Premiums Written, Net [Abstract] Supplemental Information for Property, Casualty Insurance Underwriters [Table] Supplemental Information for Property, Casualty Insurance Underwriters [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Commercial Lines Property and Casualty, Commercial Insurance Product Line [Member] Personal Lines Property and Casualty, Personal Insurance Product Line [Member] Excess and Surplus Lines Insurance Excess and Surplus Lines Insurance [Member] Excess and Surplus Lines Insurance [Member] Consolidated Property and Casualty Insurance Entity Consolidated Property and Casualty Insurance Entity [Member] Subsegments [Axis] Subsegments [Axis] Subsegments [Domain] Subsegments [Domain] Catastrophe Development Catastrophe Development [Member] Catastrophe Development Member. Workers' Compensation Workers Compensation [Member] Workers' Compensation [Member] Commercial Casualty Segment [Member] Commercial Casualty Segment [Member] Commercial Casualty Segment [Member] Commercial Property Segment [Member] Commercial Property Segment [Member] Commercial Property Segment [Member] Commercial Auto Commercial Auto Segment [Member] Commercial Auto Segment [Member] Insurance Policy [Axis] Insurance Product Line [Axis] Insurance Product Line [Domain] Insurance Product Line [Domain] Life and Health Loss Reserves Life and Health Loss Reserves [Member] Life and Health Loss Reserves [Member] Supplemental Information for Property, Casualty Insurance Underwriters [Line Items] Supplemental Information for Property, Casualty Insurance Underwriters [Line Items] Reserve for loss and loss expenses Liability for Claims and Claims Adjustment Expense Prior accident years Prior Year Claims and Claims Adjustment Expense Compensation and Retirement Disclosure [Abstract] Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Qualified Pension Plans [Member] Pension Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Matching contributions to 401(k) and Top Hat plans Defined Contribution Plan, Employer Discretionary Contribution Amount Expected contributions by employer in the remainder of year Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year. Amount of employer's best estimate of contributions expected to be paid to the plan in the current remaining fiscal period. Pension contributions Pension Contributions Statement of Comprehensive Income [Abstract] Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Other Comprehensive Income Loss, Pension And Other Postretirement Benefit Plans, Net Actuarial Loss And Prior Service Cost Arising During Period, Tax Other Comprehensive Income Loss, Pension And Other Postretirement Benefit Plans, Net Actuarial Loss And Prior Service Cost Arising During Period, Tax Other Comprehensive Income Loss, Pension And Other Postretirement Benefit Plans, Net Actuarial Loss And Prior Service Cost Arising During Period, Tax Other Comprehensive Income, Change in Life Deferred Acquisition Costs, Life Policy Reserves and Other, Tax Other Comprehensive Income, Change in Life Deferred Acquisition Costs, Life Policy Reserves and Other, Tax Other Comprehensive Income, Change in Life Deferred Acquisition Costs, Life Policy Reserves and Other, Tax Liability for Future Policy Benefits [Abstract] Life Policy And Investment Contract Reserves Liability For Future Policy Benefits Life [Text Block] The disclosure of the sum of the known and estimated amounts payable as of the balance sheet date to life insurance policyholders that relates to insured events which can be viewed as either (a) the present value of future benefits to be paid to or on behalf of policyholders and expenses less the present value of future net premiums payable under the insurance contracts or (b) the accumulated amount of net premiums already collected less the accumulated amount of benefits and expenses already paid to or on behalf of policyholders. Statement of Financial Position [Abstract] Statement [Table] Statement [Table] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Statement [Line Items] Statement [Line Items] Assets Assets [Abstract] Investments Investments [Abstract] Fixed maturities, at fair value (amortized cost: 2015—$9,224; 2014—$8,871) Available-for-sale Securities, Debt Securities Equity securities, at fair value (cost: 2015—$2,828; 2014—$2,728) Available-for-sale Securities, Equity Securities Short-term investments, at fair value (amortized cost: 2015—$75; 2014—$0) Short-term Investments Other invested assets Other Investments Total investments Investments Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Investment income receivable Accrued Investment Income Receivable Finance receivable Loans and Leases Receivable, Net Amount Premiums receivable Premiums Receivable, Net Reinsurance recoverable Reinsurance Recoverables Prepaid reinsurance premiums Prepaid Reinsurance Premiums Deferred policy acquisition costs Deferred Policy Acquisition Costs Land, building and equipment, net, for company use (accumulated depreciation: 2015—$457; 2014—$446) Property, Plant and Equipment, Net Other assets Other Assets Separate accounts