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Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re $ in Thousands | Sep. 30, 2015 USD ($) Rating | Dec. 31, 2014 USD ($)
--- | --- | ---
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | $ 37,000 | $ 56,400
Collertal provided to counterparty in cash | 2,200 | 3,500
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 39,200 | 59,900
Excess collateral provided to counterparty in cash | 14,200 | 17,700
Derivative, Collateral, Right to Reclaim Securities | 0 | 9,500
Counter-party collateral held by WMLife Re - Cash | 11,200 | 9,900
Net amount of exposure to counter-party | $ 42,200 | 77,200
S and P Credit Ratings | Rating | 23 |
Standard & Poor's, A Rating | Bank of America [Member] |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | $ 3,200 | 5,600
Collertal provided to counterparty in cash | 0 | 0
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 3,200 | 5,600
Excess collateral provided to counterparty in cash | 0 | 0
Derivative, Collateral, Right to Reclaim Securities | 0 | 0
Counter-party collateral held by WMLife Re - Cash | 0 | 0
Net amount of exposure to counter-party | 3,200 | 5,600
Standard & Poor's, A Rating | Barclays |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | 0 | 100
Collertal provided to counterparty in cash | 0 | 0
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 0 | 100
Excess collateral provided to counterparty in cash | 0 | 0
Derivative, Collateral, Right to Reclaim Securities | 0 | 0
Counter-party collateral held by WMLife Re - Cash | 0 | 0
Net amount of exposure to counter-party | 0 | 100
Standard & Poor's, A Rating | Royal Bank of Scotland |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments |  | 4,000
Collertal provided to counterparty in cash |  | 0
Collateral provided to counterparty in financial instruments |  | 0
Net amount of exposure after effect of collateral |  | 4,000
Excess collateral provided to counterparty in cash |  | 0
Derivative, Collateral, Right to Reclaim Securities |  | 0
Counter-party collateral held by WMLife Re - Cash |  | 0
Net amount of exposure to counter-party |  | 4,000
Standard & Poor's, A Rating | Citigroup - OTC |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | 18,600 | 22,200
Collertal provided to counterparty in cash | 0 | 0
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 18,600 | 22,200
Excess collateral provided to counterparty in cash | 0 | 0
Derivative, Collateral, Right to Reclaim Securities | 0 | 0
Counter-party collateral held by WMLife Re - Cash | 5,300 | 1,100
Net amount of exposure to counter-party | 13,300 | 21,100
Standard & Poor's, A Rating | Citigroup Exchange Traded [Member] |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | (2,100) | 3,700
Collertal provided to counterparty in cash | 2,100 | 0
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 0 | 3,700
Excess collateral provided to counterparty in cash | 12,800 | 16,000
Derivative, Collateral, Right to Reclaim Securities | 0 | 0
Counter-party collateral held by WMLife Re - Cash | 0 | 0
Net amount of exposure to counter-party | 12,800 | 19,700
Standard & Poor's, A plus | JP Morgan |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | 15,900 | 24,300
Collertal provided to counterparty in cash | 0 | 0
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 15,900 | 24,300
Excess collateral provided to counterparty in cash | 0 | 0
Derivative, Collateral, Right to Reclaim Securities | 0 | 0
Counter-party collateral held by WMLife Re - Cash | 5,900 | 8,800
Net amount of exposure to counter-party | 10,000 | 15,500
Standard & Poor's, BBB plus Rating | Royal Bank of Scotland |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | 1,500 |
Collertal provided to counterparty in cash | 0 |
Collateral provided to counterparty in financial instruments | 0 |
Net amount of exposure after effect of collateral | 1,500 |
Excess collateral provided to counterparty in cash | 0 |
Derivative, Collateral, Right to Reclaim Securities | 0 |
Counter-party collateral held by WMLife Re - Cash | 0 |
Net amount of exposure to counter-party | 1,500 |
Standard & Poor's, BBB plus Rating | Nomura [Member] |  |
Credit risk on derivative instruments |  |
Excess collateral provided - Financial Instruments | (100) | (3,500)
Collertal provided to counterparty in cash | 100 | 3,500
Collateral provided to counterparty in financial instruments | 0 | 0
Net amount of exposure after effect of collateral | 0 | 0
Excess collateral provided to counterparty in cash | 1,400 | 1,700
Derivative, Collateral, Right to Reclaim Securities | 0 | 9,500
Counter-party collateral held by WMLife Re - Cash | 0 | 0
Net amount of exposure to counter-party | $ 1,400 | $ 11,200

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