Notional Amount Of Derivatives, Additions

No definition available.

Name:	unm_NotionalAmountOfDerivativesAdditions
Namespace Prefix:	unm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624258-113959

+ Details

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 15
-Paragraph 83
-URI http://asc.fasb.org/extlink&oid=125514181&loc=d3e34841-113949

+ Details

Name:	us-gaap_FairValueConcentrationOfRiskDerivativeFinancialInstrumentsAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986

+ Details

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

- Definition

Amount of net gain (loss) recognized in earnings when a hedged firm commitment no longer qualifies as a fair value hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986

+ Details

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

- Definition

The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959

+ Details

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

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CreditRiskContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditDerivativesByContractTypeAxis=us-gaap_CreditDefaultSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_TotalReturnSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	unm_InterestRateDerivativesContractTypeAxis=unm_DerivativeFinancialInstrumentsReceiveFixedPayFixedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	unm_CreditExposureAxis=unm_CreditExposureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Derivative
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	$ 35.4		$ 35.0
Derivative, Notional Amount	1,029.5		970.5
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net		$ 0.6
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	47.6
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness	3.3	(7.0)
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as Fair Value Hedge	0.0	$ 0.0
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	727.9		679.8
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	301.6		290.7
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	196.3
Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	148.2		148.2
Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	181.3		181.3
Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	531.6		498.5
Credit Default Swaps \| Credit Default Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	11.3		11.6
Forwards \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	58.2		41.7
Forwards \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	15.0
Additions	15.0
Total Return Swap \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	83.9		89.2
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	148.2		148.2
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	181.3		181.3
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	531.6		498.5
Credit Exposure
Derivative
Credit Exposure on Derivatives	$ 1.7		$ 1.3