Separate Account Assets Total assets Assets Liabilities Liabilities [Abstract] Insurance reserves Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract] Loss and loss expense reserves Liability for Claims and Claims Adjustment Expense, Property Casualty Liability Life policy and investment contract reserves Liability for Future Policy Benefits, Life Unearned premiums Unearned Premiums Other liabilities Other Liabilities Deferred income tax Deferred Tax Liabilities, Gross Note payable Notes Payable Long-term debt and capital lease obligations Long-term Debt and Capital Lease Obligations Separate accounts Separate Accounts, Liability Total liabilities Liabilities Commitments and contingent liabilities (Note 12) Commitments and Contingencies Shareholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Common stock, par value—$2 per share; (authorized: 2015 and 2014—500 million shares; issued: 2015 and 2014—198.3 million shares) Common Stock, Value, Issued Paid-in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Treasury stock at cost (2015— 34.3 million shares and 2014—34.6 million shares) Treasury Stock, Value Total shareholders' equity Stockholders' Equity Attributable to Parent Total liabilities and shareholders' equity Liabilities and Equity Accumulated Other Comprehensive Income [Abstract] Accumulated Other Comprehensive Income [Abstract] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Deferred Annuities And Structured Settlements [Member] Deferred Annuities And Structured Settlements [Member] Deferred Annuities And Structured Settlements [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Quoted prices in active markets for identical assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant other observable inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Significant unobservable inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Senior Debentures 6.900 % Due 2028 Senior Debentures 6.9 Percent Due 2028 [Member] Senior Debentures 6.9 Percent Due 2028 [Member] Senior Debentures 6.920 % Due 2028 Senior Debentures 6.92 Percent Due 2028 [Member] Senior Debentures 6.92 Percent Due 2028 [Member] Senior Notes 6.125 % Due 2034 Senior Notes 6.125 Percent Due 2034 [Member] Senior Notes 6.125 Percent Due 2034 [Member] 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] Interest rate Debt Instrument, Interest Rate, Stated Percentage Debt instrument, year of maturity Debt Instrument, Maturity Date, Description Fair value of note payable Notes Payable, Fair Value Disclosure Fair value of senior debt Long-term Debt, Fair Value Total Debt Instrument, Fair Value Disclosure Liability for Future Policy Benefits, Individual and Group Annuities and Supplementary Contracts Liability for Future Policy Benefits, Individual and Group Annuities and Supplementary Contracts Segment Reporting [Abstract] Number of Industries Operating In Number of Industries Operating In Number of Industries Operating In Number of Reportable Segments Number of Reportable Segments Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Senior Debentures 6.900% Due 2028 Senior Debentures Six Point Nine Percent Due Twenty Twenty Eight [Member] Senior Debentures 6.9 Percent Due 2028 [Member] Senior Debentures 6.920% Due 2028 Senior Debentures Six Point Nine Two Percent Due Twenty Twenty Eight [Member] Senior Debentures 6.92 Percent Due 2028 [Member] Senior Notes 6.152% Due 2034 Senior Notes Six Point One Two Five Percent Due Twenty Thirty Four [Member] Senior Notes 6.125 Percent Due 2034 [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Debt issuance year Debt Instrument Issuance Year Debt instrument issuance year. Book value Long-term Debt Principal amount of debt Debt Instrument, Face Amount Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Amortization of actuarial loss and prior service cost Defined Benefit Plan, Amortization of Gains (Losses) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost Schedule of Gain (Loss) on Investments [Table] Schedule of Gain (Loss) on Investments [Table] Investment Securities Class [Axis] Investment Securities Class [Axis] Investment Securities Class [Domain] Investment Securities Class [Domain] Fixed Maturities Debt Securities [Member] Equity Securities Equity Securities [Member] Gain (Loss) on Investments [Line Items] Gain (Loss) on Investments [Line Items] Investment income summary: Net Investment Income [Abstract] Interest Investment Income, Interest Dividends Investment Income, Dividend Other Investment Income Other Long-Term Investments Income derived from those other than interest and dividends. Total Gross Investment Income, Operating Less investment expenses Investment Income, Investment Expense Total Net Investment Income Realized investment gains and losses summary: Realized Investment Gains (Losses) [Abstract] Gross realized gains Available-for-sale Securities, Gross Realized Gains Gross realized losses Available-for-sale Securities, Gross Realized Losses Other-than-temporary impairments Other Than Temporary Impairment Losses Other Than Temporary Impairment Losses Other Other Realized