Investments Federal Home Loan Bank Carrying Amount, Collateral Posted and Advances Received (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Federal Home Loan Bank Carrying Value of Common Stock, Collateral Posted and Advances
Federal Home Loan Bank Common Stock	$ 42.5	$ 40.7
Federal Home Loan Bank, Advances	691.9	643.8
Federal Home Loan Bank, Collateral Posted to FHLB	1,878.2	1,862.6
Fixed Maturity Securities
Federal Home Loan Bank Carrying Value of Common Stock, Collateral Posted and Advances
Federal Home Loan Bank, Collateral Posted to FHLB	800.2	752.4
Commercial Mortgage Loans
Federal Home Loan Bank Carrying Value of Common Stock, Collateral Posted and Advances
Federal Home Loan Bank, Collateral Posted to FHLB	$ 1,078.0	$ 1,110.2

[Line Items] for Federal Home Loan Bank Carrying Value of Common Stock, Collateral Posted and Advances [Table]

No definition available.

Name:	unm_FederalHomeLoanBankCarryingValueofCommonStockCollateralPostedandAdvancesLineItems
Namespace Prefix:	unm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of advance from Federal Home Loan Bank (FHLBank).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478878/942-470-45-1

+ Details

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

- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 470
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478878/942-470-45-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477734/942-470-50-3

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 325
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477974/942-325-45-1

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: