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Postretirement Benefit Plans - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]    
Liability related to funded defined-benefit pension plans $ 407,000,000tmk_FundedDefinedBenefitPlanLiability $ 403,000,000tmk_FundedDefinedBenefitPlanLiability
Contributions to benefit plans 20,000,000us-gaap_DefinedBenefitPlanContributionsByEmployer  
Insurance cash value and Rabbi Trust investments supporting supplemental pension plan liability 75,000,000tmk_InsuranceCashValueAndRabbiTrustInvestmentsSupportingSupplementalPensionPlanLiability 74,000,000tmk_InsuranceCashValueAndRabbiTrustInvestmentsSupportingSupplementalPensionPlanLiability
Non-qualified supplemental retirement pension plan liability $ 72,000,000tmk_UnqualifiedSupplementalRetirementPensionPlanLiability $ 71,000,000tmk_UnqualifiedSupplementalRetirementPensionPlanLiability