OneBeacon Insurance 10-Q 3 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Jul. 30, 2015
Entity Registrant Name	OneBeacon Insurance Group, Ltd.
Entity Central Index Key	1,369,817
Document Type	10-Q
Document Period End Date	Jun. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q2
Class A common
Entity Common Stock, Shares Outstanding		23,509,098
Class B common
Entity Common Stock, Shares Outstanding		71,754,738

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Investment Securities:
Fixed maturity investments, at fair value	$ 1,941.1	$ 1,799.8
Short-term investments, at amortized cost (which approximates fair value)	157.9	202.2
Common equity securities, at fair value	304.3	320
Convertible fixed maturity investments, at fair value	0	5
Other investments	174.9	198.8
Total investments	2,578.2	2,525.8
Cash	106.2	87
Reinsurance recoverables	168	173.8
Premiums receivable	292.2	241.5
Funds Held under Reinsurance Agreements, Asset	49.3	37.1
Deferred acquisition costs	111.8	103.2
Net deferred tax asset	136.5	131.8
Investment income accrued	10.3	10
Accounts receivable on unsettled investment sales	1.1	7.2
Other assets	208.7	202.7
Assets held for sale	0	58.1
Total assets	3,662.3	3,578.2
Liabilities
Unpaid loss and loss adjustment expense reserves	1,350.8	1,342.2
Unearned premiums	616.2	588.3
Funds held under reinsurance agreements, liability	102.6	81
Debt	274.7	274.7
Accounts payable on unsettled investment purchases	20.1	0.5
Other liabilities	261.2	242.2
Total liabilities	2,625.6	2,528.9
OneBeacon's common shareholders' equity
Common shares and paid-in surplus (par value $0.01; authorized, 200,000,000 shares; issued and outstanding, 95,263,836 and 95,296,387 shares)	1,023.2	1,023.7
Retained earnings	14.8	27.3
Accumulated other comprehensive loss, after tax	(4.8)	(5.2)
Total OneBeacon's common shareholders' equity	1,033.2	1,045.8
Total noncontrolling interests, after tax	3.5	3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,036.7	1,049.3
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	$ 3,662.3	$ 3,578.2

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common shares, authorized shares (in shares)	200,000,000	200,000,000
Common shares, issued shares (in shares)	95,263,836	95,296,387

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues
Earned premiums	$ 319.3	$ 290.9	$ 605.9	$ 567.4
Net investment income	10.1	12.2	20.6	22.6
Net realized and change in unrealized investment gains	(14)	21.9	0.2	40.8
Net other revenues (expenses)	(1.2)	1	(4.3)	2
Total revenues	314.2	326	622.4	632.8
Expenses
Loss and loss adjustment expenses	194.5	186.1	360.4	335.5
Policy acquisition expenses	56.4	49.6	107.4	96.3
Other underwriting expenses	52.9	51.7	108.8	101.1
General and administrative expenses	4.2	3.6	8.3	6.9
Interest expense	3.3	3.3	6.5	6.5
Total expenses	311.3	294.3	591.4	546.3
Pre-tax income from continuing operations	2.9	31.7	31	86.5
Income tax benefit (expense)	0.9	(5.9)	(2.5)	(13)
Net income from continuing operations	3.8	25.8	28.5	73.5
Loss from discontinued operations, net of tax	(0.2)	(0.1)	(0.3)	(0.6)
(Loss) gain from sale of discontinued operations, net of tax	0.3	(0.5)	0.3	(0.5)
Net income, including noncontrolling interests	3.9	25.2	28.5	72.4
Less: Net income attributable to noncontrolling interests	(0.5)	(0.5)	(1)	(0.9)
Net income attributable to OneBeacon's common shareholders	3.4	24.7	27.5	71.5
Other comprehensive income, net of tax	0.2	0.1	0.4	0.1
Comprehensive income attributable to OneBeacon's common shareholders	$ 3.6	$ 24.8	$ 27.9	$ 71.6
Earnings (loss) per share attributable to OneBeacon's common shareholders—basic and diluted
Net income from continuing operations, per share	$ 0.03	$ 0.26	$ 0.29	$ 0.76
Loss from discontinued operations, net of tax, per share	0	0	0	(0.01)
Net income attributable to OneBeacon's common shareholders per share	0.03	0.26	0.29	0.75
Dividends declared and paid per OneBeacon's common share	$ 0.21	$ 0.21	$ 0.42	$ 0.42

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus	Retained earnings	Accum. other comprehensive income (loss)	Total OneBeacon common shareholders' equity	Noncontrolling interests, after tax
Balances at Dec. 31, 2013	$ 1,106.8	$ 1,022.5	$ 74.4	$ 6.8	$ 1,103.7	$ 3.1
Increase (Decrease) in Stockholders' Equity
Net income	72.4	0	71.5	0	71.5	0.9
Net change in benefit plan assets and obligations, net of tax	0.1	0	0	0.1	0.1	0
Total comprehensive income	72.5	0	71.5	0.1	71.6	0.9
Amortization of restricted share awards	1.6	1.6	0	0	1.6	0
Issuance of common shares	0.2	0	0	0	0	0.2
Repurchase and retirement of common shares	(1.8)	(1.8)	0	0	(1.8)	0
Dividends, Common Stock, Cash	(41)	0	(40)	0	(40)	(1)
Balances at Jun. 30, 2014	1,138.3	1,022.3	105.9	6.9	1,135.1	3.2
Balances at Dec. 31, 2014	1,049.3	1,023.7	27.3	(5.2)	1,045.8	3.5
Increase (Decrease) in Stockholders' Equity
Net income	28.5	0	27.5	0	27.5	1
Net change in benefit plan assets and obligations, net of tax	0.4	0	0	0.4	0.4	0
Total comprehensive income	28.9	0	27.5	0.4	27.9	1
Amortization of restricted share awards	1.1	1.1	0	0	1.1	0
Issuance of common shares	0.1	0	0	0	0	0.1
Repurchase and retirement of common shares	(1.6)	(1.6)	0	0	(1.6)	0
Dividends, Common Stock, Cash	(41.1)	0	(40)	0	(40)	(1.1)
Balances at Jun. 30, 2015	$ 1,036.7	$ 1,023.2	$ 14.8	$ (4.8)	$ 1,033.2	$ 3.5

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operations:
Net income (loss) including noncontrolling interests	$ 28.5	$ 72.4
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net (income) loss from discontinued operations	0.3	0.6
Net loss (gain) from sale of discontinued operations	(0.3)	0.5
Net realized and change in unrealized investment gains	(0.2)	(40.8)
Net realized gain on sale of business	3.7	0
Deferred income tax expense	(3.8)	12.6
Other operating items:
Net change in loss and LAE reserves	(8.6)	(71.1)
Net change in unearned premiums	27.9	47
Net change in premiums receivable	(50.7)	(47.8)
Net change in reinsurance recoverable on paid and unpaid losses	5.8	(5.4)
Net change in funds held under reinsurance contracts	(12.2)	(30)
Net change in funds held under insurance contracts	21.6	(0.3)
Net change in other assets and liabilities	13.6	(24.4)
Net cash provided from operations—continuing operations	42.8	55.5
Net cash used for operations—discontinued operations	(0.3)	(33.9)
Net cash provided from (used for) operations	42.5	21.6
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments	44.3	80.1
Maturities of fixed maturity investments	115.8	185.6
Sales of fixed maturity investments	450	850.9
Sales of common equity securities	268.1	47.6
Sales of convertible fixed maturity investments	6.1	12.2
Distributions and redemptions of other investments	22.1	3.2
Purchases of fixed maturity investments	(714.1)	(1,101.9)
Purchases of common equity securities	(248.7)	(48.7)
Purchases of convertible fixed maturity investments	(0.8)	(8.4)
Contributions for other investments	(2.5)	(3.3)
Net change in unsettled investment purchases and sales	25.8	(31.8)
Proceeds from Sale of Property, Plant, and Equipment	56.8	0
Net acquisitions of property and equipment	(1.8)	(0.7)
Net cash provided from investing activities	21.1	(15.2)
Cash flows from financing activities:
Cash dividends paid to common shareholders	(40)	(40)
Payments for repurchase of common stock	(1.6)	(1.8)
Payments on capital lease obligation	(2.8)	(2.6)
Net cash used for financing activities	(44.4)	(44.4)
Net increase (decrease) in cash during period	19.2	(38)
Cash balance at beginning of period	87	168.1
Cash balance at end of period	$ 106.2	$ 130.1

Nature of Operations and Summar

Nature of Operations and Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Nature of Operations and Summary of Significant Accounting Policies	Nature of Operations and Summary of Significant Accounting Policies Basis of presentation These interim consolidated financial statements include the accounts of OneBeacon Insurance Group, Ltd. (the "Company" or the "Registrant") and its subsidiaries (collectively, "OneBeacon") and have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). The Company is an exempted Bermuda limited liability company with U.S.-based underwriting operating companies that are property and casualty insurance writers and a Bermuda-based reinsurance company, Split Rock Insurance, Ltd. ("Split Rock"), which primarily reinsures certain risks of affiliated entities. OneBeacon offers a wide range of specialty insurance products and services primarily through independent agencies, regional and national brokers, wholesalers and managing general agencies. OneBeacon is 75.3% owned by White Mountains Insurance Group, Ltd. ("White Mountains"), a holding company whose businesses provide property and casualty insurance, reinsurance and certain other products. The Company's headquarters are located at 14 Wesley Street, 5th Floor, Hamilton HM 11, Bermuda. The Company's U.S. corporate headquarters are located at 601 Carlson Parkway, Minnetonka, Minnesota 55305 and its registered office is located at Clarendon House, 2 Church Street, Hamilton HM 11, Bermuda. During the three months ended June 30, 2015 OneBeacon sold its building in Canton, Massachusetts, which is presented as held for sale in the December 31, 2014 consolidated balance sheets. On December 23, 2014, OneBeacon completed the sale of its run-off business to a subsidiary of Armour Group Holdings Limited (“Armour”). See Note 2—"Acquisitions and Dispositions" and Note 15—"Discontinued Operations." The run-off business included the results of OneBeacon's non-specialty commercial lines business and certain other run-off business, including the vast majority of asbestos and environmental reserves, as well as certain purchase accounting adjustments related to the run-off business (the “Runoff Business,” the sale of which is referred to as the “Runoff Transaction”). The Runoff Business has been presented as discontinued operations in the consolidated statements of operations for the three and six months ended June 30, 2015 and 2014 and in the consolidated statements of cash flows for the six months ended June 30, 2015 and 2014. The Runoff Business disposal group excludes investing and financing activities from amounts classified as discontinued operations. OneBeacon's investing and financing operations are conducted on an overall consolidated level and, accordingly, there are no separately identifiable investing or financing cash flows associated with the Runoff Business. The legal entities included in the sale held an agreed upon level of invested assets and capital at closing. OneBeacon's reportable segments are Specialty Products, Specialty Industries and Investing, Financing and Corporate. The Specialty Products segment is comprised of ten active underwriting operating segments, representing an aggregation based on those that offer distinct products and tailored coverages and services to a broad customer base across the United States. During the first quarter of 2015, the Company restructured its former Professional Insurance underwriting operating segment into four separate underwriting operating segments, which are included in Specialty Products: Healthcare, Management Liability, Financial Services and Other Professional Lines. The Specialty Industries segment is comprised of five active underwriting operating segments, representing an aggregation based on those that focus on solving the unique needs of a particular customer or industry group. The Investing, Financing and Corporate segment includes the investing and financing activities for OneBeacon on a consolidated basis, and certain other activities conducted through the Company and its intermediate subsidiaries. All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of OneBeacon. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2014 Annual Report on Form 10-K. The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Refer to the Company’s 2014 Annual Report on Form 10-K for a complete discussion regarding OneBeacon’s significant accounting policies. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. Recently Adopted Changes in Accounting Principles Qualified Affordable Housing Projects Effective January 1, 2015, OneBeacon adopted ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects ("QAHP") (ASC 323) . ASU 2014-01 allows investors in QAHP to make a policy election to use the proportional amortization method. Under the proportional amortization method, the investor amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the investment results, net of the related tax benefits, as a component of income tax expense. Prior to adoption, OneBeacon accounted for its QAHP investment under the equity method and recognized its share of its QAHP investment's losses in investment income. OneBeacon made the policy election to account for its QAHP investment using the proportional amortization method, applied retrospectively. Under the proportional amortization method, the cumulative loss recognized through December 31, 2014 increased by $1.2 million . As a result of the retrospective adoption, OneBeacon's common shareholders equity has been reduced by $0.6 million as of January 1, 2014. In addition, for the three and six months ended June 30, 2014 , the retrospective adoption resulted in increases of $0.5 million and $0.9 million , respectively, to net investment income and net increases of $0.6 million and $1.2 million , respectively, to income tax expense. Footnote disclosures for prior year amounts have been amended to be consistent with the restated amounts described above. Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity In April 2014, the Financial Accounting Standard Board ("FASB") issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (ASC 205 and ASC 360) to reduce diversity in practice for reporting discontinued operations. ASU 2014-08 limits discontinued operations treatment to disposals that represent a strategic shift and that have a major effect on a reporting entity’s operations and financial results to be reported as discontinued operations. The revised guidance also requires expanded disclosure in the financial statements for discontinued operations as well as for disposals of significant components of an entity that do not qualify for discontinued operations presentation. OneBeacon has not had any transactions that occurred since ASU 2014-08 became effective on December 15, 2014. Pushdown Accounting ASU 2014-17, Pushdown Accounting, a consensus of the FASB Emerging Issues Task Force (ASC 805) became effective upon its issuance on November 18, 2014. The new guidance, which is applicable prospectively, gives an acquired non-public company the option to apply pushdown accounting in its separate company financial statements in the period in which it is acquired in a change of control transaction. Once pushdown accounting has been applied, the election is irreversible. Acquired entities that chose not to apply pushdown accounting at the time of acquisition, may apply pushdown accounting in a subsequent period as a change in accounting principle under ASC 250, Accounting Changes and Error Corrections . OneBeacon has not had any acquisitions since ASU 2014-17 became effective. Unrecognized Tax Benefits Effective January 1, 2014, OneBeacon adopted ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists . The new ASU generally requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss ("NOL") carryforward or tax credit carryforward rather than as a liability. This adoption did not have any impact on the Company's financial position, results of operations, cash flows or financial statement presentation. Recently Issued Accounting Pronouncements Insurance Contracts In May 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944) which requires expanded footnote disclosures about loss and loss adjustment expense ("LAE") reserves. Under the new guidance, some disclosures currently presented outside of OneBeacon’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported ("IBNR") plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the disaggregated amounts of IBNR to which they relate, along with a discussion of any significant changes in methodology and assumptions and the related effect upon the loss reserves. The new guidance will be effective for annual periods beginning after December 15, 2015 and interim periods within annual periods beginning after December 15, 2016 with retrospective restatement of prior periods required. OneBeacon will modify its financial statement footnote disclosures to conform to the requirements of ASU 2015-09 upon adoption, including revisions to prior year’s disclosures. Fair Value Measurements In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement - Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or Its Equivalent) (ASC 820) which eliminates the requirement to disclose the fair value hierarchy level for investments for which fair value is measured at net asset value using the practical expedient in ASC 820. OneBeacon measures the fair value of its investments in hedge funds and private equity funds using this practical expedient and has classified those measurements within Level 3 of the fair value hierarchy. The new guidance is effective for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. Debt Issuance Costs In April 2015, the FASB issued ASU 2015-03, Imputation of Interest (ASC 835) which requires debt issuance costs related to a recognized debt liability to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. ASU 2015-03 is effective for annual and interim reporting periods beginning after December 15, 2015. OneBeacon does not expect ASU 2015-03 to impact its financial position, results of operations, cash flows, presentation and disclosures. Amendments to Consolidation Analysis In February 2015, the FASB issued ASU 2015-02, Amendments to the Consolidation Analysis (ASC 810) which amends the guidance for determining whether an entity is a variable interest entity ("VIE"). ASU 2015-02 eliminates the separate consolidation guidance for limited partnerships and with it, the presumption that a general partner should consolidate a limited partnership. In addition, ASU 2015-02 changes the guidance for determining if fee arrangements qualify as variable interests and the effect fee arrangements have on the determination of the primary beneficiary. ASU 2015-02 is effective for annual and interim reporting periods beginning after December 15, 2015 and must be applied retrospectively. OneBeacon does not expect ASU 2015-02 to affect the consolidation analysis for any of its existing investments. Share-Based Compensation Awards In June 2014, the FASB issued ASU 2014-12, Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period . The new guidance is intended to eliminate diversity in practice for employee share-based awards containing performance targets that could be achieved after the requisite service period. Some reporting entities account for performance targets that can be achieved after the requisite service period as performance conditions that affect the vesting of the award while other reporting entities treat those performance targets as non-vesting conditions that affect the grant-date fair value of the award. The updated guidance requires that a performance target that affects vesting and that can be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which service has been rendered. The new guidance is effective for annual and interim reporting periods beginning after December 15, 2015. OneBeacon does not expect adoption to have a significant impact on its financial position, results of operations, cash flows, presentation or disclosures. Revenue Recognition In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606), which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as investment management fees. The Company is in the process of evaluating the new guidance and has not yet determined the potential effect of adoption on its financial position, results of operations, or cash flows. ASU 2014-09 is effective for annual and interim reporting periods beginning after December 15, 2016.

Acqusitions and Dispositions

Acqusitions and Dispositions	6 Months Ended
	Jun. 30, 2015
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions Runoff Business As described in Note 1—"Nature of Operations and Summary of Significant Accounting Policies," on December 23, 2014, OneBeacon completed the sale of its Runoff Business to Armour. As described in Note 15—"Discontinued Operations," the Company recorded the final adjustment to the loss on sale of discontinued operations during the second quarter of 2015. Prior to the closing of the Runoff Transaction, OneBeacon Insurance Company, one of the entities that was sold upon the closing of the Runoff Transaction and which has since been renamed Bedivere Insurance Company ("Bedivere"), distributed Atlantic Specialty Insurance Company ("ASIC') to its immediate parent, as well as cash and investments such that Bedivere contained the target capital on the date of sale pursuant to the stock purchase agreement. In conjunction with the Runoff Transaction, OneBeacon provided financing in the form of surplus notes having a par value of $101.0 million , which had a fair value of $64.9 million on the date of sale. As part of the Runoff Transaction, OneBeacon and Armour entered into a limited Transition Services Agreement (“TSA”), pursuant to which OneBeacon is providing certain transition services to Armour during the term of the TSA, which has an initial term of one year. See Note 15—"Discontinued Operations" for further information regarding activity reported as discontinued operations during the three and six months ended June 30, 2015 and 2014 . 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 and recognized a pre-tax gain on sale of $23.0 million ( $15.0 million after tax) in the first quarter of 2013. During the first quarter of 2015, the Company recognized in net other revenues (expenses) a $3.7 million negative adjustment to the pre-tax gain on sale of Essentia in connection with an assessment from the Michigan Catastrophic Claims Association (MCCA) payable to Markel Corporation pursuant to the indemnification provisions in the stock purchase agreement governing the sale of Essentia. Except as described above, during the three and six months ended June 30, 2015 and 2014 , there were no significant acquisitions or dispositions.

Unpaid Loss and Loss Adjustment

Unpaid Loss and Loss Adjustment Expense (LAE) Reserves	6 Months Ended
	Jun. 30, 2015
Insurance Loss Reserves [Abstract]
Unpaid Loss and Loss Adjustment Expense (LAE) Reserves	Unpaid Loss and Loss Adjustment Expense (LAE) Reserves Loss and LAE reserve summary The following table summarizes the loss and LAE reserve activities of OneBeacon's insurance subsidiaries for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Gross beginning balance $ 1,304.0 $ 1,069.8 $ 1,342.2 $ 1,054.3 Less beginning reinsurance recoverables on unpaid losses (141.6 ) (80.1 ) (161.6 ) (80.2 ) Net beginning loss and LAE reserves 1,162.4 989.7 1,180.6 974.1 Loss and LAE incurred relating to: Current year losses 194.5 177.7 362.2 328.5 Prior year losses — 8.4 (1.8 ) 7.0 Total incurred loss and LAE from continuing operations 194.5 186.1 360.4 335.5 Loss and LAE paid relating to: Current year losses (42.7 ) (41.3 ) (64.8 ) (59.6 ) Prior year losses (110.5 ) (101.1 ) (272.5 ) (216.6 ) Total loss and LAE payments from continuing operations (153.2 ) (142.4 ) (337.3 ) (276.2 ) Net ending loss and LAE reserves 1,203.7 1,033.4 1,203.7 1,033.4 Plus ending reinsurance recoverables on unpaid losses 147.1 92.0 147.1 92.0 Gross ending loss and LAE reserves $ 1,350.8 $ 1,125.4 $ 1,350.8 $ 1,125.4 Loss and LAE development Loss and LAE development—2015 During the three months ended June 30, 2015 , OneBeacon experienced no net loss and LAE reserve development on prior accident year reserves, as favorable development from several businesses, most notably Specialty Property and Surety , was offset by unfavorable development primarily due to a large claim in Entertainment and an increase in the frequency of small to medium losses in the ocean marine business within International Marine Underwriters (IMU) . During the six months ended June 30, 2015 , OneBeacon experienced $1.8 million of net favorable loss and LAE reserve development on prior accident year reserves, primarily attributable to favorable development from Crop resulting from the 2014 crop year and favorable development in several other businesses, most notably Technology , Specialty Property , Government Risks , and Surety . This favorable development was mostly offset by unfavorable development in Entertainment driven by several large losses and small to mid-sized claims and by losses within the Company's inland marine business within IMU resulting from a few large claims and, to a lesser extent, from Tuition Reimbursement . Loss and LAE development—2014 During the three months ended June 30, 2014 , OneBeacon experienced $8.4 million of net unfavorable loss and LAE reserve development on prior accident year reserves primarily related to its Other Professional Lines and Management Liability underwriting operating segments, as well as its Entertainment, Government Risks and Accident underwriting operating segments, partially offset by favorable loss and LAE reserve development primarily in its Specialty Property underwriting operating segment. The unfavorable development was driven by a few large claims. During the six months ended June 30, 2014 , OneBeacon experienced $7.0 million of net unfavorable loss and LAE reserve development on prior accident year reserves primarily related to its Management Liability and Other Professional Lines underwriting operating segments, as well as its Entertainment, Government Risks and Accident underwriting operating segments, partially offset by favorable loss and LAE reserve development in its Specialty Property underwriting operating segment, as well as its IMU underwriting operating segment. The unfavorable development was driven by a few large claims. See Note 15—"Discontinued Operations" for a discussion of impacts to reserves for unpaid losses and LAE related to discontinued operations.

Reinsurance

Reinsurance	6 Months Ended
	Jun. 30, 2015
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance In the normal course of business, OneBeacon's insurance subsidiaries seek to limit losses that may arise from catastrophes or other events by reinsuring with third-party reinsurers. OneBeacon remains liable for risks reinsured even if the reinsurer does not honor its obligations under reinsurance contracts. Reinsurance Treaties The Company's catastrophe reinsurance coverage is discussed in Note 4—"Reinsurance" in the Company's 2014 Annual Report on Form 10-K. Except as discussed below, there have been no material changes to the Company's reinsurance coverage from that reported in the 2014 Annual Report on Form 10-K. Effective May 1, 2015, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2016. The program provides coverage for OneBeacon's property business as well as certain acts of terrorism. Under the program, the first $20.0 million of losses resulting from any single catastrophe are retained, with 95.0% of the next $10.0 million of losses and 100.0% of the next $100.0 million of losses resulting from the catastrophe being reinsured. Any part of a catastrophe loss in excess of $130.0 million would be retained in full. In the event of a catastrophe, OneBeacon's property catastrophe reinsurance program is reinstated for the remainder of the original contract term by paying a reinstatement premium that is based on the percentage of coverage reinstated and the original property catastrophe coverage premium. Also effective May 1, 2015, OneBeacon lowered its retention on its property-per-risk reinsurance program from $5.0 million to $3.0 million . Additionally, effective June 1, 2015, OneBeacon lowered its retentions on certain casualty and healthcare treaties from $5.0 million to $3.0 million . Effective January 1, 2015, OneBeacon purchased an aggregate stop loss on its multi-peril crop insurance ("MPCI") portfolio for the 2015 crop year, providing 52.0% of coverage in excess of a 98.0% loss ratio on premiums covered by the contract and a separate aggregate stop loss providing 80.0% of coverage in excess of a 100.0% loss ratio on its crop-hail portfolio. OneBeacon also purchased a new quota share reinsurance contract on 30.0% of its MPCI portfolio. In addition to the reinsurance protections outlined above, the Company also continued to purchase dedicated reinsurance protection for certain specific lines of business. Reinsurance Recoverables As of June 30, 2015 , OneBeacon had reinsurance recoverables on paid losses of $20.9 million and reinsurance recoverables on unpaid losses of $147.1 million . As reinsurance contracts do not relieve OneBeacon of its obligations, collectibility of balances due from reinsurers is critical to OneBeacon's financial strength. The following table summarizes Standard & Poor's Financial Services, LLC ("Standard & Poor's") ratings for OneBeacon's reinsurers for its continuing insurance operations, excluding industry pools and associations, based upon reinsurance recoverable amounts on paid and unpaid losses and LAE: ($ in millions) Standard & Poor's Rating (1) : Balance at June 30, 2015 % of total AA $ 63.1 38 % A 82.3 49 % BBB, Not Rated and Other 22.6 13 % Total reinsurance recoverables $ 168.0 100 % _______________________________________________________________________________ (1) Standard & Poor's ratings as detailed above are "AA" (Very strong), "A" (Strong) and "BBB" (Adequate).

