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Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3, USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013
Embedded Derivative Liability |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs | (49.9)unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByLiabilityClassAxis = us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember |  | (53.2)unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByLiabilityClassAxis = us-gaap_DerivativeFinancialInstrumentsLiabilitiesMember |
Embedded Derivative Liability | Projected Cash Flows |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | Actuarial Assumptions | [1] | Actuarial Assumptions | [1]
States, Municipalities, and Political Subdivisions |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs | 101.0 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 142.7 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
States, Municipalities, and Political Subdivisions | Minimum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Comparability Adjustments | 0.25%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2] | 0.25%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2]
States, Municipalities, and Political Subdivisions | Maximum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Comparability Adjustments | 1.00%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2] | 1.25%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2]
States, Municipalities, and Political Subdivisions | Weighted Average |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Comparability Adjustments | 0.71%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2] | 0.65%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2]
Mortgage/Asset-backed Securities |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs |  |  | 0.5 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Mortgage/Asset-backed Securities | Minimum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Discount for Size |  |  | 4.93%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [3]
Mortgage/Asset-backed Securities | Maximum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Discount for Size |  |  | 5.03%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [3]
Mortgage/Asset-backed Securities | Weighted Average |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Discount for Size |  |  | 5.01%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AssetBackedSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [3]
All Other Corporate Bonds - Private |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs | 432.8 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 371.3 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
All Other Corporate Bonds - Private | Market Convention |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | Priced at Par | [4] | Priced at Par | [4]
All Other Corporate Bonds - Private | Minimum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | 3.36%unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [5]
Comparability Adjustments | 0.50%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2] | (0.70%)us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2]
Discount for Size | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [3] | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [3]
Lack of Marketability | 0.48%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [6] | 0.20%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [6]
Volatility of Credit | 0.20%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [7] | 0.07%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [7]
All Other Corporate Bonds - Private | Maximum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | 3.36%unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [5]
Comparability Adjustments | 0.70%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2] | (0.40%)us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2]
Discount for Size | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [3] | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [3]
Lack of Marketability | 0.48%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [6] | 1.00%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [6]
Volatility of Credit | 2.00%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [7] | 4.00%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [7]
All Other Corporate Bonds - Private | Weighted Average |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | 3.36%unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [5]
Comparability Adjustments | 0.60%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2] | (0.60%)us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2]
Discount for Size | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [3] | 0.50%unm_FairValueInputsDiscountForSize / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [3]
Lack of Marketability | 0.48%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [6] | 0.55%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [6]
Volatility of Credit | 0.64%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [7] | 0.85%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_AllOtherCorporateBondsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [7]
Corporate Bond Securities - Public |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs | 128.7 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 514.4 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Corporate Bond Securities - Public | Minimum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | (0.32%)unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [5]
Comparability Adjustments | 0.10%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2] | (0.23%)us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [2]
Lack of Marketability | 0.20%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [6] | 0.20%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [6]
Volatility of Credit | (0.30%)us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [7] | (0.88%)us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MinimumMember | [7]
Corporate Bond Securities - Public | Maximum |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | 0.25%unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [5]
Comparability Adjustments | 0.50%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2] | 1.00%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [2]
Lack of Marketability | 0.35%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [6] | 0.20%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [6]
Volatility of Credit | 0.50%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [7] | 0.46%us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_MaximumMember | [7]
Corporate Bond Securities - Public | Weighted Average |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Change in Benchmark Reference |  |  | 0.04%unm_FairValueInputsChangeInBenchmarkReference / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [5]
Comparability Adjustments | 0.40%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2] | 0.41%us-gaap_FairValueInputsComparabilityAdjustments / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [2]
Lack of Marketability | 0.29%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [6] | 0.20%us-gaap_FairValueInputsDiscountForLackOfMarketability / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [6]
Volatility of Credit | (0.05%)us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [7] | (0.26%)us-gaap_FairValueInputsEntityCreditRisk / us-gaap_FairValueByAssetClassAxis = us-gaap_CorporateBondSecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_RangeAxis = us-gaap_WeightedAverageMember | [7]
Equity Securites |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs | 1.1 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |  | 4.2 unm_FairValueofFinancialInstrumentUsingInternallyDerivedUnobservableInputs / us-gaap_FairValueByAssetClassAxis = us-gaap_EquitySecuritiesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Equity Securites | Market Convention |  |  |  |
Fair Value Inputs, Assets and Liabilities, Quantitative Information |  |  |  |
Significant Assumptions to Calculating Fair Value of Level 3 Instrument | Priced at Cost or Owner's Equity | [4] | Priced at Cost or Owner's Equity | [4]
[1] | Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates
[2] | Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
[3] | Represents basis point adjustments based on issue/issuer size relative to the benchmark
[4] | Represents a decision to price based on par value, cost, or owner's equity when limited data is available
[5] | Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories
[6] | Represents basis point adjustments to apply a discount due to the illiquidity of an investment
[7] | Represents basis point adjustments for credit-specific factors

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