Acqusitions and Dispositions	3 Months Ended
Mar. 31, 2014
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions Runoff Business As described in Note 1, in October 2012, OneBeacon entered into the Stock Purchase Agreement with respect to the sale of its Runoff Business to Armour. Pursuant to the terms of the Stock Purchase Agreement, at closing, OneBeacon will transfer to Armour all of the issued and outstanding shares of common stock of certain legal entities that will contain the assets, liabilities (including gross and ceded loss reserves) and capital supporting the business as well as certain elements of the Runoff Business infrastructure, including staff and office space. Additionally, as part of the Runoff Transaction, OneBeacon may provide, under certain scenarios, financing in the form of surplus notes. The Runoff Transaction is subject to various closing conditions, primarily the receipt of regulatory approvals. The regulatory review process has included a third party actuarial review of the Runoff Business loss and LAE reserves, completed in September of 2013; in addition, an independent stochastic modeling of the future cash flows of the Runoff Business was subsequently required. At closing, Armour and/or OneBeacon Insurance Company ("OBIC") and certain legal entities within the ongoing OneBeacon structure will enter into various ancillary agreements, including the amendment of existing reinsurance agreements and administrative services agreements, to support the separation of the Runoff Business and subsequent transfer to Armour. Also as part of the Runoff Transaction, at closing, OneBeacon and Armour will enter into a Transition Services Agreement (“TSA”), pursuant to which OneBeacon will provide certain transition services to Armour during the term of the TSA, which has an initial term of one year. OneBeacon has concluded that continuing involvement after the closing of the transaction is insignificant relative to the business being sold. The Pennsylvania Insurance Department is currently conducting a required examination of the Runoff Business as part of its regulatory review of the Runoff Transaction. The Company expects the Runoff Transaction to close in the second half of 2014. As described in Note 1, the Runoff Business is presented as held for sale as of March 31, 2014 and December 31, 2013, and as discontinued operations for the three months ended March 31, 2014 and 2013. See Note 15—"Discontinued Operations" for further information regarding balances classified as held for sale and activity reported as discontinued operations. Essentia Insurance Company Effective January 1, 2013, OneBeacon completed the sale of Essentia Insurance Company ("Essentia"), an indirect wholly-owned subsidiary which wrote the collector cars and boats business, to Markel Corporation. Concurrently, OneBeacon and Hagerty Insurance Agency ("Hagerty") terminated their underwriting arrangement with respect to the collector cars and boats business. OneBeacon recognized a pre-tax gain on sale of $23.0 million ($15.0 million after tax) in the first quarter of 2013. The Company had negligible earned premiums for the three months ended March 31, 2014 and earned premiums of $40.6 million for the three months ended March 31, 2013 related to the Collector Cars and Boats underwriting operating segment.

Acquisitions and Dispositions

Runoff Business

As described in Note 1, in October 2012, OneBeacon entered into the Stock Purchase Agreement with respect to the sale of its Runoff Business to Armour. Pursuant to the terms of the Stock Purchase Agreement, at closing, OneBeacon will transfer to Armour all of the issued and outstanding shares of common stock of certain legal entities that will contain the assets, liabilities (including gross and ceded loss reserves) and capital supporting the business as well as certain elements of the Runoff Business infrastructure, including staff and office space. Additionally, as part of the Runoff Transaction, OneBeacon may provide, under certain scenarios, financing in the form of surplus notes.

The Runoff Transaction is subject to various closing conditions, primarily the receipt of regulatory approvals. The regulatory review process has included a third party actuarial review of the Runoff Business loss and LAE reserves, completed in September of 2013; in addition, an independent stochastic modeling of the future cash flows of the Runoff Business was subsequently required. At closing, Armour and/or OneBeacon Insurance Company ("OBIC") and certain legal entities within the ongoing OneBeacon structure will enter into various ancillary agreements, including the amendment of existing reinsurance agreements and administrative services agreements, to support the separation of the Runoff Business and subsequent transfer to Armour. Also as part of the Runoff Transaction, at closing, OneBeacon and Armour will enter into a Transition Services Agreement (“TSA”), pursuant to which OneBeacon will provide certain transition services to Armour during the term of the TSA, which has an initial term of one year. OneBeacon has concluded that continuing involvement after the closing of the transaction is insignificant relative to the business being sold.

The Pennsylvania Insurance Department is currently conducting a required examination of the Runoff Business as part of its regulatory review of the Runoff Transaction. The Company expects the Runoff Transaction to close in the second half of 2014.

As described in Note 1, the Runoff Business is presented as held for sale as of March 31, 2014 and December 31, 2013, and as discontinued operations for the three months ended March 31, 2014 and 2013. See Note 15—"Discontinued Operations" for further information regarding balances classified as held for sale and activity reported as discontinued operations.

Essentia Insurance Company

Effective January 1, 2013, OneBeacon completed the sale of Essentia Insurance Company ("Essentia"), an indirect wholly-owned subsidiary which wrote the collector cars and boats business, to Markel Corporation. Concurrently, OneBeacon and Hagerty Insurance Agency ("Hagerty") terminated their underwriting arrangement with respect to the collector cars and boats business. OneBeacon recognized a pre-tax gain on sale of $23.0 million ($15.0 million after tax) in the first quarter of 2013. The Company had negligible earned premiums for the three months ended March 31, 2014 and earned premiums of $40.6 million for the three months ended March 31, 2013 related to the Collector Cars and Boats underwriting operating segment.