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Derivatives (Additional Collateral) (Details) - White Mountains Life Re - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | ---
Credit risk on derivative instruments |  |  |
Collateral Cash and Investments | $ 0.0 | $ 5.8 | $ 33.2
Cash |  |  |
Credit risk on derivative instruments |  |  |
Derivative Collateral Right to Reclaim | 0.0 | $ 5.8 |
Fixed maturity investments |  |  |
Credit risk on derivative instruments |  |  |
Derivative Collateral Right to Reclaim | $ 0.0 |  |

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