Derivatives Additional Collateral (Details) - White Mountains Life Re - USD ($) $ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
Jun. 30, 2015 |
|---|---|---|---|
| Credit risk on derivative instruments | |||
| Collateral cash and investments | $ 0.0 | $ 5.8 | $ 25.3 |
| Cash | |||
| Credit risk on derivative instruments | |||
| Derivative collateral right to reclaim | 0.0 | 5.8 | 20.9 |
| Fixed maturity investments. | |||
| Credit risk on derivative instruments | |||
| Derivative collateral right to reclaim | $ 0.0 | $ 0.0 | $ 4.4 |