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Investment Securities (Investment gains (losses) for Level 3) (Details) (Level 3 Inputs, USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended | 3 Months Ended | 6 Months Ended
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Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 Fixed maturity investments. | Jun. 30, 2013 Fixed maturity investments. | Jun. 30, 2014 Fixed maturity investments. | Jun. 30, 2013 Fixed maturity investments. | Jun. 30, 2014 Common equity securities | Jun. 30, 2013 Common equity securities | Jun. 30, 2014 Common equity securities | Jun. 30, 2013 Common equity securities | Jun. 30, 2014 Convertible Debt Securities | Dec. 31, 2011 Convertible Debt Securities | Jun. 30, 2014 Convertible Debt Securities | Jun. 30, 2013 Convertible Debt Securities | Jun. 30, 2014 Other long-term investments | Jun. 30, 2013 Other long-term investments | Jun. 30, 2014 Other long-term investments | Jun. 30, 2013 Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrealized gains (losses) on investments | $ 14.3 | $ 1.8 | $ 21.4 | $ 8.3 | $ 0.2 | $ (0.4) | $ 0.4 | $ (0.2) | $ 2.0 | $ 0.8 | $ 2.8 | $ 0.7 | $ 3.2 | $ 0 | $ 3.2 | $ 0 | $ 8.9 | $ 1.4 | $ 15.0 | $ 7.8

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- Definition The aggregate increase (decrease) in the market value of unsold investments whose gains (losses) are included in earnings. + References No definition available. + Details
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