Investment Securities

Investment Securities	6 Months Ended
	Jun. 30, 2015
Schedule of Investments [Abstract]
Investment Securities	Investment Securities OneBeacon's invested assets are comprised of securities and other investments held for general investment purposes. Refer to the Company's 2014 Annual Report on Form 10-K for a complete discussion. OneBeacon classifies its portfolio of fixed maturity investments, common equity securities and convertible fixed maturity investments held for general investment purposes as trading securities. Trading securities are reported at fair value as of the balance sheet date as determined by quoted market prices when available. Realized and change in unrealized investment gains on trading securities are reported in total revenues as net realized and unrealized investment gains in revenues on a pre-tax basis. Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year. Short-term investments are carried at amortized cost, which approximates fair value. Other investments primarily include surplus notes, private equity funds and hedge funds. OneBeacon measures its investments in private equity funds and hedge funds at fair value with changes therein reported in total revenues as net realized and change in unrealized investment gains. Surplus notes provided in conjunction with the financing of the Runoff Transaction are measured at their estimated fair value based on discounted expected cash flows, with changes in fair value reported in total revenues as net realized and change in unrealized investment gains. Other investments also include an investment in a community reinvestment vehicle which is accounted for at fair value, with changes in fair value reported in total revenues as net realized and change in unrealized investment gains and a tax advantaged federal affordable housing development fund which is accounted for under the proportional amortization method. Prospector Partners, LLC (“Prospector”), was the primary manager of OneBeacon's publicly-traded common equity securities and convertible fixed maturity securities portfolio. The Prospector-managed separate accounts were liquidated during the second quarter of 2015, and the Prospector-managed hedge fund was redeemed, with the intention to convert the majority of the proceeds to passive equity vehicles. As the separate accounts were liquidated, OneBeacon reinvested the majority of the proceeds into exchange traded funds ("ETFs") that seek to provide investment results that, before expenses, generally correspond to the performance of the S&P 500, Russell 1000, and Russell 1000 Value indices. OneBeacon's net investment income is comprised primarily of interest income associated with fixed maturity investments and dividend income from its equity investments. Net investment income for the three and six months ended June 30, 2015 and 2014 consisted of the following: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Fixed maturity investments $ 10.3 $ 10.6 $ 20.5 $ 20.9 Common equity securities 1.5 2.0 3.1 3.7 Convertible fixed maturity investments — 0.1 — 0.1 Other investments (0.1 ) 1.1 — 1.2 Gross investment income 11.7 13.8 23.6 25.9 Less investment expenses (1.6 ) (1.6 ) (3.0 ) (3.3 ) Net investment income, pre-tax $ 10.1 $ 12.2 $ 20.6 $ 22.6 The composition of net realized investment gains consisted of the following: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Fixed maturity investments $ 1.2 $ 1.6 $ 1.9 $ 2.4 Common equity securities 24.6 6.5 34.4 11.9 Convertible fixed maturity investments 0.3 1.2 0.3 2.3 Other investments 9.1 — 8.1 — Net realized investment gains, pre-tax $ 35.2 $ 9.3 $ 44.7 $ 16.6 The net changes in fair value for the three and six months ended June 30, 2015 and 2014 are as follows: Three months ended June 30, 2015 Six months ended June 30, 2015 ($ in millions) Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Fixed maturity investments $ (9.1 ) $ — $ (9.1 ) $ (2.5 ) $ — $ (2.5 ) Short-term investments — — — — — — Common equity securities (26.5 ) 0.3 (26.2 ) (30.9 ) 0.2 (30.7 ) Convertible fixed maturity investments (0.3 ) — (0.3 ) 0.1 — 0.1 Other investments (13.6 ) — (13.6 ) (11.4 ) — (11.4 ) Net change, pre-tax $ (49.5 ) $ 0.3 $ (49.2 ) $ (44.7 ) $ 0.2 $ (44.5 ) Three months ended June 30, 2014 Six months ended June 30, 2014 ($ in millions) Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Fixed maturity investments $ 7.3 $ — $ 7.3 $ 12.0 $ — $ 12.0 Common equity securities 6.6 — 6.6 9.7 — 9.7 Convertible fixed maturity investments (3.0 ) — (3.0 ) (2.3 ) — (2.3 ) Other investments 1.7 — 1.7 4.8 — 4.8 Net change, pre-tax $ 12.6 $ — $ 12.6 $ 24.2 $ — $ 24.2 The components of OneBeacon's ending net unrealized investment gains and losses, excluding the impact of net unrealized foreign currency translation gains and losses, on its investment portfolio as of June 30, 2015 and December 31, 2014 were as follows: ($ in millions) June 30, December 31, Investment securities: Gross unrealized investment gains $ 62.3 $ 104.7 Gross unrealized investment losses (11.2 ) (8.9 ) Total net unrealized investment gains, pre-tax 51.1 95.8 Income taxes (18.7 ) (26.9 ) Total net unrealized investment gains, after tax $ 32.4 $ 68.9 The cost or amortized cost, gross unrealized pre-tax investment gains and losses, net foreign currency losses and carrying values of OneBeacon's fixed maturity investments as of June 30, 2015 and December 31, 2014 were as follows: June 30, 2015 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 43.8 $ 0.1 $ — $ — $ 43.9 Debt securities issued by industrial corporations 813.2 8.7 (0.6 ) — 821.3 Municipal obligations 66.8 0.7 (0.5 ) — 67.0 Asset-backed securities 922.5 2.7 (1.9 ) — 923.3 Foreign government obligations 1.0 0.2 — — 1.2 Preferred stocks 78.3 6.1 — — 84.4 Total fixed maturity investments $ 1,925.6 $ 18.5 $ (3.0 ) $ — $ 1,941.1 December 31, 2014 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value U.S. Government and agency obligations $ 38.0 $ — $ — $ — $ 38.0 Debt securities issued by industrial corporations 787.7 11.5 (1.0 ) — 798.2 Municipal obligations 62.4 1.4 (0.1 ) — 63.7 Asset-backed securities 814.4 1.5 (1.5 ) — 814.4 Foreign government obligations 1.0 0.3 — — 1.3 Preferred stocks 78.3 5.9 — — 84.2 Total fixed maturity investments $ 1,781.8 $ 20.6 $ (2.6 ) $ — $ 1,799.8 The cost or amortized cost, gross unrealized pre-tax investment gains and losses, net unrealized pre-tax foreign currency losses and carrying values of common equity securities, convertible fixed maturity investments and other investments as of June 30, 2015 and December 31, 2014 were as follows: June 30, 2015 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value Common equity securities $ 298.4 $ 12.4 $ (6.5 ) $ — $ 304.3 Convertible fixed maturity investments — — — — — Other investments 145.2 31.4 (1.7 ) — 174.9 Total common equity securities, convertible fixed maturity investments and other investments $ 443.6 $ 43.8 $ (8.2 ) $ — $ 479.2 December 31, 2014 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value Common equity securities $ 283.2 $ 39.3 $ (2.4 ) $ (0.1 ) $ 320.0 Convertible fixed maturity investments 5.2 — (0.2 ) — 5.0 Other investments 157.7 44.8 (3.7 ) — 198.8 Total common equity securities, convertible fixed maturity investments and other investments $ 446.1 $ 84.1 $ (6.3 ) $ (0.1 ) $ 523.8 As of June 30, 2015 and December 31, 2014 , the Company held unrestricted collateral from its customers, primarily relating to its surety business, of $102.6 million and $81.0 million , respectively, which is included in cash and invested assets. The obligation to return these funds is classified as funds held under insurance contracts in the consolidated balance sheets. The following table summarizes the ratings of the corporate debt securities owned by OneBeacon as of June 30, 2015 and December 31, 2014 : ($ in millions) June 30, December 31, AA $ 46.5 $ 57.9 A 309.3 328.1 BBB 465.5 409.2 Not rated — 3.0 Debt securities issued by corporations (1) $ 821.3 $ 798.2 _______________________________________________________________________________ (1) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor’s Financial Services LLC (“Standard and Poor’s”) and 2) Moody’s Investor Service (“Moody’s”). Fair value measurements Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources ("observable inputs") and a reporting entity's internal assumptions based upon the best information available when external market data is limited or unavailable ("unobservable inputs"). Quoted prices in active markets for identical assets or liabilities have the highest priority ("Level 1"), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities ("Level 2") and unobservable inputs, including the reporting entity's estimates of the assumptions that market participants would use, having the lowest priority ("Level 3"). As of June 30, 2015 and December 31, 2014 , approximately 91% and 90% , respectively, of the investment portfolio recorded at fair value was priced based upon observable inputs. Investments valued using Level 1 inputs include fixed maturity investments, primarily investments in U.S. Treasuries, common equity securities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs comprise the fixed maturity investments, which has been disaggregated into classes, including debt securities issued by corporations, municipal obligations, mortgage and asset-backed securities, foreign government obligations and preferred stocks. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Level 3 fair value estimates based upon unobservable inputs include OneBeacon's investments in surplus notes, hedge funds and private equity funds, as well as certain investments in fixed maturity investments and common equity securities, where quoted market prices are unavailable or are not considered reasonable. OneBeacon determines when transfers between levels have occurred as of the beginning of the period. OneBeacon uses brokers and outside pricing services to assist in determining fair values. For investments in active markets, OneBeacon uses the quoted market prices provided by outside pricing services to determine fair value. The outside pricing services OneBeacon uses have indicated that they will only provide prices where observable inputs are available. In circumstances where quoted market prices are unavailable or are not considered reasonable, OneBeacon estimates the fair value using industry standard pricing models and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. OneBeacon's process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, evaluation of model pricing methodologies, review of the pricing services' quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from different independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and review of assumptions utilized by the pricing service for selected measurements on an ad hoc basis throughout the year. OneBeacon also performs back-testing of selected purchases and sales activity to determine whether there are any significant differences between the market price used to value the security prior to purchase or sale and the actual purchase or sale price on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than 5% and $1.0 million from the expected price based on these procedures are considered outliers. Also considered outliers are prices that haven’t changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of OneBeacon's review process does not appear to support the market price provided by the pricing services, OneBeacon challenges the price. If OneBeacon cannot gain satisfactory evidence to support the challenged price, it relies upon its own pricing methodologies to estimate the fair value of the security in question. The valuation process above is generally applicable to all of OneBeacon’s fixed maturity investments. The techniques and inputs specific to asset classes within OneBeacon's fixed maturity investments for Level 2 securities that use observable inputs are as follows: Debt securities issued by corporations: The fair value of debt securities issued by corporations is determined from an evaluated pricing model that uses information from market sources and integrates relative credit information, observed market movements, and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, quality ratings, duration, credit enhancements, early redemption features and market research publications. Municipal obligations: The fair value of municipal obligations is determined from an evaluated pricing model that uses information from market makers, broker-dealers, buy-side firms, and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications. Mortgage and asset-backed securities: The fair value of asset backed securities is determined from an evaluated pricing model that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications. Foreign government obligations: The fair value of foreign government obligations is determined from an evaluated pricing model that uses feeds from data sources in each respective country, including active market makers and inter-dealer brokers. Key inputs include benchmark yields, reported trades, broker-dealer quotes, two-sided markets, benchmark securities, bids, offers, local exchange prices, foreign exchange rates and reference data including coupon, credit quality ratings, duration and market research publications. Preferred stocks: The fair value of preferred stocks is determined from an evaluated pricing model that calculates the appropriate spread over a comparable security for each issue. Key inputs include exchange prices (underlying and common stock of same issuer), benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable assumptions reflect OneBeacon's assumptions that market participants would use in valuing the investment. Generally, certain securities may start out as Level 3 when they are originally issued but as observable inputs become available in the market, they may be reclassified to Level 2. The fair values of OneBeacon's investments in hedge funds and private equity funds have been classified as Level 3 under the fair value hierarchy since the fund managers do not provide sufficient information to independently evaluate the pricing inputs and methods for each underlying investment, and therefore the inputs are considered to be unobservable. As of June 30, 2015 and December 31, 2014 , OneBeacon did not record a liquidity adjustment to the net asset value related to its investments in hedge funds or private equity funds. Also classified as Level 3 under the fair value hierarchy are surplus notes which are measured at their estimated fair value based on discounted expected cash flows, with changes in fair value reported in total revenues as net realized and change in unrealized investment gains. As of both June 30, 2015 and December 31, 2014 , other investments reported at fair value represented approximately 6% and 7% , respectively, of the total investment portfolio and consisted of the following: ($ in millions) June 30, December 31, Hedge funds (1) $ 27.2 $ 42.3 Private equity funds (2) 51.3 60.1 Total hedge funds and private equity funds 78.5 102.4 Surplus notes (par value $101.0) (3) 66.3 65.1 Investment in community reinvestment vehicle 14.2 14.3 Trust certificates 0.1 0.2 Total other investments (4) $ 159.1 $ 182.0 _______________________________________________________________________________ (1) Consists of 7 hedge funds as of both June 30, 2015 and December 31, 2014 . (2) Consists of 17 private equity funds as of both June 30, 2015 and December 31, 2014 . (3) The change in the fair value of the surplus notes during the six months ended June 30, 2015 was due to accretion of the discount and changes in credit spreads and U.S. Treasury rates. (4) Excludes the carrying value of $15.8 million and $16.8 million as of June 30, 2015 and December 31, 2014 , respectively, associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. The largest investment in a single hedge fund or private equity fund was $12.5 million and $15.8 million as of June 30, 2015 and December 31, 2014 , respectively. As of both June 30, 2015 and December 31, 2014 , OneBeacon held one private preferred stock that represented approximately 84% of its preferred stock portfolio. OneBeacon used quoted market prices for similar securities that were adjusted to reflect management's best estimate of fair value; this security is classified as a Level 3 measurement. The following tables summarize the Company's fair value measurements for investments as of June 30, 2015 and December 31, 2014 by level. The major security types were based on the legal form of the securities, with a separate break-out for convertible fixed maturity investments as they may react similar to either debt securities or equity securities, depending on prevailing market conditions. OneBeacon has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing asset-backed securities vary depending on the nature of the issuing entity type. OneBeacon further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, OneBeacon has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications the Company uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices. ($ in millions) Fair value at Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 43.9 $ 43.9 $ — $ — Debt securities issued by corporations: Consumer 346.4 — 346.4 — Financial 133.1 — 133.1 — Industrial 120.1 — 120.1 — Communications 56.3 — 56.3 — Energy 54.0 — 54.0 — Utilities 43.4 — 43.4 — Basic materials 39.0 — 39.0 — Technology 29.0 — 29.0 — Debt securities issued by corporations 821.3 — 821.3 — Asset-backed securities 923.3 — 917.7 5.6 Preferred stocks 84.4 — 13.2 71.2 Municipal obligations 67.0 — 67.0 — Foreign government obligations 1.2 0.6 0.6 — Fixed maturity investments 1,941.1 44.5 1,819.8 76.8 Short-term investments 157.9 157.9 — — Common equity securities: Exchange traded funds (2) 186.2 164.7 21.5 — Consumer 41.0 41.0 — — Financials 24.3 24.3 — — Energy 0.6 0.6 — — Basic Materials 1.8 1.8 — — Utilities 1.0 1.0 — — Other 49.4 49.4 — — Common equity securities 304.3 282.8 21.5 — Convertible fixed maturity investments — — — — Other investments (1) 159.1 — — 159.1 Total (1) $ 2,562.4 $ 485.2 $ 1,841.3 $ 235.9 _______________________________________________________________________________ (1) Excludes the carrying value of $15.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2015 . (2) EFTs traded on foreign exchanges are priced with an adjusted NAV and are therefore included within level 2 measurements. ($ in millions) Fair value at Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 38.0 $ 38.0 $ — $ — Debt securities issued by corporations: Consumer 286.8 — 286.8 — Financial 148.6 — 148.6 — Industrial 104.8 — 104.8 — Communications 74.9 — 74.9 — Basic materials 56.4 — 53.5 2.9 Energy 53.5 — 53.5 — Utilities 44.2 — 44.2 — Technology 29.0 — 29.0 — Debt securities issued by corporations 798.2 — 795.3 2.9 Asset-backed securities 814.4 — 814.4 — Preferred stocks 84.2 — 13.1 71.1 Municipal obligations 63.7 — 63.7 — Foreign government obligations 1.3 0.7 0.6 — Fixed maturity investments 1,799.8 38.7 1,687.1 74.0 Short-term investments 202.2 201.7 0.5 — Common equity securities: Consumer 121.7 121.7 — — Financials 72.4 72.4 — — Energy 15.6 15.6 — — Basic Materials 9.9 9.9 — — Utilities 5.1 5.1 — — Other 95.3 95.3 — — Common equity securities 320.0 320.0 — — Convertible fixed maturity investments 5.0 — 5.0 — Other investments (1) 182.0 — — 182.0 Total (1) $ 2,509.0 $ 560.4 $ 1,692.6 $ 256.0 _______________________________________________________________________________ (1) Excludes the carrying value of $16.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2014 . Rollforwards of Fair Value Measurements by Level The following tables summarize the changes in OneBeacon’s fair value measurements by level for the three and six months ended June 30, 2015 and 2014: Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities Convertible fixed maturity investments Other investments (1) Total (1)(2) Balance at January 1, 2015 $ 358.7 $ 1,692.1 $ 74.0 $ — $ — $ 182.0 $ 2,306.8 Amortization/accretion — (2.9 ) — — — — (2.9 ) Net realized and unrealized gains 5.5 7.3 0.3 — — 1.2 14.3 Purchases 62.4 208.7 28.4 — — 1.4 300.9 Sales (75.2 ) (175.4 ) — — — (3.0 ) (253.6 ) Transfers in — 2.9 — — — — 2.9 Transfers out — — (2.9 ) — — — (2.9 ) Balance at March 31, 2015 $ 351.4 $ 1,732.7 $ 99.8 $ — $ — $ 181.6 $ 2,365.5 Amortization/accretion — (3.5 ) — — — — (3.5 ) Net realized and unrealized gains (1.0 ) (8.2 ) (0.2 ) — — (4.5 ) (13.9 ) Purchases 350.8 307.4 5.6 — — 1.1 664.9 Sales (373.9 ) (215.5 ) — — — (19.1 ) (608.5 ) Transfers in — 28.4 — — — — 28.4 Transfers out — — (28.4 ) — — — (28.4 ) Balance at June 30, 2015 $ 327.3 $ 1,841.3 $ 76.8 $ — $ — $ 159.1 $ 2,404.5 _______________________________________________________________________________ (1) Excludes the carrying value of $15.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2015. (2) Excludes short-term investments. Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities Convertible fixed maturity investments Other investments (1) Total (1)(2) Balance at January 1, 2014 $ 469.5 $ 1,753.1 $ 81.9 $ 0.1 $ — $ 119.9 $ 2,424.5 Amortization/accretion — (2.7 ) — — — — (2.7 ) Net realized and unrealized gains 8.6 6.9 0.3 — — 3.1 18.9 Purchases 140.6 347.8 7.5 — — 2.3 498.2 Sales (60.0 ) (411.4 ) — — — (1.6 ) (473.0 ) Transfers in — — — — — — — Transfers out — — — — — — — Balance at March 31, 2014 $ 558.7 $ 1,693.7 $ 89.7 $ 0.1 $ — $ 123.7 $ 2,465.9 Amortization/accretion — (2.8 ) — — — — (2.8 ) Net realized and unrealized gains 14.1 5.5 0.3 0.4 — 1.7 22.0 Purchases 279.2 349.8 34.2 — — 1.0 664.2 Sales (332.7 ) (292.1 ) — — — (1.5 ) (626.3 ) Transfers in — 7.5 — — — — 7.5 Transfers out — — (7.5 ) — — — (7.5 ) Balance at June 30, 2014 $ 519.3 $ 1,761.6 $ 116.7 $ 0.5 $ — $ 124.9 $ 2,523.0 _______________________________________________________________________________ (1) Excludes the carrying value of $18.0 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2014. (2) Excludes short-term investments. “Transfers out” of Level 3 fixed maturity investments was comprised of $18.1 million in residential mortgage backed securities, $10.3 million in commercial mortgage backed securities and $2.9 million in corporate debt securities for the six months ended June 30, 2015 and $7.5 million in commercial mortgage backed securities for the six months ended June 30, 2014 , all of which were recategorized as Level 2 measurements when quoted market prices that were considered reliable and could be validated against an alternative source became available. There were no “Transfers in” to Level 3 for the six months ended June 30, 2015 and 2014 . The following table summarizes the change in net pre-tax unrealized gains or losses for assets designated as Level 3 for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Fixed maturity investments $ (0.2 ) $ 0.3 $ 0.1 $ 0.6 Short-term investments — — — — Common equity securities — 0.4 — 0.4 Convertible fixed maturity investments — — — — Other investments (13.6 ) 1.7 (11.4 ) 4.8 Total $ (13.8 ) $ 2.4 $ (11.3 ) $ 5.8 Significant Unobservable Inputs As previously described, in certain circumstances, OneBeacon estimates the fair value of investments using industry standard pricing models and both observable and unobservable inputs. The following summarizes significant unobservable inputs used in estimating the fair value of fixed maturity investments classified within Level 3, other than hedge funds and private equities, as of June 30, 2015 . The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds. Description Fair Value (in millions) Rating (2) Valuation Technique Unobservable Inputs Input Preferred stock (1) $ 71.2 N/R Discounted cash flow Discount yield 7.065% Surplus notes: N/R 12.3% - Seller priority note $ 45.4 Discounted cash flow Discount rate (3) 10.2% Timing of interest payments (4) 5 years Timing of principal payments (4) 10 years - Pari passu note $ 20.9 Discounted cash flow Discount rate (5) 15.5% Timing of interest payments (4) 5 years Timing of principal payments (4) 15 years Asset-backed securities (1) $ 5.6 A Broker pricing Broker quote N/A _________________________________________________________________________ (1) As of June 30, 2015 , each asset type consists of one security. (2) Credit ratings, if rated, are assigned based on the following hierarchy: 1) Standard & Poor's and 2) Moody's (3) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the seller priority note is roughly equivalent to that of a conventional debt security with a credit rating of ‘B’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the seller priority note. (4) For estimated value purposes, the assumption has been made that interest payouts begin in year five and principal repayments begin on a graduated basis in year ten for the seller priority note and year fifteen for the pari passu note. (5) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the pari passu note is roughly equivalent to that of a conventional debt security with a credit rating of ‘CCC’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the pari passu note. Mortgage-backed, Asset-backed Securities OneBeacon purchases commercial mortgage-backed securities ("CMBS") and residential mortgage-backed securities ("RMBS") to maximize its risk adjusted returns in the context of a diversified portfolio. OneBeacon's non-agency CMBS are generally short tenor and structurally senior, with more than 20 points of subordination on average for fixed rate and floating rate CMBS as of June 30, 2015 . In general, subordination represents the percentage of principal loss on the underlying collateral that would have to occur before the security incurs a loss. These collateral losses, instead, are first absorbed by other securities lower in the capital structure. OneBeacon believes this structural protection mitigates the risk of loss tied to refinancing challenges facing the commercial real estate market. As of June 30, 2015 , on average less than 1% of the underlying loans were reported as non-performing for both agency and non-agency CMBS held by OneBeacon. OneBeacon did not hold any RMBS categorized as sub-prime as of June 30, 2015 . OneBeacon's investments in hedge funds and private equity funds contain negligible amounts of sub-prime mortgage-backed securities as of June 30, 2015 . OneBeacon considers sub-prime mortgage-backed securities to be those that have underlying loan pools that exhibit weak credit characteristics or are issued from dedicated sub-prime shelves or dedicated second-lien shelf registrations (i.e., OneBeacon considers investments backed primarily by second-liens to be sub-prime risks regardless of credit scores or other metrics). There are also mortgage-backed securities that OneBeacon categorizes as "non-prime" (also called "Alt A" or "A-") that are backed by collateral that has overall credit quality between prime and sub-prime, as determined based on OneBeacon's review of the characteristics of their underlying mortgage loan pools, such as credit scor

Debt

Debt	6 Months Ended
	Jun. 30, 2015
Debt Disclosure [Abstract]
Debt	Debt OneBeacon's debt outstanding as of June 30, 2015 and December 31, 2014 consisted of the following: ($ in millions) June 30, December 31, Senior unsecured notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (0.3 ) (0.3 ) Senior unsecured notes, carrying value $ 274.7 $ 274.7 2012 Senior Notes In November 2012, OneBeacon U.S. Holdings, Inc. ("OBH") issued $275.0 million face value of senior unsecured notes ("2012 Senior Notes") through a public offering, at an issue price of 99.9% and received $272.9 million of proceeds. The 2012 Senior Notes bear an annual interest rate of 4.6% payable semi-annually in arrears on May 9 and November 9, until maturity on November 9, 2022, and are fully and unconditionally guaranteed as to the payment of principal and interest by the Company. Debt Covenants As of June 30, 2015 , OneBeacon was in compliance with all of the covenants under the 2012 Senior Notes.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2015
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has fifteen active underwriting operating segments, which are managed by the chief operating decision maker and are aggregated into two underwriting reportable segments. The two underwriting reportable segments were determined based on the nature of products or services, the production process, the method of distribution and the nature of the regulatory environment. The principal difference between the reportable segments is the type or class of customer. The Specialty Products reportable segment is comprised of ten active underwriting operating segments, representing an aggregation based on those that offer distinct products and tailored coverages and services to a broad customer base across the United States. During the first quarter of 2015, the Company restructured its former Professional Insurance underwriting operating segment into four separate underwriting operating segments: Healthcare, Management Liability, Financial Services and Other Professional Lines. Additionally, Specialty Products includes the Specialty Property, Environmental, Tuition Reimbursement, Crop, Programs, and Surety underwriting operating segments. The Specialty Industries reportable segment is comprised of five active underwriting operating segments, representing an aggregation based on those that focus on solving the unique needs of a particular customer or industry group. The Specialty Industries segment includes the International Marine Underwriters, Technology, Accident, Government Risks, and Entertainment underwriting operating segments. The Investing, Financing and Corporate reportable segment includes the investing and financing activities for OneBeacon on a consolidated basis, and certain other activities conducted through the Company and its intermediate subsidiaries, including the 100% quota share reinsurance agreement with Bedivere, which cedes the losses associated with the legacy Runoff Business to Bedivere, one of the transferred entities that was sold as part of the Runoff Transaction and has been an indirect wholly-owned subsidiary of Armour since December 23, 2014. There is no net retention of the legacy Runoff Business to OneBeacon. Invested assets are not allocated to the Specialty Products and Specialty Industries segments since OneBeacon does not manage them by segment. Invested assets, net investment income and net realized and change in unrealized investment gains related to OneBeacon's Specialty Products and Specialty Industries segments are included in the Investing, Financing and Corporate segment since these assets are available for payment of losses and expenses for all segments. Debt and the related interest expense on debt also are not allocated to or managed by segment and are also included in the Investing, Financing and Corporate segment. Substantially all of the Company's revenue is generated from customers located in the United States. Financial information for OneBeacon's reportable segments is as follows: Insurance Operations Investing, Financing and Corporate ($ in millions) Specialty Products Specialty Industries Consolidated Three months ended June 30, 2015 Earned premiums $ 166.5 $ 152.8 $ — $ 319.3 Loss and loss adjustment expense (99.6 ) (94.9 ) — (194.5 ) Policy acquisition expenses (27.9 ) (28.5 ) — (56.4 ) Other underwriting expenses (23.3 ) (29.6 ) — (52.9 ) Total underwriting income (loss) 15.7 (0.2 ) — 15.5 Net investment income — — 10.1 10.1 Net realized and change in unrealized investment gains — — (14.0 ) (14.0 ) Net other revenues (expenses) — 0.1 (1.3 ) (1.2 ) General and administrative expenses — (0.5 ) (3.7 ) (4.2 ) Interest expense — — (3.3 ) (3.3 ) Pre-tax income (loss) from continuing operations $ 15.7 $ (0.6 ) $ (12.2 ) $ 2.9 Three months ended June 30, 2014 Earned premiums $ 145.9 $ 145.0 $ — $ 290.9 Loss and loss adjustment expense (101.3 ) (84.8 ) — (186.1 ) Policy acquisition expenses (23.4 ) (26.2 ) — (49.6 ) Other underwriting expenses (22.7 ) (29.0 ) — (51.7 ) Total underwriting income (loss) (1.5 ) 5.0 — 3.5 Net investment income — — 12.2 12.2 Net realized and change in unrealized investment gains — — 21.9 21.9 Net other revenues 0.1 0.2 0.7 1.0 General and administrative expenses — (0.5 ) (3.1 ) (3.6 ) Interest expense — — (3.3 ) (3.3 ) Pre-tax income (loss) from continuing operations $ (1.4 ) $ 4.7 $ 28.4 $ 31.7 Insurance Operations Investing, Financing and Corporate ($ in millions) Specialty Products Specialty Industries Consolidated Six months ended June 30, 2015 Earned premiums $ 302.6 $ 303.3 $ — $ 605.9 Loss and loss adjustment expense (173.7 ) (186.7 ) — (360.4 ) Policy acquisition expenses (50.8 ) (56.6 ) — (107.4 ) Other underwriting expenses (49.0 ) (59.8 ) — (108.8 ) Total underwriting income 29.1 0.2 — 29.3 Net investment income — — 20.6 20.6 Net realized and change in unrealized investment gains — — 0.2 0.2 Net other revenues (expenses) — 0.3 (4.6 ) (4.3 ) General and administrative expenses — (1.0 ) (7.3 ) (8.3 ) Interest expense — — (6.5 ) (6.5 ) Pre-tax income (loss) from continuing operations $ 29.1 $ (0.5 ) $ 2.4 $ 31.0 Six months ended June 30, 2014 Earned premiums $ 281.3 $ 286.1 $ — $ 567.4 Loss and loss adjustment expense (179.3 ) (156.2 ) — (335.5 ) Policy acquisition expenses (44.8 ) (51.5 ) — (96.3 ) Other underwriting expenses (44.9 ) (56.2 ) — (101.1 ) Total underwriting income 12.3 22.2 — 34.5 Net investment income — — 22.6 22.6 Net realized and change in unrealized investment gains — — 40.8 40.8 Net other revenues 0.2 0.3 1.5 2.0 General and administrative expenses 0.1 (1.0 ) (6.0 ) (6.9 ) Interest expense — — (6.5 ) (6.5 ) Pre-tax income from continuing operations $ 12.6 $ 21.5 $ 52.4 $ 86.5 Insurance Operations Investing, Financing and Corporate ($ in millions) Specialty Products Specialty Industries Consolidated June 30, 2015 Assets Total investment securities $ — $ — $ 2,578.2 $ 2,578.2 Premiums receivable 119.4 172.8 — 292.2 Reinsurance recoverables (1) 120.4 29.0 18.6 168.0 Funds held under reinsurance contracts 49.3 — — 49.3 Deferred acquisition costs 55.3 56.5 — 111.8 Other assets (2) — — 462.8 462.8 Total Assets $ 344.4 $ 258.3 $ 3,059.6 $ 3,662.3 Liabilities Unpaid loss and loss adjustment expense reserves (1) $ 767.5 $ 564.7 $ 18.6 $ 1,350.8 Unearned premiums 321.9 294.3 — 616.2 Funds held under insurance contracts 102.6 — — 102.6 Debt — — 274.7 274.7 Other liabilities (2) — — 281.3 281.3 Total Liabilities $ 1,192.0 $ 859.0 $ 574.6 $ 2,625.6 December 31, 2014 Assets Total investment securities $ — $ — $ 2,525.8 $ 2,525.8 Premiums receivable 77.7 163.8 — 241.5 Reinsurance recoverables (1) 127.3 22.7 23.8 173.8 Funds held under reinsurance contracts 37.1 — — 37.1 Deferred acquisition costs 49.7 53.5 — 103.2 Other assets (2) — — 496.8 496.8 Total Assets $ 291.8 $ 240.0 $ 3,046.4 $ 3,578.2 Liabilities Unpaid loss and loss adjustment expense reserves (1) $ 798.8 $ 519.6 $ 23.8 $ 1,342.2 Unearned premiums 303.6 284.7 — 588.3 Funds held under insurance contracts 81.0 — — 81.0 Debt — — 274.7 274.7 Other liabilities (2) — — 242.7 242.7 Total Liabilities $ 1,183.4 $ 804.3 $ 541.2 $ 2,528.9 _______________________________________________________________________________ (1) As described in Note 15—"Discontinued Operations," ASIC has entered into a 100% quota share reinsurance agreement whereby ASIC is ceding to Bedivere 100% of the legacy Runoff Business that was written by ASIC or one of the ongoing entities. As of June 30, 2015 and December 31, 2014, $18.6 million and $23.8 million , respectively, are included in both unpaid loss and loss adjustment expense reserves and reinsurance recoverable included within Investing, Financing, and Corporate. (2) Other assets and other liabilities are not separately identifiable at the segment level and have therefore been included within the investing, financing, and corporate segment. The following tables provide net written premiums, earned premiums and underwriting ratios for OneBeacon's insurance operations by reportable segment and in total, for the three and six months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 Three months ended June 30, 2014 Insurance Operations Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Specialty Specialty Consolidated Net written premiums $ 159.7 $ 161.5 $ 321.2 $ 139.5 $ 156.4 $ 295.9 Earned premiums 166.5 152.8 319.3 145.9 145.0 290.9 Underwriting ratios: (1) Loss and LAE 59.8 % 62.1 % 60.9 % 69.5 % 58.5 % 64.0 % Expense 30.7 38.0 34.2 31.6 38.0 34.8 Total combined ratio 90.5 % 100.1 % 95.1 % 101.1 % 96.5 % 98.8 % Six months ended June 30, 2015 Six months ended June 30, 2014 Insurance Operations Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Specialty Specialty Consolidated Net written premiums $ 293.3 $ 315.0 $ 608.3 $ 300.3 $ 306.7 $ 607.0 Earned premiums 302.6 303.3 605.9 281.3 286.1 567.4 Underwriting ratios: (1) Loss and LAE 57.4 % 61.6 % 59.5 % 63.7 % 54.6 % 59.1 % Expense 33.0 38.3 35.7 31.9 37.6 34.8 Total combined ratio 90.4 % 99.9 % 95.2 % 95.6 % 92.2 % 93.9 % _______________________________________________________________________________ (1) Underwriting ratios are used to measure the components of underwriting profitability and include: the loss and LAE ratio, calculated by dividing loss and LAE by earned premiums; the expense ratio, calculated by dividing policy acquisition and other underwriting expenses by earned premiums; and the combined ratio, the sum of the loss and LAE ratio and the expense ratio.

