OneBeacon Insurance 10-K 26 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 24, 2016	Jun. 30, 2015
Entity Registrant Name	OneBeacon Insurance Group, Ltd.
Entity Central Index Key	1,369,817
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 329,495,721
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Class A common
Entity Common Stock, Shares Outstanding		22,589,822
Class B common
Entity Common Stock, Shares Outstanding		71,754,738

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fixed maturity investments, at fair value
Fixed maturity investments, at fair value	$ 2,080.5	$ 1,799.8
Short-term investments, at amortized cost (which approximates fair value)	69.2	202.2
Common equity securities, at fair value	298.7	320
Other investments	143	203.8
Total investment securities	2,591.4	2,525.8
Cash	95.2	87
Reinsurance recoverables	193.5	173.8
Premiums receivable	219	241.5
Funds held under reinsurance contracts	0	37.1
Deferred acquisition costs	100.7	103.2
Ceded unearned premiums	29.5	17.9
Net deferred tax asset	140.2	131.8
Investment income accrued	10.1	10
Accounts receivable on unsettled investment sales	30.5	7.2
Other assets	194.4	184.8
Assets held for sale	0	58.1
Total assets	3,604.5	3,578.2
Liabilities
Unpaid loss and loss adjustment expense reserves	1,389.8	1,342.2
Unearned premiums	560.3	588.3
Funds held under insurance contracts	137.7	81
Debt	274.8	274.7
Other liabilities	237.4	242.7
Total liabilities	2,600	2,528.9
OneBeacon's common shareholders' equity
Preferred Stock, Value, Outstanding	0	0
Common shares and paid-in surplus (Class A: par value $0.01; 200,000,000 authorized shares; 23,334,502 and 23,541,649 issued and outstanding)(Class B: par value $0.01; 200,000,000 authorized shares; 71,754,738 issued and outstanding for both periods)	1,022	1,023.7
Retained earnings (deficit)	(15.9)	27.3
Accumulated other comprehensive loss, after tax	(5.2)	(5.2)
Total OneBeacon's common shareholders' equity	1,000.9	1,045.8
Total noncontrolling interests, after tax	3.6	3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,004.5	1,049.3
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	$ 3,604.5	$ 3,578.2

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Common shares, outstanding shares (in shares)	95,089,240	95,296,387
Common shares, issued shares (in shares)	95,089,240	95,296,387
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Units, Authorized	80,000,000	80,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Class A common
Common shares, outstanding shares (in shares)	23,334,502	23,541,649
Common shares, issued shares (in shares)	23,334,502	23,541,649
Common shares, authorized shares (in shares)	200,000,000	200,000,000
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Class B common
Common shares, outstanding shares (in shares)	71,754,738	71,754,738
Common shares, issued shares (in shares)	71,754,738	71,754,738
Common shares, authorized shares (in shares)	200,000,000	200,000,000
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Earned premiums	$ 1,176.2	$ 1,177.1	$ 1,120.4
Net investment income	45.9	43.4	43
Net realized and change in unrealized investment gains	(35.1)	40.4	49.4
Net other revenues (expenses)	(0.6)	5.8	31.2
Revenues	1,186.4	1,266.7	1,244
Expenses
Loss and loss adjustment expenses	700.7	815.1	622.1
Policy acquisition expenses	213.8	203.3	208.9
Other underwriting expenses	218.2	179.2	204.8
General and administrative expenses	15.4	13.8	12
Interest expense	13	13	13
Total expenses	1,161.1	1,224.4	1,060.8
Pre-tax income (loss) from continuing operations	25.3	42.3	183.2
Income tax (expense) benefit	12.9	12.3	(36.5)
Net income from continuing operations	38.2	54.6	146.7
Loss from discontinued operations, net of tax	(0.5)	(1.8)	(46.6)
(Loss) gain from sale of discontinued operations, net of tax	0.3	(18.8)	46.6
Net income, including noncontrolling interests	38	34	146.7
Less: Net income attributable to noncontrolling interests	(1.2)	(1.1)	(1)
Net income attributable to OneBeacon's common shareholders	36.8	32.9	145.7
Net change in benefit plan assets and obligations, net of tax	0	(12)	20.6
Comprehensive income attributable to OneBeacon's common shareholders	$ 36.8	$ 20.9	$ 166.3
Earnings (loss) per share attributable to OneBeacon's common shareholders—basic and diluted
Net income (loss) from continuing operations per share	$ 0.38	$ 0.55	$ 1.52
Net Loss from discontinued operations, net of tax, per share	0	(0.02)	(0.49)
(Loss) gain from sale of discontinued operations, net of tax, per share	0	(0.19)	0.49
Net income (loss) attributable to OneBeacon's common shareholders per share	0.38	0.34	1.52
Dividends declared and paid per OneBeacon's common share (in dollars per share)	$ 0.84	$ 0.84	$ 0.84

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus	Retained earnings (deficit)	Accum. other comprehensive income (loss)	Total OneBeacon common shareholders' equity	Noncontrolling interests, after tax
Balances at Dec. 31, 2012	$ 1,017	$ 1,019.1	$ 8.9	$ (13.8)	$ 1,014.2	$ 2.8
Increase (Decrease) in Stockholders' Equity
Net income	146.7	0	145.7	0	145.7	1
Other comprehensive income item, after tax:
Net change in benefit plan assets and obligations, net of tax	20.6	0	0	20.6	20.6	0
Total comprehensive income	167.3	0	145.7	20.6	166.3	1
Amortization of restricted share and option awards	3.1	3.1	0	0	3.1	0
Issuance of common shares	0.4	0.3	0	0	0.3	0.1
Dividends	(81)	0	(80.2)	0	(80.2)	(0.8)
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	34	0	32.9	0	32.9	1.1
Other comprehensive income item, after tax:
Net change in benefit plan assets and obligations, net of tax	(12)	0	0	(12)	(12)	0
Total comprehensive income	22	0	32.9	(12)	20.9	1.1
Amortization of restricted share and option awards	3	3	0	0	3	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	(80.9)	0	(80)	0	(80)	(0.9)
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	38	0	36.8	0	36.8	1.2
Other comprehensive income item, after tax:
Net change in benefit plan assets and obligations, net of tax	0	0	0	0	0	0
Total comprehensive income	38	0	36.8	0	36.8	1.2
Amortization of restricted share and option awards	2	2	0	0	2	0
Issuance of common shares	0.1	0	0	0	0	0.1
Repurchase and retirement of common shares	(3.7)	(3.7)	0	0	(3.7)	0
Dividends	(81.2)	0	(80)	0	(80)	(1.2)
Balances at Dec. 31, 2015	$ 1,004.5	$ 1,022	$ (15.9)	$ (5.2)	$ 1,000.9	$ 3.6

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Cash Flows [Abstract]
Net income, including noncontrolling interests	$ 38	$ 34	$ 146.7
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net loss from discontinued operations	0.5	1.8	46.6
Net loss (gain) from sale of discontinued operations	(0.3)	18.8	(46.6)
Net realized and change in unrealized investment gains	35.1	(40.4)	(49.4)
Net realized loss (gain) on sale of business	3.7	0	(23)
Deferred income tax expense (benefit)	(5.8)	(19)	15
Other operating items:
Net change in loss and LAE reserves	47.6	287.9	54.3
Net change in unearned premiums	(28)	43.4	(28.9)
Net change in ceded unearned premiums	(11.6)	(3.6)	(2.8)
Net change in premiums receivable	22.5	(13.3)	(2.6)
Net change in reinsurance recoverable on paid and unpaid losses	(19.7)	(83.9)	20.7
Net change in funds held under reinsurance agreements	37.1	(35.3)	(1.8)
Net change in funds held under insurance contracts	56.7	17.7	57.4
Net change in other assets and liabilities	16.6	(56.1)	19.8
Net cash provided from operations—continuing operations	192.4	152	205.4
Net cash used for operations—discontinued operations	(0.5)	(54.5)	(76.7)
Net cash provided from operations	191.9	97.5	128.7
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments	133.1	(65.5)	72.2
Maturities of fixed maturity investments	262.4	396.4	245.2
Sales of fixed maturity investments	763.5	1,843.1	1,400
Sales of common equity securities	345.6	240.2	196.7
Return of capital and distributions of other investments	40.5	53.4	67.5
Purchases of fixed maturity investments	(1,333.5)	(2,206.8)	(1,697)
Purchases of common equity securities	(323.5)	(202.4)	(206.3)
Contributions for other investments	(4.2)	(81.9)	(22)
Proceeds from sale of business	0	0	31.3
Net change in unsettled investment purchases and sales	(23.8)	(15)	4.1
Proceeds from sale of property and equipment	56.8	0	0
Net acquisitions of property and equipment	(11.5)	(2.2)	(10.3)
Net cash (used for) provided from investing activities—continuing operations	(94.6)	(40.7)	81.4
Net cash provided from investing activities—discontinued operations	0	0	0
Net cash (used for) provided from investing activities	(94.6)	(40.7)	81.4
Cash flows from financing activities:
Repurchases of debt		0
Cash dividends paid to common shareholders	(80)	(80)	(80.2)
Repurchases and retirements of common stock	(3.7)	(1.8)	0
Payments on capital lease obligation	(5.4)	(5.3)	(5.7)
Net cash used for financing activities—continuing operations	(89.1)	(87.1)	(85.9)
Net cash used for financing activities—discontinued operations	0	0	0
Net cash used for financing activities	(89.1)	(87.1)	(85.9)
Cash transferred with sale of business	0	(50.8)	0
Net increase (decrease) before cash transferred with sale of business	8.2	(30.3)	124.2
Cash balance at beginning of period	87	168.1	43.9
Cash balance at end of period	95.2	87	168.1
Cash and Cash Equivalents, Period Increase (Decrease)	$ 8.2	$ (81.1)	$ 124.2

Nature of Operations and Summar

Nature of Operations and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 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 The accompanying 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"). 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 75.5% 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 605 North Highway 169, Plymouth, Minnesota 55441 and its registered office is located at Clarendon House, 2 Church Street, Hamilton HM 11, Bermuda. During 2015 the Company sold its building in Canton, Massachusetts, which is classified as held for sale in the December 31, 2014 balance sheet. 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 18—"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 and cash flows. 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. During the fourth quarter of 2015, the Company formed a new underwriting operating segment, Financial Institutions, which is included in Specialty Products. The Specialty Products segment also includes the Crop underwriting operating segment which was exited in 2015. The Specialty Industries segment is comprised of six active underwriting operating segments, representing an aggregation based on those that focus on solving the unique needs of a particular customer or industry group. During 2015, the Company further disaggregated its International Marine Underwriters ("IMU") underwriting operating segment into two separate underwriting operating segments, which are included in Specialty Industries: Ocean Marine and Inland Marine. 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. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. 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. Significant Accounting Policies Investment Securities OneBeacon adopted the fair value election, which allows companies to report financial assets and liabilities at fair value, on an individual basis. The election must be made at the inception of a transaction and may not be reversed. OneBeacon believes that reporting its investment results in this manner is consistent with its operating principle, of managing investments for total return. OneBeacon classifies its portfolio of fixed maturity investments and common equity securities 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 changes in unrealized investment gains on trading securities are reported, on a pre-tax basis, in revenues as net realized and change in unrealized investment gains. 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, and convertible fixed maturity investments. 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 2015, and a Prospector-managed hedge fund was redeemed. 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. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an "exit price"). 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 both December 31, 2015 and 2014 , approximately 92% and 90% , respectively, of the investment portfolio recorded at fair value was priced based upon quoted market prices or other 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 fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations, mortgage and asset-backed securities, foreign government obligations and preferred stocks. Investments valued using Level 2 inputs also include certain ETFs that track U.S. stock indices such as the S&P 500 but are traded on foreign exchanges and that management values using the fund's published NAV to account for the difference in market close times. 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 debt and equity securities, including asset-backed 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 perform 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 the 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. During the past year, 8 securities fell outside OneBeacon's expected results, thereby triggering the challenge with the pricing service. 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. OneBeacon's investments in debt securities, including asset-backed securities, are generally valued using matrix and other pricing models. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life. Private equity funds and hedge funds are carried at fair value based upon OneBeacon's proportionate interest in the underlying fund's net asset value, which is deemed to approximate fair value, as net asset value of the funds reflects the fair value of the funds' underlying investments. OneBeacon employs a number of procedures to assess the reasonableness of the fair value measurements, including obtaining and reviewing each fund's audited financial statements and discussing each fund's pricing with the fund's manager. Other investments also include surplus notes, the fair value of which are estimated using a discounted estimated cash flow method, as described in Note 5—"Investment Securities." In circumstances where the underlying investments are publicly traded, such as the investments made by hedge funds, the fair value of the underlying investments is determined using current market prices. In circumstances where the underlying investments are not publicly traded, such as the investments made by private equity funds, the private equity fund managers have considered the need for a liquidity discount on each of the underlying investments when determining the fund's net asset value. In circumstances where OneBeacon's portion of a fund's net asset value is deemed to differ from fair value due to illiquidity or other factors associated with OneBeacon's investment in the fund, including counterparty credit risk, the net asset value is adjusted accordingly. See Note 5—"Investment Securities." Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statements of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company's consolidated subsidiaries. Insurance Operations Premiums written are recognized as revenues and are earned ratably over the term of the related policy. Unearned premiums represent the portion of premiums written that are applicable to future insurance coverage provided by policies. Policy acquisition costs represent commissions, premium taxes, brokerage expenses and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period. Policy acquisition costs deferred were $237.3 million , $237.6 million and $210.3 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, all of which were included in policy acquisition expenses, with the exception of $21.3 million , $22.9 million and $23.4 million for each respective period that were deferred relating to other underwriting expenses. Policy acquisition costs amortized were $239.7 million , $227.6 million and $230.5 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, all of which were included in policy acquisition expenses, with the exception of $22.2 million , $23.0 million and $22.4 million for each respective period that were amortized relating to other underwriting expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. This limitation is referred to as a premium deficiency. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses ("LAE"), unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. There were no premium deficiencies recognized for any years presented. Loss and LAE are charged against income as incurred. Unpaid loss and LAE reserves are based on estimates (generally determined by claims adjusters, legal counsel and actuarial staff) of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management's best estimate of ultimate loss and LAE, net of reinsurance and estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any adjustments resulting therefrom are reflected in the current period. The process of estimating unpaid loss and LAE reserves involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. OneBeacon discounts certain of its long-term workers compensation loss and LAE reserves when such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual claim basis. OneBeacon discounts these reserves using the statutory rate ( 2.5% at December 31, 2015 and 2014 ). As of December 31, 2015 and 2014 , the discount on OneBeacon's workers compensation loss and LAE reserves amounted to $1.1 million and $1.0 million , respectively. OneBeacon's insurance subsidiaries enter into reinsurance contracts to protect their businesses from losses due to concentration of risk, to manage their operating leverage ratios and to limit losses arising from catastrophic events. The majority of such reinsurance contracts are executed through excess of loss treaties and catastrophe contracts under which the reinsurer indemnifies for a specified part or all of certain types of losses over stipulated amounts arising from any one occurrence or event. OneBeacon has also entered into quota share treaties with reinsurers under which all risks meeting prescribed criteria are covered on a pro rata basis. The amount of each risk ceded by OneBeacon is subject to maximum limits which vary by line of business and type of coverage. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policies. The collectibility of reinsurance recoverables is subject to the solvency of the reinsurers. OneBeacon is selective in regard to its reinsurers, principally placing reinsurance with those reinsurers with strong financial condition, reputation, industry ratings and underwriting ability. Management monitors the financial condition and ratings of its reinsurers on an ongoing basis. Reinsurance premiums, commissions, expense reimbursements and reserves related to reinsured business are accounted for on a basis consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums ceded to other companies are reported as a reduction of premiums written. Expense allowances received in connection with reinsurance ceded have been accounted for as a reduction of the related policy acquisition costs and are deferred and amortized accordingly. Funds Held Funds held under reinsurance contracts as of December 31, 2014, primarily represented amounts due to OneBeacon in connection with the Standard Reinsurance Agreement ("SRA") with the Federal Crop Insurance Corporation ("FCIC"), which is managed by an agency of the U.S. Department of Agriculture. The SRA governs the relationship, including the exchange of funds, between private insurance companies and the FCIC relating to MPCI crop insurance business, which the Company exited in 2015. Funds held under insurance contracts represents unrestricted collateral held by the Company primarily relating to the Surety business. Mandatory Shared Market Mechanisms As a condition of its licenses to do business in certain states, OneBeacon's insurance operations are required to participate in various mandatory shared market mechanisms commonly referred to as "residual" or "involuntary" markets. These markets generally consist of risks considered to be undesirable from a standard or routine underwriting perspective. Each state dictates the levels of insurance coverage that are mandatorily assigned to participating insurers within these markets. The total amount of such business an insurer must accept in a particular state is generally based on that insurer's market share of voluntary business written within that state. In certain cases, OneBeacon is obligated to write business from shared market mechanisms at a future date based on its historical market share of all voluntary policies written within that state. Involuntary business generated from mandatory shared market mechanisms may be treated as assumed reinsurance depending on the structure of the mechanism. OneBeacon's market assignments are typically required to be written in the current period, although, in certain cases OneBeacon is required to accept policy assignments at a future date. Anticipated losses associated with future market assignments are recognized when the amount of such anticipated losses is determined to be probable and can be reasonably estimated. Insurance Related Assessments Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. OneBeacon's insurance subsidiaries record guaranty fund assessments when such assessments are billed by the respective guaranty funds. In addition, OneBeacon will monitor other insurance company insolvencies and will accrue a liability when such losses are determined to be probable and the assessment amounts can be reasonably estimated. The actual amount of such assessments will depend upon the final outcome of rehabilitation proceedings and will be paid over several years. Capital Lease In December 2011, the Company entered into lease financing arrangements with US Bancorp Equipment Finance, Inc. ("US Bancorp") and Fifth Third Equipment Finance Company ("Fifth Third") whereby it sold furniture and equipment and capitalized software, respectively, at a cost equal to net book value. The Company then leased the fixed assets back from US Bancorp for a lease term of five years and leased the capitalized software back from Fifth Third for a lease term of four years . See Note 16—"Commitments and Contingencies." Deferred Software Costs OneBeacon capitalizes costs related to computer software developed for internal use during the application development stage of software development projects. These costs generally consist of certain external, payroll and payroll related costs. OneBeacon begins amortization of these costs once the project or the respective phase of the project is completed and ready for its intended use. Amortization is on a straight line basis and over the useful life which generally ranges from three to five years. During the year ended December 31, 2015 the Company recognized a $1.6 million pre-tax impairment of certain capitalized software associated with senior management restructuring. As of December 31, 2015 and 2014 , OneBeacon had unamortized deferred software costs of $12.7 million and $13.0 million , respectively. Federal and Foreign Income Taxes The majority of the Company's subsidiaries file consolidated tax returns in the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States. Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, and for other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. The deferred tax asset is recognized when it is more likely than not that it will be realized. Foreign Currency Exchange The U.S. dollar is the functional currency for all of OneBeacon's businesses. OneBeacon is subject to foreign currency fluctuations associated with foreign investment securities. Assets and liabilities recorded in foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the average exchange rates for the period. Net foreign exchange gains and losses arising from the translation are reported as a component of net income in the period in which they arise. Variable Interest Entities OneBeacon consolidates a reciprocal insurance exchange ("reciprocal") as a variable interest entity ("VIE"), when it has both the power to direct the activities of the VIE that most significantly impact its economic performance and either the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. See Note 13—"Variable Interest Entities ("VIE")." Defined Benefit Plans OneBeacon sponsors defined benefit plans and recognizes the funded status of the difference between plan assets at fair value and the projected benefit obligation (for defined benefit pension plans) or the accumulated benefit obligation (for other postretirement benefit plans) in its statement of financial position. The Company recognizes amounts previously deferred and amortized in other comprehensive income in the period in which they occur and measure plan assets and obligations as of the fiscal year end. The projected benefit obligation of the Qualified Plan was calculated using termination assumptions as of December 31, 2015 given its settlement is imminent and the likelihood that the execution of the plan termination is blocked by third parties and the Qualified Plan returns from termination is remote. See Note 8—"Retirement Plans." 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 the years ended December 31, 2014 and 2013 increased by $1.2 million and $0.6 million , respectively. As a result of the retrospective adoption, OneBeacon's common shareholders equity has been reduced by $0.3 million as of January 1, 2013. In addition, for the years ended December 31, 2014 and 2013, the retrospective adoption resulted in an increase of $1.7 million and $1.9 million to net investment income, respectively, and a net increase of $2.3 million and $2.2 million to income tax expense, respectively. 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 Financial Instruments - Recognition and Measurement On January 5, 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities . The new guidance requires all equity securities with readily determinable fair values are to be measured at fair value with changes therein required to be recognized through current period earnings. In addition, the new ASU simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment and for impaired equity security investments to be measured at fair value. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, with early adoption permitted. OneBeacon has taken the fair value election for its portfolio of equity security investments and accordingly, does not expect the adoption of ASU 2016-01 to have a significant impact on its financial statements. Business Combinations - Measurement Period Adjustments On September 25, 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments. At the date of an acquisition, fair value of certain assets and liabilities may not be accurately determinable and are therefore recognized at the acquirer's best estimate. Such amounts may be updated as additional information beco

Acqusitions and Dispositions

Acqusitions and Dispositions	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions Crop Business On July 31, 2015, Monsanto Company sold Climate Crop Insurance Agency ("CCIA"), the third party agency with which OneBeacon previously had an exclusive managing general agency agreement, to an affiliate of AmTrust Financial Services, Inc. ("AmTrust"). As a result of the sale, the Company has exited the multiple peril crop insurance ("MPCI") business and its related crop-hail business (collectively, "Crop Business"). As a result of the transaction, OneBeacon and CCIA agreed to an early termination of the existing five year agreement. In connection with the termination of the agreement, OneBeacon received a payment of $3.0 million (pre-tax) recorded in net other revenues (expenses). Also related to the transaction, OneBeacon withdrew its 2016 Plan of Operations, which previously authorized it to write MPCI for the 2016 Reinsurance Year, and affiliates of AmTrust agreed to reinsure the Company’s remaining net Crop Business exposure for the 2015 Reinsurance Year under a related 100% quota share reinsurance agreement which, coupled with other transfer and assignment agreements as well as communications with policyholders and agents, had the effect of assumption reinsurance. As a result of this transaction, the Company has no material net exposure related to the Crop Business. 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 18—"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 ("OBIC"), 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'), an indirect wholly owned insurance subsidiary of the Company at that time, 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 provided certain transition services to Armour, which were substantially completed as of December 31, 2015, with a few peripheral services extended into the first quarter of 2016. See Note 18—"Discontinued Operations" for further information regarding activity reported as discontinued operations during the years ended December 31, 2015 , 2014 and 2013 . Essentia Insurance Company Effective January 1, 2013 , OneBeacon completed the sale of Essentia Insurance Company ("Essentia"), an indirect wholly-owned subsidiary which wrote the collector cars and boats business, to Markel Corporation. Concurrently therewith, OneBeacon and Hagerty Insurance Agency ("Hagerty") terminated their underwriting arrangement with respect to the collector cars and boats business. OneBeacon recognized a pre-tax gain on sale of $23.0 million ( $15.0 million after tax) in 2013. In 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. The Company recognized earned premiums for this business of $89.1 million for 2013, and essentially no earned premiums for either 2015 or 2014. Except as described above, during the years ended December 31, 2015 , 2014 and 2013 , there were no significant acquisitions or dispositions.

Unpaid Loss and Loss Adjustment

Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves	12 Months Ended
	Dec. 31, 2015
Insurance Loss Reserves [Abstract]
Unpaid Loss and Loss Adjustment Expense (LAE) Reserves	Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves OneBeacon's insurance subsidiaries establish loss and LAE reserves that are estimates of amounts needed to pay claims and related expenses in the future for insured events that have already occurred. The process of estimating reserves involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain. Loss and LAE reserves are typically comprised of (1) case reserves for claims reported and (2) IBNR reserves, which include a provision for expected future development on case reserves and for losses that have occurred but for which claims have not yet been reported. Case reserves are estimated based on the experience and knowledge of claims staff regarding the nature and potential cost of each claim and are adjusted as additional information becomes known or payments are made. IBNR reserves are derived by subtracting paid loss and LAE and case reserves from estimates of ultimate loss and LAE. Actuaries estimate ultimate loss and LAE using various generally accepted actuarial methods applied to known losses and other relevant information. Like case reserves, IBNR reserves are adjusted as additional information becomes known or payments are made. Ultimate loss and LAE are generally determined by extrapolation of claim emergence and settlement patterns observed in the past that can reasonably be expected to persist into the future. In forecasting ultimate loss and LAE with respect to any line of business, past experience with respect to that line of business is the primary resource, but cannot be relied upon in isolation. OneBeacon's own experience, particularly claims development experience, such as trends in case reserves, payments on and closings of claims, as well as changes in business mix and coverage limits, is the most important information for estimating its reserves. External data, available from organizations such as statistical bureaus, consulting firms and reinsurance companies, is sometimes used to supplement or corroborate OneBeacon's own experience. External data can be especially useful for estimating costs on newer lines of business (e.g. Surety) or newer business segments (e.g. Programs). For some lines of business, such as "long-tail" coverages discussed below, claims data reported in the most recent accident or report year is often too limited to provide a meaningful basis for analysis due to the typical delay in reporting and settling of claims. For this type of business, OneBeacon uses an expected loss ratio method for the initial accident year or years. This is a standard and accepted actuarial reserve estimation method in these circumstances in which the loss ratio is selected based upon information used in pricing policies for that line of business, as well as any publicly available industry data, such as industry pricing, experience and trends, for that line of business. Uncertainties in estimating ultimate loss and LAE are magnified by the time lag between when a claim actually occurs and when it is reported and eventually settled. This time lag is sometimes referred to as the "claim-tail." The claim-tail for most property coverages is typically short (usually a few days up to a few months). The claim-tail for liability/casualty coverages, such as automobile liability, general liability, products liability, multiple peril coverage, and workers compensation, can be especially long as claims are often reported and ultimately paid or settled years, even decades, after the related loss events occur. During the long claims reporting and settlement period, additional facts regarding coverages written in prior accident years, as well as about actual claims and trends may become known and, as a result, OneBeacon may adjust its reserves. If management determines that an adjustment is appropriate, the adjustment is booked in the accounting period in which such determination is made. Accordingly, should reserves need to be increased or decreased in the future from amounts currently established, future results of operations would be negatively or positively impacted, respectively. In determining ultimate loss and LAE, the cost to indemnify claimants, provide needed legal defense and other services for insureds and administer the investigation and adjustment of claims are considered. These claim costs are influenced by many factors that change over time, such as expanded coverage definitions as a result of new court decisions, inflation in costs to repair or replace damaged property, inflation in the cost of medical services, and legislated changes in statutory benefits, as well as by the particular, unique facts that pertain to each claim. As a result, the rate at which claims arose in the past and the costs to settle them may not always be representative of what will occur in the future. The factors influencing changes in claim costs are often difficult to isolate or quantify and developments in paid and incurred losses from historical trends are frequently subject to multiple and conflicting interpretations. Changes in coverage terms or claims handling practices may also cause future experience and/or development patterns to vary from the past. A key objective of actuaries in developing estimates of ultimate loss and LAE, and resulting IBNR reserves, is to identify aberrations and systemic changes occurring within historical experience and accurately adjust for them so that the future can be projected more reliably. Because of the factors previously discussed, this process requires the use of informed judgment and is inherently uncertain. OneBeacon's actuaries use several generally accepted actuarial methods to evaluate its loss and LAE reserves, each of which has its own strengths and weaknesses. OneBeacon places more or less reliance on a particular method based on the facts and circumstances at the time the reserve estimates are made. These methods generally fall into one of the following categories or are hybrids of one or more of the following categories: • Historical paid loss development methods: These methods use historical loss payments over discrete periods of time to estimate future losses. Historical paid loss development methods assume that the ratio of losses paid in one period to losses paid in an earlier period will remain constant. These methods necessarily assume that factors that have affected paid losses in the past, such as inflation or the effects of litigation, will remain constant in the future. Because historical paid loss development methods do not use case reserves to estimate ultimate losses, they can be more reliable than the other methods discussed below that look to case reserves (such as actuarial methods that use incurred losses) in situations where there are significant changes in how case reserves are established by a company's claims adjusters. However, historical paid loss development methods are more leveraged, meaning that small changes in payments have a larger impact on estimates of ultimate losses, than actuarial methods that use incurred losses because cumulative loss payments take much longer to equal the expected ultimate losses than cumulative incurred amounts. In addition, and for similar reasons, historical paid loss development methods are often slow to react to situations when new or different factors arise than those that have affected paid losses in the past. • Historical incurred loss development methods: These methods, like historical paid loss development methods, assume that the ratio of losses in one period to losses in an earlier period will remain constant in the future. However, instead of using paid losses, these methods use incurred losses (i.e., the sum of cumulative historical loss payments plus outstanding case reserves) over discrete periods of time to estimate future losses. Historical incurred loss development methods can be preferable to historical paid loss development methods because they explicitly take into account open cases and the claims adjusters' evaluations of the cost to settle all known claims. However, historical incurred loss development methods necessarily assume that case reserving practices are consistently applied over time. Therefore, when there have been significant changes in how case reserves are established, using incurred loss data to project ultimate losses can be less reliable than other methods. • Expected loss ratio methods: These methods are based on the assumption that ultimate losses vary proportionately with premiums. Expected loss ratios are typically developed based upon the information used in pricing, and are multiplied by the total amount of premiums earned to calculate ultimate losses. Expected loss ratio methods are useful for estimating ultimate losses in the early years of long-tailed lines of business, when little or no paid or incurred loss information is available. • Adjusted historical paid and incurred loss development methods: These methods take traditional historical paid and incurred loss development methods and adjust them for the estimated impact of changes from the past in factors such as inflation, the speed of claim payments or the adequacy of case reserves. Adjusted historical paid and incurred loss development methods are often more reliable methods of predicting ultimate losses in periods of significant change, provided the actuaries can develop methods to reasonably quantify the impact of changes. OneBeacon performs an actuarial review of its recorded reserves each quarter. OneBeacon's actuaries compare the previous quarter's estimates of paid loss and LAE, case reserves and IBNR to amounts indicated by actual experience. Differences between previous estimates and actual experience are evaluated to determine whether a given actuarial method for estimating loss and LAE should be relied upon to a greater or lesser extent than it had been in the past. While some variance is expected each quarter due to the inherent uncertainty in loss and LAE, persistent or large variances would indicate that prior assumptions and/or reliance on certain reserving methods may need to be revised going forward. Upon completion of each quarterly review, the Company's actuaries select indicated reserve levels based on the results of the actuarial methods described previously, which are the primary consideration in determining management's best estimate of required reserves. However, in making its best estimate, management also considers other qualitative factors that may lead to a difference between held reserves and actuarially indicated reserve levels in the future. Typically, these factors exist when management and our actuaries conclude that there is insufficient historical incurred and paid loss information or that trends included in the historical incurred and paid loss information are unlikely to repeat in the future. Such factors include, among others, recent entry into new markets or new products, improvements in the claims department that are expected to lessen future ultimate loss costs, legal and regulatory developments, or other volatilities that may arise. Loss and LAE reserve summary The following table summarizes the loss and LAE reserve activities of OneBeacon's insurance subsidiaries for the years ended December 31, 2015 , 2014 , and 2013 : Year ended December 31, 2015 2014 2013 ($ in millions) Gross beginning loss and LAE reserves $ 1,342.2 $ 1,054.3 $ 1,000.0 Less beginning reinsurance recoverable on unpaid losses (161.6 ) (80.2 ) (107.3 ) Net beginning loss and LAE reserves 1,180.6 974.1 892.7 Loss and LAE incurred from continuing operations relating to: Current year losses 702.5 725.3 622.1 Prior year losses (1.8 ) 89.8 — Total incurred loss and LAE from continuing operations 700.7 815.1 622.1 Loss and LAE paid from continuing operations relating to: Current year losses (202.4 ) (199.6 ) (188.6 ) Prior year losses (475.1 ) (409.0 ) (352.1 ) Total loss and LAE payments from continuing operations (677.5 ) (608.6 ) (540.7 ) Net loss and LAE reserves 1,203.8 1,180.6 974.1 Total incurred loss and LAE from discontinued operations — (0.7 ) 78.9 Total loss and LAE payments from discontinued operations — (55.1 ) (102.3 ) Net loss and LAE reserves 1,203.8 1,124.8 950.7 Net change in loss and LAE reserves reported in liabilities held for sale — 188.4 (1) 23.4 (2) Net loss and LAE reserves sold — (132.6 ) (3) — Net ending loss and LAE reserves 1,203.8 1,180.6 974.1 Plus ending reinsurance recoverable on unpaid losses 186.0 161.6 80.2 Gross ending loss and LAE reserves $ 1,389.8 $ 1,342.2 $ 1,054.3 _______________________________________________________________________________ (1) Consists of the change in net loss and LAE reserves of $188.4 million , representing the balances classified as held for sale as December 31, 2013, in connection with the Runoff Transaction. (2) Consists of changes in net loss and LAE reserves to $188.4 million from $211.8 million , which amounts were classified as held for sale as of December 31, 2013 and 2012, respectively, in connection with the Runoff Transaction. (3) Relates to the Runoff Transaction, which closed on December 23, 2014. Loss and LAE development Loss and LAE development—2015 Net favorable prior year loss and LAE reserve development was $1.8 million during the year ended December 31, 2015 , primarily attributable to favorable development from several businesses, most notably Technology , and to a lesser extent, from Collector Cars and Boats , Specialty Property and Financial Services , along with certain other businesses . This favorable development was mostly offset by unfavorable development due to several large losses and an increase in small to mid-size claims in Entertainment , and to a lesser extent, unusually heavy loss activity of both large and small claims in Ocean Marine , as well as moderate unfavorable development from certain other businesses. Loss and LAE development—2014 Net unfavorable prior year loss and LAE reserve development was $89.8 million during the year ended December 31, 2014 , of which $75.5 million related to the 2014 fourth quarter reserve increase described below. Of the net unfavorable loss and LAE reserve development resulting from the 2014 fourth quarter reserve increase, $31.9 million related to the Other Professional Lines driven primarily by lawyers professional liability, and $11.6 million related to Entertainment resulting from several large losses. The remaining net unfavorable prior year loss and LAE reserve development for 2014 primarily related to unfavorable development recognized prior to the 2014 fourth quarter also in our Other Professional Lines (including lawyers professional liability) and Management Liability businesses, offset in part by favorable development in our Healthcare business . See the table below for a breakout of development by underwriting operating segment. 2014 Fourth Quarter Reserve Increase Through the first nine months of 2014, the Company recorded $14.3 million of unfavorable loss and LAE reserve development, driven by greater-than-expected large loss activity in several underwriting operating segments, primarily in the Other Professional Lines and Management Liability underwriting operating segments. This large loss activity, which occurred mostly during the second and third quarters of 2014, also impacted the 2014 current accident year loss and LAE estimates. Additionally, the Company incurred higher-than-usual claim coverage determination costs, a component of LAE expenses, during the first nine months of 2014. Other underwriting operating segments also reported increased claim activity, including Entertainment, Government Risks and Accident. Since the increased level of loss and LAE activity continued into the early part of the fourth quarter of 2014, the high level of activity in the second and third quarters no longer seemed to be isolated occurrences. As such, during the fourth quarter of 2014, the Company enhanced its actuarial and claims review in several areas. The Company isolated the recent large loss activity in each of its underwriting operating segments and examined the emergence of large losses relative to the timing and amounts of expected large losses. The Company also conducted additional analyses in the lawyers' professional liability Line within the Other Professional Lines underwriting operating segment. These new analyses included a claim level review and the application of additional actuarial methods and loss development assumptions. The results of these analyses indicated that the assumed tail risk included in the loss development patterns used to record IBNR reserves for this line were insufficient and needed to be increased for remaining long-tail exposures. The Company's claims and actuarial staff also conducted an in-depth review of coverage determination, litigation, and other claim-specific adjusting expenses as a result of an emerging trend of increased expenses in these areas over then-recent quarters, particularly coverage determination expenses. This review concluded that the ultimate costs of these loss adjustment expenses were larger than previously estimated, causing management to record an increase in estimated LAE expenses, primarily in the Other Professional Lines, Management Liability and Financial Services underwriting operating segments. Finally, the Company also recorded unfavorable prior year development in other underwriting units, including Entertainment and Government Risks . The unfavorable loss development in Entertainment and Government Risks resulted from heavier than expected claim activity during the fourth quarter of 2014, predominantly in the general liability and commercial auto liability lines. As a result of these enhanced actuarial and claim reviews conducted during the fourth quarter of 2014 and in order to fully reflect these recent trends, the Company recorded a $109.2 million increase in loss and LAE reserves, which included a $75.5 million increase in prior accident year loss and LAE reserves and a $33.7 million increase in the current accident year loss and LAE reserves which were previously recorded at September 30, 2014. The components of the 2014 fourth quarter reserve increase and the net loss and LAE development for the full year are provided below: 2014 Fourth Quarter Reserve Increase Full Year 2014 Net Prior Year Development Underwriting Operating Segment Current Accident Year Prior Accident Years Total Other Professional Lines $ 11.1 $ 31.9 $ 43.0 $ 42.2 Management Liability 6.6 8.4 15.0 16.4 Financial Services 2.0 6.5 8.5 6.5 Healthcare 3.2 (0.4 ) 2.8 (6.0 ) Specialty Property (1.1 ) 5.7 4.6 1.1 Crop 3.8 — 3.8 — Other 2.8 (0.4 ) 2.4 1.6 Specialty Products 28.4 51.7 80.1 61.8 Entertainment 1.5 11.6 13.1 13.5 Government Risks 1.2 7.1 8.3 8.5 Accident — 3.5 3.5 6.0 Other 2.6 1.6 4.2 — Specialty Industries 5.3 23.8 29.1 28.0 Total $ 33.7 $ 75.5 $ 109.2 $ 89.8 As noted above, the Company increased its provision for 2014 current accident year losses and LAE by $33.7 million in the fourth quarter of 2014. In recording the change in estimate of its loss and LAE reserve provision for the 2014 accident year, the Company considered the results of the enhanced actuarial and claim review and the fact that reported large claims were approaching estimated ultimate large losses sooner than originally expected. Of the $33.7 million increase, $29.9 million reflects an increase in management's best estimate of current year loss and LAE as of December 31, 2014 from those amounts recorded in the first nine months of 2014. This increase primarily affected the Other Professional Lines and Management Liability underwriting operating segments, which represented $17.7 million of the total provision. The remaining increase was primarily related to a $3.8 million increase in estimated losses in the Crop underwriting operating segment from higher-than-expected reports of crop losses that emerged in the fourth quarter of 2014. Loss and LAE development—2013 During the year ended December 31, 2013, OneBeacon experienced no net loss and LAE reserve development on prior accident year reserves. The Company experienced unfavorable development primarily related to the property line in Specialty Property, Entertainment (primarily, general liability), and the A&H line within the Accident underwriting operating segment. This amount was offset by favorable development in other liability (claims made) within the managed care E&O business included in the Healthcare underwriting operating segment, and in the Ocean Marine underwriting operating segment.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 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. The effects of reinsurance on OneBeacon's insurance subsidiaries' written and earned premiums and on loss and LAE, excluding the Runoff Business, were as follows: Year ended December 31, 2015 2014 2013 ($ in millions) Written premiums: Direct $ 1,279.9 $ 1,257.5 $ 1,103.1 Assumed 36.0 65.9 59.8 Ceded (179.3 ) (1) (106.5 ) (74.3 ) Net written premiums $ 1,136.6 $ 1,216.9 $ 1,088.6 Earned premiums: Direct $ 1,298.0 $ 1,209.1 $ 1,043.3 Assumed 45.9 70.9 148.5 (2) Ceded (167.7 ) (1) (102.9 ) (71.4 ) Net earned premiums $ 1,176.2 $ 1,177.1 $ 1,120.4 Loss and LAE: Direct $ 783.0 $ 778.7 (3) $ 584.9 Assumed 55.7 115.7 (3) 76.3 (2) Ceded (138.0 ) (1) (79.3 ) (39.1 ) Net loss and LAE $ 700.7 $ 815.1 $ 622.1 _______________________________________________________________________________ (1) During the year ended December 31, 2015, the Company recorded ceded written premiums of $33.3 million , ceded earned premiums of $33.3 million and ceded loss and loss adjustment expenses of $33.4 million as a result of the exit of the Crop Business due to the 100% quota share reinsurance agreement with AmTrust. (2) Includes assumed earned premiums and loss and LAE of $89.1 million and $41.9 million , respectively, related to the collector cars and boats business which although exited on January 1, 2013, was assumed on a runoff basis from Essentia. (3) Direct and Assumed Loss and LAE, for the year ended December 31, 2014, has been revised from the prior year's presentation to appropriately reflect Direct and Assumed Loss and LAE for that period. Direct Loss and LAE was decreased by $52 million and offset by an increase of $52 million in Assumed Loss and LAE. This revision, which had no impact on net income, was not material and has been presented correctly in the table above to improve comparability. Reinsurance Treaties The timing and size of catastrophe losses are unpredictable and the level of losses experienced in any year could be material to the Company's operating results and financial condition. Examples of catastrophes include losses caused by earthquakes, wildfires, hurricanes and other types of storms and terrorist acts. The extent of losses caused by a catastrophic event is a function of severity and the amount and type of insured exposure in the affected area. In the normal course of business, OneBeacon's insurance subsidiaries seek to limit losses that may arise from catastrophes or other events through individual risk selection, imposing deductibles and limits, limiting its concentration of insurance in catastrophe-prone areas such as coastal regions and reinsuring with third-party reinsurers. The Company uses models (primarily AIR Worldwide (AIR) Touchstone version 3.0) to estimate potential losses from catastrophes. The Company use the model output in conjunction with other data to manage its exposure to catastrophe losses based on a probable maximum loss (PML) forecast to quantify its exposure to an extreme catastrophe event. OneBeacon utilizes a general catastrophe reinsurance treaty with unaffiliated reinsurers to manage its exposure to large catastrophe losses. 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 the 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. OneBeacon's current third party reinsurance programs provide varying degrees of coverage for terrorism events. The Company's overall terrorism exposure is impacted by the Terrorism Risk Insurance Program (the “Terrorism Act”), which is a federal program administered by the Department of the Treasury that provides for a shared system of public and private compensation for commercial property and casualty losses resulting from events that reach the threshold for losses ( $120 million in 2016 and increasing $20 million in subsequent years until the threshold becomes $200 million in 2020) and are certified as an act of terrorism by the U.S. Secretary of the Treasury, in concurrence with the Secretary of Homeland Security and the Attorney General of the United States. The Terrorism Act limits the industry's aggregate liability for losses from certified terrorist acts by requiring the federal government to share a set amount of losses ( 84% in 2016 and decreasing 1% annually in subsequent years until it reaches a floor of 80% in 2020) once a company meets a specific retention or deductible as determined by its prior year's direct written premiums. It also limits the aggregate liability to be paid by the government and industry without further action by Congress to $100 billion . In exchange for this backstop, primary insurers are required to make coverage available to commercial insureds for losses from acts of terrorism as defined in the Terrorism Act. The following types of coverage are excluded from the program: commercial automobile, burglary and theft, surety, farmowners multi-peril and all professional liability coverage except directors and officers coverage. All losses that result from a nuclear, biological, chemical or radiological terrorist attack are excluded from the Company's current third party reinsurance program. OneBeacon's property catastrophe treaty also excludes acts of terrorism certified pursuant to the Terrorism Act and committed by an individual or individuals acting on behalf of any foreign person or foreign interest. OneBeacon's casualty clash treaty provides coverage for losses that result from certified and non-certified acts of terrorism, on an aggregated basis, subject to a maximum of one full treaty limit. OneBeacon's property per risk, casualty and workers compensation treaties each provide full coverage for certified acts of terrorism on behalf of a non-foreign person or interest, but are sublimited to one full treaty limit for certified acts of terrorism committed on behalf of any foreign person or foreign interest. OneBeacon's healthcare treaty is sublimited to one full treaty limit of coverage for all acts of terrorism. OneBeacon estimates its individual retention level for commercial policies subject to the Terrorism Act to be approximately $120 million in 2016. The federal government will pay 84% of covered terrorism losses that exceed the Company's or the industry's retention levels in 2016, up to a total of $100 billion . As indicated above, the Company's 16% copay will increase annually beginning in 2016 by 1% until it reaches a limit of 20% in 2020. In addition to the corporate catastrophe reinsurance protection, the Company also purchases dedicated reinsurance protection for certain lines of business. OneBeacon specialty property underwriting operating segment purchases a dedicated property catastrophe program providing 100% coverage for $34.0 million of loss in excess of $6.0 million of loss, which inures to the benefit of the broader property catastrophe reinsurance program described previously. This treaty limit cannot be reinstated. OneBeacon also purchases property-per-risk reinsurance coverage to reduce large loss volatility. The property-per-risk reinsurance program reinsures 100% of losses in excess of $3.0 million , which represents a retention decrease from $5.0 million for the previous periods property-per-risk program, up to $100.0 million . Individual risk facultative reinsurance is purchased above $100.0 million . The property-per-risk treaty provides one limit of reinsurance protection for losses in excess of $3.0 million up to $100.0 million on an individual risk basis for certified acts of terrorism committed on behalf of any foreign person or foreign interest. However, any nuclear events, or biological, chemical or radiological terrorist attacks are not covered. OneBeacon also maintains a casualty reinsurance program that provides protection for individual policies involving general liability, automobile liability, professional liability or umbrella liability. OneBeacon's healthcare professional liability treaty covers losses in excess of $3.0 million up to $10.0 million . All other casualty business is covered in a separate treaty covering losses in excess of $3.0 million up to $11.0 million . Losses in excess of $10.0 million for business subject to the healthcare professional liability treaty up to $20.0 million , and losses in excess of $11.0 million for all other casualty business up to $21.0 million are 100% reinsured by a combined Second Casualty Excess of Loss treaty layer. OneBeacon also purchases a treaty to protect against large workers compensation losses that provides coverage for 100% of the loss in excess of $2.0 million up to $10.0 million per occurrence. Additionally, for casualty, surety and/or workers compensation catastrophe losses, OneBeacon maintains a dedicated clash treaty, which provides coverage in the event that one loss event results in two or more claims, that covers losses in excess of $10.0 million up to $60.0 million for workers compensation and in excess of $10.0 million up to $40.0 million for casualty and surety losses. OneBeacon purchases a per occurrence treaty for marine business – both inland and ocean – that protects against large occurrences, whether a single large claim or a catastrophe. The marine treaty attaches at $2.5 million per occurrence. The first layer of the marine treaty is $7.5 million in excess of $2.5 million , with an annual aggregate deductible of $5.0 million for catastrophe losses. Coverage is provided up to $60.0 million . Retained catastrophe losses are subject to the corporate catastrophe treaty. Individual risk losses from inland marine exceeding $20.0 million are subject to the corporate property per risk treaty. Reinstatement premiums are paid in full or in part depending on the layer and the occurrence if the coverage is attached. OneBeacon also purchases reinsurance for its surety underwriting operating segment. Effective October 1, 2015, this treaty covers 100% of losses in excess of $5.0 million up to $50.0 million per bond and up to $100.0 million in aggregate. Additionally, effective January 1, 2015, OneBeacon placed an HMO/Provider Excess reinsurance agreement providing unlimited coverage excess of $5.0 million per member in two layers with no aggregate coverage maximum. Effective June 1, 2015, OneBeacon also purchased reinsurance on its film completion bond business included in the Entertainment underwriting operating segment in excess of $2.0 million up to $35.0 million in three layers, with a facultative treaty layer providing coverage up to $60.0 million as needed. On July 31, 2015, OneBeacon reinsured 100% of its net retained losses for both its MPCI and crop-hail business by entering into a quota share reinsurance agreement with an insurance operating affiliate of AmTrust for the remaining net exposure to the 2015 Crop reinsurance year. See Note 2—"Acquisitions and Dispositions" for further detail. Reinsurance Recoverables As of December 31, 2015 , OneBeacon had reinsurance recoverable on paid losses of $7.5 million and reinsurance recoverables on unpaid losses of $186.0 million . As reinsurance contracts do not relieve OneBeacon of its obligations, collectibility of balances due from reinsurers is critical to OneBeacon's financial strength. The following table summarizes Standard & Poor's Financial Services, LLC ("Standard & Poor's") ratings for OneBeacon's reinsurers for its continuing insurance operations, excluding industry pools and associations, based upon reinsurance recoverable amounts on paid and unpaid losses and LAE: Balance at December 31, 2015 % of total Standard & Poor's Rating (1) : ($ in millions) AA $ 41.7 22 % A 126.2 65 % BBB, Not Rated and Other 25.6 (2) 13 % Total reinsurance recoverables $ 193.5 100 % _______________________________________________________________________________ (1) Standard & Poor's ratings as detailed above are "AA" (Very strong), "A" (Strong) and "BBB" (Adequate). (2) Includes reinsurance recoverable on unpaid losses from Bedivere of $20.4 million .

