75000 - Document - Document and Entity Information
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75010 - Statement - Consolidated Statements of Income (Unaudited)
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75020 - Statement - Consolidated Statements of Comprehensive Income (Unaudited)
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75030 - Statement - Consolidated Balance Sheets
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75040 - Statement - Consolidated Balance Sheets (Parenthetical)
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75050 - Statement - Consolidated Statements of Shareholders' Equity
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75060 - Statement - Consolidated Statements of Cash Flows
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995455 - Disclosure - Basis of Presentation and Principles of Consolidation
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995465 - Disclosure - New Accounting Pronouncements
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995475 - Disclosure - Investments
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995485 - Disclosure - Fair Value
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995495 - Disclosure - Debt and Credit Arrangements
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995505 - Disclosure - Income Taxes
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995515 - Disclosure - Pension Plans
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995525 - Disclosure - Other Comprehensive Income (Loss)
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995535 - Disclosure - Segment Information
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995545 - Disclosure - Stock-based Compensation
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995555 - Disclosure - Earnings Per Share and Shareholders' Equity Transactions
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995565 - Disclosure - Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses
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995575 - Disclosure - Commitments and Contingencies
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995585 - Disclosure - Subsequent Events
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995595 - Disclosure - New Accounting Pronouncements (Policies)
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995605 - Disclosure - Investments (Tables)
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995615 - Disclosure - Fair Value (Tables)
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995625 - Disclosure - Debt and Credit Arrangements (Tables)
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995635 - Disclosure - Pension Plans (Tables)
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995645 - Disclosure - Other Comprehensive Income (Loss) (Tables)
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995655 - Disclosure - Segment Information (Tables)
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995665 - Disclosure - Stock-based Compensation (Tables)
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995675 - Disclosure - Earnings Per Share and Shareholders' Equity Transactions (Tables)
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995685 - Disclosure - Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Tables)
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995695 - Disclosure - New Accounting Pronouncements (Narrative) (Details)
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995705 - Disclosure - Investments (Schedule of Available-for-sale Fixed Maturities Reconciliation) (Details)
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995715 - Disclosure - Investments (Schedule of Available-for-sale Fixed Maturities Reconciliation) (Details) 2
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995725 - Disclosure - Investments (Investments Classified by Contractual Maturity Date) (Details)
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995735 - Disclosure - Investments (Schedule of Unrealized Loss on Investments) (Details)
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995745 - Disclosure - Investment Income and Gains and Losses (Proceeds from Sales of Available for Sale Fixed Maturities) (Details)
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995755 - Disclosure - Investments (Narrative) (Details)
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995765 - Disclosure - Investments - (Schedule of Allowance for Credit Losses) (Details)
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995775 - Disclosure - Investments (Schedule of Pre-tax Net Realized and Unrealized Gains on Equity Securities) (Details)
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995785 - Disclosure - Investments (Schedule of Pre-tax Net Realized and Unrealized Gains on Equity Securities) (Details) 2
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995795 - Disclosure - Fair Value (Fair Values of Financial Instruments) (Details)
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995805 - Disclosure - Fair Value (Fair Value, Investment Assets Measured on Recurring Basis) (Details)
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995815 - Disclosure - Fair Value (Narrative) (Details)
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995825 - Disclosure - Fair Value (Estimated Fair Values of Financial Instruments Not Carried at Fair Value) (Details)
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995835 - Disclosure - Fair Value (Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details)
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995845 - Disclosure - Fair Value (Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3) (Details)
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995855 - Disclosure - Debt and Credit Arrangements - (Schedule of Debt) (Details)
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995865 - Disclosure - Debt and Credit Arrangements - (Schedule of Debt) (Parenthetical) (Details)
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995875 - Disclosure - Debt and Credit Arrangements (Narrative) (Details)
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995885 - Disclosure - Income Taxes (Narrative) (Details)
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995895 - Disclosure - Pension Plans (Components of Net Periodic Pension Cost) (Details)
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995905 - Disclosure - Other Comprehensive Income (Loss) (Changes in Other Comprehensive Income (Loss)) (Details)
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995915 - Disclosure - Other Comprehensive Income (Loss) (Changes in Other Comprehensive Income (Loss)) (Details) 2
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995925 - Disclosure - Other Comprehensive Income (Loss) (Changes in Other Comprehensive Income (Loss)) (Details) 3
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995935 - Disclosure - Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive (Loss) Income) (Details)
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995945 - Disclosure - Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive (Loss) Income) (Parenthetical) (Details)
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995955 - Disclosure - Segment Information (Narrative) (Details)
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995965 - Disclosure - Segment Information (Financial Information with Respect to Business Segments) (Details)
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995975 - Disclosure - Segment Information (Financial Information with Respect to Business Segments) (Details) 2
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995985 - Disclosure - Segment Information (Identifiable Assets by Business Segment) (Details)
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995995 - Disclosure - Stock-based Compensation (Narrative) (Details)
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996005 - Disclosure - Stock-based Compensation (Compensation Cost and Related Tax Benefits) (Details)
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996015 - Disclosure - Stock-based Compensation (Summary of Stock Option Activity) (Details)
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996025 - Disclosure - Stock-based Compensation (Summary of Activity Information about Employee Restricted Stock Units) (Details)
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996035 - Disclosure - Earnings Per Share and Shareholders' Equity Transactions (Information Regarding Basic and Diluted Earnings Per Share) (Details)
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996045 - Disclosure - Earnings Per Share and Shareholders Equity Transactions - (Information Regarding Basic and Diluted Earnings Per Share) (Parenthetical) (Details)
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996055 - Disclosure - Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details)
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996065 - Disclosure - Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Schedule of Liability for Unpaid Losses and Loss Adjustment Expenses) (Details)
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996075 - Disclosure - Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Narrative) (Details)
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Vested, Weighted Average Grant Date Fair Value
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value
Forfeited or cancelled, Weighted Average Exercise Price
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments, Total
Reinsurance recoverable on unpaid losses, beginning of period
Reinsurance recoverable on unpaid losses, end of period
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments
Segments
Segments [Domain]
Short-Duration Insurance Contracts, Accident Year [Axis]
Entity Incorporation, State or Country Code
Entity Incorporation, State or Country Code
Preferred Stock, Shares Issued, Total
Preferred stock, issued
Preferred Stock, Shares Issued
Balance Sheet Location
Statement of Financial Position Location, Balance [Domain]
Net payments of losses and LAE in respect of losses occurring in current year
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance
Liabilities held
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value
Due in one year or less, Fair Value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One
Mortgage-Backed Securities, Issued by Private Enterprises [Member]
Residential Mortgage-Backed, Non-Agency [Member]
Plan Name
Plan Name [Axis]
Greater than 12 months, Fair Value
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer
Equity [Abstract]
Entity Current Reporting Status
Entity Current Reporting Status
Alternative Investment, Measurement Input [Extensible Enumeration]
Alternative Investment, Measurement Input [Extensible Enumeration]
Municipals [Member]
Municipal Bonds [Member]
Deferred Policy Acquisition Costs, Amortization Expense, Total
Amortization of deferred acquisition costs
Deferred Policy Acquisition Costs, Amortization Expense
Debt Instrument, Issuance Date
Debt issuance date
Level 2 [Member]
Fair Value, Inputs, Level 2 [Member]
Weighted Average Exercise Price
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Commitments and Contingencies
Commitments and Contingencies Disclosure [Text Block]
Common stock, shares authorized
Common Stock, Shares Authorized
Total incurred losses and LAE
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims
Insurance Services Revenue
Total operating revenues
Total operating revenues
Basic:
Earnings Per Share, Basic [Abstract]
Fair Value by Liability Class [Domain]
Per share effect of dilutive securities on income from continuing operations
Per Share Effect Of Dilutive Securities On Income From Continuing Operations
Per share effect of dilutive securities on income from continuing operations.
