Employee Benefit Plans UK Pension Assets, Fair Value Measurement by Input Level (Details) (Pension Benefits, Non U.S. Plans, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	$ 167.6unm_DiversifiedGrowthAssets	$ 172.0unm_DiversifiedGrowthAssets
Fixed Interest and Index-linked Securities	78.0	53.0
Cash Equivalents, at Carrying Value	0.7us-gaap_CashEquivalentsAtCarryingValue	0.7us-gaap_CashEquivalentsAtCarryingValue
Fair Value of Plan Assets	246.3	225.7	205.6
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	0	0
Fixed Interest and Index-linked Securities	78.0	52.6
Cash Equivalents, at Carrying Value	0.7	0.7
Fair Value of Plan Assets	78.7	53.3
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	167.6	172.0
Fixed Interest and Index-linked Securities	0	0.4
Cash Equivalents, at Carrying Value	0	0
Fair Value of Plan Assets	167.6	172.4
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	0	0
Fixed Interest and Index-linked Securities	0	0
Cash Equivalents, at Carrying Value	0	0
Fair Value of Plan Assets	$ 0	$ 0

Diversified Growth Assets

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- Definition

Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 35

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930

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- Definition

For an unclassified balance sheet, this item represents investments in debt securities having predetermined or determinable maturity dates.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a

-Article 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(a))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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