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Derivatives Realized and Unrealized Gains (Losses) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015 | Mar. 31, 2016 | Dec. 31, 2015 | Mar. 31, 2015 | Dec. 31, 2014
Variable Annuity Reinsurance [Line Items] |  |  |  |  |  |  |  |
Equity in earnings of unconsolidated affiliates, net of tax | $ 0.0 | $ 6.8 | $ 0.0 | $ 14.1 |  |  |  |
White Mountains Life Re |  |  |  |  |  |  |  |
Variable Annuity Reinsurance [Line Items] |  |  |  |  |  |  |  |
Derivative, Fair Value, Amount Offset Against Collateral, Net | 0.0 |  | 0.0 |  |  | $ 20.1 |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | (0.3) | (2.3) | (2.0) | (7.8) |  |  |  |
Derivative, fair value, net | 0.0 | 35.7 | 0.0 | 35.7 | $ 13.1 | 20.1 | $ 47.0 | $ 56.4
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0.0 |  | 0.0 |  |  |  |  |
Derivative Transfers In (Out), Net | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | 12.8 | 9.0 | 18.1 | 12.9 |  |  |  |
Fixed income/interest rate | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | 0.0 | (5.9) | 1.8 | 3.4 |  |  |  |
Derivative, fair value, net | 0.0 |  | 0.0 |  |  | 0.5 |  |
Foreign exchange | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | (0.6) | 9.2 | (4.8) | (2.9) |  |  |  |
Derivative, fair value, net | 0.0 |  | 0.0 |  |  | 14.8 |  |
Equity | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | 0.3 | (5.6) | 1.0 | (8.3) |  |  |  |
Derivative, fair value, net | 0.0 |  | 0.0 |  |  | 4.8 |  |
Level 2 Inputs | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | (1.8) | 0.6 | (0.7) | (5.9) |  |  |  |
Derivative, fair value, net | 0.0 | 32.5 | 0.0 | 32.5 | 10.3 | 16.5 | 31.2 | 33.8
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0.0 |  | 0.0 |  |  |  |  |
Derivative Transfers In (Out), Net | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | 8.5 | (0.7) | 15.8 | (4.6) |  |  |  |
Level 1 Inputs | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | (0.2) | 5.4 | (4.2) | 7.1 |  |  |  |
Derivative, fair value, net | 0.0 | (5.1) | 0.0 | (5.1) | 0.2 | 0.9 | (1.2) | 3.7
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0.0 |  | 0.0 |  |  |  |  |
Derivative Transfers In (Out), Net | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements |  | 9.3 | (3.3) | 15.9 |  |  |  |
Fair Value, Inputs, Level 3 [Member] | Variable Annuity | White Mountains Life Re |  |  |  |  |  |  |  |
Variable Annuity Reinsurance [Line Items] |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | 0.0 | (1.8) | 0.0 | (1.8) | (0.1) | (0.3) | (1.1) | (0.7)
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0.0 |  | 0.0 |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings | 0.1 | 0.7 | (0.3) | 1.1 |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value Measurement with Unobservable Inputs, Reconciliation, Recurring Basis, Liability Sales or Settlements | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | White Mountains Life Re |  |  |  |  |  |  |  |
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments |  |  |  |  |  |  |  |
Realized and unrealized gains (losses) | 1.7 | (8.3) | 2.9 | (9.0) |  |  |  |
Derivative, fair value, net | 0.0 | 8.3 | 0.0 | 8.3 | $ 2.6 | $ 2.7 | $ 17.0 | $ 18.9
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0.0 |  | 0.0 |  |  |  |  |
Derivative Transfers In (Out), Net | 0.0 | 0.0 | 0.0 | 0.0 |  |  |  |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | $ 4.3 | $ 0.4 | $ 5.6 | $ 1.6 |  |  |  |

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