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Investment Securities (Investment Holdings) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Investment securities |  |
Fixed maturity investments, at fair value | $ 2,639.7 | $ 2,422.0
Including Short Term Fixed |  |
Investment securities |  |
Duration of Fixed Maturities | 2 years 2 months 12 days |
US Government and agency obligations |  |
Investment securities |  |
Trading Securities, Cost | $ 160.4 | 105.4
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 160.0 | 105.2
Trading Securities, Unrealized Holding Gain | 0.0 | 0.1
Trading Securities, Unrealized Holding Loss | (0.4) | (0.3)
Debt securities issued by corporations |  |
Investment securities |  |
Trading Securities, Cost | 1,001.0 | 1,162.0
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 1,000.0 | 1,171.7
Trading Securities, Unrealized Holding Gain | 4.3 | 13.1
Trading Securities, Unrealized Holding Loss | (5.3) | (3.4)
Municipal obligations |  |
Investment securities |  |
Trading Securities, Cost | 227.8 | 81.0
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 228.8 | 82.2
Trading Securities, Unrealized Holding Gain | 2.2 | 1.4
Trading Securities, Unrealized Holding Loss | (1.2) | (0.2)
Mortgage-backed and asset-backed securities |  |
Investment securities |  |
Trading Securities, Cost | 1,170.6 | 967.5
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 1,167.0 | 967.9
Trading Securities, Unrealized Holding Gain | 2.0 | 2.8
Trading Securities, Unrealized Holding Loss | (5.6) | (2.4)
Foreign government, agency and provincial obligations |  |
Investment securities |  |
Trading Securities, Cost | 1.0 | 11.5
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 1.2 | 10.8
Trading Securities, Unrealized Holding Gain | 0.2 | 0.3
Trading Securities, Unrealized Holding Loss | 0.0 | (1.0)
Preferred stocks |  |
Investment securities |  |
Trading Securities, Cost | 78.3 | 78.3
Net foreign currency gains (losses) | 0.0 | 0.0
Fixed maturity investments, at fair value | 82.7 | 84.2
Trading Securities, Unrealized Holding Gain | 4.4 | 5.9
Trading Securities, Unrealized Holding Loss | 0.0 | 0.0
Fixed Income Investments [Member] |  |
Investment securities |  |
Trading Securities, Cost | 2,639.1 | 2,405.7
Net foreign currency gains (losses) | 0.0 | 0.0
Total fixed maturity investments | 2,639.7 | 2,422.0
Trading Securities, Unrealized Holding Gain | 13.1 | 23.6
Trading Securities, Unrealized Holding Loss | $ (12.5) | $ (7.3)
Excluding Short Term Investments |  |
Investment securities |  |
Duration of Fixed Maturities | 2 years 4 months 24 days |

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