Investment Gains Losses Net This item represents realized investment gains (losses) included in earnings for the period excluding those relating to other than temporary impairment losses on investments in debt securities. Includes realized investment gains and losses generated from the sale of debt securities, equity securities, investments in joint ventures and limited partnerships and from other than temporary impairments on investments other than debt securities. Also includes realized investment gains and losses are generated from prepayment premiums, recoveries of principal on previously impaired securities, provisions for losses on commercial mortgage and other loans, and fair value changes on embedded derivatives and derivatives that do not qualify for hedge accounting treatment, except those derivatives used in the Company's capacity as a broker or dealer. Realized investment gains, net Realized Investment Gains (Losses) Change in unrealized gains and losses summary: Other Comprehensive Income (Loss), Net of Tax [Abstract] Fixed maturities Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, before Tax Less income taxes Other Comprehensive Income (Loss), Tax Reinsurance Disclosures [Abstract] Earned Consolidated Property Casualty Insurance Premiums On Assumed And Ceded Business Property Casualty Insurance Premiums Earned On Assumed And Ceded Business [Text Block] Tabular disclosure of property casualty insurance premiums earned on assumed and ceded business. Incurred Consolidated Property Casualty Insurance Loss And Loss Expenses On Assumed And Ceded Business Property Casualty Insurance Loss And Loss Expenses Incurred On Assumed And Ceded Business [Text Block] Property Casualty Insurance Loss And Loss Expenses Incurred On Assumed And Ceded Business Earned Life Insurance Premiums On Ceded Business Life Insurance Premiums Earned On Assumed And Ceded Business Table [Text Block] Life insurance premiums earned on assumed and ceded business. Life Insurance Contract Holders' Benefits Incurred On Ceded Business Life Insurance Contract Holders Benefits Incurred On Ceded Business [Text Block] Life Insurance Contract Holders' Benefits Incurred On Ceded Business Commitments and Contingencies Disclosure [Abstract] Estimate for which the risk of loss is more than remote but not probable Estimate for Which The Risk of Loss is More than Remote But Not Probable Estimate for which the risk of loss is more than remote but not probable Schedule of Defined Benefit Plans Disclosures Schedule of Defined Benefit Plans Disclosures [Table Text Block] Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring Basis [Table] Fair Value, Assets and Liabilities Measured on Recurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Major Type [Axis] Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Major Type [Axis] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, by Major Type [Axis] Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Major Types [Domain] Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation By Major Types [Domain] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, by Major Types [Domain] Taxable Fixed Maturities Taxable Fixed Maturities [Member] Taxable Fixed Maturities [Member] Debt Securities Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] Corporate Corporate Bond Securities [Member] States, municipalities and political subdivisions US States and Political Subdivisions Debt Securities [Member] Commercial mortgage-backed Commercial Mortgage Backed Securities [Member] Government-sponsored enterprises US Government-sponsored Enterprises Debt Securities [Member] Foreign government Foreign Government Debt Securities [Member] Convertibles and bonds with warrants attached Convertibles and Bonds with Warrants Attached [Member] United States government US Government Agencies Debt Securities [Member] Common equities Common Stock [Member] Nonredeemable preferred equities Preferred Stock [Member] Short-term investments Short-term Investments [Member] Top Hat savings plan mutual funds and common equity (included in Other assets) Other Pension Plan, Postretirement or Supplemental Plans [Member] Fixed maturities, at fair value Equity securities, at fair value Top Hat savings plan mutual funds and common equity (included in Other assets) Other Investment Not Readily Marketable, Fair Value Fair value of asset Investments, Fair Value Disclosure Property Casualty Loss And Loss Expenses Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block] Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Reinsurance Premiums for Insurance Companies, by Product Segment [Table] Segment [Domain] Life Insurance Segment Life Insurance Product Line [Member] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items] Direct contract holders' benefits incurred Policyholder Benefits and Claims Incurred, Direct Ceded contract holders' benefits incurred Policyholder Benefits and Claims Incurred, Ceded Insurance losses and contract holders' benefits Policyholder Benefits and Claims Incurred, Net Direct incurred loss and loss expenses Assumed