Document Fiscal Period Focus
Document Fiscal Period Focus
Debt Instrument, Interest Rate, Stated Percentage
Debt instrument interest rate
Entity Shell Company
Entity Shell Company
Cash and Cash Equivalents, at Carrying Value, Ending Balance
Cash and Cash Equivalents, at Carrying Value, Beginning Balance
Cash and Cash Equivalents, at Carrying Value, Total
Cash and cash equivalents
Cash and Cash Equivalent
Other Comprehensive Income Loss Credit Recoveries Losses Recognized In Consolidated Income Statement Net Of Tax
Other comprehensive income loss credit recoveries losses recognized in consolidated income statement net of tax.
Amount of credit-related recoveries on prior impairments recognized in the Consolidated Statement of Income, Net of Tax
Amount of credit-related impairments (recoveries) on prior impairments recognized in the Consolidated Statement of Income, Net of Tax
Below Investment Grade [Member]
Below Investment Grade [Member]
Below Investment Grade [Member]
Common Stock, Shares, Issued, Total
Common stock, shares issued
Common Stock, Shares, Issued
Reductions for writedowns
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Writeoff
Asset Class
Asset Class [Domain]
Statement [Table]
Statement [Table]
Fair Value Transfers Out Of Level Three
Fair Value Transfers Out Of Level Three
Transfers out of Level 3
Fixed maturities intent to sell securities.
Fixed Maturities Intent to Sell Securities [Member]
Performance-Based and Market-Based Restricted Stock Units [Member]
Performance Based And Market Based Restricted Stock Units [Member]
Performance based and market-based restricted stock units.
Proceeds from Debt, Net of Issuance Costs
Proceeds from issuance of debt, net
Statement [Line Items]
Statement [Line Items]
Shares purchased at cost
Treasury Stock, Value, Acquired, Cost Method
Entity Filer Category
Entity Filer Category
Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect, Discontinued Operation
Net change in cash related to discontinued operations
Net change in cash and cash equivalents
Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect, Continuing Operation
Total liabilities and shareholders’ equity
Liabilities and Equity
Debt Instrument [Line Items]
Residential Mortgage-Backed [Member]
Residential Mortgage-Backed Securities [Member]
Industry Sector [Axis]
Long-Lived Tangible Asset [Axis]
Long-Lived Tangible Asset
Fair Value, by Balance Sheet Grouping [Table Text Block]
Fair Values of Financial Instruments
Cash and Cash Equivalents, Fair Value Disclosure
Cash and cash equivalents
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease), Total
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Period Increase (Decrease)
Additional credit losses on investments for which an allowance was previously recognized
Fair Value [Line Items]
Fair Value [Line Items]
Fair Value [Line Items]
Professional and Executive Lines, Marine, Specialty Property and Casualty Divisions [Member]
Professional And Executive Lines Marine Specialty Property And Casualty Divisions [Member]
Professional and executive lines, marine, specialty property and casualty divisions.
Noncatastrophe [Member]
Noncatastrophe.
Goodwill, Ending Balance
Goodwill, Beginning Balance
Goodwill, Total
Goodwill
Goodwill
Other Comprehensive Income Loss Net Unrealized Gain Losses Arising During Period Having Credit Losses In Consolidated Income Statement Tax
Other comprehensive income loss net unrealized gain losses arising during period having credit losses in consolidated income statement tax.
Net unrealized gains arising during period for those having credit losses in Consolidated Statements of Income, Tax Benefit (Expense)
Net unrealized losses arising during period for those having credit losses in Consolidated Statements of Income, Tax Benefit (Expense)
Employee Stock Options [Member]
Other comprehensive loss, Pre-Tax
Other Comprehensive Income (Loss), before Tax
Other comprehensive (loss) income, Pre-Tax
Additional Paid in Capital, Common Stock, Ending Balance
Additional Paid in Capital, Common Stock, Beginning Balance
Additional paid-in capital
Additional Paid in Capital, Common Stock
Fair Value Transfers Between Level2 And Level3 Amount
Fair value transfers between level 2 and level 3 amount.
Securities transferred between Level 2 and Level 3
Share Repurchase Program
Share Repurchase Program [Axis]
Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member]
Residential Mortgage-Backed, U.S. Agency Backed [Member]
Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses
Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block]
Per share effect of dilutive securities on net income (loss).
Per Share Effect Of Dilutive Securities On Net Income (Loss)
Per share effect of dilutive securities on net income
Per share effect of dilutive securities on net income
Prior Year Claims Adjustment Expense excluding catastrophes
Prior year claims adjustment expense excluding catastrophes.
Prior year favorable development, excluding catastrophes
Granted, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross
Information Regarding Basic and Diluted Earnings Per Share
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Increase (Decrease) in Other Operating Assets and Liabilities, Net, Total
Other, net
Increase (Decrease) in Other Operating Assets and Liabilities, Net
Other Comprehensive Income Loss Additional Impairment Recoveries Losses Recognized In Consolidated Income Statement Net Of Tax
Other comprehensive income loss additional impairment recoveries (losses) recognized in consolidated income statement net of tax..
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Net of Tax
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Net of Tax
Equity Securities [Member]
Equity Securities [Member]
Stock Compensation Plans [Member]
Share-Based Payment Arrangement [Member]
Investments Classified by Contractual Maturity Date
Investments Classified by Contractual Maturity Date [Table Text Block]
Earnings Per Share, Basic
Net income per share
Net income per share
Outstanding, beginning of period, Shares
Outstanding, end of period, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number
Schedule of Available-for-sale Fixed Maturities Reconciliation
Schedule of Available-for-Sale Securities Reconciliation [Table Text Block]
Due after ten years, Amortized Cost, Net of Allowance for Credit Losses
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost Net Of Allowance For Credit Losses
Available for sale securities debt maturities after ten years amortized cost net of allowance for credit losses.
Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract]
Adjustments to reconcile net income to net cash provided by operating activities:
Subsegments
Subsegments [Axis]
Share Repurchase Program
Share Repurchase Program [Domain]
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total
Proceeds from disposals and maturities of fixed maturities
Proceeds from Sale and Maturity of Debt Securities, Available-for-Sale
Reinsurance Recoverables, Including Reinsurance Premium Paid, Ending Balance
Reinsurance Recoverables, Including Reinsurance Premium Paid, Beginning Balance
Reinsurance Recoverables, Including Reinsurance Premium Paid, Total
Reinsurance recoverable on paid and unpaid losses and unearned premiums
Reinsurance Recoverables, Including Reinsurance Premium Paid
Accounting Standards Update [Axis]
Other comprehensive income loss net unrealized gains losses arising during period having no credit losses in consolidated income statement net of tax.
Other Comprehensive Income Loss Net Unrealized Gains Losses Arising During Period Having No Credit Losses In Consolidated Income Statement Net Of Tax
Net unrealized gains arising during period for those having no credit losses in Consolidated Statements of Income, Net of Tax
Net unrealized gains (losses) arising during period for those having no credit losses in Consolidated Statements of Income, Net of Tax
Shareholders’ Equity
Equity, Attributable to Parent [Abstract]
Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Entity Small Business
Entity Small Business
Short-Term Debt [Member]
Short-term [Member]
Condensed Statement Of Comprehensive Income [Table]
Condensed Statement of Comprehensive Income [Table]
Valuation, Market Approach [Member]
Market comparables [Member]
Retained Earnings (Accumulated Deficit), Ending Balance
Retained Earnings (Accumulated Deficit), Beginning Balance
Retained Earnings (Accumulated Deficit), Total
Retained earnings
Retained Earnings (Accumulated Deficit)
Other comprehensive income loss net unrealized gains losses arising during period having no credit losses in consolidated income statement tax.
Other Comprehensive Income Loss Net Unrealized Gains losses Arising During Period Having No Credit Losses In Consolidated Income Statement Tax
Net unrealized gains (losses) arising during period for those having no credit losses in Consolidated Statements of Income, Tax Benefit (Expense)
Net unrealized gains (losses) arising during period for those having no credit losses in Consolidated Statements of Income, Tax Benefit (Expense)
Industry Sector [Domain]
Preferred Stock [Member]
Asset-backed Securities [Member]
Asset-backed [Member]
Asset-Backed Securities, Securitized Loans and Receivables [Member]
Stock-based Compensation
Share-Based Payment Arrangement [Text Block]
Accumulated other comprehensive (income) loss related to net change in market risk.