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2015
Schedule of Investments [Abstract]
Investment Securities	Investment Securities OneBeacon's net investment income is comprised primarily of interest income associated with OneBeacon's fixed maturity investments, dividend income from its common equity securities and other investments, and interest income from its short-term investments. Other investments primarily include hedge funds, private equity funds, and convertible fixed maturity investments as well as surplus notes beginning in 2014. Net investment income for the years ended December 31, 2015 , 2014 , and 2013 consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Fixed maturity investments $ 43.8 $ 41.8 $ 40.6 Short-term investments — — — Common equity securities 6.1 6.5 6.2 Other investments 1.0 2.1 3.0 Gross investment income 50.9 50.4 49.8 Less investment expenses (5.0 ) (7.0 ) (6.8 ) Net investment income, pre-tax $ 45.9 $ 43.4 $ 43.0 The composition of net realized investment gains consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Fixed maturity investments $ 2.0 $ 6.6 $ 2.1 Short-term investments — — — Common equity securities 33.8 53.9 36.1 Other investments 11.4 9.2 6.0 Net realized investment gains, pre-tax 47.2 69.7 44.2 Income taxes (9.1 ) (21.0 ) (20.5 ) Net realized investment gains, after tax $ 38.1 $ 48.7 $ 23.7 OneBeacon recognized gross realized investment gains of $64.2 million , $75.0 million and $70.1 million and gross realized investment losses of $17.0 million , $5.3 million and $25.9 million on sales and other-than-temporary impairment charges on investment securities during the years ended December 31, 2015 , 2014 and 2013 , respectively. As of December 31, 2015 and 2014 , OneBeacon reported $30.5 million , and $7.2 million , respectively, in accounts receivable on unsettled investment sales and $0.5 million in accounts payable on unsettled investment purchases as of December 31, 2014 and none as of December 31, 2015 . The net changes in fair value for the years ended December 31, 2015 , 2014 , and 2013 are as follows: Year ended December 31, 2015 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ (15.7 ) $ — $ (15.7 ) Short-term investments — — — Common equity securities (33.2 ) 0.2 (33.0 ) Other investments (33.6 ) — (33.6 ) Net change, pre-tax $ (82.5 ) $ 0.2 $ (82.3 ) Year ended December 31, 2014 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ 1.9 $ — $ 1.9 Short-term investments — (0.1 ) (0.1 ) Common equity securities (32.6 ) (0.3 ) (32.9 ) Other investments 1.8 — 1.8 Net change, pre-tax $ (28.9 ) $ (0.4 ) $ (29.3 ) Year ended December 31, 2013 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ (34.4 ) $ — $ (34.4 ) Short-term investments 0.1 — 0.1 Common equity securities 32.0 0.1 32.1 Other investments 7.4 — 7.4 Net change, pre-tax $ 5.1 $ 0.1 $ 5.2 _______________________________________________________________________________ (1) Includes pre-tax changes in net deferred gains and losses on sales of investments between OneBeacon and entities under White Mountains' common control of $(0.8) million for the year ended December 31, 2013 . There were no such changes in net deferred gains and losses for the years ended December 31, 2015 and 2014, respectively. The components of OneBeacon's ending net unrealized investment gains and losses, excluding the impact of net unrealized foreign currency translation gains and losses, on its investment portfolio as of December 31, 2015 and 2014 were as follows: December 31, 2015 2014 ($ in millions) Investment securities: Gross unrealized investment gains $ 46.5 $ 104.7 Gross unrealized investment losses (33.2 ) (8.9 ) Total net unrealized investment gains, pre-tax 13.3 95.8 Income taxes (6.5 ) (26.9 ) Total net unrealized investment gains, after tax $ 6.8 $ 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 December 31, 2015 and 2014 were as follows: December 31, 2015 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency losses Carrying value ($ in millions) U.S. Government and agency obligations $ 85.4 $ — $ (0.1 ) $ — $ 85.3 Debt securities issued by industrial corporations 810.8 4.1 (4.5 ) — 810.4 Municipal obligations 67.7 1.5 (0.2 ) — 69.0 Asset-backed securities 1,035.1 1.3 (4.5 ) — 1,031.9 Foreign government obligations 1.0 0.2 — — 1.2 Preferred stocks 78.3 4.4 — — 82.7 Total fixed maturity investments $ 2,078.3 $ 11.5 $ (9.3 ) $ — $ 2,080.5 December 31, 2014 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency losses Carrying value ($ in millions) 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 and carrying value of OneBeacon's fixed maturity investments as of December 31, 2015 is presented below by contractual maturity. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. December 31, 2015 Cost or amortized cost Carrying value ($ in millions) Due in one year or less $ 154.4 $ 154.8 Due after one year through five years 678.1 678.2 Due after five years through ten years 115.2 115.0 Due after ten years 17.2 17.9 Asset-backed securities 1,035.1 1,031.9 Preferred stocks 78.3 82.7 Total $ 2,078.3 $ 2,080.5 The cost or amortized cost, gross unrealized pre-tax investment gains and losses, net foreign currency gains and carrying values of OneBeacon's common equity securities and other investments as of December 31, 2015 and 2014 were as follows: December 31, 2015 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains Carrying value ($ in millions) Common equity securities $ 295.0 $ 12.7 $ (9.0 ) $ — $ 298.7 Other investments 135.6 22.3 (14.9 ) — 143.0 Total common equity securities and other investments $ 430.6 $ 35.0 $ (23.9 ) $ — $ 441.7 December 31, 2014 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains Carrying value ($ in millions) Common equity securities $ 283.2 $ 39.3 $ (2.4 ) $ (0.1 ) $ 320.0 Other investments 162.9 44.8 (3.9 ) — 203.8 Total common equity securities and other investments $ 446.1 $ 84.1 $ (6.3 ) $ (0.1 ) $ 523.8 Sales and maturities of investments, excluding short-term investments and other investments, totaled $1,371.5 million , $2,585.1 million and $1,841.9 million for the years ended December 31, 2015 , 2014 and 2013 , respectively. There were no non-cash exchanges or involuntary sales of investment securities during the years ended December 31, 2015 , 2014 and 2013 . OneBeacon's consolidated insurance operations are required to maintain deposits with certain insurance regulatory agencies in order to maintain their insurance licenses. The fair value of such deposits totaled $82.1 million and $63.4 million , respectively, as of December 31, 2015 and 2014 . As of December 31, 2015 and 2014 , investments of $2.2 million and $2.7 million , respectively, were held in a trust required to be maintained to comply with New York surplus lines regulations and investments of $5.4 million and $3.3 million , respectively, were held in a trust required to be maintained in relation to a reinsurance agreement with Star & Shield Insurance Exchange. As of December 31, 2015 and 2014 , the Company held unrestricted collateral from its customers, which is included in cash and invested assets, relating to its Surety business of $137.7 million and $81.0 million , respectively. The following table summarizes the ratings of OneBeacon's corporate debt securities as of December 31, 2015 and 2014: December 31, 2015 2014 ($ in millions) AA (1) $ 42.7 $ 57.9 A (1) 265.4 328.1 BBB (1) 502.3 409.2 Not rated — 3.0 Debt securities issued by corporations $ 810.4 $ 798.2 _______________________________________________________________________________ (1) Credit ratings are assigned based on the following hierarchy: 1) 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 December 31, 2015 and 2014 , approximately 92% 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 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. Investments valued using Level 2 inputs also include convertible fixed maturity investments and certain ETFs that track U.S. stock indices such as the S&P 500 but are traded on foreign exchanges and that management values using the fund's published NAV to account for the difference in market close times. 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 mortgage and 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 December 31, 2015 and 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 provided in conjunction with the financing of the Runoff Transaction which are measured at their estimated fair value based on discounted expected cash flows using information as of the measurement date, with changes in fair value reported in total revenues as net realized and change in unrealized investment gains. As of both December 31, 2015 and 2014 , other investments reported at fair value represented approximately 5% and 7% , respectively, of the total investment portfolio and consisted of the following: ($ in millions) December 31, December 31, Hedge funds (1) $ 16.4 $ 42.3 Private equity funds (2) 46.1 60.1 Total hedge funds and private equity funds 62.5 102.4 Surplus notes (par value $101.0) (3) 51.5 65.1 Investment in community reinvestment vehicle 14.3 14.3 Convertible fixed maturity investments — 5.0 Trust certificates — 0.2 Total other investments (4) $ 128.3 $ 187.0 _______________________________________________________________________________ (1) Consists of 4 hedge funds and 7 hedge funds as of December 31, 2015 and 2014 , respectively. (2) Consists of 17 private equity funds as of both December 31, 2015 and 2014 . (3) The decrease in the fair value of the surplus notes during the year ended December 31, 2015 was primarily due to widening of non-investment grade credit spreads. (4) Excludes the carrying value of $14.7 million and $16.8 million as of December 31, 2015 and 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 $12.9 million and $15.8 million as of December 31, 2015 and 2014 , respectively. As of December 31, 2015 and 2014 , OneBeacon held one private preferred stock that represented approximately 85% and 84% , respectively, 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. Surplus Notes In the fourth quarter of 2014, 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 $51.5 million and $65.1 million as of December 31, 2015 and 2014 , respectively. The surplus notes, issued by one of the transferred entities, Bedivere (“Issuer”), were in the form of both seller priority and pari passu notes. The internal valuation model used to estimate the fair value is based on discounted expected cash flows using information as of the measurement date. The estimated fair value of the surplus notes is sensitive to changes in treasury rates and public debt credit spreads, as well as changes in estimates with respect to other variables including a discount to reflect the private nature of the notes (and the related lack of liquidity), the credit quality of the notes – based on the financial performance of the Issuer relative to expectations, and the timing, amount, and likelihood of interest and principal payments on the notes, which are subject to regulatory approval and therefore may vary from the contractual terms. As of December 31, 2015 and 2014 , the Company has assumed for estimating value purposes that interest payouts begin in year five (2020) and principal repayments begin on a graduating basis in year ten (2025) for the seller priority note and year fifteen (2030) for the pari passu note. Although these variables involve considerable judgment, the Company does not currently expect any resulting changes in the estimated value of the surplus notes to be material to its financial position. Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of December 31, 2015 and 2014: Type of Surplus Note Total as of December 31, 2015 Seller Priority Pari Passu (in millions) Par value $ 57.9 $ 43.1 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) (0.4 ) (14.7 ) (15.1 ) Regulatory approval (2) (11.7 ) (12.5 ) (24.2 ) Liquidity adjustment (3) (7.8 ) (2.4 ) (10.2 ) Total (19.9 ) (29.6 ) (49.5 ) Fair value (4) $ 38.0 $ 13.5 $ 51.5 Type of Surplus Note Total as of December 31, 2014 Seller Priority Pari Passu (in millions) Par value $ 57.9 $ 43.1 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) 1.6 (8.2 ) (6.6 ) Regulatory approval (2) (4.6 ) (8.0 ) (12.6 ) Liquidity adjustment (3) (11.0 ) (5.7 ) (16.7 ) Total (14.0 ) (21.9 ) (35.9 ) Fair value $ 43.9 $ 21.2 $ 65.1 _______________________________________________________________________________ (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated delay in securing regulatory approvals of interest and principal payments to reflect graduated changes in Issuer's statutory surplus. The monetary impact of the anticipated delay is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. (3) Represents impact of liquidity spread to account for OneBeacon's sole ownership of the notes, lack of a trading market, and ongoing regulatory approval risk. (4) The decrease in the fair value of the surplus notes during the year ended December 31, 2015 was primarily due to widening of non-investment grade credit spreads. Fair value measurements by level The following tables summarize the Company's fair value measurements for investments as of December 31, 2015 and 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 held as of December 31, 2014 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. Fair value at Level 1 Level 2 Level 3 ($ in millions) Fixed maturity investments: U.S. Government and agency obligations $ 85.3 $ 85.3 $ — $ — Debt securities issued by corporations: Consumer 218.3 — 218.3 — Healthcare 136.2 — 136.2 — Industrial 121.8 — 121.8 — Financial 116.0 — 116.0 — Energy 75.2 — 75.2 — Communications 46.0 — 46.0 — Utilities 42.2 — 42.2 — Technology 28.9 — 28.9 — Basic materials 25.8 — 25.8 — Debt securities issued by corporations 810.4 — 810.4 — Municipal obligations 69.0 — 69.0 — Asset-backed securities 1,031.9 — 1,031.9 — Foreign government obligations 1.2 0.6 0.6 — Preferred stocks 82.7 — 12.7 70.0 Fixed maturity investments 2,080.5 85.9 1,924.6 70.0 Short-term investments 69.2 69.2 — — Common equity securities: Exchange Traded Funds (1) 183.3 162.0 21.3 — Consumer 38.2 38.2 — — Communications 23.9 23.9 — — Health Care 19.6 19.6 — — Technology 14.7 14.7 — — Industrial 14.5 14.5 — — Financials 4.5 4.5 — — Common equity securities 298.7 277.4 21.3 — Other investments (2) 128.3 — — 128.3 Total (1)(2) $ 2,576.7 $ 432.5 $ 1,945.9 $ 198.3 _______________________________________________________________________________ (1) ETF's traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated as level 2 measurements. (2) Excludes the carrying value of $14.7 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2015 . Fair value at December 31, 2014 Level 1 Level 2 Level 3 ($ in millions) Fixed maturity investments: U.S. Government and agency obligations $ 38.0 $ 38.0 $ — $ — Debt securities issued by corporations: Consumer 174.9 — 174.9 — Financial 148.6 — 148.6 — Healthcare 111.9 — 111.9 — 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 75.2 75.2 — — Financials 72.4 72.4 — — Industrial 48.3 48.3 — — Health Care 46.5 46.5 — — Communications 24.4 24.4 — — Technology 20.6 20.6 — — Energy 15.6 15.6 — — Basic Materials 9.9 9.9 — — Utilities 5.1 5.1 — — Other 2.0 2.0 — — Common equity securities 320.0 320.0 — — Other investments (1) 187.0 — 5.0 182.0 Total (1) $ 2,509.0 $ 560.4 $ 1,692.6 $ 256.0 _______________________________________________________________________________ (1) Excludes the carrying value of $16.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2014 . Rollforwards of Fair Value Measurements by Level The following tables summarize the changes in OneBeacon’s fair value measurements by level for the year ended December 31, 2015 and 2014: Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities 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 — (13.2 ) — — — (13.2 ) Net realized and change in unrealized gains 1.3 (12.7 ) (1.1 ) — (22.6 ) (35.1 ) Purchases 638.0 985.7 34.0 — 3.4 1,661.1 Sales (634.7 ) (742.9 ) — — (34.5 ) (1,412.1 ) Transfers in — 36.9 — — — 36.9 Transfers out — — (36.9 ) — — (36.9 ) Balance at December 31, 2015 $ 363.3 $ 1,945.9 $ 70.0 $ — $ 128.3 $ 2,507.5 _______________________________________________________________________________ (1) Excludes the carrying value of $14.7 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2015. (2) Excludes short-term investments. Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities 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 0.1 (11.0 ) — — — (10.9 ) Net realized and change in unrealized gains 22.1 5.2 1.1 0.4 11.9 40.7 Purchases 752.1 1,625.1 41.7 — 68.7 2,487.6 Sales (886.2 ) (1,729.9 ) — (0.5 ) (18.5 ) (2,635.1 ) Exchanges 1.1 (3.1 ) 2.0 — — — Transfers in — 52.7 — — — 52.7 Transfers out — — (52.7 ) — — (52.7 ) Balance at December 31, 2014 $ 358.7 $ 1,692.1 $ 74.0 $ — $ 182.0 $ 2,306.8 _______________________________________________________________________________ (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. (2) Excludes short-term investments. There were no “Transfers in” to Level 3 fixed maturity investments for the years ended December 31, 2015 and 2014. During the third quarter of 2014, one convertible fixed maturity investment that was classified within Level 2 was exchanged for common shares and a corporate debt security of the same entity. As of December 31, 2014, the common shares are classified within Level 1 since a quoted market price was available. As of December 31, 2014, the corporate debt security is classified within Level 3 since the fair value based upon observable market inputs has been adjusted to reflect a liquidity discount. “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, $5.6 million in asset backed securities and $2.9 million in corporate debt securities for the year ended December 31, 2015, all of which were recategorized as Level 2 measurements when quoted market prices that were considered reliable and could be validated against alternative sources became available. “Transfers out” of Level 3 fixed maturity investments was comprised of $28.1 million in residential mortgage backed securities, $13.7 million in commercial mortgage backed securities and $10.9 million in asset backed securities for the year ended December 31, 2014, all of which were recategorized as Level 2 measurements when quoted market prices that were considered reliable and could be validated against alternative sources became available. The following table summarizes the change in net unrealized gains or losses for assets designated as Level 3 for the year ended December 31, 2015 , 2014 , and 2013 : Year ended December 31, 2015 2014 2013 ($ in millions) Fixed maturity investments $ (1.1 ) $ 1.1 $ (1.5 ) Short-term investments — — — Common equity securities — — — Other investments (33.7 ) 6.2 6.3 Total $ (34.8 ) $ 7.3 $ 4.8 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 and other investments classified within Level 3 other than hedge funds and private equity

Debt

Debt	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Debt	Debt OneBeacon's debt outstanding as of December 31, 2015 and 2014 consisted of the following: December 31, 2015 2014 ($ in millions) Senior unsecured notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (0.2 ) (0.3 ) Senior unsecured notes, carrying value $ 274.8 $ 274.7 Contractual repayments of $275.0 million for OneBeacon's outstanding debt are due more than five years after December 31, 2015 . 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. Credit Facility On September 29, 2015 the Company and OBH, as co-borrowers and co-guarantors, entered into a revolving credit facility administered by U.S. Bank N.A. and also including BMO Harris Bank N.A., which has a total commitment of $65.0 million and has a maturity date of September 29, 2019 (the "Credit Facility"). As of December 31, 2015 the credit facility was undrawn. Debt Covenants The 2012 Senior Notes were issued under indentures that contain restrictive covenants which, among other things, limit the ability of the Company, OBH, and their respective subsidiaries to create liens and enter into sale and leaseback transactions and limits the ability of OneBeacon to consolidate, merge or transfer their properties and assets. The indentures do not contain any financial ratios or specified levels of net worth or liquidity to which the Company or OBH must adhere. In addition, a failure by the Company or its subsidiaries to pay principal and interest on covered debt, where such failure results in the acceleration of at least $75 million of the principal amount of covered debt, could trigger the acceleration of the 2012 Senior Notes. The Credit Facility contains various affirmative, negative and financial covenants which OneBeacon considers to be customary for such borrowings, including certain minimum net worth and maximum debt to capitalization standards. These covenants can restrict the Company in several ways, including its ability to incur additional indebtedness. An uncured breach of these covenants could result in an event of default under the Credit Facility, which would allow lenders to declare any amounts owed under the Credit Facility to be immediately due and payable. As of December 31, 2015, OneBeacon was in compliance with all of the covenants under the 2012 Senior Notes and the Credit Facility. Interest Total interest expense incurred by OneBeacon for its indebtedness was $13.0 million during each of the years ended December 31, 2015 , 2014 and 2013 . Total cash interest paid by OneBeacon for its indebtedness was $12.7 million during each of the years ended December 31, 2015 , 2014 and 2013 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 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, Barbados, Luxembourg and the United States. U.S. operations are financed with a combination of debt and equity and the financing income and underwriting income currently account for the majority of non-U.S. earnings. OneBeacon's U.S. subsidiaries join in the filing of a federal consolidated tax return. The consolidated U.S. parent is OneBeacon U.S. Financial Services, Inc. ("OBFS"). For all years, the companies included within the U.S. consolidated tax return are parties to a tax sharing agreement which provides that each company pays the amount of income taxes or estimated tax or receives refunds that it would have to make or be entitled to if it filed its own separate tax return. As a result, certain companies have made payments, and received refunds from the consolidated U.S. parent that are different than amounts payable to the Internal Revenue Service ("IRS"). The companies that are domiciled outside of the U.S. file separate returns for the appropriate jurisdictions. The total income tax expense from continuing operations for the years ended December 31, 2015 , 2014 and 2013 consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Current tax (expense) benefit: Federal $ 9.1 $ (4.3 ) $ (20.3 ) State (1.2 ) (1.6 ) (0.8 ) Non-U.S. (0.8 ) (0.8 ) (0.4 ) Total current tax (expense) benefit 7.1 (6.7 ) (21.5 ) Deferred tax (expense) benefit: Federal 5.8 19.0 (15.0 ) State — — — Non-U.S. — — — Total deferred tax (expense) benefit 5.8 19.0 (15.0 ) Total income tax (expense) benefit $ 12.9 $ 12.3 $ (36.5 ) A reconciliation of taxes calculated using the 35% U.S. statutory rate (the tax rate at which the majority of OneBeacon's worldwide operations are taxed) to the income tax expense on pre-tax income from continuing operations follows: Year ended December 31, 2015 2014 2013 ($ in millions) Tax expense at the U.S. statutory rate $ (8.9 ) $ (14.8 ) $ (64.1 ) Differences in taxes resulting from: Non-U.S. earnings, net of foreign taxes 19.3 19.6 20.9 Tax reserve adjustments (1.7 ) 4.1 (1.0 ) Tax exempt interest and dividends 2.6 2.5 2.4 Change in valuation allowance 0.5 (0.2 ) 5.9 Other, net 1.1 1.1 (0.6 ) Total income tax (expense) benefit on pre-tax income from continuing operations $ 12.9 $ 12.3 $ (36.5 ) The non-U.S. component of pre-tax income from continuing operations which, relates to interest and underwriting income, was $57.2 million , $58.0 million and $60.3 million , respectively, for the years ended December 31, 2015 , 2014 and 2013 . The change in valuation allowance during 2013 was driven by a $6.6 million decrease due to the restructuring of a surplus note with Houston General Insurance Exchange ("HGIE"), a reciprocal which is included in the Company's consolidated results as a VIE. The income tax expense related to pre-tax income from continuing operations for the years ended December 31, 2015 , 2014 and 2013 represented net effective tax rates of (51.0)% , (29.1)% and 19.9% , respectively. For the years ended December 31, 2015 , 2014 and 2013 , the effective tax rate on non-U.S. income was 1.3% , 1.3% and 0.5% , respectively, and the effective tax rate on U.S. income or loss was 42.6% , 83.7% and 29.5% , respectively. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes. An outline of the significant components of OneBeacon's deferred tax assets and liabilities follows: December 31, 2015 2014 ($ in millions) Deferred income tax assets related to: U.S. net operating loss carryforwards $ 63.7 $ 56.3 Unearned premiums 37.2 38.1 Discounting of loss and LAE reserves 26.7 41.3 Tax credit carryforwards 16.9 13.4 Compensation and bonus accruals 15.3 10.8 Sale of Runoff Business 12.6 12.6 Deferred compensation plans 6.0 6.4 Fixed assets 4.2 4.0 Investment basis differences 3.2 6.4 Allowance for doubtful accounts 0.7 0.7 Non-U.S. net operating loss carryforwards 0.4 0.4 Other accrued compensation 0.1 0.2 Accrued rent — 3.9 Other items 0.2 5.4 Total gross deferred income tax assets 187.2 199.9 Less valuation allowance (1.3 ) (1.8 ) Total net deferred income tax assets 185.9 198.1 Deferred income tax liabilities related to: Deferred acquisition costs 35.2 32.2 Net unrealized investment gains 6.5 26.9 Prepaid pension 3.5 2.6 Other items 0.5 4.6 Total gross deferred income tax liabilities 45.7 66.3 Net deferred tax asset $ 140.2 $ 131.8 OneBeacon's deferred tax assets are net of federal and non-U.S. valuation allowances and, to the extent they relate to non-U.S. jurisdictions, they are shown at year-end exchange rates. Of the $1.3 million valuation allowance as of December 31, 2015 , $0.4 million relates to deferred tax assets on net operating losses (“NOLs”) in Luxembourg subsidiaries that are not expected to have significant income in the future, and $0.9 million relates to deferred tax assets of HGIE, which files its own tax return. OneBeacon records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in the valuation allowance are included in income tax expense in the period of the change in estimate is made. In determining whether or not to record a valuation allowance, or subsequent changes in estimate, OneBeacon considers factors such as prior earnings history, expected future earnings, carryback and carryforward periods as well as prudent and economically feasible strategies that, if executed, would result in the realization of a deferred tax asset. It is possible that certain planning strategies or projected earnings in certain subsidiaries may not be feasible to utilize the entire deferred tax asset, which could result in material changes to OneBeacon’s net deferred tax assets and related tax expense. OneBeacon believes that, based upon its prior earnings history, expected future earnings, reversing temporary differences and capacity for carry-back of losses, and available planning strategies it is more likely than not that the net deferred tax asset balances (net of valuation allowance) carried as of December 31, 2015 and 2014 will be realized. Net operating loss ("NOL") carryforwards as of December 31, 2015 and the expiration dates are as follows: December 31, 2015 United States Luxembourg Total ($ in millions) Net operating loss carryforwards by year: 2016 $ — $ — $ — From years 2017 to 2024 1.6 — 1.6 From years 2025 to 2035 180.3 — 180.3 No expiration date — 1.3 1.3 Total net operating loss carryforwards $ 181.9 $ 1.3 $ 183.2 December 31, 2015 United States Luxembourg Total ($ in millions) Gross deferred tax asset for NOL carryforwards $ 63.7 $ 0.4 $ 64.1 Valuation allowance for NOL carryforwards (0.6 ) (0.4 ) (1.0 ) Net deferred tax asset for NOL carryforwards $ 63.1 $ — $ 63.1 OneBeacon does not anticipate future taxable income in Luxembourg. Therefore, OneBeacon does not believe that it is more likely than not that these losses will be realized and has recorded a full valuation allowance against the tax benefits associated with these NOLs. Effective January 1, 2013, the Luxembourg statutory tax rate increased from 28.80% to 29.22% . As of December 31, 2015 , there were U.S. net operating loss carryforwards of approximately $181.9 million , which begin to expire in 2021. Included in these tax losses are losses of $0.4 million subject to an annual limitation on utilization under Internal Revenue Code Section 382. In addition, the losses include NOLs of $1.8 million related to HGIE, a reciprocal, which files its own tax return. As of December 31, 2015 , OBFS also had low income housing tax credits of $14.6 million which begin to expire in 2031 and alternative minimum tax credit carryovers of $1.8 million which do not expire. Recognition of the benefit of a given tax position is based upon whether or not a company determines that it is more likely than not that a tax position will be sustained upon examination based upon the technical merits of the position. In evaluating the more-likely-than-not recognition threshold, OneBeacon must presume that the tax position will be subject to examination by a taxing authority with full knowledge of all relevant information. If the recognition threshold is met, then the tax position is measured at the largest amount of benefit that is more than 50% likely of being realized upon ultimate settlement. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Permanent differences (1) Temporary differences (2) Interest and penalties (3) Total ($ in millions) January 1, 2013 $ 7.6 $ 23.6 $ 7.8 $ 39.0 Changes in prior year tax positions — — 1.0 1.0 Tax positions taken during the current year — (7.0 ) — (7.0 ) Lapse in statute of limitations — — — — Settlements with tax authorities — — (0.4 ) (0.4 ) December 31, 2013 $ 7.6 $ 16.6 $ 8.4 $ 32.6 Changes in prior year tax positions (2.2 ) (0.8 ) (1.9 ) (4.9 ) Tax positions taken during the current year — 7.3 — 7.3 Lapse in statute of limitations — — — — Settlements with tax authorities — — — — December 31, 2014 $ 5.4 $ 23.1 $ 6.5 $ 35.0 Changes in prior year tax positions — (12.4 ) 1.7 (10.7 ) Tax positions taken during the current year — — — — Lapse in statute of limitations — — — — Settlements with tax authorities — — — — December 31, 2015 $ 5.4 $ 10.7 $ 8.2 $ 24.3 _______________________________________________________________________________ (1) Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate. (2) Represents the amount of unrecognized tax benefits that, if recognized, would create a temporary difference between the reported amount of an item in OneBeacon's Consolidated Balance Sheet and its tax basis. (3) Net of tax benefit. If recognized, $13.6 million (tax plus interest and penalties) would be recorded as a reduction to income tax expense. Also included in the balance as of December 31, 2015 are $10.7 million of tax positions for which ultimate deductibility is highly certain but the timing of deductibility is uncertain. Because of the impact of deferred tax accounting, other than interest and penalties, the disallowance of the shorter deductibility period would not affect the effective tax rate but would accelerate the payment of cash to the taxing authority to an earlier period. OneBeacon classifies all interest and penalties on unrecognized tax benefits as part of income tax expense. During the years ended December 31, 2015 , 2014 and 2013 , OneBeacon recognized $1.7 million , $1.1 million and $1.0 million , respectively, of interest expense, net of federal benefit. The balance of accrued interest as of December 31, 2015 and 2014 is $8.2 million and $6.5 million , respectively, net of any tax benefit. 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 now been agreed to and resolved with the Joint Committee on Taxation ("JCT"). The total assessment, including interest is $3.3 million . However, $2.7 million of the 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 will not affect the effective tax rate. 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. Subsequent to December 31, 2015, OneBeacon received Form 870-AD (Offer to Waive Restrictions on Assessment and Collection Tax Deficiency and to Accept Overassessment) from the IRS Appeals Office relating to the examination of tax years 2007, 2008 and 2009. All disputed items have now been agreed to and resolved with the JCT. The estimated total overpayment, including interest, utilization of alternative minimum and foreign tax credit carryovers and capital loss carrybacks, is $4.0 million . However, $2.7 million of the 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. As the receipt of the Form 870-AD described above represents formal settlement, OneBeacon expects to record a tax benefit of approximately $12 million in the first quarter of 2016 related to the tax settlement of the IRS examination for tax years 2007, 2008 and 2009. On September 2, 2013, the IRS commenced an examination of OneBeacon's U.S. income tax returns for 2010, 2011 and 2012. On November 18, 2015, OneBeacon received Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2010, 2011 and 2012. The estimated total overpayment is $1.1 million . OneBeacon does not expect the resolution of this examination to result in a material change to its financial position. Net cash (refunds) payments for federal, state and non-U.S. income taxes, totaled $(6.2) million , $2.1 million and $5.6 million for the years ended December 31, 2015 , 2014 and 2013 , respectively.

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 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. 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 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 anticipates the majority of plan assets to be distributed within 12 months of the receipt of the favorable determination letter by way of annuity contract purchases and/or lump sum payments to plan participants. As part of the normal remeasurement process as of December 31, 2015, the Company considered the significant progress made throughout the year on the termination and determined that using assumptions consisting of the termination value were appropriate for that Qualified Plan as the likelihood is remote that the execution of the plan termination will be blocked by third parties and that the plan will return from termination. Therefore, as of December 31, 2015, the Company has estimated the projected benefit obligation of the Qualified Plan on a termination valuation basis based on the combination of the estimated cost of annuity contract purchases plus lump sum payments, which are anticipated to be made in the first quarter of 2016. The Company notes that the purchase of annuities, which is currently in final stages of the bidding process, is subject to availability of such contracts, with a creditworthy insurance company, at negotiated market terms deemed acceptable to the plan Sponsor. The Company does not expect the impact of the final termination to be material on the Company's financial position. 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. The following tables set forth the obligations and funded status, assumptions, plan assets and cash flows associated with the Plans as of December 31, 2015 and 2014 : December 31, 2015 2014 ($ in millions) Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 119.7 $ 102.9 Service cost 0.9 0.6 Interest cost 4.6 4.7 Settlement gain (1) (1.8 ) — Special termination benefits expense — 0.3 Assumption changes (3.5 ) 17.5 Actuarial loss 0.9 1.1 Benefits and expenses paid with plan assets (13.7 ) (5.2 ) Benefits paid directly by OneBeacon (2.2 ) (2.2 ) Remeasurement due to plan termination (2) 4.6 — Projected benefit obligation at end of year $ 109.5 $ 119.7 Change in plan assets: Fair value of plan assets at beginning of year $ 146.0 $ 142.8 Actual return on plan assets 7.5 8.4 Benefits and expenses paid (13.7 ) (5.2 ) Fair value of plan assets at end of year $ 139.8 $ 146.0 Funded status at end of year $ 30.3 $ 26.3 ___________________________________________________________________________ (1) During the fourth quarter of 2015, OneBeacon triggered settlement accounting for the Qualified Plan as the total lump sum payments exceeded the service plus interest costs, resulting in a $1.8 million adverse effect on accumulated other comprehensive income. (2) As noted in the paragraph preceding this table, the projected benefit obligation was valued on a plan termination basis as of December 31, 2015. The funded status of the consolidated pension plans as of December 31, 2015 was $30.3 million , which represents an over-funding of $55.8 million related to the Qualified Plan and an under-funding of $25.5 million related to the Non-qualified Plan. The Non-qualified Plan, which is unfunded, does not hold any assets. OneBeacon has set aside $18.6 million in an irrevocable rabbi trust for the benefit of Non-qualified Plan participants. Assets held in the rabbi trust are not reflected in the funded status of the consolidated pension plans as presented but are included in other assets in the consolidated balance sheet. The Company currently anticipates transferring some or all of the excess invested assets of the Qualified Plan into a qualified replacement plan subsequent to the plan termination. The Company has also applied for a private letter ruling from the IRS related to the wind-down of potential post-termination obligations of the Qualified Plan. Amounts recognized in the financial statements as of December 31, 2015 and 2014 consist of: December 31, 2015 2014 ($ in millions) Net balance sheet asset recorded in other assets $ 55.8 $ 53.4 Net balance sheet liability recorded in other liabilities (25.5 ) (27.1 ) Net amount recognized in the financial statements $ 30.3 $ 26.3 Information for the Non-qualified Plan, which had accumulated benefit obligations in excess of plan assets, was as follows: December 31, 2015 2014 ($ in millions) Projected benefit obligation $ 25.5 $ 27.1 Accumulated benefit obligation $ 25.5 $ 27.1 Fair value of plan assets $ — $ — Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets, was as follows: December 31, 2015 2014 ($ in millions) Projected benefit obligation $ 84.0 (1) $ 92.6 Accumulated benefit obligation $ 84.0 (1) $ 92.6 Fair value of plan net assets $ 139.8 $ 146.0 ___________________________________________________________________________ (1) Measured on a plan termination basis The amounts recognized in accumulated other comprehensive loss on a pre-tax basis for the years ended December 31, 2015 and 2014 were as follows: December 31, 2015 2014 ($ in millions) Accumulated other comprehensive income (loss) at beginning of year $ (8.0 ) $ 10.5 Increase (decrease) in accumulated other comprehensive income (loss): Amortization of net actuarial gains recognized during the year 1.3 0.3 Net actuarial losses occurring during the year (1) (1.3 ) (18.8 ) Accumulated other comprehensive loss at end of year $ (8.0 ) $ (8.0 ) _______________________________________________________________________________ (1) Net actuarial losses resulted from changes in assumptions in estimating the projected benefit obligation as well as changes in investment returns and demographic experience different than those assumed. The 2015 amount reflects the valuation of the Qualified Plan on a termination basis. The amount in accumulated other comprehensive loss, on a pre-tax basis, that has not yet been recognized as a component of net periodic benefit cost for the year ended December 31, 2015 , is attributable to net losses. During the year ending December 31, 2016 , OneBeacon expects $1.1 million will be amortized from accumulated other comprehensive loss into net periodic benefit cost. The components of net periodic benefit cost (income) for the years ended December 31, 2015 , 2014 and 2013 were as follows: December 31, 2015 2014 2013 ($ in millions) Service cost $ 0.9 $ 0.6 $ 0.8 Interest cost 4.6 4.7 4.2 Expected return on plan assets (8.7 ) (8.5 ) (7.1 ) Amortization of net actuarial losses recognized during the year 1.3 0.3 0.9 Net periodic pension income before special termination benefits (1.9 ) (2.9 ) (1.2 ) Special termination benefits expense (1) — 0.3 0.3 Total net periodic benefit income $ (1.9 ) $ (2.6 ) $ (0.9 ) _______________________________________________________________________________ (1) Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force. Assumptions The weighted average assumptions for the Plans used to determine benefit obligations as of December 31, 2015 and 2014 were as follows: December 31, 2015 2014 Discount rate 3.22 % 3.91 % The weighted average assumptions used to determine net periodic benefit cost for the years ended December 31, 2015 and 2014 were as follows: December 31, 2015 2014 Discount rate 3.91 % 4.66 % Expected long-term rate of return on plan assets 6.00 % 6.00 % OneBeacon's discount rate assumptions used to account for the Plans reflect the rates at which the benefit obligations could be effectively settled. The December 31, 2015 discount rate used to determine benefit obligations also reflects the Qualified Plan valued on a plan termination basis. In addition to consideration of published yields for high quality long-term corporate bonds, U.S. Treasuries and insurance company annuity contract pricings, consideration was given to cash flow matching analyses. OneBeacon performed an analysis of expected long-term rates of return based on the allocation of its Qualified Plan assets as of December 31, 2014 and 2013 to develop expected rates of return for 2015 and 2014 , respectively, for each significant asset class or economic indicator. A range of returns was developed based both on forecasts and on broad-market historical benchmarks for expected return, correlation, and volatility for each asset class. Plan Assets The Qualified Plan's assets are managed internally by OneBeacon. Given the anticipated Plan termination and considering the expected payments to purchase annuities or for lump sum distributions, the invested assets were reallocated during 2015 to consist substantially of U.S. Treasury securities. The Qualified Plan's investments are stated at fair value. Many factors are considered in arriving at fair market value. In general, fixed maturity investments such as corporate bonds and government securities are valued based on yields currently available on comparable securities of issuers with similar credit ratings. U.S. Treasury securities and shares of common and preferred stock are valued at quoted market prices when available. Convertible fixed maturity investments are valued based on quoted market prices, analysis of listed markets and use of sensitivity analyses. Registered investment companies are valued at the net asset value as reported by the fund at year-end. The fair value of the Qualified Plan's invested assets and their related inputs as of December 31, 2015 and 2014 by asset category were as follows: Fair value at December 31, 2015 Level 1 Level 2 Level 3 Fixed maturity investments $ 132.4 $ 132.4 $ — $ — Short-term investments 7.0 7.0 — — Total $ 139.4 $ 139.4 $ — $ — Fair value at December 31, 2014 Level 1 Level 2 Level 3 Fixed maturity investments $ 24.2 $ — $ 24.2 $ — Short-term investments 5.2 4.8 0.4 — Common equity securities: Consumer 35.2 35.2 — — Financials 17.1 17.1 — — Energy 13.9 13.9 — — Basic Materials 11.0 11.0 — — Utilities 2.6 2.6 — — Other 21.2 21.2 — — Common equity securities 101.0 101.0 — — Convertible fixed maturity investments: Consumer 4.1 — 4.1 — Financials 3.1 — 3.1 — Basic Materials 1.4 — 1.4 — Energy 0.8 — 0.8 — Other 3.4 — 3.4 — Convertible fixed maturity investments 12.8 — 12.8 — Total $ 143.2 $ 105.8 $ 37.4 $ — There were no transfers between Levels 1, 2 or 3 during the years ended December 31, 2015 and 2014 . The Qualified Plan's asset allocations as of December 31, 2015 and 2014 by asset category were as follows: Plan Assets at December 31, 2015 2014 Fixed maturity investments 95.0 % 16.9 % Common equity securities — 70.6 Convertible fixed maturity investments — 8.9 Cash and short-term investments 5.0 3.6 Total 100.0 % 100.0 % As described above, the Qualified Plan's investment securities are exposed to various risks such as interest rate, market, and credit risks. However, as a result of the Qualified Plan termination, substantially all assets as of December 31, 2015 are invested in United States Treasury securities which significantly limits the exposure to these risks. Cash Flows OneBeacon does not expect to make a contribution to its Qualified Plan in 2016 . As noted above, the termination will result in significant cash payments for the purchase of annuity and lump sum payments. OneBeacon anticipates contributing $2.1 million to the Non-qualified Plan in 2016 , for which OneBeacon has assets held in a rabbi trust. The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Expected Benefit Payments ($ in millions) 2016 (1) $ 86.8 2017 2.1 2018 2.1 2019 2.0 2020 2.0 2021 – 2025 8.9 _______________________________________________________________________________ (1) Primarily reflects the anticipated payout related to annuity purchases and lump sum payments resulting from the termination of the Qualified Plan Other Benefit Plans OneBeacon sponsors an employee savings plan (defined contribution plan) covering the majority of employees. The contributory plan provides qualifying employees with matching contributions of 50% of the first 6% of salary (subject to federal limits on allowable contributions in a given year). Total expense for the plan was $3.0 million , $2.7 million and $2.3 million in the years ended December 31, 2015 , 2014 and 2013 , respectively. The employee savings plan includes an employee stock ownership component. See Note 9—"Employee Share-Based Incentive Compensation Plans." OneBeacon had a post-employment benefit liability related to disability and health benefits available to former employees that are no longer employed by the Company of $4.1 million and $4.8 million as of December 31, 2015 and 2014 , respectively. OneBeacon also had a post-employment benefit liability related to death benefits to beneficiaries of former executives that are no longer employed by the Company of $12.5 million and $12.9 million as of December 31, 2015 and 2014 , respectively. OneBeacon has set aside funds to satisfy its obligation in a Rabbi Trust of $33.9 million and $33.2 million as of December 31, 2015 and 2014 , respectively.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Share-Based Incentive Compensation Plans	Employee Share-Based Incentive Compensation Plans The OneBeacon Long-Term Incentive Plan (the "Incentive Plan") provides for granting various types of share-based incentive awards including performance shares, options, share appreciation rights and restricted shares to certain key employees of OneBeacon. The Incentive Plan was adopted by the Board of Directors (the "Board") in October 2006. In 2007, the Board and shareholders approved the 2007 OneBeacon Long-Term Incentive Plan (the "2007 Incentive Plan"). The 2007 Incentive Plan provides for all of the awards referenced above as well as restricted stock units ("RSUs"). Awards are granted under the 2007 Incentive Plan, which also reflects amendments from 2011. OneBeacon's share-based compensation plans include performance shares and restricted shares, 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 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. 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 $7.7 million , $7.5 million and $11.9 million for the years ended December 31, 2015 , 2014 and 2013 , respectively. Performance Shares Performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. In general, grants are earned, subject to the attainment of pre-specified performance goals, at the end of a three-year period or as otherwise determined by the Compensation Committee of the Board and are valued based on the market price of an underlying OneBeacon common share at the time awards are paid. Results that significantly exceed pre-specified targets can result in a performance share payout of up to 200% of granted shares whereas results significantly below target could result in no payout. Compensation expense, based on the estimated performance share payout, is recognized ratably over the performance period. For awards granted during the year ended December 31, 2013 , the targeted performance goal for full payment of the outstanding performance shares is the attainment of a growth in book value per share ("GBVPS") of 13% for the 2013 - 2015 performance cycle. At a GBVPS of 6% or less, no performance shares would be earned and at a GBVPS of 20% or more, 200% of performance shares would be earned. For awards granted during the year ended December 31, 2014 , the targeted performance goal for full payment of the outstanding performance shares is the attainment of a GBVPS of 14% for the performance cycle 2014 - 2016 . At a GBVPS of 7% or less, no performance shares would be earned and at a GBVPS of 21% or more, 200% of performance shares would be earned. For awards granted during the year ended December 31, 2015 , the targeted performance goal for full payment of the outstanding performance shares is the attainment of a GBVPS of 13% for the performance cycle 2015 - 2017 . At a GBVPS of 6% or less, no performance shares would be earned and at a GBVPS of 20% or more, 200% of performance shares would be earned. The following summarizes performance share activity for performance shares for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Target Performance Shares outstanding Accrued expense Target Performance Shares outstanding Accrued expense Target Performance Shares outstanding Accrued expense ($ in millions) Beginning of period 517,470 $ 3.4 493,421 $ 4.0 563,190 $ 1.2 Payments and deferrals (1) (181,290 ) (1.5 ) (142,138 ) (1.0 ) (238,658 ) — New awards 154,887 — 165,800 — 179,000 — Forfeitures and net change in assumed forfeitures (41,632 ) (0.1 ) 387 — (10,111 ) (0.1 ) Expense recognized — (0.4 ) — 0.4 — 2.9 End of period 449,435 $ 1.4 517,470 $ 3.4 493,421 $ 4.0 _______________________________________________________________________________ (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% . No payments were made in 2013 for the 2010-2012 performance cycle as the performance factor was zero . The following summarizes performance shares outstanding and accrued performance share expense as of December 31, 2015 for each performance cycle: Target Performance Shares outstanding Accrued expense ($ in millions) Performance cycle: 2013 – 2015 167,300 $ 0.6 2014 – 2016 142,710 0.1 2015 – 2017 146,659 0.7 Subtotal 456,669 1.4 Assumed forfeitures (7,234 ) — Total as of December 31, 2015 449,435 $ 1.4 If 100% of the outstanding performance shares had been vested on December 31, 2015 , the total additional compensation cost to be recognized would have been $1.3 million , based on current accrual factors (common share price, accumulated dividends and payout assumptions) as of December 31, 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 $1.1 million , which are scheduled to cliff vest in full on January 1, 2018. On March 1, 2012, OneBeacon issued shares of restricted stock to certain employees. Of these restricted shares, 142,500 shares vested on February 28, 2014 and the remaining 138,500 restricted shares vested on February 28, 2015. On May 25, 2011, OneBeacon issued 630,000 shares of stock, of which 157,500 of these restricted shares vested on February 22, 2014 , 157,500 restricted shares vested on February 22, 2015, and the remaining 315,000 restricted shares held by the CEO are scheduled to vest in equal installments on February 22, 2016 and 2017. The restricted shares contain dividend participation features and therefore are considered participating securities. The following summarizes restricted shares activity for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value ($ in millions) Beginning of period 612,500 $ 3.5 915,000 $ 6.5 927,000 $ 9.6 New awards 75,950 1.1 — — — — Forfeitures (9,728 ) (0.1 ) (2,500 ) — (3,000 ) — Vested (296,000 ) — (300,000 ) — (9,000 ) — Expense recognized — (2.0 ) — (3.0 ) — (3.1 ) End of period 382,722 $ 2.5 612,500 $ 3.5 915,000 $ 6.5 Restricted shares that vested during the years ended December 31, 2015 and 2014 had a grant date fair value of $4.3 million for each period. Restricted shares that vested during the year ended December 31, 2013 had a grant date fair value of $0.1 million . As of December 31, 2015 , unrecognized compensation expense of $2.5 million related to restricted stock awards is expected to be recognized over a weighted-average period of 1.4 years. Restricted Stock Units During the year ended December 31, 2015 , 226,778 RSUs were issued, with outstanding RSUs, net of forfeitures, at 200,194 as of December 31, 2015 . The RSUs are scheduled to cliff 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 amortized over the three year vesting period, was $0.8 million for the year ended December 31, 2015 . Other Share-Based Compensation OneBeacon sponsors a defined contribution plan, the OneBeacon 401(k) Savings and Employee Stock Ownership Plan ("KSOP"). Under the KSOP, participants have the ability to invest their balances in several different investment options, including the common shares of White Mountains and the common shares of the Company. The employee stock ownership component of the KSOP provides all participants with an annual base contribution in common shares of the Company equal to 3% of their salary, up to the applicable Social Security wage base (or $118,500 with respect to 2015). Additionally, those participants not otherwise eligible to receive certain other Company benefits can earn a variable contribution up to an additional 6% of their salary, capped at the annual covered compensation limits ( $265,000 for 2015), contingent upon OneBeacon's performance. The variable contribution amounts for eligible participants constituted approximately 3% , 2% and 4% , respectively, of salary for the years ended December 31, 2015 , 2014 and 2013 . OneBeacon has recorded $5.4 million , $4.1 million and $6.0 million , respectively, in compensation expense to pay benefits and allocate common shares to participants' accounts for the years ended December 31, 2015 , 2014 and 2013 . As of December 31, 2015 and 2014 , the KSOP owned less than 3% of either of the total White Mountains common shares outstanding or the total Company common shares outstanding. All common shares held by the KSOP are considered outstanding for earnings (loss) per share computations. As of December 31, 2015 , the Company has no outstanding share appreciation rights.

