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Investment Securities (Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Investment securities |  |  |
Sales and maturities of investment securities | $ 4,924.8 | $ 6,997.5 | $ 5,034.0
Fixed maturity investments, at fair value | 5,030.5 | 5,196.2 |
Common Stock |  |  |
Investment securities |  |  |
Trading Securities, Cost | 890.2 | 895.2 |
Net foreign currency losses | (0.8) | (0.1) |
Fixed maturity investments, at fair value | 1,156.8 | 1,029.7 |
Trading Securities, Unrealized Holding Gain | 271.0 | 143.4 |
Trading Securities, Unrealized Holding Loss | (3.6) | (8.8) |
Convertible fixed maturity investments |  |  |
Investment securities |  |  |
Trading Securities, Cost | 71.7 | 121.7 |
Net foreign currency losses | (0.2) | 0 |
Fixed maturity investments, at fair value | 80.5 | 127.4 |
Trading Securities, Unrealized Holding Gain | 9.9 | 6.1 |
Trading Securities, Unrealized Holding Loss | (0.9) | (0.4) |
Other long-term investments |  |  |
Investment securities |  |  |
Trading Securities, Cost | 238.3 | 257.2 |
Net foreign currency losses | (2.4) | (6.1) |
Fixed maturity investments, at fair value | 288.9 | 294.2 |
Trading Securities, Unrealized Holding Gain | 79.6 | 65.9 |
Trading Securities, Unrealized Holding Loss | $ (26.6) | $ (22.8) |

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- Definition The cash inflow associated with the sale, maturities, repayments and calls of securities classified as trading securities and held for investment purposes. Excludes proceeds from trading securities purchased and held principally for the purpose of selling them in the near term (thus held for only a short period of time). + References No definition available. + Details
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- Definition Cost of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References No definition available. + Details
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- Definition Amount of investments in debt securities classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: 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.(a),1) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Amount of unrealized holding gain before loss recognized in the income statement for investments in trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 + Details
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- Definition Amount of unrealized holding loss before gain recognized in the income statement for investments in trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 + Details
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- Definition The net amount of unrealized gains (losses) from foreign currency transaction adjustments related to trading securities. + References No definition available. + Details
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