Cash dividends paid on common stock (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Debt securities, available-for-sale, allowance for credit loss, write-off Debt Securities, Available-for-Sale, Allowance for Credit Loss, Writeoff Net realized (gains) losses on securities Realized Investment Gains (Losses) Prior years Prior years Prior Year Claims and Claims Adjustment Expense Service expenses Non Insurance Service Expenses Expenses associated with non-insurance services provided to customers. Investments, Unrealized Loss Position Investments Unrealized Loss Position [Line Items] Investments, Unrealized Loss Position [Line Items] Award Timing Predetermined Award Timing Predetermined [Flag] Gross Unrealized Gains Investments, Accumulated Gross Unrealized Gain, Before Tax Pre-tax accumulated gross unrealized gain of total debt and equity financial instruments Entity File Number Entity File Number Paid-In Capital Additional Paid-in Capital [Member] After tax total accumulated other comprehensive income (loss), Net realized gains (losses) on securities Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax Tabular List, Table Tabular List [Table Text Block] Unearned premiums Unearned Premiums Personal auto business Personal Auto [Member] Personal Auto New Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Amortization of equity-based compensation Restricted Stock or Unit Expense Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] Accumulated Other Comprehensive Income Loss Before Tax1 [Roll Forward] Accumulated Other Comprehensive Income Loss Before Tax [Roll Forward] Debt Securities Debt Securities [Member] Gross Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Open reverse repurchase commitments Securities for Reverse Repurchase Agreements Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fixed maturities (amortized cost: $88,408, $77,754, and $82,704) Debt Securities, Available-for-sale, Fixed Maturities Amount of investment in long-term debt securities (fixed maturities) measured at fair value with changes in fair value recognized in other comprehensive income (available-for-sale). Basic: Earnings per common shares (in dollars per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Accounts payable, accrued expenses, and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Investments Category Other than Temporary Impairment, Credit Losses Recognized in Earnings, Categories of Investments [Domain] O2025Q4 O2025Q4Dividends [Member] O2025Q4Dividends Pretax underwriting profit (loss) Pretax underwriting profit (loss) Pretax underwriting profit (loss) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Distribution expenses Distribution Expenses Distribution Expenses Senior Notes 3.95% Due 2050 Senior Notes Three Point Nine Five Percent Due Twenty Fifty [Member] Senior Notes Three Point Nine Five Percent Due Twenty Fifty [Member] Adjustment to Compensation, Amount Adjustment to Compensation Amount Non-income producing securities Non-Income Producing Securities Fair value of fixed-maturity securities that were non-income producing during the preceding 12 months. Senior Notes 3.00% Due 2032 Senior Notes Three Point Zero Zero Percent Due Twenty Thirty Two [Member] Senior Notes Three Point Zero Zero Percent Due Twenty Thirty Two Employee Stock Option Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Cash and Cash Equivalents Cash and Cash Equivalents [Member] Net realized gains (losses) on security sales Debt and Equity Securities, Realized Gain (Loss) Income taxes, net of refunds Income Taxes Paid John Murphy [Member] John Murphy Senior Notes 4.125% Due 2047 Senior Notes four point one two five percent due twenty forty seven [Member] Senior Notes four point one two five percent due twenty forty seven [Member] Cash dividends declared on common shares ($0.10 and $0.10 per share) Dividends, Common Stock, Cash Total shareholders’ equity Balance, Beginning of period Balance, End of period Stockholders' Equity Attributable to Parent Equity, Attributable to Parent Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Common shares, authorized (shares) Common Stock, Shares Authorized Total liabilities and shareholders’ equity Liabilities and Equity Deferred acquisition costs Deferred Policy Acquisition Cost Total underwriting revenue Premiums Earned, Fees And Other Revenue Premiums Earned, Fees And Other Revenue Senior Notes 3.70% Due 2052 Senior Notes Three Point Seven Zero Percent Due Twenty Fifty Two [Member] Senior Notes Three Point Seven Zero Percent Due Twenty Fifty Two Available-for-sale Securities Available-for-Sale Securities [Member] Liabilities Liabilities and Equity [Abstract] Underwriting Margins and Combined Ratios for our Underwriting Operations Underwriting Margins And Combined Ratios For Underwriting Operations [Table Text Block] Underwriting Margins And Combined Ratios For Underwriting Operations Premiums receivable, net of allowance for credit losses of $528, $473, and $552 Premiums Receivable, Net Cover [Abstract] Cover [Abstract] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Under- writing Margin Underwriting Margin Pretax underwriting profit loss expressed as a percentage of net premiums earned. Total Debt Securities, Available-for-Sale, Unrealized Loss Position Ten years or greater Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 10 Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Debt Debt, Long-Term and Short-Term, Combined Amount Unearned premiums Increase (Decrease) in Unearned Premiums Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Short-term investments, amortized cost Debt Securities, Available-for-Sale Short Term Investments, Amortized Cost This item represents the cost of Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy. Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Senior Notes 4.60% Due 2031 Senior Notes Four Point Six Zero Percent Due Twenty Thirty One [Member] Senior Notes Four Point Six Zero Percent Due Twenty Thirty One Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Sales of property and equipment Proceeds from Sale of Property, Plant, and Equipment Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Loss and loss adjustment expense reserves Increase (Decrease) in Liability for Claims and Claims Adjustment Expense Reserve Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Operating Segments Operating Segments [Member] Supplemental Cash Flow Information Table Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Other underwriting expenses Other Underwriting Expense, Adjusted Other Underwriting Expense, Adjusted Long-term debt, current maturities Long-Term Debt, Current Maturities Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Cash and cash equivalents Cash Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Attributable to Parent Acquisition of treasury shares acquired in open market Payments for Repurchase of Common Stock in the Open Market Payments for Repurchase of Common Stock in the Open Market Name Measure Name O2024A O2024A Dividends [Member] O2024A Dividends Member Less than one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Total other comprehensive income (loss), pre tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Fixed maturities Proceeds from Maturities, Prepayments and Calls of Debt Securities, Available-for-Sale Document Fiscal Period Focus Document Fiscal Period Focus Award Timing Method Award Timing Method [Text Block] Change in Valuation Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease) Award Type Award Type [Axis] Foreign currency translation adjustment Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Long-term debt Long-Term Debt Deferred acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs Total assets Assets Trading Symbol Trading Symbol Equity securities Proceeds From Maturities Prepayments And Calls Of Equity Securities, FV-NI Amount of cash inflow from calls (early redemptions) on equity securities measured at fair value with changes in fair value recognized in net income (FV-NI), classified as investing activity. Entity Address, City or Town Entity Address, City or Town Cash Flows From Operating Activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Number of states, classes certified Number of States, Classes Certified Number of States, Classes Certified Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Subtotal net realized gains (losses) on security sales Debt and Equity Securities, Realized Gains (Losses) on Security Sales The net realized gains (losses) recorded during the period on sales of debt and equity securities. Excluding holding period gains (losses) on hybrid and equity securities as well as other asset impairments. Schedule of Debt Securities by Contractual Maturity [Table] Schedule of Debt Securities by Contractual Maturity [Table] Tabular disclosure of available-for-sale fixed maturities, classified by contractual maturity date. Cash dividends declared on common stock (in dollars per share) Common Stock, Dividends, Per Share, Declared Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Andrew J. Quigg [Member] Andrew J. Quigg Operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Prepaid reinsurance premiums Prepaid Reinsurance Premiums Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Restricted cash and cash equivalents Restricted Cash and Cash Equivalent Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Hybrid Instruments [Table] Hybrid Instruments [Table] Senior Notes 2.50% Due 2027 Senior Notes Two Point Five Zero Percent Due Twenty Twenty Seven [Member] Senior Notes Two Point Five Zero Percent Due Twenty Twenty Seven Senior Notes 2.45% Due 2027 Senior Notes Two Point Four Five Percent Due Twenty Twenty Seven [Member] Senior Notes Two Point Four Five Percent Due Twenty Twenty Seven Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward] Accumulated Other Comprehensive Income Loss, Net of Tax1 [Roll Forward] Accumulated Other Comprehensive Income Loss, Net of Tax1 [Roll Forward] PEO PEO [Member] Investments Classified by Contractual Maturity Date Investments Classified by Contractual Maturity Date [Table Text Block] Common equities (cost: $839, $774, and $819) Equity Securities FV NI Common Equities Fair value of common equities securities in the investment portfolio for which the change in fair value is recorded on the Income Statement as a holding period gain/(loss). Net Holding Period Gains (Losses) Debt Securities, Available-for-sale, Accumulated Gross Realized Gain (Loss), before Tax Debt Securities, Available-for-sale, Accumulated Gross Realized Gain (Loss), before Tax Changes in: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Retained Earnings Retained Earnings [Member] Accounts payable, accrued expenses, and other liabilities Accounts Payable and Accrued Liabilities Total paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Total cash, cash equivalents, restricted cash, and restricted cash equivalents Cash, cash equivalents, restricted cash, and restricted cash equivalents – January 1 Cash, cash equivalents, restricted cash, and restricted cash equivalents – March 31 Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income Statement [Abstract] Provision for income taxes Income Tax Expense (Benefit) Subtotal gross realized losses on security sales Debt and Equity Securities, Realized Losses The gross realized losses recorded during the period on sales of debt and equity securities. Excludes holding period losses on hybrid and equity securities and other-than-temporary impairments of debt securities. 