Common Shareholders' Equity

Common Shareholders' Equity	12 Months Ended
	Dec. 31, 2015
Equity [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 year ended December 31, 2015 , 166,368 shares were repurchased under the share repurchase authorization for $2.1 million at an average share price of $12.62 . No shares were repurchased under the share repurchase authorization during the years ended December 31, 2014 and 2013 . The amount of authorization remaining is $85.6 million as of December 31, 2015 . During the years ended December 31, 2015 , 2014 , and 2013 the Company repurchased 112,051 , 106,366 , and 3,300 , common shares, respectively, for $1.6 million , $1.8 million and less than $0.1 million during the years ended December 31, 2015 , 2014 , and 2013 , respectively, to satisfy employee income tax withholding, pursuant to employee benefit plans. Shares repurchased pursuant to employee benefit plans do not fall under the board authorizations referred to above. Dividends on Common Shares During the years ended December 31, 2015 and 2014 the Company declared and paid cash dividends totaling $80.0 million and during the year ended December 31, 2013 the Company declared and paid cash dividends totaling $80.2 million , or $0.84 per common share of regular quarterly cash dividends for each year. Accumulated Other Comprehensive Income (Loss) The pre-tax components of the Company's other comprehensive income (loss) and the related income tax benefit (expense) are as follows: Year ended December 31, 2015 2014 2013 ($ in millions) Net change in benefit plan assets and obligations $ — $ (18.5 ) $ 31.7 Income tax benefit (expense) — 6.5 (11.1 ) Net change in benefit plan assets and obligations, net of tax $ — $ (12.0 ) $ 20.6

Statutory Capital and Surplus

Statutory Capital and Surplus	12 Months Ended
	Dec. 31, 2015
Insurance [Abstract]
Statutory Capital and Surplus	Statutory Capital and Surplus OneBeacon's U.S. insurance operations are subject to regulation and supervision in each of the states where they are domiciled and licensed to conduct business. Generally, state regulatory authorities have broad supervisory and administrative powers over such matters as licenses, standards of solvency, premium rates, policy forms, investments, security deposits, methods of accounting, form and content of financial statements, reserves for unpaid loss and LAE, reinsurance, minimum capital and surplus requirements, dividends and other distributions to shareholders, periodic examinations, and annual and other report filings. In general, such regulation is for the protection of policyholders rather than shareholders. State insurance departments have established the insurer solvency laws and regulatory infrastructure to maintain accredited status with the National Association of Insurance Commissioners ("NAIC"). A key solvency-driven NAIC accreditation requirement is a state's adoption of risk-based capital ("RBC") requirements. As of December 31, 2015, OneBeacon's U.S. insurance operating subsidiaries exceeded their respective RBC requirements. The Insurance Act 1978 of Bermuda and related regulations, as amended (the “Insurance Act”), regulates the insurance businesses of Bermuda domiciled insurers. Under the Insurance Act, insurers are required to maintain available statutory capital and surplus at a level equal to or in excess of its enhanced capital requirement which is established by reference to either a Bermuda Solvency Capital Requirement ("BSCR") model or an approved internal capital model. Generally, the Bermuda Monetary Authority (“BMA”) has broad supervisory and administrative powers over such matters as licenses, standards of solvency, investments, methods of accounting, form and content of financial statements, minimum capital and surplus requirements, and annual and other report filings. OneBeacon’s U.S. combined statutory surplus was $622.3 million and $721.5 million as of December 31, 2015 and 2014, respectively. OneBeacon's combined U.S. statutory net income (loss) for the years ended December 31, 2015, 2014 and 2013 was $44.5 million , $(14.2) million and $100.1 million , respectively. The minimum policyholders' surplus necessary to satisfy OneBeacon's top tier regulated U.S. insurance operating subsidiary, ASIC, regulatory requirements was $117.7 million as of December 31, 2015, which equals the authorized control level of the NAIC risk-based capital of OneBeacon’s primary top tier regulated operating subsidiary. OneBeacon’s statutory capital and surplus for Split Rock was $249.5 million and $122.6 million as of December 31, 2015 and 2014, respectively, which met Bermuda's statutory capital and surplus requirements. Split Rock reported $45.5 million , $46.2 million and $(38.7) million of statutory net income (loss) for the years ended December 31, 2015, 2014 and 2013, respectively. The principal differences between OneBeacon's combined U.S. and Split Rock's statutory amounts, and the amounts reported in accordance with GAAP include deferred acquisition costs, deferred taxes and market value adjustments for debt securities. OneBeacon's insurance subsidiaries' statutory policyholders' surplus as of December 31, 2015 was in excess of the minimum requirements of relevant state and Bermuda insurance regulations. Dividend Capacity Under the insurance laws of the states and jurisdictions under which OneBeacon's insurance operating subsidiaries are domiciled, an insurer is restricted with respect to the timing and the amount of dividends it may pay without prior approval by regulatory authorities. Accordingly, there can be no assurance regarding the amount of such dividends that may be paid by such subsidiaries in the future. ASIC has the ability to pay dividends to its immediate parent during any 12-month period without the prior approval of regulatory authorities in an amount set by formula based on the lesser of net investment income, as defined by statute, or 10% of statutory surplus, in both cases as most recently reported to regulatory authorities, subject to the availability of earned surplus and subject to dividends paid in prior periods. Based upon the formula described above, most recently calculated as of December 31, 2015, ASIC has the ability to pay $26.6 million of dividends during 2016 without prior approval of regulatory authorities. As of December 31, 2015, ASIC had $622.3 million of statutory surplus and $68.3 million of earned surplus. During the year ended December 31, 2015, ASIC paid $44.9 million of dividends to its immediate parent and redeemed and retired common shares held by its immediate parent at an aggregate price of $66.0 million . Split Rock has the ability to make distributions (including share repurchases) and pay dividends without the prior approval of the Bermuda Monetary Authority, provided it does not reduce its total statutory capital, as shown in its previous financial year’s statutory financial statements, by 15% or more. During 2016, Split Rock has the ability to pay dividends and make distributions without the prior approval of regulatory authorities, subject to meeting all appropriate liquidity and solvency requirements, of up to $37.4 million , which is equal to 15% of its December 31, 2015 statutory capital and surplus. During the year ended December 31, 2015, Split Rock made no capital distributions and paid no dividends to its immediate parent. During the year ended December 31, 2014, Split Rock paid $10.0 million of capital distributions and $10.0 million of dividends to its immediate parent. During the year ended December 31, 2015, OneBeacon Ltd., through an intermediary holding company, contributed $85.0 million to Split Rock as additional paid-in capital. On December 23, 2014, Bedivere, distributed ASIC to its immediate parent at a value of $700.5 million as part of the Runoff Transaction. Bedivere also distributed $151.2 million of cash and other investments to its immediate parent in accordance with the prescribed minimum capital to be included in the company at the time of its sale to Armour, as approved by the Pennsylvania Insurance Department. During the years ended December 31, 2015 and 2014, the Company's unregulated insurance operating subsidiaries paid $5.3 million and $4.8 million , respectively, of dividends to their immediate parent. As of December 31, 2015, OneBeacon's unregulated insurance operating subsidiaries had $104.4 million of net unrestricted cash, short-term investments fixed maturity investments and surplus notes classified as other investments which had a fair value of $51.5 million and a par value of $101.0 million . As described in Note 10—"Common Shareholders' Equity," during the years ended December 31, 2015 and 2014 OneBeacon Ltd. declared and paid regular quarterly dividends to its common shareholders totaling $80.0 million . During the year ended December 31, 2013 OneBeacon Ltd. declared and paid regular quarterly dividends to its common shareholders totaling $80.2 million . As of December 31, 2015, OneBeacon Ltd. and its intermediate holding companies held $65.3 million of net unrestricted cash, short-term investments and fixed maturity investments and $54.6 million of common equity securities and other investments outside of its regulated and unregulated insurance operating subsidiaries.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Segment Information	Segment Information The Company has sixteen 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, 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 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 fourth quarter of 2015, we formed a new underwriting operating segment, Financial Institutions , which provides specialty products and tailored coverages for all classes of financial institutions. Also during 2015, we restructured our 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 Products segment also includes Programs , Tuition Reimbursement , Surety , Specialty Property and Environmental , as well as the Crop and Collector Cars and Boats underwriting operating segments, which were exited in 2015 and 2013, respectively. The Specialty Industries segment is comprised of six active underwriting operating segments, representing an aggregation based on those that focus on solving the unique needs of a particular customer or industry group. During 2015, the Company further disaggregated its IMU underwriting operating segment into two separate underwriting operating segments, which are included in Specialty Industries: Ocean Marine and Inland Marine. The Specialty Industries segment also includes the Accident, Technology , Entertainment and Government Risks underwriting operating segments. 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, 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 Specialty Products Specialty Industries Consolidated ($ in millions) Year ended December 31, 2015 Earned premiums $ 560.3 $ 615.9 $ — $ 1,176.2 Loss and loss adjustment expense (310.7 ) (390.0 ) — (700.7 ) Policy acquisition expenses (100.1 ) (113.7 ) — (213.8 ) Other underwriting expenses (97.9 ) (120.3 ) — (218.2 ) Total underwriting income (loss) 51.6 (8.1 ) — 43.5 Net investment income — — 45.9 45.9 Net realized and change in unrealized investment gains — — (35.1 ) (35.1 ) Net other revenues (expenses) (0.2 ) 1.4 (1.8 ) (0.6 ) General and administrative expenses — (2.7 ) (12.7 ) (15.4 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income (loss) from continuing operations $ 51.4 $ (9.4 ) $ (16.7 ) $ 25.3 Year ended December 31, 2014 Earned premiums $ 582.1 $ 595.0 $ — $ 1,177.1 Loss and loss adjustment expense (457.9 ) (357.2 ) — (815.1 ) Policy acquisition expenses (96.2 ) (107.1 ) — (203.3 ) Other underwriting expenses (78.4 ) (100.8 ) — (179.2 ) Total underwriting income (loss) (50.4 ) 29.9 — (20.5 ) Net investment income — — 43.4 43.4 Net realized and change in unrealized investment gains — — 40.4 40.4 Net other revenues 0.9 1.1 3.8 5.8 General and administrative expenses 0.2 (2.3 ) (11.7 ) (13.8 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income (loss) from continuing operations $ (49.3 ) $ 28.7 $ 62.9 $ 42.3 Year ended December 31, 2013 Earned premiums $ 553.5 $ 566.9 $ — $ 1,120.4 Loss and loss adjustment expense (312.3 ) (309.8 ) — (622.1 ) Policy acquisition expenses (106.3 ) (102.6 ) — (208.9 ) Other underwriting expenses (97.4 ) (107.4 ) — (204.8 ) Total underwriting income 37.5 47.1 — 84.6 Net investment income — — 43.0 43.0 Net realized and change in unrealized investment gains — — 49.4 49.4 Net other revenues 0.3 1.1 29.8 31.2 General and administrative expenses — (2.4 ) (9.6 ) (12.0 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income from continuing operations $ 37.8 $ 45.8 $ 99.6 $ 183.2 Insurance Operations Investing, Financing and Corporate Specialty Products Specialty Industries Consolidated ($ in millions) December 31, 2015 Assets Total investment securities $ — $ — $ 2,591.4 $ 2,591.4 Premiums receivable 63.0 156.0 — 219.0 Reinsurance recoverables (1) 139.5 33.6 20.4 193.5 Deferred acquisition costs 49.6 51.1 — 100.7 Ceded unearned premiums 19.2 10.3 — 29.5 Other assets (2) — — 470.4 470.4 Total Assets $ 271.3 $ 251.0 $ 3,082.2 $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves (1) $ 772.2 $ 597.2 $ 20.4 $ 1,389.8 Unearned premiums 288.1 272.2 — 560.3 Funds held under insurance contracts 137.7 — — 137.7 Debt — — 274.8 274.8 Other liabilities (2) — — 237.4 237.4 Total Liabilities $ 1,198.0 $ 869.4 $ 532.6 $ 2,600.0 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 Ceded unearned premiums 7.5 10.4 — 17.9 Other assets (2) — — 478.9 478.9 Total Assets $ 299.3 $ 250.4 $ 3,028.5 $ 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 18-"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 December 31, 2015 and 2014, $20.4 million and $23.8 million , respectively, are included in both unpaid loss and loss adjustment expense reserves and reinsurance recoverable included within Investing, Financing, and Corporate resulting from that agreement. (2) Other assets and other liabilities are not separately identifiable at the segment level and have therefore been included within the investing, financing, and corporate segment. The following tables provide net written premiums, earned premiums and underwriting ratios for OneBeacon's insurance operations by reportable segment and in total for the years ended December 31, 2015 , 2014 and 2013 : Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Year ended December 31, 2015 Net written premiums $ 533.0 $ 603.6 $ 1,136.6 Earned premiums 560.3 615.9 1,176.2 Underwriting ratios: (1) Loss and LAE 55.5 % 63.3 % 59.6 % Expense 35.3 38.0 36.7 Total combined ratio 90.8 % 101.3 % 96.3 % Year ended December 31, 2014 Net written premiums $ 606.9 $ 610.0 $ 1,216.9 Earned premiums 582.1 595.0 1,177.1 Underwriting ratios: (1) Loss and LAE 78.7 % 60.1 % 69.2 % Expense 30.0 34.9 32.5 Total combined ratio 108.7 % 95.0 % 101.7 % Year ended December 31, 2013 Net written premiums $ 509.6 $ 579.0 $ 1,088.6 Earned premiums 553.5 566.9 1,120.4 Underwriting ratios: (1) Loss and LAE 56.4 % 54.7 % 55.5 % Expense 36.8 37.0 36.9 Total combined ratio 93.2 % 91.7 % 92.4 % _______________________________________________________________________________ (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.

Variable Interest Entity

Variable Interest Entity	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities (VIE)	Variable Interest Entities ("VIE") Reciprocals Reciprocals are policyholder-owned insurance carriers organized as unincorporated associations. Each policyholder insured by the reciprocal shares risk with the other policyholders. Policyholders share profits and losses in the same proportion as the amount of insurance purchased but are not subject to assessment for net losses of the reciprocal. OneBeacon has one reciprocal that was capitalized by loaning funds in exchange for a surplus note. Houston General Insurance Management Company ("HGMC"), a wholly-owned indirect subsidiary of the Company, provides management services for a fee to the reciprocal, HGIE. The surplus note, as amended, has a remaining balance of $5.0 million . The principal and interest on the remaining surplus note is repayable to HGMC only with regulatory approval. The obligation to repay principal on the note is subordinated to all other liabilities including obligations to policyholders and claimants for benefits under insurance policies. OneBeacon has no ownership interest in the reciprocal. OneBeacon has determined that HGIE qualifies as a VIE. Furthermore, OneBeacon has determined that it is the primary beneficiary as it has both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses or receive benefits of the entity that could potentially be significant to the VIE as a result of the management services provided to the reciprocal and the funds loaned to it. Accordingly, OneBeacon consolidates HGIE. As of December 31, 2015 , consolidated amounts related to HGIE included total assets of $5.1 million and total liabilities of $5.0 million . As of December 31, 2015 , the net amount of capital at risk is equal to the surplus note of $5.0 million less the accumulated losses of $0.2 million which includes accrued interest on the surplus note of $0.3 million which eliminates in consolidation.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 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 December 31, 2015 and 2014 , the fair value of OneBeacon's 2012 Senior Notes (its fixed-rate, long-term indebtedness) was $276.4 million and $286.0 million , respectively, which compared to a carrying value of $274.8 million and $274.7 million as of December 31, 2015 and 2014 respectively. The fair value measurement of the 2012 Senior Notes is classified as Level 2 in the valuation hierarchy and determined based on the closing market price of the 2012 Senior Notes at the end of the fiscal quarter.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Disclosures	Related Party Disclosures White Mountains In 2006, White Mountains sold 27.6 million or 27.6% of the Company's common shares in an initial public offering. Prior to the initial public offering, OneBeacon was a wholly-owned subsidiary of White Mountains. As of December 31, 2015 , White Mountains owned 75.5% of the Company's outstanding common shares. Separation Agreement In connection with the initial public offering, the Company entered into a separation agreement dated November 14, 2006 with White Mountains (the "Separation Agreement") to address a number of operational, administrative and financial matters relating to the fact that OneBeacon would no longer be a wholly-owned subsidiary of White Mountains. These matters included, among others, the administration of payroll, employee benefits programs, deferred compensation and 401(k) plans, OneBeacon's travel and logistics office, certain information technology assets and functions and certain agreements with respect to finance and tax arrangements. Pursuant to the Separation Agreement, White Mountains has agreed to indemnify the Company and its subsidiaries, as well as their current and former officers, directors and employees to the extent permitted by law, for any and all claims or actions resulting in losses, expenses or damages relating to or arising out of the business, operation or ownership of any subsidiary company or business owned by the Company or its subsidiaries that, subsequent to OneBeacon's ownership, was a subsidiary or business of White Mountains (but no longer a subsidiary or business of OneBeacon). For the years ended December 31, 2015 , 2014 and 2013 , OneBeacon recorded expenses of $0.3 million , $0.3 million and $0.4 million , respectively, and received amounts of $2.0 million for each of the years ended December 31, 2015 , 2014 and 2013 , for services under the Separation Agreement. Registration Rights Agreement In connection with the initial public offering, the Company entered into a registration rights agreement dated November 14, 2006 with White Mountains that provides that White Mountains can demand that the Company register the distribution of its common shares owned by White Mountains ("demand" registration rights). In addition, White Mountains has "piggyback" registration rights, which means that White Mountains may include its shares in any future registrations of the Company's common equity securities, whether or not that registration relates to a primary offering by the Company or a secondary offering by or on behalf of any of the Company's shareholders. These registration rights are transferable by White Mountains. The Company will pay all costs and expenses in connection with each such registration, except underwriting discounts and commissions applicable to the common shares sold by White Mountains. The registration rights agreement contains customary terms and provisions with respect to, among other things, registration procedures and rights to indemnification in connection with the registration of the common shares on behalf of White Mountains. The Company will register sales of its common shares owned by employees and directors of White Mountains pursuant to employee share or option plans, but only to the extent such registration is required for the shares to be freely tradable. Investment Management Agreement with WM Advisors Pursuant to an Amended and Restated Investment Management Agreement dated December 23, 2014 (the "Investment Management Agreement"), White Mountains Advisors LLC (“WM Advisors") supervises and directs OneBeacon's managed investment portfolio in accordance with the investment objectives, policies and restrictions described in OneBeacon's investment guidelines (the "Investment Guidelines"). Under the Investment Management Agreement, WM Advisors has full discretion and authority to make all investment decisions in respect to OneBeacon's managed investment portfolio, and to do anything which WM Advisors deems is required, appropriate or advisable in connection with the foregoing, subject to and in accordance with Investment Guidelines. The assets of OneBeacon's portfolio are held in one or more separately identifiable accounts in the custody of a bank or similar entity designated by OneBeacon and acceptable to WM Advisors. The agreement is terminable by WM Advisors or OneBeacon upon 60 days prior written notice. OneBeacon is responsible for custodial arrangements and the payment of all custodial charges and fees. OneBeacon has agreed to pay annual investment management fees generally based on the quarter-end market values held under custody as set forth in the table below: Assets Under Management Annual Fee Investment Grade Fixed Income: —Up to $1 billion 10.0 basis points —Next $1 billion 8.5 basis points —Next $3 billion 7.5 basis points —Greater than $5 billion 2.5 basis points High Yield Fixed Income 25.0 basis points Equities 100.0 basis points Hedge Funds 100.0 basis points Private Equities & Deferreds: First 2 years of fund's life (committed) 100.0 basis points Thereafter (fair value) 100.0 basis points Affordable housing credit funds: First year of fund's life (committed) 100.0 basis points Thereafter (fair value) 10.0 basis points OneBeacon incurred $3.6 million , $3.4 million and $3.4 million in total fees for investment management services provided by WM Advisors under these investment management agreements during the years ended December 31, 2015 , 2014 and 2013 , respectively. WM Advisors is also paid a quarterly fee for treasury management services computed at the annual rate of 1.75 basis points ( 0.0175% ) of the aggregate value of net assets on an annual basis. OneBeacon incurred $0.4 million in treasury management fees during each of the years ended December 31, 2015 , 2014 and 2013 . Star & Shield Insurance Exchange ASIC and Split Rock each entered into a quota share agreement effective as of November 1, 2013, to reinsure certain risks of Star & Shield Insurance Exchange (“Star & Shield”), a reciprocal insurance exchange consolidated in White Mountains, which provides private passenger auto insurance. ASIC and Split Rock recorded combined written premiums of negative $2.8 million , positive $17.3 million and positive $5.6 million in 2015, 2014 and 2013, respectively, related to Star & Shield which are included in the Specialty Products reporting segment. The quota share agreement was terminated on December 31, 2014 and the negative $2.8 million net written premiums in 2015 reflects the transfer of the remaining net unearned premium balance. Prospector Investment Management Agreement with Prospector Until June 30, 2015, Prospector Partners LLC (“Prospector”) supervised and directed the publicly-traded common equity securities and convertible fixed maturity investments portions of OneBeacon's investment portfolio and managed assets for each of the Qualified Plan, the Non-Qualified Plan, and two proprietary funds under the KSOP pursuant to separate investment management agreements with OneBeacon and each of the plans. Under the agreements, OneBeacon and the plans paid annual management fees to Prospector based on aggregate net assets under management according to the following schedule: 1.00% on the first $200 million ; 0.50% on the next $200 million ; and 0.25% on amounts over $400 million . For the years ended December 31, 2015, 2014 and 2013, OneBeacon incurred $0.4 million , $2.0 million and $2.0 million , respectively, in fees for investment management services provided by Prospector. For the years ended December 31, 2015, 2014 and 2013, the employee benefit plans incurred $0.9 million , $1.3 million and $1.2 million , respectively, in fees for investment management services provided by Prospector. Richard P. Howard was a portfolio manager of Prospector and a director of the Company until his retirement from Prospector and his resignation from the Company’s Board of Directors effective December 31, 2014. John D. Gillespie was a director of White Mountains and the founder and managing member of Prospector. In conjunction with Mr. Gillespie’s retirement from the White Mountains Board of Directors, the investment management agreement between OneBeacon and Prospector and the OneBeacon benefit plans and Prospector was terminated in June 2015. Prospector Managed Limited Partnerships Prior to fully redeeming its interests in 2015, OneBeacon held investments in limited partnerships managed by Prospector. As of December 31, 2014 and 2013, OneBeacon had $15.8 million and $14.9 million , respectively, invested in these partnerships. Under the limited partnership agreements, Prospector served as general partner and general manager of the funds and was paid a management fee by OneBeacon. In addition, OneBeacon allocated a portion of its earnings from OneBeacon's limited partnership interests to Prospector as an incentive fee. For the years ended December 31, 2015, 2014 and 2013, OneBeacon incurred $0.1 million , $0.2 million , and $0.2 million , respectively, in management fees. For the years ended December 31, 2014 and 2013, OneBeacon incurred $0.2 million and $0.5 million , respectively, in incentive fees and essentially none for the year ended December 31, 2015.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases OneBeacon leases certain office space under noncancellable operating leases expiring at various dates through 2030. Net rental expense for all of OneBeacon's locations was approximately $12.0 million , $11.1 million and $11.5 million , respectively, for the years ended December 31, 2015 , 2014 and 2013 . OneBeacon's future annual minimum rental payments required under noncancellable leases primarily for office space are $10.2 million , $9.4 million , $7.8 million , $6.7 million and $ 31.1 million for 2016, 2017, 2018, 2019 and 2020 and thereafter, respectively. As described in Note 1—"Nature of Operations and Summary of Significant Accounting Policies," in December 2011, the Company sold the majority of its then owned fixed assets and capitalized software. The Company entered into lease financing arrangements with US Bancorp and Fifth Third whereby it sold furniture and equipment and capitalized software, respectively, at a cost equal to net book value. The Company then leased the fixed assets back from US Bancorp for a lease term of five years and leased the capitalized software back from Fifth Third for a lease term of four years . The Company received cash proceeds of $23.1 million as a result of entering into the sale-leaseback transactions. In December 2015 the lease agreement with Fifth Third expired and the Company purchased the leased assets under the agreement with a remaining book value of $1.3 million for a nominal fee. At the end of the lease term with US Bancorp on December 31, 2016, the Company will purchase the leased furniture and equipment assets for a nominal fee, and all rights, title and interest will transfer back to it. As of December 31, 2015 and 2014 , the Company had a capital lease obligation of $1.7 million and $7.1 million , respectively, included within other liabilities and a capital lease asset of $2.4 million and $7.0 million , respectively, included within other assets. The underlying assets of the US Bancorp lease will continue to be depreciated over their respective useful lives and OneBeacon's future annual rental payments are $1.7 million for the year ending December 31, 2016. Other Investments OneBeacon has future binding commitments to fund certain limited partnership investments which do not have fixed funding dates and totaled $8.2 million as of December 31, 2015 . Assigned Risks As a condition of license to do business in certain states, OneBeacon's insurance operations are required to participate in mandatory shared market mechanisms. Each state dictates the types of insurance and the level of coverage that must be provided. The total amount of such business an insurer is required to accept is based on its market share of voluntary business in the state. In certain cases, OneBeacon is obligated to write business from mandatory shared market mechanisms at some time in the future based on the market share of voluntary policies it is currently writing. Underwriting results related to assigned risk plans are typically adverse and are not subject to the predictability associated with OneBeacon's voluntarily written business. Guaranty Funds Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. OneBeacon's insurance subsidiaries record guaranty fund assessments when such assessments are billed by the respective guaranty funds. In addition, OneBeacon will monitor other insurance company insolvencies and will accrue a liability when such losses are determined to be probable and the assessment amounts can be reasonably estimated. The actual amount of such assessments will depend upon the final outcome of rehabilitation proceedings and will be paid over several years. As of December 31, 2015 , the reserve for such assessments at OneBeacon's insurance subsidiaries totaled $8.5 million . 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 do 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 December 31, 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. On January 14, 2016, the Commonwealth Court upheld the Department’s December 23, 2014 order approving the Runoff Transaction. The objectors did not appeal the Commonwealth Court's decision, and the time for appeal has expired. 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 December 31, 2015, as the amount of loss, if any, cannot be reasonably estimated.

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 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 and the net effect of potentially dilutive common shares outstanding. 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 years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders $ 37.0 $ 53.5 $ 145.7 Allocation of income for participating unvested restricted common shares (0.2 ) (0.4 ) (1.4 ) Dividends paid on participating restricted common shares (0.3 ) (0.5 ) (0.8 ) Total allocation to restricted common shares (0.5 ) (0.9 ) (2.2 ) Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 36.5 $ 52.6 $ 143.5 Undistributed (over-distributed) net earnings (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 36.5 $ 52.6 $ 143.5 Dividends paid, net of restricted common share amounts (79.7 ) (79.5 ) (79.4 ) Total undistributed (over-distributed) net earnings, net of restricted common share amounts $ (43.2 ) $ (26.9 ) $ 64.1 Earnings per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.4 Weighted average unvested restricted common shares (1) (0.5 ) (0.6 ) (0.9 ) Basic and diluted earnings per share denominator 94.8 94.7 94.5 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 $ 0.38 $ 0.55 $ 1.52 Dividends declared and paid (0.84 ) (0.84 ) (0.84 ) Undistributed (over-distributed) earnings $ (0.46 ) $ (0.29 ) $ 0.68 _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event. Basic and diluted income (loss) per share amounts for discontinued operations are included in Note 18—"Discontinued Operations."

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 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 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, an indirect wholly owned subsidiary of the Company at that time, 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 December 31, 2015 and 2014 , and had a fair value of $51.5 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 December 31, 2015 and 2014 , gross loss and LAE reserves of $20.4 million and $23.8 million , respectively, related to the Runoff business were ceded to Bedivere, an indirect wholly-owned subsidiary of Armour, beginning December 23, 2014, by way of a 100% quota share agreement with ASIC. Summary of Results of Operations As described in Note 1—"Nature of Operations and Summary of Significant Accounting Policies" and Note 2—"Acquisitions and Dispositions," the results of operations for the Runoff Business have been classified as discontinued operations and are presented as such, net of related income taxes, in the statements of operations and comprehensive income and cash flows for all periods. Investing and financing activities for OneBeacon are managed on a consolidated basis reported within the Investing, Financing and Corporate segment. Therefore, no investment or financing activity is included in discontinued operations. The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations: Year ended December 31, 2015 2014 2013 ($ in millions) Net written premiums $ — $ (0.1 ) $ 0.4 Revenues Earned premiums $ — $ 0.1 $ 0.8 Other revenue (expenses) (0.7 ) — 6.3 Total revenues (0.7 ) 0.1 7.1 Expenses Loss and loss adjustment expenses — (0.7 ) 78.9 Policy acquisition expenses — 0.1 — Other underwriting expenses — 3.5 (0.2 ) Total expenses — 2.9 78.7 Pre-tax loss (0.7 ) (2.8 ) (71.6 ) Income tax benefit 0.2 1.0 25.0 Loss from discontinued operations, net of tax (0.5 ) (1.8 ) (46.6 ) (Loss) gain from sale of discontinued operations, net of tax 0.3 (18.8 ) 46.6 Net loss from discontinued operations, net of tax $ (0.2 ) $ (20.6 ) $ — 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. Loss per share amounts are based on the weighted average number of common shares including unvested restricted shares and the net effect of potentially dilutive common shares outstanding. The following table outlines the computation of loss per share for discontinued operations attributable to OneBeacon's common shareholders for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Loss attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net loss from discontinued operations attributable to OneBeacon's common shareholders $ (0.2 ) $ (20.6 ) $ — Allocation of loss for participating unvested restricted common shares — 0.1 — Net loss from discontinued operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ (0.2 ) $ (20.5 ) $ — Loss per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.4 Weighted average unvested restricted common shares (1) (0.5 ) (0.6 ) (0.9 ) Basic and diluted loss per share denominator 94.8 94.7 94.5 Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Net loss from discontinued operations attributable to OneBeacon's common shareholders per share $ — $ (0.21 ) $ — _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event. Additional Disclosures Results of Discontinued Operations Discontinued Operations Results—Year ended December 31, 2015 The loss from discontinued operations, net of tax, of $0.5 million for the year ended December 31, 2015 was the result of post-closing expenses incurred in connection with the Runoff Business. The gain from sale of discontinued operations, net of tax, of $0.3 million for the year ended December 31, 2015 represents a positive adjustment to the estimated loss on sale taking into consideration the final settlement of certain post-closing items. Discontinued Operations Results—Year ended December 31, 2014 During 2014, the Company reported $20.6 million after-tax net loss in discontinued operations related to the Runoff Transaction, which included an $18.8 million after-tax loss from sale of the Runoff Business (further described below) and a $1.8 million after-tax loss from the underwriting results of the Runoff Business. As part of the closing of the Runoff Transaction on December 23, 2014, OneBeacon provided financing in the form of surplus notes having a par value of $101.0 million , which were issued by Bedivere, one of the entities that were transferred to Armour upon the closing. At closing, the surplus notes had a fair value of $64.9 million based on an internal discounted cash flow model, resulting in a total valuation adjustment of $36.1 million , pre-tax, included in loss from sale of discontinued operations. Subsequent to the closing, the surplus notes became part of the Company's investment portfolio, categorized within other investments, and subsequent changes in the value thereon are reflected in continuing operations. Also during 2014, the Company's expectation of the treatment under the Stock Purchase Agreement of the $7.4 million reserve charge recorded during the quarter ended June 30, 2013 changed. Previously, the Company had expected that the Stock Purchase Agreement would be amended to provide for the transfer of $7.4 million of additional assets to support this reserve charge; the Stock Purchase Agreement was instead revised, in part, to increase the cap on seller financing. As a result, the $7.4 million reserve charge ( $4.8 million after-tax) was recorded as a reduction to the estimated loss on sale of discontinued operations. These changes, along with certain other adjustments, resulted in a net increase in the estimated loss on sale of $28.9 million ( $18.8 million after-tax) for the full year 2014, resulting in a pre-tax loss on sale at closing of $97.9 million ( $63.7 million after-tax) recognized since the Runoff Transaction was announced in October of 2012. Discontinued Operations Results—Year ended December 31, 2013 For the full year 2013, the Company recorded $78.9 million loss and LAE provision for the Runoff Business, which includes a $7.4 million increase in loss and LAE reserves recorded in the second quarter of 2013. The $78.9 million loss and LAE adverse development recorded in 2013 was partially offset by other revenue of $7.8 million associated with a settlement award in the second quarter of 2013 in the Safeco v. American International Group, Inc. ("AIG") class action related to AIG's alleged underreporting of workers compensation premiums to the National Workers Compensation Reinsurance Pool. The $71.5 million ( $46.5 million after-tax) increase in Runoff Business loss and LAE reserves was recorded in the fourth quarter of 2013 as a component of discontinued operations and offset by an equal after tax amount which decreased the estimated ultimate loss on sale of the Runoff Business. The terms of the Stock Purchase Agreement prescribes that the buyer assumed the risk that loss and LAE reserves develop unfavorably from September 30, 2012 onward, resulting in the offset. During the fourth quarter of 2013, the Company also increased the estimated pre-tax transaction costs associated with the Runoff Transaction which was partially offset by the accretion of interest on the original purchase price and, coupled with the $46.5 million after-tax provision for loss and LAE, resulted in a $46.6 million after-tax reduction in the ultimate loss on sale from discontinued operations in the fourth quarter and full year ended December 31, 2013. This reduction in the ultimate loss on sale was essentially offset by a $46.6 million after-tax loss included in loss from discontinued operations for the fourth quarter, driven by the adverse reserve development. Asbestos and Environmental ("A&E") Loss and LAE Reserve Activity Substantially all of the Company's unpaid loss and LAE reserves for A&E relate to operations that were sold as part of the Runoff Transaction. Surplus Notes In the fourth quarter of 2014, 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. The surplus notes, issued by one of the transferred entities, Bedivere (“Issuer”), were in the form of both seller priority and pari passu notes. Under the contractual terms of both the seller priority and pari passu notes, scheduled interest payments accrue at 6% until the scheduled maturity date of March 15, 2020 and at a floating interest rate thereafter, should any principal remain outstanding. As required by the Pennsylvania Insurance Department ("PID"), interest on the notes is not compounding. The notes restrict the Issuer's ability to make distributions to the holders of its equity interest. All such distributions are prohibited while the seller priority note is outstanding, and while the pari passu note is outstanding, distributions are permitted only if the Issuer concurrently repays a pro rata amount of any outstanding principal on the pari passu note. Pursuant to the notes, the Issuer shall seek to redeem the notes annually each March 15 at a requested redemption amount such that the Issuer’s total adjusted capital following the proposed redemption payment would equal 200% of the Issuer’s “authorized control level RBC,” as such term is defined by the insurance laws of the Commonwealth of Pennsylvania and as prescribed by the PID. All redemptions or repayments of principal and payments of interest on the notes are subject to approval by the PID. Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of December 23, 2014: Type of Surplus Note Total Seller Priority Pari Passu (in millions) Par value $ 57.9 $ 43.1 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) 1.6 (8.4 ) (6.8 ) Regulatory approval (2) (4.6 ) (8.0 ) (12.6 ) Liquidity adjustment (3) (11.0 ) (5.7 ) (16.7 ) Total (14.0 ) (22.1 ) (36.1 ) Fair value $ 43.9 $ 21.0 $ 64.9 _______________________________________________________________________________ (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated delay in securing regulatory approvals of interest and principal payments to reflect graduated changes in Issuer's statutory surplus. The monetary impact of the anticipated delay is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. (3) Represents impact of liquidity spread to account for OneBeacon's sole ownership of the notes, lack of a trading market, and ongoing regulatory approval risk.

Consolidating Financial Informa

Consolidating Financial Information	12 Months Ended
	Dec. 31, 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 December 31, 2015 and 2014 , and statements of operations and comprehensive income and cash flows for the years ended December 31, 2015 , 2014 and 2013 . 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 The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2015 (in millions) Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 2,074.6 $ 5.9 $ — $ 2,080.5 Short-term investments, at amortized cost (which approximates fair value) 4.4 64.1 0.7 — 69.2 Common equity securities, at fair value — 298.7 — — 298.7 Other investments — 143.0 — — 143.0 Total investment securities 4.4 2,580.4 6.6 — 2,591.4 Cash — 94.6 0.6 — 95.2 Reinsurance recoverables — 193.5 — — 193.5 Premiums receivable — 219.0 — — 219.0 Deferred acquisition costs — 100.7 — — 100.7 Ceded unearned premiums — 29.5 — — 29.5 Net deferred tax asset — 140.1 — 0.1 140.2 Investment income accrued — 10.1 — — 10.1 Accounts receivable on unsettled investment sales — 30.5 — — 30.5 Investments in subsidiaries 996.9 — 951.3 (1,948.2 ) — Other assets 0.5 190.6 3.3 — 194.4 Total assets $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,389.8 $ — $ — $ 1,389.8 Unearned premiums — 560.3 — — 560.3 Funds held under insurance contracts — 137.7 — — 137.7 Debt — — 274.8 — 274.8 Other liabilities 0.9 230.4 6.1 — 237.4 Total liabilities 0.9 2,318.2 280.9 — 2,600.0 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,000.9 1,267.2 680.9 (1,948.1 ) 1,000.9 Noncontrolling interests — 3.6 — — 3.6 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,000.9 1,270.8 680.9 (1,948.1 ) 1,004.5 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Consolidating Balance Sheet The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2014 (in millions) 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 Other investments — 203.8 — — 203.8 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 Ceded unearned premiums — 17.9 — — 17.9 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 — 1,051.8 (2,079.2 ) — Other assets 0.3 180.1 4.4 — 184.8 Assets held for sale — 58.1 — — 58.1 Total assets $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 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 Other liabilities 0.3 235.3 7.1 — 242.7 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 1,303.4 775.7 (2,079.1 ) 1,045.8 Noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,045.8 1,306.9 775.7 (2,079.1 ) 1,049.3 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 3,578.2 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2015 (in millions) Revenues Earned premiums $ — $ 1,176.2 $ — $ — $ 1,176.2 Net investment income — 45.9 — — 45.9 Net realized and change in unrealized investment gains — (35.1 ) — — (35.1 ) Net other revenues (expenses) — (0.6 ) — — (0.6 ) Total revenues — 1,186.4 — — 1,186.4 Expenses Loss and loss adjustment expenses — 700.7 — — 700.7 Policy acquisition expenses — 213.8 — — 213.8 Other underwriting expenses — 218.2 — — 218.2 General and administrative expenses 4.8 10.3 0.3 — 15.4 Interest expense — — 13.0 — 13.0 Total expenses 4.8 1,143.0 13.3 — 1,161.1 Pre-tax income (loss) from continuing operations (4.8 ) 43.4 (13.3 ) — 25.3 Income tax benefit — 8.2 4.7 — 12.9 Net income (loss) from continuing operations (4.8 ) 51.6 (8.6 ) — 38.2 Loss from discontinued operations, net of tax — (0.5 ) — — (0.5 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (4.8 ) 51.4 (8.6 ) — 38.0 Equity in earnings of subsidiaries, net of tax 41.6 — 8.3 (49.9 ) — Net income including noncontrolling interests 36.8 51.4 (0.3 ) (49.9 ) 38.0 Less: Net income attributable to noncontrolling interests — (1.2 ) — — (1.2 ) Net income attributable to OneBeacon's common shareholders 36.8 50.2 (0.3 ) (49.9 ) 36.8 Net change in benefit plan assets and obligations, net of tax — — — — — Comprehensive income attributable to OneBeacon's common shareholders $ 36.8 $ 50.2 $ (0.3 ) $ (49.9 ) $ 36.8 Consolidating Statement of Operations and Comprehensive Income (Loss) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 (in millions) Revenues Earned premiums $ — $ 1,177.1 $ — $ — $ 1,177.1 Net investment income — 44.4 0.1 (1.1 ) 43.4 Net realized and change in unrealized investment gains — 44.6 — (4.2 ) 40.4 Net other revenues (expenses) — 5.8 (3.7 ) 3.7 5.8 Total revenues — 1,271.9 (3.6 ) (1.6 ) 1,266.7 Expenses Loss and loss adjustment expenses — 815.1 — — 815.1 Policy acquisition expenses — 203.3 — — 203.3 Other underwriting expenses — 179.2 — — 179.2 General and administrative expenses 5.1 8.4 0.3 — 13.8 Interest expense — — 14.1 (1.1 ) 13.0 Total expenses 5.1 1,206.0 14.4 (1.1 ) 1,224.4 Pre-tax income (loss) from continuing operations (5.1 ) 65.9 (18.0 ) (0.5 ) 42.3 Income tax benefit — 5.8 6.3 0.2 12.3 Net income (loss) from continuing operations (5.1 ) 71.7 (11.7 ) (0.3 ) 54.6 Loss from discontinued operations, net of tax — (1.8 ) — — (1.8 ) Loss from sale of discontinued operations, net of tax — (18.8 ) — — (18.8 ) Net income (loss) before equity in earnings of unconsolidated affiliates (5.1 ) 51.1 (11.7 ) (0.3 ) 34.0 Equity in earnings of subsidiaries, net of tax 38.0 — 9.5 (47.5 ) — Net income (loss) including noncontrolling interests 32.9 51.1 (2.2 ) (47.8 ) 34.0 Less: Net income attributable to noncontrolling interests — (1.1 ) — — (1.1 ) Net income (loss) attributable to OneBeacon's common shareholders 32.9 50.0 (2.2 ) (47.8 ) 32.9 Net change in benefit plan assets and obligations, net of tax (12.0 ) — (12.0 ) 12.0 (12.0 ) Comprehensive income (loss) attributable to OneBeacon's common shareholders $ 20.9 $ 50.0 $ (14.2 ) $ (35.8 ) $ 20.9 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 (in millions) Revenues Earned premiums $ — $ 1,120.4 $ — $ — $ 1,120.4 Net investment income — 44.5 (0.3 ) (1.2 ) 43.0 Net realized and change in unrealized investment gains — 48.9 (0.7 ) 1.2 49.4 Net other revenues — 31.2 — — 31.2 Total revenues — 1,245.0 (1.0 ) — 1,244.0 Expenses Loss and loss adjustment expenses — 622.1 — — 622.1 Policy acquisition expenses — 208.9 — — 208.9 Other underwriting expenses — 204.8 — — 204.8 General and administrative expenses 5.0 7.1 (0.1 ) — 12.0 Interest expense — — 14.2 (1.2 ) 13.0 Total expenses 5.0 1,042.9 14.1 (1.2 ) 1,060.8 Pre-tax income (loss) from continuing operations (5.0 ) 202.1 (15.1 ) 1.2 183.2 Income tax (expense) benefit 0.1 (42.6 ) 6.2 (0.2 ) (36.5 ) Net income (loss) from continuing operations (4.9 ) 159.5 (8.9 ) 1.0 146.7 Loss from discontinued operations, net of tax — (46.6 ) — — (46.6 ) Gain from sale of discontinued operations, net of tax — 46.6 — — 46.6 Income (loss) before equity in earnings of unconsolidated affiliates (4.9 ) 159.5 (8.9 ) 1.0 146.7 Equity in earnings of subsidiaries, net of tax 150.6 — 134.4 (285.0 ) — Net income including noncontrolling interests 145.7 159.5 125.5 (284.0 ) 146.7 Less: Net income attributable to noncontrolling interests — (1.0 ) — — (1.0 ) Net income attributable to OneBeacon's common shareholders 145.7 158.5 125.5 (284.0 ) 145.7 Net change in benefit plan assets and obligations, net of tax 20.6 — 20.6 (20.6 ) 20.6 Comprehensive income attributable to OneBeacon's common shareholders $ 166.3 $ 158.5 $ 146.1 $ (304.6 ) $ 166.3 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2015 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 36.8 $ 51.4 $ (0.3 ) $ (49.9 ) $ 38.0 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (41.6 ) — (8.3 ) 49.9 — Net loss from discontinued operations — 0.5 — — 0.5 Net gain from sale of discontinued operations — (0.3 ) — — (0.3 ) Net realized and change in unrealized investment gains — 35.1 — — 35.1 Net loss on sale of business — 3.7 — — 3.7 Deferred income tax benefit — (5.8 ) — — (5.8 ) Dividends received from subsidiaries 72.0 99.9 110.9 (282.8 ) — Other operating items: Net change in loss and LAE reserves — 47.6 — — 47.6 Net change in unearned premiums — (28.0 ) — — (28.0 ) Net change in ceded unearned premium — (11.6 ) — — (11.6 ) Net change in premiums receivable — 22.5 — — 22.5 Net change in reinsurance recoverable on paid and unpaid losses — (19.7 ) — — (19.7 ) Net change in funds held under reinsurance contracts — 37.1 — — 37.1 Net change in funds held under insurance contracts. — 56.7 — — 56.7 Net change in other assets and liabilities 2.5 13.6 0.5 — 16.6 Net cash provided from operations—continuing operations 69.7 302.7 102.8 (282.8 ) 192.4 Net cash used for operations—discontinued operations — (0.5 ) — — (0.5 ) Net cash provided from operations 69.7 302.2 102.8 (282.8 ) 191.9 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 14.0 118.5 0.6 — 133.1 Maturities of fixed maturity investments — 262.4 — — 262.4 Sales of fixed maturity investments — 491.5 88.7 183.3 763.5 Sales of common equity securities — 345.6 — — 345.6 Return of capital and distributions of other investments — 40.5 — — 40.5 Purchases of fixed maturity investments — (1,055.3 ) (94.9 ) (183.3 ) (1,333.5 ) Purchases of common equity securities — (323.5 ) — — (323.5 ) Contributions for other investments — (4.2 ) — — (4.2 ) Net change in unsettled investment purchases and sales — (23.8 ) — — (23.8 ) Proceeds from sale of property and equipment — 56.8 — — 56.8 Net acquisitions of property and equipment — (11.5 ) — — (11.5 ) Capital contribution from parent — 2.2 5.5 (7.7 ) — Net cash provided from (used for) investing activities—continuing operations 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash provided from (used for) investing activities 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Cash flows from financing activities: Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (182.9 ) (99.9 ) 282.8 — Capital contribution to subsidiary — (5.5 ) (2.2 ) 7.7 — Repurchases and retirements of common stock (3.7 ) — — — (3.7 ) Payments on capital lease obligation — (5.4 ) — — (5.4 ) Net cash used for financing activities—continuing operations (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net increase in cash during period — 7.6 0.6 — 8.2 Cash balance at beginning of period — 87.0 — — 87.0 Cash balance at end of period $ — $ 94.6 $ 0.6 $ — $ 95.2 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 32.9 $ 51.1 $ (2.2 ) $ (47.8 ) $ 34.0 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (38.0 ) — (9.5 ) 47.5 — Net loss from discontinued operations — 1.8 — — 1.8 Net loss from sale of discontinued operations — 18.8 — — 18.8 Net realized and change in unrealized investment gains — (44.6 ) — 4.2 (40.4 ) Net other realized losses — (3.7 ) 3.7 — — Deferred income tax benefit — (18.8 ) — (0.2 ) (19.0 ) Dividends received from subsidiaries 90.4 15.0 50.0 (155.4 ) — Other operating items: Net change in loss and LAE reserves — 287.9 — — 287.9 Net change in unearned premiums — 43.4 — — 43.4 Net change in ceded unearned premiums — (3.6 ) — — (3.6 ) Net change in premiums receivable — (13.3 ) — — (13.3 ) Net change in reinsurance recoverable on paid and unpaid losses — (83.9 ) — — (83.9 ) Net change in funds held under reinsurance contracts — (35.3 ) — — (35.3 ) Net change in funds held under insurance contracts — 17.7 — — 17.7 Net change in other assets and liabilities 1.9 (49.6 ) (1.9 ) (6.5 ) (56.1 ) Net cash provided from operations—continuing operations 87.2 182.9 40.1 (158.2 ) 152.0 Net cash used for operations—discontinued operations — (54.5 ) — — (54.5 ) Net cash provided from operations 87.2 128.4 40.1 (158.2 ) 97.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (5.4 ) (62.8 ) 2.7 — (65.5 ) Maturities of fixed maturity investments — 396.4 — — 396.4 Sales of fixed maturity investments — 1,927.9 80.3 (165.1 ) 1,843.1 Sales of common equity securities — 240.2 — — 240.2 Return of capital and distributions of other investments — 53.4 — — 53.4 Purchases of fixed maturity investments — (2,265.1 ) (80.9 ) 139.2 (2,206.8 ) Purchases of common equity securities — (202.4 ) — — (202.4 ) Contributions for other investments — (81.9 ) — — (81.9 ) Net change in unsettled investment purchases and sales — (15.0 ) — — (15.0 ) Net acquisitions of property and equipment — (2.2 ) — — (2.2 ) Capital contribution from parent — 70.0 70.0 (140.0 ) — Net cash (used for) provided from investing activities—continuing operations (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Cash flows from financing activities: Repurchases of debt — — (28.7 ) 28.7 — Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (140.4 ) (15.0 ) 155.4 — Capital contribution to subsidiary — (70.0 ) (70.0 ) 140.0 — Repurchases and retirements of common stock (1.8 ) — — — (1.8 ) Payments on capital lease obligation — (5.3 ) — — (5.3 ) Net cash used for financing activities—continuing operations (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net decrease in cash during period — (28.8 ) (1.5 ) — (30.3 ) Cash transferred with sale of business — (50.8 ) — — (50.8 ) Net decrease after cash transferred with sale of business — (79.6 ) (1.5 ) — (81.1 ) Cash balance at beginning of period — 166.6 1.5 — 168.1 Cash balance at end of period $ — $ 87.0 $ — $ — $ 87.0 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 145.7 $ 159.5 $ 125.5 $ (284.0 ) $ 146.7 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (150.6 ) — (134.4 ) 285.0 — Net loss from discontinued operations — 46.6 — — 46.6 Net gain from sale of discontinued operations — (46.6 ) — — (46.6 ) Net realized and change in unrealized investment gains — (48.9 ) 0.7 (1.2 ) (49.4 ) Net realized gain on sale of business — (23.0 ) — — (23.0 ) Deferred income tax expense (benefit) — 14.9 (0.1 ) 0.2 15.0 Dividends received from subsidiaries 92.0 — 218.0 (310.0 ) — Other operating items: Net change in loss and LAE reserves — 54.3 — — 54.3 Net change in unearned premiums — (28.9 ) — — (28.9 ) Net change in ceded unearned premiums — (2.8 ) — — (2.8 ) Net change in premiums receivable — (2.6 ) — — (2.6 ) Net change in reinsurance recoverable on paid and unpaid losses — 20.7 — — 20.7 Net change in funds held under reinsurance contracts — (1.8 ) — — (1.8 ) Net change in funds held under insurance contracts — 57.4 — — 57.4 Net change in other assets and liabilities 3.4 45.8 (29.4 ) — 19.8 Net cash provided from operations—continuing operations 90.5 244.6 180.3 (310.0 ) 205.4 Net cash used for operations—discontinued operations — (76.7 ) — — (76.7 ) Net cash provided from operations 90.5 167.9 180.3 (310.0 ) 128.7 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (10.3 ) 26.3 56.2 — 72.2 Maturities of fixed maturity investments — 223.7 21.5 — 245.2 Sales of fixed maturity investments — 1,496.7 386.7 (483.4 ) 1,400.0 Sales of common equity securities — 196.7 — — 196.7 Return of capital and distributions of other investments — 67.5 — — 67.5 Purchases of fixed maturity investments — (1,787.2 ) (393.2 ) 483.4 (1,697.0 ) Purchases of common equity securities — (206.3 ) — — (206.3 ) Contributions for other investments — (22.0 ) — — (22.0 ) Proceeds from the sale of business — 31.3 — — 31.3 Net change in unsettled investment purchases and sales — 4.1 — — 4.1 Net acquisitions of property and equipment — (10.3 ) — — (10.3 ) Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — 250.0 — (250.0 ) — Net cash (used for) provided from investing activities—continuing operations (10.3 ) 270.5 71.2 (250.0 ) 81.4 Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (10.3 ) 270.5 71.2 (250.0 ) 81.4 Cash flows from financing activities: Cash dividends paid to common shareholders (80.2 ) — — — (80.2 ) Cash dividends paid to parent — (310.0 ) — 310.0 — Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — — (250.0 ) 250.0 — Payments on capital lease obligation — (5.7 ) — — (5.7 ) Net cash used for financing activities—continuing operations (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net increase in cash during period — 122.7 1.5 — 124.2 Cash balance at beginning of period — 43.9 — — 43.9 Cash balance at end of period $ — $ 166.6 $ 1.5 $ — $ 168.1 SCHEDULE II ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) CONDENSED BALANCE SHEETS December 31, 2015 2014 ($ in millions) Assets: Short-term investments, at amortized cost (which approximates fair value) $ 4.4 $ 18.4 Investments in subsidiaries 996.9 1,027.4 Other assets 0.5 0.3 Total assets $ 1,001.8 $ 1,046.1 Liabilities $ 0.9 $ 0.3 OneBeacon's common shareholders' equity 1,000.9 1,045.8 Total liabilities and OneBeacon's common shareholders' equity $ 1,001.8 $ 1,046.1 CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME Year ended December 31, 2015 2014 2013 ($ in millions) Revenues $ — $ — $ — Expenses 4.8 5.1 5.0 Pre-tax loss from continuing operations (4.8 ) (5.1 ) (5.0 ) Income tax benefit — — 0.1 Net loss from continuing operations (4.8 ) (5.1 ) (4.9 ) Equity in earnings from subsidiaries, net of tax 41.6 38.0 150.6 Net income attributable to OneBeacon's common shareholders 36.8 32.9 145.7 Other comprehensive income (loss) items, after tax — (12.0 ) 20.6 Comprehensive income attributable to OneBeacon's common shareholders $ 36.8 $ 20.9 $ 166.3 See Notes to Financial Statements. SCHEDULE II (continued) ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, 2015 2014 2013 ($ in millions) Net income $ 36.8 $ 32.9 $ 145.7 Charges (credits) to reconcile net income to net cash from operations: Undistributed earnings from subsidiaries (41.6 ) (38.0 ) (150.6 ) Dividends received from subsidiaries 72.0 90.4 92.0 Net change in other assets and liabilities 2.5 1.9 3.4 Net cash provided from operations 69.7 87.2 90.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 14.0 (5.4 ) (10.3 ) Net cash provided from (used for) investing activities 14.0 (5.4 ) (10.3 ) Cash flows from financing activities: Cash dividends paid to common shareholders (80.0 ) (80.0 ) (80.2 ) Repurchases and retirements of common stock (3.7 ) (1.8 ) — Net cash used for financing activities (83.7 ) (81.8 ) (80.2 ) Net change in cash during the year — — — Cash balance at beginning of year — — — Cash balance at end of year $ — $ — $ — ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) NOTES TO CONDENSED FINANCIAL INFORMATION 1. General The financial statements of the Registrant should be read in conjunction with the consolidated financial statements and notes thereto included in Item 8. 2. Long-term Obligations and Guarantees The Company has fully and unconditionally guaranteed the 2012 Senior Notes maturing on November 9, 2022 presented in Note 6—"Debt" that were issued by its 100% owned subsidiary, OBH. 3. Supplemental Cash Flow Information Dividends received from subsidiaries were $72.0 million , $90.4 million and $92.0 million for the years ended December 31, 2015, 2014, and 2013, respectively.

