Document Document and Entity Information [Abstract] Document - Document and Entity Information [Abstract] Statement [Table] Statement [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Statement [Line Items] Statement [Line Items] Entity Registrant Name Entity Registrant Name Trading Symbol Trading Symbol Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Statement of Financial Position [Abstract] Investments [Abstract] Investments [Abstract] Fixed Maturity Securities, Amortized Cost Available-for-sale Securities, Debt Maturities, Amortized Cost Basis Stockholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Common Stock, Par Common Stock, Par or Stated Value Per Share Common Stock, Authorized Common Stock, Shares Authorized Common Stock, Issued Common Stock, Shares, Issued Treasury Stock, Shares Treasury Stock, Shares Statement of Stockholders' Equity [Abstract] Statement, Equity Components [Axis] Statement, Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Retained Earnings Retained Earnings [Member] Dividends to Stockholders, per common share Common Stock, Dividends, Per Share, Cash Paid Statement of Income and Comprehensive Income [Abstract] Change in Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired, tax expense Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Change in Net Unrealized Gain on Securities Other-Than-Temporarily Impaired, tax benefit Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Available-for-sale Securities Total Change in Net Unrealized Gain on Securities Before Reclassification Adjustment, tax expense Other Comprehensive Income (Loss), Available-for-sale Securities, Tax Reclassification Adjustment for Net Realized Investment Gain, tax expense Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax Change in Net Gain on Cash Flow Hedges, tax expense (benefit) Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect Change in Adjustment to Reserves for Future Policy and Contract Benefits Net of Reinsurance and Other, tax benefit Change in Adjustment to Reserves for Future Policy and Contract Benefits Net of Reinsurance and Other tax expense benefit Tax effect from the unrealized adjustment to reserves for future policy and contract benefits for unrealized loss on securities during the period net of the effects of contracts assumed and ceded Change in Unrecognized Pension and Postretirement Benefit Costs, tax expense Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract] Net Periodic Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Fair Values of Financial Instruments Additional Information [Abstract] Disclosure - Fair Values of Financial Instruments - Additional Information [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, by Balance Sheet Grouping, Disclosure Item Amounts [Axis] Fair Value, by Balance Sheet Grouping, Disclosure Item Amounts [Axis] Fair Value, Disclosure Item Amounts [Domain] Fair Value, Disclosure Item Amounts [Domain] Policy Loans Ceded Ceded Policy Loans [Member] Ceded Policy Loans [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 1 [Member] Other Than Fair Value Inputs Level 1 Fair Value Inputs Other Than Level 1 [Member] Fair Value Inputs Other Than Level 1 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value, Inputs, Level 3 [Member] Fair Value Inputs Level 2 Or Level 3 Fair Value Inputs Level 2 Or Level 3 [Member] Fair Value Inputs Level 2 Or Level 3 [Member] Fair Value, Assets and Liabilities Components [Axis] Fair Value, Assets and Liabilities Components [Axis] Fair Value, Assets and Liabilities Components Axis Fair Value, Assets and Liabilities Component [Domain] Fair Value, Assets and Liabilities Component Domain Fair Value, Assets and Liabilities Component Domain Pricing Service Pricing Service [Member] Pricing Service [Member] Other Observable Market Data Other Observable Market Data [Member] Other Observable Market Data [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] Carrying amount of policy loans Loans, Gross, Insurance Policy Debt Instrument, Fair Value Disclosure Debt Instrument, Fair Value Disclosure Percent of fixed maturity securities valued Available For Sale Securities Percent Of Total Fair Value Available For Sale Securities, Percent Of Total Fair Value Embedded Derivative in Modified Coinsurance Arrangement Embedded Derivative, Gain (Loss) on Embedded Derivative, Net Notes to Financial Statements [Abstract] Notes to Financial Statements [Abstract] Derivative Financial Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Defined Benefit Plans and Other Postretirement Benefit Plans [Domain] Pension Benefits, U.S. Plans United States Pension Plans of US Entity, Defined Benefit [Member] Pension Benefits, Non U.S. Plans Foreign Pension Plans, Defined Benefit [Member] Other Postretirement Benefit Plans Other Postretirement Benefit Plans, Defined Benefit [Member] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] 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 Defined Benefit Plan, Amortization of Gains (Losses) Amortization of Prior Service Credit Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Total Defined Benefit Plan, Net Periodic Benefit Cost Disclosure Text Block [Abstract] Stockholders' Equity and Earnings Per Common Share Stockholders Equity and Earnings Per Common Share The entire disclosure for stockholders equity and earnings per share Assets Assets [Abstract] Investments Fixed Maturity Securities - at fair value (amortized cost: $37,457.3; $36,640.7) Available-for-sale Securities Mortgage Loans Mortgage Loans on Real Estate, Commercial and Consumer, Net Policy Loans Other Long-term Investments Other Long-term Investments Short-term Investments Other Short-term Investments Total Investments Investments Other Assets Other Assets, Unclassified [Abstract] Cash and Bank Deposits Cash Accounts and Premiums Receivable Premiums and Other Receivables, Net Reinsurance Recoverable Reinsurance Recoverables Accrued Investment Income Accrued Investment Income Receivable Deferred Acquisition Costs Deferred Policy Acquisition Costs Goodwill Goodwill Property and Equipment Property, Plant and Equipment, Net Other Assets Other Assets Total Assets Assets Liabilities and Stockholders' Equity Liabilities and Equity [Abstract] Liabilities Liabilities [Abstract] Policy and Contract Benefits Liability for Claims and Claims Adjustment Expense, Disability, Accident and Health Reserves for Future Policy and Contract Benefits Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense Unearned Premiums Unearned Premiums Other Policyholders' Funds Other Policyholder Funds Income Tax Payable Taxes Payable Deferred Income Tax Deferred Income Tax Liabilities Short-term Debt Debt, Current Long-term Debt Long-term Debt and Capital Lease Obligations Other Liabilities Other Liabilities Total Liabilities Liabilities Commitments and Contingent Liabilities - Note 9 Commitments and Contingencies Common Stock, $0.10 par, Authorized: 725,000,000 shares Issued: 359,705,527 and 358,691,567 shares Common Stock, Value, Issued Additional Paid-in Capital Additional Paid in Capital, Common Stock Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired Accumulated Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Net Gain on Cash Flow