Investments Mortgage Loan Restructuring (Detail) (Commercial Real Estate Portfolio Segment [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 17.3	$ 19.9	$ 7.2
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	3	2	1
Financing Receivable, Modifications, Payoffs, Pre-Modification Recorded Investment	0	3.2	4.7
Realized Loss	$ 0	$ 0.2	$ 1.4
Financing Receivables, Modification, Payoffs, Number of Contracts	0	1	3

Financing Receivable, Modifications, Payoffs, Pre-Modification Recorded Investment

No definition available.

Name:	unm_FinancingReceivableModificationsPayoffsPreModificationRecordedInvestment
Namespace Prefix:	unm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing Receivables, Modification, Payoffs, Number of Contracts

+ References

No definition available.

+ Details

Name:	unm_FinancingReceivablesModificationPayoffsNumberOfContracts
Namespace Prefix:	unm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

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

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6951948&loc=d3e18845-111554

+ Details

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