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 24, 2016 , the Board declared a dividend of $0.21 per common share, payable on March 30, 2016 to shareholders of record on March 11, 2016 .

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) Selected quarterly financial data for 2015 and 2014 is shown in the following table. The quarterly financial data includes, in the opinion of management, all recurring adjustments necessary for a fair presentation of the results of operations for the interim periods. 2015 Three months ended 2014 Three months ended ($ in millions, except per share amounts) Mar. 31 June 30 Sept. 30 Dec. 31 Mar. 31 June 30 Sept. 30 Dec. 31 Revenues $ 308.2 $ 314.2 $ 267.8 $ 296.2 $ 306.8 $ 326.0 $ 301.5 $ 332.4 Expenses 280.1 311.3 284.6 285.1 252.0 294.3 296.6 381.5 Pre-tax income (loss) from continuing operations 28.1 2.9 (16.8 ) 11.1 54.8 31.7 4.9 (49.1 ) Tax (expense) benefit (3.4 ) 0.9 3.5 11.9 (7.1 ) (5.9 ) 1.1 24.2 Net income (loss) from continuing operations 24.7 3.8 (13.3 ) 23.0 47.7 25.8 6.0 (24.9 ) Loss from discontinued operations, net of tax (0.1 ) (0.2 ) (0.1 ) (0.1 ) (0.5 ) (0.1 ) (0.3 ) (0.9 ) Gain (loss) from sale of discontinued operations, net of tax — 0.3 — — — (0.5 ) (7.0 ) (11.3 ) Net income (loss) including noncontrolling interests 24.6 3.9 (13.4 ) 22.9 47.2 25.2 (1.3 ) (37.1 ) Less: Net income attributable to noncontrolling interests (0.5 ) (0.5 ) — (0.2 ) (0.4 ) (0.5 ) — (0.2 ) Net income (loss) attributable to OneBeacon's common shareholders $ 24.1 $ 3.4 $ (13.4 ) $ 22.7 $ 46.8 $ 24.7 $ (1.3 ) $ (37.3 ) Earnings (loss) per share attributable to OneBeacon's common shareholders—basic and diluted: (1) Net income (loss) from continuing operations per share $ 0.25 $ 0.03 $ (0.14 ) $ 0.24 $ 0.50 $ 0.26 $ 0.05 $ (0.26 ) Net Loss from discontinued operations, net of tax, per share — — — — (0.01 ) — (0.07 ) (0.13 ) Net income (loss) attributable to OneBeacon's common shareholders per share $ 0.25 $ 0.03 $ (0.14 ) $ 0.24 $ 0.49 $ 0.26 $ (0.02 ) $ (0.39 ) (1) Due to the averaging of shares, quarterly earnings per share may not add to the total for the full year.

SCHEDULE I SUMMARY OF INVESTMEN

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES	12 Months Ended
	Dec. 31, 2015
Summary of Investments, Other than Investments in Related Parties [Abstract]
SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES	SCHEDULE I ONEBEACON INSURANCE GROUP, LTD. SUMMARY OF INVESTMENTS—OTHER THAN INVESTMENTS IN RELATED PARTIES As of December 31, 2015 Amortized Cost Fair Value Carrying Value ($ in millions) Investments: Fixed maturity investments: Bonds: U.S. Government and government agencies and authorities $ 85.4 $ 85.3 $ 85.3 Corporate bonds and asset-backed securities 1,845.9 1,842.3 1,842.3 States, municipalities and political subdivisions 67.7 69.0 69.0 Foreign governments 1.0 1.2 1.2 Preferred stocks 78.3 82.7 82.7 Total fixed maturity investments 2,078.3 2,080.5 2,080.5 Short-term investments 69.2 69.2 69.2 Common equity securities: Exchange traded funds 189.7 183.3 183.3 Banks, trust and insurance companies 3.5 4.5 4.5 Industrial, miscellaneous and other 291.5 294.2 294.2 Total common equity securities 295.0 298.7 298.7 Other investments 135.6 143.0 143.0 Total investments $ 2,578.1 $ 2,591.4 $ 2,591.4

SCHEDULE II CONDENSED FINANCIAL

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT	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 December 31, 2015 and 2014 , and statements of operations and comprehensive income and cash flows for the years ended December 31, 2015 , 2014 and 2013 . 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 The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2015 (in millions) Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 2,074.6 $ 5.9 $ — $ 2,080.5 Short-term investments, at amortized cost (which approximates fair value) 4.4 64.1 0.7 — 69.2 Common equity securities, at fair value — 298.7 — — 298.7 Other investments — 143.0 — — 143.0 Total investment securities 4.4 2,580.4 6.6 — 2,591.4 Cash — 94.6 0.6 — 95.2 Reinsurance recoverables — 193.5 — — 193.5 Premiums receivable — 219.0 — — 219.0 Deferred acquisition costs — 100.7 — — 100.7 Ceded unearned premiums — 29.5 — — 29.5 Net deferred tax asset — 140.1 — 0.1 140.2 Investment income accrued — 10.1 — — 10.1 Accounts receivable on unsettled investment sales — 30.5 — — 30.5 Investments in subsidiaries 996.9 — 951.3 (1,948.2 ) — Other assets 0.5 190.6 3.3 — 194.4 Total assets $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,389.8 $ — $ — $ 1,389.8 Unearned premiums — 560.3 — — 560.3 Funds held under insurance contracts — 137.7 — — 137.7 Debt — — 274.8 — 274.8 Other liabilities 0.9 230.4 6.1 — 237.4 Total liabilities 0.9 2,318.2 280.9 — 2,600.0 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,000.9 1,267.2 680.9 (1,948.1 ) 1,000.9 Noncontrolling interests — 3.6 — — 3.6 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,000.9 1,270.8 680.9 (1,948.1 ) 1,004.5 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Consolidating Balance Sheet The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2014 (in millions) 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 Other investments — 203.8 — — 203.8 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 Ceded unearned premiums — 17.9 — — 17.9 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 — 1,051.8 (2,079.2 ) — Other assets 0.3 180.1 4.4 — 184.8 Assets held for sale — 58.1 — — 58.1 Total assets $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 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 Other liabilities 0.3 235.3 7.1 — 242.7 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 1,303.4 775.7 (2,079.1 ) 1,045.8 Noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,045.8 1,306.9 775.7 (2,079.1 ) 1,049.3 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 3,578.2 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2015 (in millions) Revenues Earned premiums $ — $ 1,176.2 $ — $ — $ 1,176.2 Net investment income — 45.9 — — 45.9 Net realized and change in unrealized investment gains — (35.1 ) — — (35.1 ) Net other revenues (expenses) — (0.6 ) — — (0.6 ) Total revenues — 1,186.4 — — 1,186.4 Expenses Loss and loss adjustment expenses — 700.7 — — 700.7 Policy acquisition expenses — 213.8 — — 213.8 Other underwriting expenses — 218.2 — — 218.2 General and administrative expenses 4.8 10.3 0.3 — 15.4 Interest expense — — 13.0 — 13.0 Total expenses 4.8 1,143.0 13.3 — 1,161.1 Pre-tax income (loss) from continuing operations (4.8 ) 43.4 (13.3 ) — 25.3 Income tax benefit — 8.2 4.7 — 12.9 Net income (loss) from continuing operations (4.8 ) 51.6 (8.6 ) — 38.2 Loss from discontinued operations, net of tax — (0.5 ) — — (0.5 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (4.8 ) 51.4 (8.6 ) — 38.0 Equity in earnings of subsidiaries, net of tax 41.6 — 8.3 (49.9 ) — Net income including noncontrolling interests 36.8 51.4 (0.3 ) (49.9 ) 38.0 Less: Net income attributable to noncontrolling interests — (1.2 ) — — (1.2 ) Net income attributable to OneBeacon's common shareholders 36.8 50.2 (0.3 ) (49.9 ) 36.8 Net change in benefit plan assets and obligations, net of tax — — — — — Comprehensive income attributable to OneBeacon's common shareholders $ 36.8 $ 50.2 $ (0.3 ) $ (49.9 ) $ 36.8 Consolidating Statement of Operations and Comprehensive Income (Loss) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 (in millions) Revenues Earned premiums $ — $ 1,177.1 $ — $ — $ 1,177.1 Net investment income — 44.4 0.1 (1.1 ) 43.4 Net realized and change in unrealized investment gains — 44.6 — (4.2 ) 40.4 Net other revenues (expenses) — 5.8 (3.7 ) 3.7 5.8 Total revenues — 1,271.9 (3.6 ) (1.6 ) 1,266.7 Expenses Loss and loss adjustment expenses — 815.1 — — 815.1 Policy acquisition expenses — 203.3 — — 203.3 Other underwriting expenses — 179.2 — — 179.2 General and administrative expenses 5.1 8.4 0.3 — 13.8 Interest expense — — 14.1 (1.1 ) 13.0 Total expenses 5.1 1,206.0 14.4 (1.1 ) 1,224.4 Pre-tax income (loss) from continuing operations (5.1 ) 65.9 (18.0 ) (0.5 ) 42.3 Income tax benefit — 5.8 6.3 0.2 12.3 Net income (loss) from continuing operations (5.1 ) 71.7 (11.7 ) (0.3 ) 54.6 Loss from discontinued operations, net of tax — (1.8 ) — — (1.8 ) Loss from sale of discontinued operations, net of tax — (18.8 ) — — (18.8 ) Net income (loss) before equity in earnings of unconsolidated affiliates (5.1 ) 51.1 (11.7 ) (0.3 ) 34.0 Equity in earnings of subsidiaries, net of tax 38.0 — 9.5 (47.5 ) — Net income (loss) including noncontrolling interests 32.9 51.1 (2.2 ) (47.8 ) 34.0 Less: Net income attributable to noncontrolling interests — (1.1 ) — — (1.1 ) Net income (loss) attributable to OneBeacon's common shareholders 32.9 50.0 (2.2 ) (47.8 ) 32.9 Net change in benefit plan assets and obligations, net of tax (12.0 ) — (12.0 ) 12.0 (12.0 ) Comprehensive income (loss) attributable to OneBeacon's common shareholders $ 20.9 $ 50.0 $ (14.2 ) $ (35.8 ) $ 20.9 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 (in millions) Revenues Earned premiums $ — $ 1,120.4 $ — $ — $ 1,120.4 Net investment income — 44.5 (0.3 ) (1.2 ) 43.0 Net realized and change in unrealized investment gains — 48.9 (0.7 ) 1.2 49.4 Net other revenues — 31.2 — — 31.2 Total revenues — 1,245.0 (1.0 ) — 1,244.0 Expenses Loss and loss adjustment expenses — 622.1 — — 622.1 Policy acquisition expenses — 208.9 — — 208.9 Other underwriting expenses — 204.8 — — 204.8 General and administrative expenses 5.0 7.1 (0.1 ) — 12.0 Interest expense — — 14.2 (1.2 ) 13.0 Total expenses 5.0 1,042.9 14.1 (1.2 ) 1,060.8 Pre-tax income (loss) from continuing operations (5.0 ) 202.1 (15.1 ) 1.2 183.2 Income tax (expense) benefit 0.1 (42.6 ) 6.2 (0.2 ) (36.5 ) Net income (loss) from continuing operations (4.9 ) 159.5 (8.9 ) 1.0 146.7 Loss from discontinued operations, net of tax — (46.6 ) — — (46.6 ) Gain from sale of discontinued operations, net of tax — 46.6 — — 46.6 Income (loss) before equity in earnings of unconsolidated affiliates (4.9 ) 159.5 (8.9 ) 1.0 146.7 Equity in earnings of subsidiaries, net of tax 150.6 — 134.4 (285.0 ) — Net income including noncontrolling interests 145.7 159.5 125.5 (284.0 ) 146.7 Less: Net income attributable to noncontrolling interests — (1.0 ) — — (1.0 ) Net income attributable to OneBeacon's common shareholders 145.7 158.5 125.5 (284.0 ) 145.7 Net change in benefit plan assets and obligations, net of tax 20.6 — 20.6 (20.6 ) 20.6 Comprehensive income attributable to OneBeacon's common shareholders $ 166.3 $ 158.5 $ 146.1 $ (304.6 ) $ 166.3 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2015 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 36.8 $ 51.4 $ (0.3 ) $ (49.9 ) $ 38.0 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (41.6 ) — (8.3 ) 49.9 — Net loss from discontinued operations — 0.5 — — 0.5 Net gain from sale of discontinued operations — (0.3 ) — — (0.3 ) Net realized and change in unrealized investment gains — 35.1 — — 35.1 Net loss on sale of business — 3.7 — — 3.7 Deferred income tax benefit — (5.8 ) — — (5.8 ) Dividends received from subsidiaries 72.0 99.9 110.9 (282.8 ) — Other operating items: Net change in loss and LAE reserves — 47.6 — — 47.6 Net change in unearned premiums — (28.0 ) — — (28.0 ) Net change in ceded unearned premium — (11.6 ) — — (11.6 ) Net change in premiums receivable — 22.5 — — 22.5 Net change in reinsurance recoverable on paid and unpaid losses — (19.7 ) — — (19.7 ) Net change in funds held under reinsurance contracts — 37.1 — — 37.1 Net change in funds held under insurance contracts. — 56.7 — — 56.7 Net change in other assets and liabilities 2.5 13.6 0.5 — 16.6 Net cash provided from operations—continuing operations 69.7 302.7 102.8 (282.8 ) 192.4 Net cash used for operations—discontinued operations — (0.5 ) — — (0.5 ) Net cash provided from operations 69.7 302.2 102.8 (282.8 ) 191.9 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 14.0 118.5 0.6 — 133.1 Maturities of fixed maturity investments — 262.4 — — 262.4 Sales of fixed maturity investments — 491.5 88.7 183.3 763.5 Sales of common equity securities — 345.6 — — 345.6 Return of capital and distributions of other investments — 40.5 — — 40.5 Purchases of fixed maturity investments — (1,055.3 ) (94.9 ) (183.3 ) (1,333.5 ) Purchases of common equity securities — (323.5 ) — — (323.5 ) Contributions for other investments — (4.2 ) — — (4.2 ) Net change in unsettled investment purchases and sales — (23.8 ) — — (23.8 ) Proceeds from sale of property and equipment — 56.8 — — 56.8 Net acquisitions of property and equipment — (11.5 ) — — (11.5 ) Capital contribution from parent — 2.2 5.5 (7.7 ) — Net cash provided from (used for) investing activities—continuing operations 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash provided from (used for) investing activities 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Cash flows from financing activities: Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (182.9 ) (99.9 ) 282.8 — Capital contribution to subsidiary — (5.5 ) (2.2 ) 7.7 — Repurchases and retirements of common stock (3.7 ) — — — (3.7 ) Payments on capital lease obligation — (5.4 ) — — (5.4 ) Net cash used for financing activities—continuing operations (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net increase in cash during period — 7.6 0.6 — 8.2 Cash balance at beginning of period — 87.0 — — 87.0 Cash balance at end of period $ — $ 94.6 $ 0.6 $ — $ 95.2 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 32.9 $ 51.1 $ (2.2 ) $ (47.8 ) $ 34.0 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (38.0 ) — (9.5 ) 47.5 — Net loss from discontinued operations — 1.8 — — 1.8 Net loss from sale of discontinued operations — 18.8 — — 18.8 Net realized and change in unrealized investment gains — (44.6 ) — 4.2 (40.4 ) Net other realized losses — (3.7 ) 3.7 — — Deferred income tax benefit — (18.8 ) — (0.2 ) (19.0 ) Dividends received from subsidiaries 90.4 15.0 50.0 (155.4 ) — Other operating items: Net change in loss and LAE reserves — 287.9 — — 287.9 Net change in unearned premiums — 43.4 — — 43.4 Net change in ceded unearned premiums — (3.6 ) — — (3.6 ) Net change in premiums receivable — (13.3 ) — — (13.3 ) Net change in reinsurance recoverable on paid and unpaid losses — (83.9 ) — — (83.9 ) Net change in funds held under reinsurance contracts — (35.3 ) — — (35.3 ) Net change in funds held under insurance contracts — 17.7 — — 17.7 Net change in other assets and liabilities 1.9 (49.6 ) (1.9 ) (6.5 ) (56.1 ) Net cash provided from operations—continuing operations 87.2 182.9 40.1 (158.2 ) 152.0 Net cash used for operations—discontinued operations — (54.5 ) — — (54.5 ) Net cash provided from operations 87.2 128.4 40.1 (158.2 ) 97.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (5.4 ) (62.8 ) 2.7 — (65.5 ) Maturities of fixed maturity investments — 396.4 — — 396.4 Sales of fixed maturity investments — 1,927.9 80.3 (165.1 ) 1,843.1 Sales of common equity securities — 240.2 — — 240.2 Return of capital and distributions of other investments — 53.4 — — 53.4 Purchases of fixed maturity investments — (2,265.1 ) (80.9 ) 139.2 (2,206.8 ) Purchases of common equity securities — (202.4 ) — — (202.4 ) Contributions for other investments — (81.9 ) — — (81.9 ) Net change in unsettled investment purchases and sales — (15.0 ) — — (15.0 ) Net acquisitions of property and equipment — (2.2 ) — — (2.2 ) Capital contribution from parent — 70.0 70.0 (140.0 ) — Net cash (used for) provided from investing activities—continuing operations (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Cash flows from financing activities: Repurchases of debt — — (28.7 ) 28.7 — Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (140.4 ) (15.0 ) 155.4 — Capital contribution to subsidiary — (70.0 ) (70.0 ) 140.0 — Repurchases and retirements of common stock (1.8 ) — — — (1.8 ) Payments on capital lease obligation — (5.3 ) — — (5.3 ) Net cash used for financing activities—continuing operations (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net decrease in cash during period — (28.8 ) (1.5 ) — (30.3 ) Cash transferred with sale of business — (50.8 ) — — (50.8 ) Net decrease after cash transferred with sale of business — (79.6 ) (1.5 ) — (81.1 ) Cash balance at beginning of period — 166.6 1.5 — 168.1 Cash balance at end of period $ — $ 87.0 $ — $ — $ 87.0 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 145.7 $ 159.5 $ 125.5 $ (284.0 ) $ 146.7 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (150.6 ) — (134.4 ) 285.0 — Net loss from discontinued operations — 46.6 — — 46.6 Net gain from sale of discontinued operations — (46.6 ) — — (46.6 ) Net realized and change in unrealized investment gains — (48.9 ) 0.7 (1.2 ) (49.4 ) Net realized gain on sale of business — (23.0 ) — — (23.0 ) Deferred income tax expense (benefit) — 14.9 (0.1 ) 0.2 15.0 Dividends received from subsidiaries 92.0 — 218.0 (310.0 ) — Other operating items: Net change in loss and LAE reserves — 54.3 — — 54.3 Net change in unearned premiums — (28.9 ) — — (28.9 ) Net change in ceded unearned premiums — (2.8 ) — — (2.8 ) Net change in premiums receivable — (2.6 ) — — (2.6 ) Net change in reinsurance recoverable on paid and unpaid losses — 20.7 — — 20.7 Net change in funds held under reinsurance contracts — (1.8 ) — — (1.8 ) Net change in funds held under insurance contracts — 57.4 — — 57.4 Net change in other assets and liabilities 3.4 45.8 (29.4 ) — 19.8 Net cash provided from operations—continuing operations 90.5 244.6 180.3 (310.0 ) 205.4 Net cash used for operations—discontinued operations — (76.7 ) — — (76.7 ) Net cash provided from operations 90.5 167.9 180.3 (310.0 ) 128.7 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (10.3 ) 26.3 56.2 — 72.2 Maturities of fixed maturity investments — 223.7 21.5 — 245.2 Sales of fixed maturity investments — 1,496.7 386.7 (483.4 ) 1,400.0 Sales of common equity securities — 196.7 — — 196.7 Return of capital and distributions of other investments — 67.5 — — 67.5 Purchases of fixed maturity investments — (1,787.2 ) (393.2 ) 483.4 (1,697.0 ) Purchases of common equity securities — (206.3 ) — — (206.3 ) Contributions for other investments — (22.0 ) — — (22.0 ) Proceeds from the sale of business — 31.3 — — 31.3 Net change in unsettled investment purchases and sales — 4.1 — — 4.1 Net acquisitions of property and equipment — (10.3 ) — — (10.3 ) Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — 250.0 — (250.0 ) — Net cash (used for) provided from investing activities—continuing operations (10.3 ) 270.5 71.2 (250.0 ) 81.4 Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (10.3 ) 270.5 71.2 (250.0 ) 81.4 Cash flows from financing activities: Cash dividends paid to common shareholders (80.2 ) — — — (80.2 ) Cash dividends paid to parent — (310.0 ) — 310.0 — Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — — (250.0 ) 250.0 — Payments on capital lease obligation — (5.7 ) — — (5.7 ) Net cash used for financing activities—continuing operations (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net increase in cash during period — 122.7 1.5 — 124.2 Cash balance at beginning of period — 43.9 — — 43.9 Cash balance at end of period $ — $ 166.6 $ 1.5 $ — $ 168.1 SCHEDULE II ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) CONDENSED BALANCE SHEETS December 31, 2015 2014 ($ in millions) Assets: Short-term investments, at amortized cost (which approximates fair value) $ 4.4 $ 18.4 Investments in subsidiaries 996.9 1,027.4 Other assets 0.5 0.3 Total assets $ 1,001.8 $ 1,046.1 Liabilities $ 0.9 $ 0.3 OneBeacon's common shareholders' equity 1,000.9 1,045.8 Total liabilities and OneBeacon's common shareholders' equity $ 1,001.8 $ 1,046.1 CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME Year ended December 31, 2015 2014 2013 ($ in millions) Revenues $ — $ — $ — Expenses 4.8 5.1 5.0 Pre-tax loss from continuing operations (4.8 ) (5.1 ) (5.0 ) Income tax benefit — — 0.1 Net loss from continuing operations (4.8 ) (5.1 ) (4.9 ) Equity in earnings from subsidiaries, net of tax 41.6 38.0 150.6 Net income attributable to OneBeacon's common shareholders 36.8 32.9 145.7 Other comprehensive income (loss) items, after tax — (12.0 ) 20.6 Comprehensive income attributable to OneBeacon's common shareholders $ 36.8 $ 20.9 $ 166.3 See Notes to Financial Statements. SCHEDULE II (continued) ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) CONDENSED STATEMENTS OF CASH FLOWS Year ended December 31, 2015 2014 2013 ($ in millions) Net income $ 36.8 $ 32.9 $ 145.7 Charges (credits) to reconcile net income to net cash from operations: Undistributed earnings from subsidiaries (41.6 ) (38.0 ) (150.6 ) Dividends received from subsidiaries 72.0 90.4 92.0 Net change in other assets and liabilities 2.5 1.9 3.4 Net cash provided from operations 69.7 87.2 90.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 14.0 (5.4 ) (10.3 ) Net cash provided from (used for) investing activities 14.0 (5.4 ) (10.3 ) Cash flows from financing activities: Cash dividends paid to common shareholders (80.0 ) (80.0 ) (80.2 ) Repurchases and retirements of common stock (3.7 ) (1.8 ) — Net cash used for financing activities (83.7 ) (81.8 ) (80.2 ) Net change in cash during the year — — — Cash balance at beginning of year — — — Cash balance at end of year $ — $ — $ — ONEBEACON INSURANCE GROUP, LTD. (Registrant Only) NOTES TO CONDENSED FINANCIAL INFORMATION 1. General The financial statements of the Registrant should be read in conjunction with the consolidated financial statements and notes thereto included in Item 8. 2. Long-term Obligations and Guarantees The Company has fully and unconditionally guaranteed the 2012 Senior Notes maturing on November 9, 2022 presented in Note 6—"Debt" that were issued by its 100% owned subsidiary, OBH. 3. Supplemental Cash Flow Information Dividends received from subsidiaries were $72.0 million , $90.4 million and $92.0 million for the years ended December 31, 2015, 2014, and 2013, respectively.

SCHEDULE III SUPPLEMENTARY INSU

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	12 Months Ended
	Dec. 31, 2015
Supplementary Insurance Information [Abstract]
SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	SCHEDULE III ONEBEACON INSURANCE GROUP, LTD. SUPPLEMENTARY INSURANCE INFORMATION (1) Column A Column B Column C Column D Column E Column F Column G Column H Column I Column J Column K Segment Deferred acquisition costs Future policy benefits, losses, claims and loss expenses Unearned premiums Other policy claims and benefits payable Premiums earned Net investment income (2) Benefits, claims, losses, and settlement expenses Amortization of policy acquisition expenses Other operating expenses Premiums written ($ in millions) Years ended: December 31, 2015: Specialty Industries $ 51.1 $ 597.2 $ 272.2 $ — $ 615.9 $ — $ (390.0 ) $ (113.7 ) $ (120.3 ) $ 603.6 Specialty Products 49.6 772.2 288.1 — 560.3 — (310.7 ) (100.1 ) (97.9 ) 533.0 Investing, Financing and Corporate (3) — 20.4 — — — 45.9 — — — — December 31, 2014: Specialty Industries $ 53.5 $ 519.6 $ 284.7 $ — $ 595.0 $ — $ (357.2 ) $ (107.1 ) $ (100.8 ) $ 610.0 Specialty Products 49.7 798.8 303.6 — 582.1 — (457.9 ) (96.2 ) (78.4 ) 606.9 Investing, Financing and Corporate (3) — 23.8 — — — 43.4 — — — — December 31, 2013: Specialty Industries $ 50.1 $ 446.5 $ 269.5 $ — $ 566.9 $ — $ (309.8 ) $ (102.6 ) $ (107.4 ) $ 579.0 Specialty Products 53.6 607.8 275.4 — 553.5 — (312.3 ) (106.3 ) (97.4 ) 509.6 Investing, Financing and Corporate (4) — — — — — 43.0 — — — — __________________________________________________________ (1) Schedule excludes activity related to discontinued operations for all periods presented. (2) Invested assets are not allocated to Specialty Industries or Specialty Products since OneBeacon does not manage its assets by segment. Net investment income related to OneBeacon's Specialty Industries and Specialty Products segments are included in the Investing, Financing and Corporate segment since these assets are available for payment of losses and expenses for all segments. (3) As described in Note 18, 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 on ASIC or one of the ongoing entities. The balance of $20.4 million and $23.8 million as of December 31, 2015 and 2014, respectively, is included in both unpaid loss and loss adjustment expense reserves and reinsurance recoverable included within Investing, Financing, and Corporate. (4) Schedule excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013.

SCHEDULE IV REINSURANCE

SCHEDULE IV REINSURANCE	12 Months Ended
	Dec. 31, 2015
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
SCHEDULE IV REINSURANCE	SCHEDULE IV ONEBEACON INSURANCE GROUP, LTD. REINSURANCE Column A Column B Column C Column D Column E Column F Premiums earned Gross amount Ceded to other companies Assumed from other companies Net amount Percentage of amount assumed to net ($ in millions) Years ended: December 31, 2015 Continuing Operations $ 1,298.0 $ (167.7 ) $ 45.9 $ 1,176.2 3.9 % December 31, 2014 Continuing Operations $ 1,209.1 $ (102.9 ) $ 70.9 $ 1,177.1 6.0 % Discontinued Operations (0.7 ) 0.7 0.1 0.1 100.0 December 31, 2013 Continuing Operations $ 1,043.3 $ (71.4 ) $ 148.5 $ 1,120.4 13.3 % Discontinued Operations 0.4 — 0.4 0.8 50.0

SCHEDULE V VALUATION AND QUALIF

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	SCHEDULE V ONEBEACON INSURANCE GROUP, LTD. VALUATION AND QUALIFYING ACCOUNTS (1) Column A Column B Column C Column D Column E Additions (subtractions) Description Balance at beginning of period Charged (credited) to costs and expenses Charged (credited) to other accounts (2) Other additions (deductions) described (3) Balance at end of period ($ in millions) Years ended: December 31, 2015 Reinsurance recoverable on paid and unpaid losses: Allowance for reinsurance balances $ 2.2 $ (0.1 ) $ — $ (1.4 ) $ 0.7 Premiums receivable: Allowance for uncollectible accounts 1.9 0.8 (0.7 ) — 2.0 December 31, 2014 Reinsurance recoverable on paid and unpaid losses: Allowance for reinsurance balances $ 14.3 $ (0.5 ) $ — $ (11.6 ) $ 2.2 Premiums receivable: Allowance for uncollectible accounts 3.1 (0.2 ) (1.0 ) — 1.9 December 31, 2013 (4) Reinsurance recoverable on paid and unpaid losses: Allowance for reinsurance balances $ 25.6 $ — $ — $ (11.3 ) $ 14.3 Premiums receivable: Allowance for uncollectible accounts 4.4 0.3 — (1.6 ) 3.1 _______________________________________________________________________________ (1) Schedule includes activity related to discontinued operations. Balances as of December 31, 2013 include an Allowance for reinsurance balance of $11.3 million and an Allowance for uncollectible premiums receivable of $0.1 million related to the Runoff Transaction that were reclassified to held for sale in the consolidated balance sheet. (2) Amount credited to other accounts represents a reduction in the Allowance for uncollectible premiums receivable which was offset by a corresponding reduction in Gross premiums receivable. There was no impact to Premiums receivable as presented in the consolidated balance sheet. (3) Represents net collections (charge offs) of balances receivable. (4) Excludes $0.1 million of allowance for uncollectible deductibles as of December 31, 2013, with no allowance for uncollectible deductibles as of December 31, 2015 and 2014.

SCHEDULE VI SUPPLEMENTAL INFORM

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	12 Months Ended
	Dec. 31, 2015
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	SCHEDULE VI ONEBEACON INSURANCE GROUP, LTD. SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (1) (2) Column A Column B Column C Column D Column E Column F Column G Column H Column I Column J Column K Deferred acquisition costs Reserves for Unpaid Claims and Claims Adjustment Expenses Discount, if any, deducted in Column C (3) Unearned Premiums Earned Premiums Net investment income (4) Claims and Claims Adjustment Expenses Incurred Related to Amortization of deferred policy acquisition costs Paid Claims and Claims Adjustment Expenses Premiums written Affiliation with registrant Current Year Prior Year ($ in millions) Specialty Industries: 2015 $ 51.1 $ 597.2 $ 1.1 $ 272.2 $ 615.9 $ — $ 368.2 $ 21.8 $ (113.7 ) $ 322.7 $ 603.6 2014 53.5 519.6 1.0 284.7 595.0 — 329.2 28.0 (107.1 ) 277.3 610.0 2013 50.1 446.5 2.8 269.5 566.9 — 315.7 (5.9 ) (102.6 ) 268.5 579.0 Specialty Products: 2015 $ 49.6 $ 772.2 $ — $ 288.1 $ 560.3 $ — $ 334.3 $ (23.6 ) $ (100.1 ) $ 354.8 $ 533.0 2014 49.7 798.8 — 303.6 582.1 — 396.1 61.8 (96.2 ) 331.3 606.9 2013 53.6 607.8 0.2 275.4 553.5 — 306.4 5.9 (106.3 ) 272.2 509.6 Investing, Financing and Corporate: (5) 2015 $ — $ 20.4 (5) $ — $ — $ — $ 45.9 $ — $ — $ — $ — $ — 2014 — 23.8 (5) — — — 43.4 — — — — — 2013 — — — — — 43.0 — — — — — __________________________________________________________ (1) Schedule excludes activity related to discontinued operations for all periods presented. (2) Schedule excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013. (3) The amounts shown represent and/or include OneBeacon's discount on its long-term workers compensation loss and LAE reserves, as such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual basis. OneBeacon discounts these reserves using an average discount rate which is determined based on various assumptions including consideration of when the claims will be settled ( 2.5% , 2.5% and 3.5% , respectively, as of December 31, 2015, 2014 and 2013). (4) Invested assets are not allocated to Specialty Industries or Specialty Products since OneBeacon does not manage its assets by segment. Net investment income related to OneBeacon's Specialty Industries and Specialty Products segments are included in the Investing, Financing and Corporate segment since these assets are available for payment of losses and expenses for all segments. (5) As described in Note 18, ASIC entered into a 100% quota share reinsurance agreement whereby ASIC is ceding to Bedivere 100% of the legacy Runoff Business that was written on ASIC or one of the ongoing entities. The balances of $20.4 million and $23.8 million as of December 31, 2015 and 2014, respectively, is included in unpaid loss and loss adjustment expense reserves within Investing, Financing, and Corporate.

Nature of Operations and Summ34

Nature of Operations and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Investment Securities	Investment Securities OneBeacon adopted the fair value election, which allows companies to report financial assets and liabilities at fair value, on an individual basis. The election must be made at the inception of a transaction and may not be reversed. OneBeacon believes that reporting its investment results in this manner is consistent with its operating principle, of managing investments for total return. OneBeacon classifies its portfolio of fixed maturity investments and common equity securities 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 changes in unrealized investment gains on trading securities are reported, on a pre-tax basis, in revenues as net realized and change in unrealized investment gains. 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, and convertible fixed maturity investments. 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 2015, and a Prospector-managed hedge fund was redeemed. 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. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an "exit price"). 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 both December 31, 2015 and 2014 , approximately 92% and 90% , respectively, of the investment portfolio recorded at fair value was priced based upon quoted market prices or other 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 fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations, mortgage and asset-backed securities, foreign government obligations and preferred stocks. Investments valued using Level 2 inputs also include certain ETFs that track U.S. stock indices such as the S&P 500 but are traded on foreign exchanges and that management values using the fund's published NAV to account for the difference in market close times. 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 debt and equity securities, including asset-backed 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 perform 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 the 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. During the past year, 8 securities fell outside OneBeacon's expected results, thereby triggering the challenge with the pricing service. 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. OneBeacon's investments in debt securities, including asset-backed securities, are generally valued using matrix and other pricing models. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life. Private equity funds and hedge funds are carried at fair value based upon OneBeacon's proportionate interest in the underlying fund's net asset value, which is deemed to approximate fair value, as net asset value of the funds reflects the fair value of the funds' underlying investments. OneBeacon employs a number of procedures to assess the reasonableness of the fair value measurements, including obtaining and reviewing each fund's audited financial statements and discussing each fund's pricing with the fund's manager. Other investments also include surplus notes, the fair value of which are estimated using a discounted estimated cash flow method, as described in Note 5—"Investment Securities." In circumstances where the underlying investments are publicly traded, such as the investments made by hedge funds, the fair value of the underlying investments is determined using current market prices. In circumstances where the underlying investments are not publicly traded, such as the investments made by private equity funds, the private equity fund managers have considered the need for a liquidity discount on each of the underlying investments when determining the fund's net asset value. In circumstances where OneBeacon's portion of a fund's net asset value is deemed to differ from fair value due to illiquidity or other factors associated with OneBeacon's investment in the fund, including counterparty credit risk, the net asset value is adjusted accordingly. See Note 5—"Investment Securities."
Cash	Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statements of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company's consolidated subsidiaries.
Insurance Operations	Insurance Operations Premiums written are recognized as revenues and are earned ratably over the term of the related policy. Unearned premiums represent the portion of premiums written that are applicable to future insurance coverage provided by policies. Policy acquisition costs represent commissions, premium taxes, brokerage expenses and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period. Policy acquisition costs deferred were $237.3 million , $237.6 million and $210.3 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, all of which were included in policy acquisition expenses, with the exception of $21.3 million , $22.9 million and $23.4 million for each respective period that were deferred relating to other underwriting expenses. Policy acquisition costs amortized were $239.7 million , $227.6 million and $230.5 million for the years ended December 31, 2015 , 2014 and 2013 , respectively, all of which were included in policy acquisition expenses, with the exception of $22.2 million , $23.0 million and $22.4 million for each respective period that were amortized relating to other underwriting expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. This limitation is referred to as a premium deficiency. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses ("LAE"), unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. There were no premium deficiencies recognized for any years presented. Loss and LAE are charged against income as incurred. Unpaid loss and LAE reserves are based on estimates (generally determined by claims adjusters, legal counsel and actuarial staff) of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management's best estimate of ultimate loss and LAE, net of reinsurance and estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any adjustments resulting therefrom are reflected in the current period. The process of estimating unpaid loss and LAE reserves involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. OneBeacon discounts certain of its long-term workers compensation loss and LAE reserves when such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual claim basis. OneBeacon discounts these reserves using the statutory rate ( 2.5% at December 31, 2015 and 2014 ). As of December 31, 2015 and 2014 , the discount on OneBeacon's workers compensation loss and LAE reserves amounted to $1.1 million and $1.0 million , respectively. OneBeacon's insurance subsidiaries enter into reinsurance contracts to protect their businesses from losses due to concentration of risk, to manage their operating leverage ratios and to limit losses arising from catastrophic events. The majority of such reinsurance contracts are executed through excess of loss treaties and catastrophe contracts under which the reinsurer indemnifies for a specified part or all of certain types of losses over stipulated amounts arising from any one occurrence or event. OneBeacon has also entered into quota share treaties with reinsurers under which all risks meeting prescribed criteria are covered on a pro rata basis. The amount of each risk ceded by OneBeacon is subject to maximum limits which vary by line of business and type of coverage. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policies. The collectibility of reinsurance recoverables is subject to the solvency of the reinsurers. OneBeacon is selective in regard to its reinsurers, principally placing reinsurance with those reinsurers with strong financial condition, reputation, industry ratings and underwriting ability. Management monitors the financial condition and ratings of its reinsurers on an ongoing basis. Reinsurance premiums, commissions, expense reimbursements and reserves related to reinsured business are accounted for on a basis consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums ceded to other companies are reported as a reduction of premiums written. Expense allowances received in connection with reinsurance ceded have been accounted for as a reduction of the related policy acquisition costs and are deferred and amortized accordingly.
Funds Held	Funds Held Funds held under reinsurance contracts as of December 31, 2014, primarily represented amounts due to OneBeacon in connection with the Standard Reinsurance Agreement ("SRA") with the Federal Crop Insurance Corporation ("FCIC"), which is managed by an agency of the U.S. Department of Agriculture. The SRA governs the relationship, including the exchange of funds, between private insurance companies and the FCIC relating to MPCI crop insurance business, which the Company exited in 2015. Funds held under insurance contracts represents unrestricted collateral held by the Company primarily relating to the Surety business.
Accounting for Mandatory Shared Market Mechanisms	Mandatory Shared Market Mechanisms As a condition of its licenses to do business in certain states, OneBeacon's insurance operations are required to participate in various mandatory shared market mechanisms commonly referred to as "residual" or "involuntary" markets. These markets generally consist of risks considered to be undesirable from a standard or routine underwriting perspective. Each state dictates the levels of insurance coverage that are mandatorily assigned to participating insurers within these markets. The total amount of such business an insurer must accept in a particular state is generally based on that insurer's market share of voluntary business written within that state. In certain cases, OneBeacon is obligated to write business from shared market mechanisms at a future date based on its historical market share of all voluntary policies written within that state. Involuntary business generated from mandatory shared market mechanisms may be treated as assumed reinsurance depending on the structure of the mechanism. OneBeacon's market assignments are typically required to be written in the current period, although, in certain cases OneBeacon is required to accept policy assignments at a future date. Anticipated losses associated with future market assignments are recognized when the amount of such anticipated losses is determined to be probable and can be reasonably estimated.
Accounting for Insurance Related Assessments	Insurance Related Assessments Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. OneBeacon's insurance subsidiaries record guaranty fund assessments when such assessments are billed by the respective guaranty funds. In addition, OneBeacon will monitor other insurance company insolvencies and will accrue a liability when such losses are determined to be probable and the assessment amounts can be reasonably estimated. The actual amount of such assessments will depend upon the final outcome of rehabilitation proceedings and will be paid over several years.
Capital Lease	Capital Lease In December 2011, the Company entered into lease financing arrangements with US Bancorp Equipment Finance, Inc. ("US Bancorp") and Fifth Third Equipment Finance Company ("Fifth Third") whereby it sold furniture and equipment and capitalized software, respectively, at a cost equal to net book value. The Company then leased the fixed assets back from US Bancorp for a lease term of five years and leased the capitalized software back from Fifth Third for a lease term of four years . See Note 16—"Commitments and Contingencies."
Deferred Software Costs	Deferred Software Costs OneBeacon capitalizes costs related to computer software developed for internal use during the application development stage of software development projects. These costs generally consist of certain external, payroll and payroll related costs. OneBeacon begins amortization of these costs once the project or the respective phase of the project is completed and ready for its intended use. Amortization is on a straight line basis and over the useful life which generally ranges from three to five years. During the year ended December 31, 2015 the Company recognized a $1.6 million pre-tax impairment of certain capitalized software associated with senior management restructuring.
Federal and Foreign Income Taxes	Federal and Foreign Income Taxes The majority of the Company's subsidiaries file consolidated tax returns in the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States. Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, and for other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. The deferred tax asset is recognized when it is more likely than not that it will be realized.
Foreign Currency Exchange	Foreign Currency Exchange The U.S. dollar is the functional currency for all of OneBeacon's businesses. OneBeacon is subject to foreign currency fluctuations associated with foreign investment securities. Assets and liabilities recorded in foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the average exchange rates for the period. Net foreign exchange gains and losses arising from the translation are reported as a component of net income in the period in which they arise.
Variable Interest Entities	Variable Interest Entities OneBeacon consolidates a reciprocal insurance exchange ("reciprocal") as a variable interest entity ("VIE"), when it has both the power to direct the activities of the VIE that most significantly impact its economic performance and either the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. See Note 13—"Variable Interest Entities ("VIE")."
Defined Benefit Plans	Defined Benefit Plans OneBeacon sponsors defined benefit plans and recognizes the funded status of the difference between plan assets at fair value and the projected benefit obligation (for defined benefit pension plans) or the accumulated benefit obligation (for other postretirement benefit plans) in its statement of financial position. The Company recognizes amounts previously deferred and amortized in other comprehensive income in the period in which they occur and measure plan assets and obligations as of the fiscal year end. The projected benefit obligation of the Qualified Plan was calculated using termination assumptions as of December 31, 2015 given its settlement is imminent and the likelihood that the execution of the plan termination is blocked by third parties and the Qualified Plan returns from termination is remote. See Note 8—"Retirement Plans."
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 the years ended December 31, 2014 and 2013 increased by $1.2 million and $0.6 million , respectively. As a result of the retrospective adoption, OneBeacon's common shareholders equity has been reduced by $0.3 million as of January 1, 2013. In addition, for the years ended December 31, 2014 and 2013, the retrospective adoption resulted in an increase of $1.7 million and $1.9 million to net investment income, respectively, and a net increase of $2.3 million and $2.2 million to income tax expense, respectively. 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 Financial Instruments - Recognition and Measurement On January 5, 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities . The new guidance requires all equity securities with readily determinable fair values are to be measured at fair value with changes therein required to be recognized through current period earnings. In addition, the new ASU simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment and for impaired equity security investments to be measured at fair value. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, with early adoption permitted. OneBeacon has taken the fair value election for its portfolio of equity security investments and accordingly, does not expect the adoption of ASU 2016-01 to have a significant impact on its financial statements. Business Combinations - Measurement Period Adjustments On September 25, 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments. At the date of an acquisition, fair value of certain assets and liabilities may not be accurately determinable and are therefore recognized at the acquirer's best estimate. Such amounts may be updated as additional information becomes available in periods subsequent to the acquisition for up to one year. Prior to the issuance of this new ASU, subsequent adjustments had to be pushed back to the acquisition date, which required retroactive adjustments to prior period amounts. Under the new guidance, adjustments to provisional amounts that are identified during the measurement period are to be recorded in the reporting period in which the adjustment amounts are determined. ASU 2015-16 is effective for fiscal years beginning after December 15, 2015 and should be applied prospectively to adjustments to estimated purchase accounting amounts that occur after the effective date. Early application is permitted. OneBeacon has not recognized any adjustments to estimated purchase accounting amounts for the year ended December 31, 2015 . Short Duration 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 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. In August 2015, the FASB issued ASU 2015-15, Imputation of Interest (ASC 835) which addresses the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. ASU 2015-03 and ASU 2015-15 are effective for annual and interim reporting periods beginning after December 15, 2015. OneBeacon does not expect ASU 2015-03 or ASU 2015-15 to impact its financial position, results of operations, or cash flows and will reflect the new presentation upon adoption in the first quarter of 2016. 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 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. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (ASC 606), which delayed the effective date of ASU 2014-09 by one year. As a result, the standard is effective for annual and interim periods beginning after December 15, 2017. 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.

