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v2.4.1.9

Distribution of the Maturity Dates for Fixed Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Available-for-Sale Securities, Total Amortized Cost |  |
1 year or less | $ 1,372.0 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost | $ 903.9 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost
Over 1 year through 5 years | 6,871.2 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost | 7,098.2 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost
Over 5 years through 10 years | 9,532.9 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost | 9,492.6 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost
Over 10 years | 18,802.4 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost | 18,936.2 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost
Available-for-sale Securities, Debt Maturities, Gross Subtotal | 36,578.5 unm_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostGrossSubtotal | 36,430.9 unm_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostGrossSubtotal
Mortgage/Asset-Backed Securities | 2,224.9 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost | 1,858.7 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost
Fixed Maturity Securities, Amortized Cost | 38,803.4 us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis | 38,289.6 us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Fair Value Maturity Distribution [Abstract] |  |
Total Fixed Maturity Securities | 45,064.9 us-gaap_AvailableForSaleSecuritiesDebtSecurities | 42,344.4 us-gaap_AvailableForSaleSecuritiesDebtSecurities
Fair Value of Fixed Maturity Securities in Unrealized Gain Position |  |
Available-for-Sale Securities, Unrealized Gain Position, Gross Gain |  |
1 year or less | 34.3 unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 20.6 unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 1 year through 5 years | 719.3 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 727.1 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 5 years through 10 years | 1,003.3 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedGainPositionGrossgain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 940.2 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedGainPositionGrossgain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 10 years | 4,422.4 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 2,486.2 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal | 6,179.3 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGainGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 4,174.1 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGainGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Mortgage/Asset-Backed Securities | 207.0 unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 184.6 unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Total Fixed Maturity Securities | 6,386.3 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 4,358.7 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossGain / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Fair Value Maturity Distribution [Abstract] |  |
1 year or less | 1,406.3 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 915.5 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 1 year through 5 years | 7,434.0 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 7,678.5 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 5 years through 10 years | 8,792.3 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 8,137.4 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Over 10 years | 22,490.6 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 18,441.5 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal | 40,123.2 unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 35,172.9 unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Mortgage/Asset-Backed Securities | 2,401.9 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 1,695.8 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Total Fixed Maturity Securities | 42,525.1 us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember | 36,868.7 us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedGainPositionFairValueMember
Fair Value of Fixed Maturity Securities in Unrealized Loss Position |  |
Fair Value Maturity Distribution [Abstract] |  |
1 year or less | 0 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 9.0 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 1 year through 5 years | 147.1 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 146.2 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 5 years through 10 years | 1,663.0 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 2,199.6 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 10 years | 699.8 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 2,777.4 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal | 2,509.9 unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 5,132.2 unm_AvailableForSaleSecuritiesDebtMaturitiesFairValueGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Mortgage/Asset-Backed Securities | 29.9 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 343.5 us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Total Fixed Maturity Securities | 2,539.8 us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 5,475.7 us-gaap_AvailableForSaleSecuritiesDebtSecurities / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Available-for-Sale Securities, Unrealized Loss Position, Gross Loss |  |
1 year or less | 0 unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 0 unm_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 1 year through 5 years | 9.4 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 0.6 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 5 years through 10 years | 80.9 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedLossPositiongrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 95.8 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsUnrealizedLossPositiongrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Over 10 years | 34.4 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 203.5 unm_AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Loss, Gross Subtotal | 124.7 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossLossGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 299.9 unm_AvailableForSaleSecuritiesDebtMaturitiesUnrealizedGainPositionGrossLossGrossSubtotal / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Mortgage/Asset-Backed Securities | 0.1 unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | 4.0 unm_AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateUnrealizedLossPositionGrossLoss / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember
Total Fixed Maturity Securities | $ 124.8 unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLossSubtoatl / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember | $ 303.9 unm_AvailableForSaleSecuritiesUnrealizedLossPositionGrossLossSubtoatl / us-gaap_GainLossOnInvestmentsByCategoryAxis = unm_AvailableForSaleSecuritiesUnrealizedLossPositionFairValueMember

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- Definition This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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- Definition Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27198-111563 + Details
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- Definition Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27198-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62586-112803 + Details
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- Definition Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27198-111563 + Details
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