Retirement Plans

Retirement Plans	6 Months Ended
	Jun. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Retirement Plans	Retirement Plans OneBeacon sponsors qualified and non-qualified, non-contributory, defined benefit pension plans covering substantially all employees who were employed as of December 31, 2001 and former employees who had met the eligibility requirements, as well as retirees. Current plans include the OneBeacon qualified pension plan (the "Qualified Plan") and the OneBeacon non-qualified pension plan (the "Non-qualified Plan") (collectively the "Plans"). OneBeacon's Plans were frozen and curtailed in 2002 and, as a result, the projected benefit obligation is equal to the accumulated benefit obligation. The benefits for the Plans are based primarily on years of service and employees’ compensation through December 31, 2002. OneBeacon’s funding policy is consistent with the funding requirements of U.S. federal laws and regulations. In April 2014, the board of managers of the Qualified Plan's plan sponsor, a wholly-owned indirect subsidiary of the Company, voted to terminate the Qualified Plan as of June 30, 2014. The plan sponsor applied for a determination letter from the Internal Revenue Service ("IRS") with respect to the Qualified Plan's tax qualified status at termination and received a favorable determination letter from the IRS on July 23, 2015. The Company has not yet made a final determination if it will proceed with the plan termination and may decide either to revoke the plan termination or to proceed. If the plan termination does proceed, OneBeacon does not expect the impact of the termination to be material on the Company's financial position. The components of net periodic benefit cost for the three and six months ended June 30, 2015 and 2014 were as follows: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Service cost $ 0.2 $ 0.2 $ 0.4 $ 0.3 Interest cost 1.1 1.1 2.3 2.3 Expected return on plan assets (2.1 ) (2.1 ) (4.3 ) (4.2 ) Amortization of unrecognized loss 0.3 0.1 0.6 0.2 Net periodic pension income before special termination benefits (0.5 ) (0.7 ) (1.0 ) (1.4 ) Special termination benefits expense (1) — — — 0.3 Total net periodic benefit income $ (0.5 ) $ (0.7 ) $ (1.0 ) $ (1.1 ) _______________________________________________________________________________ (1) Special termination benefits for 2014 represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force. OneBeacon does not expect to make a contribution to its Qualified Plan in 2015. OneBeacon anticipates contributing $2.2 million to the Non-qualified Plan in 2015, for which OneBeacon has assets held in a rabbi trust. During the three and six months ended June 30, 2015 , the Company contributed $0.5 million and $1.0 million , respectively, to the Non-qualified Plan.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	6 Months Ended
	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Share-Based Incentive Compensation Plans	Employee Share-Based Incentive Compensation Plans OneBeacon's share-based compensation plans include performance shares, restricted shares and restricted stock units, which are designed to maximize shareholder value over long periods of time by aligning the financial interests of its management with those of its owners. Performance shares are payable only upon achievement of pre-defined business goals and are valued based on the market value of OneBeacon's common shares at the time awards are earned. Performance shares and restricted stock units are typically paid in cash, though, in some instances, they may be paid in common shares or may be deferred in accordance with the terms of OneBeacon's deferred compensation plan. Restricted shares vest either annually in equal installments over the specified service period or cliff-vest in full after the 3 -year service period, depending on the award. OneBeacon expenses the full cost of all its share-based compensation over the requisite service period. The Company recognized expense related to its share-based compensation plans of $1.1 million and $1.6 million for the three months ended June 30, 2015 and 2014 , respectively, and $2.0 million and $3.0 million for the six months ended June 30, 2015 and 2014 , respectively. Performance Shares The following summarizes performance share activity for the three months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 2014 ($ in millions) Target OB Performance Shares outstanding Accrued expense Target OB Performance Shares outstanding Accrued expense Beginning of period 462,147 $ 2.1 512,938 $ 3.6 Payments and deferrals — — — — New awards — — — — Forfeitures and net change in assumed forfeitures — — — — Expense recognized — 0.3 — 0.8 End of period 462,147 $ 2.4 512,938 $ 4.4 Six months ended June 30, 2015 2014 ($ in millions) Target OB Performance Shares outstanding Accrued expense Target OB Performance Shares outstanding Accrued expense Beginning of period 517,470 $ 3.4 493,421 $ 4.0 Payments and deferrals (1) (181,290 ) (1.5 ) (142,138 ) (1.0 ) New awards 154,887 — 165,800 — Forfeitures and net change in assumed forfeitures (28,920 ) — (4,145 ) — Expense recognized — 0.5 — 1.4 End of period 462,147 $ 2.4 512,938 $ 4.4 _______________________________________________________________________________ (1) Performance share payments in 2015 for the 2012-2014 performance cycle were based upon a performance factor of 45.7% . Performance share payments in 2014 for the 2011-2013 performance cycle were based upon a performance factor of 37.1% . The following summarizes performance shares outstanding and accrued performance share expense at June 30, 2015 for each performance cycle: ($ in millions) Target OB Performance Shares outstanding Accrued expense Performance cycle: 2013 - 2015 167,300 $ 1.5 2014 - 2016 151,810 0.6 2015 - 2017 154,887 0.3 Subtotal 473,997 2.4 Assumed forfeitures (11,850 ) — Total at June 30, 2015 462,147 $ 2.4 If 100% of the outstanding performance shares had been vested on June 30, 2015 , the total additional compensation cost to be recognized would have been $2.8 million , based on current accrual factors (common share price, accumulated dividends and payout assumptions) at June 30, 2015 . All performance shares earned and paid were settled in cash or by deferral into OneBeacon's deferred compensation plan. Restricted Shares On February 24, 2015, OneBeacon issued to certain employees 75,950 shares of restricted stock having a grant date fair value of $1.1 million , which are scheduled to vest in full on January 1, 2018. On March 1, 2012, OneBeacon issued shares of restricted stock to certain employees. Of these restricted shares, 142,500 restricted shares vested on February 28, 2014 and the remaining 138,500 restricted shares vested on February 28, 2015. On May 25, 2011, OneBeacon issued to its CEO 630,000 shares of restricted stock, of which 157,500 restricted shares vested on February 22, 2014, 157,500 restricted shares vested on February 22, 2015, and the remaining 315,000 restricted shares are scheduled to vest in equal installments on February 22, 2016 and 2017. The restricted shares contain dividend participation features and therefore are considered participating securities. The following summarizes restricted shares activity for the three months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 2014 ($ in millions) Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Beginning of period 390,950 $ 4.0 612,500 $ 5.7 New awards — — — — Forfeitures — — — — Vested — — — — Expense recognized — (0.5 ) — (0.8 ) End of period 390,950 $ 3.5 612,500 $ 4.9 Six months ended June 30, 2015 2014 ($ in millions) Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Beginning of period 612,500 $ 3.5 915,000 $ 6.5 New awards 75,950 1.1 — — Forfeitures (1,500 ) — (2,500 ) — Vested (296,000 ) — (300,000 ) — Expense recognized — (1.1 ) — (1.6 ) End of period 390,950 $ 3.5 612,500 $ 4.9 Restricted shares that vested during the six months ended June 30, 2015 and 2014 had a grant date fair value of $4.3 million for each period. No shares vested during the three months ended June 30, 2015 or 2014 . As of June 30, 2015 , unrecognized compensation expense of $3.5 million related to restricted stock awards is expected to be recognized over a weighted-average period of 1.9 years. Restricted Stock Units On February 24, 2015, the Compensation Committee awarded to certain employees 207,848 restricted stock units ("RSUs"). During the three months ended June 30, 2015 an additional 6,582 RSUs were issued, increasing the outstanding RSUs, net of forfeitures, to 209,369 as of June 30, 2015 . The RSUs are scheduled to vest in full on January 1, 2018, at which time the RSUs will be paid out in cash or shares at the discretion of the Compensation Committee. The expense associated with the RSUs, which is being recognized over the vesting period, was $0.3 million and $0.4 million for the three and six months ended June 30, 2015 , respectively.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes OneBeacon and its Bermuda-domiciled subsidiaries are not subject to Bermuda income tax under current Bermuda law. In the event that there is a change in the current law such that taxes are imposed, OneBeacon and its Bermuda-domiciled subsidiaries would be exempt from such tax until March 31, 2035, pursuant to the Bermuda Exempted Undertakings Tax Protection Act of 1966. OneBeacon also has subsidiaries that operate in Gibraltar, Luxembourg and the United States. U.S. operations are financed with a combination of debt and equity and the financing income currently accounts for the majority of non-U.S. earnings. OneBeacon's income tax benefit (expense) related to pre-tax income from continuing operations for the three months ended June 30, 2015 and 2014 , represented net effective tax rates of (31.0)% and 18.6% , respectively, and for the six months ended June 30, 2015 and 2014 , represented net effective tax rates of 8.1% and 15.0% , respectively. The effective tax rates for the three and six months ended June 30, 2015 and 2014 , were lower than the U.S. statutory rate of 35% due to income generated in jurisdictions other than the United States, principally representing interest income and underwriting income taxed in a jurisdiction with a lower effective tax rate. Additionally, the rate for the six months ended June 30, 2014 was impacted by a $5.0 million favorable settlement of the 2005-2006 IRS exam, as noted below. For the three months ended June 30, 2015 and 2014 , the effective tax rate on non-U.S. income was 1.8% and 1.1% , respectively, and for the six months ended June 30, 2015 and 2014 , the effective tax rate on non-U.S. income was 1.4% and 1.1% , respectively. In arriving at the effective tax rate for the three and six months ended June 30, 2015 and 2014 , OneBeacon forecasted all income and expense items including the realized and change in unrealized investment gains for the years ending December 31, 2015 and 2014 , and included these gains in the effective tax rate calculation. OneBeacon classifies all interest and penalties on unrecognized tax benefits as part of income tax expense. With few exceptions, OneBeacon is no longer subject to U.S. federal, state or non-U.S. income tax examinations by tax authorities for years before 2007. On February 14, 2014, OneBeacon received Form 870-AD (Offer to Waive Restrictions on Assessment and Collection Tax Deficiency and to Accept Over assessment) from the IRS Appeals Office relating to the examination of tax years 2005 and 2006. All disputed items have been agreed and resolved with the Joint Committee. OneBeacon recorded a tax benefit of $5.0 million in the first quarter of 2014 relating to the settlement of the IRS examination for tax years 2005 and 2006. On July 28, 2011, the IRS commenced an examination of OneBeacon's U.S. income tax returns for 2007, 2008 and 2009. On July 17, 2013, OneBeacon received a revised Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2007, 2008 and 2009. The estimated total assessment, including interest, utilization of alternative minimum and foreign tax credit carryovers and capital loss carrybacks, is $74.8 million . However, $60.2 million of the proposed adjustments relate to items for which the expense deduction has been disallowed in a year being examined, but ultimate deductibility is highly certain to occur in a later period. Because of the impact of deferred tax accounting, other than interest and penalties, the disallowance of the deduction in the exam period would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority. OneBeacon disagrees with the adjustments proposed by the IRS and is defending its position. Although the timing of the resolution of these issues is uncertain, it is reasonably possible that the resolution could occur within the next twelve months. When ultimately settled, OneBeacon does not expect the resolution of this examination to result in a material adverse change to its financial position. On September 5, 2013, the IRS commenced an examination of OneBeacon's U.S. income tax returns for 2010, 2011 and 2012. OneBeacon does not expect the resolution of this examination to result in a material change to its financial position.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments OneBeacon carries its financial instruments on its balance sheet at fair value with the exception of its investment in qualified affordable housing projects, which is accounted for using the proportional amortization method, and fixed-rate, long-term indebtedness. For certain financial instruments where quoted market prices are not available, other independent valuation techniques and assumptions are used. Because considerable judgment is used, these estimates are not necessarily indicative of amounts that could be realized in a current market exchange. Certain financial instruments are excluded from disclosure, including insurance contracts. As of June 30, 2015 and December 31, 2014 , the fair value of OneBeacon's 2012 Senior Notes (its fixed-rate, long-term indebtedness) was $280.4 million and $286.0 million , respectively, which compared to a carrying value of $274.7 million as of both June 30, 2015 and December 31, 2014 . The fair value measurement of the 2012 Senior Notes is classified as Level 2 in the valuation hierarchy.

Legal Contingencies

Legal Contingencies	6 Months Ended
	Jun. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Legal Contingencies	Legal Contingencies OneBeacon, and the insurance and reinsurance industry in general, is routinely subject to claims related litigation and arbitration in the normal course of business, as well as litigation and arbitration that does not arise from, or directly relate to, claims activity. OneBeacon's estimates of the costs of settling matters routinely encountered in claims activity are reflected in the reserves for unpaid loss and LAE. See Note 3—"Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves." OneBeacon evaluates its exposure to non-claims related litigation and arbitration and establishes accruals for litigation and arbitration if it is probable that a loss has been incurred and it can be reasonably estimated. Disclosure of litigation and arbitration is made if it is probable that a loss has been incurred or if there is a reasonable possibility that a loss may have been incurred. Although the ultimate outcome of claims and non-claims related litigation and arbitration, and the amount or range of potential loss at any particular time, is often inherently uncertain, management does not believe that the ultimate outcome of such claims and non-claims related litigation and arbitration will have a material adverse effect on OneBeacon's financial condition, full year results of operations, or cash flows. The following summarizes significant ongoing non-claims related litigation or arbitration as of June 30, 2015 : Runoff Transaction Subsequent to the closing of the Runoff Transaction, on January 22, 2015, three holders of insurance policies issued by the companies the Company sold to Armour in the Runoff Transaction filed a Petition for Review with the Commonwealth Court of Pennsylvania ("Commonwealth Court") requesting that the Commonwealth Court vacate the Pennsylvania Insurance Department’s ("Department") orders approving the Runoff Transaction and denying their right to intervene in the Department’s regulatory review of the Runoff Transaction. The Company believes the claims made by the petitioners are without merit and has intervened in the proceedings before the Commonwealth Court to vigorously defend the propriety of the Department’s orders in their entirety. The Company believes that the possibility is remote that these proceedings could result in an adverse outcome or have a material financial impact on the Company’s financial position in the future. Deutsche Bank Litigation In June 2011, Deutsche Bank Trust Company Americas, Law Debenture Company of New York and Wilmington Trust Company (collectively referred to as “Plaintiffs”), in their capacity as trustees for certain senior notes issued by the Tribune Company (“Tribune”), filed lawsuits in various jurisdictions (the “Noteholder Actions”) against numerous defendants including OneBeacon, OneBeacon-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune seeking recovery of the proceeds from the sale of common stock of Tribune in connection with Tribune's leveraged buyout in 2007 (the “LBO”). Tribune filed for bankruptcy in 2008 in the Delaware bankruptcy court (the “Bankruptcy Court”). The Bankruptcy Court granted Plaintiffs permission to commence these LBO-related actions, and in 2011, the Judicial Panel on Multidistrict Litigation granted a motion to consolidate the actions for pretrial matters and transferred all such proceedings to the United States District Court for the Southern District of New York. Plaintiffs seek recovery of the proceeds received by the former Tribune shareholders on a theory of constructive fraudulent transfer asserting that Tribune purchased or repurchased its common shares without receiving fair consideration at a time when it was, or as a result of the purchases of shares, was rendered, insolvent. OneBeacon has entered into a joint defense agreement with other affiliates of White Mountains that are defendants in the action. OneBeacon and OneBeacon-sponsored benefit plans received approximately $32 million for Tribune common stock tendered in connection with the LBO. The Court granted an omnibus motion to dismiss the Noteholder Actions in September 2013 and Plaintiffs’ appeal is pending. In addition, OneBeacon, OneBeacon-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune, along with thousands of former Tribune shareholders, have been named as defendants in an adversary proceeding brought by the Official Committee of Unsecured Creditors of the Tribune Company (the “Committee”), on behalf of the Tribune Company, which seeks to avoid the repurchase of shares by Tribune in the LBO on a theory of intentional fraudulent transfer (the “Committee Action”). Tribune emerged from bankruptcy in 2012, and a litigation trustee replaced the Committee as plaintiff in the Committee Action. This matter was consolidated for pretrial matters with the Noteholder Actions in the United States District Court for the Southern District of New York and was stayed pending the motion to dismiss in the Noteholder Action. An omnibus motion to dismiss the shareholder defendants in the Committee Action was filed in May 2014. No amount has been accrued in connection with this matter as of June 30, 2015 , as the amount of loss, if any, cannot be reasonably estimated.

Earnings per Share

Earnings per Share	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share Basic and diluted earnings per share amounts are based on the weighted average number of common shares outstanding, including unvested restricted shares that are considered participating securities. Diluted earnings per share amounts are based on the weighted average number of common shares including unvested restricted shares. The following table outlines the Company's computation of earnings per share for net income from continuing operations attributable to OneBeacon's common shareholders for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended 2015 2014 2015 2014 Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders $ 3.3 $ 25.3 $ 27.5 $ 72.6 Allocation of income for participating unvested restricted common shares — (0.1 ) (0.1 ) (0.5 ) Dividends paid on participating restricted common shares — (0.1 ) (0.1 ) (0.2 ) Total allocation to restricted common shares — (0.2 ) (0.2 ) (0.7 ) Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 3.3 $ 25.1 $ 27.3 $ 71.9 Undistributed (over-distributed) net earnings (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 3.3 $ 25.1 $ 27.3 $ 71.9 Dividends paid, net of restricted common share amounts (20.0 ) (19.9 ) (39.9 ) (39.8 ) Total undistributed (over-distributed) net earnings, net of restricted common share amounts $ (16.7 ) $ 5.2 $ (12.6 ) $ 32.1 Earnings per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.3 95.3 Weighted average unvested restricted common shares (1) (0.4 ) (0.6 ) (0.5 ) (0.7 ) Basic and diluted earnings per share denominator 94.9 94.7 94.8 94.6 Earnings per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Net income from continuing operations attributable to OneBeacon's common shareholders $ 0.03 $ 0.26 $ 0.29 $ 0.76 Dividends declared and paid (0.21 ) (0.21 ) (0.42 ) (0.42 ) Undistributed (over-distributed) earnings $ (0.18 ) $ 0.05 $ (0.13 ) $ 0.34 _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event. Basic and diluted income per share amounts for discontinued operations are included in Note 15—"Discontinued Operations."

Common Shareholders' Equity

Common Shareholders' Equity	6 Months Ended
	Jun. 30, 2015
Stockholders' Equity Note [Abstract]
Common Shareholders' Equity	Common Shareholders' Equity Common Shares Repurchased and Retired On August 22, 2007, the Company's Board authorized the repurchase of up to $200.0 million of its Class A common shares from time to time, subject to market conditions. Shares may be repurchased on the open market or through privately negotiated transactions. This authorization does not have a stated expiration date. During the six months ended June 30, 2015 and 2014 , no shares were repurchased under the share repurchase authorization. The amount of authorization remaining is $87.7 million as of June 30, 2015 . During the six months ended June 30, 2015 and 2014 , the Company repurchased 112,051 and 106,366 common shares, respectively, to satisfy employee income tax withholding, pursuant to employee benefit plans. Shares repurchased pursuant to employee benefit plans do not reduce the board authorization referred to above. Dividends on Common Shares During the six months ended June 30, 2015 and 2014 , the Company declared and paid cash dividends to OneBeacon shareholders of $40.0 million , or $0.42 per common share, for each period. Accumulated Other Comprehensive Loss The Company recorded the following changes to accumulated other comprehensive loss for net increases in net benefit plan assets and obligations during the six months ended June 30, 2015 and 2014 : Six months ended June 30, ($ in millions) 2015 2014 Net change in benefit plan assets and obligations $ 0.6 $ 0.2 Income tax expense (0.2 ) (0.1 ) Net change in benefit plan assets and obligations, net of tax $ 0.4 $ 0.1

Discontinued Operations

Discontinued Operations	6 Months Ended
	Jun. 30, 2015
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	Discontinued Operations Runoff Business As described in Note 1—"Nature of Operations and Summary of Significant Accounting Policies" and Note 2—"Acquisitions and Dispositions," on December 23, 2014, OneBeacon completed the sale of its Runoff Business to Armour. During the second quarter of 2015, the Company recorded the final settlement of certain post-closing items related to the Runoff Transaction, resulting in a positive adjustment to the loss on sale of $0.3 million after-tax. Prior to the closing of the Runoff Transaction, Bedivere distributed ASIC to its immediate parent, as well as cash and investments such that Bedivere contained the target capital on the date of sale pursuant to the stock purchase agreement. In conjunction with the Runoff Transaction, OneBeacon provided financing in the form of surplus notes having a par value of $101.0 million , which had a fair value of $64.9 million on the date of sale. These notes are included in other investments on OneBeacon's consolidated balance sheet as of June 30, 2015 and December 31, 2014 and had a fair value of $66.3 million and $65.1 million , respectively (see Note 5—"Investment Securities" for further disclosures regarding these surplus notes). The vast majority of the gross and net run-off unpaid loss and LAE reserves were included in the entities that were transferred to Armour. As of June 30, 2015 and December 31, 2014 , gross loss and LAE reserves of $18.6 million and $23.8 million , respectively, related to the Runoff Business were ceded to Bedivere, an indirect wholly-owned subsidiary of Armour beginning December 23, 2014, by way of a 100% quota share agreement with ASIC. Summary of Results of Operations As described in Note 1—"Nature of Operations and Summary of Significant Accounting Policies" and Note 2—“Acquisitions and Dispositions,” the results of operations for the Runoff Business have been classified as discontinued operations and are presented as such, net of related income taxes, in the statements of operations and comprehensive income and cash flows for all periods. The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Net written premiums $ — $ (0.1 ) $ — $ (0.2 ) Revenues Earned premiums $ — $ (0.1 ) $ — $ (0.2 ) Other revenues (expenses) (0.2 ) — (0.3 ) — Total revenues (0.2 ) (0.1 ) (0.3 ) (0.2 ) Expenses Loss and loss adjustment expenses — (0.7 ) — (0.7 ) Other underwriting expenses — 0.7 — 1.4 Total expenses — — — 0.7 Pre-tax loss (0.2 ) (0.1 ) (0.3 ) (0.9 ) Income tax benefit — — — 0.3 Loss from discontinued operations, net of tax (0.2 ) (0.1 ) (0.3 ) (0.6 ) (Loss) gain from sale of discontinued operations, net of tax 0.3 (0.5 ) 0.3 (0.5 ) Net (loss) income from discontinued operations, net of tax $ 0.1 $ (0.6 ) $ — $ (1.1 ) The loss from discontinued operations, net of tax, of $0.2 million and $0.3 million for the three and six months ended June 30, 2015 , respectively, was the result of post-closing expenses incurred in connection with the Runoff Business. The loss from discontinued operations of $0.1 million and $0.6 million for the three and six months ended June 30, 2014 , respectively, was a result of non-claims expenses related to the Runoff Business, including dedicated staff, and partially offset by favorable activity in loss and LAE. The gain from sale of discontinued operations, net of tax, of $0.3 million for both the three and six months ended June 30, 2015 represents a positive adjustment to the estimated loss on sale taking into consideration the final settlement of certain post-closing items. The loss from sale of discontinued operations, net of tax, was $0.5 million for both the three and six months ended June 30, 2014 . The adjustment to the loss on sale in the 2014 periods related to the net effect of two items. First, the Company reduced its estimate of the fair value of the surplus notes expected to be issued at the closing of the Runoff Transaction based on our internal valuation model which, as of June 30, 2014, was $8.2 million pre-tax ( $5.3 million , after-tax) less than par value of the surplus notes, resulting in a corresponding increase to the estimated loss on sale. Second, the stock purchase agreement was revised during the second quarter of 2014 in part to increase the cap on seller financing, which resulted in the Company recording a $7.4 million reserve charge ( $4.8 million after-tax) as a reduction to the estimated loss on sale of discontinued operations. These changes resulted in a net increase in the estimated loss on sale at that time of $0.8 million ( $0.5 million after-tax) during the second quarter of 2014. OneBeacon made loss and LAE payments related to the Runoff Business of $17.7 million and $28.8 million for the three and six months ended June 30, 2014 , respectively, and made no such payments after the transaction closed on December 23, 2014. Loss per Share Related to Discontinued Operations Basic loss per share amounts are based on the weighted average number of common shares outstanding including unvested restricted shares that are considered participating securities. Diluted loss per share amounts are based on the weighted average number of common shares including unvested restricted shares. The following table outlines the computation of loss per share for discontinued operations attributable to OneBeacon's common shareholders for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended 2015 2014 2015 2014 (Loss) income attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders $ 0.1 $ (0.6 ) $ — $ (1.1 ) Allocation of loss for participating unvested restricted common shares — — — — Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 0.1 $ (0.6 ) $ — $ (1.1 ) Loss per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.3 95.3 Weighted average unvested restricted common shares (1) (0.4 ) (0.6 ) (0.5 ) (0.7 ) Basic and diluted loss per share denominator 94.9 94.7 94.8 94.6 Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Loss from discontinued operations attributable to OneBeacon's common shareholders per share $ — $ — $ — $ (0.01 ) _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event.