12 Months or Greater Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Purchases: Payments to Acquire Investments [Abstract] Other assets Other Assets Fair value, beginning balance Fair value, ending balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Maturities, paydowns, calls, and other: Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale [Abstract] Total underwriting expenses Expense Related to Distribution or Servicing and Underwriting Fees Fair Value Investments, fair value Investments, Fair Value Disclosure Preferred stock, shares issued (shares) Preferred Stock, Shares Issued Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Product and Service [Domain] Product and Service [Domain] Fair Value, Hierarchy Fair Value Hierarchy and NAV [Axis] Debt Securities, Available-for-Sale, at Fair Value Debt Securities, Available-for-Sale [Abstract] Dividends [Abstract] Dividends [Abstract] Incurred related to: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Net Investment Income Net Investment Income Net unrealized gains (losses) on fixed-maturity securities AOCI, Debt Securities, Available-for-Sale, Adjustment, after Tax Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Gross realized loss on equity securities Equity Securities, FV-NI, Realized Loss Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Income taxes Increase (Decrease) in Income Taxes City Area Code City Area Code Fair value inputs, market cap price change percentage, weighted average Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average Weighted average market capitalization percentage used to calculate the periodic increase/(decrease) in valuation of Level 3 securities. This value represents the weighted average change for the period. Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Investments Investment [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Senior Notes 3.70% Due 2045 Senior Notes three point seven zero percent due twenty forty five [Member] Senior Notes three point seven zero percent due twenty forty five Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Cash Flows From Investing Activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Fees and other revenues Fees And Other Revenues Fees collected from policyholders and other revenues Fixed maturities Proceeds from Sale of Debt Securities, Available-for-Sale Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Equity securities Equity Securities, FV-NI Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year PEO Total Compensation Amount PEO Total Compensation Amount Depreciation Depreciation Equity Components [Axis] Equity Components [Axis] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Total tax (provision) benefit, Net realized gains (losses) on securities Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Fair Value Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value Number of Reportable Segments Number of Reportable Segments Cost Debt Securities, Available-for-Sale, Amortized Cost Components of Equity Realized Gains (Losses) Components of Equity Realized Gains (Losses) [Table Text Block] [Table Text Block] for Components of Equity Realized Gains (Losses) recorded during the period, including gains (losses) on security sales and holding period gains (losses) on securities held at the end of the period. Losses and loss adjustment expenses Losses and loss adjustment expenses Policyholder Benefits and Claims Incurred, Net Other Performance Measure, Amount Other Performance Measure, Amount Entity Address, State or Province Entity Address, State or Province Investment income Interest and Dividend Income, Operating Net change in unsettled security transactions Proceeds from Payables to Broker Dealers, Investing Activities Proceeds from Payables to Broker Dealers, Investing Activities Total net gains (losses) recognized during the period on equity securities Equity Securities, FV-NI, Gain (Loss) Income taxes, net of refunds Proceeds from Income Tax Refunds Individual: Individual [Axis] Commercial Lines Commercial Lines Segment [Member] Commercial Lines Segment [Member] Dividends paid to common shareholders Dividends paid to common shareholders Payments of Ordinary Dividends, Common Stock Paid-in capital Additional Paid in Capital, Common Stock Debt and Equity Securities, at Fair Value Investments [Abstract] Net cash provided by (used in) investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Other risk investments Other Risk Investments [Member] Other Risk Investments [Member] Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Dividends Dividends [Text Block] Disclosure of dividends to shareholders. Interest Interest Paid, Excluding Capitalized Interest, Operating Activity Loss and Loss Adjustment Expense Reserves Insurance Disclosure [Text Block] Document Fiscal Year Focus Document Fiscal Year Focus Senior Notes 4.20% Due 2048 Senior Notes Four Point Two Zero Percent Due Twenty Forty Eight [Member] Senior Notes Four Point Two Zero Percent Due Twenty Forty Eight [Member] Underwriting operations Underwriting Operations [Member] Underwriting Operations [Member] Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Schedule of Gain (Loss) on Securities [Table] Schedule of Gain (Loss) on Securities [Table] Effective tax rate Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Gross realized gains on equity securities Equity Securities, FV-NI, Realized Gain Carrying (Reported) Amount, Fair Value Disclosure Reported Value Measurement [Member] Securities exceeding 10% of Shareholders' Equity Securities Exceeding 10% of Shareholders' Equity Securities held in the portfolio with a single issuer for which the aggregate cost or fair value exceeds 10% of shareholders' equity. Excludes U.S. Government Obligations. Litigation Legal Matters and Contingencies [Text Block] Fair Value Debt Securities, Held-to-Maturity, Fair Value, Maturity [Abstract] O2026Q1 O2026Q1Dividends [Member] O2026Q1Dividends Valuation allowance Deferred Tax Assets, Valuation Allowance Equity [Abstract] Equity [Abstract] % of Total Fair Value Debt Securities, Available-for-Sale, Percent Of Total Fair Value Amount of investment in debt securities measured at fair value with changes in fair value recognized in other comprehensive income (available-for-sale), reflected as a percentage of the total investment portfolio fair value. Total net realized gains (losses) on securities Total net realized gains (losses) on