Tax Benefits that Would Impact Effective Tax Rate | 74.00M | as of 2025-12-31 |
| Liability for Future Policy Benefit, before Reinsurance | 18.42B | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitReinsuranceRecoverableAfterAllowance | 286.00M | as of 2025-12-31 |
| Income Taxes Receivable, Current | 419.00M | as of 2025-12-31 |
| LiabilityForFuturePolicyBenefitRemeasurementGainLoss | 59.00M | 2025-01-01 → 2025-12-31 |
| PolicyholderAccountBalanceBenefitPayment | 248.00M | 2025-01-01 → 2025-12-31 |
| PolicyholderAccountBalancePolicyCharge | 114.00M | 2025-01-01 → 2025-12-31 |
| PolicyholderAccountBalancePremiumReceived | 847.00M | 2025-01-01 → 2025-12-31 |
| PolicyholderAccountBalanceSurrenderAndWithdrawal | 346.00M | 2025-01-01 → 2025-12-31 |
| PolicyholderAccountBalanceIncreaseDecreaseFromOtherChange | 181.00M | 2025-01-01 → 2025-12-31 |
| MarketRiskBenefitLiabilityAmount | 659.00M | as of 2025-12-31 |
| Market Risk Benefit, Change in Fair Value, Gain (Loss) | -288.00M | 2025-01-01 → 2025-12-31 |
| Separate Account, Liability, Cash Surrender Value, Amount | 6.37B | as of 2025-12-31 |
| Separate Account, Liability, Premium and Deposit | 1.39B | 2025-01-01 → 2025-12-31 |
| SeparateAccountLiabilityPolicyCharge | 164.00M | 2025-01-01 → 2025-12-31 |
| Separate Account, Liability, Surrender and Withdrawal | 997.00M | 2025-01-01 → 2025-12-31 |
| SeparateAccountLiabilityBenefitPayment | 466.00M | 2025-01-01 → 2025-12-31 |
| SeparateAccountLiabilityIncreaseDecreaseFromInvestedPerformance | 739.00M | 2025-01-01 → 2025-12-31 |
| SeparateAccountLiabilityIncreaseDecreaseFromOtherChange | 188.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments | 7.22B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 67.46B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense | 1.98B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Amortized Cost | 124.73B | as of 2025-12-31 |
| Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost | 1.65B | as of 2025-12-31 |
| State Insurance Department, Statutory to NAIC, Amount of Reconciling Item | 106.00M | as of 2025-12-31 |
| Statutory Accounting Practices, Permitted Practice, Amount | 73.00M | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Amount Available for Dividend Payments | 9.60B | as of 2025-12-31 |