incurred loss and loss expenses Policyholder Benefits and Claims Incurred, Assumed Ceded incurred loss and loss expenses Incurred loss and loss expenses Direct earned premiums Direct Premiums Earned Ceded earned premiums Ceded Premiums Earned Earned premiums Premiums Earned, Net, Life Accounting Policies [Abstract] Revenue Recognition, Policy [Policy Text Block] Revenue Recognition, Policy [Policy Text Block] Compensation Related Costs, Policy [Policy Text Block] Compensation Related Costs, Policy [Policy Text Block] Consolidation, Policy [Policy Text Block] Consolidation, Policy [Policy Text Block] Interest Capitalization, Policy [Policy Text Block] Interest Capitalization, Policy [Policy Text Block] Short-Duration Contracts, Policy [Policy Text Block] Short-Duration Contracts, Policy [Policy Text Block] Employee Retirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Reclassification Out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Net Unrealized Investment Gain (Loss) Accumulated Net Unrealized Investment Gain (Loss) [Member] Accumulated Defined Benefit Plans Adjustment Accumulated Defined Benefit Plans Adjustment [Member] Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other [Member] Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Member] Reclassification Out of Accumulated Other Comprehensive Income [Line Items] Reclassification Out of Accumulated Other Comprehensive Income [Line Items] [Line Items] for Reclassification Out of Accumulated Other Comprehensive Income [Table] Change In Accumulated Other Comprehensive Income [Roll Forward] Change In Accumulated Other Comprehensive Income [Roll Forward] Change In Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income Loss Before Tax [Abstract] Other Comprehensive Income (Loss), before Tax [Abstract] Accumulated other comprehensive income, before tax, beginning of period Accumulated Other Comprehensive Income (Loss), before Tax Other comprehensive income before reclassification, before tax Other Comprehensive Income (Loss), before Reclassifications, before Tax Reclassification adjustment, before tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Effect on other comprehensive income, before tax Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Change in unrealized gains, net, on investments available for sale, before tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, before Tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, before Tax Change in pension obligations, before tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax Change in life deferred acquisition costs, life policy reserves and other, before tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, before Tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, before Tax Effect on other comprehensive income, before tax Increase (Decrease) in Other Comprehensive Income (Loss), before Tax Increase (Decrease) in Other Comprehensive Income (Loss), before Tax Accumulated other comprehensive income, before tax, end of period Accumulated Other Comprehensive Income (Loss), Tax [Abstract] Accumulated Other Comprehensive Income Loss Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Tax [Abstract] Accumulated other comprehensive income, tax, beginning of period Accumulated Other Comprehensive Income Loss Tax Accumulated Other Comprehensive Income (Loss), Tax Other comprehensive income before reclassification, tax Other Comprehensive Income (Loss), Before Reclassifications, Tax Other Comprehensive Income (Loss), Before Reclassifications, Tax Reclassification adjustment, tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax Effect on other comprehensive income, tax Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Change in unrealized gains, net, on investments available for sale, tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Tax Change in pension obligations, tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax Change in life deferred acquisition costs, life policy reserves and other, tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Tax Effect on other comprehensive income, tax Increase (Decrease) in Other Comprehensive Income (Loss), Tax Increase (Decrease) in Other Comprehensive Income (Loss), Tax Accumulated other comprehensive income, tax, end of period Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated other comprehensive income, net of tax, beginning of period Other comprehensive income before reclassification, net of tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassification adjustment, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Effect on other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Change in unrealized gains, net, on investments available for sale, net of tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Net of Tax Other Comprehensive Income (Loss), Available-for-sale Securities and Other Assets Adjustment, Net of Tax Change in pension obligations, net of tax Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Change in life deferred acquisition costs, life policy reserves and other, net of tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Net of Tax Other Comprehensive Income (Loss), Deferred Acquisition Costs, Life Policy Reserves and Other Adjustment, Net of Tax Effect on other comprehensive income, net of tax Increase (Decrease) in Other Comprehensive Income (Loss), Net of Tax Increase (Decrease) in Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income, net of tax, end of period Segment Information Segment Reporting Disclosure [Text Block] Earnings Per Share [Abstract] Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Table] Schedule Of Earnings Per Share Basic And Diluted By Common Class [Table] Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Table] Award Type [Axis] Award Type [Axis] Share-based Compensation Arrangements by Share-based Payment Award, Award Type and Plan Name [Domain] Equity Award [Domain] Stock Options Employee Stock Option [Member] Nonvested shares Unvested Stock Awards [Member] Unvested Stock Awards [Member] Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items] Schedule Of Earnings Per Share Basic And Diluted By Common Class [Line Items] Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items] Numerator: Net Income (Loss) Attributable to Parent [Abstract] Net income-basic and diluted Net Income (Loss) Attributable to Parent Denominator: Weighted Average Number of Shares Outstanding, Diluted [Abstract] Basic weighted-average common shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of stock-based awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Diluted weighted-average shares Weighted Average Number of Shares Outstanding, Diluted Earnings per share: Earnings Per Share, Basic and Diluted [Abstract] Basic (in USD per share) Earnings Per Share, Basic Diluted (in USD per share) Earnings Per Share, Diluted Number of anti-dilutive stock-based awards (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Liability for Future Policy Benefit, by Product Segment [Table] Liability for Future Policy Benefit, by Product Segment [Table] Ordinary/Traditional Life Individual Ordinary Life Insurance [Member] Individual Ordinary Life Insurance [Member] Deferred Annuities Deferred Annuities [Member] Deferred Annuities [Member] Universal Life Universal Life [Member] Structured Settlements Structured Settlements [Member] Structured Settlements [Member]. Other Other Credit Derivatives [Member] Liability for Future Policy Benefit, by Product Segment [Line Items] Liability for Future Policy Benefit, by Product Segment [Line Items] Document Documentand Entity Information [Abstract] Document - Document and Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Derivative, by Nature [Axis] Derivative, by Nature [Axis] Derivative, Name [Domain] Derivative, Name [Domain] Debt Debt [Member] Deferred Annuities, Structured Settlements, And Other Deferred Annuities Structured Settlements And Other [Member] Deferred Annuities, Structured Settlements, And Other [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value Hierarchy for Assets Measured at Fair Value on a Recurring Basis Fair Value, Assets Measured on Recurring Basis [Table Text Block] Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Fair Values of Deferred Annuities, Structured Settlements and Other Items Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis [Table Text Block] Fair Value of Life Policy Loans Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] Accounting Policies Significant Accounting Policies [Text Block] Segments [Axis] Direct earned premiums Assumed earned premiums Assumed Premiums Earned Ceded earned premiums Earned premiums Premiums Earned, Net, Property and Casualty Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward] Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward] Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward] Gross loss and loss expense reserves, beginning of period Less reinsurance recoverable Reinsurance Recoverables on Unpaid Losses Net loss and loss expense reserves, beginning of period Liability for Unpaid Claims and Claims Adjustment Expense, Net Current accident year Current Year Claims and Claims Adjustment Expense Total incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Current accident year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior accident years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Net loss and loss expense reserves, end of period Plus reinsurance recoverable Gross loss and loss expense reserves, end of period Segment Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Corporate Fixed Maturities Corporate Debt Securities [Member] States, Municipalities And Political Subdivisions Fixed Maturities Preferred Equities Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] 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] Beginning balance Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Total gains or losses (realized/unrealized): Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Total Gains Losses Realized And Unrealized [Abstract] Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Assets, Total Gains (Losses) Realized and Unrealized [Abstract] Included in net income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Included in other comprehensive income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss) Purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases Sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales Transfers into Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Transfers out of Level 3 Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Ending balance Commitments And Contingent Liabilities Commitments and Contingencies Disclosure [Text Block] Comprehensive Income (Loss) Note Comprehensive Income (Loss) Note [Text Block] Deferred Costs [Abstract] Deferred Acquisition Costs Deferred Policy Acquisition Costs [Text Block] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Income Statement [Abstract] Revenues [Abstract] Earned premiums Premiums Earned, Net Investment income, net of expenses Realized investment gains, net Fee revenues Fees and Commissions Other revenues Other Income Total revenues Revenues Benefits and Expenses Benefits, Losses and Expenses [Abstract] Underwriting, acquisition and insurance expenses Underwriting Acquisition And Insurance Expenses Amount of commissions, insurance operating expenses, increase in deferred acquisition costs and taxes, licenses and fees. Interest expense Interest Expense Other operating expenses Other Cost and Expense, Operating Total benefits and expenses Benefits, Losses and Expenses Income Before Income Taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Provision for Income Taxes Income Tax Expense (Benefit), Continuing Operations [Abstract] Current Current Income Tax Expense (Benefit) Deferred Deferred Income Tax Expense (Benefit) Total provision for income taxes Income Tax Expense (Benefit) Net Income Per Common Share Net income-basic (in USD per share) Net income-diluted (in USD per share) Investments, Unrealized Loss Position [Table] Investments Unrealized Loss Position [Table] Investments, Unrealized Loss Position [Table] Investments, Unrealized Loss Position [Line Items] Investments Unrealized Loss Position [Line Items] Investments, Unrealized Loss Position [Line Items] Less than 12 months Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value Less than 12 months Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months Aggregate Loss 3 Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months. 12 months or more Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 12 months or more Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss 3 Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer. Total Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Total Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss 3 Amount of unrealized loss on securities classified as available-for-sale. Net Income Per Common Share Earnings Per Share [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Reserve For Losses Loss Adjustment Expenses Table [Text Block] Schedule of Liability for Future Policy Benefits, by Product Segment [Table Text Block] Structured Settlements Structured Finance [Member] Fair Value of life insurance liabilities Liabilities Related to Investment Contracts, Fair Value Disclosure Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Three Primary Contributors Life Policy Loans Policy Loans [Member] Percentage Of Level 3 Assets To Total Financial Instruments Measured At Fair Value Percentage Of Level 3 Assets To Total Financial Instruments Measured At Fair Value Percentage of Level 3 Assets to Total Financial Instruments Measured At Fair Value Tax at statutory rate, percentage Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Net Income Change in unrealized gains on investments, net of tax of $(112), $82, $(127) and $123, respectively Amortization of pension actuarial loss and prior service cost, net of tax of $1, $0, $1 and $0, respectively Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Net of Tax Change in life deferred acquisition costs, life policy reserves and other, net of tax of $2, $0, $1 and $0, respectively Other Comprehensive Income, Change in Life Deferred Acquistion Costs, Life Policy Reserves and Other, Net of Tax Other Comprehensive Income, Change in Life Deferred Acquistion Costs, Life Policy Reserves and Other, Net of Tax Other comprehensive (loss) income, net of tax Other Comprehensive Income (Loss), Net of Tax Comprehensive (Loss) Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Tax at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Increase (decrease) resulting from: Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount [Abstract] Tax-exempt income from municipal bonds Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount Dividend received exclusion Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Tax at statutory rate Increase (decrease) resulting from: Effective Income Tax Rate Reconciliation, Percent [Abstract] Tax-exempt income from municipal bonds Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent Dividend received exclusion Effective Income Tax Rate Reconciliation, Deduction, Dividend, Percent