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Investment Securities (Investment Gains (Losses) For Level 3) (Details) (Level 3 Inputs, USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Investment securities |  |  |
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments | $ 17.7 | $ (45.6) | $ 30.0
Fixed maturity investments |  |  |
Investment securities |  |  |
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments | 7.7 | (12.2) | 10.2
Common equity securities |  |  |
Investment securities |  |  |
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments | 3.0 | (16.6) | (19.2)
Convertible fixed maturity investments |  |  |
Investment securities |  |  |
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments | 0 | 0 | 0
Other long-term investments |  |  |
Investment securities |  |  |
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments | $ 7.0 | $ (16.8) | $ 39.0

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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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