Consolidating Financial Informa

Consolidating Financial Information	6 Months Ended
	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidating Financial Information	Consolidating Financial Information The Company has fully and unconditionally guaranteed the 2012 Senior Notes issued by its 100% owned subsidiary, OBH. The following tables present OneBeacon's consolidating balance sheets as of June 30, 2015 and December 31, 2014 and statements of operations and comprehensive income for the three and six months ended June 30, 2015 and 2014 and cash flows for the six months ended June 30, 2015 and 2014 . These financial statements reflect the Company's ("guarantor") financial position, results of operations and cash flows on a stand-alone basis, that of OBH ("the issuer") and of the Company's other entities ("non-guarantor subsidiaries") as well as the necessary consolidating adjustments to eliminate intercompany balances and transactions. Consolidating Balance Sheet As of June 30, 2015 (in millions) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 1,941.1 $ — $ — $ 1,941.1 Short-term investments, at amortized cost (which approximates fair value) 1.1 155.1 1.7 — 157.9 Common equity securities, at fair value — 304.3 — — 304.3 Convertible fixed maturity investments, at fair value — — — — — Other investments — 174.9 — — 174.9 Total investment securities 1.1 2,575.4 1.7 — 2,578.2 Cash — 106.1 0.1 — 106.2 Reinsurance recoverables — 168.0 — — 168.0 Premiums receivable — 292.2 — — 292.2 Funds held under reinsurance contracts — 49.3 — — 49.3 Deferred acquisition costs — 111.8 — — 111.8 Net deferred tax asset — 136.5 — — 136.5 Investment income accrued — 10.3 — — 10.3 Accounts receivable on unsettled investment sales — 1.1 — — 1.1 Investments in subsidiaries 1,032.9 — 1,020.2 (2,053.1 ) — Other assets 0.6 204.4 3.6 0.1 208.7 Total assets $ 1,034.6 $ 3,655.1 $ 1,025.6 $ (2,053.0 ) $ 3,662.3 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,350.8 $ — $ — $ 1,350.8 Unearned premiums — 616.2 — — 616.2 Funds held under insurance contracts — 102.6 — — 102.6 Debt — — 274.7 — 274.7 Accounts payable on unsettled investment purchases — 20.1 — — 20.1 Other liabilities 1.4 253.8 6.0 — 261.2 Total liabilities 1.4 2,343.5 280.7 — 2,625.6 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,033.2 1,308.1 744.9 (2,053.0 ) 1,033.2 Total noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,033.2 1,311.6 744.9 (2,053.0 ) 1,036.7 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,034.6 $ 3,655.1 $ 1,025.6 $ (2,053.0 ) $ 3,662.3 Consolidating Balance Sheet As of December 31, 2014 (in millions) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 1,799.8 $ — $ — $ 1,799.8 Short-term investments, at amortized cost (which approximates fair value) 18.4 182.5 1.3 — 202.2 Common equity securities, at fair value — 320.0 — — 320.0 Convertible fixed maturity investments, at fair value — 5.0 — — 5.0 Other investments — 198.8 — — 198.8 Total investment securities 18.4 2,506.1 1.3 — 2,525.8 Cash — 87.0 — — 87.0 Reinsurance recoverables — 173.8 — — 173.8 Premiums receivable — 241.5 — — 241.5 Funds held under reinsurance contracts — 37.1 — — 37.1 Deferred acquisition costs — 103.2 — 103.2 Net deferred tax asset — 131.7 — 0.1 131.8 Investment income accrued — 10.0 — — 10.0 Accounts receivable on unsettled investment sales — 7.2 — — 7.2 Investments in subsidiaries 1,027.4 — 1,053.0 (2,080.4 ) — Other assets 0.3 198.0 4.4 — 202.7 Assets held for sale — 58.1 — — 58.1 Total assets $ 1,046.1 $ 3,553.7 $ 1,058.7 $ (2,080.3 ) $ 3,578.2 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,342.2 $ — $ — $ 1,342.2 Unearned premiums — 588.3 — — 588.3 Funds held under insurance contracts — 81.0 — — 81.0 Debt — — 274.7 — 274.7 Accounts payable on unsettled investment purchases — 0.5 — — 0.5 Other liabilities 0.3 234.8 7.1 — 242.2 Total liabilities 0.3 2,246.8 281.8 — 2,528.9 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,045.8 1,303.4 776.9 (2,080.3 ) 1,045.8 Total noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,045.8 1,306.9 776.9 (2,080.3 ) 1,049.3 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,046.1 $ 3,553.7 $ 1,058.7 $ (2,080.3 ) $ 3,578.2 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 319.3 $ — $ — $ 319.3 Net investment income — 10.1 — — 10.1 Net realized and change in unrealized investment gains — (14.0 ) — — (14.0 ) Net other revenues (expenses) — (1.2 ) — — (1.2 ) Total revenues — 314.2 — — 314.2 Expenses Loss and loss adjustment expenses — 194.5 — — 194.5 Policy acquisition expenses — 56.4 — — 56.4 Other underwriting expenses — 52.9 — — 52.9 General and administrative expenses 1.3 2.9 — — 4.2 Interest expense — — 3.3 — 3.3 Total expenses 1.3 306.7 3.3 — 311.3 Pre-tax income (loss) from continuing operations (1.3 ) 7.5 (3.3 ) — 2.9 Income tax (expense) benefit — (0.1 ) 1.0 — 0.9 Net income (loss) from continuing operations (1.3 ) 7.4 (2.3 ) — 3.8 Loss from discontinued operations, net of tax — (0.2 ) — — (0.2 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (1.3 ) 7.5 (2.3 ) — 3.9 Equity in earnings of subsidiaries, net of tax 4.7 — 0.3 (5.0 ) — Net income (loss) including noncontrolling interests 3.4 7.5 (2.0 ) (5.0 ) 3.9 Less: Net income attributable to noncontrolling interests — (0.5 ) — — (0.5 ) Net income (loss) attributable to OneBeacon's common shareholders 3.4 7.0 (2.0 ) (5.0 ) 3.4 Other comprehensive income, net of tax 0.2 — 0.2 (0.2 ) 0.2 Comprehensive income (loss) attributable to OneBeacon's common shareholders $ 3.6 $ 7.0 $ (1.8 ) $ (5.2 ) $ 3.6 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 290.9 $ — $ — $ 290.9 Net investment income — 12.4 0.1 (0.3 ) 12.2 Net realized and change in unrealized investment gains — 22.7 — (0.8 ) 21.9 Net other revenues — 1.0 — — 1.0 Total revenues — 327.0 0.1 (1.1 ) 326.0 Expenses Loss and loss adjustment expenses — 186.1 — — 186.1 Policy acquisition expenses — 49.6 — — 49.6 Other underwriting expenses — 51.7 — — 51.7 General and administrative expenses 1.9 1.6 0.1 — 3.6 Interest expense — — 3.6 (0.3 ) 3.3 Total expenses 1.9 289.0 3.7 (0.3 ) 294.3 Pre-tax income (loss) from continuing operations (1.9 ) 38.0 (3.6 ) (0.8 ) 31.7 Income tax (expense) benefit — (7.8 ) 1.6 0.3 (5.9 ) Net income (loss) from continuing operations (1.9 ) 30.2 (2.0 ) (0.5 ) 25.8 Loss from discontinued operations, net of tax — (0.1 ) — — (0.1 ) Loss from sale of discontinued operations, net of tax — (0.5 ) — — (0.5 ) Net income (loss) before equity in earnings of unconsolidated affiliates (1.9 ) 29.6 (2.0 ) (0.5 ) 25.2 Equity in earnings of subsidiaries, net of tax 26.6 — 11.8 (38.4 ) — Net income including noncontrolling interests 24.7 29.6 9.8 (38.9 ) 25.2 Less: Net income attributable to noncontrolling interests — (0.5 ) — — (0.5 ) Net income attributable to OneBeacon's common shareholders 24.7 29.1 9.8 (38.9 ) 24.7 Other comprehensive income, net of tax 0.1 — 0.1 (0.1 ) 0.1 Comprehensive income attributable to OneBeacon's common shareholders $ 24.8 $ 29.1 $ 9.9 $ (39.0 ) $ 24.8 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 605.9 $ — $ — $ 605.9 Net investment income — 20.6 — — 20.6 Net realized and change in unrealized investment gains — 0.2 — — 0.2 Net other revenues (expenses) — (4.3 ) — — (4.3 ) Total revenues — 622.4 — — 622.4 Expenses Loss and loss adjustment expenses — 360.4 — — 360.4 Policy acquisition expenses — 107.4 — — 107.4 Other underwriting expenses — 108.8 — — 108.8 General and administrative expenses 2.6 5.6 0.1 — 8.3 Interest expense — — 6.5 — 6.5 Total expenses 2.6 582.2 6.6 — 591.4 Pre-tax income (loss) from continuing operations (2.6 ) 40.2 (6.6 ) — 31.0 Income tax (expense) benefit — (4.9 ) 2.4 — (2.5 ) Net income (loss) from continuing operations (2.6 ) 35.3 (4.2 ) — 28.5 Loss from discontinued operations, net of tax — (0.3 ) — — (0.3 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (2.6 ) 35.3 (4.2 ) — 28.5 Equity in earnings of subsidiaries, net of tax 30.1 — 12.9 (43.0 ) — Net income including noncontrolling interests 27.5 35.3 8.7 (43.0 ) 28.5 Less: Net income attributable to noncontrolling interests — (1.0 ) — — (1.0 ) Net income attributable to OneBeacon's common shareholders 27.5 34.3 8.7 (43.0 ) 27.5 Other comprehensive income, net of tax 0.4 — 0.4 (0.4 ) 0.4 Comprehensive income attributable to OneBeacon's common shareholders $ 27.9 $ 34.3 $ 9.1 $ (43.4 ) $ 27.9 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 567.4 $ — $ — $ 567.4 Net investment income — 23.1 0.1 (0.6 ) 22.6 Net realized and change in unrealized investment gains — 42.1 — (1.3 ) 40.8 Net other revenues — 2.0 — — 2.0 Total revenues — 634.6 0.1 (1.9 ) 632.8 Expenses Loss and loss adjustment expenses — 335.5 — — 335.5 Policy acquisition expenses — 96.3 — — 96.3 Other underwriting expenses — 101.1 — — 101.1 General and administrative expenses 3.5 3.2 0.2 — 6.9 Interest expense — — 7.1 (0.6 ) 6.5 Total expenses 3.5 536.1 7.3 (0.6 ) 546.3 Pre-tax income (loss) from continuing operations (3.5 ) 98.5 (7.2 ) (1.3 ) 86.5 Income tax (expense) benefit — (16.7 ) 3.2 0.5 (13.0 ) Net income (loss) from continuing operations (3.5 ) 81.8 (4.0 ) (0.8 ) 73.5 Loss from discontinued operations, net of tax — (0.6 ) — — (0.6 ) Loss from sale of discontinued operations, net of tax — (0.5 ) — — (0.5 ) Net income (loss) before equity in earnings of unconsolidated affiliates (3.5 ) 80.7 (4.0 ) (0.8 ) 72.4 Equity in earnings of subsidiaries, net of tax 75.0 — 52.9 (127.9 ) — Net income including noncontrolling interests 71.5 80.7 48.9 (128.7 ) 72.4 Less: Net income attributable to noncontrolling interests — (0.9 ) — — (0.9 ) Net income attributable to OneBeacon's common shareholders 71.5 79.8 48.9 (128.7 ) 71.5 Other comprehensive income, net of tax 0.1 — 0.1 (0.1 ) 0.1 Comprehensive income attributable to OneBeacon's common shareholders $ 71.6 $ 79.8 $ 49.0 $ (128.8 ) $ 71.6 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Cash flows from operations: Net income including noncontrolling interests $ 27.5 $ 35.3 $ 8.7 $ (43.0 ) $ 28.5 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (30.1 ) — (12.9 ) 43.0 — Net loss from discontinued operations — 0.3 — — 0.3 Net gain from sale of discontinued operations — (0.3 ) — — (0.3 ) Net realized and change in unrealized investment gains — (0.2 ) — — (0.2 ) Net adjustment to gain on sale of business — 3.7 — — 3.7 Deferred income tax benefit — (3.8 ) — — (3.8 ) Dividends received from subsidiaries 25.0 39.9 44.9 (109.8 ) — Other operating items: Net change in loss and LAE reserves — 8.6 — — 8.6 Net change in unearned premiums — 27.9 — — 27.9 Net change in premiums receivable — (50.7 ) — — (50.7 ) Net change in reinsurance recoverables on paid and unpaid losses — 5.8 — — 5.8 Net change in funds held under reinsurance contracts — (12.2 ) — — (12.2 ) Net change in funds held under insurance contracts — 21.6 — — 21.6 Net change in other assets and liabilities 1.9 12.6 (0.9 ) — 13.6 Net cash provided from (used for) operations—continuing operations 24.3 88.5 39.8 (109.8 ) 42.8 Net cash used for operations—discontinued operations — (0.3 ) — — (0.3 ) Net cash provided from (used for) operations 24.3 88.2 39.8 (109.8 ) 42.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 17.3 26.6 0.4 — 44.3 Maturities of fixed maturity investments — 115.8 — — 115.8 Sales of fixed maturity investments — 361.0 29.7 59.3 450.0 Sales of common equity securities — 268.1 — — 268.1 Sales of convertible fixed maturity investments — 6.1 — — 6.1 Return of capital and distributions of other investments — 22.1 — — 22.1 Purchases of fixed maturity investments — (624.9 ) (29.9 ) (59.3 ) (714.1 ) Purchases of common equity securities — (248.7 ) — — (248.7 ) Purchases of convertible fixed maturity investments — (0.8 ) — — (0.8 ) Contributions for other investments — (2.5 ) — — (2.5 ) Net change in unsettled investment purchases and sales — 25.8 — — 25.8 Proceeds from sale of property and equipment — 56.8 — — 56.8 Net acquisitions of property and equipment — (1.8 ) — — (1.8 ) Net cash provided from investing activities 17.3 3.6 0.2 — 21.1 Cash flows from financing activities: Cash dividends paid to common shareholders (40.0 ) — — — (40.0 ) Cash dividends paid to parent — (69.9 ) (39.9 ) 109.8 — Repurchases and retirements of common stock (1.6 ) — — — (1.6 ) Payments on capital lease obligation — (2.8 ) — — (2.8 ) Net cash used for financing activities (41.6 ) (72.7 ) (39.9 ) 109.8 (44.4 ) Net increase in cash during period — 19.1 0.1 — 19.2 Cash balance at beginning of period — 87.0 — — 87.0 Cash balance at end of period $ — $ 106.1 $ 0.1 $ — $ 106.2 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Cash flows from operations: Net income including noncontrolling interests $ 71.5 $ 80.7 $ 48.9 $ (128.7 ) $ 72.4 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (75.0 ) — (52.9 ) 127.9 — Net loss from discontinued operations — 0.6 — — 0.6 Net loss from sale of discontinued operations — 0.5 — — 0.5 Net realized and change in unrealized investment gains — (42.1 ) — 1.3 (40.8 ) Deferred income tax expense — 13.0 — (0.4 ) 12.6 Dividends received from subsidiaries 30.0 — 5.0 (35.0 ) — Other operating items: Net change in loss and LAE reserves — 71.1 — — 71.1 Net change in unearned premiums — 47.0 — — 47.0 Net change in premiums receivable — (47.8 ) — — (47.8 ) Net change in reinsurance recoverables on paid and unpaid losses — (5.4 ) — — (5.4 ) Net change in funds held under reinsurance contracts — (30.0 ) — — (30.0 ) Net change in funds held under insurance contracts — (0.3 ) — — (0.3 ) Net change in other assets and liabilities 2.6 (24.4 ) (2.5 ) (0.1 ) (24.4 ) Net cash provided from (used for) operations—continuing operations 29.1 62.9 (1.5 ) (35.0 ) 55.5 Net cash used for operations—discontinued operations — (33.9 ) — — (33.9 ) Net cash provided from (used for) operations 29.1 29.0 (1.5 ) (35.0 ) 21.6 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 12.7 65.4 2.0 — 80.1 Maturities of fixed maturity investments — 185.6 — — 185.6 Sales of fixed maturity investments — 844.2 6.7 — 850.9 Sales of common equity securities — 47.6 — — 47.6 Sales of convertible fixed maturity investments — 12.2 — — 12.2 Return of capital and distributions of other investments — 3.2 — — 3.2 Purchases of fixed maturity investments — (1,093.2 ) (8.7 ) — (1,101.9 ) Purchases of common equity securities — (48.7 ) — — (48.7 ) Purchases of convertible fixed maturity investments — (8.4 ) — — (8.4 ) Contributions for other investments — (3.3 ) — — (3.3 ) Net change in unsettled investment purchases and sales — (31.8 ) — — (31.8 ) Net acquisitions of property and equipment — (0.7 ) — — (0.7 ) Net cash provided from (used for) investing activities 12.7 (27.9 ) — — (15.2 ) Cash flows from financing activities: Cash dividends paid to common shareholders (40.0 ) — — — (40.0 ) Cash dividends paid to parent — (35.0 ) — 35.0 — Repurchases and retirements of common stock (1.8 ) — — — (1.8 ) Payments on capital lease obligation — (2.6 ) — — (2.6 ) Net cash used for financing activities (41.8 ) (37.6 ) — 35.0 (44.4 ) Net decrease in cash during period — (36.5 ) (1.5 ) — (38.0 ) Cash balance at beginning of period — 166.6 1.5 — 168.1 Cash balance at end of period $ — $ 130.1 $ — $ — $ 130.1

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Notes)	6 Months Ended
	Jun. 30, 2015
Subsequent Event [Line Items]
Subsequent Events [Text Block]	On July 31, 2015, the Company exited the its multiple peril crop insurance ("MPCI") and its related crop-hail business (collectively, "Crop Business") due to the sale of its exclusive managing general agency, Climate Crop Insurance Agency, to an affiliate of AmTrust Financial Services, Inc. (“AmTrust”). As a result of the sale, OneBeacon and Climate Crop Insurance Agency agreed to terminate the existing five year agreement early and OneBeacon received a payment of $3.0 million in consideration. Also related to the sale, OneBeacon has withdrawn its 2016 Plan of Operations, which previously authorized it to write MPCI for the 2016 Reinsurance Year (July 1, 2015 to June 30, 2016) and affiliates of AmTrust will reinsure the Company’s remaining net Crop Business exposure for the 2015 Reinsurance Year (July 1, 2014 to June 30, 2015) under related 100% quota share reinsurance agreements. During the six months ended June 30, 2015, OneBeacon recorded net written premiums related to the Crop Business of $26.6 million and a net pre-tax underwriting loss of $1.3 million (excluding allocated other underwriting expenses of $1.5 million ). During the year ended December 31, 2014, OneBeacon recorded net written premiums related to the Crop Business of $35.1 million and a net pre-tax underwriting loss of $3.5 million (excluding allocated other underwriting expenses of $1.0 million ).

Nature of Operations and Summ24

Nature of Operations and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Recently Adopted Changes in Accounting Principles	Recently Adopted Changes in Accounting Principles Qualified Affordable Housing Projects Effective January 1, 2015, OneBeacon adopted ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects ("QAHP") (ASC 323) . ASU 2014-01 allows investors in QAHP to make a policy election to use the proportional amortization method. Under the proportional amortization method, the investor amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the investment results, net of the related tax benefits, as a component of income tax expense. Prior to adoption, OneBeacon accounted for its QAHP investment under the equity method and recognized its share of its QAHP investment's losses in investment income. OneBeacon made the policy election to account for its QAHP investment using the proportional amortization method, applied retrospectively. Under the proportional amortization method, the cumulative loss recognized through December 31, 2014 increased by $1.2 million . As a result of the retrospective adoption, OneBeacon's common shareholders equity has been reduced by $0.6 million as of January 1, 2014. In addition, for the three and six months ended June 30, 2014 , the retrospective adoption resulted in increases of $0.5 million and $0.9 million , respectively, to net investment income and net increases of $0.6 million and $1.2 million , respectively, to income tax expense. Footnote disclosures for prior year amounts have been amended to be consistent with the restated amounts described above. Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity In April 2014, the Financial Accounting Standard Board ("FASB") issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (ASC 205 and ASC 360) to reduce diversity in practice for reporting discontinued operations. ASU 2014-08 limits discontinued operations treatment to disposals that represent a strategic shift and that have a major effect on a reporting entity’s operations and financial results to be reported as discontinued operations. The revised guidance also requires expanded disclosure in the financial statements for discontinued operations as well as for disposals of significant components of an entity that do not qualify for discontinued operations presentation. OneBeacon has not had any transactions that occurred since ASU 2014-08 became effective on December 15, 2014. Pushdown Accounting ASU 2014-17, Pushdown Accounting, a consensus of the FASB Emerging Issues Task Force (ASC 805) became effective upon its issuance on November 18, 2014. The new guidance, which is applicable prospectively, gives an acquired non-public company the option to apply pushdown accounting in its separate company financial statements in the period in which it is acquired in a change of control transaction. Once pushdown accounting has been applied, the election is irreversible. Acquired entities that chose not to apply pushdown accounting at the time of acquisition, may apply pushdown accounting in a subsequent period as a change in accounting principle under ASC 250, Accounting Changes and Error Corrections . OneBeacon has not had any acquisitions since ASU 2014-17 became effective. Unrecognized Tax Benefits Effective January 1, 2014, OneBeacon adopted ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists . The new ASU generally requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss ("NOL") carryforward or tax credit carryforward rather than as a liability. This adoption did not have any impact on the Company's financial position, results of operations, cash flows or financial statement presentation. Recently Issued Accounting Pronouncements Insurance Contracts In May 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944) which requires expanded footnote disclosures about loss and loss adjustment expense ("LAE") reserves. Under the new guidance, some disclosures currently presented outside of OneBeacon’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported ("IBNR") plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the disaggregated amounts of IBNR to which they relate, along with a discussion of any significant changes in methodology and assumptions and the related effect upon the loss reserves. The new guidance will be effective for annual periods beginning after December 15, 2015 and interim periods within annual periods beginning after December 15, 2016 with retrospective restatement of prior periods required. OneBeacon will modify its financial statement footnote disclosures to conform to the requirements of ASU 2015-09 upon adoption, including revisions to prior year’s disclosures. Fair Value Measurements In May 2015, the FASB issued ASU 2015-07, Fair Value Measurement - Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or Its Equivalent) (ASC 820) which eliminates the requirement to disclose the fair value hierarchy level for investments for which fair value is measured at net asset value using the practical expedient in ASC 820. OneBeacon measures the fair value of its investments in hedge funds and private equity funds using this practical expedient and has classified those measurements within Level 3 of the fair value hierarchy. The new guidance is effective for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. Debt Issuance Costs In April 2015, the FASB issued ASU 2015-03, Imputation of Interest (ASC 835) which requires debt issuance costs related to a recognized debt liability to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. ASU 2015-03 is effective for annual and interim reporting periods beginning after December 15, 2015. OneBeacon does not expect ASU 2015-03 to impact its financial position, results of operations, cash flows, presentation and disclosures. Amendments to Consolidation Analysis In February 2015, the FASB issued ASU 2015-02, Amendments to the Consolidation Analysis (ASC 810) which amends the guidance for determining whether an entity is a variable interest entity ("VIE"). ASU 2015-02 eliminates the separate consolidation guidance for limited partnerships and with it, the presumption that a general partner should consolidate a limited partnership. In addition, ASU 2015-02 changes the guidance for determining if fee arrangements qualify as variable interests and the effect fee arrangements have on the determination of the primary beneficiary. ASU 2015-02 is effective for annual and interim reporting periods beginning after December 15, 2015 and must be applied retrospectively. OneBeacon does not expect ASU 2015-02 to affect the consolidation analysis for any of its existing investments. Share-Based Compensation Awards In June 2014, the FASB issued ASU 2014-12, Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period . The new guidance is intended to eliminate diversity in practice for employee share-based awards containing performance targets that could be achieved after the requisite service period. Some reporting entities account for performance targets that can be achieved after the requisite service period as performance conditions that affect the vesting of the award while other reporting entities treat those performance targets as non-vesting conditions that affect the grant-date fair value of the award. The updated guidance requires that a performance target that affects vesting and that can be achieved after the requisite service period be treated as a performance condition. Compensation cost should be recognized in the period it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which service has been rendered. The new guidance is effective for annual and interim reporting periods beginning after December 15, 2015. OneBeacon does not expect adoption to have a significant impact on its financial position, results of operations, cash flows, presentation or disclosures. Revenue Recognition In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606), which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as investment management fees. The Company is in the process of evaluating the new guidance and has not yet determined the potential effect of adoption on its financial position, results of operations, or cash flows. ASU 2014-09 is effective for annual and interim reporting periods beginning after December 15, 2016.

Unpaid Loss and Loss Adjustme25

Unpaid Loss and Loss Adjustment Expense (LAE) Reserves (Tables)	6 Months Ended
	Jun. 30, 2015
Insurance Loss Reserves [Abstract]
Loss and loss adjustment expense (LAE) reserve activities	The following table summarizes the loss and LAE reserve activities of OneBeacon's insurance subsidiaries for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Gross beginning balance $ 1,304.0 $ 1,069.8 $ 1,342.2 $ 1,054.3 Less beginning reinsurance recoverables on unpaid losses (141.6 ) (80.1 ) (161.6 ) (80.2 ) Net beginning loss and LAE reserves 1,162.4 989.7 1,180.6 974.1 Loss and LAE incurred relating to: Current year losses 194.5 177.7 362.2 328.5 Prior year losses — 8.4 (1.8 ) 7.0 Total incurred loss and LAE from continuing operations 194.5 186.1 360.4 335.5 Loss and LAE paid relating to: Current year losses (42.7 ) (41.3 ) (64.8 ) (59.6 ) Prior year losses (110.5 ) (101.1 ) (272.5 ) (216.6 ) Total loss and LAE payments from continuing operations (153.2 ) (142.4 ) (337.3 ) (276.2 ) Net ending loss and LAE reserves 1,203.7 1,033.4 1,203.7 1,033.4 Plus ending reinsurance recoverables on unpaid losses 147.1 92.0 147.1 92.0 Gross ending loss and LAE reserves $ 1,350.8 $ 1,125.4 $ 1,350.8 $ 1,125.4

Reinsurance (Tables)

Reinsurance (Tables)	6 Months Ended
	Jun. 30, 2015
Reinsurance Disclosures [Abstract]
Reinsurers	($ in millions) Standard & Poor's Rating (1) : Balance at June 30, 2015 % of total AA $ 63.1 38 % A 82.3 49 % BBB, Not Rated and Other 22.6 13 % Total reinsurance recoverables $ 168.0 100 % _______________________________________________________________________________ (1) Standard & Poor's ratings as detailed above are "AA" (Very strong), "A" (Strong) and "BBB" (Adequate).

Investment Securities (Tables)

Investment Securities (Tables)	6 Months Ended
	Jun. 30, 2015
Investment Holdings [Line Items]
Other Investments Not Readily Marketable [Table Text Block]	($ in millions) June 30, December 31, Hedge funds (1) $ 27.2 $ 42.3 Private equity funds (2) 51.3 60.1 Total hedge funds and private equity funds 78.5 102.4 Surplus notes (par value $101.0) (3) 66.3 65.1 Investment in community reinvestment vehicle 14.2 14.3 Trust certificates 0.1 0.2 Total other investments (4) $ 159.1 $ 182.0 _______________________________________________________________________________ (1) Consists of 7 hedge funds as of both June 30, 2015 and December 31, 2014 . (2) Consists of 17 private equity funds as of both June 30, 2015 and December 31, 2014 . (3) The change in the fair value of the surplus notes during the six months ended June 30, 2015 was due to accretion of the discount and changes in credit spreads and U.S. Treasury rates. (4) Excludes the carrying value of $15.8 million and $16.8 million as of June 30, 2015 and December 31, 2014 , respectively, associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method.
Net investment income, pre-tax	Net investment income for the three and six months ended June 30, 2015 and 2014 consisted of the following: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Fixed maturity investments $ 10.3 $ 10.6 $ 20.5 $ 20.9 Common equity securities 1.5 2.0 3.1 3.7 Convertible fixed maturity investments — 0.1 — 0.1 Other investments (0.1 ) 1.1 — 1.2 Gross investment income 11.7 13.8 23.6 25.9 Less investment expenses (1.6 ) (1.6 ) (3.0 ) (3.3 ) Net investment income, pre-tax $ 10.1 $ 12.2 $ 20.6 $ 22.6
Net realized and unrealized investment gains (losses), pre-tax	The composition of net realized investment gains consisted of the following: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Fixed maturity investments $ 1.2 $ 1.6 $ 1.9 $ 2.4 Common equity securities 24.6 6.5 34.4 11.9 Convertible fixed maturity investments 0.3 1.2 0.3 2.3 Other investments 9.1 — 8.1 — Net realized investment gains, pre-tax $ 35.2 $ 9.3 $ 44.7 $ 16.6
Net unrealized investment gains (losses)	The net changes in fair value for the three and six months ended June 30, 2015 and 2014 are as follows: Three months ended June 30, 2015 Six months ended June 30, 2015 ($ in millions) Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Fixed maturity investments $ (9.1 ) $ — $ (9.1 ) $ (2.5 ) $ — $ (2.5 ) Short-term investments — — — — — — Common equity securities (26.5 ) 0.3 (26.2 ) (30.9 ) 0.2 (30.7 ) Convertible fixed maturity investments (0.3 ) — (0.3 ) 0.1 — 0.1 Other investments (13.6 ) — (13.6 ) (11.4 ) — (11.4 ) Net change, pre-tax $ (49.5 ) $ 0.3 $ (49.2 ) $ (44.7 ) $ 0.2 $ (44.5 ) Three months ended June 30, 2014 Six months ended June 30, 2014 ($ in millions) Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Changes in net unrealized investment gains Changes in net foreign currency gains (losses) Total net changes in fair value reflected in revenues Fixed maturity investments $ 7.3 $ — $ 7.3 $ 12.0 $ — $ 12.0 Common equity securities 6.6 — 6.6 9.7 — 9.7 Convertible fixed maturity investments (3.0 ) — (3.0 ) (2.3 ) — (2.3 ) Other investments 1.7 — 1.7 4.8 — 4.8 Net change, pre-tax $ 12.6 $ — $ 12.6 $ 24.2 $ — $ 24.2
Gross unrealized investment gains or losses	The components of OneBeacon's ending net unrealized investment gains and losses, excluding the impact of net unrealized foreign currency translation gains and losses, on its investment portfolio as of June 30, 2015 and December 31, 2014 were as follows: ($ in millions) June 30, December 31, Investment securities: Gross unrealized investment gains $ 62.3 $ 104.7 Gross unrealized investment losses (11.2 ) (8.9 ) Total net unrealized investment gains, pre-tax 51.1 95.8 Income taxes (18.7 ) (26.9 ) Total net unrealized investment gains, after tax $ 32.4 $ 68.9
Investment holdings, fixed maturity investments	The cost or amortized cost, gross unrealized pre-tax investment gains and losses, net foreign currency losses and carrying values of OneBeacon's fixed maturity investments as of June 30, 2015 and December 31, 2014 were as follows: June 30, 2015 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 43.8 $ 0.1 $ — $ — $ 43.9 Debt securities issued by industrial corporations 813.2 8.7 (0.6 ) — 821.3 Municipal obligations 66.8 0.7 (0.5 ) — 67.0 Asset-backed securities 922.5 2.7 (1.9 ) — 923.3 Foreign government obligations 1.0 0.2 — — 1.2 Preferred stocks 78.3 6.1 — — 84.4 Total fixed maturity investments $ 1,925.6 $ 18.5 $ (3.0 ) $ — $ 1,941.1 December 31, 2014 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value U.S. Government and agency obligations $ 38.0 $ — $ — $ — $ 38.0 Debt securities issued by industrial corporations 787.7 11.5 (1.0 ) — 798.2 Municipal obligations 62.4 1.4 (0.1 ) — 63.7 Asset-backed securities 814.4 1.5 (1.5 ) — 814.4 Foreign government obligations 1.0 0.3 — — 1.3 Preferred stocks 78.3 5.9 — — 84.2 Total fixed maturity investments $ 1,781.8 $ 20.6 $ (2.6 ) $ — $ 1,799.8
Investment holdings, common equity securities, convertible fixed maturity investments and other investments	The cost or amortized cost, gross unrealized pre-tax investment gains and losses, net unrealized pre-tax foreign currency losses and carrying values of common equity securities, convertible fixed maturity investments and other investments as of June 30, 2015 and December 31, 2014 were as follows: June 30, 2015 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value Common equity securities $ 298.4 $ 12.4 $ (6.5 ) $ — $ 304.3 Convertible fixed maturity investments — — — — — Other investments 145.2 31.4 (1.7 ) — 174.9 Total common equity securities, convertible fixed maturity investments and other investments $ 443.6 $ 43.8 $ (8.2 ) $ — $ 479.2 December 31, 2014 ($ in millions) Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign Carrying value Common equity securities $ 283.2 $ 39.3 $ (2.4 ) $ (0.1 ) $ 320.0 Convertible fixed maturity investments 5.2 — (0.2 ) — 5.0 Other investments 157.7 44.8 (3.7 ) — 198.8 Total common equity securities, convertible fixed maturity investments and other investments $ 446.1 $ 84.1 $ (6.3 ) $ (0.1 ) $ 523.8
Fair value measurements by level, investment securities	The following tables summarize the Company's fair value measurements for investments as of June 30, 2015 and December 31, 2014 by level. The major security types were based on the legal form of the securities, with a separate break-out for convertible fixed maturity investments as they may react similar to either debt securities or equity securities, depending on prevailing market conditions. OneBeacon has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing asset-backed securities vary depending on the nature of the issuing entity type. OneBeacon further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, OneBeacon has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications the Company uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices. ($ in millions) Fair value at Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 43.9 $ 43.9 $ — $ — Debt securities issued by corporations: Consumer 346.4 — 346.4 — Financial 133.1 — 133.1 — Industrial 120.1 — 120.1 — Communications 56.3 — 56.3 — Energy 54.0 — 54.0 — Utilities 43.4 — 43.4 — Basic materials 39.0 — 39.0 — Technology 29.0 — 29.0 — Debt securities issued by corporations 821.3 — 821.3 — Asset-backed securities 923.3 — 917.7 5.6 Preferred stocks 84.4 — 13.2 71.2 Municipal obligations 67.0 — 67.0 — Foreign government obligations 1.2 0.6 0.6 — Fixed maturity investments 1,941.1 44.5 1,819.8 76.8 Short-term investments 157.9 157.9 — — Common equity securities: Exchange traded funds (2) 186.2 164.7 21.5 — Consumer 41.0 41.0 — — Financials 24.3 24.3 — — Energy 0.6 0.6 — — Basic Materials 1.8 1.8 — — Utilities 1.0 1.0 — — Other 49.4 49.4 — — Common equity securities 304.3 282.8 21.5 — Convertible fixed maturity investments — — — — Other investments (1) 159.1 — — 159.1 Total (1) $ 2,562.4 $ 485.2 $ 1,841.3 $ 235.9 _______________________________________________________________________________ (1) Excludes the carrying value of $15.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2015 . (2) EFTs traded on foreign exchanges are priced with an adjusted NAV and are therefore included within level 2 measurements. ($ in millions) Fair value at Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 38.0 $ 38.0 $ — $ — Debt securities issued by corporations: Consumer 286.8 — 286.8 — Financial 148.6 — 148.6 — Industrial 104.8 — 104.8 — Communications 74.9 — 74.9 — Basic materials 56.4 — 53.5 2.9 Energy 53.5 — 53.5 — Utilities 44.2 — 44.2 — Technology 29.0 — 29.0 — Debt securities issued by corporations 798.2 — 795.3 2.9 Asset-backed securities 814.4 — 814.4 — Preferred stocks 84.2 — 13.1 71.1 Municipal obligations 63.7 — 63.7 — Foreign government obligations 1.3 0.7 0.6 — Fixed maturity investments 1,799.8 38.7 1,687.1 74.0 Short-term investments 202.2 201.7 0.5 — Common equity securities: Consumer 121.7 121.7 — — Financials 72.4 72.4 — — Energy 15.6 15.6 — — Basic Materials 9.9 9.9 — — Utilities 5.1 5.1 — — Other 95.3 95.3 — — Common equity securities 320.0 320.0 — — Convertible fixed maturity investments 5.0 — 5.0 — Other investments (1) 182.0 — — 182.0 Total (1) $ 2,509.0 $ 560.4 $ 1,692.6 $ 256.0 _______________________________________________________________________________ (1) Excludes the carrying value of $16.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2014 .
Debt securities, credit ratings
Fair Value Assets Measured on Recurring Basis Measurement Input Reconciliation	The following tables summarize the changes in OneBeacon’s fair value measurements by level for the three and six months ended June 30, 2015 and 2014: Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities Convertible fixed maturity investments Other investments (1) Total (1)(2) Balance at January 1, 2015 $ 358.7 $ 1,692.1 $ 74.0 $ — $ — $ 182.0 $ 2,306.8 Amortization/accretion — (2.9 ) — — — — (2.9 ) Net realized and unrealized gains 5.5 7.3 0.3 — — 1.2 14.3 Purchases 62.4 208.7 28.4 — — 1.4 300.9 Sales (75.2 ) (175.4 ) — — — (3.0 ) (253.6 ) Transfers in — 2.9 — — — — 2.9 Transfers out — — (2.9 ) — — — (2.9 ) Balance at March 31, 2015 $ 351.4 $ 1,732.7 $ 99.8 $ — $ — $ 181.6 $ 2,365.5 Amortization/accretion — (3.5 ) — — — — (3.5 ) Net realized and unrealized gains (1.0 ) (8.2 ) (0.2 ) — — (4.5 ) (13.9 ) Purchases 350.8 307.4 5.6 — — 1.1 664.9 Sales (373.9 ) (215.5 ) — — — (19.1 ) (608.5 ) Transfers in — 28.4 — — — — 28.4 Transfers out — — (28.4 ) — — — (28.4 ) Balance at June 30, 2015 $ 327.3 $ 1,841.3 $ 76.8 $ — $ — $ 159.1 $ 2,404.5 _______________________________________________________________________________ (1) Excludes the carrying value of $15.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2015. (2) Excludes short-term investments. Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities Convertible fixed maturity investments Other investments (1) Total (1)(2) Balance at January 1, 2014 $ 469.5 $ 1,753.1 $ 81.9 $ 0.1 $ — $ 119.9 $ 2,424.5 Amortization/accretion — (2.7 ) — — — — (2.7 ) Net realized and unrealized gains 8.6 6.9 0.3 — — 3.1 18.9 Purchases 140.6 347.8 7.5 — — 2.3 498.2 Sales (60.0 ) (411.4 ) — — — (1.6 ) (473.0 ) Transfers in — — — — — — — Transfers out — — — — — — — Balance at March 31, 2014 $ 558.7 $ 1,693.7 $ 89.7 $ 0.1 $ — $ 123.7 $ 2,465.9 Amortization/accretion — (2.8 ) — — — — (2.8 ) Net realized and unrealized gains 14.1 5.5 0.3 0.4 — 1.7 22.0 Purchases 279.2 349.8 34.2 — — 1.0 664.2 Sales (332.7 ) (292.1 ) — — — (1.5 ) (626.3 ) Transfers in — 7.5 — — — — 7.5 Transfers out — — (7.5 ) — — — (7.5 ) Balance at June 30, 2014 $ 519.3 $ 1,761.6 $ 116.7 $ 0.5 $ — $ 124.9 $ 2,523.0 _______________________________________________________________________________ (1) Excludes the carrying value of $18.0 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of June 30, 2014. (2) Excludes short-term investments.
Fair value, significant unobservable inputs	The following summarizes significant unobservable inputs used in estimating the fair value of fixed maturity investments classified within Level 3, other than hedge funds and private equities, as of June 30, 2015 . The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds. Description Fair Value (in millions) Rating (2) Valuation Technique Unobservable Inputs Input Preferred stock (1) $ 71.2 N/R Discounted cash flow Discount yield 7.065% Surplus notes: N/R 12.3% - Seller priority note $ 45.4 Discounted cash flow Discount rate (3) 10.2% Timing of interest payments (4) 5 years Timing of principal payments (4) 10 years - Pari passu note $ 20.9 Discounted cash flow Discount rate (5) 15.5% Timing of interest payments (4) 5 years Timing of principal payments (4) 15 years Asset-backed securities (1) $ 5.6 A Broker pricing Broker quote N/A _________________________________________________________________________ (1) As of June 30, 2015 , each asset type consists of one security. (2) Credit ratings, if rated, are assigned based on the following hierarchy: 1) Standard & Poor's and 2) Moody's (3) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the seller priority note is roughly equivalent to that of a conventional debt security with a credit rating of ‘B’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the seller priority note. (4) For estimated value purposes, the assumption has been made that interest payouts begin in year five and principal repayments begin on a graduated basis in year ten for the seller priority note and year fifteen for the pari passu note. (5) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the pari passu note is roughly equivalent to that of a conventional debt security with a credit rating of ‘CCC’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the pari passu note.
Net unrealized gains or losses for Level 3 investments	The following summarizes significant unobservable inputs used in estimating the fair value of fixed maturity investments classified within Level 3, other than hedge funds and private equities, as of June 30, 2015 . The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds. Description Fair Value (in millions) Rating (2) Valuation Technique Unobservable Inputs Input Preferred stock (1) $ 71.2 N/R Discounted cash flow Discount yield 7.065% Surplus notes: N/R 12.3% - Seller priority note $ 45.4 Discounted cash flow Discount rate (3) 10.2% Timing of interest payments (4) 5 years Timing of principal payments (4) 10 years - Pari passu note $ 20.9 Discounted cash flow Discount rate (5) 15.5% Timing of interest payments (4) 5 years Timing of principal payments (4) 15 years Asset-backed securities (1) $ 5.6 A Broker pricing Broker quote N/A _________________________________________________________________________ (1) As of June 30, 2015 , each asset type consists of one security. (2) Credit ratings, if rated, are assigned based on the following hierarchy: 1) Standard & Poor's and 2) Moody's (3) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the seller priority note is roughly equivalent to that of a conventional debt security with a credit rating of ‘B’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the seller priority note. (4) For estimated value purposes, the assumption has been made that interest payouts begin in year five and principal repayments begin on a graduated basis in year ten for the seller priority note and year fifteen for the pari passu note. (5) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the pari passu note is roughly equivalent to that of a conventional debt security with a credit rating of ‘CCC’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, which was added to the treasury rate to determine the discount rate for the pari passu note.
Mortgage-backed and asset-backed securities	The following table summarizes the carrying value of OneBeacon's asset-backed securities as of June 30, 2015 and December 31, 2014 : June 30, 2015 December 31, 2014 ($ in millions) Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 235.0 $ 235.0 $ — $ 259.2 $ 259.2 $ — FNMA 1.7 1.7 — 1.9 1.9 — FHLMC — — — — — — Total agency (1) 236.7 236.7 — 261.1 261.1 — Non-agency: Residential 100.0 100.0 — 67.4 67.4 — Commercial 126.1 126.1 — 96.7 96.7 — Total Non-agency 226.1 226.1 — 164.1 164.1 — Total mortgage-backed securities 462.8 462.8 — 425.2 425.2 — Other asset-backed securities: Credit card receivables 210.9 210.9 — 197.6 197.6 — Vehicle receivables 191.1 191.1 — 145.8 145.8 — Other 58.5 52.9 5.6 45.8 45.8 — Total other asset-backed securities 460.5 454.9 5.6 389.2 389.2 — Total mortgage-backed and asset-backed securities $ 923.3 $ 917.7 $ 5.6 $ 814.4 $ 814.4 $ — _______________________________________________________________________________ (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guarantee of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
Schedule of security issuance years of investments in non-agency RMBS and non-agency CMBS securities	The security issuance years of OneBeacon's investments in non-agency RMBS and non-agency CMBS securities as of June 30, 2015 are as follows: Fair Value Security Issuance Year ($ in millions) 2004 2005 2006 2008 2010 2011 2012 2013 2014 2015 Total non-agency RMBS $ 100.0 $ 16.3 $ 3.3 $ 4.4 $ 4.7 $ 19.5 $ 16.1 $ 1.5 $ 13.9 $ 20.3 $ — Total non-agency CMBS 126.1 — — — — 6.0 — 8.5 23.5 53.3 34.8 Total non-agency $ 226.1 $ 16.3 $ 3.3 $ 4.4 $ 4.7 $ 25.5 $ 16.1 $ 10.0 $ 37.4 $ 73.6 $ 34.8
Non-agency RMBS, collateral quality and tranche levels	The classification of the underlying collateral quality and the tranche levels of OneBeacon's non-agency RMBS securities are as follows as of June 30, 2015 : ($ in millions) Fair Value Super Senior (1) Senior (2) Subordinate (3) Prime $ 99.3 $ 32.8 $ 66.5 $ — Non-prime 0.7 — 0.7 — Total non-agency RMBS $ 100.0 $ 32.8 $ 67.2 $ — _______________________________________________________________________________ (1) At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated AAA by Standard & Poor's, Aaa by Moody's, or AAA by Fitch Ratings ("Fitch") and were senior to other AAA or Aaa securities. (2) At issuance, Senior, or in the case of resecuritization, the underlying securities, were rated AAA by Standard & Poor's, Aaa by Moody's, or AAA by Fitch and were senior to non-AAA or non-Aaa securities. (3) At issuance, Subordinate were not rated AAA by Standard & Poor's, Aaa by Moody's, or AAA by Fitch and were junior to other AAA or Aaa securities.
Non-agency CMBS, type of interest rate and tranche levels	The amount of fixed and floating rate securities and their tranche levels of OneBeacon's non-agency CMBS securities are as follows as of June 30, 2015 : ($ in millions) Fair Value Super Senior (1) Senior (2) Subordinate (3) Fixed rate CMBS $ 85.0 $ 6.1 $ 32.8 $ 46.1 Floating rate CMBS 41.1 — — 41.1 Total non-agency CMBS $ 126.1 $ 6.1 $ 32.8 $ 87.2 _______________________________________________________________________________ (1) At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated AAA by Standard & Poor's, Aaa by Moody's or AAA by Fitch and were senior to other AAA or Aaa securities. (2) At issuance, Senior, or in the case of resecuritization, the underlying securities, were rated AAA by Standard & Poor's, Aaa by Moody's, or AAA by Fitch and were senior to non-AAA or non-Aaa securities. (3) At issuance, Subordinate were not rated AAA by Standard & Poor's, Aaa by Moody's, or AAA by Fitch and were junior to other AAA or Aaa securities.
Other investments	The following table summarizes investments in hedge funds and private equity funds as of June 30, 2015 and December 31, 2014 : June 30, 2015 December 31, 2014 ($ in millions) Fair Value (1) Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity banks and financial $ 12.8 $ — $ 28.5 $ — Long/short credit and distressed 8.4 — 8.4 — Other 6.0 — 5.4 — Total hedge funds 27.2 — 42.3 — Private equity funds Energy infrastructure and services 25.7 4.3 33.1 4.8 Multi-sector 14.4 2.1 14.5 2.2 Private equity secondaries 5.0 2.1 5.6 2.0 Healthcare 3.2 0.4 3.1 1.4 Insurance 2.1 0.1 2.1 0.1 Real estate 0.9 0.1 1.7 0.1 Distressed residential real estate — — — — Total private equity funds 51.3 9.1 60.1 10.6 Total hedge funds and private equity funds $ 78.5 $ 9.1 $ 102.4 $ 10.6
Fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds	The following summarizes the June 30, 2015 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds: Hedge Funds Notice Period ($ in millions) 30 - 59 days notice 60 - 89 days notice 90 - 119 days notice 120+ days notice Total Redemption frequency Monthly $ 2.1 $ — $ — $ — $ 2.1 Quarterly 13.8 8.4 — — 22.2 Annual — — 2.9 — 2.9 Total hedge funds $ 15.9 $ 8.4 $ 2.9 $ — $ 27.2
Fair Value of private equity funds subject to lock-up periods	As of June 30, 2015 , investments in private equity funds were subject to lock-up periods as follows: ($ in millions) 1 - 3 years 3 - 5 years 5 - 10 years >10 years Total Private Equity Funds—expected lock-up period remaining $ 19.9 $ 15.8 $ 15.6 $ — $ 51.3 See Note 15—"Discontinued Operations" for further disclosures regarding the valuation of the surplus notes provided in conjunction with the financing of the Runoff Transaction.