Hedges Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax Foreign Currency Translation Adjustment Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Unrecognized Pension and Postretirement Benefit Costs Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax Retained Earnings Retained Earnings (Accumulated Deficit) Treasury Stock - at cost: 84,620,240 shares and 65,975,613 shares Treasury Stock, Value Total Stockholders' Equity Stockholders' Equity Attributable to Parent Total Liabilities and Stockholders' Equity Liabilities and Equity Statement of Cash Flows [Abstract] Cash Flows from Operating Activities Net Cash Provided by (Used in) Operating Activities [Abstract] Net Income Net Income (Loss) Attributable to Parent 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] Change in Receivables Increase (Decrease) in Receivables Change in Deferred Acquisition Costs Increase (Decrease) in Deferred Policy Acquisition Costs Change in Insurance Reserves and Liabilities Increase (Decrease) in Insurance Liabilities Change in Income Taxes Increase (Decrease) in Income Taxes Payable Change in Other Accrued Liabilities Increase (Decrease) in Other Accrued Liabilities Non-cash Adjustments to Net Investment Income Increase (Decrease) in Accrued Investment Income Receivable Net Realized Investment Gain (Loss) Realized Investment Gains (Losses) Depreciation Depreciation, Amortization and Accretion, Net Other, Net Other Noncash Income (Expense) 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] Proceeds from Sales of Fixed Maturity Securities Proceeds from Sale of Available-for-sale Securities Proceeds from Maturities of Fixed Maturity Securities Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Proceeds from Sales and Maturities of Other Investments Proceeds from Sale and Maturity of Other Investments Purchase of Fixed Maturity Securities Payments to Acquire Available-for-sale Securities Purchase of Other Investments Payments to Acquire Other Investments Net Sales (Purchases) of Short-term Investments Payments for (Proceeds from) Short-term Investments Other, Net Payments for (Proceeds from) Other Investing Activities Net Cash Used by Investing Activities Net Cash Provided by (Used in) Investing Activities Cash Flows from Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Net Short-term Debt Borrowings Proceeds from (Repayments of) Short-term Debt Issuance of Long-term Debt Proceeds from Issuance of Long-term Debt Long-term Debt Repayments Repayments of Long-term Debt Issuance of Common Stock Proceeds from Issuance of Common Stock Repurchase of Common Stock Payments for Repurchase of Common Stock Dividends Paid to Stockholders Payments of Dividends Other, Net Proceeds from (Payments for) Other Financing Activities Net Cash Used by Financing Activities Net Cash Provided by (Used in) Financing Activities Effect of Foreign Exchange Rate Changes on Cash Effect of Exchange Rate on Cash and Cash Equivalents Net Decrease in Cash and Bank Deposits Cash and Cash Equivalents, Period Increase (Decrease) Cash and Bank Deposits at Beginning of Year Cash and Bank Deposits at End of Period Disclosure Mortgage Loans by Geographic Region [Abstract] Disclosure - Mortgage Loans by Geographic Region [Abstract] Mortgage Loans on Real Estate Schedule [Table] Mortgage Loans on Real Estate Schedule [Table] Region Reporting Information, by Region [Axis] Investment Geographic Region [Axis] Reporting Region [Domain] Investment Geographic Region [Domain] New England New England [Member] New England [Member] Mid-Atlantic Middle Atlantic [Member] Middle Atlantic [Member] East North Central East North Central [Member] East North Central [Member] West North Central West North Central [Member] West North Central [Member] South Atlantic South Atlantic [Member] South Atlantic [Member] East South Central East South Central [Member] East South Central [Member] West South Central West South Central [Member] West South Central [Member] Mountain Mountain [Member] Mountain [Member] Pacific Pacific [Member] Pacific [Member] Mortgage Loans on Real Estate [Line Items] Mortgage Loans on Real Estate [Line Items] Mortgage Loans Percent of Total Percentage of loan portfolio Percentage Of Loan Portfolio Carrying Amount and Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Fair Value, Measurement Inputs, Disclosure Fair Value, Measurement Inputs, Disclosure [Table Text Block] Transfers of Assets between Level 1 and Level 2 Fair Value Measurments Transfers of Assets between Level 1 and Level 2 Disclosure of the transfers between Level 1 and Level 2 during the period. Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Level 3) Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs Level 3 Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Level 3 Quantitative Sensitivity Analysis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Table Text Block] Significant Accounting Policies [Abstract] Significant Accounting Policies [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Previous Accounting Guidance [Member] Previous Accounting Guidance [Member] Adjustments for New Accounting Pronouncement [Member] Adjustments for New Accounting Pronouncement [Member] Restatement Adjustment [Member] Restatement Adjustment [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Deferral of Acquisition Costs Deferred Policy Acquisition Costs, Additions Amortization of Deferred Acquisition Costs Deferred Policy Acquisition Cost, Amortization Expense Income Tax - Deferred Deferred Income Tax Expense (Benefit) Basic Earnings Per Share, Basic Assuming Dilution Earnings Per Share, Diluted Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other Change in Adjustment to Reserves for Future Policy and Contract Benefits Net of Reinsurance and Other net of tax expense benefit Unrealized adjustment to reserves for future policy and contract benefits for unrealized loss on securities during the period net of the effects of contracts assumed and ceded, net of tax. Change in Foreign Currency Translation Adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Retained Earnings (Accumulated Deficit) Disclosure Mortgage Loans by Property Type [Abstract] Disclosure - Mortgage Loans by Property Type [Abstract] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Mortgage Loans on Real Estate, Name, Property Type [Domain] Mortgage Loans on Real Estate, Name, Property Type [Domain] Apartment Apartment [Member] Apartments [Member] Industrial Industrial Building [Member] Industrial Building [Member] Mixed Mixed Use and Other [Member] Mixed Use and Other [Member] Office Office [Member] Office [Member] Retail Retail [Member] Retail [Member] Other Other Properties [Member] Other Properties [Member] Earnings Per Share, Basic and Diluted [Abstract] Earnings Per Share Disclosure [Table] Schedule of Earnings Per Share, Basic, by Common Class, Including Two Class Method [Table] Earnings Per Share Disclosure [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Denominator (000s) Weighted Average Number of Shares Outstanding, Diluted [Abstract] Weighted Average Common Shares - Basic Weighted Average Number of Shares Outstanding, Basic Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards Weighted Average Number Diluted Shares Outstanding Adjustment