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Debt - Additional Information Domain (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2007 | Dec. 31, 2006 | Dec. 31, 1998 | Dec. 31, 2011
Debt Narrative Detail Information |  |  |  |  |  |  |
Repayments of Principal in Next Twelve Months | $ 151.9 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths |  |  |  |  |  |
Repayments of Principal in 2016 | 350.0 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo |  |  |  |  |  |
Repayments of Principal in 2018 | 200.0 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour |  |  |  |  |  |
Repayments of Principal Thereafter | 2,081.0 us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive |  |  |  |  |  |
Repayments of Long-term Debt | 186.6 us-gaap_RepaymentsOfLongTermDebt | 116.2 us-gaap_RepaymentsOfLongTermDebt | 70.0 us-gaap_RepaymentsOfLongTermDebt |  |  |  |
Payments of Debt Extinguishment Costs | 13.2 us-gaap_PaymentsOfDebtExtinguishmentCosts | 0 us-gaap_PaymentsOfDebtExtinguishmentCosts | 0 us-gaap_PaymentsOfDebtExtinguishmentCosts |  |  |  |
Notional Amount of Derivatives | 1,687.4 invest_DerivativeNotionalAmount | 1,477.4 invest_DerivativeNotionalAmount | 1,432.8 invest_DerivativeNotionalAmount |  |  |  | 1,413.0 invest_DerivativeNotionalAmount
Unum Group Percentage Ownership of Provident Financing Trust | 100.00%unm_UnumGroupPercentageOwnershipofProvidentFinancingTrust |  |  |  |  |  |
Interest Paid | 145.9 us-gaap_InterestPaid | 144.6 us-gaap_InterestPaid | 139.6 us-gaap_InterestPaid |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | 400.0 us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity |  |  |  |  |  |
Line Of Credit Facility Maximum Borrowing Capacity If Requested | 600.0 unm_LineOfCreditFacilityMaximumBorrowingCapacityIfRequested |  |  |  |  |  |
Letters of Credit Outstanding | 2.1 us-gaap_LettersOfCreditOutstandingAmount | 0 us-gaap_LettersOfCreditOutstandingAmount |  |  |  |  |
Amount Outstanding on Line of Credit | 0 us-gaap_LineOfCredit | 0 us-gaap_LineOfCredit |  |  |  |  |
Receive Fixed/Pay Variable | Swaps |  |  |  |  |  |  |
Debt Narrative Detail Information |  |  |  |  |  |  |
Notional Amount of Derivatives | 600.0 invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = unm_DerivativeFinancialInstrumentsReceiveFixedPayVariableMember | 600.0 invest_DerivativeNotionalAmount / us-gaap_DerivativeByNatureAxis = us-gaap_SwapMember / us-gaap_DerivativeInstrumentRiskAxis = unm_DerivativeFinancialInstrumentsReceiveFixedPayVariableMember |  |  |  |  |
Northwind Holdings LLC |  |  |  |  |  |  |
Debt Narrative Detail Information |  |  |  |  |  |  |
Proceeds from Issuance of Senior Long-term Debt |  |  |  | 800.0 us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt / dei_LegalEntityAxis = unm_NorthwindHoldingsLlcMember |  |  |
Basis Spread on LIBOR | 0.78%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / dei_LegalEntityAxis = unm_NorthwindHoldingsLlcMember |  |  |  |  |  |
Debt service coverage account (DSCA) | 5.4 unm_DebtServiceCoverageAccountDsca / dei_LegalEntityAxis = unm_NorthwindHoldingsLlcMember |  |  |  |  |  |
Periodic Principal Payments | 41.6 us-gaap_DebtInstrumentPeriodicPaymentPrincipal / dei_LegalEntityAxis = unm_NorthwindHoldingsLlcMember | 60.0 us-gaap_DebtInstrumentPeriodicPaymentPrincipal / dei_LegalEntityAxis = unm_NorthwindHoldingsLlcMember |  |  |  |  |
Tailwind Holdings LLC |  |  |  |  |  |  |
Debt Narrative Detail Information |  |  |  |  |  |  |
Proceeds from Issuance of Senior Long-term Debt |  |  |  |  | 130.0 us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt / dei_LegalEntityAxis = unm_TailwindHoldingsLlcMember |  |
Periodic Principal Payments |  |  | 10.0 us-gaap_DebtInstrumentPeriodicPaymentPrincipal / dei_LegalEntityAxis = unm_TailwindHoldingsLlcMember |  |  |  |
Repayments of Long-term Debt |  | 62.5 us-gaap_RepaymentsOfLongTermDebt / dei_LegalEntityAxis = unm_TailwindHoldingsLlcMember |  |  |  |  |
Gains (Losses) on Extinguishment of Debt |  | 4.0 us-gaap_GainsLossesOnExtinguishmentOfDebt / dei_LegalEntityAxis = unm_TailwindHoldingsLlcMember |  |  |  |  |