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2015
Debt Disclosure [Abstract]
Schedule of debt outstanding	OneBeacon's debt outstanding as of June 30, 2015 and December 31, 2014 consisted of the following: ($ in millions) June 30, December 31, Senior unsecured notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (0.3 ) (0.3 ) Senior unsecured notes, carrying value $ 274.7 $ 274.7

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2015
Segment Reporting [Abstract]
Financial information for OneBeacon's segments	Financial information for OneBeacon's reportable segments is as follows: Insurance Operations Investing, Financing and Corporate ($ in millions) Specialty Products Specialty Industries Consolidated Three months ended June 30, 2015 Earned premiums $ 166.5 $ 152.8 $ — $ 319.3 Loss and loss adjustment expense (99.6 ) (94.9 ) — (194.5 ) Policy acquisition expenses (27.9 ) (28.5 ) — (56.4 ) Other underwriting expenses (23.3 ) (29.6 ) — (52.9 ) Total underwriting income (loss) 15.7 (0.2 ) — 15.5 Net investment income — — 10.1 10.1 Net realized and change in unrealized investment gains — — (14.0 ) (14.0 ) Net other revenues (expenses) — 0.1 (1.3 ) (1.2 ) General and administrative expenses — (0.5 ) (3.7 ) (4.2 ) Interest expense — — (3.3 ) (3.3 ) Pre-tax income (loss) from continuing operations $ 15.7 $ (0.6 ) $ (12.2 ) $ 2.9 Three months ended June 30, 2014 Earned premiums $ 145.9 $ 145.0 $ — $ 290.9 Loss and loss adjustment expense (101.3 ) (84.8 ) — (186.1 ) Policy acquisition expenses (23.4 ) (26.2 ) — (49.6 ) Other underwriting expenses (22.7 ) (29.0 ) — (51.7 ) Total underwriting income (loss) (1.5 ) 5.0 — 3.5 Net investment income — — 12.2 12.2 Net realized and change in unrealized investment gains — — 21.9 21.9 Net other revenues 0.1 0.2 0.7 1.0 General and administrative expenses — (0.5 ) (3.1 ) (3.6 ) Interest expense — — (3.3 ) (3.3 ) Pre-tax income (loss) from continuing operations $ (1.4 ) $ 4.7 $ 28.4 $ 31.7 Insurance Operations Investing, Financing and Corporate ($ in millions) Specialty Products Specialty Industries Consolidated Six months ended June 30, 2015 Earned premiums $ 302.6 $ 303.3 $ — $ 605.9 Loss and loss adjustment expense (173.7 ) (186.7 ) — (360.4 ) Policy acquisition expenses (50.8 ) (56.6 ) — (107.4 ) Other underwriting expenses (49.0 ) (59.8 ) — (108.8 ) Total underwriting income 29.1 0.2 — 29.3 Net investment income — — 20.6 20.6 Net realized and change in unrealized investment gains — — 0.2 0.2 Net other revenues (expenses) — 0.3 (4.6 ) (4.3 ) General and administrative expenses — (1.0 ) (7.3 ) (8.3 ) Interest expense — — (6.5 ) (6.5 ) Pre-tax income (loss) from continuing operations $ 29.1 $ (0.5 ) $ 2.4 $ 31.0 Six months ended June 30, 2014 Earned premiums $ 281.3 $ 286.1 $ — $ 567.4 Loss and loss adjustment expense (179.3 ) (156.2 ) — (335.5 ) Policy acquisition expenses (44.8 ) (51.5 ) — (96.3 ) Other underwriting expenses (44.9 ) (56.2 ) — (101.1 ) Total underwriting income 12.3 22.2 — 34.5 Net investment income — — 22.6 22.6 Net realized and change in unrealized investment gains — — 40.8 40.8 Net other revenues 0.2 0.3 1.5 2.0 General and administrative expenses 0.1 (1.0 ) (6.0 ) (6.9 ) Interest expense — — (6.5 ) (6.5 ) Pre-tax income from continuing operations $ 12.6 $ 21.5 $ 52.4 $ 86.5
Schedule of selected balance sheet of the segments	_______________________________________________________________________________
Schedule of net written premiums, earned premiums and ratios for OneBeacon's insurance operations by segment and in total, as well as for the three major underwriting units within Specialty Insurance Operations	The following tables provide net written premiums, earned premiums and underwriting ratios for OneBeacon's insurance operations by reportable segment and in total, for the three and six months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 Three months ended June 30, 2014 Insurance Operations Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Specialty Specialty Consolidated Net written premiums $ 159.7 $ 161.5 $ 321.2 $ 139.5 $ 156.4 $ 295.9 Earned premiums 166.5 152.8 319.3 145.9 145.0 290.9 Underwriting ratios: (1) Loss and LAE 59.8 % 62.1 % 60.9 % 69.5 % 58.5 % 64.0 % Expense 30.7 38.0 34.2 31.6 38.0 34.8 Total combined ratio 90.5 % 100.1 % 95.1 % 101.1 % 96.5 % 98.8 % Six months ended June 30, 2015 Six months ended June 30, 2014 Insurance Operations Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Specialty Specialty Consolidated Net written premiums $ 293.3 $ 315.0 $ 608.3 $ 300.3 $ 306.7 $ 607.0 Earned premiums 302.6 303.3 605.9 281.3 286.1 567.4 Underwriting ratios: (1) Loss and LAE 57.4 % 61.6 % 59.5 % 63.7 % 54.6 % 59.1 % Expense 33.0 38.3 35.7 31.9 37.6 34.8 Total combined ratio 90.4 % 99.9 % 95.2 % 95.6 % 92.2 % 93.9 % _______________________________________________________________________________ (1) Underwriting ratios are used to measure the components of underwriting profitability and include: the loss and LAE ratio, calculated by dividing loss and LAE by earned premiums; the expense ratio, calculated by dividing policy acquisition and other underwriting expenses by earned premiums; and the combined ratio, the sum of the loss and LAE ratio and the expense ratio.

Retirement Plans (Tables)

Retirement Plans (Tables)	6 Months Ended
	Jun. 30, 2015
Compensation and Retirement Disclosure [Abstract]
Schedule of components of net periodic benefit cost (income)	The components of net periodic benefit cost for the three and six months ended June 30, 2015 and 2014 were as follows: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Service cost $ 0.2 $ 0.2 $ 0.4 $ 0.3 Interest cost 1.1 1.1 2.3 2.3 Expected return on plan assets (2.1 ) (2.1 ) (4.3 ) (4.2 ) Amortization of unrecognized loss 0.3 0.1 0.6 0.2 Net periodic pension income before special termination benefits (0.5 ) (0.7 ) (1.0 ) (1.4 ) Special termination benefits expense (1) — — — 0.3 Total net periodic benefit income $ (0.5 ) $ (0.7 ) $ (1.0 ) $ (1.1 ) _______________________________________________________________________________ (1) Special termination benefits for 2014 represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.

Employee Share-Based Incentiv31

Employee Share-Based Incentive Compensation Plans (Tables)	6 Months Ended
	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of performance share activity	The following summarizes performance share activity for the three months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 2014 ($ in millions) Target OB Performance Shares outstanding Accrued expense Target OB Performance Shares outstanding Accrued expense Beginning of period 462,147 $ 2.1 512,938 $ 3.6 Payments and deferrals — — — — New awards — — — — Forfeitures and net change in assumed forfeitures — — — — Expense recognized — 0.3 — 0.8 End of period 462,147 $ 2.4 512,938 $ 4.4 Six months ended June 30, 2015 2014 ($ in millions) Target OB Performance Shares outstanding Accrued expense Target OB Performance Shares outstanding Accrued expense Beginning of period 517,470 $ 3.4 493,421 $ 4.0 Payments and deferrals (1) (181,290 ) (1.5 ) (142,138 ) (1.0 ) New awards 154,887 — 165,800 — Forfeitures and net change in assumed forfeitures (28,920 ) — (4,145 ) — Expense recognized — 0.5 — 1.4 End of period 462,147 $ 2.4 512,938 $ 4.4 _______________________________________________________________________________ (1) Performance share payments in 2015 for the 2012-2014 performance cycle were based upon a performance factor of 45.7% . Performance share payments in 2014 for the 2011-2013 performance cycle were based upon a performance factor of 37.1% .
Summary of performance shares outstanding and accrued expense for performance shares awarded under the OB Incentive Plan	The following summarizes performance shares outstanding and accrued performance share expense at June 30, 2015 for each performance cycle: ($ in millions) Target OB Performance Shares outstanding Accrued expense Performance cycle: 2013 - 2015 167,300 $ 1.5 2014 - 2016 151,810 0.6 2015 - 2017 154,887 0.3 Subtotal 473,997 2.4 Assumed forfeitures (11,850 ) — Total at June 30, 2015 462,147 $ 2.4
Summary of restricted shares activity	The following summarizes restricted shares activity for the three months ended June 30, 2015 and 2014 : Three months ended June 30, 2015 2014 ($ in millions) Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Beginning of period 390,950 $ 4.0 612,500 $ 5.7 New awards — — — — Forfeitures — — — — Vested — — — — Expense recognized — (0.5 ) — (0.8 ) End of period 390,950 $ 3.5 612,500 $ 4.9 Six months ended June 30, 2015 2014 ($ in millions) Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Beginning of period 612,500 $ 3.5 915,000 $ 6.5 New awards 75,950 1.1 — — Forfeitures (1,500 ) — (2,500 ) — Vested (296,000 ) — (300,000 ) — Expense recognized — (1.1 ) — (1.6 ) End of period 390,950 $ 3.5 612,500 $ 4.9

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Schedule of computation of earnings per share	The following table outlines the Company's computation of earnings per share for net income from continuing operations attributable to OneBeacon's common shareholders for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended 2015 2014 2015 2014 Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders $ 3.3 $ 25.3 $ 27.5 $ 72.6 Allocation of income for participating unvested restricted common shares — (0.1 ) (0.1 ) (0.5 ) Dividends paid on participating restricted common shares — (0.1 ) (0.1 ) (0.2 ) Total allocation to restricted common shares — (0.2 ) (0.2 ) (0.7 ) Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 3.3 $ 25.1 $ 27.3 $ 71.9 Undistributed (over-distributed) net earnings (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 3.3 $ 25.1 $ 27.3 $ 71.9 Dividends paid, net of restricted common share amounts (20.0 ) (19.9 ) (39.9 ) (39.8 ) Total undistributed (over-distributed) net earnings, net of restricted common share amounts $ (16.7 ) $ 5.2 $ (12.6 ) $ 32.1 Earnings per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.3 95.3 Weighted average unvested restricted common shares (1) (0.4 ) (0.6 ) (0.5 ) (0.7 ) Basic and diluted earnings per share denominator 94.9 94.7 94.8 94.6 Earnings per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Net income from continuing operations attributable to OneBeacon's common shareholders $ 0.03 $ 0.26 $ 0.29 $ 0.76 Dividends declared and paid (0.21 ) (0.21 ) (0.42 ) (0.42 ) Undistributed (over-distributed) earnings $ (0.18 ) $ 0.05 $ (0.13 ) $ 0.34 _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event.

Common Shareholders' Equity Acc

Common Shareholders' Equity Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The Company recorded the following changes to accumulated other comprehensive loss for net increases in net benefit plan assets and obligations during the six months ended June 30, 2015 and 2014 : Six months ended June 30, ($ in millions) 2015 2014 Net change in benefit plan assets and obligations $ 0.6 $ 0.2 Income tax expense (0.2 ) (0.1 ) Net change in benefit plan assets and obligations, net of tax $ 0.4 $ 0.1

Discontinued Operations (Tables

Discontinued Operations (Tables)	6 Months Ended
	Jun. 30, 2015
Discontinued Operations and Disposal Groups [Abstract]
Schedule of discontinued operations statement of operations and other disclosures	The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations: Three months ended Six months ended ($ in millions) 2015 2014 2015 2014 Net written premiums $ — $ (0.1 ) $ — $ (0.2 ) Revenues Earned premiums $ — $ (0.1 ) $ — $ (0.2 ) Other revenues (expenses) (0.2 ) — (0.3 ) — Total revenues (0.2 ) (0.1 ) (0.3 ) (0.2 ) Expenses Loss and loss adjustment expenses — (0.7 ) — (0.7 ) Other underwriting expenses — 0.7 — 1.4 Total expenses — — — 0.7 Pre-tax loss (0.2 ) (0.1 ) (0.3 ) (0.9 ) Income tax benefit — — — 0.3 Loss from discontinued operations, net of tax (0.2 ) (0.1 ) (0.3 ) (0.6 ) (Loss) gain from sale of discontinued operations, net of tax 0.3 (0.5 ) 0.3 (0.5 ) Net (loss) income from discontinued operations, net of tax $ 0.1 $ (0.6 ) $ — $ (1.1 ) The following table outlines the computation of loss per share for discontinued operations attributable to OneBeacon's common shareholders for the three and six months ended June 30, 2015 and 2014 : Three months ended Six months ended 2015 2014 2015 2014 (Loss) income attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders $ 0.1 $ (0.6 ) $ — $ (1.1 ) Allocation of loss for participating unvested restricted common shares — — — — Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 0.1 $ (0.6 ) $ — $ (1.1 ) Loss per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.3 95.3 Weighted average unvested restricted common shares (1) (0.4 ) (0.6 ) (0.5 ) (0.7 ) Basic and diluted loss per share denominator 94.9 94.7 94.8 94.6 Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Loss from discontinued operations attributable to OneBeacon's common shareholders per share $ — $ — $ — $ (0.01 ) _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event.

