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Derivatives (Realized and Unrealized Gains (Losses) (Details) (White Mountains Life Re, USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012 | Dec. 31, 2012
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |
Realized and unrealized (losses) gains | $ (63.5) | $ 95.5 | $ (245.3) | $ (111.0) |
Derivative, fair value, net | 141.3 |  | 141.3 |  | 98.3
Fixed income/interest rate |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |
Realized and unrealized (losses) gains | (8.5) | 28.6 | (39.3) | (50.5) |
Derivative, fair value, net | 11.4 |  | 11.4 |  | 27.1
Foreign exchange |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |
Realized and unrealized (losses) gains | (22.0) | 27.4 | (75.6) | (27.5) |
Derivative, fair value, net | 70.6 |  | 70.6 |  | 52.8
Equity |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |
Realized and unrealized (losses) gains | (33.0) | 39.5 | (130.4) | (33.0) |
Derivative, fair value, net | $ 59.3 |  | $ 59.3 |  | $ 18.4

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