Other Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Provision for income taxes Effective Income Tax Rate Reconciliation, Percent Investment Secondary Categorization [Axis] Investment Secondary Categorization [Axis] Investments by Secondary Categorization [Domain] Investments by Secondary Categorization [Domain] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Procter And Gamble Company, Exxon Mobile Corporation And Chevron Corporation [Member] Procter Gamble Company Exxon Mobil Corporation And Chevron Corporation [Member] Procter & Gamble Company, Exxon Mobil Corporation and Chevron Corporation [Member] Number of securities Number Of Securities Number Of Securities Unrealized investment gains due to a net gain position Available-for-sale Securities, Gross Unrealized Gain 1 Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities. Largest equity holdings to total equity portfolio largest equity holdings to total equity portfolio largest equity holdings to total equity portfolio Largest equity holdings to total portfolio Largest equity holdings to total portfolio Largest equity holdings to total portfolio Number Of Securities Other Than Temporary Impairment Losses1 Number Of Securities Other Than Temporary Impairment Losses1 Number Of Securities Other Than Temporary Impairment Losses Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months Number Of Securities Continuous Unrealized Loss Position More Than Twelve Months Unrealized losses 12 months or more (equity investment less than $500,000) Number Of Securities Other Than Temporary Impairment Losses Number Of Securities Other Than Temporary Impairment Losses Number of Securities, Other Than Temporary Impairment Losses Fixed maturity investments, Percentage of amortized costs Fixed maturity investments, Percentage of amortized costs Fixed maturity investments, Percentage of amortized costs. Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss, Accumulated in Investments Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss, Accumulated in Investments Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss, Accumulated in Investments Statement of Cash Flows [Abstract] Interest Paid, Net Interest Paid, Net Cash Flows From Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Amortization and Accretion, Net Realized investment gains, net Stock-based compensation Share-based Compensation Interest credited to contract holders' Interest Credited to Policy Owner Accounts Deferred income tax expense Changes in: Increase (Decrease) in Operating Capital [Abstract] Investment income receivable Increase (Decrease) in Accrued Investment Income Receivable Premiums and reinsurance receivable Increase (Decrease) in Insurance Assets Deferred policy acquisition costs Increase (Decrease) in Deferred Policy Acquisition Costs Other assets Increase (Decrease) in Other Operating Assets Loss and loss expense reserves Increase (Decrease) in Loss and Loss Adjustment Expense Reserve Life policy reserves Increase (Decrease) in Future Policy Benefit Reserves Unearned premiums Increase (Decrease) in Unearned Premiums Other liabilities Increase (Decrease) in Operating Liabilities Current income tax receivable/payable Increase (Decrease) in Deferred Income Taxes Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash Flows From Investing Activities Net Cash Provided by (Used in) Investing Activities [Abstract] Sale of fixed maturities Proceeds from Sale of Available-for-sale Securities, Debt Call or maturity of fixed maturities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Sale of equity securities Proceeds from Sale of Available-for-sale Securities, Equity Purchase of fixed maturities Payments to Acquire Available-for-sale Securities, Debt Purchase of equity securities Payments to Acquire Available-for-sale Securities, Equity Purchase of short-term investments Payments for (Proceeds from) Short-term Investments Investment in finance receivables Payments to Acquire Finance Receivables Collection of finance receivables Proceeds from Sale and Collection of Finance Receivables Investment in buildings and equipment, net Payments to Acquire Property, Plant, and Equipment Change in other invested assets, net Payments for (Proceeds from) Other Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash Flows From Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Payment of cash dividends to shareholders Payments of Ordinary Dividends, Common Stock Purchase of treasury shares Payments for Repurchase of Common Stock Repayments of Notes Payable Repayments of Notes Payable Proceeds from stock options exercised Proceeds from Stock Options Exercised Contract holders' funds deposited Additions to Contract Holders Funds Contract holders' funds withdrawn Withdrawal from Contract Holders Funds Excess tax benefits on stock-based compensation Excess Tax Benefit from Share-based Compensation, Financing Activities Other Proceeds from (Payments for) Other Financing Activities Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Net change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of year Cash and