Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Loss) [Table] Equity Components Equity Components [Axis] Equity Component Equity Component [Domain] Net Unrealized Gain on Securities Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Net Gain on Cash Flow Hedges Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Foreign Currency Translation Adjustment Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Unrecognized Pension and Postretirement Benefit Costs Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) [Line Items] Balance at Beginning of Year Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts Reclassified from Accumulated Other Comprehensive Income or Loss Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Net Other Comprehensive Income (Loss) Other Comprehensive Income (Loss), Net of Tax Balance at End of Year Condensed Financial Information of Parent Company Only Disclosure [Abstract] Condensed Cash Flow Statement Condensed Cash Flow Statement [Table] Consolidated Entities Consolidated Entities [Axis] Consolidated Entities Consolidated Entities [Domain] Parent Company Parent Company [Member] Condensed Cash Flow Statements, Captions Condensed Cash Flow Statements, Captions [Line Items] 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 Cash Distributions to Subsidiaries Payments to Acquire Additional Interest in Subsidiaries Net Purchases of Property and Equipment Payments to Acquire Property, Plant, and Equipment Acquisition of Business Payments to Acquire Businesses, Gross 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] Issuance of Long-term Debt Proceeds from Issuance of Long-term Debt Long-term Debt Repayment 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 Net Increase (Decrease) in Cash and Bank Deposits Cash and Cash Equivalents, Period Increase (Decrease) Mortgage Loans Sorted by Applicable Credit Quality Indicators Internal Rating [Abstract] Disclosure - Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal rating [Abstract] Mortgage Loans on Real Estate Schedule Mortgage Loans on Real Estate Schedule [Table] Internal Credit Assessment Internal Credit Assessment [Axis] Internal Credit Assessment Internal Credit Assessment [Domain] Aa Credit Rating AA Credit Rating [Member] AA Credit Rating [Member] A Credit Rating A Credit Rating [Member] A Credit Rating [Member] Baa Credit Rating Baa Credit Rating [Member] Baa Credit Rating [Member] Ba Credit Rating Ba Credit Rating [Member] Ba Credit Rating [Member] 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] Mortgage Loans on Real Estate Mortgage Loans on Real Estate [Line Items] Mortgage Loans Mortgage Loans on Real Estate, Commercial and Consumer, Net Retirement Benefits [Abstract] Pension and Other Postretirement Benefits Disclosure Pension and Other Postretirement Benefits Disclosure [Text Block] Statutory Financial Information [Abstract] Statutory Financial Information [Abstract] Statutory Accounting Practices Statutory Accounting Practices [Table] Legal Entity Legal Entity [Axis] Legal Entity Entity [Domain] Fairwind Insurance Company Fairwind Insurance Company [Member] Fairwind Insurance [Member] Unum Limited Unum Limited [Member] Unum Limited [Member] Traditional U.S. Life Insurance Subsidiaries United States Traditional Insurance Subsidiaries [Member] United States Traditional Insurance Subsidiaries [Member] Statutory Accounting Practices Statutory Accounting Practices [Line Items] Statutory Accounting Practices, Permitted Practice, Amount Statutory Accounting Practices, Permitted Practice, Amount Statutory Net Income Statutory Accounting Practices, Statutory Net Income Amount Statutory Combined Capital and Surplus Statutory Accounting Practices, Statutory Capital and Surplus, Balance Statutory Accounting Practices, Statutory Amount Available for Dividend Payments Statutory Accounting Practices, Statutory Amount Available for Dividend Payments Cash and Securities Segregated under Federal and Other Regulations Cash and Securities Segregated under Federal and Other Regulations Segment Reporting [Abstract] Number of Operating Segments Number of Operating Segments Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Segments Segments [Axis] Segments Segments [Domain] Unum US and Colonial Unum US and Colonial [Member] Unum US and Colonial [Member] Unum US Unum US [Member] Unum US [Member] Colonial Life Colonial Life [Member] Colonial Life [Member] Unum UK Unum UK [Member] Unum UK [Member] Payment Increments Payment Increments [Axis] Payment Increments [Axis] Payment Increments [Domain] Payment Increments [Domain] [Domain] for Payment Increments [Axis] Payable due 18 Months After Acquisition Payable due 18 Months After Acquisition [Member] Payable due 18 Months After Acquisition [Member] Payable due 24 Months After Acquisition Payable due 24 Months After Acquisition [Member] Payable due 24 Months After Acquisition [Member] Supplementary Insurance Information, by Segment Supplementary Insurance Information, by Segment [Line Items] Percentage Ownership of Acquired Business Business Acquisition, Percentage of Voting Interests Acquired Name of Acquired Businesses Business Acquisition, Name of Acquired Entity Total Cash Purchase Price to Acquire Business Business Combination, Contingent Consideration, Liability, Noncurrent Business Combination, Contingent Consideration, Liability, Noncurrent Assets of Acquiree at Acquisition Date Total Acquiree Assets Purchased Total Acquiree Assets Purchased Liabilities of Acquiree at Acquisition Date Total Acquiree Liabilities Purchased Total Acquiree Liabilities Purchased Goodwill at Acquisition Date Goodwill at Acquisition Date Goodwill at Acquisition Date Percent of Goodwill Allocated to a Business Segment Percent of Goodwill Allocated to a Business Segment Percent of Goodwill Allocated to a Business Segment Goodwill Goodwill Notes to Financial Statements [Abstract] Notes to Financial Statements [Abstract] Amortized Cost and Fair Values of Securities by Security Type 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] Low Income Housing Tax Credits Activity in Affordable Housing Program Obligation [Table Text Block] Mortgage Loans by Property Type and Geographic Region Mortgage Loans by Property Type and Geographic Regioin [Table Text Block] Mortgage Loans by Property Type and Geographic Region [Table Text Block] Mortgage Loans by Credit Quality Indicators Financing Receivable Credit Quality Indicators [Table Text Block] Remaining Contractual Maturity of Securities Lending Agreements Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Table Text Block] Schedule of Financial Instrument and Derivative Offsetting Schedule of Financial Instrument and Derivative Offsetting [Table Text Block] Schedule of Financial Instrument and Derivative Offsetting [Table Text Block] Net Investment Income Investment Income [Table Text Block] Realized Investment Gains and Losses Reported in Consolidated Statements of Income Gain (Loss) on Investments [Table Text Block] Investments Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] Employee Benefit Plans Disclosure Pension and Other Postretirement Benefits Disclosure [Table] Pension and Other Postretirement Benefits Disclosure [Table] Retirement Plan Sponsor Location Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location Retirement Plan Sponsor Location [Domain] Domestic Plan Domestic Plan [Member] Foreign Plan Foreign Plan [Member] Range Range [Axis] Range Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Defined Benefit Plan, Asset Categories Defined Benefit Plan, Asset Categories [Axis] Plan Asset Categories Plan Asset Categories [Domain] Equity Securities Equity Securities [Member] Fixed Maturity Securities Debt Securities [Member] Alternative Investments Alternative Investments [Member] Alternative Investments [Member] Diversified Growth Assets Diversified Growth Assets [Member] Diversified Growth Assets [Member] Interest Rate Contract Interest Rate Contract [Member] Private Equity Funds Private Equity Funds [Member] Retirement Plan Type Retirement Plan Type [Axis] Retirement Plan Type Retirement Plan Type [Domain] Pension Plan Pension Plan [Member] Other Postretirement Benefit Plans Other Postretirement Benefits Plan [Member] Pension and Other Postretirement Benefits Disclosure Pension and Other Postretirement Benefits Disclosure [Line Items] Pension and Other Postretirement Benefits Disclosure [Line Items] Plan Amendments Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment Average Remaining Life Expectancy of Plan Participants Average Remaining Life Expectancy of Plan Participants Average Remaining Life Expectancy of Plan Participants Defined Benefit Plan, Target Allocation Percentage Defined Benefit Plan, Target Allocation Percentage Private Equity Partnership Future Liquidation Term Private Equity Partnership Future Liquidation Term Private Equity Partnership Future Liquidation Term 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 Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets Interest Rate During Period Debt Instrument, Interest Rate During Period Health Care Cost Trend Rate Assumed for Next Fiscal Year Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year Ultimate Health Care Cost Trend Rate Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation Future Amortization of Actuarial Gain (Loss) Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year