Accumulated Other Comprehensive (Income) Loss Related To Net Change In Market Risk [Member]
Net change in market risk
Payments of Dividends
Payments of Dividends, Total
Dividends paid to shareholders
Catastrophic Event [Axis]
Amendment Flag
Amendment Flag
Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3
Schedule Of Additional Information About Significant Unobservable Inputs Used In Fair Valuations Of Level Three Table [Text Block]
Schedule of additional information about significant unobservable inputs used in fair valuations of level three.
Entity Address, Postal Zip Code
Entity Address, Postal Zip Code
Net cash provided by operating activities
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation
Available For Sale Securities Debt Maturities Without Single Maturity Date Amortized Cost Net Of Allowance For Credit Losses
Available for sale securities debt maturities without single maturity date amortized cost net of allowance for credit losses.
Mortgage-backed and other asset-backed securities, Amortized Cost, Net of Allowance for Credit Losses
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description
Segment reporting, codm, profit (loss) measure, how used, description
Common Stock, $.01 Par Value [Member]
Common Stock [Member]
Common Stock [Member]
Loss adjustment expenses and other operating expenses
Losses and loss adjustment expenses
Total losses and LAE
Amortization of net actuarial losses recognized as net periodic benefit cost, Pre-Tax
Amortization of defined benefit plan costs
Granted, Weighted Average Exercise Price
Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price
Schedule of Available-for-sale Securities [Line Items]
Debt Securities, Available-for-Sale [Line Items]
Other asset-backed securities, securitized loans and receivables.
Other Asset-Backed Securities, Securitized Loans and Receivables [Member]
Other Asset-Backed [Member]
Portion at Fair Value Measurement [Member] [Default]
Fair Value Disclosure Item Amounts [Default]
Portion at Fair Value Measurement [Member]
Entity Address, Address Line One
Entity Address, Address Line One
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]
Change in accounting principle, accounting standards update, immaterial effect
Senior debentures unsecured maturing on April fifteenth two thousand twenty six.
Senior Debentures Unsecured Maturing On April Fifteenth Two Thousand Twenty Six [Member]
Senior debentures unsecured mature on April 15, 2026 [Member]
Senior debentures maturing April 15, 2026 [Member]
Level 2 [Member]
Fair Value Hierarchy and NAV [Axis]
ShortDurationInsuranceContractsAccidentYears2014To2019Member
ShortDurationInsuranceContractsAccidentYears2014To2019Member
Years 2014 To 2019 [Member]
Other Comprehensive Income Loss Available For Sale Securities Having No Credit Losses Recognized In The Consolidated Statements Of Income
Other comprehensive income loss available for sale securities having no credit losses recognized in the consolidated statements of income.
Having no credit losses recognized in the Consolidated Statements of Income
Earnings per common share:
Earnings Per Share [Abstract]
Balance Sheet Location
Statement of Financial Position Location, Balance [Axis]
Short-Duration Insurance Contracts, Accident Year [Domain]
Investment Type
Investment Type [Axis]
Gain Losses on Intent to Sell Securities
Gain losses on intent to sell securities.
Losses on intent to sell securities
Total, Fair Value
Debt Securities, Available-for-Sale, Unrealized Loss Position
Purchase of fixed maturities
Payments to Acquire Debt Securities, Available-for-Sale
Net appreciation (depreciation) on available-for-sale securities
Total available-for-sale securities
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax
Net appreciation (depreciation) on available-for-sale securities
Document Type
Document Type
Collaborative Arrangement and Arrangement Other than Collaborative [Axis]
Collaborative Arrangement and Arrangement Other than Collaborative [Domain]
Entity Central Index Key
Entity Central Index Key
Available-for-sale securities:
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax [Abstract]
Investments, Debt and Equity Securities [Abstract]
Valuation Approach and Technique
Valuation Approach and Technique [Axis]
Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation
Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation, Total
Rule 10b5-1 Plan [Member]
Rule 10b5-1 Plan [Member]
Dennis F. Kerrigan [Member]
Dennis F. Kerrigan.
Accrued Investment Income Receivable, Total
Accrued investment income
Accrued Investment Income Receivable
Antidilutive securities excluded from calculation of earnings per share
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Other Comprehensive Income (Loss)
Included in other comprehensive income (loss) - changes in net unrealized gains (losses) on investment securities
Net realized and unrealized investment gains (losses):
Gain (Loss) on Investments [Abstract]
Disposal Group Classification
Disposal Group Classification [Domain]
Common stock, par value
Common Stock, Par or Stated Value Per Share
Accounting Standards Update [Domain]
Increase (Decrease) in Payout, Maximum Percentage
Increase (decrease) in payout, maximum percentage.
Increase or decrease in payout, maximum percentage
Liabilities
Liabilities [Abstract]
Other personal lines.
Other Personal Lines [Member]
Other Personal Lines [Member]
Other Personal Lines
Amortized Cost
Fixed maturities, amortized cost
Amortized Cost
Debt Securities, Available-for-Sale, Amortized Cost
Fixed maturities
Fair Value
Fixed maturities, Fair Value
Fixed maturities, at fair value (amortized cost of $10,211.8 and $9,685.7)
Realized Investment Gains (Losses)
Net realized losses from sales and other
Total net realized and unrealized investment losses
Personal Lines [Member]
Personal Lines Segment [Member]
Personal lines segment.
Exercised, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period
Debt Disclosure [Abstract]
Purchase
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases
Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Axis]
Estimated Fair Value [Member]
Estimate of Fair Value Measurement [Member]
Commercial Multiple Peril Commercial Automobile And Worker's Compensation [Member]
Commercial multiple peril, commercial automobile and worker's compensation.
Commercial Multiple Peril Lines, Commercial Automobile Line and Workers' Compensation [Member]
Surety and Specialty P&C divisions [Member]
Surety And Specialty Property And Casualty Divisions [Member]
Surety and Specialty P&C divisions.
Current Fiscal Year End Date
Current Fiscal Year End Date
Debt Instrument [Table]
Schedule of Long-Term Debt Instruments [Table]
Document Quarterly Report
Document Quarterly Report
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]
Other operating expenses
Other Cost and Expense, Operating
Other Cost and Expense, Operating, Total
Fair Value By Balance Sheet Grouping [Table]
Fair Value, by Balance Sheet Grouping [Table]
Entity Address, State or Province
Entity Address, State or Province
Outstanding, beginning of period, Shares
Outstanding, end of period, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number
NonRule10b51ArrModifiedFlag
NonRule10b51ArrModifiedFlag
Non-Rule 10b5-1 Arrangement Modified
Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Comprehensive income
Gross Unrealized Gains
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax
Incremental Common Shares Attributable to Share-based Payment Arrangements, Total
Dilutive effect of securities
Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]
Equity Securities, FV-NI, Unrealized Gain
On securities still held
Compensation Cost and Related Tax Benefits
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
Prior Year Favorable Catastrophe Development
Prior year favorable catastrophe development.
Prior year favorable catastrophe development
Schedule of Liability for Unpaid Losses and Loss Adjustment Expenses
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block]
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other comprehensive income (loss), net of tax:
Increase (Decrease) in Deferred Income Taxes
Deferred income tax expense (benefit)
Income (Loss) from Continuing Operations, Per Outstanding Share, Total
Income (Loss) from Continuing Operations, Per Basic Share
Income from continuing operations
Deferred Income Tax Assets, Net, Total
Deferred income tax asset
Deferred Income Tax Assets, Net
Per share effect of dilutive securities on net income
Per Share Effect Of Dilutive Securities On Net Income
Per share effect of dilutive securities on net income.
Debt
Long-Term Debt, Fair Value
Commercial Multiple Peril Line [Member]
Commercial Multiple Peril Line [Member]
Commercial multiple peril line.
Open market purchases.
Open Market Purchases [Member]
Open Market Purchases [Member]
Antidilutive Securities
Antidilutive Securities [Axis]
Accumulated other comprehensive (income) loss related to long duration insurance contracts.