Long-term Debt |  |  |  |  |  |  |
Debt Narrative Detail Information |  |  |  |  |  |  |
Extinguishment of Debt, Amount | 145.0 us-gaap_ExtinguishmentOfDebtAmount / us-gaap_ExtinguishmentOfDebtAxis = us-gaap_LongTermDebtMember |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 6.85%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_ExtinguishmentOfDebtAxis = us-gaap_LongTermDebtMember |  |  |  |  |  |
Payments of Debt Extinguishment Costs | 13.2 us-gaap_PaymentsOfDebtExtinguishmentCosts / us-gaap_ExtinguishmentOfDebtAxis = us-gaap_LongTermDebtMember |  |  |  |  |  |
Repayment of Long-term Debt, Including Cost of Make-whole Call Premium | 158.2 unm_RepaymentofLongtermDebtIncludingCostofMakewholeCallPremium / us-gaap_ExtinguishmentOfDebtAxis = us-gaap_LongTermDebtMember |  |  |  |  |  |
Hedge Gain Reclassification from AOCI to Earnings | 13.1 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax / us-gaap_ExtinguishmentOfDebtAxis = us-gaap_LongTermDebtMember |  |  |  |  |  |
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt |  |  |  |  |  |  |
Debt Narrative Detail Information |  |  |  |  |  |  |
Proceeds from Issuance of Senior Long-term Debt |  |  |  |  |  | $ 300.0 us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt / us-gaap_DebtInstrumentAxis = unm_NotesIssuedin1998with2038MaturityDateMember / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember |
Debt Instrument, Interest Rate, Stated Percentage | 7.405%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = unm_NotesIssuedin1998with2038MaturityDateMember / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember |  |  |  |  |  |
Liquidation value per capital security | $ 1,000 unm_LiquidationValuePerCapitalSecurity / us-gaap_DebtInstrumentAxis = unm_NotesIssuedin1998with2038MaturityDateMember / us-gaap_LongtermDebtTypeAxis = us-gaap_JuniorSubordinatedDebtMember |  |  |  |  |  |

X
- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Details
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- Definition Debt service coverage account (DSCA) + References No definition available. + Details
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- Definition Line Of Credit Facility Maximum Borrowing Capacity If Requested + References No definition available. + Details
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- Definition Debt Instrument Liquidation Amount Per Share + References No definition available. + Details
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- Definition Repayment of Long-term Debt, Including Cost of Make-whole Call Premium + References No definition available. + Details
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- Definition Unum Group Percentage Ownership of Provident Financing Trust + References No definition available. + Details
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- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Gross amount of debt extinguished. + References No definition available. + Details
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- Definition Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12317-112629 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6850294&loc=d3e12355-112629 + Details
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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth 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 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next 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 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth 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 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second 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 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(a)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 + Details
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- Definition Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e689-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph c -URI http://asc.fasb.org/extlink&oid=35706170&loc=d3e41638-113959 + Details
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