Future Amortization of Prior Service Cost (Credit) Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year Retirement Benefits, Description Retirement Benefits, Description Payment for Pension Benefits Payment for Pension Benefits Matching Contribution Percent of Employees' Gross Pay Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Employer Discretionary Contribution Percentage of earnings Defined Contribution Plan, Employer Discretionary Contribution Percentage of Earnings Defined Contribution Plan, Employer Discretionary Contribution Percentage of Earnings Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions Defined Contribution Plan, Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions Defined Contribution Plan, Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions Employee Contribution Percentage Received 2-for-1 Employer Match Defined Contribution Plan, Employee Contribution Percentage Received 2-for-1 Employer Match Defined Contribution Plan, Employee Contribution Percentage Received 2-for-1 Employer Match Cost Recognized Defined Contribution Plan, Cost Reconciliation of Revenue from Segments to Consolidated Reconciliation of Revenue from Segments to Consolidated [Table] Consolidation Items Consolidation Items [Axis] Consolidation Items Consolidation Items [Domain] Operating Segments Operating Segments [Member] Segment Reporting, Revenue Reconciling Item Segment Reporting, Revenue Reconciling Item [Line Items] Total Revenue Revenues Net Realized Investment Gain (Loss) Gain (Loss) on Investments Adjusted Operating Revenue Operating Revenue Operating Revenue Income Before Income Tax Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Net Realized Investment Gain (Loss) Loss from Guaranty Fund Assessment Loss Related to Guaranty Fund Assessment Loss Related to Guaranty Fund Assessment Unclaimed Death Benefit Reserve Increase Before Taxes Unclaimed Death Benefit Reserve Increase Before Taxes Unclaimed Death Benefit Reserve Increase Before Taxes - the before tax increase adjustment to reserves for unclaimed death benefits. Adjusted Operating Income Operating Income (Loss) Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Schedule of Changes in Projected Benefit Obligations and Fair Value of Plan Assets Schedule of Changes in Projected Benefit Obligations [Table Text Block] Schedule of Amounts Recognized in Balance Sheet Schedule of Amounts Recognized in Balance Sheet [Table Text Block] Schedule of Amounts Recognized in Other Comprehensive Income (Loss) Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Fair Values by Fair Value Hierarchy Input Level Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Schedule of Assumptions Used Schedule of Assumptions Used [Table Text Block] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Schedule of Expected Benefit Payments Schedule of Expected Benefit Payments [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Future Minimum Lease Payments Due Operating Leases, Future Minimum Payments Due Future Minimum Lease Payments Due Within Twelve Months Operating Leases, Future Minimum Payments Due, Next Twelve Months Future Minimum Lease Payments Due Within Two Years Operating Leases, Future Minimum Payments, Due in Two Years Future Minimum Lease Payments Due Within Three Years Operating Leases, Future Minimum Payments, Due in Three Years Future Minimum Lease Payments Due Within Four Years Operating Leases, Future Minimum Payments, Due in Four Years Future Minimum Lease Payments Due Within Five Years Operating Leases, Future Minimum Payments, Due in Five Years Future Minimum Lease Payments Due Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Rental Expense Operating Leases, Rent Expense, Minimum Rentals Total Unfunded Commitments Other Commitment Loss Contingencies [Table] Loss Contingencies [Table] Before or After Tax Before or After Tax [Axis] Before or After Tax [Axis] Before or After Tax Before or After Tax [Domain] [Domain] for Before or After Tax [Axis] Net of Tax Net of Tax [Member] Net of Tax [Member] Litigation Status Litigation Status [Axis] Litigation Status Litigation Status [Domain] Settled Litigation Settled Litigation [Member] Loss Contingency Nature Loss Contingency Nature [Axis] Loss Contingency, Nature Loss Contingency, Nature [Domain] Unfavorable Regulatory Action Unfavorable Regulatory Action [Member] Loss Contingencies Loss Contingencies [Line Items] Loss Contingency, Loss in Period Loss Contingency, Loss in Period Loss Contingency Accrual, Insurance-related Assessment, Premium Tax Offset Loss Contingency Accrual, Insurance-related Assessment, Premium Tax Offset Loss Contingency, Loss in Period, Tax Loss Contingency, Loss in Period, Tax Loss