Unpaid Loss and Loss Adjustme35

Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves (Tables)	12 Months Ended
	Dec. 31, 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 years ended December 31, 2015 , 2014 , and 2013 : Year ended December 31, 2015 2014 2013 ($ in millions) Gross beginning loss and LAE reserves $ 1,342.2 $ 1,054.3 $ 1,000.0 Less beginning reinsurance recoverable on unpaid losses (161.6 ) (80.2 ) (107.3 ) Net beginning loss and LAE reserves 1,180.6 974.1 892.7 Loss and LAE incurred from continuing operations relating to: Current year losses 702.5 725.3 622.1 Prior year losses (1.8 ) 89.8 — Total incurred loss and LAE from continuing operations 700.7 815.1 622.1 Loss and LAE paid from continuing operations relating to: Current year losses (202.4 ) (199.6 ) (188.6 ) Prior year losses (475.1 ) (409.0 ) (352.1 ) Total loss and LAE payments from continuing operations (677.5 ) (608.6 ) (540.7 ) Net loss and LAE reserves 1,203.8 1,180.6 974.1 Total incurred loss and LAE from discontinued operations — (0.7 ) 78.9 Total loss and LAE payments from discontinued operations — (55.1 ) (102.3 ) Net loss and LAE reserves 1,203.8 1,124.8 950.7 Net change in loss and LAE reserves reported in liabilities held for sale — 188.4 (1) 23.4 (2) Net loss and LAE reserves sold — (132.6 ) (3) — Net ending loss and LAE reserves 1,203.8 1,180.6 974.1 Plus ending reinsurance recoverable on unpaid losses 186.0 161.6 80.2 Gross ending loss and LAE reserves $ 1,389.8 $ 1,342.2 $ 1,054.3 _______________________________________________________________________________ (1) Consists of the change in net loss and LAE reserves of $188.4 million , representing the balances classified as held for sale as December 31, 2013, in connection with the Runoff Transaction. (2) Consists of changes in net loss and LAE reserves to $188.4 million from $211.8 million , which amounts were classified as held for sale as of December 31, 2013 and 2012, respectively, in connection with the Runoff Transaction. (3) Relates to the Runoff Transaction, which closed on December 23, 2014.
Loss and LAE Reserve and Net Loss and LAE Development	The components of the 2014 fourth quarter reserve increase and the net loss and LAE development for the full year are provided below: 2014 Fourth Quarter Reserve Increase Full Year 2014 Net Prior Year Development Underwriting Operating Segment Current Accident Year Prior Accident Years Total Other Professional Lines $ 11.1 $ 31.9 $ 43.0 $ 42.2 Management Liability 6.6 8.4 15.0 16.4 Financial Services 2.0 6.5 8.5 6.5 Healthcare 3.2 (0.4 ) 2.8 (6.0 ) Specialty Property (1.1 ) 5.7 4.6 1.1 Crop 3.8 — 3.8 — Other 2.8 (0.4 ) 2.4 1.6 Specialty Products 28.4 51.7 80.1 61.8 Entertainment 1.5 11.6 13.1 13.5 Government Risks 1.2 7.1 8.3 8.5 Accident — 3.5 3.5 6.0 Other 2.6 1.6 4.2 — Specialty Industries 5.3 23.8 29.1 28.0 Total $ 33.7 $ 75.5 $ 109.2 $ 89.8

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2015
Reinsurance Disclosures [Abstract]
Effects of Reinsurance	The effects of reinsurance on OneBeacon's insurance subsidiaries' written and earned premiums and on loss and LAE, excluding the Runoff Business, were as follows: Year ended December 31, 2015 2014 2013 ($ in millions) Written premiums: Direct $ 1,279.9 $ 1,257.5 $ 1,103.1 Assumed 36.0 65.9 59.8 Ceded (179.3 ) (1) (106.5 ) (74.3 ) Net written premiums $ 1,136.6 $ 1,216.9 $ 1,088.6 Earned premiums: Direct $ 1,298.0 $ 1,209.1 $ 1,043.3 Assumed 45.9 70.9 148.5 (2) Ceded (167.7 ) (1) (102.9 ) (71.4 ) Net earned premiums $ 1,176.2 $ 1,177.1 $ 1,120.4 Loss and LAE: Direct $ 783.0 $ 778.7 (3) $ 584.9 Assumed 55.7 115.7 (3) 76.3 (2) Ceded (138.0 ) (1) (79.3 ) (39.1 ) Net loss and LAE $ 700.7 $ 815.1 $ 622.1 _______________________________________________________________________________ (1) During the year ended December 31, 2015, the Company recorded ceded written premiums of $33.3 million , ceded earned premiums of $33.3 million and ceded loss and loss adjustment expenses of $33.4 million as a result of the exit of the Crop Business due to the 100% quota share reinsurance agreement with AmTrust. (2) Includes assumed earned premiums and loss and LAE of $89.1 million and $41.9 million , respectively, related to the collector cars and boats business which although exited on January 1, 2013, was assumed on a runoff basis from Essentia. (3) Direct and Assumed Loss and LAE, for the year ended December 31, 2014, has been revised from the prior year's presentation to appropriately reflect Direct and Assumed Loss and LAE for that period. Direct Loss and LAE was decreased by $52 million and offset by an increase of $52 million in Assumed Loss and LAE. This revision, which had no impact on net income, was not material and has been presented correctly in the table above to improve comparability.
Reinsurer by S&P Rating	The following table summarizes Standard & Poor's Financial Services, LLC ("Standard & Poor's") ratings for OneBeacon's reinsurers for its continuing insurance operations, excluding industry pools and associations, based upon reinsurance recoverable amounts on paid and unpaid losses and LAE: Balance at December 31, 2015 % of total Standard & Poor's Rating (1) : ($ in millions) AA $ 41.7 22 % A 126.2 65 % BBB, Not Rated and Other 25.6 (2) 13 % Total reinsurance recoverables $ 193.5 100 % _______________________________________________________________________________ (1) Standard & Poor's ratings as detailed above are "AA" (Very strong), "A" (Strong) and "BBB" (Adequate). (2) Includes reinsurance recoverable on unpaid losses from Bedivere of $20.4 million .

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2015
Schedule of Investments [Abstract]
Net investment income, pre-tax	Net investment income for the years ended December 31, 2015 , 2014 , and 2013 consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Fixed maturity investments $ 43.8 $ 41.8 $ 40.6 Short-term investments — — — Common equity securities 6.1 6.5 6.2 Other investments 1.0 2.1 3.0 Gross investment income 50.9 50.4 49.8 Less investment expenses (5.0 ) (7.0 ) (6.8 ) Net investment income, pre-tax $ 45.9 $ 43.4 $ 43.0
Net realized investment gains (losses), pre-tax	The composition of net realized investment gains consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Fixed maturity investments $ 2.0 $ 6.6 $ 2.1 Short-term investments — — — Common equity securities 33.8 53.9 36.1 Other investments 11.4 9.2 6.0 Net realized investment gains, pre-tax 47.2 69.7 44.2 Income taxes (9.1 ) (21.0 ) (20.5 ) Net realized investment gains, after tax $ 38.1 $ 48.7 $ 23.7
Net unrealized investment gains (losses)	The net changes in fair value for the years ended December 31, 2015 , 2014 , and 2013 are as follows: Year ended December 31, 2015 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ (15.7 ) $ — $ (15.7 ) Short-term investments — — — Common equity securities (33.2 ) 0.2 (33.0 ) Other investments (33.6 ) — (33.6 ) Net change, pre-tax $ (82.5 ) $ 0.2 $ (82.3 ) Year ended December 31, 2014 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ 1.9 $ — $ 1.9 Short-term investments — (0.1 ) (0.1 ) Common equity securities (32.6 ) (0.3 ) (32.9 ) Other investments 1.8 — 1.8 Net change, pre-tax $ (28.9 ) $ (0.4 ) $ (29.3 ) Year ended December 31, 2013 Changes in net unrealized investment gains (1) Changes in net foreign currency translation gains (losses) (1) Total net changes in fair value reflected in revenues (1) ($ in millions) Fixed maturity investments $ (34.4 ) $ — $ (34.4 ) Short-term investments 0.1 — 0.1 Common equity securities 32.0 0.1 32.1 Other investments 7.4 — 7.4 Net change, pre-tax $ 5.1 $ 0.1 $ 5.2 _______________________________________________________________________________ (1) Includes pre-tax changes in net deferred gains and losses on sales of investments between OneBeacon and entities under White Mountains' common control of $(0.8) million for the year ended December 31, 2013 . There were no such changes in net deferred gains and losses for the years ended December 31, 2015 and 2014, respectively.
Gross unrealized investment gains or losses	The components of OneBeacon's ending net unrealized investment gains and losses, excluding the impact of net unrealized foreign currency translation gains and losses, on its investment portfolio as of December 31, 2015 and 2014 were as follows: December 31, 2015 2014 ($ in millions) Investment securities: Gross unrealized investment gains $ 46.5 $ 104.7 Gross unrealized investment losses (33.2 ) (8.9 ) Total net unrealized investment gains, pre-tax 13.3 95.8 Income taxes (6.5 ) (26.9 ) Total net unrealized investment gains, after tax $ 6.8 $ 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 December 31, 2015 and 2014 were as follows: December 31, 2015 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency losses Carrying value ($ in millions) U.S. Government and agency obligations $ 85.4 $ — $ (0.1 ) $ — $ 85.3 Debt securities issued by industrial corporations 810.8 4.1 (4.5 ) — 810.4 Municipal obligations 67.7 1.5 (0.2 ) — 69.0 Asset-backed securities 1,035.1 1.3 (4.5 ) — 1,031.9 Foreign government obligations 1.0 0.2 — — 1.2 Preferred stocks 78.3 4.4 — — 82.7 Total fixed maturity investments $ 2,078.3 $ 11.5 $ (9.3 ) $ — $ 2,080.5 December 31, 2014 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency losses Carrying value ($ in millions) 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
Investments Classified by Contractual Maturity Date	The cost or amortized cost and carrying value of OneBeacon's fixed maturity investments as of December 31, 2015 is presented below by contractual maturity. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. December 31, 2015 Cost or amortized cost Carrying value ($ in millions) Due in one year or less $ 154.4 $ 154.8 Due after one year through five years 678.1 678.2 Due after five years through ten years 115.2 115.0 Due after ten years 17.2 17.9 Asset-backed securities 1,035.1 1,031.9 Preferred stocks 78.3 82.7 Total $ 2,078.3 $ 2,080.5
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 foreign currency gains and carrying values of OneBeacon's common equity securities and other investments as of December 31, 2015 and 2014 were as follows: December 31, 2015 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains Carrying value ($ in millions) Common equity securities $ 295.0 $ 12.7 $ (9.0 ) $ — $ 298.7 Other investments 135.6 22.3 (14.9 ) — 143.0 Total common equity securities and other investments $ 430.6 $ 35.0 $ (23.9 ) $ — $ 441.7 December 31, 2014 Cost or amortized cost Gross unrealized gains Gross unrealized losses Net unrealized foreign currency gains Carrying value ($ in millions) Common equity securities $ 283.2 $ 39.3 $ (2.4 ) $ (0.1 ) $ 320.0 Other investments 162.9 44.8 (3.9 ) — 203.8 Total common equity securities 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 December 31, 2015 and 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 held as of December 31, 2014 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. Fair value at Level 1 Level 2 Level 3 ($ in millions) Fixed maturity investments: U.S. Government and agency obligations $ 85.3 $ 85.3 $ — $ — Debt securities issued by corporations: Consumer 218.3 — 218.3 — Healthcare 136.2 — 136.2 — Industrial 121.8 — 121.8 — Financial 116.0 — 116.0 — Energy 75.2 — 75.2 — Communications 46.0 — 46.0 — Utilities 42.2 — 42.2 — Technology 28.9 — 28.9 — Basic materials 25.8 — 25.8 — Debt securities issued by corporations 810.4 — 810.4 — Municipal obligations 69.0 — 69.0 — Asset-backed securities 1,031.9 — 1,031.9 — Foreign government obligations 1.2 0.6 0.6 — Preferred stocks 82.7 — 12.7 70.0 Fixed maturity investments 2,080.5 85.9 1,924.6 70.0 Short-term investments 69.2 69.2 — — Common equity securities: Exchange Traded Funds (1) 183.3 162.0 21.3 — Consumer 38.2 38.2 — — Communications 23.9 23.9 — — Health Care 19.6 19.6 — — Technology 14.7 14.7 — — Industrial 14.5 14.5 — — Financials 4.5 4.5 — — Common equity securities 298.7 277.4 21.3 — Other investments (2) 128.3 — — 128.3 Total (1)(2) $ 2,576.7 $ 432.5 $ 1,945.9 $ 198.3 _______________________________________________________________________________ (1) ETF's traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated as level 2 measurements. (2) Excludes the carrying value of $14.7 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2015 . Fair value at December 31, 2014 Level 1 Level 2 Level 3 ($ in millions) Fixed maturity investments: U.S. Government and agency obligations $ 38.0 $ 38.0 $ — $ — Debt securities issued by corporations: Consumer 174.9 — 174.9 — Financial 148.6 — 148.6 — Healthcare 111.9 — 111.9 — 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 75.2 75.2 — — Financials 72.4 72.4 — — Industrial 48.3 48.3 — — Health Care 46.5 46.5 — — Communications 24.4 24.4 — — Technology 20.6 20.6 — — Energy 15.6 15.6 — — Basic Materials 9.9 9.9 — — Utilities 5.1 5.1 — — Other 2.0 2.0 — — Common equity securities 320.0 320.0 — — Other investments (1) 187.0 — 5.0 182.0 Total (1) $ 2,509.0 $ 560.4 $ 1,692.6 $ 256.0 _______________________________________________________________________________ (1) Excludes the carrying value of $16.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2014 . The following tables summarize the changes in OneBeacon’s fair value measurements by level for the year ended December 31, 2015 and 2014: Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities 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 — (13.2 ) — — — (13.2 ) Net realized and change in unrealized gains 1.3 (12.7 ) (1.1 ) — (22.6 ) (35.1 ) Purchases 638.0 985.7 34.0 — 3.4 1,661.1 Sales (634.7 ) (742.9 ) — — (34.5 ) (1,412.1 ) Transfers in — 36.9 — — — 36.9 Transfers out — — (36.9 ) — — (36.9 ) Balance at December 31, 2015 $ 363.3 $ 1,945.9 $ 70.0 $ — $ 128.3 $ 2,507.5 _______________________________________________________________________________ (1) Excludes the carrying value of $14.7 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2015. (2) Excludes short-term investments. Level 3 Investments ($ in millions) Level 1 Investments Level 2 Investments Fixed maturity investments Common equity securities 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 0.1 (11.0 ) — — — (10.9 ) Net realized and change in unrealized gains 22.1 5.2 1.1 0.4 11.9 40.7 Purchases 752.1 1,625.1 41.7 — 68.7 2,487.6 Sales (886.2 ) (1,729.9 ) — (0.5 ) (18.5 ) (2,635.1 ) Exchanges 1.1 (3.1 ) 2.0 — — — Transfers in — 52.7 — — — 52.7 Transfers out — — (52.7 ) — — (52.7 ) Balance at December 31, 2014 $ 358.7 $ 1,692.1 $ 74.0 $ — $ 182.0 $ 2,306.8 _______________________________________________________________________________ (1) Excludes the carrying value of $16.8 million associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method as of December 31, 2014. (2) Excludes short-term investments.
Fair value, significant unobservable inputs	The following summarizes significant unobservable inputs used in estimating the fair value of fixed maturity investments and other investments classified within Level 3 other than hedge funds and private equity funds as of December 31, 2015 and 2014 . The fair value of investments in hedge funds and private equity funds, which are classified with Level 3, are estimated using the net asset value of the funds. ($ in millions) As of December 31, 2015 Description Fair Value Rating (1) Valuation Technique Unobservable Inputs Input Preferred stock (2) $ 70.0 N/R Par value (3) Issuer's intent to call $ 70.0 Surplus notes: 16.1% - Seller priority note $ 38.0 N/R Discounted cash flow Discount rate (4) 13.0% Timing of interest payments (5) 5 years Timing of principal payments (5) 10 years - Pari passu note $ 13.5 N/R Discounted cash flow Discount rate (6) 22.4% Timing of interest payments (5) 5 years Timing of principal payments (5) 15 years ($ in millions) As of December 31, 2014 Description Fair Value Rating (1) Valuation Technique Unobservable Inputs Input Preferred stock (2) $ 71.1 N/R Discounted cash flow Discount yield 7.1% Surplus notes: 11.0% - Seller priority note $ 44.0 N/R Discounted cash flow Discount rate (4) 9.3% Timing of interest payments (5) 5 years Timing of principal payments (5) 10 years - Pari passu note $ 21.1 N/R Discounted cash flow Discount rate (6) 13.5% Timing of interest payments (5) 5 years Timing of principal payments (5) 15 years Debt securities issued by corporations (2) $ 2.9 N/R Discounted cash flow Illiquidity discount (7) 10.0% _________________________________________________________________________ (1) Credit ratings, if rated, are assigned based on the following hierarchy: 1) Standard & Poor's and 2) Moody's (2) As of December 31, 2015 and 2014 , the preferred stock and debt securities issued by corporations categories each consist of one security. (3) Valuation based on issuer's intent as of December 31, 2015 to call the security in the near term. (4) 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, was added to the treasury rate to determine the discount rate for the seller priority note. (5) As of December 31, 2015 and 2014, the Company has assumed for estimating the fair value that 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. (6) 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, was added to the treasury rate to determine the discount rate for the seller priority note. (7) Judgmentally determined based on the Company's limited trading ability of the issuer.
Mortgage-backed and asset-backed securities	The following table summarizes the carrying value of OneBeacon's asset-backed securities as of December 31, 2015 and 2014 : December 31, 2015 2014 Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 ($ in millions) Mortgage-backed securities: Agency: GNMA $ 220.5 $ 220.5 $ — $ 259.2 $ 259.2 $ — FNMA 1.4 1.4 — 1.9 1.9 — FHLMC 3.1 3.1 — — — — Total agency (1) 225.0 225.0 — 261.1 261.1 — Non-agency: Residential (RMBS) 132.7 132.7 — 67.4 67.4 — Commercial (CMBS) 140.4 140.4 — 96.7 96.7 — Total non-agency 273.1 273.1 — 164.1 164.1 — Total mortgage-backed securities 498.1 498.1 — 425.2 425.2 — Other asset-backed securities: Credit card receivables 202.7 202.7 — 197.6 197.6 — Vehicle receivables 255.6 255.6 — 145.8 145.8 — Other 75.5 75.5 — 45.8 45.8 — Total other asset-backed securities 533.8 533.8 — 389.2 389.2 — Total asset-backed securities $ 1,031.9 $ 1,031.9 $ — $ 814.4 $ 814.4 $ — _______________________________________________________________________________ (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty 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 December 31, 2015 are as follows: Fair Value Security Issuance Year 2004 2005 2006 2008 2010 2011 2012 2013 2014 2015 ($ in millions) Total non-agency RMBS $ 132.7 $ 16.7 $ 8.6 $ 3.9 $ 3.6 $ 15.2 $ 13.5 $ 9.8 $ 14.0 $ 47.4 $ — Total non-agency CMBS 140.4 — — — — 5.4 — 18.1 17.2 54.9 44.8 Total non-agency $ 273.1 $ 16.7 $ 8.6 $ 3.9 $ 3.6 $ 20.6 $ 13.5 $ 27.9 $ 31.2 $ 102.3 $ 44.8
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 December 31, 2015 : Fair Value Super Senior (1) Senior (2) Subordinate (3) ($ in millions) Prime $ 132.7 $ 65.6 $ 67.1 $ — Non-prime — — — — Total non-agency RMBS $ 132.7 $ 65.6 $ 67.1 $ — _______________________________________________________________________________ (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 securities.
Non-agency CMBS, type of interest rate and tranche levels	The amount of fixed and floating rate securities and their tranche levels are as follows as of December 31, 2015 : Fair Value Super Senior (1) Senior (2) Subordinate (3) ($ in millions) Fixed rate CMBS $ 101.1 $ 8.7 $ 48.6 $ 43.8 Floating rate CMBS 39.3 — — 39.3 Total non-agency CMBS $ 140.4 $ 8.7 $ 48.6 $ 83.1 _______________________________________________________________________________ (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 securities.
Other investments	The following table summarizes investments in hedge funds and private equity funds as of December 31, 2015 and 2014 : December 31, 2015 2014 Fair Value Unfunded Commitments Fair Value Unfunded Commitments ($ in millions) Hedge funds Long/short equity banks and financial $ 12.8 $ — $ 28.5 $ — Long/short credit and distressed — — 8.4 — Other 3.6 — 5.4 — Total hedge funds 16.4 — 42.3 — Private equity funds Energy infrastructure and services 20.7 3.4 33.1 4.8 Multi-sector 14.8 2.1 14.5 2.2 Private equity secondaries 4.4 2.1 5.6 2.0 Healthcare 3.8 0.4 3.1 1.4 Insurance 2.0 0.1 2.1 0.1 Real estate 0.4 0.1 1.7 0.1 Total private equity funds 46.1 8.2 60.1 10.6 Total hedge funds and private equity funds $ 62.5 $ 8.2 $ 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 December 31, 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—Active Funds 30 - 59 days notice 60 - 89 days notice 90 - 119 days notice 120+ days notice Total ($ in millions) Redemption frequency Monthly $ — $ — $ — $ — $ — Quarterly 13.8 — — — 13.8 Annual — — 2.6 — 2.6 Total hedge funds $ 13.8 $ — $ 2.6 $ — $ 16.4
Fair Value of private equity funds subject to lock-up periods	As of December 31, 2015 , investments in private equity funds were subject to lock-up periods as follows: 1 - 3 years 3 - 5 years 5 - 10 years >10 years Total ($ in millions) Private Equity Funds—expected lock-up period remaining $ 22.1 $ 10.9 $ 13.1 $ — $ 46.1

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Schedule of debt outstanding	OneBeacon's debt outstanding as of December 31, 2015 and 2014 consisted of the following: December 31, 2015 2014 ($ in millions) Senior unsecured notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (0.2 ) (0.3 ) Senior unsecured notes, carrying value $ 274.8 $ 274.7

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The total income tax expense from continuing operations for the years ended December 31, 2015 , 2014 and 2013 consisted of the following: Year ended December 31, 2015 2014 2013 ($ in millions) Current tax (expense) benefit: Federal $ 9.1 $ (4.3 ) $ (20.3 ) State (1.2 ) (1.6 ) (0.8 ) Non-U.S. (0.8 ) (0.8 ) (0.4 ) Total current tax (expense) benefit 7.1 (6.7 ) (21.5 ) Deferred tax (expense) benefit: Federal 5.8 19.0 (15.0 ) State — — — Non-U.S. — — — Total deferred tax (expense) benefit 5.8 19.0 (15.0 ) Total income tax (expense) benefit $ 12.9 $ 12.3 $ (36.5 )
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of taxes calculated using the 35% U.S. statutory rate (the tax rate at which the majority of OneBeacon's worldwide operations are taxed) to the income tax expense on pre-tax income from continuing operations follows: Year ended December 31, 2015 2014 2013 ($ in millions) Tax expense at the U.S. statutory rate $ (8.9 ) $ (14.8 ) $ (64.1 ) Differences in taxes resulting from: Non-U.S. earnings, net of foreign taxes 19.3 19.6 20.9 Tax reserve adjustments (1.7 ) 4.1 (1.0 ) Tax exempt interest and dividends 2.6 2.5 2.4 Change in valuation allowance 0.5 (0.2 ) 5.9 Other, net 1.1 1.1 (0.6 ) Total income tax (expense) benefit on pre-tax income from continuing operations $ 12.9 $ 12.3 $ (36.5 )
Schedule of Deferred Tax Assets and Liabilities	An outline of the significant components of OneBeacon's deferred tax assets and liabilities follows: December 31, 2015 2014 ($ in millions) Deferred income tax assets related to: U.S. net operating loss carryforwards $ 63.7 $ 56.3 Unearned premiums 37.2 38.1 Discounting of loss and LAE reserves 26.7 41.3 Tax credit carryforwards 16.9 13.4 Compensation and bonus accruals 15.3 10.8 Sale of Runoff Business 12.6 12.6 Deferred compensation plans 6.0 6.4 Fixed assets 4.2 4.0 Investment basis differences 3.2 6.4 Allowance for doubtful accounts 0.7 0.7 Non-U.S. net operating loss carryforwards 0.4 0.4 Other accrued compensation 0.1 0.2 Accrued rent — 3.9 Other items 0.2 5.4 Total gross deferred income tax assets 187.2 199.9 Less valuation allowance (1.3 ) (1.8 ) Total net deferred income tax assets 185.9 198.1 Deferred income tax liabilities related to: Deferred acquisition costs 35.2 32.2 Net unrealized investment gains 6.5 26.9 Prepaid pension 3.5 2.6 Other items 0.5 4.6 Total gross deferred income tax liabilities 45.7 66.3 Net deferred tax asset $ 140.2 $ 131.8
Summary of Operating Loss Carryforwards	Net operating loss ("NOL") carryforwards as of December 31, 2015 and the expiration dates are as follows: December 31, 2015 United States Luxembourg Total ($ in millions) Net operating loss carryforwards by year: 2016 $ — $ — $ — From years 2017 to 2024 1.6 — 1.6 From years 2025 to 2035 180.3 — 180.3 No expiration date — 1.3 1.3 Total net operating loss carryforwards $ 181.9 $ 1.3 $ 183.2 December 31, 2015 United States Luxembourg Total ($ in millions) Gross deferred tax asset for NOL carryforwards $ 63.7 $ 0.4 $ 64.1 Valuation allowance for NOL carryforwards (0.6 ) (0.4 ) (1.0 ) Net deferred tax asset for NOL carryforwards $ 63.1 $ — $ 63.1
Schedule of Unrecognized Tax Benefits Roll Forward	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Permanent differences (1) Temporary differences (2) Interest and penalties (3) Total ($ in millions) January 1, 2013 $ 7.6 $ 23.6 $ 7.8 $ 39.0 Changes in prior year tax positions — — 1.0 1.0 Tax positions taken during the current year — (7.0 ) — (7.0 ) Lapse in statute of limitations — — — — Settlements with tax authorities — — (0.4 ) (0.4 ) December 31, 2013 $ 7.6 $ 16.6 $ 8.4 $ 32.6 Changes in prior year tax positions (2.2 ) (0.8 ) (1.9 ) (4.9 ) Tax positions taken during the current year — 7.3 — 7.3 Lapse in statute of limitations — — — — Settlements with tax authorities — — — — December 31, 2014 $ 5.4 $ 23.1 $ 6.5 $ 35.0 Changes in prior year tax positions — (12.4 ) 1.7 (10.7 ) Tax positions taken during the current year — — — — Lapse in statute of limitations — — — — Settlements with tax authorities — — — — December 31, 2015 $ 5.4 $ 10.7 $ 8.2 $ 24.3 _______________________________________________________________________________ (1) Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate. (2) Represents the amount of unrecognized tax benefits that, if recognized, would create a temporary difference between the reported amount of an item in OneBeacon's Consolidated Balance Sheet and its tax basis. (3) Net of tax benefit.

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Schedule of Net Funded Status	The following tables set forth the obligations and funded status, assumptions, plan assets and cash flows associated with the Plans as of December 31, 2015 and 2014 : December 31, 2015 2014 ($ in millions) Change in projected benefit obligation: Projected benefit obligation at beginning of year $ 119.7 $ 102.9 Service cost 0.9 0.6 Interest cost 4.6 4.7 Settlement gain (1) (1.8 ) — Special termination benefits expense — 0.3 Assumption changes (3.5 ) 17.5 Actuarial loss 0.9 1.1 Benefits and expenses paid with plan assets (13.7 ) (5.2 ) Benefits paid directly by OneBeacon (2.2 ) (2.2 ) Remeasurement due to plan termination (2) 4.6 — Projected benefit obligation at end of year $ 109.5 $ 119.7 Change in plan assets: Fair value of plan assets at beginning of year $ 146.0 $ 142.8 Actual return on plan assets 7.5 8.4 Benefits and expenses paid (13.7 ) (5.2 ) Fair value of plan assets at end of year $ 139.8 $ 146.0 Funded status at end of year $ 30.3 $ 26.3
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the financial statements as of December 31, 2015 and 2014 consist of: December 31, 2015 2014 ($ in millions) Net balance sheet asset recorded in other assets $ 55.8 $ 53.4 Net balance sheet liability recorded in other liabilities (25.5 ) (27.1 ) Net amount recognized in the financial statements $ 30.3 $ 26.3
Schedule of components of net periodic benefit cost (income)	The components of net periodic benefit cost (income) for the years ended December 31, 2015 , 2014 and 2013 were as follows: December 31, 2015 2014 2013 ($ in millions) Service cost $ 0.9 $ 0.6 $ 0.8 Interest cost 4.6 4.7 4.2 Expected return on plan assets (8.7 ) (8.5 ) (7.1 ) Amortization of net actuarial losses recognized during the year 1.3 0.3 0.9 Net periodic pension income before special termination benefits (1.9 ) (2.9 ) (1.2 ) Special termination benefits expense (1) — 0.3 0.3 Total net periodic benefit income $ (1.9 ) $ (2.6 ) $ (0.9 ) _______________________________________________________________________________ (1) Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets	Information for the Non-qualified Plan, which had accumulated benefit obligations in excess of plan assets, was as follows: December 31, 2015 2014 ($ in millions) Projected benefit obligation $ 25.5 $ 27.1 Accumulated benefit obligation $ 25.5 $ 27.1 Fair value of plan assets $ — $ — Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets, was as follows: December 31, 2015 2014 ($ in millions) Projected benefit obligation $ 84.0 (1) $ 92.6 Accumulated benefit obligation $ 84.0 (1) $ 92.6 Fair value of plan net assets $ 139.8 $ 146.0 ___________________________________________________________________________ (1) Measured on a plan termination basis
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The amounts recognized in accumulated other comprehensive loss on a pre-tax basis for the years ended December 31, 2015 and 2014 were as follows: December 31, 2015 2014 ($ in millions) Accumulated other comprehensive income (loss) at beginning of year $ (8.0 ) $ 10.5 Increase (decrease) in accumulated other comprehensive income (loss): Amortization of net actuarial gains recognized during the year 1.3 0.3 Net actuarial losses occurring during the year (1) (1.3 ) (18.8 ) Accumulated other comprehensive loss at end of year $ (8.0 ) $ (8.0 ) _______________________________________________________________________________ (1) Net actuarial losses resulted from changes in assumptions in estimating the projected benefit obligation as well as changes in investment returns and demographic experience different than those assumed. The 2015 amount reflects the valuation of the Qualified Plan on a termination basis.
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Expected Benefit Payments ($ in millions) 2016 (1) $ 86.8 2017 2.1 2018 2.1 2019 2.0 2020 2.0 2021 – 2025 8.9 _______________________________________________________________________________ (1) Primarily reflects the anticipated payout related to annuity purchases and lump sum payments resulting from the termination of the Qualified Plan
Schedule of Defined Benefit Plans Disclosures	The weighted average assumptions for the Plans used to determine benefit obligations as of December 31, 2015 and 2014 were as follows: December 31, 2015 2014 Discount rate 3.22 % 3.91 % The weighted average assumptions used to determine net periodic benefit cost for the years ended December 31, 2015 and 2014 were as follows: December 31, 2015 2014 Discount rate 3.91 % 4.66 % Expected long-term rate of return on plan assets 6.00 % 6.00 %
Schedule of Allocation of Plan Assets	The Qualified Plan's asset allocations as of December 31, 2015 and 2014 by asset category were as follows: Plan Assets at December 31, 2015 2014 Fixed maturity investments 95.0 % 16.9 % Common equity securities — 70.6 Convertible fixed maturity investments — 8.9 Cash and short-term investments 5.0 3.6 Total 100.0 % 100.0 % The fair value of the Qualified Plan's invested assets and their related inputs as of December 31, 2015 and 2014 by asset category were as follows: Fair value at December 31, 2015 Level 1 Level 2 Level 3 Fixed maturity investments $ 132.4 $ 132.4 $ — $ — Short-term investments 7.0 7.0 — — Total $ 139.4 $ 139.4 $ — $ — Fair value at December 31, 2014 Level 1 Level 2 Level 3 Fixed maturity investments $ 24.2 $ — $ 24.2 $ — Short-term investments 5.2 4.8 0.4 — Common equity securities: Consumer 35.2 35.2 — — Financials 17.1 17.1 — — Energy 13.9 13.9 — — Basic Materials 11.0 11.0 — — Utilities 2.6 2.6 — — Other 21.2 21.2 — — Common equity securities 101.0 101.0 — — Convertible fixed maturity investments: Consumer 4.1 — 4.1 — Financials 3.1 — 3.1 — Basic Materials 1.4 — 1.4 — Energy 0.8 — 0.8 — Other 3.4 — 3.4 — Convertible fixed maturity investments 12.8 — 12.8 — Total $ 143.2 $ 105.8 $ 37.4 $ —

Employee Share-Based Incentiv41

Employee Share-Based Incentive Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of performance share activity	The following summarizes performance share activity for performance shares for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Target Performance Shares outstanding Accrued expense Target Performance Shares outstanding Accrued expense Target Performance Shares outstanding Accrued expense ($ in millions) Beginning of period 517,470 $ 3.4 493,421 $ 4.0 563,190 $ 1.2 Payments and deferrals (1) (181,290 ) (1.5 ) (142,138 ) (1.0 ) (238,658 ) — New awards 154,887 — 165,800 — 179,000 — Forfeitures and net change in assumed forfeitures (41,632 ) (0.1 ) 387 — (10,111 ) (0.1 ) Expense recognized — (0.4 ) — 0.4 — 2.9 End of period 449,435 $ 1.4 517,470 $ 3.4 493,421 $ 4.0 _______________________________________________________________________________ (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% . No payments were made in 2013 for the 2010-2012 performance cycle as the performance factor was zero .
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 as of December 31, 2015 for each performance cycle: Target Performance Shares outstanding Accrued expense ($ in millions) Performance cycle: 2013 – 2015 167,300 $ 0.6 2014 – 2016 142,710 0.1 2015 – 2017 146,659 0.7 Subtotal 456,669 1.4 Assumed forfeitures (7,234 ) — Total as of December 31, 2015 449,435 $ 1.4
Summary of restricted shares activity	The following summarizes restricted shares activity for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value ($ in millions) Beginning of period 612,500 $ 3.5 915,000 $ 6.5 927,000 $ 9.6 New awards 75,950 1.1 — — — — Forfeitures (9,728 ) (0.1 ) (2,500 ) — (3,000 ) — Vested (296,000 ) — (300,000 ) — (9,000 ) — Expense recognized — (2.0 ) — (3.0 ) — (3.1 ) End of period 382,722 $ 2.5 612,500 $ 3.5 915,000 $ 6.5

Common Shareholders' Equity Acc

Common Shareholders' Equity Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2015
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The pre-tax components of the Company's other comprehensive income (loss) and the related income tax benefit (expense) are as follows: Year ended December 31, 2015 2014 2013 ($ in millions) Net change in benefit plan assets and obligations $ — $ (18.5 ) $ 31.7 Income tax benefit (expense) — 6.5 (11.1 ) Net change in benefit plan assets and obligations, net of tax $ — $ (12.0 ) $ 20.6

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 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 Specialty Products Specialty Industries Consolidated ($ in millions) Year ended December 31, 2015 Earned premiums $ 560.3 $ 615.9 $ — $ 1,176.2 Loss and loss adjustment expense (310.7 ) (390.0 ) — (700.7 ) Policy acquisition expenses (100.1 ) (113.7 ) — (213.8 ) Other underwriting expenses (97.9 ) (120.3 ) — (218.2 ) Total underwriting income (loss) 51.6 (8.1 ) — 43.5 Net investment income — — 45.9 45.9 Net realized and change in unrealized investment gains — — (35.1 ) (35.1 ) Net other revenues (expenses) (0.2 ) 1.4 (1.8 ) (0.6 ) General and administrative expenses — (2.7 ) (12.7 ) (15.4 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income (loss) from continuing operations $ 51.4 $ (9.4 ) $ (16.7 ) $ 25.3 Year ended December 31, 2014 Earned premiums $ 582.1 $ 595.0 $ — $ 1,177.1 Loss and loss adjustment expense (457.9 ) (357.2 ) — (815.1 ) Policy acquisition expenses (96.2 ) (107.1 ) — (203.3 ) Other underwriting expenses (78.4 ) (100.8 ) — (179.2 ) Total underwriting income (loss) (50.4 ) 29.9 — (20.5 ) Net investment income — — 43.4 43.4 Net realized and change in unrealized investment gains — — 40.4 40.4 Net other revenues 0.9 1.1 3.8 5.8 General and administrative expenses 0.2 (2.3 ) (11.7 ) (13.8 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income (loss) from continuing operations $ (49.3 ) $ 28.7 $ 62.9 $ 42.3 Year ended December 31, 2013 Earned premiums $ 553.5 $ 566.9 $ — $ 1,120.4 Loss and loss adjustment expense (312.3 ) (309.8 ) — (622.1 ) Policy acquisition expenses (106.3 ) (102.6 ) — (208.9 ) Other underwriting expenses (97.4 ) (107.4 ) — (204.8 ) Total underwriting income 37.5 47.1 — 84.6 Net investment income — — 43.0 43.0 Net realized and change in unrealized investment gains — — 49.4 49.4 Net other revenues 0.3 1.1 29.8 31.2 General and administrative expenses — (2.4 ) (9.6 ) (12.0 ) Interest expense — — (13.0 ) (13.0 ) Pre-tax income from continuing operations $ 37.8 $ 45.8 $ 99.6 $ 183.2 Insurance Operations Investing, Financing and Corporate Specialty Products Specialty Industries Consolidated ($ in millions) December 31, 2015 Assets Total investment securities $ — $ — $ 2,591.4 $ 2,591.4 Premiums receivable 63.0 156.0 — 219.0 Reinsurance recoverables (1) 139.5 33.6 20.4 193.5 Deferred acquisition costs 49.6 51.1 — 100.7 Ceded unearned premiums 19.2 10.3 — 29.5 Other assets (2) — — 470.4 470.4 Total Assets $ 271.3 $ 251.0 $ 3,082.2 $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves (1) $ 772.2 $ 597.2 $ 20.4 $ 1,389.8 Unearned premiums 288.1 272.2 — 560.3 Funds held under insurance contracts 137.7 — — 137.7 Debt — — 274.8 274.8 Other liabilities (2) — — 237.4 237.4 Total Liabilities $ 1,198.0 $ 869.4 $ 532.6 $ 2,600.0 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 Ceded unearned premiums 7.5 10.4 — 17.9 Other assets (2) — — 478.9 478.9 Total Assets $ 299.3 $ 250.4 $ 3,028.5 $ 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
Schedule of selected balance sheet of the segments	Insurance Operations Investing, Financing and Corporate Specialty Products Specialty Industries Consolidated ($ in millions) December 31, 2015 Assets Total investment securities $ — $ — $ 2,591.4 $ 2,591.4 Premiums receivable 63.0 156.0 — 219.0 Reinsurance recoverables (1) 139.5 33.6 20.4 193.5 Deferred acquisition costs 49.6 51.1 — 100.7 Ceded unearned premiums 19.2 10.3 — 29.5 Other assets (2) — — 470.4 470.4 Total Assets $ 271.3 $ 251.0 $ 3,082.2 $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves (1) $ 772.2 $ 597.2 $ 20.4 $ 1,389.8 Unearned premiums 288.1 272.2 — 560.3 Funds held under insurance contracts 137.7 — — 137.7 Debt — — 274.8 274.8 Other liabilities (2) — — 237.4 237.4 Total Liabilities $ 1,198.0 $ 869.4 $ 532.6 $ 2,600.0 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 Ceded unearned premiums 7.5 10.4 — 17.9 Other assets (2) — — 478.9 478.9 Total Assets $ 299.3 $ 250.4 $ 3,028.5 $ 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 18-"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 December 31, 2015 and 2014, $20.4 million and $23.8 million , respectively, are included in both unpaid loss and loss adjustment expense reserves and reinsurance recoverable included within Investing, Financing, and Corporate resulting from that agreement. (2) Other assets and other liabilities are not separately identifiable at the segment level and have therefore been included within the investing, financing, and corporate segment.
Schedule of net written premiums, earned premiums and ratios for OneBeacon's insurance operations by segment and in total	The following tables provide net written premiums, earned premiums and underwriting ratios for OneBeacon's insurance operations by reportable segment and in total for the years ended December 31, 2015 , 2014 and 2013 : Insurance Operations ($ in millions) Specialty Products Specialty Industries Consolidated Year ended December 31, 2015 Net written premiums $ 533.0 $ 603.6 $ 1,136.6 Earned premiums 560.3 615.9 1,176.2 Underwriting ratios: (1) Loss and LAE 55.5 % 63.3 % 59.6 % Expense 35.3 38.0 36.7 Total combined ratio 90.8 % 101.3 % 96.3 % Year ended December 31, 2014 Net written premiums $ 606.9 $ 610.0 $ 1,216.9 Earned premiums 582.1 595.0 1,177.1 Underwriting ratios: (1) Loss and LAE 78.7 % 60.1 % 69.2 % Expense 30.0 34.9 32.5 Total combined ratio 108.7 % 95.0 % 101.7 % Year ended December 31, 2013 Net written premiums $ 509.6 $ 579.0 $ 1,088.6 Earned premiums 553.5 566.9 1,120.4 Underwriting ratios: (1) Loss and LAE 56.4 % 54.7 % 55.5 % Expense 36.8 37.0 36.9 Total combined ratio 93.2 % 91.7 % 92.4 % _______________________________________________________________________________ (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.

Related Party Disclosures (Tabl

Related Party Disclosures (Tables)	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Management Fees	OneBeacon is responsible for custodial arrangements and the payment of all custodial charges and fees. OneBeacon has agreed to pay annual investment management fees generally based on the quarter-end market values held under custody as set forth in the table below: Assets Under Management Annual Fee Investment Grade Fixed Income: —Up to $1 billion 10.0 basis points —Next $1 billion 8.5 basis points —Next $3 billion 7.5 basis points —Greater than $5 billion 2.5 basis points High Yield Fixed Income 25.0 basis points Equities 100.0 basis points Hedge Funds 100.0 basis points Private Equities & Deferreds: First 2 years of fund's life (committed) 100.0 basis points Thereafter (fair value) 100.0 basis points Affordable housing credit funds: First year of fund's life (committed) 100.0 basis points Thereafter (fair value) 10.0 basis points

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 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 years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders $ 37.0 $ 53.5 $ 145.7 Allocation of income for participating unvested restricted common shares (0.2 ) (0.4 ) (1.4 ) Dividends paid on participating restricted common shares (0.3 ) (0.5 ) (0.8 ) Total allocation to restricted common shares (0.5 ) (0.9 ) (2.2 ) Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 36.5 $ 52.6 $ 143.5 Undistributed (over-distributed) net earnings (in millions): Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ 36.5 $ 52.6 $ 143.5 Dividends paid, net of restricted common share amounts (79.7 ) (79.5 ) (79.4 ) Total undistributed (over-distributed) net earnings, net of restricted common share amounts $ (43.2 ) $ (26.9 ) $ 64.1 Earnings per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.4 Weighted average unvested restricted common shares (1) (0.5 ) (0.6 ) (0.9 ) Basic and diluted earnings per share denominator 94.8 94.7 94.5 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 $ 0.38 $ 0.55 $ 1.52 Dividends declared and paid (0.84 ) (0.84 ) (0.84 ) Undistributed (over-distributed) earnings $ (0.46 ) $ (0.29 ) $ 0.68 _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event.

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2015
Discontinued Operations and Disposal Groups [Abstract]
Schedule of discontinued operations balance sheet statement of operations and other disclosures	The following table outlines the computation of loss per share for discontinued operations attributable to OneBeacon's common shareholders for the years ended December 31, 2015 , 2014 and 2013 : Year ended December 31, 2015 2014 2013 Loss attributable to OneBeacon's common shareholders—basic and diluted (in millions): Net loss from discontinued operations attributable to OneBeacon's common shareholders $ (0.2 ) $ (20.6 ) $ — Allocation of loss for participating unvested restricted common shares — 0.1 — Net loss from discontinued operations attributable to OneBeacon's common shareholders, net of restricted common share amounts $ (0.2 ) $ (20.5 ) $ — Loss per share denominator—basic and diluted (in millions): Total weighted average common shares outstanding 95.3 95.3 95.4 Weighted average unvested restricted common shares (1) (0.5 ) (0.6 ) (0.9 ) Basic and diluted loss per share denominator 94.8 94.7 94.5 Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars): Net loss from discontinued operations attributable to OneBeacon's common shareholders per share $ — $ (0.21 ) $ — _______________________________________________________________________________ (1) Restricted shares outstanding vest in equal installments upon a stated date or upon the occurrence of a specified event. The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations: Year ended December 31, 2015 2014 2013 ($ in millions) Net written premiums $ — $ (0.1 ) $ 0.4 Revenues Earned premiums $ — $ 0.1 $ 0.8 Other revenue (expenses) (0.7 ) — 6.3 Total revenues (0.7 ) 0.1 7.1 Expenses Loss and loss adjustment expenses — (0.7 ) 78.9 Policy acquisition expenses — 0.1 — Other underwriting expenses — 3.5 (0.2 ) Total expenses — 2.9 78.7 Pre-tax loss (0.7 ) (2.8 ) (71.6 ) Income tax benefit 0.2 1.0 25.0 Loss from discontinued operations, net of tax (0.5 ) (1.8 ) (46.6 ) (Loss) gain from sale of discontinued operations, net of tax 0.3 (18.8 ) 46.6 Net loss from discontinued operations, net of tax $ (0.2 ) $ (20.6 ) $ —
Surplus Note Valuation	Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of December 23, 2014: Type of Surplus Note Total Seller Priority Pari Passu (in millions) Par value $ 57.9 $ 43.1 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) 1.6 (8.4 ) (6.8 ) Regulatory approval (2) (4.6 ) (8.0 ) (12.6 ) Liquidity adjustment (3) (11.0 ) (5.7 ) (16.7 ) Total (14.0 ) (22.1 ) (36.1 ) Fair value $ 43.9 $ 21.0 $ 64.9 _______________________________________________________________________________ (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated delay in securing regulatory approvals of interest and principal payments to reflect graduated changes in Issuer's statutory surplus. The monetary impact of the anticipated delay is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. (3) Represents impact of liquidity spread to account for OneBeacon's sole ownership of the notes, lack of a trading market, and ongoing regulatory approval risk.

