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Transfers of Assets between Level 1 and Level 2 (Detail) (USD $) In Millions, unless otherwise specified | Mar. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Fixed Maturity Securities |  |
Level 1 from Level 2 | $ 3,025.3 | $ 3,869.0
Level 2 from Level 1 | 1,213.7 | 2,386.9
United States Government and Government Agencies and Authorities |  |
Fixed Maturity Securities |  |
Level 1 from Level 2 | 256.9 | 0
Level 2 from Level 1 | 0 | 204.2
States, Municipalities, and Political Subdivisions |  |
Fixed Maturity Securities |  |
Level 1 from Level 2 | 0 | 0
Level 2 from Level 1 | 19.4 | 43.8
Public Utilities |  |
Fixed Maturity Securities |  |
Level 1 from Level 2 | 502.1 | 826.2
Level 2 from Level 1 | 53.5 | 454.4
All Other Corporate Bonds |  |
Fixed Maturity Securities |  |
Level 1 from Level 2 | 2,266.3 | 3,042.8
Level 2 from Level 1 | $ 1,140.8 | $ 1,684.5

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- Definition Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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- Definition Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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