Accumulated Other Comprehensive (Income) Loss Related To Long Duration Insurance Contracts [member]
Long Duration Insurance Contracts [Member]
Interest Expense, Debt, Total
Interest on debt
Interest expense
Interest Expense, Debt
Stock-based compensation expense, net of taxes
Share-Based Payment Arrangement, Expense, after Tax
Proceeds from sales
Proceeds from Sale of Debt Securities, Available-for-Sale
Unamortized debt issuance costs
Debt Instrument, Unamortized Discount
Debt Instrument, Unamortized Discount, Total
Favorable Catastrophe Development [Member]
Favorable catastrophe development.
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]
Treasury Stock, Common, Shares
Treasury stock, shares
Treasury Stock [Member]
Discontinued operations (net of taxes):
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract]
Impairments on fixed maturities credit related losses
Impairments On Fixed Maturities Credit Related Losses
Impairments on fixed maturities credit related losses.
Preferred Stock, Value, Issued, Ending Balance
Preferred Stock, Value, Issued, Beginning Balance
Preferred Stock, Value, Issued, Total
Preferred stock, par value $0.01 per share; 20.0 million shares authorized; none issued
Preferred Stock, Value, Issued
Reclassification out of Accumulated Other Comprehensive Income
Reclassification out of Accumulated Other Comprehensive Income [Domain]
Debt Instrument, Maturity Date
Maturity date
Minimum [Member]
Minimum [Member]
Minimum [Member]
Granted, Weighted Average Grant Date Fair Value
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value
Financial Instrument
Financial Instrument [Axis]
Other comprehensive loss, Tax Benefit (Expense)
Other Comprehensive Income (Loss), Tax
Other comprehensive income (loss), Tax Benefit (Expense)
Other comprehensive (loss) income, Tax Benefit (Expense)
Change in reinsurance recoverable
Increase (Decrease) in Reinsurance Recoverable
Level 3 [Member]
Fair Value, Inputs, Level 3 [Member]
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income tax expense (benefit):
Fair Value Through Net Income [Member]
Fair Value Through Net Income [Member]
Fair value through net income.
Segment Reporting [Abstract]
Fair Value, Investment Assets Measured on Recurring Basis
Fair Value, Assets Measured on Recurring Basis [Table Text Block]
Other Comprehensive Income Loss Additional Impairment Recoveries Losses Recognized In Consolidated Income Statement Before Tax
Other comprehensive income loss additional impairment recoveries (losses) recognized in consolidated income statement before tax.
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Pre-Tax
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Pre-Tax
Measurement Input, Discount For Lease Structure [Member]
Measurement Input Discount Rate For Lease Structure [Member]
Measurement Input Discount Rate For Lease Structure [Member]
Richard W.Lavey [Member]
Richard W.Lavey [Member]
Schedule of Unrealized Loss on Investments
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block]
Fair Value Measurements [Line Items]
Fair Value Measurements [Line Items]
Fair Value Measurements [Line Items]
Net unrealized gains (losses), Tax Benefit (Expense)
Net unrealized losses, Tax Benefit (Expense)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, Tax
Net unrealized gains, Tax Benefit (Expense)
Commitments and contingencies
Commitments and Contingencies
Total payments
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid
Outstanding, beginning of period, Weighted Average Grant Date Fair Value
Outstanding, end of period, Weighted Average Grant Date Fair Value
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Reclassification Out Of Accumulated Other Comprehensive Income [Table]
Reclassification out of Accumulated Other Comprehensive Income [Table]
Change in premiums receivable, net of reinsurance premiums payable
Increase (Decrease) in Premiums Receivable
Short-Term Debt, Total
Short-Term Debt
Short-term debt
Depreciation, Amortization and Accretion, Net
Net amortization and depreciation
Liability for Claims and Claims Adjustment Expense, Total
Loss and loss adjustment expense reserves
Gross reserve for losses and LAE, beginning of period
Gross reserve for losses and LAE, end of period
Liability for Claims and Claims Adjustment Expense
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest
Net income (loss)
Net income
Personal Automobile Lines [Member]
Personal Automobile Lines [Member]
Personal automobile lines.
Identifiable Assets by Business Segment
Reconciliation of Assets from Segment to Consolidated [Table Text Block]
Accounting Standards Update 2018-12 [Member]
ASU 2018-12
Cost Approach Valuation Technique [Member]
Valuation, Cost Approach [Member]
Weighted Average Number of Shares Outstanding, Basic, Total
Basic shares used in the calculation of earnings per share
Weighted average shares outstanding
Weighted Average Number of Shares Outstanding, Basic
Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table]
Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table]
Income from continuing operations
Amortization of net actuarial losses recognized as net periodic benefit cost, Net of Tax
Net amount recognized as net periodic benefit cost
Net change in net actuarial loss
Income from continuing operations
Greater than 12 months, Gross Unrealized Losses
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss
Fair Value Measured Using NAV [Member]
Fair Value Measured at Net Asset Value Per Share [Member]
Segments
Segments [Axis]
Long-Lived Tangible Asset
Long-Lived Tangible Asset [Domain]
Subsequent Events
Subsequent Events [Text Block]
Long-Term Debt
Long-term debt
Total long-term debt
Amortized Cost/Cost [Member]
Amortized Cost Or Cost [Member]
Amortized cost or cost.
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition, Total
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition
Employee and director stock-based awards and other
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Amortization of Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]
Due after five years through ten years, Amortized Cost, Net of Allowance for Credit Losses
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost Net Of Allowance For Credit Losses
Available for sale securities debt maturities after five through ten years amortized cost net of allowance for credit losses.
Total shareholders’ equity
Balance at beginning of period
Balance at end of period
Equity, Attributable to Parent
Preferred stock, par value
Preferred Stock, Par or Stated Value Per Share
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax, Total
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Tax Benefit (Expense)
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Tax Benefit (Expense)
Statement of Stockholders' Equity [Abstract]
Other Comprehensive Income Loss Credit Recoveries Losses Recognized In Consolidated Income Statement Tax
Other comprehensive income loss credit recoveries losses recognized in consolidated income statement tax.
Amount of credit-related impairments (recoveries) on prior impairments recognized in the Consolidated Statement of Income, Tax Benefit (Expense)
Debt, Long-Term and Short-Term, Combined Amount
Total debt
Valuation Approach and Technique
Valuation Approach and Technique [Domain]
Accelerated Share Repurchase Agreement [Member]
Accelerated Share Repurchase Program [Member]
Accelerated Share Repurchase Program.
Treasury Stock, Common [Member]
Treasury Stock [Member]
Other comprehensive income long duration insurance contracts.
Other Comprehensive Income Long Duration Insurance Contracts [Abstract]
Long-duration insurance contracts:
Federal, State, and Local, Income Tax Expense (Benefit), Continuing Operations
Federal, State, and Local, Income Tax Expense (Benefit), Continuing Operations, Total
U.S. federal and state income tax expense
Life [Member]
Life [Member]
Life business.
Fair Value
Fair Value Disclosures [Text Block]
Defined Benefit Pension and Postretirement Plans [Member]
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Debt Instrument, Name [Domain]
Debt Instrument, Name
Noncatastrophic Event [Axis]
Investment Grade [Member]
Investment Grade [Member]
Investment Grade [Member]
Income from discontinued life businesses
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share, Total
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share
Other segment items
Segment Reporting, Other Segment Item, Amount
Other segment items
Plan Name
Plan Name [Domain]
Revenue Market Multiples
Revenue Market Multiples [Member]
Revenue market multiples.
Subordinated Debentures Maturing February Third, Two Thousand Twenty Seven [Member]
Subordinated Debentures Maturing February Third Two Thousand Twenty Seven [Member]
Subordinated debentures maturing February 3, 2027 [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]
Due after ten years, Fair Value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 10
Schedule of Investments [Line Items]
Schedule of Investments [Line Items]
Purchase of equity securities and other investments
Payments To Acquire Equity Securities And Other Investments
Payments to acquire equity securities and other investments.