securities Debt and Equity Securities, Gain (Loss) Segment Information Segment Reporting Disclosure [Text Block] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Reinsurance recoverables Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Unrealized Losses Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss [Abstract] Sales: Proceeds from Sale, Maturity and Collection of Investments [Abstract] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Less reinsurance recoverables on unpaid losses Plus reinsurance recoverables on unpaid losses Reinsurance Recoverable for Unpaid Claims and Claims Adjustments and Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item Reinsurance Recoverable for Unpaid Claims and Claims Adjustments and Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Pretax total accumulated other comprehensive income (loss), beginning balance Pretax total accumulated other comprehensive income (loss), ending balance AOCI before Tax, Attributable to Parent Senior Notes 4.95% Due 2033 Senior Notes Four Point Nine Five Percent Due Twenty Thirty Three [Member] Senior Notes Four Point Nine Five Percent Due Twenty Thirty Three Net federal deferred income taxes Deferred Income Tax Assets, Net Components of Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Supplemental Cash Flow Information Table Other Significant Noncash Transactions [Table] Entity Central Index Key Entity Central Index Key PEO Name PEO Name Premium Receivable, Allowance for Credit Loss Premium Receivable, Allowance for Credit Loss [Table Text Block] Foreign currency translation adjustment Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Total revenues Revenues Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Elements [Abstract] Residential mortgage-backed Residential Mortgage-Backed Securities [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Total incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Senior Notes 5.15% Due 2036 Senior Notes Five Point One Five Percent Due Twenty Thirty Six [Member] Senior Notes Five Point One Five Percent Due Twenty Thirty Six Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Personal property Personal Property [Member] Personal Property Premium receivable, allowance for credit loss Allowance for credit losses, beginning of period Allowance for credit losses, end of period Premium Receivable, Allowance for Credit Loss Segments [Axis] Segments [Axis] Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Class of Stock [Domain] Class of Stock [Domain] Local Phone Number Local Phone Number Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Assets Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Nonredeemable preferred stocks, cost Equity Securities Nonredeemable Preferred Stock Cost Equity Securities Nonredeemable Preferred Stock Cost Underlying Security Market Price Change Underlying Security Market Price Change, Percent Balance Sheet Location Statement of Financial Position Location, Balance [Axis] Senior Notes 6.25% Due 2032 Senior Notes Six Point Two Five Percent Due Twenty Thirty Two [Member] 6.25% Senior Notes due 2032 Debt Instrument Debt Instrument [Axis] Catastrophe losses Policyholder Benefits And Claims Incurred, Catastrophe Loss Policyholder Benefits And Claims Incurred, Catastrophe Loss Fair Value Fair Value Disclosures [Text Block] Nonredeemable preferred stocks Nonredeemable Preferred Stock [Member] Total reclassification adjustment for amounts realized in net income, pre tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Credit Facility [Domain] Credit Facility [Domain] Shareholders' Equity Equity, Attributable to Parent [Abstract] Net holding period gains (losses) on securities Subtotal net holding period gains (losses) Debt and Equity Securities, Unrealized Gain (Loss) Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Total expenses Benefits, Losses and Expenses Entity Address, Address Line One Entity Address, Address Line One Treasury shares purchased Treasury Stock, Value, Acquired, Cost Method Net unrealized losses on forecasted transactions, expected to reclassify into income within the next 12 months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Debt, stated interest rate Debt Instrument, Interest Rate, Stated Percentage Net Holding Period Gains (Losses) Investments, Gross Realized Gains (Losses), before Tax Pre-tax accumulated net holding period gain/(loss) for hybrid fixed-maturity securities and FV-NI equity securities for which the net change in unrealized gain/(loss) recorded as a component of realized gain/(loss) on the Income Statement Third Party Pricing Exemption Securities Third Party Pricing Exemption Securities [Member] Third Party Pricing Exemption Securities [Member] Investments [Domain] Investments [Domain] Short-duration Insurance Contracts, Accident Year [Domain] Short-Duration Insurance Contracts, Accident Year [Domain] Fair Value as of Grant Date Award Grant Date Fair Value Cost Equity Securities, FV-NI, Cost Entity Registrant Name Entity Registrant Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Accrued income taxes Accrued Income Taxes Reconciliation of Revenue and operating Income from Segments to Consolidated Reconciliation Of Revenue And Operating Income From Segments To Consolidated [Table Text Block] Reconciliation Of Revenue And Operating Income From Segments To Consolidated Debt Table Schedule of Long-Term Debt Instruments [Table Text Block] Document Quarterly Report Document Quarterly Report Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Fair value Long-Term Debt, Fair Value Total Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions Fair Value Measurement Inputs and Valuation Techniques Fair Value Measurement Inputs and Valuation Techniques [Table Text Block] Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Net amortization (accretion) of fixed-income securities Accretion (Amortization) of Discounts and Premiums, Investments Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Fair Value Measurements [Table] Fair Value Measurements [Table] Fair Value Measurements [Table] Total Quantitative Level Three Securities Total Quantitative Level Three Securities [Member] Total Quantitative Level Three Securities [Member] Equity securities Payments to Acquire Equity Securities, FV-NI Accrued investment income Accrued Investment Income Receivable O2025A O2025A Dividends [Member] O2025A Dividends Investment Type Investment Type [Axis] Total investments Investments Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Investment Category [Domain] Investment Category [Domain] [Domain] for Investment Category [Axis] Other underwriting expenses Other Underwriting Expense Restatement Determination Date: Restatement Determination Date [Axis] Non-PEO NEO Non-PEO NEO [Member] Dividends Dividends [Table Text Block] [Table Text Block] for Dividends [Table] Debt securities, available-for-sale, allowance for credit loss Debt Securities, Available-for-Sale, Allowance for Credit Loss Interest expense Interest expense Interest Expense, Debt Net (purchases) sales of short-term investments Payments for (Proceeds from) Short-Term Investments Total reclassification adjustment for amounts realized in net income, after tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Name Trading Arrangement, Individual Name All Award Types Award Type [Domain] Equity Awards Adjustments Equity Awards Adjustments [Member] % of Total Fair Value Investments, Percent Of Total Fair Value Securities held in the investment portfolio, reflected as a percentage of the total investment portfolio fair value. Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] % of Total Fair Value Equity Securities, FV-NI, Percent Of Total Fair Value Amount of investment in equity securities measured at fair value with changes in fair value recognized in earnings (FV-NI), reflected as a percentage of the total investment portfolio fair value. Investments, Unrealized Loss Position [Table] Investments Unrealized Loss Position [Table] Investments, Unrealized Loss Position [Table] Compensation Amount Outstanding Recovery Compensation Amount Debt, face amount Debt Instrument, Face Amount Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Schedule of Liability for Unpaid Claims and Claims Adjustment Expense Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] One to five years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year One Through Five Name Awards Close in Time to MNPI Disclosures, Individual Name Net unrealized losses on forecasted transactions AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Pretax total accumulated other comprehensive income (loss), Net realized gains (losses) on securities Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax Gross Unrealized Losses Investments, Accumulated Gross Unrealized Loss, Before Tax Pre-tax accumulated gross unrealized loss of total debt and equity financial instruments Revenues Revenues [Abstract] Principal amount of bonds and certificates of deposit Deposit Assets Five to ten years Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 12 Months or Greater Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions Amortization of equity-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Susan Patricia Griffith [Member] Susan Patricia Griffith Total tax (provision) benefit, Investment securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax Total accumulated other comprehensive income (loss) After tax total accumulated other comprehensive income (loss), beginning balance After tax total accumulated other comprehensive income (loss), ending balance Accumulated Other Comprehensive Income (Loss), Net of Tax Financial Instruments [Domain] Financial Instruments [Domain] Change in total net unrealized gains (losses) on fixed-maturity securities OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Schedule of Debt and Equity Securities [Table] Schedule of Debt and Equity Securities [Table] Tabular disclosure of the debt and equity securities, reconciled from cost basis to fair value. Segments [Domain] Segments [Domain] Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Acquisition of treasury shares for equity award tax liabilities Payments for Repurchase of Common Stock for Restricted Stock Tax Liabilities Payments for Repurchase of Common Stock for Restricted Stock Tax Liabilities Total fixed maturities Fixed Maturities [Member] Nonredeemable preferred stocks (cost: $259, $608, and $419) Equity Securities FV NI Nonredeemable Preferred Stock Fair Value of Nonredeemable Preferred Stocks in the investment portfolio for which the change in fair value is recorded on the income statement as a holding period gain/(loss). Accumulated other comprehensive income (loss): Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Net Investment Income [Line Items] Net Investment Income [Line Items] Balance Sheet Location [Domain] Statement of Financial Position Location, Balance [Domain] Prepaid reinsurance premiums Increase (Decrease) in Prepaid Reinsurance Premiums Total net unrealized gains (losses) on securities AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member] Property and equipment, accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Company Selected Measure Name Company Selected Measure Name Premiums receivable Increase (Decrease) in Premiums Receivable U.S. government US Government Debt Securities [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Fixed maturities Payments to Acquire Debt Securities, Available-for-Sale Debt Debt Disclosure [Text Block] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount State and local government US States and Political Subdivisions Debt Securities [Member] Senior Notes 3.20% Due 2030 Senior Notes Three Point Two Zero Percent Due Twenty Thirty [Member] Senior Notes Three Point Two Zero Percent Due Twenty Thirty Gross Unrealized Gains Equity Securities, FV-NI, Gross Unrealized Gains, before Taxes Pre-tax accumulated gross unrealized gains of equity securities in the