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Reinsurance - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2014
Number of companies that make up majority of reinsurance recoverable 14unm_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