Debt Securities [Member]
Debt Securities [Member]
Treasury Stock, Value, Ending Balance
Treasury Stock, Value, Beginning Balance
Treasury Stock, Value, Total
Balance at beginning of period
Balance at end of period
Treasury Stock, Value
Treasury stock at cost (25.4 and 25.1 million shares)
Disposal Group Name
Disposal Group Name [Domain]
Accounting Standards Update [Extensible Enumeration]
Accounting Standards Update [Extensible Enumeration]
Core Commercial [Member]
Core Commercial Lines Segment [Member]
Core commercial lines segment.
Entity Address, City or Town
Entity Address, City or Town
Other Comprehensive Income Loss Net Unrealized Gain Losses Arising During Period Having Credit Losses In Consolidated Income Statement Net Of Tax
Other comprehensive income loss net unrealized gain losses arising during period having credit losses in consolidated income statement net of tax.
Net unrealized gains arising during period for those having credit losses in Consolidated Statements of Income, Net of Tax
Repurchased common shares
Stock Repurchased During Period, Shares
Decrease as grant in period, percentage
Share Based Compensation Arrangement By Share Based Payment Award Decrease As Forfeited In Period Percentage
Share based compensation arrangement by share based payment award decrease as forfeited in period percentage.
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]
Current Year Catastrophe Losses
Current year catastrophe losses.
Current year catastrophe losses
Number of Reportable Segments
Reportable segments
Rule10b51ArrModifiedFlag
Rule10b51ArrModifiedFlag
Rule 10b5-1 Arrangement Modified
Security Exchange Name
Security Exchange Name
Long-Term Debt, Gross
Long-term debt principal
Liability for Unpaid Claims and Claims Adjustment Expense, Net, Total
Net reserve for losses and LAE, beginning of period
Net reserve for losses and LAE, end of period
Liability for Unpaid Claims and Claims Adjustment Expense, Net
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest
Income before income taxes
Amortization of net actuarial losses recognized as net periodic benefit cost, Pre-Tax
Loss adjustment expenses and other operating expenses
Amortization of net actuarial losses recognized as net periodic benefit cost, Pre-Tax
Investments measured at net asset value based on an ownership interest in partners'
Percentage Of Investments Not Included In Fair Value Of Financial Instruments
Percentage Of Investments Not Included In Fair Value Of Financial Instruments
Liability For Claims And Claims Adjustment Expense [Table]
Liability for Claims and Claims Adjustment Expense [Table]
Debt Securities, Available-for-Sale, Amortized Cost, after Allowance for Credit Loss
Amortized Cost, Net of Allowance for Credit Losses
Fixed maturities, amortized cost
Other Comprehensive Income Loss Available For Sale Securities Having Credit Losses Recognized In The Consolidated Statements Of Income
Other comprehensive income loss available for sale securities having credit losses recognized in the consolidated statements of income.
Having credit losses recognized in the Consolidated Statements of Income
Measurement Input Type
Measurement Input Type [Domain]
Antidilutive Securities, Name
Antidilutive Securities, Name [Domain]
Senior Debentures Unsecured Maturing September One Two Thousand Thirty Five [Member]
Senior debentures unsecured maturing September one two thousand thirty five.
Senior debentures maturing September 1, 2035 [Member]
Income from discontinued life businesses
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share, Total
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share
Performance-Based Restricted Stock Units [Member]
Performance Based Restricted Stock Unit [Member]
Performance Based Restricted Stock Unit [Member]
Accounts Payable and Accrued Liabilities, Total
Expenses and taxes payable
Accounts Payable and Accrued Liabilities
Measurement Basis
Measurement Basis [Axis]
Statistical Measurement
Statistical Measurement [Domain]
Stock-based compensation expense
Share-Based Payment Arrangement, Expense
Document Period End Date
Document Period End Date
Reinsurance premiums payable
Reinsurance Payable
Title of Individual
Title and Position [Axis]
Fair Value Hierarchy and NAV
Fair Value Hierarchy and NAV [Domain]
Net unrealized losses, Per-Tax
OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment, before Tax
Net unrealized gains (losses), Pre-Tax
Amortized Cost, Net of Allowance for Credit Losses
Available For Sale Debt Securities Amortized Cost Basis Net Of Allowance For Credit Losses
Available for sale debt securities amortized cost basis net of allowance for credit losses.
Credit related recoveries (impairments).
Credit Related Recoveries Impairments
Credit-related recoveries on investments
Credit-related impairments
Commercial Multiple Peril, Commercial Automobile, Workers' Compensation And Other Commercial Lines [Member]
Commercial Multiple Peril, Commercial Automobile, Workers' Compensation And Other Commercial Lines [Member]
Other Comprehensive Income Loss Credit Recoveries Losses Recognized In Consolidated Income Statement Before Tax
Other comprehensive income loss credit recoveries losses recognized in consolidated income statement before tax.
Amount of credit-related recoveries on prior impairments recognized in the Consolidated Statement of Income, Pre-Tax
Amount of credit-related impairments (recoveries) on prior impairments recognized in the Consolidated Statement of Income, Pre-Tax
Percentage of other operating expenses
Other Comprehensive Income Loss Percentage Of Amounts Reclassified From Accumulated Other Comprehensive Income For Pension And Post Retirement Benefits Allocated To Other Operating Expenses
Percentage of amounts reclassified from AOCI for pension and post retirement benefits allocated to other operating expenses.
Statement of Financial Position [Abstract]
Cumulative Effect, Period of Adoption, Adjustment [Member]
Adjustment [Member]
OCI, Liability for Future Policy Benefit, Gain (Loss), after Reclassification Adjustment and Tax
OCI, Liability for Future Policy Benefit, Gain (Loss), after Reclassification Adjustment and Tax, Total
Net change in market risk
Net change in market risk, Net of Tax
Gross losses
Debt Securities, Available-for-Sale, Realized Loss
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Pension Plans
Compensation and Employee Benefit Plans [Text Block]
Losses and expenses
Benefits, Losses and Expenses [Abstract]
Current Income Tax Expense (Benefit), Total
Current
Current Income Tax Expense (Benefit)
Total liabilities
Liabilities
Other Comprehensive Income Loss Net Unrealized Gain Losses Arising During Period Having Credit Losses In Consolidated Income Statement Before Tax
Other comprehensive income loss net unrealized gain losses arising during period having credit losses in consolidated income statement before tax.
Net unrealized losses arising during period for those having credit losses in Consolidated Statements of Income,Pre-Tax
Financial Instruments
Financial Instruments [Domain]
Income Loss From Continuing Operations Excluding Nonoperating Items Before Income Taxes Extraordinary Items Noncontrolling Interest
This element represents the income or loss from continuing operations excluding non-operating items attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.
Operating income before income taxes
Operating income before income taxes
Expected return on plan assets
Defined Benefit Plan, Expected Return (Loss) on Plan Assets
12 months or less, Gross Unrealized Losses
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss
Diluted shares used in the calculation of earnings per share
Weighted average shares outstanding
Weighted Average Number of Shares Outstanding, Diluted
Entity File Number
Securities Act File Number
Other Assets, Total
Other Assets
Other assets
Fair Value Measurements [Table]
Fair Value Measurements [Table]
Fair Value Measurements [Table]
Cover [Abstract]
Schedule Of Pre Tax Net Realized And Unrealized Gains And Losses On Equity Securities Table [Text Block]
Schedule of pre-tax net realized and unrealized gains and losses on equity securities.
Schedule of Pre-tax Net Realized and Unrealized Gains on Equity Securities
Measurement Input Type
Measurement Input Type [Axis]
Increase (Decrease) in Accounts Payable and Accrued Liabilities, Total
Change in expenses and taxes payable
Increase (Decrease) in Accounts Payable and Accrued Liabilities
Cumulative Effect, Period of Adoption [Axis]
Forfeited, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period
Forfeited, Shares
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax, Total
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Pre-Tax
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Pre-Tax
Investments [Domain]
Investments
Securities Held as Collateral, at Fair Value
Securities on loan, fair value
Performance metric, potential range
Performance Metric Potential Range
Performance Metric, Potential Range
Mortgage Loans [Member]
Mortgages [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized
Number of shares authorized under plan
Operating segments
Number of Operating Segments
Sale of Stock [Domain]
Sale of Stock
Segment Information
Segment Reporting Disclosure [Text Block]
Range
Alternative Investment, Measurement Input
Loss adjustment expenses
Other Comprehensive Income Loss Percentage Of Amounts Reclassified From Accumulated Other Comprehensive Income For Pension And Post Retirement Benefits Allocated To Loss Adjustment Expenses
Percentage of amounts reclassified from AOCI for pension and post retirement benefits allocated to loss adjustment expenses.