investment portfolio, reflecting the balance recorded in AOCI for periods prior to adoption of ASU 2016-01. Operating lease liabilities Operating Lease, Payments Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Dividends payable on common shares Dividends Payable All Executive Categories All Executive Categories [Member] Current year Current Year Claims and Claims Adjustment Expense Policy acquisition costs Deferred Policy Acquisition Costs, Amortization Expense Senior Notes 6.625% Due 2029 Senior Notes Six Point Six Two Five Percent Due Twenty Twenty Nine [Member] 6 5/8% Senior Notes due 2029 Liability for Claims and Claims Adjustment Expense [Table] Liability for Claims and Claims Adjustment Expense [Table] Short-term investments (amortized cost: $2,126, $2,595, and $10,005) Short-Term Investments Net premiums earned Premiums Earned, Net Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Total average equivalent common shares - Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Realized Gain (Loss) on Investments Realized Gain (Loss) on Investments [Table Text Block] Loss and Loss Adjustment Expenses Reserves [Abstract] Loss and Loss Adjustment Expenses Reserves [Abstract] Loss and Loss Adjustment Expenses Reserves [Abstract] Entity Information, Former Legal or Registered Name Entity Information, Former Legal or Registered Name Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Discretionary Line of Credit Discretionary Line of Credit [Member] Discretionary Line of Credit Entity Small Business Entity Small Business Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Document Transition Report Document Transition Report Components of Net Investment Income Investment Income [Table Text Block] One to five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Short-term investments Short-Term Investments [Member] Premium Receivable, Allowance for Credit Loss [Roll Forward] Premium Receivable, Allowance for Credit Loss [Roll Forward] Underlying Securities Award Underlying Securities Amount Gross realized gains on available-for-sale securities Debt Securities, Available-for-Sale, Realized Gain Senior Notes 4.35% Due 2044 Senior Notes Four Point Three Five Percent Due Twenty Forty Four [Member] Senior Notes 4.35% due 2044 Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date Vendor quoted prices, percent of FV hierarchy level Vendor Quoted Prices, Percent of FV Hierarchy Level The percentage of securities with prices quoted by vendors, calculated based on the total Fair Value in the hierarchy level (Level 1, Level 2, or Level 3). PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Ten years or greater Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10 Income Taxes Income Tax Disclosure [Text Block] Borrowings outstanding Proceeds from Lines of Credit Hybrid Instruments [Line Items] Hybrid Instruments [Line Items] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Fair value inputs, market cap price change percentage, range, maximum Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum Weighted average market capitalization percentage used to calculate the periodic increase/(decrease) in valuation of Level 3 securities. This value represents the maximum change in the range of valuation changes for the period. Serial Preferred Stock Serial Preferred Stock [Member] Serial Preferred Stock Liability for Claims and Claims Adjustment Expense [Line Items] Liability for Claims and Claims Adjustment Expense [Line Items] Document Type Document Type Fair Value, Inputs, Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position [Abstract] Name Outstanding Recovery, Individual Name Product and Service [Axis] Product and Service [Axis] Common equities, cost Equity Securities Common Equities Cost Equity Securities Common Equities Cost Net Transfers In (Out) Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net Gross realized loss on available-for-sale securities Debt Securities, Available-for-Sale, Realized Loss All Individuals All Individuals [Member] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name Investment Income [Table] Investment Income [Table] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Investment Category [Axis] Investment Category [Axis] Investment Category [Axis] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Fair Value Measurement Inputs and Valuation Techniques [Line Items] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount O2024Q4 O2024Q4Dividends [Member] O2024Q4Dividends Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract] Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract] Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Total other comprehensive income (loss), after tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Total tax (provision) benefit, beginning balance Total tax (provision) benefit, ending balance AOCI Tax, Attributable to Parent Other, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Personal Lines Personal Lines Segment [Member] Personal Lines Segment [Member] Senior Notes 4.00% Due 2029 Senior Notes Four Point Zero Zero Percent Due Twenty Twenty Nine [Member] Senior Notes Four Point Zero Zero Percent Due Twenty Twenty Nine[Member] Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Total fair value of non-insurance subsidiary portfolio Securities Held In Consolidated Non Insurance Subsidiary Securities held in the portfolio of a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. Cost Investments, Amortized Cost Amortized cost of total debt and equity financial instruments Diluted: Earnings per common share (in dollars per share) Earnings Per Share, Diluted Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Title of 12(b) Security Title of 12(b) Security Five to ten years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10 Write-offs Premium Receivable, Allowance for Credit Loss, Writeoff Dividends [Axis] Dividends [Axis] Treasury shares (shares) Treasury Stock, Common, Shares Computation of Earnings Per Common Share