Contingency, Loss in Period, Tax Supplementary Insurance Information [Abstract] Supplementary Insurance Information, for Insurance Companies Disclosure Supplementary Insurance Information, for Insurance Companies Disclosure [Text Block] Supplementary Insurance Information, by Segment Supplementary Insurance Information, by Segment [Table] Closed Block Closed Block [Member] Closed Block [Member] Corporate and Other Segment Corporate and Other [Member] Deferred Acquisition Costs Supplementary Insurance Information, Deferred Policy Acquisition Costs Reserves for Future Policy Contract Benefits Supplementary Insurance Information, Liability for Future Policy Benefits, Losses, Claims and Loss Expense Reserves Unearned Premiums Supplementary Insurance Information, Unearned Premiums Policy and Contract Benefits Supplementary Insurance Information, Other Policy Claims and Benefits Payable Premium Income Supplementary Insurance Information, Premium Revenue Net Investment Income Supplementary Insurance Information, Net Investment Income Benefits and Change in Reserves for Future Benefits Supplementary Insurance Information, Benefits, Claims, Losses and Settlement Expense Amortization of Deferred Acquisition Costs Supplementary Insurance Information, Amortization of Deferred Policy Acquisition Costs All Other Expenses Supplementary Insurance Information, Other Operating Expense Premiums Written Supplementary Insurance Information, Premiums Written Notional Amounts for Each Category of Derivative Activity Schedule of Derivative Instruments [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 Gains and Losses on 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to Interest [Member] Incurred Claims Incurred Claims [Member] Incurred Claims [Member] Foreign Currency Foreign Currency [Member] Foreign Currency [Member] Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] Balance at January 1 Liability for Claims and Claims Adjustment Expense Less Reinsurance Recoverable Reinsurance Recoverables, Incurred but Not Reported Claims Net Balance at January 1 Liability for Unpaid Claims and Claims Adjustment Expense, Net Incurred Related to Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current Year Current Year Claims and Claims Adjustment Expense Prior Years Prior Year Claims and Claims Adjustment Expense Total Incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Paid Related to Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current Year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior Years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total Paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Net Balance at December 31 Plus Reinsurance Recoverable Balance at December 31 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] Deferred Policy Acquisition Costs by Segment Deferred Policy Acquisition Costs [Text Block] Assets by Segment Reconciliation of Assets from Segment to Consolidated [Table Text Block] Reconciliation of Total Revenue and Income Before Income Tax to Adjusted Operating Revenue and Adjusted Operating Income Reconciliation of Revenue from Segments to Consolidated [Table Text Block] Statement of Financial Position [Abstract] Assets Assets [Abstract] Investments Investments [Abstract] Fixed Maturity Securities - at fair value (amortized cost: $39,780.5; $39,552.7) Available-for-sale Securities Policy Loans Loans, Gross, Insurance Policy 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, Including Reinsurance Premium Paid Accrued Investment Income Accrued Investment Income Receivable Deferred Acquisition Costs Deferred Policy Acquisition Costs 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 Tax Liabilities, Net Short-term Debt Debt, Current Long-term Debt Long-term Debt and Capital Lease Obligations Payables for Collateral on Investments Collateralized Financings Other Liabilities Other Liabilities Total Liabilities Liabilities Commitments and Contingent Liabilities - Note 14 Commitments and Contingencies Stockholders' Equity Stockholders' Equity Attributable to Parent [Abstract] Common Stock, $0.10 par; authorized: 725,000,000 shares; issued: 304,448,032 and 303,552,934 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 Retained Earnings Retained Earnings (Accumulated Deficit) Treasury Stock - at cost: 81,900,950 and 73,729,992 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 Deferred Policy Acquisition Costs, Period Increase (Decrease) 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 Components of Net Investment Income Increase (Decrease) in Accrued Investment Income Receivable Net Realized Investment (Gain) Loss Depreciation Depreciation, Amortization and Accretion, Net Other, Net