Consolidating Financial Infor47

Consolidating Financial Information (Tables)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Consolidating Balance Sheet	The following tables present OneBeacon's consolidating balance sheets as of December 31, 2015 and 2014 , and statements of operations and comprehensive income and cash flows for the years ended December 31, 2015 , 2014 and 2013 . 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 The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2015 (in millions) Assets Investment Securities: Fixed maturity investments, at fair value $ — $ 2,074.6 $ 5.9 $ — $ 2,080.5 Short-term investments, at amortized cost (which approximates fair value) 4.4 64.1 0.7 — 69.2 Common equity securities, at fair value — 298.7 — — 298.7 Other investments — 143.0 — — 143.0 Total investment securities 4.4 2,580.4 6.6 — 2,591.4 Cash — 94.6 0.6 — 95.2 Reinsurance recoverables — 193.5 — — 193.5 Premiums receivable — 219.0 — — 219.0 Deferred acquisition costs — 100.7 — — 100.7 Ceded unearned premiums — 29.5 — — 29.5 Net deferred tax asset — 140.1 — 0.1 140.2 Investment income accrued — 10.1 — — 10.1 Accounts receivable on unsettled investment sales — 30.5 — — 30.5 Investments in subsidiaries 996.9 — 951.3 (1,948.2 ) — Other assets 0.5 190.6 3.3 — 194.4 Total assets $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Liabilities Unpaid loss and loss adjustment expense reserves $ — $ 1,389.8 $ — $ — $ 1,389.8 Unearned premiums — 560.3 — — 560.3 Funds held under insurance contracts — 137.7 — — 137.7 Debt — — 274.8 — 274.8 Other liabilities 0.9 230.4 6.1 — 237.4 Total liabilities 0.9 2,318.2 280.9 — 2,600.0 OneBeacon's common shareholders' equity and noncontrolling interests Total OneBeacon's common shareholders' equity 1,000.9 1,267.2 680.9 (1,948.1 ) 1,000.9 Noncontrolling interests — 3.6 — — 3.6 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,000.9 1,270.8 680.9 (1,948.1 ) 1,004.5 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,001.8 $ 3,589.0 $ 961.8 $ (1,948.1 ) $ 3,604.5 Consolidating Balance Sheet The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated as of December 31, 2014 (in millions) 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 Other investments — 203.8 — — 203.8 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 Ceded unearned premiums — 17.9 — — 17.9 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 — 1,051.8 (2,079.2 ) — Other assets 0.3 180.1 4.4 — 184.8 Assets held for sale — 58.1 — — 58.1 Total assets $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 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 Other liabilities 0.3 235.3 7.1 — 242.7 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 1,303.4 775.7 (2,079.1 ) 1,045.8 Noncontrolling interests — 3.5 — — 3.5 Total OneBeacon's common shareholders' equity and noncontrolling interests 1,045.8 1,306.9 775.7 (2,079.1 ) 1,049.3 Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests $ 1,046.1 $ 3,553.7 $ 1,057.5 $ (2,079.1 ) $ 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 Year ended December 31, 2015 (in millions) Revenues Earned premiums $ — $ 1,176.2 $ — $ — $ 1,176.2 Net investment income — 45.9 — — 45.9 Net realized and change in unrealized investment gains — (35.1 ) — — (35.1 ) Net other revenues (expenses) — (0.6 ) — — (0.6 ) Total revenues — 1,186.4 — — 1,186.4 Expenses Loss and loss adjustment expenses — 700.7 — — 700.7 Policy acquisition expenses — 213.8 — — 213.8 Other underwriting expenses — 218.2 — — 218.2 General and administrative expenses 4.8 10.3 0.3 — 15.4 Interest expense — — 13.0 — 13.0 Total expenses 4.8 1,143.0 13.3 — 1,161.1 Pre-tax income (loss) from continuing operations (4.8 ) 43.4 (13.3 ) — 25.3 Income tax benefit — 8.2 4.7 — 12.9 Net income (loss) from continuing operations (4.8 ) 51.6 (8.6 ) — 38.2 Loss from discontinued operations, net of tax — (0.5 ) — — (0.5 ) Gain from sale of discontinued operations, net of tax — 0.3 — — 0.3 Income (loss) before equity in earnings of unconsolidated affiliates (4.8 ) 51.4 (8.6 ) — 38.0 Equity in earnings of subsidiaries, net of tax 41.6 — 8.3 (49.9 ) — Net income including noncontrolling interests 36.8 51.4 (0.3 ) (49.9 ) 38.0 Less: Net income attributable to noncontrolling interests — (1.2 ) — — (1.2 ) Net income attributable to OneBeacon's common shareholders 36.8 50.2 (0.3 ) (49.9 ) 36.8 Net change in benefit plan assets and obligations, net of tax — — — — — Comprehensive income attributable to OneBeacon's common shareholders $ 36.8 $ 50.2 $ (0.3 ) $ (49.9 ) $ 36.8 Consolidating Statement of Operations and Comprehensive Income (Loss) The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 (in millions) Revenues Earned premiums $ — $ 1,177.1 $ — $ — $ 1,177.1 Net investment income — 44.4 0.1 (1.1 ) 43.4 Net realized and change in unrealized investment gains — 44.6 — (4.2 ) 40.4 Net other revenues (expenses) — 5.8 (3.7 ) 3.7 5.8 Total revenues — 1,271.9 (3.6 ) (1.6 ) 1,266.7 Expenses Loss and loss adjustment expenses — 815.1 — — 815.1 Policy acquisition expenses — 203.3 — — 203.3 Other underwriting expenses — 179.2 — — 179.2 General and administrative expenses 5.1 8.4 0.3 — 13.8 Interest expense — — 14.1 (1.1 ) 13.0 Total expenses 5.1 1,206.0 14.4 (1.1 ) 1,224.4 Pre-tax income (loss) from continuing operations (5.1 ) 65.9 (18.0 ) (0.5 ) 42.3 Income tax benefit — 5.8 6.3 0.2 12.3 Net income (loss) from continuing operations (5.1 ) 71.7 (11.7 ) (0.3 ) 54.6 Loss from discontinued operations, net of tax — (1.8 ) — — (1.8 ) Loss from sale of discontinued operations, net of tax — (18.8 ) — — (18.8 ) Net income (loss) before equity in earnings of unconsolidated affiliates (5.1 ) 51.1 (11.7 ) (0.3 ) 34.0 Equity in earnings of subsidiaries, net of tax 38.0 — 9.5 (47.5 ) — Net income (loss) including noncontrolling interests 32.9 51.1 (2.2 ) (47.8 ) 34.0 Less: Net income attributable to noncontrolling interests — (1.1 ) — — (1.1 ) Net income (loss) attributable to OneBeacon's common shareholders 32.9 50.0 (2.2 ) (47.8 ) 32.9 Net change in benefit plan assets and obligations, net of tax (12.0 ) — (12.0 ) 12.0 (12.0 ) Comprehensive income (loss) attributable to OneBeacon's common shareholders $ 20.9 $ 50.0 $ (14.2 ) $ (35.8 ) $ 20.9 Consolidating Statement of Operations and Comprehensive Income The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 (in millions) Revenues Earned premiums $ — $ 1,120.4 $ — $ — $ 1,120.4 Net investment income — 44.5 (0.3 ) (1.2 ) 43.0 Net realized and change in unrealized investment gains — 48.9 (0.7 ) 1.2 49.4 Net other revenues — 31.2 — — 31.2 Total revenues — 1,245.0 (1.0 ) — 1,244.0 Expenses Loss and loss adjustment expenses — 622.1 — — 622.1 Policy acquisition expenses — 208.9 — — 208.9 Other underwriting expenses — 204.8 — — 204.8 General and administrative expenses 5.0 7.1 (0.1 ) — 12.0 Interest expense — — 14.2 (1.2 ) 13.0 Total expenses 5.0 1,042.9 14.1 (1.2 ) 1,060.8 Pre-tax income (loss) from continuing operations (5.0 ) 202.1 (15.1 ) 1.2 183.2 Income tax (expense) benefit 0.1 (42.6 ) 6.2 (0.2 ) (36.5 ) Net income (loss) from continuing operations (4.9 ) 159.5 (8.9 ) 1.0 146.7 Loss from discontinued operations, net of tax — (46.6 ) — — (46.6 ) Gain from sale of discontinued operations, net of tax — 46.6 — — 46.6 Income (loss) before equity in earnings of unconsolidated affiliates (4.9 ) 159.5 (8.9 ) 1.0 146.7 Equity in earnings of subsidiaries, net of tax 150.6 — 134.4 (285.0 ) — Net income including noncontrolling interests 145.7 159.5 125.5 (284.0 ) 146.7 Less: Net income attributable to noncontrolling interests — (1.0 ) — — (1.0 ) Net income attributable to OneBeacon's common shareholders 145.7 158.5 125.5 (284.0 ) 145.7 Net change in benefit plan assets and obligations, net of tax 20.6 — 20.6 (20.6 ) 20.6 Comprehensive income attributable to OneBeacon's common shareholders $ 166.3 $ 158.5 $ 146.1 $ (304.6 ) $ 166.3
Consolidating Statement of Cash Flows	Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2015 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 36.8 $ 51.4 $ (0.3 ) $ (49.9 ) $ 38.0 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (41.6 ) — (8.3 ) 49.9 — Net loss from discontinued operations — 0.5 — — 0.5 Net gain from sale of discontinued operations — (0.3 ) — — (0.3 ) Net realized and change in unrealized investment gains — 35.1 — — 35.1 Net loss on sale of business — 3.7 — — 3.7 Deferred income tax benefit — (5.8 ) — — (5.8 ) Dividends received from subsidiaries 72.0 99.9 110.9 (282.8 ) — Other operating items: Net change in loss and LAE reserves — 47.6 — — 47.6 Net change in unearned premiums — (28.0 ) — — (28.0 ) Net change in ceded unearned premium — (11.6 ) — — (11.6 ) Net change in premiums receivable — 22.5 — — 22.5 Net change in reinsurance recoverable on paid and unpaid losses — (19.7 ) — — (19.7 ) Net change in funds held under reinsurance contracts — 37.1 — — 37.1 Net change in funds held under insurance contracts. — 56.7 — — 56.7 Net change in other assets and liabilities 2.5 13.6 0.5 — 16.6 Net cash provided from operations—continuing operations 69.7 302.7 102.8 (282.8 ) 192.4 Net cash used for operations—discontinued operations — (0.5 ) — — (0.5 ) Net cash provided from operations 69.7 302.2 102.8 (282.8 ) 191.9 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments 14.0 118.5 0.6 — 133.1 Maturities of fixed maturity investments — 262.4 — — 262.4 Sales of fixed maturity investments — 491.5 88.7 183.3 763.5 Sales of common equity securities — 345.6 — — 345.6 Return of capital and distributions of other investments — 40.5 — — 40.5 Purchases of fixed maturity investments — (1,055.3 ) (94.9 ) (183.3 ) (1,333.5 ) Purchases of common equity securities — (323.5 ) — — (323.5 ) Contributions for other investments — (4.2 ) — — (4.2 ) Net change in unsettled investment purchases and sales — (23.8 ) — — (23.8 ) Proceeds from sale of property and equipment — 56.8 — — 56.8 Net acquisitions of property and equipment — (11.5 ) — — (11.5 ) Capital contribution from parent — 2.2 5.5 (7.7 ) — Net cash provided from (used for) investing activities—continuing operations 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash provided from (used for) investing activities 14.0 (100.8 ) (0.1 ) (7.7 ) (94.6 ) Cash flows from financing activities: Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (182.9 ) (99.9 ) 282.8 — Capital contribution to subsidiary — (5.5 ) (2.2 ) 7.7 — Repurchases and retirements of common stock (3.7 ) — — — (3.7 ) Payments on capital lease obligation — (5.4 ) — — (5.4 ) Net cash used for financing activities—continuing operations (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (83.7 ) (193.8 ) (102.1 ) 290.5 (89.1 ) Net increase in cash during period — 7.6 0.6 — 8.2 Cash balance at beginning of period — 87.0 — — 87.0 Cash balance at end of period $ — $ 94.6 $ 0.6 $ — $ 95.2 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2014 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 32.9 $ 51.1 $ (2.2 ) $ (47.8 ) $ 34.0 Charges (credits) to reconcile net income to cash flows provided from (used for) operations: Undistributed earnings from subsidiaries (38.0 ) — (9.5 ) 47.5 — Net loss from discontinued operations — 1.8 — — 1.8 Net loss from sale of discontinued operations — 18.8 — — 18.8 Net realized and change in unrealized investment gains — (44.6 ) — 4.2 (40.4 ) Net other realized losses — (3.7 ) 3.7 — — Deferred income tax benefit — (18.8 ) — (0.2 ) (19.0 ) Dividends received from subsidiaries 90.4 15.0 50.0 (155.4 ) — Other operating items: Net change in loss and LAE reserves — 287.9 — — 287.9 Net change in unearned premiums — 43.4 — — 43.4 Net change in ceded unearned premiums — (3.6 ) — — (3.6 ) Net change in premiums receivable — (13.3 ) — — (13.3 ) Net change in reinsurance recoverable on paid and unpaid losses — (83.9 ) — — (83.9 ) Net change in funds held under reinsurance contracts — (35.3 ) — — (35.3 ) Net change in funds held under insurance contracts — 17.7 — — 17.7 Net change in other assets and liabilities 1.9 (49.6 ) (1.9 ) (6.5 ) (56.1 ) Net cash provided from operations—continuing operations 87.2 182.9 40.1 (158.2 ) 152.0 Net cash used for operations—discontinued operations — (54.5 ) — — (54.5 ) Net cash provided from operations 87.2 128.4 40.1 (158.2 ) 97.5 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (5.4 ) (62.8 ) 2.7 — (65.5 ) Maturities of fixed maturity investments — 396.4 — — 396.4 Sales of fixed maturity investments — 1,927.9 80.3 (165.1 ) 1,843.1 Sales of common equity securities — 240.2 — — 240.2 Return of capital and distributions of other investments — 53.4 — — 53.4 Purchases of fixed maturity investments — (2,265.1 ) (80.9 ) 139.2 (2,206.8 ) Purchases of common equity securities — (202.4 ) — — (202.4 ) Contributions for other investments — (81.9 ) — — (81.9 ) Net change in unsettled investment purchases and sales — (15.0 ) — — (15.0 ) Net acquisitions of property and equipment — (2.2 ) — — (2.2 ) Capital contribution from parent — 70.0 70.0 (140.0 ) — Net cash (used for) provided from investing activities—continuing operations (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (5.4 ) 58.5 72.1 (165.9 ) (40.7 ) Cash flows from financing activities: Repurchases of debt — — (28.7 ) 28.7 — Cash dividends paid to common shareholders (80.0 ) — — — (80.0 ) Cash dividends paid to parent — (140.4 ) (15.0 ) 155.4 — Capital contribution to subsidiary — (70.0 ) (70.0 ) 140.0 — Repurchases and retirements of common stock (1.8 ) — — — (1.8 ) Payments on capital lease obligation — (5.3 ) — — (5.3 ) Net cash used for financing activities—continuing operations (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (81.8 ) (215.7 ) (113.7 ) 324.1 (87.1 ) Net decrease in cash during period — (28.8 ) (1.5 ) — (30.3 ) Cash transferred with sale of business — (50.8 ) — — (50.8 ) Net decrease after cash transferred with sale of business — (79.6 ) (1.5 ) — (81.1 ) Cash balance at beginning of period — 166.6 1.5 — 168.1 Cash balance at end of period $ — $ 87.0 $ — $ — $ 87.0 Consolidating Statement of Cash Flows The Company (guarantor) Non-guarantor subsidiaries OBH (issuer) Consolidating adjustments Consolidated Year ended December 31, 2013 ($ in millions) Cash flows from operations: Net income including noncontrolling interests $ 145.7 $ 159.5 $ 125.5 $ (284.0 ) $ 146.7 Charges (credits) to reconcile net income to cash flows provided from operations: Undistributed earnings from subsidiaries (150.6 ) — (134.4 ) 285.0 — Net loss from discontinued operations — 46.6 — — 46.6 Net gain from sale of discontinued operations — (46.6 ) — — (46.6 ) Net realized and change in unrealized investment gains — (48.9 ) 0.7 (1.2 ) (49.4 ) Net realized gain on sale of business — (23.0 ) — — (23.0 ) Deferred income tax expense (benefit) — 14.9 (0.1 ) 0.2 15.0 Dividends received from subsidiaries 92.0 — 218.0 (310.0 ) — Other operating items: Net change in loss and LAE reserves — 54.3 — — 54.3 Net change in unearned premiums — (28.9 ) — — (28.9 ) Net change in ceded unearned premiums — (2.8 ) — — (2.8 ) Net change in premiums receivable — (2.6 ) — — (2.6 ) Net change in reinsurance recoverable on paid and unpaid losses — 20.7 — — 20.7 Net change in funds held under reinsurance contracts — (1.8 ) — — (1.8 ) Net change in funds held under insurance contracts — 57.4 — — 57.4 Net change in other assets and liabilities 3.4 45.8 (29.4 ) — 19.8 Net cash provided from operations—continuing operations 90.5 244.6 180.3 (310.0 ) 205.4 Net cash used for operations—discontinued operations — (76.7 ) — — (76.7 ) Net cash provided from operations 90.5 167.9 180.3 (310.0 ) 128.7 Cash flows from investing activities: Net maturities, purchases and sales of short-term investments (10.3 ) 26.3 56.2 — 72.2 Maturities of fixed maturity investments — 223.7 21.5 — 245.2 Sales of fixed maturity investments — 1,496.7 386.7 (483.4 ) 1,400.0 Sales of common equity securities — 196.7 — — 196.7 Return of capital and distributions of other investments — 67.5 — — 67.5 Purchases of fixed maturity investments — (1,787.2 ) (393.2 ) 483.4 (1,697.0 ) Purchases of common equity securities — (206.3 ) — — (206.3 ) Contributions for other investments — (22.0 ) — — (22.0 ) Proceeds from the sale of business — 31.3 — — 31.3 Net change in unsettled investment purchases and sales — 4.1 — — 4.1 Net acquisitions of property and equipment — (10.3 ) — — (10.3 ) Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — 250.0 — (250.0 ) — Net cash (used for) provided from investing activities—continuing operations (10.3 ) 270.5 71.2 (250.0 ) 81.4 Net cash provided from investing activities—discontinued operations — — — — — Net cash (used for) provided from investing activities (10.3 ) 270.5 71.2 (250.0 ) 81.4 Cash flows from financing activities: Cash dividends paid to common shareholders (80.2 ) — — — (80.2 ) Cash dividends paid to parent — (310.0 ) — 310.0 — Return of capital to OneBeacon U.S. Enterprises Holdings, Inc. — — (250.0 ) 250.0 — Payments on capital lease obligation — (5.7 ) — — (5.7 ) Net cash used for financing activities—continuing operations (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net cash used for financing activities—discontinued operations — — — — — Net cash used for financing activities (80.2 ) (315.7 ) (250.0 ) 560.0 (85.9 ) Net increase in cash during period — 122.7 1.5 — 124.2 Cash balance at beginning of period — 43.9 — — 43.9 Cash balance at end of period $ — $ 166.6 $ 1.5 $ — $ 168.1

Selected Quarterly Financial 48

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Selected quarterly financial data for 2015 and 2014 is shown in the following table. The quarterly financial data includes, in the opinion of management, all recurring adjustments necessary for a fair presentation of the results of operations for the interim periods. 2015 Three months ended 2014 Three months ended ($ in millions, except per share amounts) Mar. 31 June 30 Sept. 30 Dec. 31 Mar. 31 June 30 Sept. 30 Dec. 31 Revenues $ 308.2 $ 314.2 $ 267.8 $ 296.2 $ 306.8 $ 326.0 $ 301.5 $ 332.4 Expenses 280.1 311.3 284.6 285.1 252.0 294.3 296.6 381.5 Pre-tax income (loss) from continuing operations 28.1 2.9 (16.8 ) 11.1 54.8 31.7 4.9 (49.1 ) Tax (expense) benefit (3.4 ) 0.9 3.5 11.9 (7.1 ) (5.9 ) 1.1 24.2 Net income (loss) from continuing operations 24.7 3.8 (13.3 ) 23.0 47.7 25.8 6.0 (24.9 ) Loss from discontinued operations, net of tax (0.1 ) (0.2 ) (0.1 ) (0.1 ) (0.5 ) (0.1 ) (0.3 ) (0.9 ) Gain (loss) from sale of discontinued operations, net of tax — 0.3 — — — (0.5 ) (7.0 ) (11.3 ) Net income (loss) including noncontrolling interests 24.6 3.9 (13.4 ) 22.9 47.2 25.2 (1.3 ) (37.1 ) Less: Net income attributable to noncontrolling interests (0.5 ) (0.5 ) — (0.2 ) (0.4 ) (0.5 ) — (0.2 ) Net income (loss) attributable to OneBeacon's common shareholders $ 24.1 $ 3.4 $ (13.4 ) $ 22.7 $ 46.8 $ 24.7 $ (1.3 ) $ (37.3 ) Earnings (loss) per share attributable to OneBeacon's common shareholders—basic and diluted: (1) Net income (loss) from continuing operations per share $ 0.25 $ 0.03 $ (0.14 ) $ 0.24 $ 0.50 $ 0.26 $ 0.05 $ (0.26 ) Net Loss from discontinued operations, net of tax, per share — — — — (0.01 ) — (0.07 ) (0.13 ) Net income (loss) attributable to OneBeacon's common shareholders per share $ 0.25 $ 0.03 $ (0.14 ) $ 0.24 $ 0.49 $ 0.26 $ (0.02 ) $ (0.39 ) (1) Due to the averaging of shares, quarterly earnings per share may not add to the total for the full year.

Nature of Operations and Summ49

Nature of Operations and Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Sep. 30, 2014USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2015USD ($)segmentsecurity	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Jan. 01, 2013USD ($)
Basis of presentation
Number of underwriting segments | segment									16
Percentage of fair value investments using observable inputs	92.00%				90.00%				92.00%	90.00%
Minimum percentage of variation from expected price required to treat prices of investments provided by pricing services as outliers	5.00%								5.00%
Minimum variation from expected price require to treat prices of investments provided by pricing services as outliers	$ 1								$ 1
Number of securities outside expected price results | security									8
Deferred policy acquisitions costs									$ 237.3	$ 237.6	$ 210.3
Deferred policy acquisition costs related ot other underwriting expenses									21.3	22.9	23.4
Unamortized discount									(239.7)	(227.6)	(230.5)
Amortization of deferred policy acquisition costs included in underwriting expense									$ (22.2)	$ (23)	(22.4)
Workers’ compensation statutory discount rate									2.50%	2.50%
Amount of workers' compensation discount	1.1				$ 1				$ 1.1	$ 1
Impairment of capitalized software									1.6
Unamortized deferred software cost	12.7				13				12.7	13
Cumulative loss recognized					(1.2)					(1.2)	0.6	$ 0.3
Net investment income									45.9	43.4	43
Income tax benefit	$ (11.9)	$ (3.5)	$ (0.9)	$ 3.4	$ (24.2)	$ (1.1)	$ 5.9	$ 7.1	$ (12.9)	(12.3)	36.5
White Mountains Insurance Group Ltd
Basis of presentation
Ownership interest (as a percent)	75.50%								75.50%
Specialty Products
Basis of presentation
Number of underwriting segments | segment									10
Net investment income									$ 0	0	0
Specialty Industries
Basis of presentation
Number of underwriting segments | segment									6
Net investment income									$ 0	0	0
Restatement Adjustment | Accounting Standards Update 2014-01
Basis of presentation
Net investment income										1.7	1.9
Income tax benefit										$ 2.3	$ 2.2

Acqusitions and Dispositions (D

Acqusitions and Dispositions (Details)	Jan. 02, 2013USD ($)	Dec. 31, 2015USD ($)Rate	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)entity	Sep. 30, 2014USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2015USD ($)Rate	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2015	Dec. 31, 2015USD ($)	Dec. 23, 2014USD ($)
Dispositions
Reinsurance recoverables						$ 173,800,000					$ 173,800,000			$ 193,500,000
(Loss) gain from sale of discontinued operations, net of tax		$ 0	$ 0	$ 300,000	$ 0	$ (11,300,000)	$ (7,000,000)	$ (500,000)	$ 0	$ 300,000	(18,800,000)	$ 46,600,000
Earned premiums										1,176,200,000	1,177,100,000	1,120,400,000
Runoff
Dispositions
Entity Distributions | entity						1
Surplus notes issued as seller financing in sale of discontinued operations															$ 101,000,000
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value															$ 64,900,000
Essentia Insurance Company
Dispositions
Gain on sale of discontinued operation, pre-tax	$ 23,000,000				$ 3,700,000
(Loss) gain from sale of discontinued operations, net of tax	$ 15,000,000
Earned premiums										$ 0	$ 0	$ 89,100,000
Crop
Dispositions
Agreement Length										5 years
Consideration received														3,000,000
Quota share reinsurance agreement percentage		100.00%								100.00%			100.00%
Net business exposure														$ 0

Unpaid Loss and Loss Adjustme51

Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross beginning balance		$ 1,054.3	$ 1,342.2	$ 1,054.3	$ 1,000
Less beginning reinsurance recoverable on unpaid losses		(80.2)	(161.6)	(80.2)	(107.3)
Net ending loss and LAE reserves	$ 1,180.6		1,203.8	1,180.6	974.1	$ 892.7
Claims and Claims Adjustment Expenses Incurred Related to	33.7		702.5	725.3	622.1
Loss and LAE incurred relating to prior year losses	75.5	$ 14.3	(1.8)	89.8	0
Total incurred loss and LAE from continuing operations			700.7	815.1	622.1
Loss and LAE paid relating to Current year losses			(202.4)	(199.6)	(188.6)
Loss and LAE paid relating to Prior year losses			(475.1)	(409)	(352.1)
Total loss and LAE payments from continuing operations			(677.5)	(608.6)	(540.7)
Net loss and LAE reserves	109.2		1,203.8	1,180.6	974.1
Total incurred loss and LAE from discontinued operations			0	(0.7)	78.9
Total loss and LAE payments from discontinued operations			0	(55.1)	(102.3)
Net loss and LAE reserves			1,203.8	1,124.8	950.7
Net change in loss and LAE reserves reported in liabilities held for sale			0		23.4
Net loss and LAE reserves sold			0	(132.6)	0
Plus ending reinsurance recoverable on unpaid losses	(161.6)		(186)	(161.6)	(80.2)
Gross ending balance	1,342.2		$ 1,389.8	1,342.2	1,054.3
Runoff
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net change in loss and LAE reserves reported in liabilities held for sale				188.4
Loss and Loss Adjustment Expense Reserves Reclassified to from Held For Sale					$ 188.4	$ 211.8
One Beacon
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Claims and Claims Adjustment Expenses Incurred Related to	33.7
Loss and LAE incurred relating to prior year losses	75.5
Net loss and LAE reserves	$ 109.2			$ 89.8

Unpaid Loss and Loss Adjustme52

Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Loss and LAE incurred relating to prior year losses	$ 75.5	$ 14.3	$ (1.8)	$ 89.8	$ 0
Liability for unpaid claims and claims adjustment expense for prior years			475.1	409	352.1
Net loss and LAE reserves	109.2		1,203.8	1,180.6	974.1
Claims and Claims Adjustment Expenses Incurred Related to	33.7		702.5	725.3	$ 622.1
Specialty Product Lines [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to			$ 29.9
One Beacon
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Loss and LAE incurred relating to prior year losses	75.5
Net loss and LAE reserves	109.2			89.8
Claims and Claims Adjustment Expenses Incurred Related to	33.7
One Beacon | Other Professional Lines [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Loss and LAE incurred relating to prior year losses	31.9
Liability for unpaid claims and claims adjustment expense for prior years	31.9
Net loss and LAE reserves	43			42.2
Claims and Claims Adjustment Expenses Incurred Related to	11.1
One Beacon | Entertainment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Loss and LAE incurred relating to prior year losses	11.6
Liability for unpaid claims and claims adjustment expense for prior years	11.6
Net loss and LAE reserves	13.1			13.5
Claims and Claims Adjustment Expenses Incurred Related to	1.5
One Beacon | Crop
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Loss and LAE incurred relating to prior year losses	0
Net loss and LAE reserves	3.8			$ 0
Claims and Claims Adjustment Expenses Incurred Related to	$ 3.8

Unpaid Loss and Loss Adjustme53

Unpaid Loss and Loss Adjustment Expense ("LAE") Reserves - LAE Development (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	$ 33.7		$ 702.5	$ 725.3	$ 622.1
Loss and LAE incurred relating to prior year losses	75.5	$ 14.3	(1.8)	89.8	0
Net loss and LAE reserves	109.2		$ 1,203.8	1,180.6	$ 974.1
One Beacon
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	33.7
Loss and LAE incurred relating to prior year losses	75.5
Net loss and LAE reserves	109.2			89.8
One Beacon | Other Professional Lines and Management Liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	17.7
One Beacon | Other Professional Lines [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	11.1
Loss and LAE incurred relating to prior year losses	31.9
Net loss and LAE reserves	43			42.2
One Beacon | Management Liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	6.6
Loss and LAE incurred relating to prior year losses	8.4
Net loss and LAE reserves	15			16.4
One Beacon | Financial Services [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	2
Loss and LAE incurred relating to prior year losses	6.5
Net loss and LAE reserves	8.5			6.5
One Beacon | Healthcare Segment [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	3.2
Loss and LAE incurred relating to prior year losses	(0.4)
Net loss and LAE reserves	2.8			(6)
One Beacon | Crop
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	3.8
Loss and LAE incurred relating to prior year losses	0
Net loss and LAE reserves	3.8			0
One Beacon | Other Insurance Product Line [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	2.8
Loss and LAE incurred relating to prior year losses	(0.4)
Net loss and LAE reserves	2.4			1.6
One Beacon | Specialty Product Lines [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	(1.1)
Loss and LAE incurred relating to prior year losses	5.7
Net loss and LAE reserves	4.6			1.1
One Beacon | Entertainment
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	1.5
Loss and LAE incurred relating to prior year losses	11.6
Net loss and LAE reserves	13.1			13.5
One Beacon | Government Risk [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	1.2
Loss and LAE incurred relating to prior year losses	7.1
Net loss and LAE reserves	8.3			8.5
One Beacon | Specialty Products
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	28.4
Loss and LAE incurred relating to prior year losses	51.7
Net loss and LAE reserves	80.1			61.8
One Beacon | Accident [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	0
Loss and LAE incurred relating to prior year losses	3.5
Net loss and LAE reserves	3.5			6
One Beacon | Other Specialty Industries [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	2.6
Loss and LAE incurred relating to prior year losses	1.6
Net loss and LAE reserves	4.2			0
One Beacon | Specialty Industries
Liability for Claims and Claims Adjustment Expense [Line Items]
Claims and Claims Adjustment Expenses Incurred Related to	5.3
Loss and LAE incurred relating to prior year losses	23.8
Net loss and LAE reserves	$ 29.1			$ 28

Reinsurance - Effects of Reinsu

Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct	$ 1,279.9	$ 1,257.5	$ 1,103.1
Assumed	36	65.9	59.8
Ceded	(179.3)	(106.5)	(74.3)
Net written premiums	1,136.6	1,216.9	1,088.6
Direct	1,298	1,209.1	1,043.3
Assumed	45.9	70.9	148.5
Ceded	(167.7)	(102.9)	(71.4)
Net earned premiums	1,176.2	1,177.1	1,120.4
Direct	783	778.7	584.9
Assumed	55.7	115.7	76.3
Ceded	(138)	(79.3)	(39.1)
Net loss and LAE	700.7	815.1	622.1
Collector Cars and Boat Business
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Assumed			89.1
Assumed			$ 41.9
Crop
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Ceded	(33.3)
Ceded	(33.3)
Ceded	$ (33.4)
Quota share reinsurance agreement percentage	100.00%			100.00%
Restatement Adjustment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct		52
Assumed		$ 52

Reinsurance - Reinsurance Treat

Reinsurance - Reinsurance Treaties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2012
Reinsurance Retention Policy [Line Items]
Reinsurance Program Reinsured Terrorism Losses	$ 20,000,000
Reinsurance Retention Policy, Reinsured Risk, Percentage, Minimum in 2020	80.00%
Reinsurance recoverable on paid losses				$ 7,500,000
Reinsurance recoverable on unpaid losses		$ 161,600,000		186,000,000	$ 80,200,000	$ 107,300,000
Reinsurance recoverables		173,800,000		193,500,000
Workers compensation | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance amount reinsured for more than one insured	$ 10,000,000
Workers compensation | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount reinsured for more than one insured	60,000,000
Property Catastrophe Reinsurance | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	$ 20,000,000
Property Per Risk Reinsurance Program
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	100.00%
Property Per Risk Reinsurance Program | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 3,000,000	$ 5,000,000
Property Per-Risk, Acts of Terrorism
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	$ 120,000,000
Reinsurance reinsured risk, percentage	84.00%
Terrorism Risk Insurance Program, initial annual aggregate industry loss minimum in order for a loss to be covered				120,000,000
Reinsurance Retention Policy, Amount Retained, Limit in 2020				$ 200,000,000
Co-Participation Percentage	16.00%
Co-Participation Percentage, Annual Increase	1.00%
Property Per-Risk, Acts of Terrorism | Maximum
Reinsurance Retention Policy [Line Items]
Co-Participation Percentage	20.00%
Reinsurance program reinsured losses	$ 100,000,000,000
Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance amount reinsured for more than one insured	10,000,000
Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount reinsured for more than one insured	40,000,000
Property Per Risk Treaty | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	3,000,000
Property Per Risk Treaty | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	100,000,000
HMO Provider Excess [Member] [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	5,000,000
Film Completion [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	2,000,000
Film Completion [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 35,000,000
Layer One | Property Catastrophe Reinsurance | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	95.00%
Layer One | Property Catastrophe Reinsurance | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 10,000,000
Layer Two | Property Catastrophe Reinsurance | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	100.00%
Layer Two | Property Catastrophe Reinsurance | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 100,000,000
Layer Three | Property Catastrophe Reinsurance | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	130,000,000
Facultative Layer [Member] | Film Completion [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	60,000,000
Specialty Product Lines [Member] | Property Catastrophe Reinsurance | Minimum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	6,000,000
Amount retained, per risk	1
Specialty Product Lines [Member] | Property Catastrophe Reinsurance | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	34,000,000
Healthcare Professional Liability | Layer One | Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	3,000,000
Healthcare Professional Liability | Layer One | Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	10,000,000
Healthcare Professional Liability | Layer Two | Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	10,000,000
Healthcare Professional Liability | Layer Two | Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	20,000,000
Casualty Business | Layer One | Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	3,000,000
Casualty Business | Layer One | Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	11,000,000
Casualty Business | Layer Two | Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	11,000,000
Casualty Business | Layer Two | Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 21,000,000
Casualty Reinsurance Program [Member] | Layer Two
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	100.00%
Workers Compensation Losses | Casualty Reinsurance Program [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	100.00%
Workers Compensation Losses | Casualty Reinsurance Program [Member] | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 2,000,000
Workers Compensation Losses | Casualty Reinsurance Program [Member] | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	10,000,000
Inland and Ocean Marine | Marine Treaty Per Occurrence
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	2,500,000
Inland and Ocean Marine | Property Per Risk Treaty | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	20,000,000
Inland and Ocean Marine | Catastrophic Losses | Minimum
Reinsurance Retention Policy [Line Items]
Insurance deductible for individual large claims	5,000,000
Inland and Ocean Marine | Catastrophic Losses | Maximum
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	60,000,000
Inland and Ocean Marine | Layer One | Marine Treaty
Reinsurance Retention Policy [Line Items]
Reinsurance amount retained	7,500,000
Amount retained, per risk	2,500,000
Surety Underwriting | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 100,000,000
Surety Underwriting | Insurance Per Bond
Reinsurance Retention Policy [Line Items]
Reinsurance reinsured risk, percentage	100.00%
Surety Underwriting | Insurance Per Bond | Minimum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 5,000,000
Surety Underwriting | Insurance Per Bond | Maximum
Reinsurance Retention Policy [Line Items]
Amount retained, per risk	$ 50,000,000
Crop
Reinsurance Retention Policy [Line Items]
Quota share reinsurance agreement percentage	100.00%		100.00%

Reinsurance - Credit Risk (Deta

Reinsurance - Credit Risk (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Reinsurance recoverables	$ 193.5	$ 173.8
% of total	100.00%
AA
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Reinsurance recoverables	$ 41.7
% of total	22.00%
A
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Reinsurance recoverables	$ 126.2
% of total	65.00%
BBB, Not Rated and Other
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Reinsurance recoverables	$ 25.6
% of total	13.00%

Investment Securities (Net inve

Investment Securities (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross investment income	$ 50.9	$ 50.4	$ 49.8
Less investment expenses	(5)	(7)	(6.8)
Net investment income, pre-tax	45.9	43.4	43
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross investment income	43.8	41.8	40.6
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross investment income	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross investment income	6.1	6.5	6.2
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross investment income	$ 1	$ 2.1	$ 3

Investment Securities (Net real

Investment Securities (Net realized investment gains (losses)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 47.2	$ 69.7	$ 44.2
Trading Securities, Tax Realized Holding Gain (Loss) on Investments	(9.1)	(21)	(20.5)
Trading Securities, Tax Realized Holding Gain (Loss) on Investments, After Tax	38.1	48.7	23.7
Trading Securities, Realized Gain	64.2	75	70.1
Trading Securities, Realized Loss	(17)	(5.3)	(25.9)
Accounts receivable on unsettled investment sales	30.5	7.2
Accounts payable on unsettled investment purchases	0	0.5
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	2	6.6	2.1
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	33.8	53.9	36.1
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	$ 11.4	$ 9.2	$ 6

Investment Securities (Changes

Investment Securities (Changes in fair value) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	$ (82.5)	$ (28.9)	$ 5.1
Changes in net foreign currency translation gains (losses)	0.2	(0.4)	0.1
Total net changes in fair value reflected in revenues	(82.3)	(29.3)	5.2
Change in Deferred Gains (Losses)	0	0	(0.8)
Fixed maturity investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(15.7)	1.9	(34.4)
Changes in net foreign currency translation gains (losses)	0	0	0
Total net changes in fair value reflected in revenues	(15.7)	1.9	(34.4)
Short-term investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	0	0	0.1
Changes in net foreign currency translation gains (losses)	0	(0.1)	0
Total net changes in fair value reflected in revenues	0	(0.1)	0.1
Common equity securities
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(33.2)	(32.6)	32
Changes in net foreign currency translation gains (losses)	0.2	(0.3)	0.1
Total net changes in fair value reflected in revenues	(33)	(32.9)	32.1
Other investments
Total net changes in fair value reflected in revenues
Changes in net unrealized investment gains (losses)	(33.6)	1.8	7.4
Changes in net foreign currency translation gains (losses)	0	0	0
Total net changes in fair value reflected in revenues	$ (33.6)	$ 1.8	$ 7.4

Investment Securities (Net unre

Investment Securities (Net unrealized investment gains and losses) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investments [Abstract]
Gross unrealized gains	$ 46.5	$ 104.7
Gross unrealized losses	(33.2)	(8.9)
Trading Securities Unrealized Holding Gains and Losses, Pre-Tax	13.3	95.8
Trading Securities, Unrealized Gains and Losses, Tax	(6.5)	(26.9)
Unrealized gains (losses) on trading securities, net of tax	$ 6.8	$ 68.9

Investment Securities (Fixed ma

Investment Securities (Fixed maturity investment gains and losses) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Gross unrealized gains	$ 46.5	$ 104.7
Gross unrealized losses	(33.2)	(8.9)
Carrying value	2,080.5	1,799.8
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	85.4	38
Gross unrealized gains	0	0
Gross unrealized losses	(0.1)	0
Net unrealized foreign currency losses	0	0
Carrying value	85.3	38
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	810.8	787.7
Gross unrealized gains	4.1	11.5
Gross unrealized losses	(4.5)	(1)
Net unrealized foreign currency losses	0	0
Carrying value	810.4	798.2
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	67.7	62.4
Gross unrealized gains	1.5	1.4
Gross unrealized losses	(0.2)	(0.1)
Net unrealized foreign currency losses	0	0
Carrying value	69	63.7
Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,035.1	814.4
Gross unrealized gains	1.3	1.5
Gross unrealized losses	(4.5)	(1.5)
Net unrealized foreign currency losses	0	0
Carrying value	1,031.9	814.4
Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1	1
Gross unrealized gains	0.2	0.3
Gross unrealized losses	0	0
Net unrealized foreign currency 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
Gross unrealized gains	4.4	5.9
Gross unrealized losses	0	0
Net unrealized foreign currency losses	0	0
Carrying value	82.7	84.2
Total fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2,078.3	1,781.8
Gross unrealized gains	11.5	20.6
Gross unrealized losses	(9.3)	(2.6)
Net unrealized foreign currency losses	0	0
Carrying value	$ 2,080.5	$ 1,799.8

Investment Securities (Cost or

Investment Securities (Cost or amortized cost fixed maturity investments) (Details) $ in Millions	Dec. 31, 2015USD ($)
Trading Securities by Maturity Cost or Amortized Cost [Abstract]
Total	$ 2,078.3
Trading Securities by Maturity Fair Value [Abstract]
Total	2,080.5
Fixed Maturities and Convertible Fixed Maturities Excluding Mortgage backed securities, Asset backed securities and Preferred Stock [Member]
Trading Securities by Maturity Cost or Amortized Cost [Abstract]
Due in one year or less	154.4
Due after one year through five years	678.1
Due after five years through ten years	115.2
Due after ten years	17.2
Trading Securities by Maturity Fair Value [Abstract]
Due in one year or less	154.8
Due after one year through five years	678.2
Due after five years through ten years	115
Due after ten years	17.9
Asset-backed securities
Trading Securities by Maturity Cost or Amortized Cost [Abstract]
Without Single Maturity Date	1,035.1
Trading Securities by Maturity Fair Value [Abstract]
Without Single Maturity Date	1,031.9
Preferred stocks
Trading Securities by Maturity Cost or Amortized Cost [Abstract]
Without Single Maturity Date	78.3
Trading Securities by Maturity Fair Value [Abstract]
Without Single Maturity Date	$ 82.7

Investment Securities (Converti

Investment Securities (Convertible fixed maturity investments and other investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	$ 2,507.5	$ 2,306.8	$ 2,424.5
Gross unrealized gains	46.5	104.7
Gross unrealized investment losses	(33.2)	(8.9)
Carrying value	2,080.5	1,799.8
Proceeds from Sale, Maturity and Collection of Long-term Investments	1,371.5	2,585.1	$ 1,841.9
Assets Held by Insurance Regulators	82.1	63.4
Unrestricted collateral from customers	137.7	81
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2,078.3	1,781.8
Gross unrealized gains	11.5	20.6
Gross unrealized investment losses	(9.3)	(2.6)
Net unrealized foreign currency gains	0	0
Carrying value	2,080.5	1,799.8
Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	78.3	78.3
Gross unrealized gains	4.4	5.9
Gross unrealized investment losses	0	0
Net unrealized foreign currency gains	0	0
Carrying value	82.7	84.2
Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,031.9	814.4
Cost or amortized cost	1,035.1	814.4
Gross unrealized gains	1.3	1.5
Gross unrealized investment losses	(4.5)	(1.5)
Net unrealized foreign currency gains	0	0
Carrying value	1,031.9	814.4
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	810.4	798.2
Cost or amortized cost	810.8	787.7
Gross unrealized gains	4.1	11.5
Gross unrealized investment losses	(4.5)	(1)
Net unrealized foreign currency gains	0	0
Carrying value	810.4	798.2
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	85.4	38
Gross unrealized gains	0	0
Gross unrealized investment losses	(0.1)	0
Net unrealized foreign currency gains	0	0
Carrying value	85.3	38
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	295	283.2
Gross unrealized gains	12.7	39.3
Gross unrealized investment losses	(9)	(2.4)
Net unrealized foreign currency gains	0	(0.1)
Carrying value	298.7	320
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	135.6	162.9
Gross unrealized gains	22.3	44.8
Gross unrealized investment losses	(14.9)	(3.9)
Net unrealized foreign currency gains	0	0
Carrying value	143	203.8
Total common equity securities and other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	430.6	446.1
Gross unrealized gains	35	84.1
Gross unrealized investment losses	(23.9)	(6.3)
Net unrealized foreign currency gains	0	(0.1)
Carrying value	441.7	523.8
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	67.7	62.4
Gross unrealized gains	1.5	1.4
Gross unrealized investment losses	(0.2)	(0.1)
Net unrealized foreign currency gains	0	0
Carrying value	69	63.7
Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1	1
Gross unrealized gains	0.2	0.3
Gross unrealized investment losses	0	0
Net unrealized foreign currency gains	0	0
Carrying value	1.2	1.3
Other Entities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments Held in Trusts	2.2	2.7
Star and Shield Insurance Exchange [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments Held in Trusts	5.4	3.3
A | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	265.4	328.1
AA | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	42.7	57.9
BBB | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	502.3	409.2
Not rated | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	$ 0	$ 3

Investment Securities (Fair val

Investment Securities (Fair value measurements) (Details) $ in Millions	Dec. 31, 2015USD ($)fund	Dec. 31, 2014USD ($)fund	Dec. 23, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Percentage of fair value investments using observable inputs	92.00%	90.00%
Fair value of investments	$ 2,507.5	$ 2,306.8		$ 2,424.5
Other investments	$ 143	$ 203.8
Percentage of private preferred stock	85.00%	84.00%
Minimum percentage of variation from expected price required to treat prices of investments provided by pricing services as outliers	5.00%
Minimum variation from expected price require to treat prices of investments provided by pricing services as outliers	$ 1
Other Investments At Fair Value	128.3	$ 187
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	363.3	358.7		469.5
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	$ 1,945.9	$ 1,692.1		1,753.1
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Investments | fund	4	7
Other investments	$ 16.4	$ 42.3
Other investments at fair value	$ 16.4	$ 42.3
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Investments | fund	17	17
Other investments	$ 46.1	$ 60.1
Other investments at fair value	46.1	60.1
Hedge funds and private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	62.5	102.4
Community Reinvestment Vehicle [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	14.3	14.3
Single Fund
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	12.9	15.8
Tax Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	14.7	16.8
Trust Certificates Issued Upon Dissolution of a Private Equity Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	0	0.2
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	810.4	798.2
Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,031.9	814.4
Asset-backed securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,031.9	814.4
Asset-backed securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Fixed maturity investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	70	74		81.9
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments	$ 0	$ 5
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments, Percent of Total	5.00%	7.00%
Other investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	$ 128.3	$ 182		$ 119.9
Surplus Notes For Sale Of Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments			$ 64.9
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	51.5	65.1
Recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	2,576.7	2,509
Recurring basis | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	432.5	560.4
Recurring basis | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,945.9	1,692.6
Recurring basis | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	198.3	256
Recurring basis | U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	85.3	38
Recurring basis | U.S. Government and agency obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	85.3	38
Recurring basis | U.S. Government and agency obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | U.S. Government and agency obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	810.4	798.2
Recurring basis | Debt securities issued by industrial corporations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	810.4	795.3
Recurring basis | Debt securities issued by industrial corporations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	2.9
Recurring basis | Debt securities issued by industrial corporations | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	218.3	174.9
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	218.3	174.9
Recurring basis | Debt securities issued by industrial corporations | Consumer | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Health care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	136.2	111.9
Recurring basis | Debt securities issued by industrial corporations | Health care [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Health care [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	136.2	111.9
Recurring basis | Debt securities issued by industrial corporations | Health care [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	121.8	104.8
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	121.8	104.8
Recurring basis | Debt securities issued by industrial corporations | Industrial | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	116	148.6
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	116	148.6
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Communications
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	46	74.9
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	46	74.9
Recurring basis | Debt securities issued by industrial corporations | Communications | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	75.2	53.5
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	75.2	53.5
Recurring basis | Debt securities issued by industrial corporations | Energy | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	25.8	56.4
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	25.8	53.5
Recurring basis | Debt securities issued by industrial corporations | Basic materials | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	2.9
Recurring basis | Debt securities issued by industrial corporations | Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	42.2	44.2
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	42.2	44.2
Recurring basis | Debt securities issued by industrial corporations | Utilities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	28.9	29
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	28.9	29
Recurring basis | Debt securities issued by industrial corporations | Technology | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	69	63.7
Recurring basis | Municipal obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Municipal obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	69	63.7
Recurring basis | Municipal obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,031.9	814.4
Recurring basis | Asset-backed securities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Asset-backed securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,031.9	814.4
Recurring basis | Asset-backed securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	82.7	84.2
Recurring basis | Preferred stocks | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Preferred stocks | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	12.7	13.1
Recurring basis | Preferred stocks | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	70	71.1
Recurring basis | Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	2,080.5	1,799.8
Recurring basis | Fixed maturity investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	85.9	38.7
Recurring basis | Fixed maturity investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1,924.6	1,687.1
Recurring basis | Fixed maturity investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	70	74
Recurring basis | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	69.2	202.2
Recurring basis | Short-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	69.2	201.7
Recurring basis | Short-term investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0.5
Recurring basis | Short-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	298.7	320
Recurring basis | Common equity securities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	277.4	320
Recurring basis | Common equity securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	21.3	0
Recurring basis | Common equity securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	38.2	75.2
Recurring basis | Common equity securities | Consumer | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	38.2	75.2
Recurring basis | Common equity securities | Consumer | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Consumer | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Health care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	19.6	46.5
Recurring basis | Common equity securities | Health care [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	19.6	46.5
Recurring basis | Common equity securities | Health care [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Health care [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	14.5	48.3
Recurring basis | Common equity securities | Industrial | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	14.5	48.3
Recurring basis | Common equity securities | Industrial | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Industrial | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	4.5	72.4
Recurring basis | Common equity securities | Energy | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	4.5	72.4
Recurring basis | Common equity securities | Energy | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Energy | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Communications
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	23.9	24.4
Recurring basis | Common equity securities | Communications | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	23.9	24.4
Recurring basis | Common equity securities | Communications | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Communications | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		15.6
Recurring basis | Common equity securities | Energy | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		15.6
Recurring basis | Common equity securities | Energy | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Energy | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Exchange Traded Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	183.3
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	162
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	21.3
Recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0
Recurring basis | Common equity securities | Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		9.9
Recurring basis | Common equity securities | Basic materials | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		9.9
Recurring basis | Common equity securities | Basic materials | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Basic materials | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		5.1
Recurring basis | Common equity securities | Utilities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		5.1
Recurring basis | Common equity securities | Utilities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Utilities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	14.7	20.6
Recurring basis | Common equity securities | Technology | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	14.7	20.6
Recurring basis | Common equity securities | Technology | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Technology | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Common equity securities | Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		2
Recurring basis | Common equity securities | Other | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		2
Recurring basis | Common equity securities | Other | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Common equity securities | Other | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments		0
Recurring basis | Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	128.3	187
Recurring basis | Other investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	0
Recurring basis | Other investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0	5
Recurring basis | Other investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	128.3	182
Recurring basis | Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	1.2	1.3
Recurring basis | Foreign government obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0.6	0.7
Recurring basis | Foreign government obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	0.6	0.6
Recurring basis | Foreign government obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of investments	$ 0	$ 0
Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Investments | fund	1	1

