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Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re $ in Thousands | Dec. 31, 2015 USD ($) Rating
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Variable Annuity Reinsurance [Line Items] |
Net amounts recognized in Other Assets | $ 20,100
Credit risk on derivative instruments |
Net exposure on fair value of OTC instruments | $ 19,000
S&P Credit Ratings | Rating | 23
Derivative, Collateral, Right to Reclaim Cash | $ 0
Derivative, Collateral, Right to Reclaim Securities | 0
Derivative Asset, Fair Value, Amount Offset Against Collateral | 20,100
Excess collateral provided to counterparty in cash | 5,800
Excess collateral providedto counterparty in financial instruments | 0
Derivative, Collateral, Obligation to Return Cash | 6,900
A | Citigroup OTC [Member] |
Variable Annuity Reinsurance [Line Items] |
Net amounts recognized in Other Assets | 9,900
Credit risk on derivative instruments |
Net exposure on fair value of OTC instruments | 8,500
Derivative, Collateral, Right to Reclaim Cash | 0
Derivative, Collateral, Right to Reclaim Securities | 0
Derivative Asset, Fair Value, Amount Offset Against Collateral | 9,900
Excess collateral provided to counterparty in cash | 0
Excess collateral providedto counterparty in financial instruments | 0
Derivative, Collateral, Obligation to Return Cash | 1,400
A | Bank of America [Member] |
Variable Annuity Reinsurance [Line Items] |
Net amounts recognized in Other Assets | 700
Credit risk on derivative instruments |
Net exposure on fair value of OTC instruments | 700
Derivative, Collateral, Right to Reclaim Cash | 0
Derivative, Collateral, Right to Reclaim Securities | 0
Derivative Asset, Fair Value, Amount Offset Against Collateral | 700
Excess collateral provided to counterparty in cash | 0
Excess collateral providedto counterparty in financial instruments | 0
Derivative, Collateral, Obligation to Return Cash | 0
A | Citigroup Exchange Traded [Member] |
Variable Annuity Reinsurance [Line Items] |
Net amounts recognized in Other Assets | 1,000
Credit risk on derivative instruments |
Net exposure on fair value of OTC instruments | 6,800
Derivative, Collateral, Right to Reclaim Cash | 0
Derivative, Collateral, Right to Reclaim Securities | 0
Derivative Asset, Fair Value, Amount Offset Against Collateral | 1,000
Excess collateral provided to counterparty in cash | 5,800
Excess collateral providedto counterparty in financial instruments | 0
Derivative, Collateral, Obligation to Return Cash | 0
Standard & Poor's, A+ Rating [Member] | J P Morgan Chase [Member] |
Variable Annuity Reinsurance [Line Items] |
Net amounts recognized in Other Assets | 8,500
Credit risk on derivative instruments |
Net exposure on fair value of OTC instruments | 3,000
Derivative, Collateral, Right to Reclaim Cash | 0
Derivative, Collateral, Right to Reclaim Securities | 0
Derivative Asset, Fair Value, Amount Offset Against Collateral | 8,500
Excess collateral provided to counterparty in cash | 0
Excess collateral providedto counterparty in financial instruments | 0
Derivative, Collateral, Obligation to Return Cash | $ 5,500

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