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Liability for Unpaid Claims - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Impairment of Deferred Acquisition Costs | $ 289.8 | $ 0 | $ 0
Long-term Care |  |  |
Reserve Increase Due to Unlocking | 573.6 |  |
Claim Reserve Total [Member] | Long-term Care |  |  |
Reserve Increase Due to Unlocking | 248.1 |  |
Claim Reserve Total [Member] | Individual Disability Closed Block |  |  |
Reserve Increase Due to Unlocking | 183.5 |  |
Claim Reserve Prior Year [Member] | Long-term Care |  |  |
Reserve Increase Due to Unlocking | 215.0 |  |
Claim Reserve Prior Year [Member] | Individual Disability Closed Block |  |  |
Reserve Increase Due to Unlocking | $ 176.0 |  |

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- Definition The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 46 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6905858&loc=d3e16373-109275 + Details
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