Investment Securities (Corporat

Investment Securities (Corporate debt securites) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,507.5	$ 2,306.8	$ 2,424.5
Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	810.4	798.2
AA | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	42.7	57.9
A | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	265.4	328.1
BBB | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	502.3	409.2
Not rated | Debt securities issued by industrial corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0	$ 3

Investment Securities (Fair v66

Investment Securities (Fair value rollforward) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 23, 2014USD ($)
Investment securities
Other investments	$ 143	$ 203.8
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	2,306.8	2,424.5
Amortization/accretion	(13.2)	(10.9)
Total net realized and unrealized gains (losses)	35.1	(40.7)
Purchases	1,661.1	2,487.6
Sales	(1,412.1)	(2,635.1)
Non-Cash Acquisition (Disposition) Of Investments	0	0	$ 0
Transfers in	36.9	52.7
Transfers out	(36.9)	(52.7)
Investments at fair value ending balance	2,507.5	2,306.8	2,424.5
Level 1 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	358.7	469.5
Amortization/accretion	0	0.1
Total net realized and unrealized gains (losses)	(1.3)	(22.1)
Purchases	638	752.1
Sales	(634.7)	(886.2)
Non-Cash Acquisition (Disposition) Of Investments		1.1
Transfers in	0	0
Transfers out	0	0
Investments at fair value ending balance	363.3	358.7	469.5
Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	1,692.1	1,753.1
Amortization/accretion	(13.2)	(11)
Total net realized and unrealized gains (losses)	12.7	(5.2)
Purchases	985.7	1,625.1
Sales	(742.9)	(1,729.9)
Non-Cash Acquisition (Disposition) Of Investments		(3.1)
Transfers in	36.9	52.7
Transfers out	0	0
Investments at fair value ending balance	1,945.9	1,692.1	1,753.1
Fixed maturity investments | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	74	81.9
Amortization/accretion	0	0
Total net realized and unrealized gains (losses)	1.1	(1.1)
Purchases	34	41.7
Sales	0	0
Non-Cash Acquisition (Disposition) Of Investments		2
Transfers in	0	0
Transfers out	(36.9)	(52.7)
Investments at fair value ending balance	70	74	81.9
Common equity securities | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	0	0.1
Amortization/accretion	0	0
Total net realized and unrealized gains (losses)	0	(0.4)
Purchases	0	0
Sales	0	(0.5)
Non-Cash Acquisition (Disposition) Of Investments		0
Transfers in	0	0
Transfers out	0	0
Investments at fair value ending balance	0	0	0.1
Convertible fixed maturity investments
Investment securities
Other investments	0	$ 5
Convertible fixed maturity investments | Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Exchanged Investments		1
Other investments | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	182	$ 119.9
Amortization/accretion	0	0
Total net realized and unrealized gains (losses)	22.6	(11.9)
Purchases	3.4	68.7
Sales	(34.5)	(18.5)
Non-Cash Acquisition (Disposition) Of Investments		0
Transfers in	0	0
Transfers out	0	0
Investments at fair value ending balance	128.3	182	$ 119.9
Surplus Notes For Sale Of Discontinued Operations [Member]
Investment securities
Other investments				$ 64.9
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	51.5	65.1
Non-agency RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	67.4
Investments at fair value ending balance	132.7	67.4
Non-agency RMBS | Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	67.4
Investments at fair value ending balance	132.7	67.4
Non-agency RMBS | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	0
Transfers out	(18.1)	(28.1)
Investments at fair value ending balance	0	0
Non-agency CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	96.7
Investments at fair value ending balance	140.4	96.7
Non-agency CMBS | Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	96.7
Investments at fair value ending balance	140.4	96.7
Non-agency CMBS | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	0
Transfers out	(10.3)	(13.7)
Investments at fair value ending balance	0	0
Asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	814.4
Investments at fair value ending balance	1,031.9	814.4
Asset-backed securities | Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	814.4
Investments at fair value ending balance	1,031.9	814.4
Asset-backed securities | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	0
Transfers out	(5.6)	(10.9)
Investments at fair value ending balance	0	0
Debt securities issued by industrial corporations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	798.2
Investments at fair value ending balance	810.4	798.2
Debt securities issued by industrial corporations | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out	(2.9)
Total mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	425.2
Investments at fair value ending balance	498.1	425.2
Total mortgage-backed securities | Level 2 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	425.2
Investments at fair value ending balance	498.1	425.2
Total mortgage-backed securities | Level 3 Inputs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Investments at fair value beginning balance	0
Investments at fair value ending balance	$ 0	$ 0

Investment Securities (Securiti

Investment Securities (Securities classified as level 3) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)security	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Significant unobservable inputs
Debt securities issued by corporations	$ 2,507.5	$ 2,306.8	$ 2,424.5
Accretion (Amortization) of Discounts and Premiums, Investments	(13.2)	(10.9)
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings	(35.1)	40.7
Payments to Acquire Investments	1,661.1	2,487.6
Sales	(1,412.1)	(2,635.1)
Transfers out	(36.9)	(52.7)
Transfers in	$ 36.9	52.7
Preferred stocks
Significant unobservable inputs
Number of Securities in each Asset type | security	1
Standard Poors N R Rating [Member] | Preferred stocks | Par Value Valuation Technique [Member]
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 70	$ 71.1
Standard Poors N R Rating [Member] | Preferred stocks | Discounted cash flow
Significant unobservable inputs
Discount Rate		7.10%
Standard Poors N R Rating [Member] | Surplus Notes For Sale Of Discontinued Operations [Member] | Discounted cash flow
Significant unobservable inputs
Discount Rate	16.10%	11.00%
Standard Poors N R Rating [Member] | Debt Securities | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure		$ 2.9
Fair Value Inputs, Discount for Lack of Marketability		0.00%
Fixed maturity investments | Level 3 Inputs
Significant unobservable inputs
Debt securities issued by corporations	$ 70	$ 74	81.9
Accretion (Amortization) of Discounts and Premiums, Investments	0	0
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings	(1.1)	1.1
Payments to Acquire Investments	34	41.7
Sales	0	0
Transfers out	(36.9)	(52.7)
Transfers in	0	0
Common equity securities | Level 3 Inputs
Significant unobservable inputs
Debt securities issued by corporations	0	0	0.1
Accretion (Amortization) of Discounts and Premiums, Investments	0	0
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings	0	0.4
Payments to Acquire Investments	0	0
Sales	0	(0.5)
Transfers out	0	0
Transfers in	0	0
Other investments | Level 3 Inputs
Significant unobservable inputs
Debt securities issued by corporations	128.3	182	$ 119.9
Accretion (Amortization) of Discounts and Premiums, Investments	0	0
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings	(22.6)	11.9
Payments to Acquire Investments	3.4	68.7
Sales	(34.5)	(18.5)
Transfers out	0	0
Transfers in	0	0
Seller priority [Member] | Standard Poors N R Rating [Member] | Surplus Notes For Sale Of Discontinued Operations [Member] | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 38	$ 44
Discount Rate	13.00%	9.30%
Fair Value Inputs, Interest Payment Schedule	5 years	5 years
Fair Value Inputs, Principal Payment Schedule	10 years	10 years
Pari passu [Member] | Standard Poors N R Rating [Member] | Surplus Notes For Sale Of Discontinued Operations [Member] | Discounted cash flow
Significant unobservable inputs
Assets, Fair Value Disclosure	$ 13.5	$ 21.1
Discount Rate	22.40%	13.50%
Fair Value Inputs, Interest Payment Schedule	5 years	5 years
Fair Value Inputs, Principal Payment Schedule	15 years	15 years

Investment Securities (Change i

Investment Securities (Change in net unrealized gains or losses for Level 3 assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	$ (82.5)	$ (28.9)	$ 5.1
Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(15.7)	1.9	(34.4)
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	0	0	0.1
Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(33.6)	1.8	7.4
Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(34.8)	7.3	4.8
Level 3 | Fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	(1.1)	1.1	(1.5)
Level 3 | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	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	0
Level 3 | Other investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on unsold securities	$ (33.7)	$ 6.2	$ 6.3

Investment Securities (Asset ba

Investment Securities (Asset backed securities) (Details) $ in Millions	Dec. 31, 2015USD ($)fund	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,507.5	$ 2,306.8	$ 2,424.5
Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 1,945.9	1,692.1	$ 1,753.1
Fixed rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average basis points of subordination	3000.00%
Debt securities issued by corporations	$ 101.1
Floating rate CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39.3
GNMA
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	220.5	259.2
GNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	220.5	259.2
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	1.4	1.9
FNMA | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1.4	1.9
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	3.1	0
FHLMC | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	3.1	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	225	261.1
Agency commercial mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	225	261.1
Agency commercial mortgage-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	0
Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	132.7	67.4
Non-agency RMBS | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	132.7	67.4
Non-agency RMBS | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	0
Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	140.4	96.7
Non-agency CMBS | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	140.4	96.7
Non-agency CMBS | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0	0
Non-agency CMBS | Maximum
Schedule of Trading Securities and Other Trading Assets [Line Items]
Percentage of underlying loans reported as non-performing	1.00%
Total non-agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 273.1	164.1
Total non-agency | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	273.1	164.1
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	498.1	425.2
Total mortgage-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	498.1	425.2
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	202.7	197.6
Credit card receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	202.7	197.6
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	255.6	145.8
Vehicle receivables | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	255.6	145.8
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	75.5	45.8
Other | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	75.5	45.8
Other | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	0
Total other asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	533.8	389.2
Total other asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	533.8	389.2
Total other asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	0
Total asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,031.9	814.4
Total asset-backed securities | Level 2
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	1,031.9	814.4
Total asset-backed securities | Level 3
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0	$ 0
Non-Agency Residential Mortgage Backed Security [Domain]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39.6
Non-prime | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0
Total mortgage-backed securities | Non-prime
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of Investments | fund	0

Investment Securities (Non-agen

Investment Securities (Non-agency securities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 2,507.5	$ 2,306.8	$ 2,424.5
Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	132.7	67.4
Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	140.4	96.7
Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	273.1	$ 164.1
Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	101.1
Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39.3
Super Senior | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	65.6
Super Senior | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	8.7
Super Senior | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	8.7
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 [Member] | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	67.1
Senior [Member] | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	48.6
Senior [Member] | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	48.6
Senior [Member] | Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Subordinate | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Subordinate | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	83.1
Subordinate | Commercial Mortgage Backed Securities Fixed Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	43.8
Subordinate | Commercial Mortgage Backed Securities Floating Rate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	39.3
Securities Issued in 2004 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	16.7
Securities Issued in 2004 | Non-agency CMBS
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	16.7
Securities Issued in 2005 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	8.6
Securities Issued in 2005 | Non-agency CMBS
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	8.6
Securities Issued in 2006 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	3.9
Securities Issued in 2006 | Non-agency CMBS
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	3.9
Securities Issued in 2008 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	3.6
Securities Issued in 2008 | Non-agency CMBS
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	3.6
Securities issued in 2010 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	15.2
Securities issued in 2010 | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	5.4
Securities issued in 2010 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	20.6
Securities issued in 2011 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	13.5
Securities issued in 2011 | Non-agency CMBS
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	13.5
Securities issued in 2012 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	9.8
Securities issued in 2012 | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	18.1
Securities issued in 2012 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	27.9
Securities Issued in 2013 | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	14
Securities Issued in 2013 | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	17.2
Securities Issued in 2013 | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	31.2
Securities Issued in 2014 [Member] | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	47.4
Securities Issued in 2014 [Member] | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	54.9
Securities Issued in 2014 [Member] | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	102.3
Security Issued in 2015 [Member] | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Security Issued in 2015 [Member] | Non-agency CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	44.8
Security Issued in 2015 [Member] | Total
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	44.8
Prime | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	132.7
Prime | Super Senior | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	65.6
Prime | Senior [Member] | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	67.1
Prime | Subordinate | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Non-prime | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Non-prime | Super Senior | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Non-prime | Senior [Member] | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	0
Non-prime | Subordinate | Non-agency RMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Debt securities issued by corporations	$ 0

Investment Securities (Other in

Investment Securities (Other investments) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Surplus Notes For Sale Of Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	$ 51.5	$ 65.1
Hedge Funds Equity Banks and Financial [Domain]
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
Long/short credit and distressed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0	8.4
Net asset value per share of unfunded commitments	0	0
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	16.4	42.3
Net asset value per share of unfunded commitments	0	0
Distributions from inactive hedge funds	1
Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	13.8
Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.6
Hedge funds | 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Hedge Funds Other [Domain]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	3.6	5.4
Net asset value per share of unfunded commitments	0	0
Insurance
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2	2.1
Net asset value per share of unfunded commitments	0.1	0.1
Energy infrastructure and services
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	20.7	33.1
Net asset value per share of unfunded commitments	3.4	4.8
Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	3.8	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	14.8	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	4.4	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	0.4	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 at fair value	46.1	60.1
Net asset value per share of unfunded commitments	8.2	10.6
Private equity funds | 1 - 3 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	22.1
Private equity funds | 3 - 5 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	10.9
Private equity funds | 5 - 10 years
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	13.1
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	62.5	102.4
Net asset value per share of unfunded commitments	8.2	$ 10.6
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Monthly [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Monthly [Member] | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Monthly [Member] | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Monthly [Member] | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Monthly [Member] | Hedge funds | 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Quarterly [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	13.8
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Quarterly [Member] | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	13.8
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Quarterly [Member] | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Quarterly [Member] | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Quarterly [Member] | Hedge funds | 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Annual [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.6
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Annual [Member] | Hedge funds | 30 - 59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Annual [Member] | Hedge funds | 60 - 89 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	0
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Annual [Member] | Hedge funds | 90 - 119 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	2.6
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Frequency Annual [Member] | Hedge funds | 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other investments at fair value	$ 0

Investment Securities Investmen

Investment Securities Investment Securities (Surplus notes) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 23, 2014
Surplus Note Valuation [Line Items]
Statutory Excess Capital Percentage			250.00%
Runoff
Surplus Note Valuation [Line Items]
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
Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	$ 101	$ 101	101
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	51.5	65.1
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(49.5)	(35.9)	(36.1)
Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	43.1		43.1
Pari passu [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	13.5	21.2
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(29.6)	(21.9)	(22.1)
Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	57.9		57.9
Seller priority [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	38	43.9
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(19.9)	(14)	(14)
Liquidity adjustment [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(10.2)	(16.7)	(16.7)
Liquidity adjustment [Member] | Pari passu [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(2.4)	(5.7)	(5.7)
Liquidity adjustment [Member] | Seller priority [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(7.8)	(11)	(11)
Regulatory approval [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(24.2)	(12.6)	(12.6)
Regulatory approval [Member] | Pari passu [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(12.5)	(8)	(8)
Regulatory approval [Member] | Seller priority [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(11.7)	(4.6)	(4.6)
Current market rates on public debt and contract-based repayments [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(15.1)	(6.6)	(6.8)
Current market rates on public debt and contract-based repayments [Member] | Pari passu [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(14.7)	(8.2)	(8.4)
Current market rates on public debt and contract-based repayments [Member] | Seller priority [Member] | Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	$ (0.4)	$ 1.6	$ 1.6

Debt (Details)

Debt (Details) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt
Debt		$ 274,800,000	$ 274,700,000
Interest expense		13,000,000	13,000,000	$ 13,000,000
Interest Paid		12,700,000	12,700,000	$ 12,700,000
OBH (issuer)
Debt
Unamortized original issue discount		(200,000)	(300,000)
Debt		274,800,000	274,700,000
OBH Senior Notes | OBH (issuer)
Debt
Senior unsecured notes, at face value		275,000,000	$ 275,000,000
2012 OBH Senior Notes | OBH (issuer)
Debt
Senior unsecured notes, at face value	$ 275,000,000
Percentage of par value at which debt was issued	99.90%
Issuance of debt, net of debt issuance costs	$ 272,900,000
Interest rate (as a percent)	4.60%
Scenario, amount due per acceleration clause		75,000,000
Revolving Credit Facility [Member] | OBH (issuer)
Debt
Total commitment		65,000,000
Amount outstanding on credit facility		$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Non-U.S. component of pre-tax income from continuing operations										$ 57.2	$ 58	$ 60.3
Effective tax rate as a percent										(51.00%)	(29.10%)	19.90%
Effective tax rate on U.S. income or loss										35.00%	35.00%	35.00%
Less valuation allowance		$ 1.3				$ 1.8				$ 1.3	$ 1.8
Gross deferred tax assets		187.2				199.9				187.2	199.9
Total net operating loss carryforwards		183.2								183.2
Losses included in loss carryforwards subject to annual limitation on utilization		0.4								0.4
Unrecognized tax benefits that would impact effective tax rate		13.6								13.6
Unrecognized tax benefits		24.3				35				24.3	35	$ 32.6	$ 39
Interest expense, net of federal benefit										$ 1.7	1.1	1
Percentage of Likelihood for Realization of Benefit upon Ultimate Settlement										50.00%
Income tax benefit		(11.9)	$ (3.5)	$ (0.9)	$ 3.4	(24.2)	$ (1.1)	$ 5.9	$ 7.1	$ (12.9)	(12.3)	36.5
Income Taxes Paid, Net										(6.2)	$ 2.1	$ 5.6
Temporary Differences [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits		10.7								$ 10.7
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Effective tax rate on non-U.S. income										1.30%	1.30%	0.50%
Domestic Tax Authority
Income Tax Contingency [Line Items]
Effective tax rate on U.S. income or loss										42.60%	83.70%	29.50%
Total net operating loss carryforwards		181.9								$ 181.9
Unrecognized tax benefits		8.2				$ 6.5				8.2	$ 6.5
Houston General Insurance Exchange [Member]
Income Tax Contingency [Line Items]
Change in valuation allowance											$ (6.6)
Net operating income (loss)										(1.8)
LUXEMBOURG
Income Tax Contingency [Line Items]
Effective tax rate on non-U.S. income												29.22%	28.80%
Gross deferred tax asset for NOL carryforwards		0.4								0.4
Total net operating loss carryforwards		1.3								1.3
HGIE [Member]
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards		64.1								64.1
Gross deferred tax assets		0.9								0.9
HGIE [Member] | Domestic Tax Authority
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards		63.7								63.7
HGIE [Member] | LUXEMBOURG
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards		0.4								0.4
OneBeacon U S Financial Services Inc [Member]
Income Tax Contingency [Line Items]
Tax credit carryforward		14.6								14.6
Alternative minimum tax credit carryovers		1.8								1.8
Tax Year 2005 to 2006 [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Incom tax liability including interest		3.3								3.3
Income Tax Examination, Increase (Decrease) in Liability from Prior Year, Related to Items with Unallowable Deductions		2.7								2.7
Income tax benefit										5
Tax Assessment Year 2007 to 2009 [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Incom tax liability including interest		4								4
Income Tax Examination, Increase (Decrease) in Liability from Prior Year, Related to Items with Unallowable Deductions		$ 2.7								2.7
Tax Years 2010 - 2012 [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Increase (Decrease) in Income Taxes Receivable										$ 1.1
Subsequent Event [Member] | Tax Years 2007 to 2009 [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Income tax benefit	$ 12

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax (expense) benefit:
Total deferred tax (expense) benefit									$ 5.8	$ 19	$ (15)
Tax (expense) benefit	$ 11.9	$ 3.5	$ 0.9	$ (3.4)	$ 24.2	$ 1.1	$ (5.9)	$ (7.1)	12.9	12.3	(36.5)
Continuing Operations [Member]
Current tax (expense) benefit:
Federal									9.1	(4.3)	(20.3)
State									(1.2)	(1.6)	(0.8)
Non-U.S.									(0.8)	(0.8)	(0.4)
Total current tax (expense) benefit									7.1	(6.7)	(21.5)
Deferred tax (expense) benefit:
Federal									5.8	19	(15)
State									0	0	0
Non-U.S.									0	0	0
Total deferred tax (expense) benefit									5.8	19	(15)
Tax (expense) benefit									$ 12.9	$ 12.3	$ (36.5)
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Effective tax rate on non-U.S. income									1.30%	1.30%	0.50%

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Contingency [Line Items]
Effective tax rate on U.S. income or loss	35.00%	35.00%	35.00%
Continuing Operations [Member]
Income Tax Contingency [Line Items]
Tax expense at the U.S. statutory rate	$ (8.9)	$ (14.8)	$ (64.1)
Non-U.S. earnings, net of foreign taxes	19.3	19.6	20.9
Tax reserve adjustments	(1.7)	4.1	(1)
Tax exempt interest and dividends	2.6	2.5	2.4
Change in valuation allowance	(0.5)	0.2	(5.9)
Other, net	1.1	1.1	(0.6)
Total income tax (expense) benefit on pre-tax income from continuing operations	$ 12.9	$ 12.3	$ (36.5)
Domestic Tax Authority
Income Tax Contingency [Line Items]
Effective tax rate on U.S. income or loss	42.60%	83.70%	29.50%

Income Taxes - Deferred Income

Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets related to:
U.S. net operating loss carryforwards	$ 63.7	$ 56.3
Unearned premiums	37.2	38.1
Discounting of loss and LAE reserves	26.7	41.3
Tax credit carryforwards	16.9	13.4
Compensation and bonus accruals	15.3	10.8
Sale of Runoff Business	12.6	12.6
Deferred compensation plans	6	6.4
Fixed assets	4.2	4
Investment basis differences	3.2	6.4
Allowance for doubtful accounts	0.7	0.7
Non-U.S. net operating loss carryforwards	0.4	0.4
Other accrued compensation	0.1	0.2
Accrued rent	0	3.9
Other items	0.2	5.4
Total gross deferred income tax assets	187.2	199.9
Less valuation allowance	(1.3)	(1.8)
Total net deferred income tax assets	185.9	198.1
Deferred income tax liabilities related to:
Deferred acquisition costs	35.2	32.2
Net unrealized investment gains	6.5	26.9
Prepaid pension	3.5	2.6
Other items	0.5	4.6
Total gross deferred income tax liabilities	45.7	66.3
Net deferred tax asset	$ 140.2	$ 131.8

Income Taxes - Carry Forwards (

Income Taxes - Carry Forwards (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	$ 183.2
Total net deferred income tax assets	185.9	$ 198.1
Domestic Tax Authority
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	181.9
LUXEMBOURG
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	1.3
Gross deferred tax asset for NOL carryforwards	0.4
Tax Year 2014
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
Tax Year 2014 | Domestic Tax Authority
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
Tax Year 2014 | LUXEMBOURG
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
Tax Years 2015 to 2022
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	1.6
Tax Years 2015 to 2022 | Domestic Tax Authority
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	1.6
Tax Years 2015 to 2022 | LUXEMBOURG
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
Tax Years 2023 to 2033
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	180.3
Tax Years 2023 to 2033 | Domestic Tax Authority
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	180.3
Tax Years 2023 to 2033 | LUXEMBOURG
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
No Expiration Date
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	1.3
No Expiration Date | Domestic Tax Authority
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	0
No Expiration Date | LUXEMBOURG
Income Tax Contingency [Line Items]
Total net operating loss carryforwards	1.3
HGIE [Member]
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards	64.1
Valuation allowance for NOL carryforwards	(1)
Total net deferred income tax assets	63.1
HGIE [Member] | Domestic Tax Authority
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards	63.7
Valuation allowance for NOL carryforwards	(0.6)
Total net deferred income tax assets	63.1
HGIE [Member] | LUXEMBOURG
Income Tax Contingency [Line Items]
Gross deferred tax asset for NOL carryforwards	0.4
Valuation allowance for NOL carryforwards	(0.4)
Total net deferred income tax assets	$ 0

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits	$ 35	$ 32.6	$ 39
Changes in prior year tax positions			1
Tax positions taken during the current year			(7)
Lapse in statute of limitations	0	0	0
Settlements with tax authorities	0	0	(0.4)
Changes in prior year tax positions	(10.7)	(4.9)
Tax positions taken during the current year	0	7.3
Unrecognized Tax Benefits	24.3	35	32.6
Permanent Differences [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits	5.4	7.6	7.6
Changes in prior year tax positions	0		0
Tax positions taken during the current year			0
Lapse in statute of limitations	0	0	0
Settlements with tax authorities	0	0	0
Changes in prior year tax positions		(2.2)
Tax positions taken during the current year	0	0
Unrecognized Tax Benefits	5.4	5.4	7.6
Temporary Differences [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits	23.1	16.6	23.6
Changes in prior year tax positions			0
Tax positions taken during the current year			(7)
Lapse in statute of limitations	0	0	0
Settlements with tax authorities	0	0	0
Changes in prior year tax positions	(12.4)	(0.8)
Tax positions taken during the current year	0	7.3
Unrecognized Tax Benefits	10.7	23.1	16.6
Interest and Penalties [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits	6.5	8.4	7.8
Changes in prior year tax positions	1.7		1
Tax positions taken during the current year			0
Lapse in statute of limitations	0	0	0
Settlements with tax authorities	0	0	(0.4)
Changes in prior year tax positions		(1.9)
Tax positions taken during the current year	0	0
Unrecognized Tax Benefits	$ 8.2	$ 6.5	$ 8.4

Retirement Plans - Obligations

Retirement Plans - Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 119.7	$ 102.9
Service cost	0.9	0.6	$ 0.8
Interest cost	4.6	4.7	4.2
Defined Benefit Plan, Effect of Settlements and Curtailments on Accumulated Benefit Obligation	(1.8)	0
Special termination benefits expense	0	0.3	0.3
Assumption changes	(3.5)	17.5
Actuarial loss	0.9	1.1
Benefits and expenses paid with plan assets	(13.7)	(5.2)
Benefits paid directly by OneBeacon	(2.2)	(2.2)
Remeasurement due to Plan Termination	4.6	0
Projected benefit obligation at end of year	109.5	119.7	102.9
Change in plan assets:
Fair value of plan assets at beginning of year	146	142.8
Actual return on plan assets	7.5	8.4
Fair value of plan assets at end of year	139.8	146	$ 142.8
Funded status at end of year	30.3	26.3
Qualified Plan
Change in plan assets:
Fair value of plan assets at beginning of year	143.2
Fair value of plan assets at end of year	139.4	143.2
Funded status at end of year	55.8	53.4
Non-Qualified Plan
Change in plan assets:
Fair value of plan assets at end of year	18.6
Funded status at end of year	$ (25.5)	$ (27.1)

Retirement Plans - Funded Statu

Retirement Plans - Funded Status (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	$ 30.3	$ 26.3
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	55.8	53.4
Non-Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status at end of year	$ (25.5)	$ (27.1)

Retirement Plans - Non-qualifie

Retirement Plans - Non-qualified (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Projected benefit obligation	$ 25.5	$ 27.1
Accumulated benefit obligation	25.5	27.1
Fair value of plan assets	$ 0	$ 0

Retirement Plans - Qualified Pl

Retirement Plans - Qualified Plan (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Projected benefit obligation	$ 84	$ 92.6
Accumulated benefit obligation	84	92.6
Fair value of plan net assets	$ 139.8	$ 146

Retirement Plans - Accumulated

Retirement Plans - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Accumulated Other Comprehensive Income [Roll Forward]
Accumulated other comprehensive income (loss) at beginning of year	$ (8)	$ 10.5
Amortization of net actuarial gains recognized during the year	1.3	0.3
Net actuarial losses occurring during the year(1)	(1.3)	(18.8)
Accumulated other comprehensive loss at end of year	$ (8)	$ (8)

Retirement Plans - Net Benefit

Retirement Plans - Net Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Amount expected to be amortized from accumulated other comprehensive income (loss) into net periodic benefit cost	$ 1.1
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.9	$ 0.6	$ 0.8
Interest cost	4.6	4.7	4.2
Expected return on plan assets	(8.7)	(8.5)	(7.1)
Amortization of net actuarial losses recognized during the year	1.3	0.3	0.9
Net periodic pension income before special termination benefits	(1.9)	(2.9)	(1.2)
Special termination benefits expense	0	0.3	0.3
Total net periodic benefit income	$ (1.9)	$ (2.6)	$ (0.9)

Retirement Plans - Assumptions

Retirement Plans - Assumptions (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Discount rate	3.22%	3.91%
Discount rate	3.91%	4.66%
Expected long-term rate of return on plan assets	6.00%	6.00%

Retirement Plans - Fair Value (

Retirement Plans - Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 139.8	$ 146	$ 142.8
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	139.4	143.2
Qualified Plan | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	139.4	105.8
Qualified Plan | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	37.4
Qualified Plan | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Qualified Plan | Fixed maturity investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	132.4	24.2
Qualified Plan | Fixed maturity investments | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	132.4	0
Qualified Plan | Fixed maturity investments | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	24.2
Qualified Plan | Fixed maturity investments | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0
Qualified Plan | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7	5.2
Qualified Plan | Short-term investments | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7	4.8
Qualified Plan | Short-term investments | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	0.4
Qualified Plan | Short-term investments | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0	0
Qualified Plan | Equity Financial Investment [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		17.1
Qualified Plan | Equity Financial Investment [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		17.1
Qualified Plan | Equity Financial Investment [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Financial Investment [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Basic Material Investment [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		11
Qualified Plan | Equity Basic Material Investment [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		11
Qualified Plan | Equity Basic Material Investment [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Basic Material Investment [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Consumer Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		35.2
Qualified Plan | Equity Consumer Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		35.2
Qualified Plan | Equity Consumer Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Consumer Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Energy Consumer Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		13.9
Qualified Plan | Energy Consumer Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		13.9
Qualified Plan | Energy Consumer Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Energy Consumer Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Utilities Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2.6
Qualified Plan | Equity Utilities Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2.6
Qualified Plan | Equity Utilities Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Utilities Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		21.2
Qualified Plan | Equity Other Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		21.2
Qualified Plan | Equity Other Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Equity Other Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Common equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		101
Qualified Plan | Common equity securities | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		101
Qualified Plan | Common equity securities | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Common equity securities | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Financial Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3.1
Qualified Plan | Convertible Financial Debt Securities [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Financial Debt Securities [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3.1
Qualified Plan | Convertible Financial Debt Securities [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Basic Materials Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		1.4
Qualified Plan | Convertible Basic Materials Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Basic Materials Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		1.4
Qualified Plan | Convertible Basic Materials Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Consumer Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		4.1
Qualified Plan | Convertible Consumer Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Consumer Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		4.1
Qualified Plan | Convertible Consumer Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Energy Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0.8
Qualified Plan | Convertible Energy Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Energy Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0.8
Qualified Plan | Convertible Energy Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3.4
Qualified Plan | Convertible Other Investments [Member] | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible Other Investments [Member] | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		3.4
Qualified Plan | Convertible Other Investments [Member] | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible fixed maturity investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		12.8
Qualified Plan | Convertible fixed maturity investments | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0
Qualified Plan | Convertible fixed maturity investments | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		12.8
Qualified Plan | Convertible fixed maturity investments | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 0

Retirement Plans - Plan Assets

Retirement Plans - Plan Assets (Details) - Qualified Plan	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%	100.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	95.00%	16.90%
Common equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	0.00%	70.60%
Convertible fixed maturity investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	0.00%	8.90%
Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	5.00%	3.60%

Retirement Plans - Cash Flow (D

Retirement Plans - Cash Flow (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Postemployment Benefits [Abstract]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	$ 2.1
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	86.8
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	2.1
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	2.1
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	2
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	2
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	$ 8.9

Retirement Plans - Other Benefi

Retirement Plans - Other Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Cost recognized	$ 3	$ 2.7	$ 2.3
Employer matching contribution, percent of employees' gross pay	6.00%
Percentage of matching contribution made by company	50.00%
Supplemental Employee Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Noncurrent benefit liability	$ 4.1	4.8
Postretirement Life Insurance [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Noncurrent benefit liability	12.5	12.9
Assets Held-in-trust, Noncurrent	$ 33.9	$ 33.2

Employee Share-Based Incentiv91

Employee Share-Based Incentive Compensation Plans Employee Share-Based Incentive Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expense recognized	$ 7.7	$ 7.5	$ 11.9

Employee Share-Based Incentiv92

Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Expense amortized
Expense recognized	$ (7.7)	$ (7.5)	$ (11.9)
Additional disclosures
Performance share payments factor	45.70%	37.10%	0.00%
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 1.3
Share-based Compensation Arrangement by Share-based Payment Award, Payout for Maximum Growth Target Percentage	200.00%	200.00%	200.00%
Share-based compensation Arrangement by Share-based Payment Award, Targeted Performance Goal for Personnel Expressed as Percentage of Growth in Intrinsic Business Value Per Share	13.00%	14.00%	13.00%
Share-based Compensation Arragement by Share-based Payment Award, Performance Goal Percentage for Minimum Payout	6.00%	7.00%	6.00%
Performance goal percentage for minimum payout	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award Performance Goal Percentage for Maximum Payout	20.00%	21.00%	20.00%
Long Term Incentive Plan | Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Number before Forfeitures	449,435
Activity in plan
Payments and deferrals (in shares)	(181,290)	(142,138)	(238,658)
Beginning of period (in shares)	517,470	493,421	563,190
New awards (in shares)	154,887	165,800	179,000
Forfeitures and net change in assumed forfeitures (in shares)	(41,632)	387	(10,111)
End of period (in shares)	449,435	517,470	493,421
Expense amortized
Accrued expense at beginning of period	$ 3.4	$ 4	$ 1.2
Payments and deferrals	(1.5)	(1)	0
Forfeitures and net change in assumed forfeitures	(0.1)	0	(0.1)
Expense recognized	(0.4)	(0.4)	(2.9)
Accrued expense at end of period	$ 1.4	$ 3.4	$ 4
Additional disclosures
Assumed forfeitures (in shares)	(7,234)
Assumed forfeitures	$ 0
Long Term Incentive Plan | Performance shares | Performance Cycle 2013 - 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Number before Forfeitures	167,300
Expense amortized
Accrued expense at end of period	$ 0.6
Long Term Incentive Plan | Performance shares | Performance Cycle 2014 - 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Number before Forfeitures	142,710
Expense amortized
Accrued expense at end of period	$ 0.1
Long Term Incentive Plan | Performance shares | Performance Cycle 2015 - 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Number before Forfeitures	146,659
Expense amortized
Accrued expense at end of period	$ 0.7
Long Term Incentive Plan | Performance shares | Performance Cycles 2013 - 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Nonvested Number before Forfeitures	456,669
Expense amortized
Accrued expense at end of period	$ 1.4

Employee Share-Based Incentiv93

Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - USD ($) $ in Millions	Feb. 24, 2015	May. 25, 2011	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unamortized grant date fair value
Expense recognized			$ (7.7)	$ (7.5)	$ (11.9)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms			1 year 4 months 24 days
Restricted Stock
Activity in plan
Beginning of period (in shares)			612,500	915,000	927,000
New awards (in shares)			75,950	0	0
Forfeitures (in shares)			(9,728)	(2,500)	(3,000)
Vested (in shares)			(296,000)	(300,000)	(9,000)
End of period (in shares)			382,722	612,500	915,000
Unamortized grant date fair value
Unamortized grant date fair value, beginning of period			$ 3.5	$ 6.5	$ 9.6
Issued	$ 1.1		1.1	0	0
Employee Service Share Based Compensation Nonvested Awards Forfeited in Period Total Compensation Cost Not Yet Recognized			(0.1)	0	0
Expense recognized			(2)	(3)	(3.1)
Unamortized grant date fair value, end of period			2.5	3.5	6.5
Grant date fair value			$ (4.3)	$ (4.3)	$ (0.1)
RSAs Granted in 2012 [Member] | Restricted Stock
Activity in plan
Vested (in shares)			(142,500)
RSAs Granted in 2011 [Member] | Restricted Stock
Activity in plan
Vested (in shares)			(157,500)	(157,500)
RSAs Granted in 2011 [Member] | Restricted Stock
Activity in plan
New awards (in shares)		630,000
Restricted Stock | RSAs Granted in 2012 [Member]
Activity in plan
End of period (in shares)			138,500
Restricted Stock | RSAs Granted in 2011 [Member]
Activity in plan
End of period (in shares)			315,000
Awards Issued in 2015 [Member] | Restricted Stock
Activity in plan
New awards (in shares)	75,950

Employee Share-Based Incentiv94

Employee Share-Based Incentive Compensation Plans - Stock Options (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized	$ 7.7	$ 7.5	$ 11.9

Employee Share-Based Incentiv95

Employee Share-Based Incentive Compensation Plans - Restricted Stock Units (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized	$ 7.7	$ 7.5	$ 11.9
Awards Issued in 2015 [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
New awards (in shares)	226,778
Expense recognized	$ 0.8
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	200,194

Employee Share-Based Incentiv96

Employee Share-Based Incentive Compensation Plans - Other Share-Based Compensation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Stock Ownership Plan (ESOP), Annual Contribution Provided to Participants Expressed as Percentage of Salary	3.00%
Employee Stock Ownership Plan (ESOP), Social Security Wage Base Amount Maximum	$ 118,500
Employee Stock Ownership Plan (ESOP), Annual Base Contribution Provided to Participants Expressed as Percentage of Salary	6.00%
Employee Stock Ownership Plan (ESOP), Variable Contribution Provided to Participants Not Eligible to Certain Benefits Expressed as Percentage of Salary	3.00%	2.00%	4.00%
Annual Compensation Cap	$ 265,000
Expense recognized	$ 7,700,000	$ 7,500,000	$ 11,900,000
Percentage Owned of Common Stock	3.00%
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	0
KSOP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized	$ 5,400,000	$ 4,100,000	$ 6,000,000

Common Shareholders' Equity (De

Common Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 22, 2007
Equity, Class of Treasury Stock [Line Items]
Other investments	$ 143	$ 203.8
Dividends	81.2	80.9	$ 81
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Net change in benefit plan assets and obligations	0	(18.5)	31.7
Income tax benefit (expense)	0	6.5	(11.1)
Net change in benefit plan assets and obligations, net of tax	0	$ 12	$ (20.6)
Class A common
Equity, Class of Treasury Stock [Line Items]
Stock repurchase, authorized amount				$ 200
Stock repuchase, remaining authorized repurchase amount	$ 85.6
Repurchases and retirements of common shares	166,368	0	0
Stock Repurchased During Period, Value	$ 2.1
Treasury Stock Acquired, Average Cost Per Share	$ 12.62
OneBeacon
Equity, Class of Treasury Stock [Line Items]
Dividends	$ 80	$ 80	$ 80.2
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Net change in benefit plan assets and obligations, net of tax	0	12	(20.6)
Accumulated Other Comprehensive Income (Loss) [Member]
Equity, Class of Treasury Stock [Line Items]
Dividends	0	0	0
AOCI Including Portion Attributable to Noncontrolling Interest [Abstract]
Net change in benefit plan assets and obligations, net of tax	$ 0	$ 12	$ (20.6)
Restricted Stock | Class A common
Equity, Class of Treasury Stock [Line Items]
Shares Paid for Tax Withholding for Share Based Compensation	112,051	106,366	3,300
Repurchases and retirements of common shares		0
Stock Repurchased During Period, Value	$ 1.6	$ 1.8	$ 0.1

Statutory Capital and Surplus (

Statutory Capital and Surplus (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 23, 2014
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus Required	$ 117.7
Dividend Payment without Prior Approval of Regulatory Authorities Percentage of Prior Year Statutory Surplus	10.00%
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval	$ 26.6
Statutory Accounting Practices, Statutory Net Income Amount	44.5	$ (14.2)	$ 100.1
Cash dividends paid to parent	0	0	0
Payments for Repurchase of Common Stock	3.7	1.8	0
Net Unrestricted Cash, Short Term and Fixed Maturity Investments	65.3
Dividends, Common Stock, Cash	81.2	80.9	81
Total	2,080.5
Other investments	143	203.8
Unregulated Operation [Member]
Statutory Accounting Practices [Line Items]
Payments of Dividends	5.3	4.8
Net Unrestricted Cash, Short Term and Fixed Maturity Investments	104.4
UNITED STATES
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	622.3	721.5
BERMUDA
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	249.5	122.6
Atlantic Specialty Insurance Company (ASIC) | Regulated Operation [Member]
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	622.3
Statutory Accounting Practices, Statutory Earned Surplus	68.3
Cash dividends paid to parent	44.9
Payments for Repurchase of Common Stock	66
Split Rock Insurance, Ltd. (Split Rock)
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Net Income Amount	$ 45.5	46.2	(38.7)
Statutory Accounting Practices, Statutory Capital, Percent	15.00%
Proceeds from Contributions from Affiliates	$ 85
Cash dividends paid to parent	0	10
Payments of Dividends	0	10
Runoff
Statutory Accounting Practices [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations				$ 101
Retained earnings (deficit)
Statutory Accounting Practices [Line Items]
Dividends, Common Stock, Cash	80	80	80.2
Retained earnings (deficit) | Split Rock Insurance, Ltd. (Split Rock)
Statutory Accounting Practices [Line Items]
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval	37.4
OneBeacon
Statutory Accounting Practices [Line Items]
Dividends, Common Stock, Cash	80	80	$ 80.2
Surplus Notes For Sale Of Discontinued Operations [Member]
Statutory Accounting Practices [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	101	101		101
Other investments				$ 64.9
Equity Securities and Convertible Fixed Maturity Investments [Member]
Statutory Accounting Practices [Line Items]
Total	$ 54.6
Distribution of ASIC by OBIC [Member] | OneBeacon Insurance Company
Statutory Accounting Practices [Line Items]
Dividends		700.5
Cash and short-term investments | OneBeacon Insurance Company
Statutory Accounting Practices [Line Items]
Dividends		$ 151.2

Segment Information (Details)

Segment Information (Details) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Sep. 30, 2014USD ($)	Jun. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2015USD ($)segment$ / shares	Dec. 31, 2014USD ($)$ / shares	Dec. 31, 2013USD ($)$ / shares	Dec. 31, 2012USD ($)
Segment Information
Number of underwriting segments | segment										16
Earned premiums										$ 1,176.2	$ 1,177.1	$ 1,120.4
Loss and loss adjustment expense										(700.7)	(815.1)	(622.1)
Policy acquisition expenses										(213.8)	(203.3)	(208.9)
Other underwriting expenses										(218.2)	(179.2)	(204.8)
Total underwriting income (loss)										43.5	(20.5)	84.6
Net investment income										45.9	43.4	43
Net realized and change in unrealized investment gains										(35.1)	40.4	49.4
Net other revenues (expenses)										(0.6)	5.8	31.2
General and administrative expenses										(15.4)	(13.8)	(12)
Interest expense										(13)	(13)	(13)
Pre-tax income (loss) from continuing operations	$ 11.1	$ (16.8)	$ 2.9	$ 28.1	$ (49.1)	$ 4.9	$ 31.7	$ 54.8		25.3	42.3	183.2
Segment Information, Additional Disclosure
Total investment securities	2,591.4				2,525.8					2,591.4	2,525.8
Premiums receivable	219				241.5					219	241.5
Reinsurance recoverables	193.5				173.8					193.5	173.8
Funds held under reinsurance contracts	0				37.1					0	37.1
Deferred acquisition costs	100.7				103.2					100.7	103.2
Ceded unearned premiums	29.5				17.9					29.5	17.9
Other assets not separately identifiable at the segment level	470.4				478.9					470.4	478.9
Total assets	3,604.5				3,578.2					3,604.5	3,578.2
Unpaid loss and loss adjustment expense reserves	1,389.8				1,342.2				$ 1,054.3	1,389.8	1,342.2	1,054.3	$ 1,000
Unearned premiums	560.3				588.3					560.3	588.3
Funds held under insurance contracts	137.7				81					137.7	81
Debt	274.8				274.7					274.8	274.7
Other liabilities not separately identifiable at the segment level	237.4				242.7					237.4	242.7
Total liabilities	2,600				2,528.9					2,600	2,528.9
Net written premiums										$ 1,136.6	$ 1,216.9	$ 1,088.6
Insurance Ratios [Abstract]
Dividends, per share, cash paid | $ / shares										$ (0.84)	$ (0.84)	$ (0.84)
Loss Ratio										59.60%	69.20%	55.50%
Underwriting Expense Ratio										36.70%	32.50%	36.90%
Combined Ratio										96.30%	101.70%	92.40%
Underwriting Segment [Member]
Segment Information
Number of underwriting segments | segment										2
Specialty Products
Segment Information
Number of underwriting segments | segment										10
Earned premiums										$ 560.3	$ 582.1	$ 553.5
Loss and loss adjustment expense										(310.7)	(457.9)	(312.3)
Policy acquisition expenses										(100.1)	(96.2)	(106.3)
Other underwriting expenses										(97.9)	(78.4)	(97.4)
Total underwriting income (loss)										51.6	(50.4)	37.5
Net investment income										0	0	0
Net realized and change in unrealized investment gains										0	0	0
Net other revenues (expenses)										(0.2)	0.9	0.3
General and administrative expenses										0	0.2	0
Interest expense										0	0	0
Pre-tax income (loss) from continuing operations										51.4	(49.3)	37.8
Segment Information, Additional Disclosure
Total investment securities	0				0					0	0
Premiums receivable	63				77.7					63	77.7
Reinsurance recoverables	139.5				127.3					139.5	127.3
Funds held under reinsurance contracts					37.1						37.1
Deferred acquisition costs	49.6				49.7					49.6	49.7
Ceded unearned premiums	19.2				7.5					19.2	7.5
Other assets not separately identifiable at the segment level	0				0					0	0
Total assets	271.3				299.3					271.3	299.3
Unpaid loss and loss adjustment expense reserves	772.2				798.8					772.2	798.8
Unearned premiums	288.1				303.6					288.1	303.6
Funds held under insurance contracts	137.7				81					137.7	81
Debt	0				0					0	0
Other liabilities not separately identifiable at the segment level	0				0					0	0
Total liabilities	1,198				1,183.4					1,198	1,183.4
Net written premiums										$ 533	$ 606.9	$ 509.6
Insurance Ratios [Abstract]
Loss Ratio										55.50%	78.70%	56.40%
Underwriting Expense Ratio										35.30%	30.00%	36.80%
Combined Ratio										90.80%	108.70%	93.20%
Specialty Industries
Segment Information
Number of underwriting segments | segment										6
Earned premiums										$ 615.9	$ 595	$ 566.9
Loss and loss adjustment expense										(390)	(357.2)	(309.8)
Policy acquisition expenses										(113.7)	(107.1)	(102.6)
Other underwriting expenses										(120.3)	(100.8)	(107.4)
Total underwriting income (loss)										(8.1)	29.9	47.1
Net investment income										0	0	0
Net realized and change in unrealized investment gains										0	0	0
Net other revenues (expenses)										1.4	1.1	1.1
General and administrative expenses										(2.7)	(2.3)	(2.4)
Interest expense										0	0	0
Pre-tax income (loss) from continuing operations										(9.4)	28.7	45.8
Segment Information, Additional Disclosure
Total investment securities	0				0					0	0
Premiums receivable	156				163.8					156	163.8
Reinsurance recoverables	33.6				22.7					33.6	22.7
Funds held under reinsurance contracts					0						0
Deferred acquisition costs	51.1				53.5					51.1	53.5
Ceded unearned premiums	10.3				10.4					10.3	10.4
Other assets not separately identifiable at the segment level	0				0					0	0
Total assets	251				250.4					251	250.4
Unpaid loss and loss adjustment expense reserves	597.2				519.6					597.2	519.6
Unearned premiums	272.2				284.7					272.2	284.7
Funds held under insurance contracts	0				0					0	0
Debt	0				0					0	0
Other liabilities not separately identifiable at the segment level	0				0					0	0
Total liabilities	869.4				804.3					869.4	804.3
Net written premiums										$ 603.6	$ 610	$ 579
Insurance Ratios [Abstract]
Loss Ratio										63.30%	60.10%	54.70%
Underwriting Expense Ratio										38.00%	34.90%	37.00%
Combined Ratio										101.30%	95.00%	91.70%
Investing, Financing and Corporate
Segment Information
Earned premiums										$ 0	$ 0	$ 0
Loss and loss adjustment expense										0	0	0
Policy acquisition expenses										0	0	0
Other underwriting expenses										0	0	0
Total underwriting income (loss)										0	0	0
Net investment income										45.9	43.4	43
Net realized and change in unrealized investment gains										(35.1)	40.4	49.4
Net other revenues (expenses)										(1.8)	3.8	29.8
General and administrative expenses										(12.7)	(11.7)	(9.6)
Interest expense										(13)	(13)	(13)
Pre-tax income (loss) from continuing operations										(16.7)	62.9	99.6
Segment Information, Additional Disclosure
Total investment securities	2,591.4				2,525.8					2,591.4	2,525.8
Premiums receivable	0				0					0	0
Reinsurance recoverables	20.4				23.8					20.4	23.8
Funds held under reinsurance contracts					0						0
Deferred acquisition costs	0				0					0	0
Ceded unearned premiums	0				0					0	0
Other assets not separately identifiable at the segment level	470.4				478.9					470.4	478.9
Total assets	3,082.2				3,028.5					3,082.2	3,028.5
Unpaid loss and loss adjustment expense reserves	20.4				23.8					20.4	23.8
Unearned premiums	0				0					0	0
Funds held under insurance contracts	0				0					0	0
Debt	274.8				274.7					274.8	274.7
Other liabilities not separately identifiable at the segment level	237.4				242.7					237.4	242.7
Total liabilities	$ 532.6				$ 541.2					532.6	541.2
Segment, Discontinued Operations
Segment Information
Earned premiums										0	0.1	0.8
Loss and loss adjustment expense									$ (71.5)	0	0.7	(78.9)
Other underwriting expenses										0	(3.5)	0.2
Segment Information, Additional Disclosure
Net written premiums										$ 0	$ (0.1)	$ 0.4
Atlantic Specialty Insurance Company (ASIC)
Segment Information, Additional Disclosure
Quota share reinsurance agreement percentage	100.00%									100.00%

