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Reserves for Unpaid Losses and Loss Adjustment Expenses Reserves for Unpaid Losses and Loss Adjustment Expenses (Schedule of Ending Liabilities for Unpaid Loss and LAE, Net of Reinsurance) (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Less: Discount on workers compensation reserves | $ (1.6) | $ (1.1) |  |
Total unpaid loss and LAE reserves, net of reinsurance | 1,192.7 | 1,203.8 | $ 1,180.6 | $ 974.1
Plus: Total Reinsurance recoverables on unpaid losses | 172.9 | 186.0 |  |
Total unpaid loss and LAE reserves | 1,365.6 | $ 1,389.8 | $ 1,342.2 | $ 1,054.3
OneBeacon |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 1,153.0 |  |  |
Less: Discount on workers compensation reserves | (1.6) |  |  |
Total unpaid loss and allocated LAE reserves, net of reinsurance | 1,151.4 |  |  |
Plus: Unallocated LAE | 41.3 |  |  |
Total unpaid loss and LAE reserves, net of reinsurance | 1,192.7 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | $ 172.9 |  |  |
Percentage of quota share reinsurance agreement | 100.00% |  |  |
Total unpaid loss and LAE reserves | $ 1,365.6 |  |  |
OneBeacon | Investing, Financing and Corporate |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 18.3 |  |  |
Total unpaid loss and LAE reserves | 18.3 |  |  |
Property | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 30.2 |  |  |
Property | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 108.5 |  |  |
Property | OneBeacon | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 30.2 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 40.9 |  |  |
Property | OneBeacon | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 108.5 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 13.2 |  |  |
Casualty | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 568.7 |  |  |
Casualty | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 360.0 |  |  |
Casualty | OneBeacon | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 568.7 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 64.0 |  |  |
Casualty | OneBeacon | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 360.0 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 19.9 |  |  |
Other | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 38.2 |  |  |
Other | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 47.4 |  |  |
Other | OneBeacon | Specialty Products |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 38.2 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | 16.0 |  |  |
Other | OneBeacon | Specialty Industries |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Total unpaid and undiscounted loss and allocated LAE reserves, net of reinsurance | 47.4 |  |  |
Plus: Total Reinsurance recoverables on unpaid losses | $ 0.6 |  |  |

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