Catastrophe [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Total
Forfeited or cancelled, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period
Fair Value Through AOCI [Member]
Fair Value Through Accumulated Other Comprehensive Income [Member]
Fair value through accumulated other comprehensive income.
Schedule Of Investments [Table]
Schedule of Investments [Table]
New Accounting Pronouncements
New Accounting Pronouncements, Policy [Policy Text Block]
Vesting period
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period
Comprehensive Income (Loss) Note [Text Block]
Other Comprehensive Income (Loss)
Measurement Input, Discount for Small Issue Size [Member]
Measurement Input Discount For Small Issue Size [Member]
Measurement Input Discount For Small Issue Size [Member]
Pension and postretirement benefits:
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Carrying Value [Member]
Reported Value Measurement [Member]
Short-duration insurance contract, accident year 2019 through 2022.
Short-Duration Insurance Contract, Accident Year 2019 Through 2022 [Member]
Years 2019 To 2022 [Member]
Investment, Type [Extensible Enumeration]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)
Amortization of prior service cost
Document Transition Report
Document Transition Report
Discounted cash flow [Member]
Income Approach Valuation Technique [Member]
Valuation Technique, Discounted Cash Flow [Member]
Repurchases of common stock
Payments for Repurchase of Common Stock
Statement of Cash Flows [Abstract]
Share-Based Payment Arrangement, Option, Activity [Table Text Block]
Summary of Stock Option Activity
Impairments on investments
Impairments on investments.
Impairments (recoveries) losses on investments
Total impairments on investments
Total Impairments on investments
Net impairments
Net payments of losses and LAE in respect of losses occurring in prior years
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years
Earnings Per Share and Shareholders' Equity Transactions
Earnings Per Share [Text Block]
Debt Security, Government, Non-US [Member]
Foreign governments [Member]
Summary of Activity Information about Employee Restricted Stock Units
Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]
Beginning Balance
Ending Balance
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value
Assets of Discontinued Operations [Member]
Discontinued Operations, Disposed of by Sale [Member]
Net income
Net income
Specialty [Member]
Specialty Lines Segment [Member]
Specialty lines segment.
Other financing activities
Proceeds from (Payment for) Other Financing Activity
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-Sale Securities, Debt Maturities [Abstract]
Market-Based Restricted Stock Units [Member]
Market Based Restricted Stock Units [Member]
Market-Based Restricted Stock Units [Member]
Assets
Assets [Abstract]
Fixed Maturities Including Held For Sale [Member]
Fixed Maturities Including Held For Sale [Member]
Fixed maturities including held for sale.
Repayments of Debt
Repayment of debt
Repayment of debt
Document Fiscal Year Focus
Document Fiscal Year Focus
Fair value measurement market multiples
Equity Securities, FV-NI, Measurement Input
Cash Flows From Investing Activities
Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract]
Retirement Benefits [Abstract]
Investments
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
Non-Vested Stock Grants [Member]
Non Vested Stock Grants [Member]
Non-vested stock grants.
Other [Member]
Other Operating Segment [Member]
Schedule of Net Benefit Costs [Table Text Block]
Components of Net Periodic Pension Cost
Accounting Standards Update and Change in Accounting Principle [Abstract]
Percentage of excise tax imposed on common stock repurchase activity
Percentage of Excise Tax Imposed on Common Stock Repurchase Activity
Percentage of excise tax imposed on common stock repurchase activity.
Equity Securities, FV-NI, Gain (Loss)
Net change in fair value of equity securities and other
On securities sold during the period
Total net realized and unrealized gains on equity securities recognized in income
Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture, Total
Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture
Net shares reissued at cost under employee stock-based compensation plans and other
Current Accident Year Losses And LAE
Current accident year losses and LAE.
Current accident year losses and LAE
Recoveries (Impairments) on Investments [Abstract]
Recoveries (Impairments) on Investments.
Impairments on investments:
Impairments on investments:
Unrealized Gain (Loss) on Investments [Table Text Block]
Changes in Other Comprehensive Income (Loss)
Equity Securities And Other [Member]
Equity Securities And Other [Member]
Equities and Other [Member]
Fixed Maturities [Member]
Fixed Maturities [Member]
Net investment income
Net Investment Income, Total
Net Investment Income
Net Tangible Asset [Member]
Net Tangible Asset [Member]
Net tangible asset.
Proceeds from exercise of employee stock options
Proceeds from Stock Options Exercised
Fair Value Disclosures [Abstract]
Commitments and Contingencies Disclosure [Abstract]
Increase as grant in period, percentage
Share Based Compensation Arrangement By Share Based Payment Award Increase As Grant In Period Percentage
Share-based compensation arrangement by share-based payment award, increase as grant in period, percentage.
Disposal Group, Including Discontinued Operation, Liabilities, Total
Liabilities of discontinued businesses
Disposal Group, Including Discontinued Operation, Liabilities
Debt Instrument [Axis]
Debt Instrument
Interest cost
Defined Benefit Plan, Interest Cost
Share-Based Payment Arrangement [Abstract]
Fees and other income
Fees Commissions And Other Income
Fees, commissions and other income.
Total financial instruments
Assets, Fair Value Disclosure
Sale of Stock
Sale of Stock [Axis]
Revenues
Total revenues
Net cash used in investing activities
Cash Provided by (Used in) Investing Activity, Including Discontinued Operation
Professional and Executive Lines
Professional and Executive Lines [Member]
Professional and executive lines.
Specialty P&C Lines [Member]
Specialty P and C Lines [Member]
Specialty P and C Lines.
Title of 12(b) Security
Title of 12(b) Security
Schedule Of Segment Reporting Information By Segment [Table]
Schedule of Segment Reporting Information, by Segment [Table]
Stock repurchase program, available authorized repurchase amount
Share Repurchase Program, Remaining Authorized, Amount
Forfeited, Weighted Average Grant Date Fair Value
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value
Subsegments
Subsegments [Domain]
Income Taxes
Income Tax Disclosure [Text Block]
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]
Debt Securities, Available-for-sale, Allowance for Credit Loss, Total
Allowance for Credit Losses
Allowance for credit losses
Debt Securities, Available-for-Sale, Allowance for Credit Loss
Allowance for credit losses as of the beginning of the period
Allowance for credit losses as of the end of the period
Due after one year through five years, Fair Value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five
Outstanding, beginning of period, Weighted Average Exercise Price
Outstanding, end of period, Weighted Average Exercise Price
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Income Tax Disclosure [Abstract]
Fair Value Measurements, Recurring and Nonrecurring [Table]
Fair Value, Recurring and Nonrecurring [Table]
Lower Property Losses [Member]
Lower Property Losses [Member]
Lower property losses.
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
Other comprehensive income loss net unrealized gains losses arising during period having no credit losses in consolidated income statement before tax.
Other Comprehensive Income Loss Net Unrealized Gains Losses Arising During Period Having No Credit Losses In Consolidated Income Statement Before Tax
Net unrealized gains arising during period for those having no credit losses in Consolidated Statements of Income, Pre-Tax
Net unrealized gains (losses) arising during period for those having no credit losses in Consolidated Statements of Income, Pre-Tax
Commercial Mortgage-Backed [Member]
Commercial Mortgage-Backed Securities [Member]
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Net realized and unrealized gains on equity securities recognized in income:
Measurement Frequency
Measurement Frequency [Domain]
Repurchases common stock, authorized
Share Repurchase Program, Authorized, Amount
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date
Change in accounting principle, accounting standards update, adoption date
Trading Symbol
Trading Symbol
Short Duration Insurance Contracts Accident Years2013 TO2017and2020Member
Short Duration Insurance Contracts Accident Years 2013 TO 2017 and 2020.
