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Reinsurance - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2014
Number of companies that make up majority of reinsurance recoverable | 14 unm_NumberOfCompaniesThatMakeUpMajorityOfReinsuranceRecoverable
AM Best A Rating or Better | Reinsurer Concentration Risk | Reinsurance Recoverable | Top 14 Reinsurers |
Percentage of Concentration Risk | 92.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_CededCreditRiskAxis = unm_Top14ReinsurersMember / us-gaap_ConcentrationRiskByBenchmarkAxis = unm_ReinsuranceRecoverableMember / us-gaap_ConcentrationRiskByTypeAxis = unm_ReinsurerConcentrationRiskMember / us-gaap_CreditRatingAMBestAxis = us-gaap_AMBestARatingMember
AM Best, A- Rating | Reinsurer Concentration Risk | Reinsurance Recoverable | Other Reinsurers |
Percentage of Concentration Risk | 7.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_CededCreditRiskAxis = unm_OtherReinsurersMember / us-gaap_ConcentrationRiskByBenchmarkAxis = unm_ReinsuranceRecoverableMember / us-gaap_ConcentrationRiskByTypeAxis = unm_ReinsurerConcentrationRiskMember / us-gaap_CreditRatingAMBestAxis = us-gaap_AMBestAMinusRatingMember
AM Best, Below A- or Not Rated | Reinsurer Concentration Risk | Reinsurance Recoverable | Other Reinsurers |
Percentage of Concentration Risk | 1.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_CededCreditRiskAxis = unm_OtherReinsurersMember / us-gaap_ConcentrationRiskByBenchmarkAxis = unm_ReinsuranceRecoverableMember / us-gaap_ConcentrationRiskByTypeAxis = unm_ReinsurerConcentrationRiskMember / us-gaap_CreditRatingAMBestAxis = unm_AMBestBelowAorNotRatedMember

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