| Current Federal Tax Expense (Benefit) | 130.00M | 2025-01-01 → 2025-12-31 |
| Current State and Local Tax Expense (Benefit) | 45.00M | 2025-01-01 → 2025-12-31 |
| Current Foreign Tax Expense (Benefit) | 0 | 2025-01-01 → 2025-12-31 |
| Current Income Tax Expense (Benefit) | 175.00M | 2025-01-01 → 2025-12-31 |
| Cash and Cash Equivalents, Fair Value Disclosure | 3.94B | as of 2025-12-31 |
| Deferred Federal Income Tax Expense (Benefit) | 89.00M | 2025-01-01 → 2025-12-31 |
| Deferred State and Local Income Tax Expense (Benefit) | -14.00M | 2025-01-01 → 2025-12-31 |
| Capitalized Computer Software, Amortization | 536.00M | 2025-01-01 → 2025-12-31 |
| Deferred Foreign Income Tax Expense (Benefit) | 0 | 2025-01-01 → 2025-12-31 |
| Operating Lease, Liability, Current | 126.00M | as of 2025-12-31 |
| Share-based Payment Arrangement, Amount Capitalized | 0 | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense | 241.00M | 2025-01-01 → 2025-12-31 |
| Dividends | 426.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount | 302.00M | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount | -6.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense, after Tax | 197.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Expense, Tax Benefit | 44.00M | 2025-01-01 → 2025-12-31 |
| Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount | 6.00M | as of 2025-12-31 |
| Equity Securities, FV-NI, Realized Gain | 0 | 2025-01-01 → 2025-12-31 |
| Equity Securities, FV-NI, Realized Loss | 0 | 2025-01-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Tax Contingency, Amount | 47.00M | 2025-01-01 → 2025-12-31 |
| Dividends, Common Stock, Cash | 430.00M | 2025-01-01 → 2025-12-31 |
| Dividends, Common Stock | 107.00M | 2025-10-01 → 2025-12-31 |
| Effective Income Tax Rate Reconciliation, Other Adjustments, Amount | 9.00M | 2025-01-01 → 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year One | 24.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Two | 14.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Three | 9.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Four | 8.00M | as of 2025-12-31 |
| Finite-Lived Intangible Asset, Expected Amortization, Year Five | 8.00M | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One | 1.00B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 4.41B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 4.04B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 | 1.31B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Amortized Cost | 6.26B | as of 2025-12-31 |
| Treasury Stock, Value, Acquired, Cost Method | 151.00M | 2025-01-01 → 2025-12-31 |
| Intangible Assets, Gross (Excluding Goodwill) | 2.04B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One | 999.00M | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five | 4.33B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 | 3.92B | as of 2025-12-31 |
| Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 | 1.11B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Maturity, without Single Maturity Date, Fair Value | 5.83B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 16.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 851.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 867.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 46.00M | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 867.00M | as of 2025-12-31 |
| Tangible Asset Impairment Charges | 28.00M | 2025-01-01 → 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months | 2.33B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer | 8.74B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Unrealized Loss Position | 11.07B | as of 2025-12-31 |
| Deferred Tax Assets, Operating Loss Carryforwards | 148.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | 0 | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value | 0 | 2025-01-01 → 2025-12-31 |
| Goodwill, Acquired During Period | 72.00M | 2025-01-01 → 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | 0 | as of 2025-12-31 |
| Goodwill, Written off Related to Sale of Business Unit | 17.00M | 2025-01-01 → 2025-12-31 |
| Securities Loaned, Fair Value of Collateral | 638.00M | as of 2025-12-31 |
| Unrecorded Unconditional Purchase Obligation, to be Paid, Year One | 1.20B | as of 2025-12-31 |
| Unrecorded Unconditional Purchase Obligation, to be Paid, Year Two | 953.00M | as of 2025-12-31 |
| Unrecorded Unconditional Purchase Obligation, to be Paid, Year Three | 595.00M | as of 2025-12-31 |