Years 2013 To 2017 and 2020 [Member]
Equity securities
Equity securities, at fair value
Equity Securities, FV-NI, Current
Extinguishment of Debt [Axis]
Schedule of Allowance for Credit Losses
Financing Receivable, Allowance for Credit Loss [Table Text Block]
Cash Flows From Financing Activities
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract]
Fair Value, Measurements, Recurring [Member]
Fair Value, Recurring [Member]
Equity Components
Equity Components [Axis]
Equity Component
Equity Component [Domain]
Asset Class
Asset Class [Axis]
Deferred Policy Acquisition Cost, Ending Balance
Deferred Policy Acquisition Cost, Beginning Balance
Deferred Policy Acquisition Cost, Total
Deferred acquisition costs
Deferred Policy Acquisition Cost
Schedule of Realized Gain (Loss)
Schedule of Realized Gain (Loss) [Table Text Block]
Investments
Total investments
Due after one year through five years, Amortized Cost, Net of Allowance for Credit Losses
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost Net Of Allowance For Credit Losses
Available for sale securities debt maturities after one through five years amortized cost net of allowance for credit losses.
Per share effect of dilutive securities on income (loss) from continuing operations.
Per Share Effect Of Dilutive Securities On Income (Loss) From Continuing Operations
Per share effect of dilutive securities on income (loss) from continuing operations
Per share effect of dilutive securities on income (loss) from continuing operations
Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank Borrowings [Member]
U.S. Treasury and Government Agencies [Member]
US Treasury and Government [Member]
Statement of Comprehensive Income [Abstract]
Maximum [Member]
Maximum [Member]
Maximum [Member]
Alternative Investment, Valuation Technique [Extensible Enumeration]
Alternative Investment, Valuation Technique [Extensible Enumeration]
Statistical Measurement
Statistical Measurement [Axis]
Exercised, Weighted Average Exercise Price
Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price
Valuation for Equity Security Based on Dealer Quote
Valuation for equity security based on dealer quote.
Valuation for equity security based on dealer quote
Senior debentures unsecured maturing on October fifteenth two thousand twenty five.
Senior Debentures Unsecured Maturing On October Fifteenth Two Thousand Twenty Five [Member]
Senior debentures unsecured mature on October 15, 2025 [Member]
Senior debentures maturing October 15, 2025 [Member]
Senior Management [Member]
Senior Management [Member]
Senior management.
Common Stock, Value, Issued, Ending Balance
Common Stock, Value, Issued, Beginning Balance
Common Stock, Value, Issued, Total
Common stock, par value $0.01 per share; 300.0 million shares authorized; 60.5 million shares issued
Common Stock, Value, Issued
Other comprehensive income loss, net change in market risk before tax.
Other Comprehensive Income Loss, Net Change In Market Risk Before Tax
Net change in market risk, Pre-tax
Surety lines.
Surety Lines [Member]
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]
Reclassifications Out of Accumulated Other Comprehensive (Loss) Income
Time-Based Restricted Stock Units [Member]
Time Based Restricted Stock Units [Member]
Time based restricted stock units.
Gross gains
Debt Securities, Available-for-Sale, Realized Gain
Income (Loss) from Continuing Operations, Per Diluted Share
Income from continuing operations
Change in deferred acquisition costs
Increase (Decrease) in Deferred Policy Acquisition Costs
Due in one year or less, Amortized Cost, Net of Allowance for Credit Losses
Available For Sale Securities Debt Maturities Within One Year Amortized Cost Net Of Allowance For Credit Losses
Available for sale securities debt maturities within one year amortized cost net of allowance for credit losses.
Marine Line [Member]
Marine Line.
Fair Value [Table]
Fair Value [Table]
Fair Value [Table]
Internal Model Pricing Approach Valuation Technique [Member]
Internal model pricing approach valuation technique.
Internal Price based on Financing Round [Member]
Estimated Fair Values of Financial Instruments Not Carried at Fair Value
Carrying Amounts And Estimated Fair Values Of Financial Instruments Not Measured At Fair Value Table [Text Block]
The tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities that are not carried at fair value.
Total losses and expenses
Benefits, Losses and Expenses
Net incurred losses and LAE in respect of losses occurring in current year
Current Year Claims and Claims Adjustment Expense
Preferred stock, shares authorized
Preferred Stock, Shares Authorized
Schedule of Debt [Table Text Block]
Schedule of Debt
Premiums Earned, Net, Total
Premiums
Premiums Earned, Net
Hanover insurance group 2014 employee stock purchase plan.
Hanover Insurance Group 2014 Employee Stock Purchase Plan [Member]
Hanover Insurance Group 2014 Employee Stock Purchase Plan [Member]
Total, Gross Unrealized Losses
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross fixed maturities, Fair Value
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value
ESPP Plan [Member]
Employee Stock [Member]
Entity Registrant Name
Entity Registrant Name
Debt Disclosure [Text Block]
Debt and Credit Arrangements
Gross Unrealized Loss
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax
Other Nonoperating Income (Expense), Total
Other Nonoperating Income (Expense)
Non-operating income (loss) items:
Accumulated Other Comprehensive Income (Loss) [Table]
Hanover Insurance Group 2022 Long-Term Incentive Plan.
Hanover Insurance Group 2022 Long-Term Incentive Plan [Member]
Hanover Insurance Group 2022 Long-Term Incentive Plan [Member]
Subsequent Events [Abstract]
Liability For Claims And Claims Adjustment Expense [Line Items]
Liability for Claims and Claims Adjustment Expense [Line Items]
Impairment Loss Debt Securities Available For Sale Recognized In Earnings
Impairment loss debt securities available for sale recognized in earnings.
(Impairments) recoveries on investments
Income tax (expense) benefit
Income Tax Expense (Benefit)
Total income tax expense
Amortization of net actuarial losses recognized as net periodic benefit cost, Tax Benefit (Expense)
Income tax (expense) benefit
Amortization of net actuarial losses recognized as net periodic benefit cost, Tax Benefit (Expense)
Measurement Frequency
Measurement Frequency [Axis]
Other Investments, Total
Other investments
Other Investments
Four Point Five Zero Unsecured Senior Debentures [Member]
Four point five zero unsecured senior debentures.
4.50% Unsecured Senior Debentures [Member]
Stock Repurchased During Period, Value
Repurchased common shares aggregate cost
Repurchased common shares value
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements
Settlements
Settlements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Entity Common Stock, Shares Outstanding
Entity Common Stock, Shares Outstanding
Liability Class [Axis]
Disposal Group Classification
Disposal Group Classification [Axis]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Total
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive loss
Federal Income Tax Expense (Benefit), Continuing Operations, Total
Federal income tax expense (benefit)
Federal Income Tax Expense (Benefit), Continuing Operations
Payments to Acquire Property, Plant, and Equipment, Total
Capital expenditures
Payments to Acquire Property, Plant, and Equipment
Gain (Loss) on Investments, Total
Gain (Loss) on Investments
Net realized and unrealized investment (gains) losses
Granted, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period
Years 2013 To 2018 and 2020 [Member]
Short Duration Insurance Contracts Accident Years 2013 To 2018 And 2020 [Member]
Short duration insurance contracts accident years 2013 To 2018 and 2020.
Gain Loss On Investments From Continuing Operations
Net realized and unrealized investment losses
Gain (loss) on investments from continuing operations.
Total net realized and unrealized investment losses
Assets
Total assets
Identifiable assets
Income Statement [Abstract]
Homeowners [Member]
Homeowners Line Segment [Member]
Homeowners line segment.
Other Comprehensive Income Loss Net Of Tax Changes In Net Unrealized Losses On Investment Securities [Abstract]
Other comprehensive income loss net of tax changes in net unrealized losses on investment securities.
Changes in net unrealized gains (losses) on investment securities:
Recognized net actuarial loss
Defined Benefit Plan, Amortization of Gain (Loss)
Proceeds from disposals of equity securities and other investments
Proceeds From Sale Of Equity Securities And Other Investments
Proceeds from sale of equity securities and other investments.
