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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | $ (3.9) | $ (2.0) | $ 17.5 | $ 6.3
Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 1.8 | (2.2) | 2.2 | (2.4)
Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 0.9 | (0.7) | 3.7 | 0
Convertible Debt Securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 0.1 | 0 | 3.3 | 0
Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | $ (6.7) | $ 0.9 | $ 8.3 | $ 8.7

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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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