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Derivatives (Realized and Unrealized Gains (Losses)) (Details) - White Mountains Life Re - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |
Change in fair value of derivatives, included in other revenue | $ (2.0) | $ (8.8) |
Carrying value | 0.0 | 20.1 | $ 56.4
Fixed income/interest rate |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |
Change in fair value of derivatives, included in other revenue | 1.8 | 6.4 |
Carrying value | 0.0 |  |
Foreign exchange |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |
Change in fair value of derivatives, included in other revenue | (4.8) | (7.3) |
Carrying value | 0.0 |  |
Equity |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |
Change in fair value of derivatives, included in other revenue | 1.0 | $ (7.9) |
Carrying value | $ 0.0 |  |

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