Consolidating Financial Infor35

Consolidating Financial Information (Tables)	6 Months Ended
	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidating Balance Sheet	The following tables present OneBeacon's consolidating balance sheets as of June 30, 2015 and December 31, 2014 and statements of operations and comprehensive income for the three and six months ended June 30, 2015 and 2014 and cash flows for the six months ended June 30, 2015 and 2014 . These financial statements reflect the Company's ("guarantor") financial position, results of operations and cash flows on a stand-alone basis, that of OBH ("the issuer") and of the Company's other entities ("non-guarantor subsidiaries") as well as the necessary consolidating adjustments to eliminate intercompany balances and transactions. Consolidating Balance Sheet As of June 30, 2015 (in millions) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 1,941.1 $ — $ — $ 1,941.1 Short-term investments, at amortized cost (which approximates fair value) 1.1 155.1 1.7 — 157.9 Common equity securities, at fair value — 304.3 — — 304.3 Convertible fixed maturity investments, at fair value — — — — — Other investments — 174.9 — — 174.9 Total investment securities 1.1 2,575.4 1.7 — 2,578.2 Cash — 106.1 0.1 — 106.2 Reinsurance recoverables — 168.0 — — 168.0 Premiums receivable — 292.2 — — 292.2 Funds held under reinsurance contracts — 49.3 — — 49.3 Deferred acquisition costs — 111.8 — — 111.8 Net deferred tax asset — 136.5 — — 136.5 Investment income accrued — 10.3 — — 10.3 Accounts receivable on unsettled investment sales — 1.1 — — 1.1 Investments in subsidiaries 1,032.9 — 1,020.2 (2,053.1 ) — Other assets 0.6 204.4 3.6 0.1 208.7 Total assets $ 1,034.6 $ 3,655.1 $ 1,025.6 $ (2,053.0 ) $ 3,662.3 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,350.8 $ — $ — $ 1,350.8 Unearned premiums — 616.2 — — 616.2 Funds held under insurance contracts — 102.6 — — 102.6 Debt — — 274.7 — 274.7 Accounts payable on unsettled investment purchases — 20.1 — — 20.1 Other liabilities 1.4 253.8 6.0 — 261.2 Total liabilities 1.4 2,343.5 280.7 — 2,625.6 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,033.2 1,308.1 744.9 (2,053.0 ) 1,033.2 Total noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,033.2 1,311.6 744.9 (2,053.0 ) 1,036.7 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,034.6 $ 3,655.1 $ 1,025.6 $ (2,053.0 ) $ 3,662.3 Consolidating Balance Sheet As of December 31, 2014 (in millions) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 1,799.8 $ — $ — $ 1,799.8 Short-term investments, at amortized cost (which approximates fair value) 18.4 182.5 1.3 — 202.2 Common equity securities, at fair value — 320.0 — — 320.0 Convertible fixed maturity investments, at fair value — 5.0 — — 5.0 Other investments — 198.8 — — 198.8 Total investment securities 18.4 2,506.1 1.3 — 2,525.8 Cash — 87.0 — — 87.0 Reinsurance recoverables — 173.8 — — 173.8 Premiums receivable — 241.5 — — 241.5 Funds held under reinsurance contracts — 37.1 — — 37.1 Deferred acquisition costs — 103.2 — 103.2 Net deferred tax asset — 131.7 — 0.1 131.8 Investment income accrued — 10.0 — — 10.0 Accounts receivable on unsettled investment sales — 7.2 — — 7.2 Investments in subsidiaries 1,027.4 — 1,053.0 (2,080.4 ) — Other assets 0.3 198.0 4.4 — 202.7 Assets held for sale — 58.1 — — 58.1 Total assets $ 1,046.1 $ 3,553.7 $ 1,058.7 $ (2,080.3 ) $ 3,578.2 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,342.2 $ — $ — $ 1,342.2 Unearned premiums — 588.3 — — 588.3 Funds held under insurance contracts — 81.0 — — 81.0 Debt — — 274.7 — 274.7 Accounts payable on unsettled investment purchases — 0.5 — — 0.5 Other liabilities 0.3 234.8 7.1 — 242.2 Total liabilities 0.3 2,246.8 281.8 — 2,528.9 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,045.8 1,303.4 776.9 (2,080.3 ) 1,045.8 Total noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,045.8 1,306.9 776.9 (2,080.3 ) 1,049.3 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,046.1 $ 3,553.7 $ 1,058.7 $ (2,080.3 ) $ 3,578.2
Consolidating Statement of Operations and Comprehensive (Loss) Income	Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 319.3 $ — $ — $ 319.3 Net investment income — 10.1 — — 10.1 Net realized and change in unrealized investment gains — (14.0 ) — — (14.0 ) Net other revenues (expenses) — (1.2 ) — — (1.2 ) Total revenues — 314.2 — — 314.2 Expenses Loss and loss adjustment expenses — 194.5 — — 194.5 Policy acquisition expenses — 56.4 — — 56.4 Other underwriting expenses — 52.9 — — 52.9 General and administrative expenses 1.3 2.9 — — 4.2 Interest expense — — 3.3 — 3.3 Total expenses 1.3 306.7 3.3 — 311.3 Pre-tax income (loss) from continuing operations (1.3 ) 7.5 (3.3 ) — 2.9 Income tax (expense) benefit — (0.1 ) 1.0 — 0.9 Net income (loss) from continuing operations (1.3 ) 7.4 (2.3 ) — 3.8 Loss from discontinued operations, net of tax — (0.2 ) — — (0.2 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (1.3 ) 7.5 (2.3 ) — 3.9 Equity in earnings of subsidiaries, net of tax 4.7 — 0.3 (5.0 ) — Net income (loss) including noncontrolling interests 3.4 7.5 (2.0 ) (5.0 ) 3.9 Less: Net income attributable to noncontrolling interests — (0.5 ) — — (0.5 ) Net income (loss) attributable to OneBeacon's common shareholders 3.4 7.0 (2.0 ) (5.0 ) 3.4 Other comprehensive income, net of tax 0.2 — 0.2 (0.2 ) 0.2 Comprehensive income (loss) attributable to OneBeacon's common shareholders $ 3.6 $ 7.0 $ (1.8 ) $ (5.2 ) $ 3.6 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 290.9 $ — $ — $ 290.9 Net investment income — 12.4 0.1 (0.3 ) 12.2 Net realized and change in unrealized investment gains — 22.7 — (0.8 ) 21.9 Net other revenues — 1.0 — — 1.0 Total revenues — 327.0 0.1 (1.1 ) 326.0 Expenses Loss and loss adjustment expenses — 186.1 — — 186.1 Policy acquisition expenses — 49.6 — — 49.6 Other underwriting expenses — 51.7 — — 51.7 General and administrative expenses 1.9 1.6 0.1 — 3.6 Interest expense — — 3.6 (0.3 ) 3.3 Total expenses 1.9 289.0 3.7 (0.3 ) 294.3 Pre-tax income (loss) from continuing operations (1.9 ) 38.0 (3.6 ) (0.8 ) 31.7 Income tax (expense) benefit — (7.8 ) 1.6 0.3 (5.9 ) Net income (loss) from continuing operations (1.9 ) 30.2 (2.0 ) (0.5 ) 25.8 Loss from discontinued operations, net of tax — (0.1 ) — — (0.1 ) Loss from sale of discontinued operations, net of tax — (0.5 ) — — (0.5 ) Net income (loss) before equity in earnings of unconsolidated affiliates (1.9 ) 29.6 (2.0 ) (0.5 ) 25.2 Equity in earnings of subsidiaries, net of tax 26.6 — 11.8 (38.4 ) — Net income including noncontrolling interests 24.7 29.6 9.8 (38.9 ) 25.2 Less: Net income attributable to noncontrolling interests — (0.5 ) — — (0.5 ) Net income attributable to OneBeacon's common shareholders 24.7 29.1 9.8 (38.9 ) 24.7 Other comprehensive income, net of tax 0.1 — 0.1 (0.1 ) 0.1 Comprehensive income attributable to OneBeacon's common shareholders $ 24.8 $ 29.1 $ 9.9 $ (39.0 ) $ 24.8 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 605.9 $ — $ — $ 605.9 Net investment income — 20.6 — — 20.6 Net realized and change in unrealized investment gains — 0.2 — — 0.2 Net other revenues (expenses) — (4.3 ) — — (4.3 ) Total revenues — 622.4 — — 622.4 Expenses Loss and loss adjustment expenses — 360.4 — — 360.4 Policy acquisition expenses — 107.4 — — 107.4 Other underwriting expenses — 108.8 — — 108.8 General and administrative expenses 2.6 5.6 0.1 — 8.3 Interest expense — — 6.5 — 6.5 Total expenses 2.6 582.2 6.6 — 591.4 Pre-tax income (loss) from continuing operations (2.6 ) 40.2 (6.6 ) — 31.0 Income tax (expense) benefit — (4.9 ) 2.4 — (2.5 ) Net income (loss) from continuing operations (2.6 ) 35.3 (4.2 ) — 28.5 Loss from discontinued operations, net of tax — (0.3 ) — — (0.3 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (2.6 ) 35.3 (4.2 ) — 28.5 Equity in earnings of subsidiaries, net of tax 30.1 — 12.9 (43.0 ) — Net income including noncontrolling interests 27.5 35.3 8.7 (43.0 ) 28.5 Less: Net income attributable to noncontrolling interests — (1.0 ) — — (1.0 ) Net income attributable to OneBeacon's common shareholders 27.5 34.3 8.7 (43.0 ) 27.5 Other comprehensive income, net of tax 0.4 — 0.4 (0.4 ) 0.4 Comprehensive income attributable to OneBeacon's common shareholders $ 27.9 $ 34.3 $ 9.1 $ (43.4 ) $ 27.9 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Revenues Earned premiums $ — $ 567.4 $ — $ — $ 567.4 Net investment income — 23.1 0.1 (0.6 ) 22.6 Net realized and change in unrealized investment gains — 42.1 — (1.3 ) 40.8 Net other revenues — 2.0 — — 2.0 Total revenues — 634.6 0.1 (1.9 ) 632.8 Expenses Loss and loss adjustment expenses — 335.5 — — 335.5 Policy acquisition expenses — 96.3 — — 96.3 Other underwriting expenses — 101.1 — — 101.1 General and administrative expenses 3.5 3.2 0.2 — 6.9 Interest expense — — 7.1 (0.6 ) 6.5 Total expenses 3.5 536.1 7.3 (0.6 ) 546.3 Pre-tax income (loss) from continuing operations (3.5 ) 98.5 (7.2 ) (1.3 ) 86.5 Income tax (expense) benefit — (16.7 ) 3.2 0.5 (13.0 ) Net income (loss) from continuing operations (3.5 ) 81.8 (4.0 ) (0.8 ) 73.5 Loss from discontinued operations, net of tax — (0.6 ) — — (0.6 ) Loss from sale of discontinued operations, net of tax — (0.5 ) — — (0.5 ) Net income (loss) before equity in earnings of unconsolidated affiliates (3.5 ) 80.7 (4.0 ) (0.8 ) 72.4 Equity in earnings of subsidiaries, net of tax 75.0 — 52.9 (127.9 ) — Net income including noncontrolling interests 71.5 80.7 48.9 (128.7 ) 72.4 Less: Net income attributable to noncontrolling interests — (0.9 ) — — (0.9 ) Net income attributable to OneBeacon's common shareholders 71.5 79.8 48.9 (128.7 ) 71.5 Other comprehensive income, net of tax 0.1 — 0.1 (0.1 ) 0.1 Comprehensive income attributable to OneBeacon's common shareholders $ 71.6 $ 79.8 $ 49.0 $ (128.8 ) $ 71.6
Consolidating Statement of Cash Flows	Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Cash flows from operations: Net income including noncontrolling interests $ 27.5 $ 35.3 $ 8.7 $ (43.0 ) $ 28.5 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (30.1 ) — (12.9 ) 43.0 — Net loss from discontinued operations — 0.3 — — 0.3 Net gain from sale of discontinued operations — (0.3 ) — — (0.3 ) Net realized and change in unrealized investment gains — (0.2 ) — — (0.2 ) Net adjustment to gain on sale of business — 3.7 — — 3.7 Deferred income tax benefit — (3.8 ) — — (3.8 ) Dividends received from subsidiaries 25.0 39.9 44.9 (109.8 ) — Other operating items: Net change in loss and LAE reserves — 8.6 — — 8.6 Net change in unearned premiums — 27.9 — — 27.9 Net change in premiums receivable — (50.7 ) — — (50.7 ) Net change in reinsurance recoverables on paid and unpaid losses — 5.8 — — 5.8 Net change in funds held under reinsurance contracts — (12.2 ) — — (12.2 ) Net change in funds held under insurance contracts — 21.6 — — 21.6 Net change in other assets and liabilities 1.9 12.6 (0.9 ) — 13.6 Net cash provided from (used for) operations—continuing operations 24.3 88.5 39.8 (109.8 ) 42.8 Net cash used for operations—discontinued operations — (0.3 ) — — (0.3 ) Net cash provided from (used for) operations 24.3 88.2 39.8 (109.8 ) 42.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 17.3 26.6 0.4 — 44.3 Maturities of fixed maturity investments — 115.8 — — 115.8 Sales of fixed maturity investments — 361.0 29.7 59.3 450.0 Sales of common equity securities — 268.1 — — 268.1 Sales of convertible fixed maturity investments — 6.1 — — 6.1 Return of capital and distributions of other investments — 22.1 — — 22.1 Purchases of fixed maturity investments — (624.9 ) (29.9 ) (59.3 ) (714.1 ) Purchases of common equity securities — (248.7 ) — — (248.7 ) Purchases of convertible fixed maturity investments — (0.8 ) — — (0.8 ) Contributions for other investments — (2.5 ) — — (2.5 ) Net change in unsettled investment purchases and sales — 25.8 — — 25.8 Proceeds from sale of property and equipment — 56.8 — — 56.8 Net acquisitions of property and equipment — (1.8 ) — — (1.8 ) Net cash provided from investing activities 17.3 3.6 0.2 — 21.1 Cash flows from financing activities: Cash dividends paid to common shareholders (40.0 ) — — — (40.0 ) Cash dividends paid to parent — (69.9 ) (39.9 ) 109.8 — Repurchases and retirements of common stock (1.6 ) — — — (1.6 ) Payments on capital lease obligation — (2.8 ) — — (2.8 ) Net cash used for financing activities (41.6 ) (72.7 ) (39.9 ) 109.8 (44.4 ) Net increase in cash during period — 19.1 0.1 — 19.2 Cash balance at beginning of period — 87.0 — — 87.0 Cash balance at end of period $ — $ 106.1 $ 0.1 $ — $ 106.2 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Cash flows from operations: Net income including noncontrolling interests $ 71.5 $ 80.7 $ 48.9 $ (128.7 ) $ 72.4 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (75.0 ) — (52.9 ) 127.9 — Net loss from discontinued operations — 0.6 — — 0.6 Net loss from sale of discontinued operations — 0.5 — — 0.5 Net realized and change in unrealized investment gains — (42.1 ) — 1.3 (40.8 ) Deferred income tax expense — 13.0 — (0.4 ) 12.6 Dividends received from subsidiaries 30.0 — 5.0 (35.0 ) — Other operating items: Net change in loss and LAE reserves — 71.1 — — 71.1 Net change in unearned premiums — 47.0 — — 47.0 Net change in premiums receivable — (47.8 ) — — (47.8 ) Net change in reinsurance recoverables on paid and unpaid losses — (5.4 ) — — (5.4 ) Net change in funds held under reinsurance contracts — (30.0 ) — — (30.0 ) Net change in funds held under insurance contracts — (0.3 ) — — (0.3 ) Net change in other assets and liabilities 2.6 (24.4 ) (2.5 ) (0.1 ) (24.4 ) Net cash provided from (used for) operations—continuing operations 29.1 62.9 (1.5 ) (35.0 ) 55.5 Net cash used for operations—discontinued operations — (33.9 ) — — (33.9 ) Net cash provided from (used for) operations 29.1 29.0 (1.5 ) (35.0 ) 21.6 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 12.7 65.4 2.0 — 80.1 Maturities of fixed maturity investments — 185.6 — — 185.6 Sales of fixed maturity investments — 844.2 6.7 — 850.9 Sales of common equity securities — 47.6 — — 47.6 Sales of convertible fixed maturity investments — 12.2 — — 12.2 Return of capital and distributions of other investments — 3.2 — — 3.2 Purchases of fixed maturity investments — (1,093.2 ) (8.7 ) — (1,101.9 ) Purchases of common equity securities — (48.7 ) — — (48.7 ) Purchases of convertible fixed maturity investments — (8.4 ) — — (8.4 ) Contributions for other investments — (3.3 ) — — (3.3 ) Net change in unsettled investment purchases and sales — (31.8 ) — — (31.8 ) Net acquisitions of property and equipment — (0.7 ) — — (0.7 ) Net cash provided from (used for) investing activities 12.7 (27.9 ) — — (15.2 ) Cash flows from financing activities: Cash dividends paid to common shareholders (40.0 ) — — — (40.0 ) Cash dividends paid to parent — (35.0 ) — 35.0 — Repurchases and retirements of common stock (1.8 ) — — — (1.8 ) Payments on capital lease obligation — (2.6 ) — — (2.6 ) Net cash used for financing activities (41.8 ) (37.6 ) — 35.0 (44.4 ) Net decrease in cash during period — (36.5 ) (1.5 ) — (38.0 ) Cash balance at beginning of period — 166.6 1.5 — 168.1 Cash balance at end of period $ — $ 130.1 $ — $ — $ 130.1

Nature of Operations and Summ36

Nature of Operations and Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Jun. 30, 2015USD ($)segment	Jun. 30, 2014USD ($)	Dec. 31, 2014USD ($)	Jan. 01, 2014USD ($)
Basis of presentation
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets					$ (1.2)	$ (0.6)
Net investment income	$ 10.1	$ 12.2	$ 20.6	$ 22.6
Number of underwriting segments | segment			15
Income tax benefit	$ (0.9)	5.9	$ 2.5	13
White Mountains Insurance Group Ltd
Basis of presentation
Ownership interest (as a percent)	75.30%		75.30%
Specialty Products
Basis of presentation
Net investment income	$ 0	0	$ 0	0
Number of underwriting segments | segment			10
Specialty Industries
Basis of presentation
Net investment income	0	0	$ 0	0
Number of underwriting segments | segment			5
Accounting Standards Update 2014-01 [Member] | Restatement Adjustment [Member]
Basis of presentation
Net investment income		$ 0.5		0.9
Income tax benefit	$ 0.6			$ 1.2

Acqusitions and Dispositions (D

Acqusitions and Dispositions (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2013	Jun. 30, 2015	Jun. 30, 2014	Dec. 23, 2014
Dispositions
Net loss from sale of discontinued operations	$ 0.3		$ (0.5)		$ 0.3	$ (0.5)
Runoff [Member]
Dispositions
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations							$ 101
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value							$ 64.9
Net loss from sale of discontinued operations	$ 0.3
Essentia Insurance Company [Member]
Dispositions
Gain on sale of discontinued operation, pre-tax		$ 3.7		$ 23
Net loss from sale of discontinued operations				$ 15

Unpaid Loss and Loss Adjustme38

Unpaid Loss and Loss Adjustment Expense (LAE) Reserves (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross beginning balance	$ 1,304	$ 1,069.8	$ 1,342.2	$ 1,054.3
Less beginning reinsurance recoverables on unpaid losses	(141.6)	(80.1)	(161.6)	(80.2)
Loss and LAE incurred relating to Current year losses	194.5	177.7	362.2	328.5
Loss and LAE incurred relating to prior year losses	0	8.4	(1.8)	7
Total incurred loss and LAE from continuing operations	194.5	186.1	360.4	335.5
Loss and LAE paid relating to Current year losses	(42.7)	(41.3)	(64.8)	(59.6)
Loss and LAE paid relating to Prior year losses	(110.5)	(101.1)	(272.5)	(216.6)
Total loss and LAE payments from continuing operations	(153.2)	(142.4)	(337.3)	(276.2)
Net ending loss and LAE reserves	1,203.7	1,033.4	1,203.7	1,033.4	$ 1,162.4	$ 1,180.6	$ 989.7	$ 974.1
Plus ending reinsurance recoverables on unpaid losses	(147.1)	(92)	(147.1)	(92)
Gross ending balance	$ 1,350.8	$ 1,125.4	$ 1,350.8	$ 1,125.4

Reinsurance (Details)

Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Reinsurance Retention Policy [Line Items]
Reinsurance recoverables on paid losses	$ 20.9		$ 20.9
Reinsurance recoverable on unpaid losses	147.1	$ 141.6	147.1	$ 161.6	$ 92	$ 80.1	$ 80.2
Reinsurance recoverables	168		$ 168	$ 173.8
Percentage of total paid and unpaid reinsurance recoverables			100.00%
Property Catastrophe Reinsurance [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	130
Property Catastrophe Reinsurance Layer One [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	$ 20
Reinsurance Retention Policy, Reinsured Risk, Percentage	95.00%
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	$ 10
Property Catastrophe Reinsurance Layer Two [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Reinsured Risk, Percentage	100.00%
Reinsurance Retention Policy, Excess Retention, Amount Reinsured	$ 100
Property Per Risk Reinsurance Program [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	3	5
Casualty Reinsurance Program [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	3	5
HMO Provider Excess [Member] [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	$ 3	$ 5
MPCI Portfolio [Member]
Reinsurance Retention Policy [Line Items]
Coverage in Excess of Retained Amount			52.00%
Retained Losses			98.00%
Quota Share Reinsurance Agreement Percentage	30.00%		30.00%
Crop-Hail Portfolio [Member]
Reinsurance Retention Policy [Line Items]
Coverage in Excess of Retained Amount			80.00%
Retained Losses			100.00%
Standard & Poor's, AA Rating [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance recoverables	$ 63.1		$ 63.1
Percentage of total paid and unpaid reinsurance recoverables			38.00%
Standard & Poor's, A Rating [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance recoverables	82.3		$ 82.3
Percentage of total paid and unpaid reinsurance recoverables			49.00%
Standard & Poor's, BBB rating
Reinsurance Retention Policy [Line Items]
Reinsurance recoverables	$ 22.6		$ 22.6
Percentage of total paid and unpaid reinsurance recoverables			13.00%

Investment Securities (Net inve

Investment Securities (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross Investment Income	$ 11.7	$ 13.8	$ 23.6	$ 25.9
Less investment expenses	(1.6)	(1.6)	(3)	(3.3)
Net investment income, pre-tax	10.1	12.2	20.6	22.6
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross Investment Income	10.3	10.6	20.5	20.9
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross Investment Income	1.5	2	3.1	3.7
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross Investment Income	0	0.1	0	0.1
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross Investment Income	$ (0.1)	$ 1.1	$ 0	$ 1.2

Investment Securities (Net real

Investment Securities (Net realized investment gains (losses)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 35.2	$ 9.3	$ 44.7	$ 16.6
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	1.2	1.6	1.9	2.4
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	24.6	6.5	34.4	11.9
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0.3	1.2	0.3	2.3
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 9.1	$ 0	$ 8.1	$ 0

Investment Securities (Changes

Investment Securities (Changes in fair value) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	$ (49.5)	$ 12.6	$ (44.7)	$ 24.2
Changes in net foreign currency translation gains (losses)	0.3	0	0.2	0
Total net changes in fair value reflected in revenues	(49.2)	12.6	(44.5)	24.2
Fixed maturity investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(9.1)	7.3	(2.5)	12
Changes in net foreign currency translation gains (losses)	0	0	0	0
Total net changes in fair value reflected in revenues	(9.1)	7.3	(2.5)	12
Short-term investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	0		0
Changes in net foreign currency translation gains (losses)	0		0
Total net changes in fair value reflected in revenues	0		0
Common equity securities
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(26.5)	6.6	(30.9)	9.7
Changes in net foreign currency translation gains (losses)	0.3	0	0.2	0
Total net changes in fair value reflected in revenues	(26.2)	6.6	(30.7)	9.7
Convertible fixed maturity investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(0.3)	(3)	0.1	(2.3)
Changes in net foreign currency translation gains (losses)	0	0	0	0
Total net changes in fair value reflected in revenues	(0.3)	(3)	0.1	(2.3)
Other investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(13.6)	1.7	(11.4)	4.8
Changes in net foreign currency translation gains (losses)	0	0	0	0
Total net changes in fair value reflected in revenues	$ (13.6)	$ 1.7	$ (11.4)	$ 4.8

Investment Securities (Net unre

Investment Securities (Net unrealized investment gains and losses) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Investments [Abstract]
Trading Securities Gross Unrealized Gain	$ 62.3	$ 104.7
Trading Securities Gross Unrealized Loss	(11.2)	(8.9)
Gross Unrealized Gains (Losses) on Trading Securities Pretax	51.1	95.8
Trading Securities, Unrealized Gains and Losses, Tax	(18.7)	(26.9)
Unrealized gains (losses) on trading securities, net of tax	$ 32.4	$ 68.9

Investment Securities (Fixed ma

Investment Securities (Fixed maturity investment gains and losses) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Gross Unrealized Gain	$ 62.3	$ 104.7
Gross unrealized losses	(11.2)	(8.9)
Carrying value	1,941.1	1,799.8
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	43.8	38
Trading Securities Gross Unrealized Gain	0.1	0
Gross unrealized losses	0	0
Net unrealized foreign currency gains (losses)	0	0
Carrying value	43.9	38
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	813.2	787.7
Trading Securities Gross Unrealized Gain	8.7	11.5
Gross unrealized losses	(0.6)	(1)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	821.3	798.2
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	66.8	62.4
Trading Securities Gross Unrealized Gain	0.7	1.4
Gross unrealized losses	(0.5)	(0.1)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	67	63.7
Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	922.5	814.4
Trading Securities Gross Unrealized Gain	2.7	1.5
Gross unrealized losses	(1.9)	(1.5)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	923.3	814.4
Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1	1
Trading Securities Gross Unrealized Gain	0.2	0.3
Gross unrealized losses	0	0
Net unrealized foreign currency gains (losses)	0	0
Carrying value	1.2	1.3
Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	78.3	78.3
Trading Securities Gross Unrealized Gain	6.1	5.9
Gross unrealized losses	0	0
Net unrealized foreign currency gains (losses)	0	0
Carrying value	84.4	84.2
Total fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,925.6	1,781.8
Trading Securities Gross Unrealized Gain	18.5	20.6
Gross unrealized losses	(3)	(2.6)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	$ 1,941.1	$ 1,799.8

Investment Securities (Converti

Investment Securities (Convertible fixed maturity investments and other investments) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Funds held under reinsurance agreements, liability	$ 102.6	$ 81
Trading Securities Gross Unrealized Gain	62.3	104.7
Gross unrealized losses	(11.2)	(8.9)
Carrying value	1,941.1	1,799.8
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	298.4	283.2
Trading Securities Gross Unrealized Gain	12.4	39.3
Gross unrealized losses	(6.5)	(2.4)
Net unrealized foreign currency gains (losses)	0	(0.1)
Carrying value	304.3	320
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	0	5.2
Trading Securities Gross Unrealized Gain	0	0
Gross unrealized losses	0	(0.2)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	0	5
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	145.2	157.7
Trading Securities Gross Unrealized Gain	31.4	44.8
Gross unrealized losses	(1.7)	(3.7)
Net unrealized foreign currency gains (losses)	0	0
Carrying value	174.9	198.8
Total common equity securities, convertible fixed maturity investments and other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	443.6	446.1
Trading Securities Gross Unrealized Gain	43.8	84.1
Gross unrealized losses	(8.2)	(6.3)
Net unrealized foreign currency gains (losses)	0	(0.1)
Carrying value	$ 479.2	$ 523.8

Investment Securities (Fair val

Investment Securities (Fair value measurements) (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2015USD ($)fund	Mar. 31, 2015USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Jun. 30, 2015USD ($)fund	Jun. 30, 2014USD ($)	Dec. 31, 2014USD ($)fund	Dec. 23, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 35.2		$ 9.3		$ 44.7	$ 16.6
Other investments	174.9				174.9		$ 198.8
Debt securities issued by corporations	$ 2,404.5	$ 2,365.5	2,523	$ 2,465.9	$ 2,404.5	2,523	$ 2,306.8		$ 2,424.5
Percentage of Fair Value Investments Using Observable Inputs	91.00%				91.00%		90.00%
Maximum Percentage Differences Between Prices Provided by Pricing Services Considered Outliers	5.00%				5.00%
Maximum Differences Between Prices Provided By Pricing Services Considered Outliers					$ 1
Percentage of private preferred stock	84.00%				84.00%		84.00%
Fair Value Assets Measured on Recurring Basis Transfers out	$ 28.4	2.9	7.5	0
Other investments at fair value	159.1				$ 159.1		$ 182
Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	327.3	351.4	519.3	558.7	327.3	519.3	358.7		469.5
Fair Value Assets Measured on Recurring Basis Transfers out	0	0	0	0
Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,841.3	1,732.7	1,761.6	1,693.7	1,841.3	1,761.6	1,692.1		1,753.1
Fair Value Assets Measured on Recurring Basis Transfers out	0	0	0	0
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	27.2				27.2		42.3
Other investments at fair value	$ 27.2				$ 27.2		$ 42.3
Number of Investments | fund	7				7		7
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	$ 51.3				$ 51.3		$ 60.1
Other investments at fair value	$ 51.3				$ 51.3		$ 60.1
Number of Investments | fund	17				17		17
Community reinvestment vehicle
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	$ 14.2				$ 14.2		$ 14.3
Trust certificates
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	0.1				0.1		0.2
Single Fund
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	12.5				12.5		15.8
Tax development fund
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	15.8		18		15.8	18	16.8
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	821.3				821.3		798.2
Debt securities issued by industrial corporations | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value Assets Measured on Recurring Basis Transfers out					(2.9)
Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	923.3				923.3		814.4
Asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	917.7				917.7		814.4
Asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5.6				5.6		0
Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	126.1				126.1		96.7
Commercial Mortgage Backed Securities [Member] | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	126.1				126.1		96.7
Commercial Mortgage Backed Securities [Member] | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0				0		$ 0
Fair Value Assets Measured on Recurring Basis Transfers out					$ (10.3)	7.5
Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Investments | fund	1				1		1
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 1.2		1.6		$ 1.9	2.4
Fixed maturity investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	76.8	99.8	116.7	89.7	76.8	116.7	$ 74		81.9
Fair Value Assets Measured on Recurring Basis Transfers out	28.4	2.9	7.5	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	24.6		6.5		34.4	11.9
Hedge funds and private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	78.5				78.5		$ 102.4
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0.3		1.2		0.3	2.3
Convertible fixed maturity investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	0	0	0	0	0			0
Fair Value Assets Measured on Recurring Basis Transfers out	0	0	0	0
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 9.1		0		$ 8.1	0
Investments, Percent of Total	6.00%				6.00%		7.00%
Other investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 159.1	181.6	124.9	123.7	$ 159.1	$ 124.9			$ 119.9
Fair Value Assets Measured on Recurring Basis Transfers out	0	$ 0	$ 0	$ 0
Surplus notes
Schedule of Trading Securities and Other Trading Assets [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	66.3				66.3		$ 65.1
Recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	2,562.4				2,562.4		2,509
Recurring basis | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	485.2				485.2		560.4
Recurring basis | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,841.3				1,841.3		1,692.6
Recurring basis | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	235.9				235.9		256
Recurring basis | U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	43.9				43.9		38
Recurring basis | U.S. Government and agency obligations | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	43.9				43.9		38
Recurring basis | U.S. Government and agency obligations | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | U.S. Government and agency obligations | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	821.3				821.3		798.2
Recurring basis | Debt securities issued by industrial corporations | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	821.3				821.3		795.3
Recurring basis | Debt securities issued by industrial corporations | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		2.9
Recurring basis | Debt securities issued by industrial corporations | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	346.4				346.4		286.8
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	346.4				346.4		286.8
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	120.1				120.1		104.8
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	120.1				120.1		104.8
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Financial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	133.1				133.1		148.6
Recurring basis | Debt securities issued by industrial corporations | Financial | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Financial | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	133.1				133.1		148.6
Recurring basis | Debt securities issued by industrial corporations | Financial | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Communications
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	56.3				56.3		74.9
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	56.3				56.3		74.9
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54				54		53.5
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54				54		53.5
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39				39		56.4
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39				39		53.5
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		2.9
Recurring basis | Debt securities issued by industrial corporations | Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	43.4				43.4		44.2
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	43.4				43.4		44.2
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	29				29		29
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	29				29		29
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	67				67		63.7
Recurring basis | Municipal obligations | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Municipal obligations | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	67				67		63.7
Recurring basis | Municipal obligations | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	923.3				923.3		814.4
Recurring basis | Asset-backed securities | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	917.7				917.7		814.4
Recurring basis | Asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5.6				5.6		0
Recurring basis | Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1.2				1.2		1.3
Recurring basis | Foreign government obligations | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.6				0.6		0.7
Recurring basis | Foreign government obligations | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.6				0.6		0.6
Recurring basis | Foreign government obligations | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	84.4				84.4		84.2
Recurring basis | Preferred stocks | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Preferred stocks | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	13.2				13.2		13.1
Recurring basis | Preferred stocks | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	71.2				71.2		71.1
Recurring basis | Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,941.1				1,941.1		1,799.8
Recurring basis | Fixed maturity investments | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	44.5				44.5		38.7
Recurring basis | Fixed maturity investments | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,819.8				1,819.8		1,687.1
Recurring basis | Fixed maturity investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	76.8				76.8		74
Recurring basis | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	157.9				157.9		202.2
Recurring basis | Short-term investments | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	157.9				157.9		201.7
Recurring basis | Short-term investments | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0.5
Recurring basis | Short-term investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	304.3				304.3		320
Recurring basis | Common equity securities | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	282.8				282.8		320
Recurring basis | Common equity securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	21.5				21.5		0
Recurring basis | Common equity securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41				41		121.7
Recurring basis | Common equity securities | Consumer | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41				41		121.7
Recurring basis | Common equity securities | Consumer | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Consumer | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Financial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	24.3				24.3		72.4
Recurring basis | Common equity securities | Financial | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	24.3				24.3		72.4
Recurring basis | Common equity securities | Financial | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Financial | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.6				0.6		15.6
Recurring basis | Common equity securities | Energy | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.6				0.6		15.6
Recurring basis | Common equity securities | Energy | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Energy | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1.8				1.8		9.9
Recurring basis | Common equity securities | Basic materials | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1.8				1.8		9.9
Recurring basis | Common equity securities | Basic materials | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Basic materials | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1				1		5.1
Recurring basis | Common equity securities | Utilities | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1				1		5.1
Recurring basis | Common equity securities | Utilities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Utilities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Exchange Traded Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	186.2				186.2
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	164.7				164.7
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	21.5				21.5
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0
Recurring basis | Common equity securities | Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	49.4				49.4		95.3
Recurring basis | Common equity securities | Other | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	49.4				49.4		95.3
Recurring basis | Common equity securities | Other | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Common equity securities | Other | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		5
Recurring basis | Convertible fixed maturity investments | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Convertible fixed maturity investments | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		5
Recurring basis | Convertible fixed maturity investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	159.1				159.1		182
Recurring basis | Other investments | Level 1
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Other investments | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0				0		0
Recurring basis | Other investments | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 159.1				$ 159.1		$ 182
Runoff [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value								$ 64.9
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations								$ 101

Investment Securities (Corporat

Investment Securities (Corporate debt securites) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,404.5	$ 2,365.5	$ 2,306.8	$ 2,523	$ 2,465.9	$ 2,424.5
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	821.3		798.2
AA | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	46.5		57.9
A | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	309.3		328.1
BBB | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	465.5		409.2
Other | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		3
Recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	2,562.4		2,509
Recurring basis | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 821.3		$ 798.2