Weighted Average Common Shares - Assuming Dilution Weighted Average Number of Shares Outstanding, Diluted Net Income Per Common Share Earnings Per Share [Abstract] Basic Basis of Presentation [Abstract] Basis of Presentation [Abstract] Basis of Presentation Basis of Accounting [Text Block] Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Unum U.S. Unum US [Member] Unum US [Member] Unum U.K. Unum UK [Member] Unum UK [Member] Colonial Life Colonial Life [Member] Colonial Life [Member] Closed Block Closed Block [Member] Closed Block [Member] Products and Services [Axis] Products and Services [Axis] Products and Services [Domain] Products and Services [Domain] Group Long term Disability Group Long term Disability [Member] Group Long Term Disability [Member] Group Short-term Disability Group Short term Disability [Member] Group Short Term Disability [Member] Group Life Group Life [Member] Group Life [Member] Accidental Death & Dismemberment Accidental Death Dismemberment [Member] Accidental Death And Dismemberment [Member] Individual Disability-Recently Issued Individual Disability Recently Issued [Member] Individual Disability Recently Issued [Member] Voluntary Benefits Voluntary Benefits [Member] Voluntary Benefits [Member] Group Long term Disability UK Group Long term Disability UK [Member] Group Long-term Disability - UK [Member] Group Life UK Group Life UK [Member] Group Life - UK [Member] Supplemental and Voluntary UK Supplemental and Voluntary UK [Member] Supplemental and Voluntary - UK [Member] Accident, Sickness, and Disability - Colonial Accident Sickness and Disability Colonial [Member] Accident Sickness And Disability - Colonial [Member] Life Colonial Life Colonial [Member] Life - Colonial [Member] Cancer and Critical Illness - Colonial Cancer and Critical Illness Colonial [Member] Cancer And Critical Illness - Colonial [Member] Individual Disability Closed Block Individual Disability Closed Block [Member] Individual Disability Closed Block [Member] Long-term Care Long term Care [Member] Long Term Care [Member] All Other Segments All Other Segments [Member] Segment Reporting Information [Line Items] Premiums Earned, Net Premiums Earned, Net Stockholders Equity and Earnings Per Common Share Additional Information [Abstract] Disclosure - Stockholders' Equity and Earnings Per Common Share - Additional Information [Abstract] Stockholders Equity Note [Table] Stockholders Equity Note [Table] Stockholders Equity Note [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum [Member] Minimum [Member] Maximum [Member] Maximum [Member] Share Repurchases, Date [Axis] Accelerated Share Repurchases, Date [Axis] Share Repurchases, Date [Domain] Accelerated Share Repurchases, Date [Domain] Share Repurchase Program Expire In August 2012 Share Repurchase Program Expire In August 2012 [Member] Share Repurchase Program Expire In August 2012 [Member] Share Repurchase Program Expire in May 2011 [Member] Share Repurchase Program Expire in May 2011 [Member] Accelerated share repurchase agreement Accelerated share repurchase program [Member] Accelerated Share Repurchase Program [Member] Stockholders Equity Note [Line Items] Stockholders Equity Note [Line Items] Stockholders Equity Note [Line Items] Outstanding stock options, exercise prices range Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Outstanding Nonvested stock awards, grant prices range Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Outstanding Performance restricted stock units, threshold stock price Outstanding Performance restricted stock units threshold stock price Share Based Compensation Arrangement by Share Based Payment Award Performance Restricted Stock Units Threshold Stock Price Antidilutive common shares not included in the computation of dilutive earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Authorized repurchase of common stock, value Stock Repurchase Program, Authorized Amount Treasury Stock Acquired, Shares Treasury Stock, Shares, Acquired Common stock repurchased Treasury Stock, Value, Acquired, Cost Method Shares repurchased cost, Commissions Shares repurchased cost Commissions Fees and Commission Expenses Stock Repurchase Program Remaining Authorized Repurchase Amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Treasury Stock Shares Retired Treasury Stock, Shares, Retired Preferred stock, authorized Preferred Stock, Shares Authorized Preferred stock, par value Preferred Stock, Par or Stated Value Per Share Preferred stock, issued Preferred Stock, Shares Issued Income Statement [Abstract] Revenue Revenues [Abstract] Premium Income Net Investment Income Net Investment Income Realized Investment Gain (Loss) Realized Investment Gains (Losses) [Abstract] Other-Than-Temporary Impairment Loss on Fixed Maturity Securities Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount Other Net Realized Investment Gain (Loss) Gain (Loss) on Investments, Excluding Other than Temporary Impairments Net Realized Investment Gain (Loss) Gain (Loss) on Investments Other Income Other Income Total Revenue Revenues Benefits and Expenses Benefits, Losses and Expenses [Abstract] Benefits and Change in Reserves for Future Benefits Policyholder Benefits and Claims Incurred, Net Commissions Insurance Commissions Interest and Debt Expense Interest and Debt Expense Compensation Expense Labor and Related Expense Other Expenses Other Cost and Expense, Operating Total Benefits and Expenses Benefits, Losses and Expenses Income Before Income Tax Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest Income Tax Income Tax Expense (Benefit) [Abstract] Current Current Income Tax Expense (Benefit) Deferred Total Income Tax Income Tax Expense (Benefit) Net Income Assuming Dilution Mortgage Loans by Applicable Credit Quality Indicators Loan to Value Ratio [Abstract] Disclosure - Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio [Abstract] Accounts, Notes, Loans and Financing Receivable by Receivable Type [Axis] Accounts, Notes, Loans and Financing Receivable by Receivable Type [Axis] Receivable Type [Domain] Receivable Type [Domain] Loan to Value Ratio Below or Equal to 65 Percent Loan to Value Ratio Below or Equal to 65 Percent [Member] Loan to Value Ratio Below or Equal to 65 Percent [Member] Loan To Value Ratio Above 65 To 75 Percent Loan To Value Ratio Above 65 To 75 Percent [Member] Loan To Value Ratio Above 65 To 75 Percent [Member] Loan To Value Ratio Above 75 To 85 Percent Loan To Value Ratio Above 75 To 85 Percent [Member] Loan To Value Ratio Above 75 To 85 Percent [Member] Loan To Value Ratio Above 85 Percent Loan To Value Ratio Above 85 Percent [Member] Loan To Value Ratio Above 85 Percent [Member] Pensions and Other Postretirement Benefits Pension and Other Postretirement Benefits Disclosure [Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis] Schedule of Available-for-sale Securities, Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] States, Municipalities, and Political Subdivisions US States and Political Subdivisions Debt Securities [Member] Foreign Government Debt Securities Foreign Government Debt Securities [Member] Public Utilities Public Utility, Bonds [Member] Mortgage/Asset-backed Securities Asset-backed Securities [Member] All Other Corporate Bonds All