Amortization of Prepaid Reinsurance Premium

No definition available.

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

- Definition

Increase in Benefits and Change in Reserves for Future Benefits

+ References

No definition available.

+ Details

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

- Definition

Negative Ceding Commission

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of assets as of the balance sheet date pertaining to amounts paid by the insured (including a ceding company) under insurance or reinsurance contracts for which insurance risk is not transferred.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99397363&loc=d3e9420-108338

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99383045&loc=d3e9351-108337

+ Details

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

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

- Definition

Amount of realized and unrealized gain (loss) on investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27405-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c),9(a))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

+ Details

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

- Definition

The total amount of other operating cost and expense items that are associated with the entity's normal revenue producing operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

+ Details

Name:	us-gaap_OtherCostAndExpenseOperating
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The unexpired portion of premiums ceded on policies in force as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 340
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6485982&loc=d3e22818-158507

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 825
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123600520&loc=SL75241803-196195

+ Details

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

- Definition

Estimated amount after valuation allowance of reinsurance recoverables, due from reinsurers for incurred claims not yet reported, and claims settlement expenses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21409-158489

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489

+ Details

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

- Details

Name:	unm_SignificantTransactionAxis=unm_ClosedBlockIndividualDisabilityReinsuranceTransactionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	unm_PhaseOfSignificantTransactionAxis=unm_Phase2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	unm_PhaseOfSignificantTransactionAxis=unm_Phases1And2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended
Reinsurance (Details) - USD ($) $ in Millions	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 16, 2020
Effects of Reinsurance
Net Investment Gain (Loss)	$ (13.8)	$ 84.6
Transaction Costs Related to Reinsurance Transaction	243.8	245.0
Reinsurance Recoverables, Incurred but Not Reported Claims	8,535.3	9,225.8	$ 8,697.8	$ 8,378.9
Closed Block Individual Disability Reinsurance Transaction
Effects of Reinsurance
Amortization of the Cost of Reinsurance	16.7	20.0
Closed Block Individual Disability Reinsurance Transaction \| Phase 2
Effects of Reinsurance
Negative Ceding Commission	(18.2)
Net Investment Gain (Loss)		67.6
Increase in Benefits and Change in Reserves for Future Benefits	$ 133.1	133.1
Transaction Costs Related to Reinsurance Transaction		6.2
Reinsurance Recoverables, Incurred but Not Reported Claims		990.0
Prepaid Reinsurance Premiums		43.1
Deposit Contracts, Assets		5.0
Closed Block Individual Disability Reinsurance Transaction \| Phases 1 and 2
Effects of Reinsurance
Prepaid Reinsurance Premiums		854.8			$ 854.8
Deposit Contracts, Assets		$ 91.8			$ 91.8