cash equivalents at end of period Supplemental Disclosures of Cash Flow Information: Supplemental Cash Flow Information [Abstract] Income taxes paid Income Taxes Paid Conversion of Stock, Amount Converted Conversion of Stock, Amount Converted Noncash Activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Equipment acquired under capital lease obligations Capital Lease Obligations Incurred Cashless exercise of stock options Purchase Of Treasury Shares Non Cash Purchase Of Treasury Shares Non Cash Calculations For Basic And Diluted Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Consolidated Property Casualty Loss And Loss Expense Reserves Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Statement of Stockholders' Equity [Abstract] Paid-In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income Treasury Stock Treasury Stock [Member] Balance (in shares) Common Stock, Shares, Outstanding Balance Other comprehensive income, net Dividends declared Dividends, Common Stock, Cash Stock-based awards exercised and vested Stock Issued During Period, Value, Stock Options Exercised Treasury Stock, Shares, Acquired Treasury Stock, Shares, Acquired Purchases Treasury Stock, Value, Acquired, Cost Method Stock Issued During Period, Shares, Other Stock Issued During Period, Shares, Other Stockholders' Equity, Other Stockholders' Equity, Other Balance (in shares) Balance Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] Fixed Maturities And Equity Securities Fixed Maturities And Equity Securities [Member] Fixed Maturities And Equity Securities Member Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [Line Items] Cost or Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gains Gross Unrealized Losses Available-for-sale Securities, Gross Unrealized Loss 2 Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities. Fair Value Available-for-sale Securities Fixed maturities, amortized cost Available-for-sale Debt Securities, Amortized Cost Basis Equity securities, cost Available For Sale Securities Equity Securities Cost This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any. Short-term investments, amortized cost Available-for-sale Securities, Short-term Investments, Amortized Cost Land, building and equipment, accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Common stock, par value Common Stock, Par or Stated Value Per Share Common stock, authorized Common Stock, Shares Authorized Common stock, issued Common Stock, Shares, Issued Common stock, outstanding Treasury stock, shares Treasury Stock, Shares Analysis Of Cost Or Amortized Cost, Gross Unrealized Gains And Losses And Fair Value for Investments Available-for-sale Securities [Table Text Block] Fair Values And Unrealized Losses by Investment Category And By The Duration Of The Securities' Continuous Unrealized Loss Position Schedule of Unrealized Loss on Investments [Table Text Block] Investment Income, Realized Investment Gains And Losses And Change In Unrealized Investment Gains And Losses Schedule Of Investment Income Realized Gain Loss Comprehensive Income Loss Table [Text Block] Tabular disclosure of investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities, and income or expense derived from the amortization of investment related discounts or premiums; proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales; components of comprehensive income. Fair value of life policy loans Loans Receivable, Fair Value Disclosure Deferred Policy Acquisition Costs And Asset Reconciliation, Including the Amortized Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs [Table Text Block] Differences Between The 35 Percent Statutory Income Tax Rate And Effective Income Tax Rate Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Reinsurance Reinsurance [Text Block] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Deferred policy acquisition costs asset, beginning of period Capitalized deferred policy acquisition costs Deferred Policy Acquisition Costs, Additions Amortized deferred policy acquisition costs Deferred Policy Acquisition Cost, Amortization Expense, Net Investment Gains (Losses) Amortized shadow deferred policy acquisition costs Deferred Policy Acquisition Cost, Unrealized Investment Gain (Loss) Deferred policy acquisition costs asset, end of period Fair Value Measurements Fair Value Disclosures [Text Block] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Commercial Casualty Commercial Property Other Commercial Lines Other Commercial Lines [Member] Other Commercial Lines [Member] Personal Auto Personal Auto [Member] Personal Auto [Member] Home Owner Segment Home Owner Segment [Member] Home Owner Segment [Member] Other Personal Lines Other Personal Lines [Member] Other Personal Lines [Member] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate and Other Non-Segment Corporate and Other Non-Segment [Member] Corporate and Other Non-Segment [Member] Investments Segment Investments Product Line [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Investment income, net of expenses Other Income (loss) before income taxes Identifiable assets