Earnings Per Share [Abstract] Paid related to: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Consolidation Items [Domain] Consolidation Items [Domain] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Debt Security Category [Axis] Debt Security Category [Axis] Other asset-backed Asset-Backed Securities, Securitized Loans and Receivables [Member] Debt securities, available-for-sale, allowance for credit loss, not previously recorded Debt Securities, Available-for-Sale, Allowance for Credit Loss, Not Previously Recorded Other, net Stockholders' Equity, Other Gain (Loss) on Securities [Line Items] Gain (Loss) on Securities [Line Items] Equity securities Proceeds from Sale of Equity Securities, FV-NI Fair value inputs, market cap price change percentage, range, minimum Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum Weighted average market capitalization percentage used to calculate the periodic increase/(decrease) in valuation of Level 3 securities. This value represents the minimum change in the range of valuation changes for the period. Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Voting Preference Shares Voting Preferred Stock [Member] Voting Preferred Stock [Member] Award Timing Disclosures [Line Items] Net balance at January 1 Net balance at March 31 Liability for Unpaid Claims and Claims Adjustment Expense, Net After tax total accumulated other comprehensive income (loss), Investment securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Hybrid securities Hybrid Instruments at Fair Value, Net Other Indemnity Other Indemnity Segment [Member] Other Indemnity Segment Short-Duration Insurance Contract, Accident Year 2024 Short-Duration Insurance Contract, Accident Year 2024 [Member] Net income Net income Net Income (Loss) Attributable to Parent Dividends [Domain] Dividends [Domain] Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Expiration Date Trading Arrangement Expiration Date Unsettled security transactions, payable Other Payable to Broker-Dealer and Clearing Organization Equity securities Net holding period gains (losses) recognized during the period on equity securities held at period end Equity Securities, FV-NI, Unrealized Gain (Loss) Foreign government Debt Security, Government, Non-US [Member] Subtotal gross realized gains on security sales Debt and Equity Securities, Realized Gains The gross realized gains recorded during the period on sales of debt and equity securities. Excludes holding period gains on hybrid and equity securities. Property and equipment, net of accumulated depreciation of $1,416, $1,490, and $1,460 Property, Plant and Equipment, Net Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Preferred stock, shares authorized (shares) Preferred Stock, Shares Authorized Net Income Net Income (Loss) Attributable to Parent [Abstract] Adoption Date Trading Arrangement Adoption Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Entity Current Reporting Status Entity Current Reporting Status Schedule of Debt Securities by Contractual Maturity [Line Items] Schedule of Debt Securities by Contractual Maturity [Line Items] [Line Items] for Tabular disclosure of available-for-sale fixed maturities, classified by contractual maturity date. Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Net Holding Period Gains (Losses) Equity Securities, FV-NI, Gross Realized Gains (Losses), before Tax Equity Securities, FV-NI, Gross Realized Gains (Losses), before Tax Less than one year Debt Securities, Available-for-Sale, Amortized Cost, Maturity, Allocated and Single Maturity Date, Year One Retained earnings Retained Earnings (Accumulated Deficit) Number of Securities Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Number of Positions [Abstract] Service businesses profit (loss) Non Insurance Service Income (Loss), Adjusted Non Insurance Service Income (Loss), Adjusted Net (gains) losses on disposition of property and equipment Gain (Loss) on Disposition of Property Plant Equipment Major Types of Debt and Equity Securities Financial Instrument [Axis] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Expenses Benefits, Losses and Expenses [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Service revenues Non Insurance Service Revenues Revenue recognized for non-insurance services provided to customers. Components Of Other Comprehensive Income Loss [Table] Components Of Other Comprehensive Income Loss [Table] Components Of Other Comprehensive Income Loss [Table] 12 Months or Greater Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions Class of Stock [Axis] Class of Stock [Axis] Current Fiscal Year End Date Current Fiscal Year End Date Net unrealized losses on forecasted transactions Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Steven A. Broz [Member] Steven A. Broz Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Statement [Table] Statement [Table] Net realized gains (losses) on securities: Realized Investment Gains (Losses) [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Short-duration Insurance Contracts, Accident Year [Axis] Short-Duration Insurance Contracts, Accident Year [Axis] Cash Flows From Financing Activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] O2025Q1 O2025Q1Dividends [Member] O2025Q1Dividends Total Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Total equity securities Fair Value Equity Securities, FV-NI, Current Unrecognized tax benefits Unrecognized Tax Benefits Schedule of Debt and Equity Securities [Line Items] Schedule of Debt and Equity Securities [Line Items] Schedule of Debt and Equity Securities [Line Items] Net proceeds from debt issuances Proceeds from Debt, Net of Issuance Costs Officer Trading Arrangement [Member] Officer Trading Arrangement Common Stocks, excluding Other Risk Common Stocks, by Industry [Member] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag Short-Duration Insurance Contract, Accident Year 2025 Short-Duration Insurance Contract, Accident Year 2025 [Member] Loss and loss adjustment expense