| Unrecorded Unconditional Purchase Obligation, to be Paid, Year Four | 298.00M | as of 2025-12-31 |
| Unrecorded Unconditional Purchase Obligation, to be Paid, Year Five | 273.00M | as of 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits | 172.00M | as of 2025-12-31 |
| Operating Lease, Cost | 128.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits | 174.00M | as of 2025-12-31 |
| Variable Lease, Cost | 114.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Unearned Premiums Reserve | 35.00M | as of 2025-12-31 |
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value | 152.00M | 2025-01-01 → 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year One | 150.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Two | 127.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Three | 104.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Four | 67.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, Year Five | 46.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid, after Year Five | 138.00M | as of 2025-12-31 |
| Deferred Tax Assets, Investments | 544.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, to be Paid | 632.00M | as of 2025-12-31 |
| Deferred Tax Assets, Other | 26.00M | as of 2025-12-31 |
| Deferred Tax Assets, Gross | 1.13B | as of 2025-12-31 |
| Deferred Tax Assets, Valuation Allowance | 139.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net of Valuation Allowance | 995.00M | as of 2025-12-31 |
| Lessee, Operating Lease, Liability, Undiscounted Excess Amount | 88.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Gross | 911.00M | as of 2025-12-31 |
| Deferred Tax Assets, Net | 84.00M | as of 2025-12-31 |
| Deferred Tax Liabilities, Prepaid Expenses | 353.00M | as of 2025-12-31 |
| Assets, Fair Value Disclosure | 20.78B | as of 2025-12-31 |
| Debt and Equity Securities, Gain (Loss) | -50.00M | 2025-01-01 → 2025-12-31 |
| Deferred Tax Liabilities, Other | 35.00M | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount | 6.60B | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions | 0 | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year One | 0 | as of 2025-12-31 |
| Defined Contribution Plan, Cost | 304.00M | 2025-01-01 → 2025-12-31 |
| Current Year Claims and Claims Adjustment Expense | 111.84B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Two | 1.03B | as of 2025-12-31 |
| Long-Term Debt, Maturity, Year Three | 993.00M | as of 2025-12-31 |
| Prior Year Claims and Claims Adjustment Expense | -1.03B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims | 110.81B | 2025-01-01 → 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year | 102.22B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Four | 979.00M | as of 2025-12-31 |
| Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years | 9.07B | 2025-01-01 → 2025-12-31 |
| Long-Term Debt, Maturity, Year Five | 500.00M | as of 2025-12-31 |
| Long-Term Debt, Maturity, after Year Five | 9.00B | as of 2025-12-31 |
| Interest Rate Fair Value Hedge Asset at Fair Value | 57.00M | as of 2025-12-31 |
| Interest Rate Fair Value Hedge Liability at Fair Value | 51.00M | as of 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Domestic | 1.49B | 2025-01-01 → 2025-12-31 |
| Income (Loss) from Continuing Operations before Income Taxes, Foreign | -47.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | 440.00M | as of 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) | 9.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | 128.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements | 19.00M | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 0 | 2025-01-01 → 2025-12-31 |
| Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 | 0 | 2025-01-01 → 2025-12-31 |
| Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net | 300.85B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net | 290.88B | as of 2025-12-31 |
| Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 9.97B | as of 2025-12-31 |
| Debt Securities, Available-for-sale, Amortized Cost | 17.02B | as of 2025-12-31 |
| Transfer of Financial Assets Accounted for as Sales, Cash Proceeds Received for Assets Derecognized, Amount | 1.50B | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Capital and Surplus Required | 6.90B | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Capital and Surplus, Balance | 14.10B | as of 2025-12-31 |
| Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval | 1.10B | as of 2025-12-31 |
| APIC, Share-based Payment Arrangement, Increase for Cost Recognition | 241.00M | 2025-01-01 → 2025-12-31 |