Investment Securities (Fair v48

Investment Securities (Fair value rollforward) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Investment securities
Changes in net unrealized investment gains (losses)	$ (49.5)		$ 12.6		$ (44.7)	$ 24.2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,365.5	$ 2,306.8	2,465.9	$ 2,424.5	2,306.8	2,424.5
Amortization/accretion	(3.5)	(2.9)	(2.8)	(2.7)
Total net realized and unrealized gains (losses)	(13.9)	14.3	22	18.9
Purchases	664.9	300.9	664.2	498.2
Sales	(608.5)	(253.6)	(626.3)	(473)
Transfers in	28.4	2.9	7.5	0
Transfers out	(28.4)	(2.9)	(7.5)	0
Ending Balance	2,404.5	2,365.5	2,523	2,465.9	2,404.5	2,523
Other investments	174.9				174.9		$ 198.8
Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	1,732.7	1,692.1	1,693.7	1,753.1	1,692.1	1,753.1
Amortization/accretion	(3.5)	(2.9)	(2.8)	(2.7)
Total net realized and unrealized gains (losses)	(8.2)	7.3	5.5	6.9
Purchases	307.4	208.7	349.8	347.8
Sales	(215.5)	(175.4)	(292.1)	(411.4)
Transfers in	28.4	2.9	7.5	0
Transfers out	0	0	0	0
Ending Balance	1,841.3	1,732.7	1,761.6	1,693.7	1,841.3	1,761.6
Level 3
Investment securities
Changes in net unrealized investment gains (losses)	(13.8)		2.4		(11.3)	5.8
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in			0		0
Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	351.4	358.7	558.7	469.5	358.7	469.5
Amortization/accretion	0	0	0	0
Total net realized and unrealized gains (losses)	(1)	5.5	14.1	8.6
Purchases	350.8	62.4	279.2	140.6
Sales	(373.9)	(75.2)	(332.7)	(60)
Transfers in	0	0	0	0
Transfers out	0	0	0	0
Ending Balance	327.3	351.4	519.3	558.7	327.3	519.3
Tax development fund
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Other investments	15.8		18		15.8	18	$ 16.8
Residential Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		67.4			67.4
Ending Balance	100				100
Residential Mortgage Backed Securities [Member] | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		67.4			67.4
Ending Balance	100				100
Residential Mortgage Backed Securities [Member] | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0			0
Transfers out					18.1
Ending Balance	0				0
Commercial Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		96.7			96.7
Ending Balance	126.1				126.1
Commercial Mortgage Backed Securities [Member] | Level 2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		96.7			96.7
Ending Balance	126.1				126.1
Commercial Mortgage Backed Securities [Member] | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		0			0
Transfers out					10.3	(7.5)
Ending Balance	0				0
Debt securities issued by industrial corporations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance		798.2			798.2
Ending Balance	821.3				821.3
Debt securities issued by industrial corporations | Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out					2.9
Short-term investments
Investment securities
Changes in net unrealized investment gains (losses)	0				0
Short-term investments | Level 3
Investment securities
Changes in net unrealized investment gains (losses)	0		0		0	0
Common equity securities | Level 3
Investment securities
Changes in net unrealized investment gains (losses)	0		0.4		0	0.4
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0	0	0.1	0.1	0	0.1
Amortization/accretion	0	0	0	0
Total net realized and unrealized gains (losses)	0	0	0.4	0
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers in	0	0	0	0
Transfers out	0	0	0	0
Ending Balance	0	0	0.5	0.1	0	0.5
Convertible fixed maturity investments
Investment securities
Changes in net unrealized investment gains (losses)	(0.3)		(3)		0.1	(2.3)
Convertible fixed maturity investments | Level 3
Investment securities
Changes in net unrealized investment gains (losses)	0		0		0	0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0		0	0		0
Amortization/accretion	0	0	0	0
Total net realized and unrealized gains (losses)	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Transfers in	0	0	0	0
Transfers out	0	0	0	0
Ending Balance	0	0	0	0	0	0
Other investments
Investment securities
Changes in net unrealized investment gains (losses)	$ (13.6)		1.7		$ (11.4)	4.8
Investments, Percent of Total	6.00%				6.00%		7.00%
Other investments | Level 3
Investment securities
Changes in net unrealized investment gains (losses)	$ (13.6)		1.7		$ (11.4)	4.8
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	181.6		123.7	119.9		119.9
Amortization/accretion	0	0	0	0
Total net realized and unrealized gains (losses)	(4.5)	1.2	1.7	3.1
Purchases	1.1	1.4	1	2.3
Sales	(19.1)	(3)	(1.5)	(1.6)
Transfers in	0	0	0	0
Transfers out	0	0	0	0
Ending Balance	159.1	181.6	124.9	123.7	159.1	124.9
Fixed maturity investments
Investment securities
Changes in net unrealized investment gains (losses)	(9.1)		7.3		(2.5)	12
Fixed maturity investments | Level 3
Investment securities
Changes in net unrealized investment gains (losses)	(0.2)		0.3		0.1	0.6
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	99.8	74	89.7	81.9	74	81.9
Amortization/accretion	0	0	0	0
Total net realized and unrealized gains (losses)	(0.2)	0.3	0.3	0.3
Purchases	5.6	28.4	34.2	7.5
Sales	0	0	0	0
Transfers in	0	0	0	0
Transfers out	(28.4)	(2.9)	(7.5)	0
Ending Balance	$ 76.8	$ 99.8	$ 116.7	$ 89.7	$ 76.8	$ 116.7

Investment Securities (Signific

Investment Securities (Significant unobservable inputs) (Details) - Jun. 30, 2015 - USD ($) $ in Millions	Total
Standard Poors N R Rating [Member] | Commercial Mortgage Backed Securities [Member] | Discounted cash flow
Significant unobservable inputs
Default rate	50.00%
Standard Poors N R Rating [Member] | Preferred stocks | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 71.2
Discount Rate	7.065%
Standard Poors N R Rating [Member] | Surplus notes | Discounted cash flow
Significant unobservable inputs
Discount Rate	12.30%
Standard & Poor's, A- Rating [Member] | Commercial Mortgage Backed Securities [Member] | Broker Pricing [Member]
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 5.6
Seller priority [Member] | Standard Poors N R Rating [Member] | Surplus notes | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 45.4
Discount Rate	10.20%
Fair Value Inputs, Interest Payment Schedule	5 years
Fair Value Inputs, Principal Payment Schedule	10 years
Increase in credit spread	2.50%
Pari passu [Member] | Standard Poors N R Rating [Member] | Surplus notes | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 20.9
Discount Rate	15.50%
Fair Value Inputs, Interest Payment Schedule	5 years
Fair Value Inputs, Principal Payment Schedule	15 years
Increase in credit spread	2.50%

Investment Securities (Change i

Investment Securities (Change in net unrealized gains or losses for Level 3 assets) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	$ (49.5)	$ 12.6	$ (44.7)	$ 24.2
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(9.1)	7.3	(2.5)	12
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	0		0
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(0.3)	(3)	0.1	(2.3)
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(13.6)	1.7	(11.4)	4.8
Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(13.8)	2.4	(11.3)	5.8
Level 3 | Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(0.2)	0.3	0.1	0.6
Level 3 | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	0	0	0	0
Level 3 | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	0	0.4	0	0.4
Level 3 | Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	0	0	0	0
Level 3 | Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	$ (13.6)	$ 1.7	$ (11.4)	$ 4.8

Investment Securities (Asset ba

Investment Securities (Asset backed securities) (Details)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,404,500,000	$ 2,365,500,000	$ 2,306,800,000	$ 2,523,000,000	$ 2,465,900,000	$ 2,424,500,000
Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,841,300,000	$ 1,732,700,000	1,692,100,000	$ 1,761,600,000	$ 1,693,700,000	$ 1,753,100,000
Fixed rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 85,000,000
Average basis points of subordination	20.00%
Floating rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 41,100,000
GNMA
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	235,000,000		259,200,000
GNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	235,000,000		259,200,000
GNMA | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FNMA
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,700,000		1,900,000
FNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,700,000		1,900,000
FNMA | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FHLMC
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FHLMC | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
FHLMC | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Agency commercial mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	236,700,000		261,100,000
Agency commercial mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	236,700,000		261,100,000
Agency commercial mortgage-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	100,000,000		67,400,000
Residential | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	100,000,000		67,400,000
Residential | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	126,100,000		96,700,000
Commercial Mortgage Backed Securities [Member] | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	126,100,000		96,700,000
Commercial Mortgage Backed Securities [Member] | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Total Non-agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	226,100,000		164,100,000
Total Non-agency | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	226,100,000		164,100,000
Total Non-agency | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Total mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	462,800,000		425,200,000
Total mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	462,800,000		425,200,000
Total mortgage-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Credit card receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	210,900,000		197,600,000
Credit card receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	210,900,000		197,600,000
Credit card receivables | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Vehicle receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	191,100,000		145,800,000
Vehicle receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	191,100,000		145,800,000
Vehicle receivables | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0		0
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	58,500,000		45,800,000
Other | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	52,900,000		45,800,000
Other | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5,600,000		0
Total other asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	460,500,000		389,200,000
Total other asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	454,900,000		389,200,000
Total other asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5,600,000		0
Total mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	923,300,000		814,400,000
Total mortgage-backed and asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	917,700,000		814,400,000
Total mortgage-backed and asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5,600,000		$ 0
Non-Prime Residential Mortgage Backed Security
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	700,000
Non-Agency Residential Mortgage Backed Security [Domain]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 38,800,000
Maximum | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Percentage of underlying loans reported as non-performing	1.00%
Residential | Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 100,000,000
Residential, Subprime, Financing Receivable [Member] | Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 700,000
Residential, Subprime, Financing Receivable [Member] | Total mortgage-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1
Subordinate | Fixed rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 46,100,000
Subordinate | Floating rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41,100,000
Subordinate | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	87,200,000
Subordinate | Residential | Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0
Debt securities issued by corporations	0
Subordinate | Residential, Subprime, Financing Receivable [Member] | Residential
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0

Investment Securities (Non-agen

Investment Securities (Non-agency securities) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,404.5	$ 2,365.5	$ 2,306.8	$ 2,523	$ 2,465.9	$ 2,424.5
Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	100		67.4
Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	126.1		96.7
Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	85
Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41.1
Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	226.1		$ 164.1
Super Senior | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	6.1
Super Senior | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	6.1
Super Senior | Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Senior | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	32.8
Senior | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	32.8
Senior | Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Subordinate | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	87.2
Subordinate | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	46.1
Subordinate | Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	41.1
Securities Issued in 2004 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	16.3
Securities Issued in 2004 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities Issued in 2004 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	16.3
Securities Issued in 2005 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	3.3
Securities Issued in 2005 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities Issued in 2005 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	3.3
Securities Issued in 2006 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	4.4
Securities Issued in 2006 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities Issued in 2006 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	4.4
Securities Issued in 2008 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	4.7
Securities Issued in 2008 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities Issued in 2008 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	4.7
Securities issued in 2010 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	19.5
Securities issued in 2010 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	6
Securities issued in 2010 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	25.5
Securities issued in 2011 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	16.1
Securities issued in 2011 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities issued in 2011 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	16.1
Securities issued in 2012 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1.5
Securities issued in 2012 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	8.5
Securities issued in 2012 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	10
Securities Issued in 2013 | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	13.9
Securities Issued in 2013 | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	23.5
Securities Issued in 2013 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	37.4
Securities Issued in 2014 [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	20.3
Securities Issued in 2014 [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	53.3
Securities Issued in 2014 [Member] | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	73.6
Securities Issued in 2015 [Member] [Domain] | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Securities Issued in 2015 [Member] [Domain] | Commercial Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	34.8
Securities Issued in 2015 [Member] [Domain] | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	34.8
Residential, Prime, Financing Receivable [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	99.3
Residential, Prime, Financing Receivable [Member] | Super Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	32.8
Residential, Prime, Financing Receivable [Member] | Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	66.5
Residential, Prime, Financing Receivable [Member] | Subordinate | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Residential, Subprime, Financing Receivable [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.7
Residential, Subprime, Financing Receivable [Member] | Super Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Residential, Subprime, Financing Receivable [Member] | Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0.7
Residential, Subprime, Financing Receivable [Member] | Subordinate | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Residential Mortgage Backed Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	100
Residential Mortgage Backed Securities [Member] | Super Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	32.8
Residential Mortgage Backed Securities [Member] | Senior | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	67.2
Residential Mortgage Backed Securities [Member] | Subordinate | Residential Mortgage Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	$ 174.9	$ 198.8
Trust Certificates Issued Upon Dissolution of a Private Equity Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	0.1	0.2
Surplus notes
Schedule of Trading Securities and Other Trading Assets [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	66.3	65.1
Community reinvestment vehicle
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	14.2	14.3
Long/short credit and distressed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	8.4	8.4
Net asset value per share of unfunded commitments	0	0
Hedge funds other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	6	5.4
Net asset value per share of unfunded commitments	0	0
Long/short equity banks and financial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	12.8	28.5
Net asset value per share of unfunded commitments	0	0
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	27.2	42.3
Other investments at fair value	27.2	42.3
Net asset value per share of unfunded commitments	0	0
Distributions from inactive hedge funds	1
Redemption requests	3.2
Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	15.9
Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	8.4
Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.9
Hedge funds | Over 120 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Insurance
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.1	2.1
Net asset value per share of unfunded commitments	0.1	0.1
Distressed residential real estate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0	0
Net asset value per share of unfunded commitments	0	0
Energy infrastructure and services
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	25.7	33.1
Net asset value per share of unfunded commitments	4.3	4.8
Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	3.2	3.1
Net asset value per share of unfunded commitments	0.4	1.4
Multi-sector
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	14.4	14.5
Net asset value per share of unfunded commitments	2.1	2.2
Private equity secondaries
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	5	5.6
Net asset value per share of unfunded commitments	2.1	2
Real estate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0.9	1.7
Net asset value per share of unfunded commitments	0.1	0.1
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	51.3	60.1
Other investments at fair value	51.3	60.1
Net asset value per share of unfunded commitments	9.1	10.6
Private equity funds | 1 - 3 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	19.9
Private equity funds | 3 - 5 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	15.8
Private equity funds | 5 - 10 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	15.6
Private equity funds | >10 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Hedge funds and private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	78.5	102.4
Net asset value per share of unfunded commitments	9.1	$ 10.6
Monthly | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.1
Monthly | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.1
Monthly | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Monthly | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Monthly | Hedge funds | Over 120 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Quarterly | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	22.2
Quarterly | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	13.8
Quarterly | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	8.4
Quarterly | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Quarterly | Hedge funds | Over 120 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Annually | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.9
Annually | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Annually | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Annually | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.9
Annually | Hedge funds | Over 120 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	$ 0

Debt (Details)

Debt (Details) - USD ($) $ in Millions	1 Months Ended
	Nov. 30, 2012	Jun. 30, 2015	Dec. 31, 2014
Debt
Senior unsecured notes, carrying value		$ 274.7	$ 274.7
OBH (issuer)
Debt
Unamortized original issue discount		(0.3)	(0.3)
OBH Senior Notes [Member] | OBH (issuer)
Debt
Senior unsecured notes, at face value		275	275
2012 OBH Senior Notes | OBH (issuer)
Debt
Senior unsecured notes, at face value	$ 275
Percentage of par value at which debt was issued	99.90%
Issuance of debt, net of debt issuance costs	$ 272.9
Interest rate (as a percent)	4.60%
Carrying Value | OBH (issuer)
Debt
Senior unsecured notes, carrying value		$ 274.7	$ 274.7

Segment Information (Details)

Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Jun. 30, 2015USD ($)segmentUnits	Jun. 30, 2014USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Segment Information
Number of underwriting segments | segment			15
Number of Major Underwriting Units | Units			2
Net written premiums	$ 321.2	$ 295.9	$ 608.3	$ 607
Earned premiums	319.3	290.9	605.9	567.4
Loss and loss adjustment expense	(194.5)	(186.1)	(360.4)	(335.5)
Policy acquisition expenses	(56.4)	(49.6)	(107.4)	(96.3)
Other underwriting expenses	(52.9)	(51.7)	(108.8)	(101.1)
Total underwriting income (loss)	15.5	3.5	29.3	34.5
Net investment income	10.1	12.2	20.6	22.6
Net realized and change in unrealized investment gains	(14)	21.9	0.2	40.8
Net other revenues (expenses)	(1.2)	1	(4.3)	2
General and administrative expenses	(4.2)	(3.6)	(8.3)	(6.9)
Interest expense	(3.3)	(3.3)	(6.5)	(6.5)
Pre-tax income from continuing operations	2.9	31.7	31	86.5
Total investment securities	2,578.2		2,578.2			$ 2,525.8
Premiums receivable	292.2		292.2			241.5
Reinsurance recoverables	168		168			173.8
Funds Held under Reinsurance Agreements, Asset	49.3		49.3			37.1
Deferred acquisition costs	111.8		111.8			103.2
Other assets not separately identifiable at the segment level	462.8		462.8			496.8
Total assets	3,662.3		3,662.3			3,578.2
Unpaid loss and loss adjustment expense reserves	1,350.8	$ 1,125.4	1,350.8	$ 1,125.4	$ 1,304	1,342.2	$ 1,069.8	$ 1,054.3
Unearned premiums	616.2		616.2			588.3
Funds held under reinsurance agreements, liability	102.6		102.6			81
Debt	274.7		274.7			274.7
Other Liabilities Not Separately Identifiable at the Segment Level	281.3		281.3			242.7
Total liabilities	$ 2,625.6		$ 2,625.6			2,528.9
Segment Information, Additional Disclosure
Loss Ratio	60.90%	64.00%	59.50%	59.10%
Underwriting Expense Ratio	34.20%	34.80%	35.70%	34.80%
Combined Ratio	95.10%	98.80%	95.20%	93.90%
Specialty Products
Segment Information
Number of underwriting segments | segment			10
Net written premiums	$ 159.7	$ 139.5	$ 293.3	$ 300.3
Earned premiums	166.5	145.9	302.6	281.3
Loss and loss adjustment expense	(99.6)	(101.3)	(173.7)	(179.3)
Policy acquisition expenses	(27.9)	(23.4)	(50.8)	(44.8)
Other underwriting expenses	(23.3)	(22.7)	(49)	(44.9)
Total underwriting income (loss)	15.7	(1.5)	29.1	12.3
Net investment income	0	0	0	0
Net realized and change in unrealized investment gains	0	0	0	0
Net other revenues (expenses)	0	0.1	0	0.2
General and administrative expenses	0	0	0	0.1
Interest expense	0	0	0	0
Pre-tax income from continuing operations	15.7	$ (1.4)	29.1	$ 12.6
Total investment securities	0		0			0
Premiums receivable	119.4		119.4			77.7
Reinsurance recoverables	120.4		120.4			127.3
Funds Held under Reinsurance Agreements, Asset	49.3		49.3			37.1
Deferred acquisition costs	55.3		55.3			49.7
Other assets not separately identifiable at the segment level	0		0			0
Total assets	344.4		344.4			291.8
Unpaid loss and loss adjustment expense reserves	767.5		767.5			798.8
Unearned premiums	321.9		321.9			303.6
Funds held under reinsurance agreements, liability	102.6		102.6			81
Debt	0		0			0
Other Liabilities Not Separately Identifiable at the Segment Level	0		0			0
Total liabilities	$ 1,192		$ 1,192			1,183.4
Segment Information, Additional Disclosure
Loss Ratio	59.80%	69.50%	57.40%	63.70%
Underwriting Expense Ratio	30.70%	31.60%	33.00%	31.90%
Combined Ratio	90.50%	101.10%	90.40%	95.60%
Specialty Industries
Segment Information
Number of underwriting segments | segment			5
Net written premiums	$ 161.5	$ 156.4	$ 315	$ 306.7
Earned premiums	152.8	145	303.3	286.1
Loss and loss adjustment expense	(94.9)	(84.8)	(186.7)	(156.2)
Policy acquisition expenses	(28.5)	(26.2)	(56.6)	(51.5)
Other underwriting expenses	(29.6)	(29)	(59.8)	(56.2)
Total underwriting income (loss)	(0.2)	5	0.2	22.2
Net investment income	0	0	0	0
Net realized and change in unrealized investment gains	0	0	0	0
Net other revenues (expenses)	0.1	0.2	0.3	0.3
General and administrative expenses	(0.5)	(0.5)	(1)	(1)
Interest expense	0	0	0	0
Pre-tax income from continuing operations	(0.6)	$ 4.7	(0.5)	$ 21.5
Total investment securities	0		0			0
Premiums receivable	172.8		172.8			163.8
Reinsurance recoverables	29		29			22.7
Funds Held under Reinsurance Agreements, Asset	0		0			0
Deferred acquisition costs	56.5		56.5			53.5
Other assets not separately identifiable at the segment level	0		0			0
Total assets	258.3		258.3			240
Unpaid loss and loss adjustment expense reserves	564.7		564.7			519.6
Unearned premiums	294.3		294.3			284.7
Funds held under reinsurance agreements, liability	0		0			0
Debt	0		0			0
Other Liabilities Not Separately Identifiable at the Segment Level	0		0			0
Total liabilities	$ 859		$ 859			804.3
Segment Information, Additional Disclosure
Loss Ratio	62.10%	58.50%	61.60%	54.60%
Underwriting Expense Ratio	38.00%	38.00%	38.30%	37.60%
Combined Ratio	100.10%	96.50%	99.90%	92.20%
Investing, Financing and Corporate
Segment Information
Earned premiums	$ 0	$ 0	$ 0	$ 0
Loss and loss adjustment expense	0	0	0	0
Policy acquisition expenses	0	0	0	0
Other underwriting expenses	0	0	0	0
Total underwriting income (loss)	0	0	0	0
Net investment income	10.1	12.2	20.6	22.6
Net realized and change in unrealized investment gains	(14)	21.9	0.2	40.8
Net other revenues (expenses)	(1.3)	0.7	(4.6)	1.5
General and administrative expenses	(3.7)	(3.1)	(7.3)	(6)
Interest expense	(3.3)	(3.3)	(6.5)	(6.5)
Pre-tax income from continuing operations	(12.2)	$ 28.4	2.4	$ 52.4
Total investment securities	2,578.2		2,578.2			2,525.8
Premiums receivable	0		0			0
Reinsurance recoverables	18.6		18.6			23.8
Funds Held under Reinsurance Agreements, Asset	0		0			0
Deferred acquisition costs	0		0			0
Other assets not separately identifiable at the segment level	462.8		462.8			496.8
Total assets	3,059.6		3,059.6			3,046.4
Unpaid loss and loss adjustment expense reserves	18.6		18.6			23.8
Unearned premiums	0		0			0
Funds held under reinsurance agreements, liability	0		0			0
Debt	274.7		274.7			274.7
Other Liabilities Not Separately Identifiable at the Segment Level	281.3		281.3			242.7
Total liabilities	$ 574.6		$ 574.6			$ 541.2

Retirement Plans (Periodic Bene

Retirement Plans (Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 0.2	$ 0.2	$ 0.4	$ 0.3
Interest cost	1.1	1.1	2.3	2.3
Expected return on plan assets	(2.1)	(2.1)	(4.3)	(4.2)
Amortization of unrecognized loss	0.3	0.1	0.6	0.2
Net periodic pension income before special termination benefits	(0.5)	(0.7)	(1)	(1.4)
Special termination benefits expense(1)	0	0	0	0.3
Total net periodic benefit cost	(0.5)	$ (0.7)	(1)	$ (1.1)
Estimated contributions to pension plan in 2015			2.2
Defined Benefit Plan, Contributions by Employer	$ 0.5		$ 1

Employee Share-Based Incentiv57

Employee Share-Based Incentive Compensation Plans Employee Share-Based Compensation Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Employee Share-Based Incentive Compensation Plans
Expense recognized	$ 1.1	$ 1.6	$ 2	$ 3
Restricted Stock [Member]
Employee Share-Based Incentive Compensation Plans
Expense recognized	$ 0.5	$ 0.8	$ 1.1	$ 1.6
Long Term Incentive Plan | Restricted Stock [Member]
Employee Share-Based Incentive Compensation Plans
Vesting period			3 years

Employee Share-Based Incentiv58

Employee Share-Based Incentive Compensation Plans (Performance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Expense amortized
Expense recognized	$ 1.1	$ 1.6	$ 2	$ 3
Long Term Incentive Plan | Performance shares
Activity in plan
Beginning of period (in shares)	462,147	512,938	517,470	493,421
Payments and deferrals (in shares)	0	0	(181,290)	(142,138)
New awards (in shares)	0	0	154,887	165,800
Forfeitures and net change in assumed forfeitures (in shares)	0	0	(28,920)	(4,145)
End of period (in shares)	462,147	512,938	462,147	512,938
Expense amortized
Accrued expense at beginning of period	$ 2.1	$ 3.6	$ 3.4	$ 4
Payments and deferrals	0	0	(1.5)	(1)
Forfeitures and net change in assumed forfeitures	0	0	0	0
Expense recognized	0.3	0.8	0.5	1.4
Accrued expense at end of period	$ 2.4	$ 4.4	$ 2.4	$ 4.4
Additional disclosures
Target OB Performance Shares outstanding	462,147		462,147
Assumed forfeitures (in shares)	(11,850)		(11,850)
Assumed forfeitures	$ 0		$ 0
Percentage of shares required to vest	100.00%		100.00%
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 2.8		$ 2.8
Long Term Incentive Plan | Performance shares | Performance cycle 2011 - 2013
Additional disclosures
Growth target percentage				37.10%
Long Term Incentive Plan | Performance shares | Performance cycle 2012 - 2014
Expense amortized
Accrued expense at end of period	$ 1.5		$ 1.5
Additional disclosures
Growth target percentage			45.70%
Target OB Performance Shares outstanding	167,300		167,300
Long Term Incentive Plan | Performance shares | Performance cycle 2013 - 2015
Expense amortized
Accrued expense at end of period	$ 0.6		$ 0.6
Additional disclosures
Target OB Performance Shares outstanding	151,810		151,810
Long Term Incentive Plan | Performance shares | Performance cycle 2014 - 2016
Expense amortized
Accrued expense at end of period	$ 0.3		$ 0.3
Additional disclosures
Target OB Performance Shares outstanding	154,887		154,887
Long Term Incentive Plan | Performance shares | Performance cycle 2013 - 2017
Expense amortized
Accrued expense at end of period	$ 2.4		$ 2.4
Additional disclosures
Target OB Performance Shares outstanding	473,997		473,997

Employee Share-Based Incentiv59

Employee Share-Based Incentive Compensation Plans (Restricted) (Details) - USD ($) $ in Millions	Feb. 24, 2015	May. 25, 2011	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Unamortized grant date fair value
Expense recognized			$ (1.1)	$ (1.6)	$ (2)	$ (3)
Restricted Stock [Member]
Employee Share-Based Incentive Compensation Plans
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms					1 year 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested					$ 4.3
Activity in plan
Beginning of period (in shares)			390,950	612,500	612,500	915,000
New awards (in shares)			0	0	75,950	0
Forfeitures (in shares)			0	0	(1,500)	(2,500)
Vested (in shares)			0	0	(296,000)	(300,000)
End of period (in shares)			390,950	612,500	390,950	612,500
Unamortized grant date fair value
Unamortized grant date fair value, beginning of period			$ 4	$ 5.7	$ 3.5	$ 6.5
Issued	$ 1.1		0	0	1.1	0
Expense recognized			(0.5)	(0.8)	(1.1)	(1.6)
Unamortized grant date fair value, end of period			$ 3.5	$ 4.9	$ 3.5	$ 4.9
Awards Issued in 2015 [Member] | Restricted Stock [Member]
Activity in plan
New awards (in shares)	75,950
Awards Issued in 2015 [Member] | Restricted Stock Units (RSUs) [Member]
Activity in plan
New awards (in shares)	207,848		6,582
End of period (in shares)			209,369		209,369
Unamortized grant date fair value
Expense recognized			$ (0.3)		$ (0.4)
Awards Issued in 2012 [Member] | Restricted Stock [Member]
Activity in plan
Vested (in shares)					(138,500)	(142,500)
Chief Executive Officer [Member] | Awards Issued in 2011 [Member] | Restricted Stock [Member]
Activity in plan
New awards (in shares)		630,000
Vested (in shares)					(157,500)	(157,500)
End of period (in shares)			315,000		315,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Contingency [Line Items]
Effective tax rate	(31.00%)	18.60%	8.10%	15.00%
Federal statutory rate	35.00%	35.00%	35.00%	35.00%
Income tax benefit	$ (0.9)	$ 5.9	$ 2.5	$ 13
Foreign Tax Authority
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	1.80%	1.10%	1.40%	1.10%
Tax Year 2005 to 2006 [Member] | Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Income tax benefit			$ 5
Tax Assessment Year 2007 to 2009 | Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Income Tax Examination, Increase (Decrease) in Liability from Prior Year	$ 74.8		74.8
Income Tax Examination, Increase (Decrease) in Liability from Prior Year, Related to Items with Unallowable Deductions	$ 60.2		$ 60.2

Fair Value of Financial Instr61

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Fair Value of Financial Instruments
Debt	$ 274.7	$ 274.7
Fair Value | OBH (issuer)
Fair Value of Financial Instruments
Long-term Debt, Fair Value	280.4	286
Carrying Value | OBH (issuer)
Fair Value of Financial Instruments
Debt	$ 274.7	$ 274.7

Legal Contingencies (Details)

Legal Contingencies (Details) $ in Millions	6 Months Ended
	Jun. 30, 2015USD ($)
Pending Litigation | Tribune Company Litigation
Loss Contingencies [Line Items]
Proceeds common stock, litigation settlement	$ 32

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net income from continuing operations attributable to OneBeacon's common shareholders	$ 3.3	$ 25.3	$ 27.5	$ 72.6
Allocation of loss (income) for participating unvested restricted common shares	0	(0.1)	(0.1)	(0.5)
Dividends paid on participating restricted common shares	0	(0.1)	(0.1)	(0.2)
Total allocation to restricted common shares	0	(0.2)	(0.2)	(0.7)
Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts	3.3	25.1	27.3	71.9
Undistributed Earnings, Basic [Abstract]
Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts	3.3	25.1	27.3	71.9
Dividends paid, net of restricted common share amounts	(20)	(19.9)	(39.9)	(39.8)
Total undistributed (over-distributed) net earnings, net of restricted common share amounts	$ (16.7)	$ 5.2	$ (12.6)	$ 32.1
Weighted Average Number of Shares Outstanding, Basic [Abstract]
Total weighted average common shares outstanding	95.3	95.3	95.3	95.3
Weighted average unvested restricted common shares	(0.4)	(0.6)	(0.5)	(0.7)
Basic and diluted earnings (loss) per share denominator	94.9	94.7	94.8	94.6
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income from continuing operations attributable to OneBeacon's common shareholders	$ 0.03	$ 0.26	$ 0.29	$ 0.76
Dividends declared and paid	(0.21)	(0.21)	(0.42)	(0.42)
Undistributed (over-distributed) earnings	(0.18)	0.05	(0.13)	0.34
Total OneBeacon common shareholders' equity
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Dividends declared and paid	$ (0.21)	$ (0.21)	$ (0.42)	$ (0.42)

Common Shareholders' Equity (De

Common Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Aug. 22, 2007
Equity, Class of Treasury Stock [Line Items]
Dividends			$ 41.1	$ 41
Dividends, per share, cash paid	$ 0.21	$ 0.21	$ 0.42	$ 0.42
Pre-tax changes to accumulated other comprehensive income			$ 0.6	$ 0.2
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax			0.2	0.1
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	$ (0.2)	$ (0.1)	(0.4)	(0.1)
Class A common
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount					$ 200
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 87.7		87.7
Total OneBeacon common shareholders' equity
Equity, Class of Treasury Stock [Line Items]
Dividends			$ 40	$ 40
Dividends, per share, cash paid	$ 0.21	$ 0.21	$ 0.42	$ 0.42
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax			$ (0.4)	$ (0.1)
Accum. other comprehensive income (loss)
Equity, Class of Treasury Stock [Line Items]
Dividends			0	0
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax			$ (0.4)	$ (0.1)
Share Repurchase Program [Domain] | Class A common
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Shares				0
Restricted Stock [Member] | Class A common
Equity, Class of Treasury Stock [Line Items]
Shares Paid for Tax Withholding for Share Based Compensation			112,051	106,366