Other Noncash Income (Expense) Net Cash Provided by Operating Activities Net Increase (Decrease) in Payables for Collateral on Investments Increase (Decrease) in Cash Collateral for Loaned Securities Acquisition of Business (Net of Cash Acquired) Payments to Acquire Businesses, Net of Cash Acquired Repurchase of Common Stock Net Increase (Decrease) in Cash and Bank Deposits Cash and Bank Deposits at Beginning of Year Cash and Bank Deposits at End of Year 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 Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Hedging Designation Hedging Designation [Axis] Hedging Designation Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Derivative Instrument Derivative Instrument [Axis] Derivative Contract Derivative Contract [Domain] Interest Rate Swaps Interest Rate Swap [Member] Foreign Exchange Contracts Foreign Exchange Contract [Member] Credit Risk Contract Credit Risk Contract [Member] Embedded Derivative in Modified Coinsurance Arrangement Embedded Derivative Financial Instruments [Member] Derivative Instrument by Balance Sheet Location Balance Sheet Location [Axis] Balance Sheet Location Balance Sheet Location [Domain] Other Long-term Investments Other Long-term Investments [Member] Other Liability Other Liabilities [Member] Derivative Derivative [Line Items] Asset Derivatives Fair Value Derivative Asset, Fair Value, Gross Asset Liability Derivatives Fair Value Derivative Liability, Fair Value, Gross Liability Reinsurance Disclosures [Abstract] Direct Premium Income Direct Premiums Earned Reinsurance Assumed Assumed Premiums Earned Reinsurance Ceded Ceded Premiums Earned Premium Income Premiums Earned, Net Ceded Benefits and Change in Reserves for Future Benefits Policyholder Benefits and Claims Incurred, Ceded Liability for Unpaid Claims and CAE [Abstract] Liability for Unpaid Claims and CAE [Abstract] Liability for Unpaid Claims and CAE Narrative Information Liability for Unpaid Claims and CAE Narrative Information [Table] Liability for Unpaid Claims and CAE Narrative Information [Table] Insurance Product Line Products and Services [Axis] Insurance Product Line Products and Services [Domain] Group Life Group Life [Member] Group Life [Member] Voluntary Benefits Voluntary Benefits [Member] Voluntary Benefits [Member] Life Insurance Life Insurance Product Line [Member] Liability for Unpaid Claims and CAE Narrative Information Liability for Unpaid Claims and CAE Narrative Information [Line Items] [Line Items] for Liability for Unpaid Claims and CAE Narrative Information [Table] Unclaimed Death Benefit Reserve Increase Before Taxes Debt - Additional Information [Abstract] Debt - Additional Information [Abstract] Debt Narrative Detail Information [Table] Debt Narrative Detail Information [Table] Debt Narrative Detail Information Northwind Holdings LLC Northwind Holdings LLC [Member] Northwind Holdings LLC [Member] Debt Instrument Debt Instrument [Axis] Debt Instrument, Name Debt Instrument, Name [Domain] Secured Notes acquired 2016 Secured Notes acquired 2016 [Member] Secured Notes acquired 2016 [Member] Notes Issued in 2009 Notes Issued in 2009 [Member] Notes Issued in 2009 [Member] Notes Payable Due 2021 Notes Payable Due 2021 [Member] Notes Payable Due 2021 Notes Payable due 2042 Notes Payable due 2042 [Member] Notes Payable due 2042 Notes Issued in 2012 Notes Issued in 2012 [Member] Notes Issued in 2012 Notes Issued in 2005 Notes Issued in 2005 [Member] Notes Issued in 2005 [Member] Notes Issued in 1998 with 2038 Maturity Date Notes Issued in 1998 with 2038 Maturity Date [Member] Notes Issued in 1998 with 2038 Maturity Date [Member] Income Statement Location Income Statement Location [Axis] Income Statement Location Income Statement Location [Domain] Net Realized Investments Gain Loss Net Realized Investments Gain Loss [Member] Net Realized Investments Gain (Loss) [Member] Extinguishment of Debt Extinguishment of Debt [Axis] Extinguishment of Debt, Type Extinguishment of Debt, Type [Domain] Long-term Debt Long-term Debt [Member] Receive Variable/Pay Fixed Derivative Financial Instruments Receive Variable Pay Fixed [Member] Derivative Financial Instruments, Receive Variable Pay Fixed [Member] Receive Fixed/Pay Variable Derivative Financial Instruments Receive Fixed Pay Variable [Member] Derivative Financial Instruments, Receive Fixed Pay Variable [Member] Long-term Debt, Type Long-term Debt, Type [Axis] Long-term Debt, Type Long-term Debt, Type [Domain] Junior Subordinated Debt Junior Subordinated Debt [Member] Debt Narrative Detail Information Debt Narrative Detail Information [Line Items] [Line Items] for Debt Narrative Detail Information Repayments of Principal in 2018 