Other Corporate Bonds [Member] Redeemable Preferred Stocks Redeemable Preferred Stock [Member] Equity Securities Equity Securities [Member] Embedded Derivative in Modified Coinsurance Arrangement Embedded Derivative Financial Instruments [Member] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fixed Maturity Securities Available for Sale Abstract [Abstract] Available for Sale Abstract [Abstract] Beginning of Year Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value Earnings Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Other Comprehensive Income or Loss 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 Level 3 Transfers Into Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Level 3 Transfers Out of Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 End of Year Mortgage Loans Sorted by Applicable Credit Quality Indicators Internal Rating [Abstract] Disclosure - Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal rating [Abstract] Payment and Performance Risk (Credit Rating) [Axis] Payment and Performance Risk (Credit Rating) [Axis] Credit Rating [Domain] Credit Rating [Domain] Aa AA Credit Rating [Member] AA Credit Rating [Member] A A Credit Rating [Member] A Credit Rating [Member] Baa Baa Credit Rating [Member] Baa Credit Rating [Member] Ba Ba Credit Rating [Member] Ba Credit Rating [Member] B B Credit Rating [Member] B Credit Rating [Member] Location of Gains and Losses on Derivative Financial Instruments Designated as Cash Flow Hedging Instruments [Abstract] Disclosure - Location of Gains and Losses on Derivative Financial Instruments Designated as Cash Flow Hedging Instruments [Abstract] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instrument Risk [Axis] Derivative Instrument Risk [Axis] Derivative Contract Type [Domain] Derivative Contract Type [Domain] Interest Rate Swaps and Forwards Interest Rate Swap [Member] Foreign Exchange Contracts Foreign Exchange Contract [Member] Derivative Instruments, Gain (Loss) by Income Statement Location [Axis] Derivative Instruments, Gain (Loss) by Income Statement Location [Axis] Income Statement and Other Comprehensive Income (Loss) Location [Domain] Income Statement and Other Comprehensive Income (Loss) Location [Domain] Net Investment Income Investment Income [Member] Net Realized Investment Gain (Loss) Net Realized Investments Gain Loss [Member] Net Realized Investments Gain (Loss) [Member] Interest and Debt Expenses Interest and Debt Expenses [Member] Interest and Debt Expense [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Gain (Loss) Recognized in OCI on Derivatives (Effective Portion) Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion) Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Loss) [Member] Treasury Stock Treasury Stock [Member] Balance at Beginning of Year Common Stock Activity Stock Issued During Period, Value, New Issues Retirement of Repurchased Common Shares Stock Repurchased and Retired During Period, Value All Other Changes During Year Other Comprehensive Income (Loss), Net of Tax Dividends to Stockholders (per common share: $0.34; $0.29) Dividends, Cash Purchases of Treasury Stock Balance at End of Period Investments Additional Information [Abstract] Disclosure - Investments - Additional Information [Abstract] Schedule of Investments [Table] Schedule of Investments [Table] External Credit Rating, Investment Grade External Credit Rating, Investment Grade [Member] External Credit Rating, Non Investment Grade External Credit Rating, Non Investment Grade [Member] Summary of Investments, Other than Investments in Related Parties, by Type [Axis] Summary of Investments, Other than Investments in Related Parties, by Type [Axis] Summary of Investments, by Type [Domain] Summary of Investments, by Type [Domain] Bonds Bonds [Member] Nonredeemable Preferred Stock Nonredeemable Preferred Stock [Member] Partnership Interest Partnership Interest [Member] Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entities by Classification of Entity [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Partnership Interests In Tax Credit Investments Partnership Interests In Tax Credit Investments [Member] Partnership Interests In Tax Credit Investments [Member] Equity Method Investments Equity Method Investments [Member] Financing Receivable, Recorded Investment, by Class of Financing Receivable [Axis] Financing Receivable, Recorded Investment, Class of Financing Receivable [Domain] Nonperforming Financing Receivable [Member] Schedule of Investments [Line Items] Schedule of Investments [Line Items] Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Fair value of fixed maturity securities, investment grade Available-for-sale Securities, Debt Securities Fair value of fixed maturity securities, gross unrealized gain Available-for-sale Securities, Gross Unrealized Gains Fair Value of fixed maturity securities, gross unrealized loss Available-for-sale Securities, Gross Unrealized Losses Fixed maturity securities in unrealized loss position, percent of total Fixed maturity securities in unrealized loss position percent of total This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities expressed as a percentage. Number of fixed maturity securities that were in an unrealized loss position Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Number of fixed maturity securities in an unrealized loss position continuously for over one year Number of fixed maturity securities in an unrealized loss position continuously for over one year Available for Sale Securities Continuous Unrealized Loss Position, 12 Months Or Longer, Number of Positions Defaults on securities not OTTI Defaults on securities not OTTI Defaults on securities not OTTI Commitment to fund private placement fixed maturity securities Commitment to fund private placement fixed maturity securities Amount of non-binding funding commitments for private placement securities. Carrying amount of variable interest entity investments Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets Unfunded commitment to fund Investment Partnerships Unfunded commitment to fund tax credit partnership investments Unfunded Commitments and Standby Letters of Credit Commitment to fund partnership Equity Investments Commitment to fund partnership Equity Investments Commitment To Fund Partnership Equity Investments Commitment to fund SPE - consolidated Commitment to fund SPE - consolidated Commitment to fund SPE - consolidated Mortgage Loan policy is not to exceed a loan-to-value ratio, percent Loan to value ratio maximum Loan To Value Ratio Maximum Mortage Loan Policy Debt Service coverage ratio lower range Mortage Loan Policy Debt Service coverage ratio lower range Mortage Loan Policy Debt Service coverage ratio lower range Mortgage Loans issuance, term years Mortgage loan policy, amortization period Mortgage loan policy, amortization period Impaired Financing Receivable, Average Recorded Investment Impaired Financing Receivable, Average Recorded Investment Interest income recognized on mortgage loans subsequent to impairment Impaired Financing Receivable, Interest Income, Accrual Method realized loss on foreclosure realized loss on foreclosure realized loss on foreclosure Financing Receivable, Recorder Investment, Nonaccrual