reserves Balance at January 1 Balance at March 31 Liability for Claims and Claims Adjustment Expense Termination Date Trading Arrangement Termination Date Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Basis of Reporting and Accounting Basis of Presentation and Significant Accounting Policies [Text Block] Dividends Payable Dividends Payable [Table] Composition of Investment Portfolio by Major Security Type Fair Value, Assets Measured on Recurring Basis [Table Text Block] Average common shares outstanding - Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Investment Portfolio Investment Portfolio [Domain] Investment Portfolio [Domain] Loss adjustment expenses Policyholder Benefits And Claims Incurred, Loss Adjustment Expense Policyholder Benefits And Claims Incurred, Loss Adjustment Expense Segment Reporting [Abstract] Segment Reporting [Abstract] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Fair Value Measurements [Line Items] Fair Value Measurements [Line Items] Fair Value Measurements [Line Items] Investment expenses Investment expenses Investment Income, Investment Expense Entity Tax Identification Number Entity Tax Identification Number Schedule of Supplemental Cash Flow Information, Non Cash Activity Schedule of Supplemental Cash Flow Information, Non Cash Activity [Table Text Block] Schedule of Supplemental Cash Flow Information, Non Cash Activity Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit Reclassification from AOCI, Current Period, Tax Net realized gains (losses) on available-for-sale securities sales Debt Securities, Available-for-Sale, Realized Gain (Loss) Pretax total accumulated other comprehensive income (loss), Investment securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Common shares, par value (USD per share) Common Stock, Par or Stated Value Per Share Common shares, issued (shares) Common Stock, Shares, Issued Commercial mortgage-backed Commercial Mortgage-Backed Securities [Member] Net realized gains (losses) on equity securities sales Less: Net gains (losses) recognized on equity securities sold during the period Equity Securities, FV-NI, Realized Gain (Loss) Fixed maturities, amortized cost Debt Securities, Available-for-Sale Fixed Maturities, Amortized Cost Amortized cost of investments in long-term debt securities (fixed maturities) measured at fair value with changes in fair value recognized in other comprehensive income (available-for-sale). Calls/ Maturities/ Paydowns/Other Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Total other comprehensive income (loss), tax (provision) benefit Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Increase in allowance Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease) Schedule of Debt and Equity Securities Reconciliation Schedule of Debt and Equity Securities [Table Text Block] [Table Text Block] for Tabular disclosure of the debt and equity securities, reconciled from cost basis to fair value. Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward] Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward] Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward] Components Of Other Comprehensive Income Loss [Line Items] Components Of Other Comprehensive Income Loss [Line Items] Components Of Other Comprehensive Income Loss [Line Items] Trading Arrangement: Trading Arrangement [Axis] Total Shareholder Return Amount Total Shareholder Return Amount Hybrid securities Unrealized Gain (Loss) on Hybrid Instrument, Net Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Reinsurance recoverables Increase (Decrease) in Reinsurance Recoverable Total equity securities Equity Securities [Member] Equity securities, at Fair Value Equity Securities, FV-NI [Abstract] Total liabilities Liabilities Gross Unrealized Losses Equity Securities, FV-NI, Gross Unrealized Losses, before Taxes Pre-tax accumulated gross unrealized losses of equity securities in the investment portfolio, reflecting the balance recorded in AOCI for periods prior to adoption of ASU 2016-01. Cost Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost Investment profit (loss) Investment Income, Net Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Short-Duration Insurance Contract, Accident Year 2023 Short-Duration Insurance Contract, Accident Year 2023 [Member] Common shares, $1.00 par value (authorized 900; issued 798, including treasury shares of 214, 212, and 212) Common Stock, Value, Outstanding Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Combined Ratio Combined Ratio Investment Portfolio Investment Portfolio [Axis] Investment Portfolio [Axis] Net Realized (Gain)/Loss on Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Statement [Line Items] Statement [Line Items] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward] Asset-backed Securities Asset-Backed Securities [Member] Consolidation Items [Axis] Consolidation Items [Axis] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Losses (excluding catastrophe losses) Policyholder Benefits And Claims Incurred, Adjusted To Exclude Catastrophe Losses Policyholder Benefits And Claims Incurred, Adjusted To Exclude Catastrophe Losses Fair Value Measurement Inputs and Valuation Techniques [Table] Fair Value Measurement Inputs and Valuation Techniques [Table] Gross investment income Gross Investment Income, Operating Common Shares, $1.00 Par Value Common equities Common Stock [Member] Total available-for-sale securities Total available-for-sale securities Debt Securities, Available-for-Sale Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Hybrid Instruments Table Hybrid Instruments Table [Table Text Block] Tabular disclosure of hybrid instruments. Non-NEOs Non-NEOs [Member] Corporate and other debt Corporate Debt Securities [Member] Increase in cash, cash equivalents, restricted cash, and restricted cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Net effect of dilutive stock-based compensation (in shares) Weighted Average Number of Shares Outstanding, Diluted, Adjustment