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Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | $ 30.5 | $ 22.8 | $ 52.2 | $ 59.4
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 83.4 | (60.1) | 125.5 | (21.5)
Net Realized and Unrealized Gain (Loss) on Trading Securities | 113.9 | (37.3) | 177.7 | 37.9
Tax on net realized and unrealized gains (loss), trading securities | (23.0) | 12.5 | (38.7) | (1.2)
Realized and unrealized gain | 90.9 | (24.8) | 139.0 | 36.7
Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | 8.7 | 2.8 | 9.6 | 10.8
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 53.1 | (44.3) | 84.7 | (70.3)
Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | 0 | 0.7 | 0 | 0.8
Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | 19.4 | 22.9 | 38.2 | 45.3
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 22.4 | (19.4) | 26.9 | 42.5
Convertible fixed maturity investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | 1.5 | (3.4) | 3.9 | (0.6)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | (2.1) | (1.4) | (1.4) | (2.8)
Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | 0.9 | 0 | 0.6 | 2.9
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 10.0 | 5.0 | 15.3 | 9.1
Forward Contracts |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss), Total | $ 0 | $ (0.2) | $ (0.1) | $ 0.2

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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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