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Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2014 | Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Fixed maturity investments, at fair value | $ 4,785.5 | $ 5,030.5
Common shareholders' equity. |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Cost or amortized cost | 766.7 | 890.2
Trading Securities, Unrealized Holding Gain | 229.9 | 271.0
Trading Securities, Unrealized Holding Loss | (9.1) | (3.6)
Net foreign currency gains (losses) | (1.4) | (0.8)
Fixed maturity investments, at fair value | 986.1 | 1,156.8
Convertible Debt Securities |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Cost or amortized cost | 45.0 | 71.7
Trading Securities, Unrealized Holding Gain | 4.4 | 9.9
Trading Securities, Unrealized Holding Loss | (1.1) | (0.9)
Net foreign currency gains (losses) | 0.6 | (0.2)
Fixed maturity investments, at fair value | 48.9 | 80.5
Other long-term investments. |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Cost or amortized cost | 256.1 | 238.3
Trading Securities, Unrealized Holding Gain | 85.5 | 79.6
Trading Securities, Unrealized Holding Loss | (21.6) | (26.6)
Net foreign currency gains (losses) | 0.9 | (2.4)
Fixed maturity investments, at fair value | $ 320.9 | $ 288.9

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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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