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Investment Securities OneBeacon Surplus Notes (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Dec. 31, 2016 | Dec. 23, 2014
Interest Paid | $ 0.2 | $ 0.2 |  |
OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | (31.4) |  | $ (29.1) |
Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | $ (9.8) |  |  |
Surplus Note |  |  |  |
Interest Paid |  | $ 2.4 |  |
Surplus Note | OneBeacon [Member] |  |  |  |
Basis points | 4.00% |  | 2.50% |
Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | $ (21.6) |  |  |
Surplus Note |  |  |  |
RBC Score | 250.00% |  | 250.00% |
Par Value [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | $ 101.0 |  | $ 101.0 | $ 101.0
Par Value [Member] | Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | 57.9 |  |  |
Par Value [Member] | Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | 43.1 |  |  |
Fair Value [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | 69.6 |  | 71.9 |
Fair Value [Member] | Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | 48.1 |  |  |
Fair Value [Member] | Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Surplus Notes | 21.5 |  |  |
Current market rates on repayments [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | 9.0 |  | 5.1 |
Current market rates on repayments [Member] | Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | 7.2 |  |  |
Current market rates on repayments [Member] | Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | 1.8 |  |  |
Regulatory Approval [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | (10.3) |  | (15.6) |
Regulatory Approval [Member] | Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | 2.9 |  |  |
Regulatory Approval [Member] | Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | (13.2) |  |  |
Liquidity Adjustment [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | (30.1) |  | $ (18.6) |
Liquidity Adjustment [Member] | Seller Priority Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | (19.9) |  |  |
Liquidity Adjustment [Member] | Pari Passu Surplus Note [Member] | OneBeacon [Member] |  |  |  |
Assets, Fair Value Adjustment | $ (10.2) |  |  |

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