Discontinued Operations (Summar

Discontinued Operations (Summary of the Results of Operations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 23, 2014
Discontinued Operations
Reinsurance recoverables	$ 168		$ 168		$ 173.8
Net written premiums	321.2	$ 295.9	608.3	$ 607
Revenues
Earned premiums	319.3	290.9	605.9	567.4
Total revenues	314.2	326	622.4	632.8
Expenses
Loss and loss adjustment expenses	194.5	186.1	360.4	335.5
Other underwriting expenses	56.4	49.6	107.4	96.3
Total expenses	311.3	294.3	591.4	546.3
Income tax benefit	0.9	(5.9)	$ (2.5)	(13)
Document Fiscal Year Focus			2,015
(Loss) gain from sale of discontinued operations, net of tax	0.3	(0.5)	$ 0.3	(0.5)
Loss from discontinued operations, net of tax	(0.2)	(0.1)	(0.3)	(0.6)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Description	0	8.4	(1.8)	7
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	153.2	142.4	337.3	276.2
Segment, Discontinued Operations
Discontinued Operations
Net written premiums	0	(0.1)	0	(0.2)
Revenues
Earned premiums	0	(0.1)	0	(0.2)
Other revenues (expenses)	(0.2)	0	(0.3)	0
Total revenues	(0.2)	(0.1)	(0.3)	(0.2)
Expenses
Loss and loss adjustment expenses	0	(0.7)	0	(0.7)
Other underwriting expenses	0	0.7	0	1.4
Total expenses	0	0	0	0.7
Pre-tax loss	(0.2)	(0.1)	(0.3)	(0.9)
Income tax benefit	0	0	0	0.3
Income (loss) from discontinued operations, net of tax	(0.2)	(0.1)	(0.3)	(0.6)
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax		(0.8)
(Loss) gain from sale of discontinued operations, net of tax		(0.5)	0.3	(0.5)
Loss from discontinued operations, net of tax	$ 0.1	(0.6)	$ 0	(1.1)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Description		7.4
Causes Of Increase Decrease In Liability For Unpaid Claims And Claims Adjustment Expense Amount, net of tax		4.8
Runoff [Member]
Discontinued Operations
Quota Share Reinsurance Agreement Percentage	100.00%		100.00%
Expenses
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	$ 0	17.7		28.8
Investing, Financing and Corporate
Discontinued Operations
Reinsurance recoverables	18.6		$ 18.6		23.8
Revenues
Earned premiums	0	0	0	0
Expenses
Loss and loss adjustment expenses	0	0	0	0
Other underwriting expenses	0	0	0	$ 0
Surplus notes
Expenses
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax		8.2
(Loss) gain from sale of discontinued operations, net of tax		$ 5.3
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	66.3		$ 66.3		$ 65.1
Runoff [Member]
Expenses
(Loss) gain from sale of discontinued operations, net of tax	$ 0.3
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations						$ 101
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value						$ 64.9

Discontinued Operations (Loss p

Discontinued Operations (Loss per Share Related to Discontinued Operations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Discontinued Operations
Document Fiscal Year Focus			2,015
(Loss) income attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders	$ (0.2)	$ (0.1)	$ (0.3)	$ (0.6)
Allocation of loss for participating unvested restricted common shares	$ 0	$ (0.1)	$ (0.1)	$ (0.5)
Loss per share denominator—basic and diluted (in millions):
Total weighted average common shares outstanding	95.3	95.3	95.3	95.3
Weighted average unvested restricted common shares	(0.4)	(0.6)	(0.5)	(0.7)
Basic and diluted earnings (loss) per share denominator	94.9	94.7	94.8	94.6
Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars):
Loss from discontinued operations attributable to OneBeacon's common shareholders per share	$ 0.03	$ 0.26	$ 0.29	$ 0.75
Segment, Discontinued Operations
(Loss) income attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net (loss) income from discontinued operations attributable to OneBeacon's common shareholders	$ 0.1	$ (0.6)	$ 0	$ (1.1)
Allocation of loss for participating unvested restricted common shares	0	0	0	0
Income (loss) from discontinued operations, net of tax	$ 0.1	$ (0.6)	$ 0	$ (1.1)
Loss per share denominator—basic and diluted (in millions):
Total weighted average common shares outstanding	95.3	95.3	95.3	95.3
Weighted average unvested restricted common shares	(0.4)	(0.6)	(0.5)	(0.7)
Basic and diluted earnings (loss) per share denominator	94.9	94.7	94.8	94.6
Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars):
Loss from discontinued operations attributable to OneBeacon's common shareholders per share	$ 0	$ 0	$ 0	$ (0.01)

Consolidating Financial Infor67

Consolidating Financial Information (Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Fixed maturity investments, at fair value	$ 1,941.1		$ 1,799.8
Short-term investments, at amortized cost (which approximates fair value)	157.9		202.2
Common equity securities, at fair value	304.3		320
Convertible fixed maturity investments, at fair value	0		5
Other investments	174.9		198.8
Total investments	2,578.2		2,525.8
Cash	106.2		87	$ 130.1		$ 168.1
Reinsurance recoverables	168		173.8
Premiums receivable	292.2		241.5
Funds Held under Reinsurance Agreements, Asset	49.3		37.1
Deferred acquisition costs	111.8		103.2
Net deferred tax asset	136.5		131.8
Investment income accrued	10.3		10
Accounts receivable on unsettled investment sales	1.1		7.2
Investments in subsidiaries	0		0
Other assets	208.7		202.7
Assets held for sale	0		58.1
Total assets	3,662.3		3,578.2
Liabilities
Unpaid loss and loss adjustment expense reserves	1,350.8	$ 1,304	1,342.2	1,125.4	$ 1,069.8	1,054.3
Unearned premiums	616.2		588.3
Funds held under reinsurance agreements, liability	102.6		81
Debt	274.7		274.7
Accounts payable on unsettled investment purchases	20.1		0.5
Other liabilities	261.2		242.2
Total liabilities	2,625.6		2,528.9
Equity [Abstract]
OneBeacon's common shareholders' equity	1,033.2		1,045.8
Total noncontrolling interests	3.5		3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,036.7		1,049.3	1,138.3		1,106.8
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	3,662.3		3,578.2
The Company (guarantor)
Investments, Debt and Equity Securities [Abstract]
Fixed maturity investments, at fair value	0		0
Short-term investments, at amortized cost (which approximates fair value)	1.1		18.4
Common equity securities, at fair value	0		0
Convertible fixed maturity investments, at fair value	0		0
Other investments	0		0
Total investments	1.1		18.4
Cash	0		0	0		0
Reinsurance recoverables	0		0
Premiums receivable	0		0
Funds Held under Reinsurance Agreements, Asset	0		0
Deferred acquisition costs	0		0
Net deferred tax asset	0		0
Investment income accrued	0		0
Accounts receivable on unsettled investment sales	0		0
Investments in subsidiaries	1,032.9		1,027.4
Other assets	0.6		0.3
Assets held for sale			0
Total assets	1,034.6		1,046.1
Liabilities
Unpaid loss and loss adjustment expense reserves	0		0
Unearned premiums	0		0
Funds held under reinsurance agreements, liability	0		0
Debt	0		0
Accounts payable on unsettled investment purchases	0		0
Other liabilities	1.4		0.3
Total liabilities	1.4		0.3
Equity [Abstract]
OneBeacon's common shareholders' equity	1,033.2		1,045.8
Total noncontrolling interests	0		0
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,033.2		1,045.8
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	1,034.6		1,046.1
Non-guarantor subsidiaries
Investments, Debt and Equity Securities [Abstract]
Fixed maturity investments, at fair value	1,941.1		1,799.8
Short-term investments, at amortized cost (which approximates fair value)	155.1		182.5
Common equity securities, at fair value	304.3		320
Convertible fixed maturity investments, at fair value	0		5
Other investments	174.9		198.8
Total investments	2,575.4		2,506.1
Cash	106.1		87	130.1		166.6
Reinsurance recoverables	168		173.8
Premiums receivable	292.2		241.5
Funds Held under Reinsurance Agreements, Asset	49.3		37.1
Deferred acquisition costs	111.8		103.2
Net deferred tax asset	136.5		131.7
Investment income accrued	10.3		10
Accounts receivable on unsettled investment sales	1.1		7.2
Investments in subsidiaries	0		0
Other assets	204.4		198
Assets held for sale			58.1
Total assets	3,655.1		3,553.7
Liabilities
Unpaid loss and loss adjustment expense reserves	1,350.8		1,342.2
Unearned premiums	616.2		588.3
Funds held under reinsurance agreements, liability	102.6		81
Debt	0		0
Accounts payable on unsettled investment purchases	20.1		0.5
Other liabilities	253.8		234.8
Total liabilities	2,343.5		2,246.8
Equity [Abstract]
OneBeacon's common shareholders' equity	1,308.1		1,303.4
Total noncontrolling interests	3.5		3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,311.6		1,306.9
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	3,655.1		3,553.7
OBH (issuer)
Investments, Debt and Equity Securities [Abstract]
Fixed maturity investments, at fair value	0		0
Short-term investments, at amortized cost (which approximates fair value)	1.7		1.3
Common equity securities, at fair value	0		0
Convertible fixed maturity investments, at fair value	0		0
Other investments	0		0
Total investments	1.7		1.3
Cash	0.1		0	0		1.5
Reinsurance recoverables	0		0
Premiums receivable	0		0
Funds Held under Reinsurance Agreements, Asset	0		0
Deferred acquisition costs	0		0
Net deferred tax asset	0		0
Investment income accrued	0		0
Accounts receivable on unsettled investment sales	0		0
Investments in subsidiaries	1,020.2		1,053
Other assets	3.6		4.4
Assets held for sale			0
Total assets	1,025.6		1,058.7
Liabilities
Unpaid loss and loss adjustment expense reserves	0		0
Unearned premiums	0		0
Funds held under reinsurance agreements, liability	0		0
Debt	274.7		274.7
Accounts payable on unsettled investment purchases	0		0
Other liabilities	6		7.1
Total liabilities	280.7		281.8
Equity [Abstract]
OneBeacon's common shareholders' equity	744.9		776.9
Total noncontrolling interests	0		0
Total OneBeacon's common shareholders' equity and noncontrolling interests	744.9		776.9
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	1,025.6		1,058.7
Consolidating adjustments
Investments, Debt and Equity Securities [Abstract]
Fixed maturity investments, at fair value	0		0
Short-term investments, at amortized cost (which approximates fair value)	0		0
Common equity securities, at fair value	0		0
Convertible fixed maturity investments, at fair value	0		0
Other investments	0		0
Total investments	0		0
Cash	0		0	$ 0		$ 0
Reinsurance recoverables	0		0
Premiums receivable	0		0
Funds Held under Reinsurance Agreements, Asset	0		$ 0
Deferred acquisition costs	0
Net deferred tax asset	0		$ 0.1
Investment income accrued	0		0
Accounts receivable on unsettled investment sales	0		0
Investments in subsidiaries	(2,053.1)		(2,080.4)
Other assets	0.1		0
Assets held for sale			0
Total assets	(2,053)		(2,080.3)
Liabilities
Unpaid loss and loss adjustment expense reserves	0		0
Unearned premiums	0		0
Funds held under reinsurance agreements, liability	0		0
Debt	0		0
Accounts payable on unsettled investment purchases	0		0
Other liabilities	0		0
Total liabilities	0		0
Equity [Abstract]
OneBeacon's common shareholders' equity	(2,053)		(2,080.3)
Total noncontrolling interests	0		0
Total OneBeacon's common shareholders' equity and noncontrolling interests	(2,053)		(2,080.3)
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	$ (2,053)		$ (2,080.3)

Consolidating Financial Infor68

Consolidating Financial Information (Consolidating Statement of Operations and Comprehensive (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues
Earned premiums	$ 319.3	$ 290.9	$ 605.9	$ 567.4
Net investment income (expense)	10.1	12.2	20.6	22.6
Net realized and change in unrealized investment gains	(14)	21.9	0.2	40.8
Net other revenues (expenses)	(1.2)	1	(4.3)	2
Total revenues	314.2	326	622.4	632.8
Expenses
Loss and loss adjustment expenses	194.5	186.1	360.4	335.5
Policy acquisition expenses	56.4	49.6	107.4	96.3
Other underwriting expenses	52.9	51.7	108.8	101.1
General and administrative expenses	4.2	3.6	8.3	6.9
Interest expense	3.3	3.3	6.5	6.5
Total expenses	311.3	294.3	591.4	546.3
Pre-tax income from continuing operations	2.9	31.7	31	86.5
Income tax benefit (expense)	0.9	(5.9)	(2.5)	(13)
(Loss) gain from sale of discontinued operations, net of tax	0.3	(0.5)	0.3	(0.5)
Net income from continuing operations	3.8	25.8	28.5	73.5
Net (income) loss from discontinued operations	0.2	0.1	0.3	0.6
(Loss) income before equity in (losses) earnings of unconsolidated affiliates	3.9	25.2	28.5	72.4
Equity in earnings of subsidiaries, net of tax	0	0	0	0
Net income, including noncontrolling interests	3.9	25.2	28.5	72.4
Less: Net income attributable to noncontrolling interests	(0.5)	(0.5)	(1)	(0.9)
Net income attributable to OneBeacon's common shareholders	3.4	24.7	27.5	71.5
Net change in benefit plan assets and obligations, net of tax	0.2	0.1	0.4	0.1
Comprehensive income attributable to OneBeacon's common shareholders	3.6	24.8	27.9	71.6
The Company (guarantor)
Revenues
Earned premiums	0	0	0	0
Net investment income (expense)	0	0	0	0
Net realized and change in unrealized investment gains	0	0	0	0
Net other revenues (expenses)	0	0	0	0
Total revenues	0	0	0	0
Expenses
Loss and loss adjustment expenses	0	0	0	0
Policy acquisition expenses	0	0	0	0
Other underwriting expenses	0	0	0	0
General and administrative expenses	1.3	1.9	2.6	3.5
Interest expense	0	0	0	0
Total expenses	1.3	1.9	2.6	3.5
Pre-tax income from continuing operations	(1.3)	(1.9)	(2.6)	(3.5)
Income tax benefit (expense)	0	0	0	0
(Loss) gain from sale of discontinued operations, net of tax	0	0	0	0
Net income from continuing operations	(1.3)	(1.9)	(2.6)	(3.5)
Net (income) loss from discontinued operations	0	0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates	(1.3)	(1.9)	(2.6)	(3.5)
Equity in earnings of subsidiaries, net of tax	4.7	26.6	30.1	75
Net income, including noncontrolling interests	3.4	24.7	27.5	71.5
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to OneBeacon's common shareholders	3.4	24.7	27.5	71.5
Net change in benefit plan assets and obligations, net of tax	0.2	0.1	0.4	0.1
Comprehensive income attributable to OneBeacon's common shareholders	3.6	24.8	27.9	71.6
Non-guarantor subsidiaries
Revenues
Earned premiums	319.3	290.9	605.9	567.4
Net investment income (expense)	10.1	12.4	20.6	23.1
Net realized and change in unrealized investment gains	(14)	22.7	0.2	42.1
Net other revenues (expenses)	(1.2)	1	(4.3)	2
Total revenues	314.2	327	622.4	634.6
Expenses
Loss and loss adjustment expenses	194.5	186.1	360.4	335.5
Policy acquisition expenses	56.4	49.6	107.4	96.3
Other underwriting expenses	52.9	51.7	108.8	101.1
General and administrative expenses	2.9	1.6	5.6	3.2
Interest expense	0	0	0	0
Total expenses	306.7	289	582.2	536.1
Pre-tax income from continuing operations	7.5	38	40.2	98.5
Income tax benefit (expense)	(0.1)	(7.8)	(4.9)	(16.7)
(Loss) gain from sale of discontinued operations, net of tax	0.3	(0.5)	0.3	(0.5)
Net income from continuing operations	7.4	30.2	35.3	81.8
Net (income) loss from discontinued operations	0.2	0.1	0.3	0.6
(Loss) income before equity in (losses) earnings of unconsolidated affiliates	7.5	29.6	35.3	80.7
Equity in earnings of subsidiaries, net of tax	0	0	0	0
Net income, including noncontrolling interests	7.5	29.6	35.3	80.7
Less: Net income attributable to noncontrolling interests	(0.5)	(0.5)	(1)	(0.9)
Net income attributable to OneBeacon's common shareholders	7	29.1	34.3	79.8
Net change in benefit plan assets and obligations, net of tax	0	0	0	0
Comprehensive income attributable to OneBeacon's common shareholders	7	29.1	34.3	79.8
OBH (issuer)
Revenues
Earned premiums	0	0	0	0
Net investment income (expense)	0	0.1	0	0.1
Net realized and change in unrealized investment gains	0	0	0	0
Net other revenues (expenses)	0	0	0	0
Total revenues	0	0.1	0	0.1
Expenses
Loss and loss adjustment expenses	0	0	0	0
Policy acquisition expenses	0	0	0	0
Other underwriting expenses	0	0	0	0
General and administrative expenses	0	0.1	0.1	0.2
Interest expense	3.3	3.6	6.5	7.1
Total expenses	3.3	3.7	6.6	7.3
Pre-tax income from continuing operations	(3.3)	(3.6)	(6.6)	(7.2)
Income tax benefit (expense)	1	1.6	2.4	3.2
(Loss) gain from sale of discontinued operations, net of tax	0	0	0	0
Net income from continuing operations	(2.3)	(2)	(4.2)	(4)
Net (income) loss from discontinued operations	0	0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates	(2.3)	(2)	(4.2)	(4)
Equity in earnings of subsidiaries, net of tax	0.3	11.8	12.9	52.9
Net income, including noncontrolling interests	(2)	9.8	8.7	48.9
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to OneBeacon's common shareholders	(2)	9.8	8.7	48.9
Net change in benefit plan assets and obligations, net of tax	0.2	0.1	0.4	0.1
Comprehensive income attributable to OneBeacon's common shareholders	(1.8)	9.9	9.1	49
Consolidating adjustments
Revenues
Earned premiums	0	0	0	0
Net investment income (expense)	0	(0.3)	0	(0.6)
Net realized and change in unrealized investment gains	0	(0.8)	0	(1.3)
Net other revenues (expenses)	0	0	0	0
Total revenues	0	(1.1)	0	(1.9)
Expenses
Loss and loss adjustment expenses	0	0	0	0
Policy acquisition expenses	0	0	0	0
Other underwriting expenses	0	0	0	0
General and administrative expenses	0	0	0	0
Interest expense	0	(0.3)	0	(0.6)
Total expenses	0	(0.3)	0	(0.6)
Pre-tax income from continuing operations	0	(0.8)	0	(1.3)
Income tax benefit (expense)	0	0.3	0	0.5
(Loss) gain from sale of discontinued operations, net of tax	0	0	0	0
Net income from continuing operations	0	(0.5)	0	(0.8)
Net (income) loss from discontinued operations	0	0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates	0	(0.5)	0	(0.8)
Equity in earnings of subsidiaries, net of tax	(5)	(38.4)	(43)	(127.9)
Net income, including noncontrolling interests	(5)	(38.9)	(43)	(128.7)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net income attributable to OneBeacon's common shareholders	(5)	(38.9)	(43)	(128.7)
Net change in benefit plan assets and obligations, net of tax	(0.2)	(0.1)	(0.4)	(0.1)
Comprehensive income attributable to OneBeacon's common shareholders	$ (5.2)	$ (39)	$ (43.4)	$ (128.8)

Consolidating Financial Infor69

Consolidating Financial Information (Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]
Net increase (decrease) in cash during period			$ 19.2	$ (38)
Cash balance at beginning of period			87	168.1
Cash balance at end of period	$ 106.2	$ 130.1	106.2	130.1
Net income (loss) including noncontrolling interests	3.9	25.2	28.5	72.4
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Undistributed earnings from subsidiaries	0	0	0	0
Net loss from discontinued operations	0.2	0.1	0.3	0.6
Net loss from sale of discontinued operations	0.3	(0.5)	0.3	(0.5)
Net realized and change in unrealized investment gains	14	(21.9)	(0.2)	(40.8)
Net realized gain on sale of business			3.7	0
Deferred income tax expense			(3.8)	12.6
Dividends received from subsidiaries			0	0
Net cash provided from operations—continuing operations			42.8	55.5
Net cash used for operations—discontinued operations			(0.3)	(33.9)
Net cash provided from (used for) operations			42.5	21.6
Other operating items:
Net change in loss and LAE reserves			8.6	71.1
Net change in unearned premiums			27.9	47
Net change in premiums receivable			(50.7)	(47.8)
Net change in reinsurance recoverable on paid and unpaid losses			5.8	(5.4)
Net change in funds held under reinsurance contracts			(12.2)	(30)
Net change in funds held under insurance contracts			21.6	(0.3)
Net change in other assets and liabilities			13.6	(24.4)
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments			44.3	80.1
Maturities of fixed maturity investments			115.8	185.6
Sales of fixed maturity investments			450	850.9
Sales of common equity securities			268.1	47.6
Sales of convertible fixed maturity investments			6.1	12.2
Distributions and redemptions of other investments			22.1	3.2
Purchases of fixed maturity investments			(714.1)	(1,101.9)
Purchases of common equity securities			(248.7)	(48.7)
Purchases of convertible fixed maturity investments			(0.8)	(8.4)
Contributions for other investments			(2.5)	(3.3)
Net change in unsettled investment purchases and sales			25.8	(31.8)
Proceeds from Sale of Property, Plant, and Equipment			56.8	0
Net acquisitions of property and equipment			(1.8)	(0.7)
Net cash provided from investing activities			21.1	(15.2)
Cash flows from financing activities:
Cash dividends paid to common shareholders			(40)	(40)
Cash dividends paid to parent			0	0
Return of capital to OneBeacon U.S. Enterprises Holdings, Inc.			(1.6)	(1.8)
Payments on capital lease obligation			(2.8)	(2.6)
Net cash used for financing activities			(44.4)	(44.4)
The Company (guarantor)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]
Net increase (decrease) in cash during period			0	0
Cash balance at beginning of period			0	0
Cash balance at end of period	0	0	0	0
Net income (loss) including noncontrolling interests	3.4	24.7	27.5	71.5
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Undistributed earnings from subsidiaries	(4.7)	(26.6)	(30.1)	(75)
Net loss from discontinued operations	0	0	0	0
Net loss from sale of discontinued operations	0	0	0	0
Net realized and change in unrealized investment gains	0	0	0	0
Net realized gain on sale of business			0
Deferred income tax expense			0	0
Dividends received from subsidiaries			25	30
Net cash provided from operations—continuing operations			24.3	29.1
Net cash used for operations—discontinued operations			0	0
Net cash provided from (used for) operations			24.3	29.1
Other operating items:
Net change in loss and LAE reserves			0	0
Net change in unearned premiums			0	0
Net change in premiums receivable			0	0
Net change in reinsurance recoverable on paid and unpaid losses			0	0
Net change in funds held under reinsurance contracts			0	0
Net change in funds held under insurance contracts			0	0
Net change in other assets and liabilities			1.9	2.6
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments			17.3	12.7
Maturities of fixed maturity investments			0	0
Sales of fixed maturity investments			0	0
Sales of common equity securities			0	0
Sales of convertible fixed maturity investments			0	0
Distributions and redemptions of other investments			0	0
Purchases of fixed maturity investments			0	0
Purchases of common equity securities			0	0
Purchases of convertible fixed maturity investments			0	0
Contributions for other investments			0	0
Net change in unsettled investment purchases and sales			0	0
Proceeds from Sale of Property, Plant, and Equipment			0
Net acquisitions of property and equipment			0	0
Net cash provided from investing activities			17.3	12.7
Cash flows from financing activities:
Cash dividends paid to common shareholders			(40)	(40)
Cash dividends paid to parent			0	0
Return of capital to OneBeacon U.S. Enterprises Holdings, Inc.			(1.6)	(1.8)
Payments on capital lease obligation			0	0
Net cash used for financing activities			(41.6)	(41.8)
Non-guarantor subsidiaries
Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]
Net increase (decrease) in cash during period			19.1	(36.5)
Cash balance at beginning of period			87	166.6
Cash balance at end of period	106.1	130.1	106.1	130.1
Net income (loss) including noncontrolling interests	7.5	29.6	35.3	80.7
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Undistributed earnings from subsidiaries	0	0	0	0
Net loss from discontinued operations	0.2	0.1	0.3	0.6
Net loss from sale of discontinued operations	0.3	(0.5)	0.3	(0.5)
Net realized and change in unrealized investment gains	14	(22.7)	(0.2)	(42.1)
Net realized gain on sale of business			3.7
Deferred income tax expense			(3.8)	13
Dividends received from subsidiaries			39.9	0
Net cash provided from operations—continuing operations			88.5	62.9
Net cash used for operations—discontinued operations			(0.3)	(33.9)
Net cash provided from (used for) operations			88.2	29
Other operating items:
Net change in loss and LAE reserves			8.6	71.1
Net change in unearned premiums			27.9	47
Net change in premiums receivable			(50.7)	(47.8)
Net change in reinsurance recoverable on paid and unpaid losses			5.8	(5.4)
Net change in funds held under reinsurance contracts			(12.2)	(30)
Net change in funds held under insurance contracts			21.6	(0.3)
Net change in other assets and liabilities			12.6	(24.4)
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments			26.6	65.4
Maturities of fixed maturity investments			115.8	185.6
Sales of fixed maturity investments			361	844.2
Sales of common equity securities			268.1	47.6
Sales of convertible fixed maturity investments			6.1	12.2
Distributions and redemptions of other investments			22.1	3.2
Purchases of fixed maturity investments			(624.9)	(1,093.2)
Purchases of common equity securities			(248.7)	(48.7)
Purchases of convertible fixed maturity investments			(0.8)	(8.4)
Contributions for other investments			(2.5)	(3.3)
Net change in unsettled investment purchases and sales			25.8	(31.8)
Proceeds from Sale of Property, Plant, and Equipment			56.8
Net acquisitions of property and equipment			(1.8)	(0.7)
Net cash provided from investing activities			3.6	(27.9)
Cash flows from financing activities:
Cash dividends paid to common shareholders			0	0
Cash dividends paid to parent			(69.9)	(35)
Return of capital to OneBeacon U.S. Enterprises Holdings, Inc.			0	0
Payments on capital lease obligation			(2.8)	(2.6)
Net cash used for financing activities			(72.7)	(37.6)
OBH (issuer)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]
Net increase (decrease) in cash during period			0.1	(1.5)
Cash balance at beginning of period			0	1.5
Cash balance at end of period	0.1	0	0.1	0
Net income (loss) including noncontrolling interests	(2)	9.8	8.7	48.9
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Undistributed earnings from subsidiaries	(0.3)	(11.8)	(12.9)	(52.9)
Net loss from discontinued operations	0	0	0	0
Net loss from sale of discontinued operations	0	0	0	0
Net realized and change in unrealized investment gains	0	0	0	0
Net realized gain on sale of business			0
Deferred income tax expense			0	0
Dividends received from subsidiaries			44.9	5
Net cash provided from operations—continuing operations			39.8	(1.5)
Net cash used for operations—discontinued operations			0	0
Net cash provided from (used for) operations			39.8	(1.5)
Other operating items:
Net change in loss and LAE reserves			0	0
Net change in unearned premiums			0	0
Net change in premiums receivable			0	0
Net change in reinsurance recoverable on paid and unpaid losses			0	0
Net change in funds held under reinsurance contracts			0	0
Net change in funds held under insurance contracts			0	0
Net change in other assets and liabilities			(0.9)	(2.5)
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments			0.4	2
Maturities of fixed maturity investments			0	0
Sales of fixed maturity investments			29.7	6.7
Sales of common equity securities			0	0
Sales of convertible fixed maturity investments			0	0
Distributions and redemptions of other investments			0	0
Purchases of fixed maturity investments			(29.9)	(8.7)
Purchases of common equity securities			0	0
Purchases of convertible fixed maturity investments			0	0
Contributions for other investments			0	0
Net change in unsettled investment purchases and sales			0	0
Proceeds from Sale of Property, Plant, and Equipment			0
Net acquisitions of property and equipment			0	0
Net cash provided from investing activities			0.2	0
Cash flows from financing activities:
Cash dividends paid to common shareholders			0	0
Cash dividends paid to parent			(39.9)	0
Return of capital to OneBeacon U.S. Enterprises Holdings, Inc.			0	0
Payments on capital lease obligation			0	0
Net cash used for financing activities			(39.9)	0
Consolidating adjustments
Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]
Net increase (decrease) in cash during period			0	0
Cash balance at beginning of period			0	0
Cash balance at end of period	0	0	0	0
Net income (loss) including noncontrolling interests	(5)	(38.9)	(43)	(128.7)
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Undistributed earnings from subsidiaries	5	38.4	43	127.9
Net loss from discontinued operations	0	0	0	0
Net loss from sale of discontinued operations	0	0	0	0
Net realized and change in unrealized investment gains	$ 0	$ 0.8	0	1.3
Net realized gain on sale of business			0
Deferred income tax expense			0	(0.4)
Dividends received from subsidiaries			(109.8)	(35)
Net cash provided from operations—continuing operations			(109.8)	(35)
Net cash used for operations—discontinued operations			0	0
Net cash provided from (used for) operations			(109.8)	(35)
Other operating items:
Net change in loss and LAE reserves			0	0
Net change in unearned premiums			0	0
Net change in premiums receivable			0	0
Net change in reinsurance recoverable on paid and unpaid losses			0	0
Net change in funds held under reinsurance contracts			0	0
Net change in funds held under insurance contracts			0	0
Net change in other assets and liabilities			0	(0.1)
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments			0	0
Maturities of fixed maturity investments			0	0
Sales of fixed maturity investments			59.3	0
Sales of common equity securities			0	0
Sales of convertible fixed maturity investments			0	0
Distributions and redemptions of other investments			0	0
Purchases of fixed maturity investments			(59.3)	0
Purchases of common equity securities			0	0
Purchases of convertible fixed maturity investments			0	0
Contributions for other investments			0	0
Net change in unsettled investment purchases and sales			0	0
Proceeds from Sale of Property, Plant, and Equipment			0
Net acquisitions of property and equipment			0	0
Net cash provided from investing activities			0	0
Cash flows from financing activities:
Cash dividends paid to common shareholders			0	0
Cash dividends paid to parent			109.8	35
Return of capital to OneBeacon U.S. Enterprises Holdings, Inc.			0	0
Payments on capital lease obligation			0	0
Net cash used for financing activities			$ 109.8	$ 35

Subsequent Events Subsequent 70

Subsequent Events Subsequent Events (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Subsequent Event [Line Items]
Net written premiums	$ 321.2	$ 295.9	$ 608.3	$ 607
Underwriting Income (Loss)	15.5	3.5	29.3	34.5
Other underwriting expenses	52.9	$ 51.7	108.8	$ 101.1
Crop [Member]
Subsequent Event [Line Items]
Disposal Group, Including Discontinued Operation, Consideration	$ 3		$ 3
Quota Share Reinsurance Agreement Percentage	100.00%		100.00%
Net written premiums			$ 26.6		$ 35.1
Underwriting Income (Loss)			1.3		3.5
Other underwriting expenses			$ 1.5		$ 1