Deferred Income Tax Expense (Benefit), Total
Deferred
Deferred Income Tax Expense (Benefit)
Weighted Average [Member]
Weighted Average [Member]
Equity Securities, FV-NI, Realized Gain (Loss)
Equity Securities, FV-NI, Realized Gain (Loss), Total
On securities sold during the period
Commercial automobile line.
Commercial Automobile Line [Member]
Commercial Automobile Line [Member]
Unearned Premiums
Unearned Premiums, Total
Unearned premiums
Vested, Shares
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period
Diluted:
Earnings Per Share, Diluted [Abstract]
Earnings Per Share, Diluted
Net income per share
Net income per share
Time-based, Market-based and Performance-based Restricted Stock Units [Member]
Time Based Market Based And Performance Based Restricted Stock Units [Member]
Time-based, market-based and performance-based restricted stock units.
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Financial Information with Respect to Reporting Segments
Premiums and Other Receivables, Net, Total
Premiums and accounts receivable, net
Premiums and Other Receivables, Net
Increase (Decrease) in Insurance Liabilities, Total
Change in loss, loss adjustment expense and unearned premium reserves
Increase (Decrease) in Insurance Liabilities
Title Of Individual With Relationship To Entity [Domain]
Title and Position [Domain]
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value
Mortgage-backed and other asset-backed securities, Fair Value
Identifiable assets
Disposal Group, Including Discontinued Operation, Assets, Total
Assets of discontinued businesses
Disposal Group, Including Discontinued Operation, Assets
City Area Code
City Area Code
Long-Term Debt, Unclassified [Abstract]
Long-term:
Other Comprehensive Income (Loss), Net of Tax
Other comprehensive income, Net of tax
Total other comprehensive income (loss), net of tax
Debt Instrument, Face Amount
Aggregate principal amount
Income from discontinued life businesses
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest, Total
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest
Income from discontinued life businesses
Certain Liability Lines [Member]
Certain liability lines.
Insurance [Abstract]
Foreign Governments [Member]
Foreign Government Debt [Member]
Dividends, Cash, Total
Dividends to shareholders
Dividends, Cash
Segment Reporting Information [Line Items]
Segment Reporting Information [Line Items]
Disposal Group Name
Disposal Group Name [Axis]
Net incurred losses and LAE in respect of losses occurring in prior years
(Favorable) unfavorable loss and LAE development
Prior Year Claims and Claims Adjustment Expense
Net incurred losses and LAE in respect of losses occurring in prior years
(Favorable) unfavorable loss and LAE development
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total
Cash and cash equivalents, beginning of period
Cash and cash equivalents, end of period
Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation
Operating Income (Loss)
Operating income before interest expense and income taxes
Property and casualty.
Property And Casualty [Member]
Property and Casualty [Member]
Retained Earnings [Member]
Retained Earnings [Member]
Condensed Statement of Income Captions [Line Items]
Condensed Statement Of Income Captions [Line Items]
Share-based Payment Arrangement, Noncash Expense, Total
Stock-based compensation expense
Share-Based Payment Arrangement, Noncash Expense
Other Comprehensive Income Loss Additional Impairment Recoveries Losses Recognized In Consolidated Income Statement Tax
Other comprehensive income loss additional impairment (recoveries) losses recognized in consolidated income statement tax.
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Tax Benefit (Expense)
Amount of additional impairment losses recognized in the Consolidated Statements of Income, Tax Benefit (Expense)
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Securities Sold
Reductions for disposals
12 months or less, Fair Value
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months
Level 1 [Member]
Fair Value, Inputs, Level 1 [Member]
Class Of Stock [Line Items]
Class of Stock [Line Items]
Cash Provided by (Used in) Financing Activity, Including Discontinued Operation
Net cash used in financing activities
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss)
Changes in net unrealized gains (losses) for the period included in other comprehensive income (loss) for assets held at the end of the period
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]
Change in accounting principle, accounting standards update, adopted
Long-Term Debt [Member]
Long-term [Member]
Measurement Input, Discount For Above-market coupon [Member]
Measurement Input Discount Rate For Above Market Coupon [Member]
Measurement Input Discount Rate For Above Market Coupon [Member]
Deferred Income Tax Liabilities, Net, Total
Deferred income tax liability
Deferred Income Tax Liabilities, Net
Extinguishment of Debt, Type [Domain]
Due after five years through ten years, Fair Value
Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year 5 Through 10
Total investment assets at fair value
Fair value of investments
Investments, Fair Value Disclosure
Other investments
Investments measured at fair value using net asset value
Fair Value
Sales
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax, Total
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Net of Tax
Amount of losses realized from sales and other recognized in Consolidated Statements of Income, Net of Tax
Corporates [Member]
Corporate Debt Securities [Member]
Debt Securities Available For Sale [Table]
Debt Securities, Available-for-Sale [Table]
Entity Interactive Data Current
Entity Interactive Data Current
Senior debentures unsecured maturing September one two thousand thirty.
Senior Debentures Unsecured Maturing September One Two Thousand Thirty [Member]
Senior debentures maturing September 1, 2030 [Member]
Fair Value Measurement
Fair Value Measurement [Domain]
Cash Flows From Operating Activities
Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract]
Significant Unobservable Inputs
Debt Securities Available For Sale Measurement Input1
Debt securities available for sale measurement input.
New Accounting Pronouncements
Accounting Standards Update and Change in Accounting Principle [Text Block]
Noncatastrophic Event [Domain]
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Adjusted Balance [Member]
Amortization of deferred acquisition costs and other underwriting expenses
Amortization of deferred acquisition costs and other underwriting expenses.
Amortization of deferred acquisition costs and other underwriting expenses
Catastrophic Event [Domain]
Amortization of defined benefit plan costs.
Amortization of defined benefit plan costs
Amortization Of Defined Benefit Plan Costs
Defined Benefit Plan, Type [Extensible Enumeration]
Defined Benefit Plan, Type [Extensible List]
Cumulative Effect, Period of Adoption [Domain]
Tax benefit
Share-Based Payment Arrangement, Expense, Tax Benefit
Entity Tax Identification Number
Entity Tax Identification Number
Revenues
Revenues [Abstract]
Available For Sale Securities Debt Maturities Single Maturity Date Amortized Cost Net Of Allowance For Credit Losses
Gross fixed maturities, Amortized Cost, Net of Allowance for Credit Losses
Available for sale securities debt maturities single maturity date amortized cost net of allowance for credit losses.
Hanover Insurance Group 2023 Employee Stock Purchase Plan.
Hanover Insurance Group 2023 Employee Stock Purchase Plan [Member]
Short-Term Debt [Abstract]
Short-term:
Stock available for additional repurchases
Stock Available for Additional Repurchases
Stock available for additional repurchases.
Other Investments [Member]
Other Investments [Member]
Equity Securities, FV-NI, Unrealized Gain (Loss) and Other
Equity securities, FV-NI, unrealized gain (loss) and other.
Net change in fair value of equity securities and other
Basis of Presentation and Principles of Consolidation
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]
Workers' Compensation Line [Member]
Workers Compensation Line [Member]
Workers compensation line.
Included in net realized and unrealized investment gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings
Local Phone Number
Local Phone Number
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Net periodic pension cost
Performance-Based Awards [Member]
Performance Based Awards [Member]
Performance-based awards.
Accounting Policies [Abstract]
Underwriting income (loss)
Underwriting Income (Loss)
Total financial instruments
Financial Instrument That Were Not Carried At Fair Values Including Held For Sale
Financial instrument, that were not carried at fair values including held-for-sale.
Schedule Of Earnings Per Share Basic By Common Class [Table]
Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table]
Net Unrealized Appreciation (Depreciation) on Investments [Member]
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Parent [Member]
Other comprehensive income loss, net change in market risk tax benefit (expense).
Other Comprehensive Income Loss, Net Change In Market Risk Tax Benefit (Expense)
Net change in market risk, Tax Benefit (Expense)
Number of shares available for grant
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant
Schedule Of Stock By Class [Table]
Stock, Class of Stock [Table]
Entity Emerging Growth Company
Entity Emerging Growth Company