status Count of Financing Receivable, Recorded Investment, Nonaccrual status Number (Count) of Financing Receivable, Recorded Investment, Nonaccrual status Amount of days past due-DelinquentMortgageLoan Amount of days past due-DelinquentMortgageLoan Amount of days past due-DelinquentMortgageLoan Financing Receivable, Recorded Investment, 60 to 89 Days Past Due Financing Receivable, Recorded Investment, 60 to 89 Days Past Due Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due commitment to fund commercial mortgage loans commitment to fund commercial mortgage loans commitment to fund commercial mortgage loans Repurchase agreements - Typical Days outstanding Repurchase Agreements, Maturities Minimum percent of the fair value of securities loaned or securities purchased under repurchase agreements be maintained as collateral Collateral Requirements Minimum Percentage Collateral To Fair Value Of Securities Loaned Or Purchased Under Repurchase Agreements Collateral Requirements, Minimum Percentage, Collateral To Fair Value Of Securities Loaned Or Purchased Under Repurchase Agreements Securities Loaned Securities Loaned Cash Collateral for Borrowed Securities Cash Collateral for Borrowed Securities Securities Received as Collateral Securities Received as Collateral Outstanding Repurchase Agreements Securities Sold under Agreements to Repurchase Reconciliation of Total Operating Revenue and Operating Income by Segment to Revenue and Net Income Reconciliation of Revenue from Segments to Consolidated [Table Text Block] Premium Income by Major Line of Business within Each Segment Revenue from External Customers by Products and Services [Table Text Block] Selected Operating Statement Data by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Assets by Segment Reconciliation of Assets from Segment to Consolidated [Table Text Block] Schedule of Impaired Financing Receivable [Table] Impaired Financing Receivable [Axis] Impaired Financing Receivable [Axis] Impaired Financing Receivable [Axis] Impaired Financing Receivable [Domain] Impaired Financing Receivable [Domain] Impaired Financing Receivable [Domain] Impaired Financing Receivable with No related allowance [Axis] Impaired Financing Receivable with No Related Allowance [Axis] Impaired Financing Receivable with No Related Allowance [Domain] Impaired Fin Receivables with No Related Allowance [Member] Impaired Fin Receivables with No Related Allowance [Member] Impaired Financing Receivable with Related Allowance [Axis] Impaired Financing Receivable with Related Allowance [Domain] Impaired Fin Receivables with Allowance [Member] Impaired Fin Receivables with Related Allowance [Member] Recorded Investment Impaired Financing Receivable, Recorded Investment Unpaid Principal Balance Impaired Financing Receivable, Unpaid Principal Balance Related Allowance Impaired Financing Receivable, Related Allowance Commitments and Contingent Liabilities Additional Information [Abstract] Disclosure - Commitments and Contingent Liabilities - Additional Information [Abstract] Commitments and Contingencies Disclosure [Table] Commitments and Contingencies Disclosure [Table] Commitments and Contingencies Disclosure [Table] Loss Contingencies by Nature of Contingency Loss Contingencies by Nature of Contingency [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Commitments and Contingencies Disclosure [Line Items] Commitments and Contingencies Disclosure [Line Items] Commitments and Contingencies Disclosure [Line Items] States involved in unclaimed property examination States involved in unclaimed property examination States involved in unclaimed property examination Insurers requested to cross-check benefits Insurers requested to cross-check benefits Insurers requested to cross-check benefits Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Other [Abstract] Other [Abstract] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Issuance of Debt [Member] Issuance of Debt [Member] Unsecuredseniornotes5point75percentdue2042 [Member] Unsecuredseniornotes5point75percentdue2042 [Member] Unsecuredseniornotes5point75percentdue2042 [Member] Long-term Debt [Member] Long-term Debt [Member] Northwind Holdings LLC [Member] Northwind Holdings LLC [Member] Northwind Holdings LLC [Member] Tailwind Holdings LLC [Member] Tailwind Holdings LLC [Member] Tailwind Holdings LLC [Member] 2010 UK Tax Rate 2010 UK Tax Rate 2010 UK Tax Rate 2011 New UK Tax rate 2011 New UK Tax rate 2011 New Tax rate Long-term Debt Long-term Debt Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Repayments of Long-term Debt Unrecognized Tax Benefits Unrecognized Tax Benefits Unrecognized Tax Benefits, Period Increase (Decrease) Unrecognized Tax Benefits, Period Increase (Decrease) Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Unrecognized Tax Benefits Reasonably Possible Decreases Resulting from Settlements with Taxing Authorities Unrecognized Tax Benefits Reasonably Possible Decreases Resulting from Settlements with Taxing Authorities Unrecognized Tax Benefits, Reasonably Possible Decreases Resulting From Settlements With Taxing Authorities 2012 UK Tax rate - old 2012 UK Tax rate - old 2012 UK Tax rate - old 2012 UK Tax rate - new 2012 UK Tax rate - new 2012 UK Tax rate - new Ultimate UK Tax rate Ultimate UK Tax rate Ultimate UK Tax rate UK Tax Rate - 2013 UK Tax Rate - 2013 UK Tax Rate - 2013 Income Tax Reconciliation, Change in Enacted Tax Rate Income Tax Reconciliation, Change in Enacted Tax Rate Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax [Abstract] Change in Net Unrealized Gain on Securities Before Reclassification Adjustment: Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax [Abstract] Change in Net Unrealized Gain on Securities Not Other-Than-Temporarily Impaired (net of tax expense of $303.1; $599.6; $496.5; $754.9) Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Change in Net Unrealized Gain on Securities Other-Than-Temporarily Impaired (net of tax benefit of $-; $-; $-; $1.1) Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Available-for-sale Securities Total Change in Net Unrealized Gain on Securities Before Reclassification Adjustment (net of tax expense of $303.1; $599.6; $496.5; $753.8) Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax Reclassification Adjustment for Net Realized Investment Gain (net of tax expense of $1.4; $3.4; $2.0; $4.6) Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax Change in Net Gain on Cash Flow Hedges (net of tax expense (benefit) of ($6.0); $34.7; ($5.3); $32.0) Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Change in Adjustment to Reserves for Future Policy and Contract Benefits, Net of Reinsurance and Other (net of tax benefit of $213.5; $377.6; $344.0; $498.8) Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense of $3.5; $2.8; $11.0; $6.9) Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax Total Other Comprehensive Income Comprehensive Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Timing of Anticipated Settlements of Interest Rate Swaps Outstanding [Abstract] Disclosure - Timing of Anticipated Settlements of Interest Rate Swaps Outstanding [Abstract] Derivative [Table] Derivative [Table] Derivative, by Nature [Axis] Derivative, by Nature [Axis] Derivative, Name [Domain] Derivative, Name [Domain] 2012 Forecasted in 2012 [Member] Forecasted in 2012 [Member] 2013 Forecasted in 2013 [Member] Forecasted in 2013 [Member] Receive Fixed/Pay Variable Derivative Financial Instruments Receive Fixed Pay Variable [Member] Derivative Financial Instruments, Receive Fixed Pay Variable [Member] Derivative [Line Items] Derivative [Line Items] Notional Amount of Derivatives Notional Amount of Derivatives Weighted Average Receive Rate Derivative Weighted Average Receive Rate Derivative, Weighted Average Receive Rate Weighted Average pay rate Derivative Weighted Average Pay Rate Derivative, Weighted Average Pay Rate Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position [Abstract] Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position [Abstract] Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] United States Government and Government Agencies and Authorities US Government and Government Agencies and Authorities [Member] Schedule of Available-for-sale Securities [Line Items] Schedule of Available-for-sale Securities [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 Gross Unrealized Loss Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses 12 Months or Greater Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 12 Months or Greater Gross Unrealized Loss Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses Segment Information Segment Reporting Disclosure [Text Block] Realized Investment Gains and Losses Reported in Consolidated Statements of Income [Abstract] Disclosure - Realized Investment Gains and Losses Reported in Consolidated Statements of Income [Abstract] Schedule of Gain (Loss) on Investments [Table] Schedule of Gain (Loss) on Investments [Table] Gain (Loss) on Investments by Category [Axis] Gain (Loss) on Investments, Including Marketable Securities and Investments Held at Cost, Categories of Investments [Domain] Gain (Loss) on Investments [Line Items] Gain (Loss) on Investments [Line Items] Gross Gains on Sales Available-for-sale Securities, Gross Realized Gains Gross Losses on Sales Available-for-sale Securities, Gross Realized Losses Other-Than-Temporary Impairment Loss Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net Gross Gains on Sales Other Investments Gross Realized Gains This item represents the gross profit realized on the sale of investments not otherwise specified in the taxonomy Gross Losses on Sales Other Investments Gross Realized Losses This item represents the gross loss realized on the sale of investments not otherwise specified in the taxonomy Impairment Loss Other than Temporary Impairment Losses, Investments Foreign Currency Transactions Foreign Currency Transaction Gain (Loss), before Tax Notional Amounts for Each Category of Derivative Activity [Abstract] Disclosure - Notional Amounts for Each Category of Derivative Activity [Abstract] Swaps Swap [Member] Forwards Forward Contracts [Member] Receive Variable/Pay Fixed Derivative Financial Instruments Receive Variable Pay Fixed [Member] Derivative Financial Instruments, Receive Variable Pay Fixed [Member] Receive Fixed/Pay Fixed Derivative Financial Instruments Receive Fixed Pay Fixed [Member] Derivative Financial Instruments, Receive Fixed Pay Fixed [Member] Balance at beginning of period Additions Notional Amount Of Derivatives Additions Notional Amount Of Derivatives, Additions Terminations Notional Amount Of Derivatives Terminations Notional Amount Of Derivatives, Terminations Balance at ending of period Corporate Corporate and Other [Member] Corporate and Other [Member] Operating Revenue Segment Reporting Information, Revenue for Reportable Segment Operating Income (Loss) Operating Income (Loss) Disclosure Before Tax Credit Related Portion of Other Than Temporary Impairments on Fixed Maturity Securities Still Held and Recognized in Other Comprehensive Income [Abstract] Disclosure - Before-Tax Credit Related Portion of Other-Than-Temporary Impairments on Fixed Maturity Securities Still Held and Recognized in Other Comprehensive Income [Abstract] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Schedule of Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items] Balance at Beginning of Year Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held Sales or Maturities of Securities in the Period Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold Balance at End of Year Other Items Disclosure Other Items Disclosure [Text Block] Other Items Disclosure. Disclosure Fair Value Measurements by Input Level [Abstract] Disclosure - Fair Value Measurements by Input Level [Abstract] Fair Value, Measurement Inputs, Disclosure [Table] Fair Value, Measurement Inputs, Disclosure [Table] Fair Value, Measurement Inputs, Disclosure [Table] Fair Value, Measurement Inputs, Disclosure [Line Items] Fair Value, Measurement Inputs, Disclosure [Line Items] Fair Value, Measurement Inputs, Disclosure [Line Items] Fixed Maturity Securities Available-for-sale Securities, Fair Value Disclosure Other Long-term Investments Other Investments [Abstract] Derivative Assets Equity Securities Marketable Securities, Equity Securities Other Liabilities Other Liabilities, Unclassified [Abstract] Derivative Liabilities Location and Fair Values of Derivative Financial Instruments [Abstract] Disclosure - Location and Fair Values of Derivative Financial Instruments [Abstract] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Derivatives, Fair Value, by Balance Sheet Location [Axis] Derivatives, Fair Value, by Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Long term Investments Other Long-term Investments [Member] Other Liabilities Other Liabilities [Member] Notional Amount of Interest Rate Derivatives Notional Amount of Interest Rate Derivatives Asset Derivatives Fair Value Derivative Asset, Fair Value, Gross Asset Liability Derivatives Fair Value Derivative Liability, Fair Value, Gross Liability Accounting Developments [Abstract] Accounting Developments [Abstract] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Domain] Adjustments for Change in Accounting Principle [Domain] Impact of Restatement on Opening Stockholders Equity, Net of Tax Impact of Restatement on Opening Retained Earnings, Net of Tax Distribution of the Maturity Dates for Fixed Maturity Securities [Abstract] Disclosure - Distribution of the Maturity Dates for Fixed Maturity Securities [Abstract] Gain (Loss) on Investments by Category [Axis] Gain (Loss) on Investments, Including Marketable Securities and Investments Held at Cost, Categories of Investments [Domain] Available-for-Sale Securities, Unrealized Gain Position, Fair Value Available for Sale Securities Unrealized Gain Position Fair Value [Member] Available For Sale Securities Gross Unrealized Gain [Member] Available-for-Sale Securities, Unrealized Loss Position, Fair Value Available for Sale Securities Unrealized Loss Position Fair Value [Member] Available For Sale Securities Gross Unrealized Loss [Member] Available-for-Sale Securities, Total Amortized Cost Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract] 1 year or less Available-for-sale Securities, Debt Maturities, within One Year, Amortized Cost Basis Over 1 year through 5 years Available-for-sale Securities, Debt