Available For Sale Securities, Percent Of Total Fair Value

No definition available.

Name:	unm_AvailableForSaleSecuritiesPercentOfTotalFairValue
Namespace Prefix:	unm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans ceded to reinsurers. These loans use insurance policy funds such as cash surrender values as collateral.

+ References

No definition available.

+ Details

Name:	unm_PolicyLoansCededtoReinsurers
Namespace Prefix:	unm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Private Equity Partnership Future Liquidation Term

+ References

No definition available.

+ Details

Name:	unm_PrivateEquityPartnershipFutureLiquidationTerm
Namespace Prefix:	unm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Net Increase or Decrease in the fair value of the embedded derivative or group of embedded derivatives included in earnings in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959

+ Details

Name:	us-gaap_EmbeddedDerivativeGainLossOnEmbeddedDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

+ 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 210.5-02.22)

-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 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section H

+ Details

Name:	us-gaap_LongTermDebtAndCapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=unm_FairValueInputsLevel2OrLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=unm_FairValueInputsOtherThanLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value of Financial Instruments Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Ceded Policy Loans	$ 3,042.7unm_PolicyLoansCededtoReinsurers		$ 3,068.4unm_PolicyLoansCededtoReinsurers
Long-term Debt	2,603.3		2,628.7
Gain (Loss) on Embedded Derivative	(3.9)	8.5
Fair Value Inputs Other Than Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	82.80%
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	2,568.4		849.7
Percentage of Total Fair Value of Fixed Maturities Securities	17.20%
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	$ 338.4		$ 2,062.9
Fair Value, Inputs, Level 2 \| Pricing Service
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	68.30%
Fair Value, Inputs, Level 2 \| Other Observable Market Data
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	2.40%
Fair Value Inputs Level 2 Or Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Percentage of Total Fair Value of Fixed Maturities Securities	12.10%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Private Equity Partnership Future Liquidation Term	1 year
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Private Equity Partnership Future Liquidation Term	12 years