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Notional Amounts for Each Category of Derivative Activity (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Derivative [Line Items] |  |  |
Balance at beginning of period | $ 1,681.9 | $ 1,620.7 | $ 2,532.1
Additions | 46.9 | 715.6 | 76.8
Terminations | 315.8 | 654.4 | 988.2
Balance at ending of period | 1,413.0 | 1,681.9 | 1,620.7
Swaps | Receive Variable/Pay Fixed |  |  |
Derivative [Line Items] |  |  |
Balance at beginning of period | 174.0 | 174.0 | 174.0
Additions | 0 | 250.0 | 0
Terminations | 0 | 250.0 | 0
Balance at ending of period | 174.0 | 174.0 | 174.0
Swaps | Receive Fixed/Pay Fixed |  |  |
Derivative [Line Items] |  |  |
Balance at beginning of period | 617.9 | 661.9 | 931.8
Additions | 0 | 0 | 70.9
Terminations | 63.9 | 44.0 | 340.8
Balance at ending of period | 554.0 | 617.9 | 661.9
Swaps | Receive Fixed/Pay Variable |  |  |
Derivative [Line Items] |  |  |
Balance at beginning of period | 890.0 | 780.0 | 1,160.0
Additions | 0 | 350.0 | 0
Terminations | 205.0 | 240.0 | 380.0
Balance at ending of period | 685.0 | 890.0 | 780.0
Forwards |  |  |
Derivative [Line Items] |  |  |
Balance at beginning of period | 0 | 4.8 | 266.3
Additions | 46.9 | 115.6 | 5.9
Terminations | 46.9 | 120.4 | 267.4
Balance at ending of period | $ 0 | $ 0 | $ 4.8

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- Definition Notional Amount Of Derivatives, Additions + References No definition available. + Details
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Balance Type: | debit
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- Definition Notional Amount Of Derivatives, Terminations + References No definition available. + Details
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Namespace Prefix: | unm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Details
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- Definition Aggregate notional amount of all derivatives. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Notional Amount -URI http://asc.fasb.org/extlink&oid=6519104 + Details
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