Maturities, after One Through Five Years, Amortized Cost Basis Over 5 years through 10 years Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis Over 10 years Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Available-for-sale Securities, Debt Maturities, Gross Subtotal Available for sale Securities Debt Maturities Amortized Cost Gross Subtotal Available-for-sale Securities, Debt Maturities, Amortized Cost, Gross Subtotal Mortgage/Asset-Backed Securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis Total Fixed Maturity Securities Available-for-Sale Securities, Unrealized Gain Position, Gross Gain Available for Sale Securities Unrealized Gain Position Gross Gain Available-For-Sale Securities, Debt Maturities Unrealized Gain Position Gross Gain Abstract 1 year or less Available For Sale Securities Debt Maturities Within One Year Unrealized Gain Position Gross Gain Available-For-Sale Securities, Debt Maturities Within One Year Unrealized Gain Position Gross Gain Over 1 year through 5 years Available For Sale Securities Debt Maturities After One Through Five Years Unrealized Gain Position Gross Gain Available-For-Sale-Securities, Debt Maturities After One Through Five Years Unrealized Gain Position Gross Gain Over 5 years through 10 years Available For Sale Securities Debt Maturities After Five Through Ten Years Unrealized Gain Position GrossGain Available-For-Sale Securities, Debt Maturities After Five Through Ten Years Unrealized Gain Position GrossGain Over 10 years Available For Sale Securities Debt Maturities After Ten Years Unrealized Gain Position Gross Gain Available-For-Sale, Securities Debt Maturities After Ten Years Unrealized Gain Position Gross Gain Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal, Total Available For Sale Securities Debt Maturities Unrealized Gain Position Gross Gain Gross Subtotal Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal Mortgage/Asset-Backed Securities Available For Sale Securities Debt Maturities Without Single Maturity Date Unrealized Gain Position Gross Gain Available-For-Sale Securities, Debt Maturities Without Single Maturity Date Unrealized Gain Position Gross Gain Total Fixed Maturity Securities Available for sale Securities, Debt Maturities Unrealized Gain Position Gross Gain Available for sale Securities, Debt Maturities Unrealized Gain Position Gross Gain Fair Value Maturity Distribution [Abstract] Fair Value Maturity Distribution [Abstract] 1 year or less Available-for-sale Securities, Debt Maturities, within One Year, Fair Value Over 1 year through 5 years Available-for-sale Securities, Debt Maturities, after One Through Five Years, Fair Value Over 5 years through 10 years Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Fair Value Over 10 years Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal, Total Available for sale Securities Debt Maturities Fair Value Gross Subtotal Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal Mortgage/Asset-Backed Securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value Total Fixed Maturity Securities Available-for-Sale Securities, Unrealized Loss Position, Gross Loss Available for Sale Securities Unrealized Loss Position Gross Loss Available-For-Sale Securities, Debt Maturities Unrealized Loss Position Gross Loss Abstract 1 year or less Available For Sale Securities Debt Maturities Within One Year Unrealized Loss Position Gross Loss Available-For-Sale Securities, Debt Maturities Within One Year Unrealized Loss Position Gross Loss Over 1 year through 5 years Available For Sale Securities Debt Maturities After One Through Five Years Unrealized Loss Position Gross Loss Available-For- Sale Securities, Debt Maturities After One Through Five Years Unrealized Loss PositionGrossLoss Over 5 years through 10 years Available For Sale Securities Debt Maturities After Five Through Ten Years Unrealized Loss PositionGross Loss Available-For-Sale Securities, Debt Maturities After Five Through Ten Years Unrealized Loss PositionGross Loss Over 10 years Available For Sale Securities Debt Maturities After Ten Years Unrealized Loss Position Gross Loss Available-For-Sale Securities, Debt Maturities After Ten Years Unrealized Loss Position Gross Loss Available-For-Sale Securities, Debt Maturities Unrealized Loss Position, Gross Loss, Gross Subtotal, Total Available For Sale Securities Debt Maturities Unrealized Gain Position Gross Loss Gross Subtotal Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Loss, Gross Subtotal Mortgage/Asset-Backed Securities Available For Sale Securities Debt Maturities Without Single Maturity Date Unrealized Loss Position Gross Loss Available-For-Sale Securities, Debt Maturities Without Single Maturity Date Unrealized Loss Position Gross Loss Total Fixed Maturity Securities Available For Sale Securities Unrealized Loss Position Gross Loss Subtoatl Available-For-Sale Securities, Unrealized Loss Position Gross Loss Schedule of Financing Receivable, Troubled Debt Restructurings [Table] Schedule of Financing Receivable, Troubled Debt Restructurings [Table] Financing Receivable, Troubled Debt Restructurings that Subsequently Defaulted [Axis] Financing Receivable, Troubled Debt Restructurings that Subsequently Defaulted [Axis] Financing Receivable, Troubled Debt Restructurings that Subsequently Defaulted [Domain] Financing Receivable, Troubled Debt Restructurings that Subsequently Defaulted [Domain] Commercial Real Estate Portfolio Segment [Member] Commercial Real Estate Portfolio Segment [Member] Financing Receivable, Modifications [Line Items] Financing Receivable, Modifications [Line Items] Carrying Amount Troubled Debt Restructuring, Debtor, Other Financing Receivables, modifications, number of contracts Financing Receivables, modifications, number of contracts Financing Receivables, modifications, number of contracts Net Income Per Common Share Schedule of Earnings Per Share Reconciliation [Table Text Block] New Accounting Pronouncements and Changes in Accounting Principles [Abstract] Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Fair Values of Financial Instruments Fair Value Disclosures [Text Block] Segment Reporting Information [Line Items] Assets Fair Value, by Balance Sheet Grouping [Table] Carrying Amount Carrying (Reported) Amount, Fair Value Disclosure [Member] Fair Value Portion at Fair Value, Fair Value Disclosure [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Derivatives Miscellaneous Long-term Investments Policyholders' Funds Policyholder Funds [Abstract] Deferred Annuity Products Deferred Annuity Products Deferred Annuity Products Supplementary Contracts without Life Contingencies Supplementary Contracts without Life Contingencies Supplementary Contracts Without Life Contingencies Derivatives Embedded Derivative in Modified Coinsurance Arrangement Embedded Derivative, Fair Value of Embedded Derivative Liability Schedule of Available-for-sale Securities Reconciliation Schedule of Available-for-sale Securities Reconciliation [Table Text Block] Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position Schedule of Unrealized Loss on Investments [Table Text Block] Distribution of the Maturity Dates for Fixed Maturity Securities Investments Classified by Contractual Maturity Date [Table Text Block] Credit Losses Remaining in Retained Earnings Related to Adoption of Accounting Standard Other than Temporary Impairment, Credit Losses Recognized in Earnings [Table Text Block] Mortgage Loans by Property Type Mortgage Loans by Property Type Text Block Schedule Of Mortgage Loans By Property Type Text Block Mortgage Loans by Geographic Region Mortgage Loans on Real Estate, Geographic Location of Property Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal Rating Mortgage Loans Sorted by Applicable Credit Quality Indicators Internal Rating Schedule Of Mortgage Loans By Credit Rating Text Block Mortgage Loans by Applicable Credit Quality Indicators Loan to Value Ratio Mortgage Loans by Applicable Credit Quality Indicators Loan to Value Ratio Schedule Of Mortgage Loans To Value Ratio Text Block Activity in the Allowance for Credit Losses Allowance for Credit Losses on Financing Receivables [Table Text Block] Impaired Mortgage Loans Impaired Financing Receivables [Table Text Block] Troubled Debt Restructurings Troubled Debt Restructurings on Financing Receivables [Table Text Block] Realized Investment Gains and Losses Reported in Consolidated Statements of Income Gain (Loss) on Investments [Table Text Block] Derivative Financial Instruments Additional Information [Abstract] Disclosure - Derivative Financial Instruments - Additional Information [Abstract] Forward Starting interest rate swap on anticipation of issuance of LT debt [Member] Forward Starting interest rate swap on anticipation of issuance of LT debt [Member] Current credit exposure on derivatives Current credit exposure on derivatives Loss Exposure on derivatives Cash collateral from counterparties Derivative, Collateral, Obligation to Return Cash Carrying value of fixed maturity securities posted as collateral to our counterparties Available-for-sale Securities Pledged as Collateral Cash Collateral to counterparties Derivative, Collateral, Right to Reclaim Cash Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position Derivative, Net Liability Position, Aggregate Fair Value Notional Amount of forward starting interest rate swaps Notional Amount of Interest Rate Cash Flow Hedge Derivatives Notional amount of foreign currency cash flow hedges Notional Amount of Foreign Currency Cash Flow Hedge Derivatives Notional Amount Of Derivatives Terminations Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Notional amount of receive variable, pay fixed interest rate swaps to hedge changes in fair value of certain fixed rate securities held Notional Amount of Interest Rate Fair Value Hedge Derivatives Hedged benchmark interest rate, on the related interest rate swaps Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments Notional Amount of receive fixed, pay variable interest rate swap Notional Amount of Fair Value Hedge Instruments Notional Amounts for Each Category of Derivative Activity Schedule of Derivative Instruments [Table Text Block] Timing of Anticipated Settlements of Interest Rate Swaps Outstanding Schedule of Interest Rate Derivatives [Table Text Block] Location and Fair Values of Derivative Financial Instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Location of and Gains and Losses on Derivative Financial Instruments Designated as Cash Flow Hedging Instruments Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block] Location of and Gain (Loss) on Embedded Derivative in a Modified Coinsurance Arrangement Location of and Gain Loss on Embedded Derivative in a Modified Coinsurance Arrangement The Tabular disclosure of the location of the gain (loss) of embedded derivative. Pension and Other Postretirement Benefits Disclosure [Table] Pension and Other Postretirement Benefits Disclosure [Table] Pension and Other Postretirement Benefits Disclosure [Table] United Kingdom, Pounds Pension and Other Postretirement Benefits Disclosure [Line Items] Pension and Other Postretirement Benefits Disclosure [Line Items] Pension and Other Postretirement Benefits Disclosure [Line Items] Defined Benefit Plan, Contributions by Employer Defined Benefit Plan, Contributions by Employer Reconciliation of Revenue from Segments to Consolidated [Table] Reconciliation of Revenue from Segments to Consolidated [Table] Segment Reporting, Revenue Reconciling Item [Line Items] Segment Reporting, Revenue Reconciling Item [Line Items] Operating Revenue by Segment Net Realized Investment Gain (Loss) Revenue Operating Income by Segment Net Realized Investment Gain (Loss) Non-operating Retirement-related Loss Income Tax Disclosure Activity in Allowance for Credit Losses [Abstract] Disclosure - Activity in Allowance for Credit Losses [Abstract] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Balance at Beginning of Year Financing Receivable, Allowance for Credit Losses Provisions Financing Receivable, Allowance for Credit Losses, Provisions Charge-offs, Net of Recoveries Financing Receivable, Allowance for Credit Losses, Charge-offs Balance at End of Period Transfers of Assets between Level 1 and Level 2 [Abstract] Disclosure - Transfers of Assets between Level 1 and Level 2 [Abstract] Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Level 1 from Level 2 Fair Value, Level 2 to level 1 Transfers, Amount Level 2 from Level 1 Fair Value, Level 1 to level 2 Transfers, Amount Available-for-sale Securities, Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross Unrealized Gain Gross Unrealized Loss Fixed Maturity Securities Commitments and Contingent Liabilities Commitments and Contingencies Disclosure [Text Block] Fair Value of Financial Instruments [Abstract] Fair Value of Financial Instruments [Abstract] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Table] Fair Value by Measurement Basis [Axis] Fair Value by Measurement Basis [Axis] Estimate of Fair Value, Fair Value Disclosure [Member] Estimate of Fair Value, Fair Value Disclosure [Member] Public_Utilities [Member] Public_Utilities [Member] Public_Utilities [Member] Corporate Bond Securities Corporate Bond Securities [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items] Fixed Maturity Securities Level 3 quantitative analysis - fair value of fixed maturity securities Level 3 quantitative analysis - fair value of fixed maturity securities Equity Securities Level 3 quantitative analysis - fair value of equity securities Level 3 quantitative analysis - fair value of equity securities Embedded Derivative, Fair Value of Embedded Derivative Liability Level 3 quantitative analysis - fair value of embedded derivatives Level 3 quantitative analysis - fair value of embedded derivatives Fair Value, Investments, Valuation Techniques Fair Value, Investments, Valuation Techniques Fair Value, Derivative Financial Instruments, Liabilities, Valuation Techniques Fair Value, Derivative Financial Instruments, Liabilities, Valuation Techniques Investments, Fair Value Disclosure, Significant Assumptions Investments, Fair Value Disclosure, Significant Assumptions Location of and Gain Loss on Embedded Derivative in a Modified Coinsurance Arrangement [Abstract] Disclosure - Location of and Gain (Loss) on Embedded Derivative in a Modified Coinsurance Arrangement [Abstract] Accounting Developments Accounting Changes and Error Corrections [Text Block]