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Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | $ 21.7 | $ 36.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 42.1 | 38.7
Net Realized and Unrealized Gain (Loss) on Trading Securities | 63.8 | 75.2
Tax on net realized and unrealized gains (loss), trading securities | 15.7 | 13.7
Realized and unrealized gain | 48.1 | 61.5
Fixed maturity investments. |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | 0.9 | 8.0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 31.6 | (26.0)
Short-term investments |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | 0 | 0.1
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 0 | 0
Common equity securities |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | 18.8 | 22.4
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 4.5 | 61.9
Convertible fixed maturity investments |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | 2.4 | 2.7
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 0.7 | (1.3)
Other long-term investments |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | (0.3) | 2.9
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 5.3 | 4.1
Forward Contracts |  |
Investment securities |  |
Trading Securities, Realized Gain (Loss), Total | (0.1) | 0.4
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | $ 0 | $ 0

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- Definition The sum of the realized and unrealized net gain (loss) on trading securities during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + Details
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- Definition Net Realized and Unrealized Gain (Loss) on Trading Securities, Net of Tax + References No definition available. + Details
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- Definition The aggregate of the change in unrealized holding gain (loss) and foreign currency gain (loss) included in earnings during the reporting period. + References No definition available. + Details
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- Definition Tax on net realized and unrealized gains (loss), trading securities + References No definition available. + Details
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- Definition Trading Securities, Realized Gain (Loss), Total + References No definition available. + Details
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