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months Repayments of Principal in 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three Repayments of Principal in 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four Repayments of Principal Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Proceeds from Issuance of Senior Long-term Debt Proceeds from Issuance of Senior Long-term Debt Basis Spread on LIBOR Debt Instrument, Basis Spread on Variable Rate Debt service coverage account (DSCA) Debt service coverage account (DSCA) Debt service coverage account (DSCA) Periodic Principal Payments Debt Instrument, Periodic Payment, Principal Extinguishment of Debt, Amount Extinguishment of Debt, Amount Loss on Contract Termination Loss on Contract Termination Current Maturities of Long-term Debt Long-term Debt, Current Maturities Stated Interest Rate of Debt Debt Instrument, Interest Rate, Stated Percentage Proceeds from Issuance of Debt Proceeds from Issuance of Debt Long-term Debt, Excluding Current Maturities Long-term Debt, Excluding Current Maturities Notional Amount of Derivatives Derivative, Notional Amount Unum Group Percentage Ownership of Provident Financing Trust Unum Group Percentage Ownership of Provident Financing Trust Unum Group Percentage Ownership of Provident Financing Trust Liquidation value per capital security Liquidation value per capital security Debt Instrument Liquidation Amount Per Share Interest Paid Interest Paid Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Line Of Credit Facility Maximum Borrowing Capacity If Requested Line Of Credit Facility Maximum Borrowing Capacity If Requested Line Of Credit Facility Maximum Borrowing Capacity If Requested Letters of Credit Outstanding Letters of Credit Outstanding, Amount Amount Outstanding on Line of Credit Long-term Line of Credit Income Tax [Abstract] Income Tax [Abstract] Deferred Acquisition Cost Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost Deferred Tax Liabilities for Fixed Assets Deferred Tax Liabilities, Property, Plant and Equipment Deferred Tax Liabilities on Invested Assets Deferred Tax Liabilities, Investments Other Deferred Tax Liabilities, Other Gross Deferred Tax Liability Deferred Tax Liabilities, Gross Reserves Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross Employee Benefits Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits Other Deferred Tax Assets, Other Gross Deferred Tax Asset Deferred Tax Assets, Gross Less: Valuation Allowance Deferred Tax Assets, Valuation Allowance Net Deferred Tax Asset Deferred Tax Assets, Net of Valuation Allowance Net Deferred Tax Liability Summary of Investments, Other than Investments in Related Parties [Abstract] Summary of Investments, Other than Investments in Related Parties [Table] Summary of Investments, Other than Investments in Related Parties [Table] Summary of Investments, Other than Investments in Related Parties, by Type Investment Type [Axis] Investments Investments [Domain] United States Government and Government Agencies and Authorities US Treasury and Government [Member] States, Municipalities, and Political Subdivisions US States and Political Subdivisions Debt Securities [Member] Foreign Governments Foreign Government Debt [Member] Public Utilities Public Utility, Bonds [Member] Mortgage/Asset-backed Securities Asset-backed Securities [Member] All Other Corporate Bonds Other Corporate Bonds [Member] Redeemable Preferred Stock Mandatorily Redeemable Preferred Stock [Member] Fixed Maturities Fixed Maturities [Member] Mortgages Mortgages [Member] Policy Loans Policy Loans [Member] Derivatives Derivative [Member] Equity Securities Equity Securities, Investment Summary [Member] Miscellaneous Long-term Investments Miscellaneous Long-term Investments [Member] Miscellaneous Long-term Investments [Member] Short-term Investments Short-term Investments [Member] Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items] Cost or Amortized Cost of Investments Summary of Investments, Other than Investments in Related Parties, Cost Fair Value of Investments Summary of Investments, Other than Investments in Related Parties, Fair Value Amount Shown on the Balance Sheet Summary of Investments, Other than Investments in Related Parties, Carrying Amount Distribution of the Maturity Dates for Fixed Maturity Securities [Abstract] Disclosure - Distribution of the Maturity Dates for Fixed Maturity Securities [Abstract] Schedule of Available-for-sale Securities Schedule of Available-for-sale Securities [Table] Gain (Loss) on Investments by Category Investments by Category [Axis] Marketable Securities and Investments Held at Cost Marketable Securities and Investments Held at Cost [Domain] Fair Value of Fixed Maturity Securities in Unrealized Gain Position Available for Sale Securities Unrealized Gain Position Fair Value [Member] Available For Sale Securities Gross Unrealized Gain [Member] Fair Value of Fixed Maturity Securities in Unrealized Loss Position Available for Sale Securities Unrealized Loss Position Fair Value [Member] Available For Sale Securities Gross Unrealized Loss [Member] Schedule of Available-for-sale Securities Schedule of Available-for-sale Securities [Line Items] Available-for-Sale Securities, Total Amortized 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Basis 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 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, Next Twelve Months, Fair Value Over 1 year through 5 years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value Over 5 years through 10 years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, 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 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, Debt 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 Gain Position, Gross Loss, Gross Subtotal 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 Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table] Segment Reporting Information Segment Reporting Information [Line Items] Premium Income Net Investment Income Net Investment Income Other Income Other Income Adjusted Operating 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Settled Awards [Member] Activity for PSUs Classified as Equity Share-based Compensation, Performance Shares Award Nonvested Activity [Table Text Block] Valuation Assumptions on PSU Grants Schedule of Share-based Payment Award, Performance-based Units, Valuation Assumptions [Table Text Block] Tabular disclosure of the significant assumptions used during the year to estimate the fair value of performance share unit awards. 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Measured with Unobservable Inputs, Ending Balance Earnings Per Share, Basic and Diluted [Abstract] Numerator Net Income (Loss), Including Portion Attributable to Noncontrolling Interest [Abstract] Denominator 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 Discount Rate Assumptions Used Calculating Benefit Obligation Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate Rate of Compensation Increase Assumptions Used Calculating Benefit Obligation Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase Discount Rate Assumptions Used Calculating Net Periodic Benefit 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2002 [Member] Notes Issued in 2002 [Member] Notes Issued in 2010 Notes Issued in 2010 [Member] Notes Issued in 2010 [Member] Notes Issued in 2014 Notes Issued in 2014 [Member] Notes Issued in 2014 [Member] Notes Issued in 2015 Notes Issued in 2015 [Member] Notes Issued in 2015 [Member] Notes Issued in 2016 Notes Issued in 2016 [Member] Notes Issued in 2016 [Member] Notes Issued 1990 to 1996 Notes Issued 1990 to 1996 [Member] Notes Issued 1990 to 1996 [Member] Senior Notes Senior Notes [Member] Medium-term Notes Medium-term Notes [Member] Fair Value Hedge Adjustment, LT Debt Fair Value Hedge Adjustment, LT Debt [Member] Fair Value Hedge Adjustment, LT Debt [Member] Short-term Debt, Type Short-term Debt, Type [Axis] Short-term Debt, Type Short-term Debt, Type [Domain] Debt Instrument Debt Instrument [Line Items] Debt Instrument, Unamortized Premium (Discount), Net Debt Instrument, Unamortized Discount (Premium), Net Debt Issuance Costs, Noncurrent, Net Debt Issuance Costs, Noncurrent, 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[Abstract] Disclosure - Realized Investment Gains and Losses Reported in Consolidated Statements of Income [Abstract] Fixed Maturity Securities Available-for-sale Securities [Abstract] 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 Mortgage Loans and Other Invested Assets Other Investments [Abstract] 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 Other Investments Gross Realized Losses Impairment Loss Other than Temporary Impairment Losses, Investments Gain (Loss) on Embedded Derivative Embedded Derivative, Gain (Loss) on Embedded Derivative, Net All Other Derivatives Foreign 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[Abstract] 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 Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float Schedule of New Accounting Pronouncements [Abstract] Schedule of New Accounting Pronouncements [Abstract] Prospective Adoption of New Accounting Pronouncements Prospective Adoption of New Accounting Pronouncements [Table] Retained Earnings 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