Variable Interest Entity (Detai

Variable Interest Entity (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)reciprocal	Dec. 31, 2014USD ($)
Variable Interest Entity [Line Items]
Retained earnings (deficit)	$ (15.9)	$ 27.3
Reciprocals [Member]
Variable Interest Entity [Line Items]
Number of reciprocals capitalized | reciprocal	1
Houston General Insurance [Member]
Variable Interest Entity [Line Items]
Surplus notes	$ 5
Carrying amount of total assets related to VIE	5.1
Carrying amount of total liabilities related to VIE	5
Retained earnings (deficit)	0.2
Accrued interest on surplus notes	$ 0.3

Fair Value of Financial Inst101

Fair Value of Financial Instruments (Details) - OBH (issuer) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Carrying Value
Fair Value of Financial Instruments
Senior unsecured notes, carrying value	$ 274.8	$ 274.7
Fair Value
Fair Value of Financial Instruments
Senior unsecured notes, carrying value	$ 276.4	$ 286

Related Party Disclosures (Deta

Related Party Disclosures (Details) - USD ($) shares in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2006	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Expenses Recognized Under Seperation Agreement										$ 300,000	$ 300,000	$ 400,000
Revenue Recognized Under Seperation Agreement										2,000,000	2,000,000	2,000,000
Total noncontrolling interests, after tax	$ 3,600,000				$ 3,500,000					3,600,000	3,500,000
Proceeds from sale of business										0	0	31,300,000
Operating Leases, Rent Expense, Net										12,000,000	11,100,000	11,500,000
Income tax benefit	$ (11,900,000)	$ (3,500,000)	$ (900,000)	$ 3,400,000	(24,200,000)	$ (1,100,000)	$ 5,900,000	$ 7,100,000		(12,900,000)	(12,300,000)	36,500,000
Net written premiums										1,136,600,000	1,216,900,000	1,088,600,000
White Mountains Advisors L L C [Member]
Related Party Transaction [Line Items]
Asset Management Fees										$ 3,600,000	3,400,000	3,400,000
Asset Managment Fee, Treasury Percentage										0.0175%
Asset Managment Fee, Treasury										$ 400,000	400,000	400,000
Star and Shield Insurance Exchange [Member]
Related Party Transaction [Line Items]
Net written premiums										2,800,000	17,300,000	5,600,000
Limited Liability Company [Member]
Related Party Transaction [Line Items]
Limited Partnership Investments Under Management, Carrying Amount					$ 15,800,000						15,800,000	14,900,000
Related Party Transaction Management Fees from Transactions with Related Party										100,000	200,000	200,000
Related Party Transaction Incentive Fees from Transactions with Related Party										$ 0	200,000	500,000
White Mountains Insurance Group Ltd
Related Party Transaction [Line Items]
Stock Issued During Period, Shares, New Issues									27.6
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners									27.60%
Ownership interest (as a percent)	75.50%									75.50%
Prospective Partners LLC [Member] | Limited Liability Company [Member]
Related Party Transaction [Line Items]
Investment Advisory Fees on First Threshold of Assets Under Management in Basis Points	1.00%									1.00%
First Specified Threshold Limit of Assets Under Management	$ 200,000,000									$ 200,000,000
Investment Advisory Fees on Second Threshold of Assets Under Management in Basis Points	0.50%									0.50%
Second Specified Threshold Limit of Assets Under Management	$ 200,000,000									$ 200,000,000
Investment Advisory Fees on Third Threshold of Assets Under Management in Basis Points	0.25%									0.25%
Specified Threshold Limit of Assets under Management	$ 400,000,000									$ 400,000,000
Noninterest Expense Investment Advisory Fees										400,000	2,000,000	2,000,000
Share-based Compensation										$ 900,000	$ 1,300,000	$ 1,200,000

Related Party Disclosures - Ass

Related Party Disclosures - Asset Management (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Net written premiums	$ 1,136.6	$ 1,216.9	$ 1,088.6
Up to $1 Billion
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party, amount of asset portfolio	$ 1,000
Related party transaction, expenses from Transactions with related party, percent	0.10%
Next $1 billion
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party, amount of asset portfolio	$ 1,000
Related party transaction, expenses from Transactions with related party, percent	0.085%
Next $3 Billion
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party, amount of asset portfolio	$ 3,000
Related party transaction, expenses from Transactions with related party, percent	0.075%
Greater than $5 billion
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party, amount of asset portfolio	$ 5,000
Related party transaction, expenses from Transactions with related party, percent	0.025%
High Yield
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	0.25%
Equities
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
Hedge funds
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
First Two Years of Funds Life
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
Fair Value After Two Years
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
First Year of Funds Life
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
Fair Value After One Year
Related Party Transaction [Line Items]
Related party transaction, expenses from Transactions with related party, percent	1.00%
Limited Liability Company [Member]
Related Party Transaction [Line Items]
Limited Partnership Investments Under Management, Carrying Amount		15.8	14.9
Related Party Transaction Management Fees from Transactions with Related Party	$ 0.1	0.2	0.2
Related Party Transaction Incentive Fees from Transactions with Related Party	0	0.2	0.5
Star and Shield Insurance Exchange [Member]
Related Party Transaction [Line Items]
Net written premiums	2.8	17.3	5.6
White Mountains Advisors L L C [Member]
Related Party Transaction [Line Items]
Asset Managment Fee, Treasury	0.4	0.4	0.4
Prospective Partners LLC [Member] | Limited Liability Company [Member]
Related Party Transaction [Line Items]
Noninterest Expense Investment Advisory Fees	0.4	2	2
Share-based Compensation	$ 0.9	$ 1.3	$ 1.2

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
Loss Contingencies [Line Items]
Operating Leases, Rent Expense, Net	$ 12	$ 11.1	$ 11.5
Operating Leases, Future Minimum Payments Due, Next Twelve Months	10.2
Operating Leases, Future Minimum Payments, Due in Two Years	9.4
Operating Leases, Future Minimum Payments, Due in Three Years	7.8
Operating Leases, Future Minimum Payments, Due in Four Years	6.7
Operating Leases, Future Minimum Payments, Due Thereafter	31.1
Sale Leaseback Transaction, Net Proceeds				$ 23.1
Sale Leaseback Buyback, Net Book Value	1.3
Capital Lease Obligations	1.7	7.1
Capital Leased Assets, Gross	2.4	7
Capital Leases, Future Minimum Payments Due, Next Twelve Months	1.7
Pending Guranty Fund Assessments	8.5
Pending Litigation | Tribune Company Litigation
Loss Contingencies [Line Items]
Proceeds Common Stock, Litigation Settlement	32
Estimated Litigation Liability	0
Hedge funds and private equity funds
Loss Contingencies [Line Items]
Net asset value per share of unfunded commitments	$ 8.2	$ 10.6
US Bancorp
Loss Contingencies [Line Items]
Lessee Leasing Arrangements, Capital Leases, Term of Contract	5 years
Fifth Third Bank
Loss Contingencies [Line Items]
Lessee Leasing Arrangements, Capital Leases, Term of Contract	4 years

Earnings per Share (Details)

Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net income from continuing operations attributable to OneBeacon's common shareholders	$ 37	$ 53.5	$ 145.7
Allocation of loss (income) for participating unvested restricted common shares	(0.2)	(0.4)	(1.4)
Dividends paid on participating restricted common shares	(0.3)	(0.5)	(0.8)
Total allocation to restricted common shares	(0.5)	(0.9)	(2.2)
Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts	36.5	52.6	143.5
Undistributed Earnings, Basic [Abstract]
Net income from continuing operations attributable to OneBeacon's common shareholders, net of restricted common share amounts	36.5	52.6	143.5
Dividends paid, net of restricted common share amounts	(79.7)	(79.5)	(79.4)
Total undistributed (over-distributed) net earnings, net of restricted common share amounts	$ (43.2)	$ (26.9)	$ 64.1
Weighted Average Number of Shares Outstanding, Basic [Abstract]
Total weighted average common shares outstanding	95.3	95.3	95.4
Weighted average unvested restricted common shares	(0.5)	(0.6)	(0.9)
Basic and diluted earnings (loss) per share denominator	94.8	94.7	94.5
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Net income from continuing operations attributable to OneBeacon's common shareholders	$ 0.38	$ 0.55	$ 1.52
Dividends, per share, cash paid	(0.84)	(0.84)	(0.84)
Undistributed (over-distributed) earnings	(0.46)	(0.29)	0.68
OneBeacon
Earnings Per Share, Basic and Diluted, Other Disclosures [Abstract]
Dividends, per share, cash paid	$ (0.84)	$ (0.84)	$ (0.84)

Discontinued Operations (Additi

Discontinued Operations (Additional Disclosures) (Details) - USD ($) $ in Millions	3 Months Ended										9 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 23, 2014	Dec. 31, 2012
Dispositions
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings												$ (35.1)	$ 40.7
Reinsurance recoverable on unpaid losses	$ 186				$ 161.6				$ 80.2			186	161.6	$ 80.2		$ 107.3
Unpaid loss and loss adjustment expense reserves	1,389.8				1,342.2				1,054.3			1,389.8	1,342.2	1,054.3		$ 1,000
Net Loss from discontinued operations, net of tax												(0.5)	(1.8)	(46.6)
Loss from discontinued operations, net of tax	(0.1)	$ (0.1)	$ (0.2)	$ (0.1)	(0.9)	$ (0.3)	$ (0.1)	$ (0.5)
Loss and loss adjustment expenses												700.7	815.1	622.1
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount					75.5						$ 14.3	$ (1.8)	$ 89.8	0
Workers’ compensation statutory discount rate												2.50%	2.50%
(Loss) gain from sale of discontinued operations, net of tax	0	$ 0	$ 0.3	$ 0	(11.3)	$ (7)	$ (0.5)	$ 0				$ 0.3	$ (18.8)	46.6
Reinsurance recoverables	193.5				173.8							193.5	173.8
Reinsurance recoverable on paid losses	7.5											7.5
Other investments	143				203.8							143	203.8
Segment, Discontinued Operations
Dispositions
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent												(0.2)	(20.6)	0
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax													(28.9)
Pre-tax loss												(0.7)	(2.8)	(71.6)
Net Loss from discontinued operations, net of tax												(0.2)	(20.6)	0
Net other revenues (expenses)										$ 7.8		(0.7)	0	6.3
Loss from discontinued operations, net of tax												(0.5)	(1.8)	(46.6)
Loss and loss adjustment expenses									$ 71.5			0	(0.7)	78.9
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Amount													7.4
Causes Of Increase Decrease In Liability For Unpaid Claims And Claims Adjustment Expense Amount, net of tax													4.8	7.4
(Loss) gain from sale of discontinued operations, net of tax												0.3	(18.8)	46.6
Runoff
Dispositions
Quota share reinsurance agreement percentage															100.00%
Net Loss from discontinued operations, net of tax														46.6
Runoff | Segment, Discontinued Operations
Dispositions
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax													97.9
Net Loss from discontinued operations, net of tax													63.7
(Loss) gain from sale of discontinued operations, net of tax														46.5
Surplus Notes For Sale Of Discontinued Operations [Member] | Segment, Discontinued Operations
Dispositions
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax													36.1
Investing, Financing and Corporate
Dispositions
Unpaid loss and loss adjustment expense reserves	20.4				23.8							20.4	23.8
Loss and loss adjustment expenses												0	0	$ 0
Reinsurance recoverables	20.4				23.8							20.4	23.8
Surplus Notes For Sale Of Discontinued Operations [Member]
Dispositions
Surplus notes issued as seller financing in sale of discontinued operations	101				101							101	101		$ 101
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Fair Value	$ 51.5				$ 65.1							51.5	65.1
Other investments															64.9
Level 3 Inputs | Other investments
Dispositions
Fair Value Assets Measured on Recurring Basis Gain (Loss) Included in Earnings												$ (22.6)	$ 11.9
Runoff
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

Discontinued Operations (Summar

Discontinued Operations (Summary of the Results of Operations) (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Discontinued Operations
Net written premiums											$ 1,136.6	$ 1,216.9	$ 1,088.6
Revenues
Earned premiums											1,176.2	1,177.1	1,120.4
Revenues	$ 296.2	$ 267.8	$ 314.2	$ 308.2	$ 332.4	$ 301.5	$ 326	$ 306.8			1,186.4	1,266.7	1,244
Expenses
Loss and loss adjustment expenses											700.7	815.1	622.1
Other underwriting expenses											218.2	179.2	204.8
Total expenses	285.1	284.6	311.3	280.1	381.5	296.6	294.3	252			1,161.1	1,224.4	1,060.8
Tax (expense) benefit	11.9	3.5	0.9	(3.4)	24.2	1.1	(5.9)	(7.1)			12.9	12.3	(36.5)
Loss from discontinued operations, net of tax	(0.1)	(0.1)	(0.2)	(0.1)	(0.9)	(0.3)	(0.1)	(0.5)
(Loss) gain from sale of discontinued operations, net of tax	$ 0	$ 0	$ 0.3	$ 0	$ (11.3)	$ (7)	$ (0.5)	$ 0			0.3	(18.8)	46.6
Loss from discontinued operations, net of tax											$ (0.5)	$ (1.8)	(46.6)
Workers’ compensation statutory discount rate											2.50%	2.50%
Segment, Discontinued Operations
Discontinued Operations
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax												$ (28.9)
Net written premiums											$ 0	(0.1)	0.4
Revenues
Earned premiums											0	0.1	0.8
Other revenue (expenses)										$ 7.8	(0.7)	0	6.3
Revenues											(0.7)	0.1	7.1
Expenses
Loss and loss adjustment expenses									$ 71.5		0	(0.7)	78.9
Policy acquisition expenses											0	0.1	0
Other underwriting expenses											0	3.5	(0.2)
Total expenses											0	2.9	78.7
Pre-tax loss											(0.7)	(2.8)	(71.6)
Tax (expense) benefit											0.2	1	25
Loss from discontinued operations, net of tax											(0.5)	(1.8)	(46.6)
(Loss) gain from sale of discontinued operations, net of tax											0.3	(18.8)	46.6
Loss from discontinued operations, net of tax											(0.2)	(20.6)	0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent											$ (0.2)	(20.6)	0
Runoff
Expenses
Loss from discontinued operations, net of tax													46.6
Runoff | Segment, Discontinued Operations
Discontinued Operations
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax												97.9
Expenses
(Loss) gain from sale of discontinued operations, net of tax													$ 46.5
Loss from discontinued operations, net of tax												$ 63.7

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								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net loss from discontinued operations attributable to OneBeacon's common shareholders									$ (0.5)	$ (1.8)	$ (46.6)
Allocation of loss for participating unvested restricted common shares									(0.2)	(0.4)	(1.4)
Net income (loss) attributable to OneBeacon's common shareholders	$ 22.7	$ (13.4)	$ 3.4	$ 24.1	$ (37.3)	$ (1.3)	$ 24.7	$ 46.8	$ 36.8	$ 32.9	$ 145.7
Loss per share denominator—basic and diluted (in millions):
Total weighted average common shares outstanding									95.3	95.3	95.4
Weighted average unvested restricted common shares									(0.5)	(0.6)	(0.9)
Basic and diluted earnings (loss) per share denominator									94.8	94.7	94.5
Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars):
Net loss from discontinued operations attributable to OneBeacon's common shareholders per share	$ 0.24	$ (0.14)	$ 0.03	$ 0.25	$ (0.39)	$ (0.02)	$ 0.26	$ 0.49	$ 0.38	$ 0.34	$ 1.52
Segment, Discontinued Operations
Loss attributable to OneBeacon's common shareholders—basic and diluted (in millions):
Net loss from discontinued operations attributable to OneBeacon's common shareholders									$ (0.2)	$ (20.6)	$ 0
Allocation of loss for participating unvested restricted common shares									0	0.1	0
Net income (loss) attributable to OneBeacon's common shareholders									$ (0.2)	$ (20.5)	$ 0
Loss per share denominator—basic and diluted (in millions):
Total weighted average common shares outstanding									95.3	95.3	95.4
Weighted average unvested restricted common shares									(0.5)	(0.6)	(0.9)
Basic and diluted earnings (loss) per share denominator									94.8	94.7	94.5
Loss per share attributable to OneBeacon's common shareholders—basic and diluted (in dollars):
Net loss from discontinued operations attributable to OneBeacon's common shareholders per share									$ 0	$ (0.21)	$ 0

Discontinued Operations Surplus

Discontinued Operations Surplus Notes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 23, 2014
Surplus Note Valuation [Line Items]
Proposed Redemption Payment Percentage			200.00%
Surplus Note Valuation	Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of December 23, 2014: Type of Surplus Note Total Seller Priority Pari Passu (in millions) Par value $ 57.9 $ 43.1 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) 1.6 (8.4 ) (6.8 ) Regulatory approval (2) (4.6 ) (8.0 ) (12.6 ) Liquidity adjustment (3) (11.0 ) (5.7 ) (16.7 ) Total (14.0 ) (22.1 ) (36.1 ) Fair value $ 43.9 $ 21.0 $ 64.9 _______________________________________________________________________________ (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated delay in securing regulatory approvals of interest and principal payments to reflect graduated changes in Issuer's statutory surplus. The monetary impact of the anticipated delay is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. (3) Represents impact of liquidity spread to account for OneBeacon's sole ownership of the notes, lack of a trading market, and ongoing regulatory approval risk.
Other investments	$ 143	$ 203.8
Statutory Excess Capital Percentage			250.00%
Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	43.1		$ 43.1
Surplus Note, Interest Rate			6.00%
Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	57.9		$ 57.9
Surplus Note, Interest Rate			6.00%
Surplus Notes For Sale Of Discontinued Operations [Member]
Surplus Note Valuation [Line Items]
Surplus notes issued as seller financing in sale of discontinued operations	101	101	$ 101
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(49.5)	(35.9)	(36.1)
Other investments			64.9
Surplus Notes For Sale Of Discontinued Operations [Member] | Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(29.6)	(21.9)	(22.1)
Other investments			21
Surplus Notes For Sale Of Discontinued Operations [Member] | Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(19.9)	(14)	(14)
Other investments			43.9
Surplus Notes For Sale Of Discontinued Operations [Member] | Current market rates on public debt and contract-based repayments [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(15.1)	(6.6)	(6.8)
Surplus Notes For Sale Of Discontinued Operations [Member] | Current market rates on public debt and contract-based repayments [Member] | Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(14.7)	(8.2)	(8.4)
Surplus Notes For Sale Of Discontinued Operations [Member] | Current market rates on public debt and contract-based repayments [Member] | Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(0.4)	1.6	1.6
Surplus Notes For Sale Of Discontinued Operations [Member] | Regulatory approval [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(24.2)	(12.6)	(12.6)
Surplus Notes For Sale Of Discontinued Operations [Member] | Regulatory approval [Member] | Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(12.5)	(8)	(8)
Surplus Notes For Sale Of Discontinued Operations [Member] | Regulatory approval [Member] | Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(11.7)	(4.6)	(4.6)
Surplus Notes For Sale Of Discontinued Operations [Member] | Liquidity adjustment [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(10.2)	(16.7)	(16.7)
Surplus Notes For Sale Of Discontinued Operations [Member] | Liquidity adjustment [Member] | Pari passu [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	(2.4)	(5.7)	(5.7)
Surplus Notes For Sale Of Discontinued Operations [Member] | Liquidity adjustment [Member] | Seller priority [Member]
Surplus Note Valuation [Line Items]
Surplus Notes Issued As Seller Financing In Sale Of Discontinued Operations, Adjustments to Fair Value	$ (7.8)	$ (11)	$ (11)

Consolidating Financial Info110

Consolidating Financial Information (Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investment Securities:
Fixed maturity investments, at fair value	$ 2,080.5	$ 1,799.8
Short-term investments, at amortized cost (which approximates fair value)	69.2	202.2
Common equity securities, at fair value	298.7	320
Other investments	143	203.8
Total investment securities	2,591.4	2,525.8
Cash	95.2	87	$ 168.1	$ 43.9
Reinsurance recoverables	193.5	173.8
Premiums receivable	219	241.5
Funds held under reinsurance contracts	0	37.1
Deferred acquisition costs	100.7	103.2
Ceded unearned premiums	29.5	17.9
Net deferred tax asset	140.2	131.8
Investment income accrued	10.1	10
Accounts receivable on unsettled investment sales	30.5	7.2
Investments in subsidiaries	0	0
Other assets	194.4	184.8
Assets held for sale	0	58.1
Total assets	3,604.5	3,578.2
Liabilities
Unpaid loss and loss adjustment expense reserves	1,389.8	1,342.2	1,054.3	1,000
Unearned premiums	560.3	588.3
Funds held under insurance contracts	137.7	81
Debt	274.8	274.7
Other liabilities	237.4	242.7
Total liabilities	2,600	2,528.9
OneBeacon's common shareholders' equity and noncontrolling interests
Total OneBeacon's common shareholders' equity	1,000.9	1,045.8
Noncontrolling interests	3.6	3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,004.5	1,049.3	1,106.8	1,017
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	3,604.5	3,578.2
OneBeacon
Investment Securities:
Fixed maturity investments, at fair value	0	0
Short-term investments, at amortized cost (which approximates fair value)	4.4	18.4
Common equity securities, at fair value	0	0
Other investments	0	0
Total investment securities	4.4	18.4
Cash	0	0	0	0
Reinsurance recoverables	0	0
Premiums receivable	0	0
Funds held under reinsurance contracts		0
Deferred acquisition costs	0	0
Ceded unearned premiums	0	0
Net deferred tax asset	0	0
Investment income accrued	0	0
Accounts receivable on unsettled investment sales	0	0
Investments in subsidiaries	996.9	1,027.4
Other assets	0.5	0.3
Assets held for sale		0
Total assets	1,001.8	1,046.1
Liabilities
Unpaid loss and loss adjustment expense reserves	0	0
Unearned premiums	0	0
Funds held under insurance contracts	0	0
Debt	0	0
Other liabilities	0.9	0.3
Total liabilities	0.9	0.3
OneBeacon's common shareholders' equity and noncontrolling interests
Total OneBeacon's common shareholders' equity	1,000.9	1,045.8
Noncontrolling interests	0	0
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,000.9	1,045.8
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	1,001.8	1,046.1
Non-guarantor subsidiaries
Investment Securities:
Fixed maturity investments, at fair value	2,074.6	1,799.8
Short-term investments, at amortized cost (which approximates fair value)	64.1	182.5
Common equity securities, at fair value	298.7	320
Other investments	143	203.8
Total investment securities	2,580.4	2,506.1
Cash	94.6	87	166.6	43.9
Reinsurance recoverables	193.5	173.8
Premiums receivable	219	241.5
Funds held under reinsurance contracts		37.1
Deferred acquisition costs	100.7	103.2
Ceded unearned premiums	29.5	17.9
Net deferred tax asset	140.1	131.7
Investment income accrued	10.1	10
Accounts receivable on unsettled investment sales	30.5	7.2
Investments in subsidiaries	0	0
Other assets	190.6	180.1
Assets held for sale		58.1
Total assets	3,589	3,553.7
Liabilities
Unpaid loss and loss adjustment expense reserves	1,389.8	1,342.2
Unearned premiums	560.3	588.3
Funds held under insurance contracts	137.7	81
Debt	0	0
Other liabilities	230.4	235.3
Total liabilities	2,318.2	2,246.8
OneBeacon's common shareholders' equity and noncontrolling interests
Total OneBeacon's common shareholders' equity	1,267.2	1,303.4
Noncontrolling interests	3.6	3.5
Total OneBeacon's common shareholders' equity and noncontrolling interests	1,270.8	1,306.9
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	3,589	3,553.7
OBH (issuer)
Investment Securities:
Fixed maturity investments, at fair value	5.9	0
Short-term investments, at amortized cost (which approximates fair value)	0.7	1.3
Common equity securities, at fair value	0	0
Other investments	0	0
Total investment securities	6.6	1.3
Cash	0.6	0	1.5	0
Reinsurance recoverables	0	0
Premiums receivable	0	0
Funds held under reinsurance contracts		0
Deferred acquisition costs	0	0
Ceded unearned premiums	0	0
Net deferred tax asset	0	0
Investment income accrued	0	0
Accounts receivable on unsettled investment sales	0	0
Investments in subsidiaries	951.3	1,051.8
Other assets	3.3	4.4
Assets held for sale		0
Total assets	961.8	1,057.5
Liabilities
Unpaid loss and loss adjustment expense reserves	0	0
Unearned premiums	0	0
Funds held under insurance contracts	0	0
Debt	274.8	274.7
Other liabilities	6.1	7.1
Total liabilities	280.9	281.8
OneBeacon's common shareholders' equity and noncontrolling interests
Total OneBeacon's common shareholders' equity	680.9	775.7
Noncontrolling interests	0	0
Total OneBeacon's common shareholders' equity and noncontrolling interests	680.9	775.7
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	961.8	1,057.5
Consolidating adjustments
Investment Securities:
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
Other investments	0	0
Total investment securities	0	0
Cash	0	0	$ 0	$ 0
Reinsurance recoverables	0	0
Premiums receivable	0	0
Funds held under reinsurance contracts		0
Deferred acquisition costs	0	0
Ceded unearned premiums	0	0
Net deferred tax asset	0.1	0.1
Investment income accrued	0	0
Accounts receivable on unsettled investment sales	0	0
Investments in subsidiaries	(1,948.2)	(2,079.2)
Other assets	0	0
Assets held for sale		0
Total assets	(1,948.1)	(2,079.1)
Liabilities
Unpaid loss and loss adjustment expense reserves	0	0
Unearned premiums	0	0
Funds held under insurance contracts	0	0
Debt	0	0
Other liabilities	0	0
Total liabilities	0	0
OneBeacon's common shareholders' equity and noncontrolling interests
Total OneBeacon's common shareholders' equity	(1,948.1)	(2,079.1)
Noncontrolling interests	0	0
Total OneBeacon's common shareholders' equity and noncontrolling interests	(1,948.1)	(2,079.1)
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	$ (1,948.1)	$ (2,079.1)

Consolidating Financial Info111

Consolidating Financial Information (Consolidating Statement of Operations and Comprehensive (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Earned premiums									$ 1,176.2	$ 1,177.1	$ 1,120.4
Net investment income									45.9	43.4	43
Net realized and change in unrealized investment gains									(35.1)	40.4	49.4
Net other revenues (expenses)									0.6	(5.8)	(31.2)
Revenues	$ 296.2	$ 267.8	$ 314.2	$ 308.2	$ 332.4	$ 301.5	$ 326	$ 306.8	1,186.4	1,266.7	1,244
Expenses
Loss and loss adjustment expenses									700.7	815.1	622.1
Policy acquisition expenses									213.8	203.3	208.9
Other underwriting expenses									218.2	179.2	204.8
General and administrative expenses									15.4	13.8	12
Interest expense									13	13	13
Total expenses	285.1	284.6	311.3	280.1	381.5	296.6	294.3	252	1,161.1	1,224.4	1,060.8
Pre-tax income (loss) from continuing operations	11.1	(16.8)	2.9	28.1	(49.1)	4.9	31.7	54.8	25.3	42.3	183.2
Income tax (expense) benefit	11.9	3.5	0.9	(3.4)	24.2	1.1	(5.9)	(7.1)	12.9	12.3	(36.5)
Net income from continuing operations	23	(13.3)	3.8	24.7	(24.9)	6	25.8	47.7	38.2	54.6	146.7
Net loss from discontinued operations attributable to OneBeacon's common shareholders									(0.5)	(1.8)	(46.6)
(Loss) gain from sale of discontinued operations, net of tax	0	0	0.3	0	(11.3)	(7)	(0.5)	0	0.3	(18.8)	46.6
(Loss) income before equity in (losses) earnings of unconsolidated affiliates									38	34	146.7
Equity in earnings of subsidiaries, net of tax									0	0	0
Net income, including noncontrolling interests	22.9	(13.4)	3.9	24.6	(37.1)	(1.3)	25.2	47.2	38	34	146.7
Less: Net income attributable to noncontrolling interests	(0.2)	0	(0.5)	(0.5)	(0.2)	0	(0.5)	(0.4)	(1.2)	(1.1)	(1)
Net income (loss) attributable to OneBeacon's common shareholders	$ 22.7	$ (13.4)	$ 3.4	$ 24.1	$ (37.3)	$ (1.3)	$ 24.7	$ 46.8	36.8	32.9	145.7
Net change in benefit plan assets and obligations, net of tax									0	(12)	20.6
Comprehensive income attributable to OneBeacon's common shareholders									36.8	20.9	166.3
OneBeacon
Revenues
Earned premiums									0	0	0
Net investment income									0	0	0
Net realized and change in unrealized investment gains									0	0	0
Net other revenues (expenses)									0	0	0
Revenues									0	0	0
Expenses
Loss and loss adjustment expenses									0	0	0
Policy acquisition expenses									0	0	0
Other underwriting expenses									0	0	0
General and administrative expenses									4.8	5.1	5
Interest expense									0	0	0
Total expenses									4.8	5.1	5
Pre-tax income (loss) from continuing operations									(4.8)	(5.1)	(5)
Income tax (expense) benefit									0	0	0.1
Net income from continuing operations									(4.8)	(5.1)	(4.9)
Net loss from discontinued operations attributable to OneBeacon's common shareholders									0	0	0
(Loss) gain from sale of discontinued operations, net of tax									0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates									(4.8)	(5.1)	(4.9)
Equity in earnings of subsidiaries, net of tax									41.6	38	150.6
Net income, including noncontrolling interests									36.8	32.9	145.7
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to OneBeacon's common shareholders									36.8	32.9	145.7
Net change in benefit plan assets and obligations, net of tax									0	(12)	20.6
Comprehensive income attributable to OneBeacon's common shareholders									36.8	20.9	166.3
Non-guarantor subsidiaries
Revenues
Earned premiums									1,176.2	1,177.1	1,120.4
Net investment income									45.9	44.4	44.5
Net realized and change in unrealized investment gains									(35.1)	44.6	48.9
Net other revenues (expenses)									0.6	(5.8)	(31.2)
Revenues									1,186.4	1,271.9	1,245
Expenses
Loss and loss adjustment expenses									700.7	815.1	622.1
Policy acquisition expenses									213.8	203.3	208.9
Other underwriting expenses									218.2	179.2	204.8
General and administrative expenses									10.3	8.4	7.1
Interest expense									0	0	0
Total expenses									1,143	1,206	1,042.9
Pre-tax income (loss) from continuing operations									43.4	65.9	202.1
Income tax (expense) benefit									8.2	5.8	(42.6)
Net income from continuing operations									51.6	71.7	159.5
Net loss from discontinued operations attributable to OneBeacon's common shareholders									(0.5)	(1.8)	(46.6)
(Loss) gain from sale of discontinued operations, net of tax									0.3	(18.8)	46.6
(Loss) income before equity in (losses) earnings of unconsolidated affiliates									51.4	51.1	159.5
Equity in earnings of subsidiaries, net of tax									0	0	0
Net income, including noncontrolling interests									51.4	51.1	159.5
Less: Net income attributable to noncontrolling interests									(1.2)	(1.1)	(1)
Net income (loss) attributable to OneBeacon's common shareholders									50.2	50	158.5
Net change in benefit plan assets and obligations, net of tax									0	0	0
Comprehensive income attributable to OneBeacon's common shareholders									50.2	50	158.5
OBH (issuer)
Revenues
Earned premiums									0	0	0
Net investment income									0	0.1	(0.3)
Net realized and change in unrealized investment gains									0	0	(0.7)
Net other revenues (expenses)									0	3.7	0
Revenues									0	(3.6)	(1)
Expenses
Loss and loss adjustment expenses									0	0	0
Policy acquisition expenses									0	0	0
Other underwriting expenses									0	0	0
General and administrative expenses									0.3	0.3	(0.1)
Interest expense									13	14.1	14.2
Total expenses									13.3	14.4	14.1
Pre-tax income (loss) from continuing operations									(13.3)	(18)	(15.1)
Income tax (expense) benefit									4.7	6.3	6.2
Net income from continuing operations									(8.6)	(11.7)	(8.9)
Net loss from discontinued operations attributable to OneBeacon's common shareholders									0	0	0
(Loss) gain from sale of discontinued operations, net of tax									0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates									(8.6)	(11.7)	(8.9)
Equity in earnings of subsidiaries, net of tax									8.3	9.5	134.4
Net income, including noncontrolling interests									(0.3)	(2.2)	125.5
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to OneBeacon's common shareholders									(0.3)	(2.2)	125.5
Net change in benefit plan assets and obligations, net of tax									0	(12)	20.6
Comprehensive income attributable to OneBeacon's common shareholders									(0.3)	(14.2)	146.1
Consolidating adjustments
Revenues
Earned premiums									0	0	0
Net investment income									0	(1.1)	(1.2)
Net realized and change in unrealized investment gains									0	(4.2)	1.2
Net other revenues (expenses)									0	(3.7)	0
Revenues									0	(1.6)	0
Expenses
Loss and loss adjustment expenses									0	0	0
Policy acquisition expenses									0	0	0
Other underwriting expenses									0	0	0
General and administrative expenses									0	0	0
Interest expense									0	(1.1)	(1.2)
Total expenses									0	(1.1)	(1.2)
Pre-tax income (loss) from continuing operations									0	(0.5)	1.2
Income tax (expense) benefit									0	0.2	(0.2)
Net income from continuing operations									0	(0.3)	1
Net loss from discontinued operations attributable to OneBeacon's common shareholders									0	0	0
(Loss) gain from sale of discontinued operations, net of tax									0	0	0
(Loss) income before equity in (losses) earnings of unconsolidated affiliates									0	(0.3)	1
Equity in earnings of subsidiaries, net of tax									(49.9)	(47.5)	(285)
Net income, including noncontrolling interests									(49.9)	(47.8)	(284)
Less: Net income attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to OneBeacon's common shareholders									(49.9)	(47.8)	(284)
Net change in benefit plan assets and obligations, net of tax									0	12	(20.6)
Comprehensive income attributable to OneBeacon's common shareholders									$ (49.9)	$ (35.8)	$ (304.6)

Consolidating Financial Info112

Consolidating Financial Information (Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net income, including noncontrolling interests	$ 22.9	$ (13.4)	$ 3.9	$ 24.6	$ (37.1)	$ (1.3)	$ 25.2	$ 47.2	$ 38	$ 34	$ 146.7
Undistributed earnings from subsidiaries									0	0	0
Net loss from discontinued operations									0.5	1.8	46.6
Net loss from sale of discontinued operations	0	$ 0	$ (0.3)	0	11.3	$ 7	$ 0.5	0	(0.3)	18.8	(46.6)
Net realized and change in unrealized investment gains									35.1	(40.4)	(49.4)
Net other realized losses										0
Net realized gain on sale of business									3.7	0	(23)
Deferred income tax expense (benefit)									(5.8)	(19)	15
Dividends received from subsidiaries									0	0	0
Other operating items:
Net change in loss and LAE reserves									47.6	287.9	54.3
Net change in unearned premiums									28	(43.4)	28.9
Net change in ceded unearned premiums									(11.6)	(3.6)	(2.8)
Net change in premiums receivable									22.5	(13.3)	(2.6)
Net change in reinsurance recoverable on paid and unpaid losses									(19.7)	(83.9)	20.7
Net change in funds held under reinsurance contracts									37.1	(35.3)	(1.8)
Net change in funds held under insurance contracts									56.7	17.7	57.4
Net change in other assets and liabilities									16.6	(56.1)	19.8
Net cash provided from operations—continuing operations									192.4	152	205.4
Net cash used for operations—discontinued operations									(0.5)	(54.5)	(76.7)
Net cash provided from operations									191.9	97.5	128.7
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments									133.1	(65.5)	72.2
Maturities of fixed maturity investments									262.4	396.4	245.2
Sales of fixed maturity investments									763.5	1,843.1	1,400
Sales of common equity securities									345.6	240.2	196.7
Return of capital and distributions of other investments									40.5	53.4	67.5
Purchases of fixed maturity investments									(1,333.5)	(2,206.8)	(1,697)
Purchases of common equity securities									(323.5)	(202.4)	(206.3)
Contributions for other investments									(4.2)	(81.9)	(22)
Proceeds from sale of business									0	0	31.3
Net change in unsettled investment purchases and sales									(23.8)	(15)	4.1
Proceeds from sale of property and equipment									56.8	0	0
Net acquisitions of property and equipment									(11.5)	(2.2)	(10.3)
Capital contribution from parent									0	0	0
Net cash provided from (used for) investing activities—continuing operations									(94.6)	(40.7)	81.4
Net cash provided from investing activities—discontinued operations									0	0	0
Net cash provided from (used for) investing activities									(94.6)	(40.7)	81.4
Cash flows from financing activities:
Repurchases of debt										0
Cash dividends paid to common shareholders									(80)	(80)	(80.2)
Cash dividends paid to parent									0	0	0
Proceeds from Contributed Capital											0
Capital contribution to subsidiary									0	0
Repurchases and retirements of common stock									(3.7)	(1.8)	0
Payments on capital lease obligation									(5.4)	(5.3)	(5.7)
Net cash used for financing activities—continuing operations									(89.1)	(87.1)	(85.9)
Net cash used for financing activities—discontinued operations									0	0	0
Net cash used for financing activities									(89.1)	(87.1)	(85.9)
Cash balance at beginning of period				87				168.1	87	168.1	43.9
Net increase (decrease) before cash transferred with sale of business									8.2	(30.3)	124.2
Cash transferred with sale of business									0	(50.8)	0
Cash and Cash Equivalents, Period Increase (Decrease)									8.2	(81.1)	124.2
Cash balance at end of period	95.2				87				95.2	87	168.1
OneBeacon
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net income, including noncontrolling interests									36.8	32.9	145.7
Undistributed earnings from subsidiaries									(41.6)	(38)	(150.6)
Net loss from discontinued operations									0	0	0
Net loss from sale of discontinued operations									0	0	0
Net realized and change in unrealized investment gains									0	0	0
Net other realized losses										0
Net realized gain on sale of business									0		0
Deferred income tax expense (benefit)									0	0	0
Dividends received from subsidiaries									72	90.4	92
Other operating items:
Net change in loss and LAE reserves									0	0	0
Net change in unearned premiums									0	0	0
Net change in ceded unearned premiums									0	0	0
Net change in premiums receivable									0	0	0
Net change in reinsurance recoverable on paid and unpaid losses									0	0	0
Net change in funds held under reinsurance contracts									0	0	0
Net change in funds held under insurance contracts									0	0	0
Net change in other assets and liabilities									2.5	1.9	3.4
Net cash provided from operations—continuing operations									69.7	87.2	90.5
Net cash used for operations—discontinued operations									0	0	0
Net cash provided from operations									69.7	87.2	90.5
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments									14	(5.4)	(10.3)
Maturities of fixed maturity investments									0	0	0
Sales of fixed maturity investments									0	0	0
Sales of common equity securities									0	0	0
Return of capital and distributions of other investments									0	0	0
Purchases of fixed maturity investments									0	0	0
Purchases of common equity securities									0	0	0
Contributions for other investments									0	0	0
Proceeds from sale of business											0
Net change in unsettled investment purchases and sales									0	0	0
Proceeds from sale of property and equipment									0
Net acquisitions of property and equipment									0	0	0
Capital contribution from parent									0	0	0
Net cash provided from (used for) investing activities—continuing operations									14	(5.4)	(10.3)
Net cash provided from investing activities—discontinued operations									0	0	0
Net cash provided from (used for) investing activities									14	(5.4)	(10.3)
Cash flows from financing activities:
Repurchases of debt										0
Cash dividends paid to common shareholders									(80)	(80)	(80.2)
Cash dividends paid to parent									0	0	0
Proceeds from Contributed Capital											0
Capital contribution to subsidiary									0	0
Repurchases and retirements of common stock									(3.7)	(1.8)
Payments on capital lease obligation									0	0	0
Net cash used for financing activities—continuing operations									(83.7)	(81.8)	(80.2)
Net cash used for financing activities—discontinued operations									0	0	0
Net cash used for financing activities									(83.7)	(81.8)	(80.2)
Cash balance at beginning of period				0				0	0	0	0
Net increase (decrease) before cash transferred with sale of business										0
Cash transferred with sale of business										0
Cash and Cash Equivalents, Period Increase (Decrease)									0	0	0
Cash balance at end of period	0				0				0	0	0
Non-guarantor subsidiaries
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net income, including noncontrolling interests									51.4	51.1	159.5
Undistributed earnings from subsidiaries									0	0	0
Net loss from discontinued operations									0.5	1.8	46.6
Net loss from sale of discontinued operations									(0.3)	18.8	(46.6)
Net realized and change in unrealized investment gains									35.1	(44.6)	(48.9)
Net other realized losses										(3.7)
Net realized gain on sale of business									3.7		(23)
Deferred income tax expense (benefit)									(5.8)	(18.8)	14.9
Dividends received from subsidiaries									99.9	15	0
Other operating items:
Net change in loss and LAE reserves									47.6	287.9	54.3
Net change in unearned premiums									28	(43.4)	28.9
Net change in ceded unearned premiums									(11.6)	(3.6)	(2.8)
Net change in premiums receivable									22.5	(13.3)	(2.6)
Net change in reinsurance recoverable on paid and unpaid losses									(19.7)	(83.9)	20.7
Net change in funds held under reinsurance contracts									37.1	(35.3)	(1.8)
Net change in funds held under insurance contracts									56.7	17.7	57.4
Net change in other assets and liabilities									13.6	(49.6)	45.8
Net cash provided from operations—continuing operations									302.7	182.9	244.6
Net cash used for operations—discontinued operations									(0.5)	(54.5)	(76.7)
Net cash provided from operations									302.2	128.4	167.9
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments									118.5	(62.8)	26.3
Maturities of fixed maturity investments									262.4	396.4	223.7
Sales of fixed maturity investments									491.5	1,927.9	1,496.7
Sales of common equity securities									345.6	240.2	196.7
Return of capital and distributions of other investments									40.5	53.4	67.5
Purchases of fixed maturity investments									(1,055.3)	(2,265.1)	(1,787.2)
Purchases of common equity securities									(323.5)	(202.4)	(206.3)
Contributions for other investments									(4.2)	(81.9)	(22)
Proceeds from sale of business											31.3
Net change in unsettled investment purchases and sales									(23.8)	(15)	4.1
Proceeds from sale of property and equipment									56.8
Net acquisitions of property and equipment									(11.5)	(2.2)	(10.3)
Capital contribution from parent									2.2	70	250
Net cash provided from (used for) investing activities—continuing operations									(100.8)	58.5	270.5
Net cash provided from investing activities—discontinued operations									0	0	0
Net cash provided from (used for) investing activities									(100.8)	58.5	270.5
Cash flows from financing activities:
Repurchases of debt										0
Cash dividends paid to common shareholders									0	0	0
Cash dividends paid to parent									(182.9)	(140.4)	(310)
Proceeds from Contributed Capital											0
Capital contribution to subsidiary									(5.5)	(70)
Repurchases and retirements of common stock									0	0
Payments on capital lease obligation									(5.4)	(5.3)	(5.7)
Net cash used for financing activities—continuing operations									(193.8)	(215.7)	(315.7)
Net cash used for financing activities—discontinued operations									0	0	0
Net cash used for financing activities									(193.8)	(215.7)	(315.7)
Cash balance at beginning of period				87				166.6	87	166.6	43.9
Net increase (decrease) before cash transferred with sale of business										(28.8)
Cash transferred with sale of business										(50.8)
Cash and Cash Equivalents, Period Increase (Decrease)									7.6	(79.6)	122.7
Cash balance at end of period	94.6				87				94.6	87	166.6
OBH (issuer)
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net income, including noncontrolling interests									(0.3)	(2.2)	125.5
Undistributed earnings from subsidiaries									(8.3)	(9.5)	(134.4)
Net loss from discontinued operations									0	0	0
Net loss from sale of discontinued operations									0	0	0
Net realized and change in unrealized investment gains									0	0	0.7
Net other realized losses										3.7
Net realized gain on sale of business									0		0
Deferred income tax expense (benefit)									0	0	(0.1)
Dividends received from subsidiaries									110.9	50	218
Other operating items:
Net change in loss and LAE reserves									0	0	0
Net change in unearned premiums									0	0	0
Net change in ceded unearned premiums									0	0	0
Net change in premiums receivable									0	0	0
Net change in reinsurance recoverable on paid and unpaid losses									0	0	0
Net change in funds held under reinsurance contracts									0	0	0
Net change in funds held under insurance contracts									0	0	0
Net change in other assets and liabilities									0.5	(1.9)	(29.4)
Net cash provided from operations—continuing operations									102.8	40.1	180.3
Net cash used for operations—discontinued operations									0	0	0
Net cash provided from operations									102.8	40.1	180.3
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments									0.6	2.7	56.2
Maturities of fixed maturity investments									0	0	21.5
Sales of fixed maturity investments									88.7	80.3	386.7
Sales of common equity securities									0	0	0
Return of capital and distributions of other investments									0	0	0
Purchases of fixed maturity investments									(94.9)	(80.9)	(393.2)
Purchases of common equity securities									0	0	0
Contributions for other investments									0	0	0
Proceeds from sale of business											0
Net change in unsettled investment purchases and sales									0	0	0
Proceeds from sale of property and equipment									0
Net acquisitions of property and equipment									0	0	0
Capital contribution from parent									5.5	70	0
Net cash provided from (used for) investing activities—continuing operations									(0.1)	72.1	71.2
Net cash provided from investing activities—discontinued operations									0	0	0
Net cash provided from (used for) investing activities									(0.1)	72.1	71.2
Cash flows from financing activities:
Repurchases of debt										(28.7)
Cash dividends paid to common shareholders									0	0	0
Cash dividends paid to parent									(99.9)	(15)	0
Proceeds from Contributed Capital											(250)
Capital contribution to subsidiary									(2.2)	(70)
Repurchases and retirements of common stock									0	0
Payments on capital lease obligation									0	0	0
Net cash used for financing activities—continuing operations									(102.1)	(113.7)	(250)
Net cash used for financing activities—discontinued operations									0	0	0
Net cash used for financing activities									(102.1)	(113.7)	(250)
Cash balance at beginning of period				0				1.5	0	1.5	0
Net increase (decrease) before cash transferred with sale of business										(1.5)
Cash transferred with sale of business										0
Cash and Cash Equivalents, Period Increase (Decrease)									0.6	(1.5)	1.5
Cash balance at end of period	0.6				0				0.6	0	1.5
Consolidating adjustments
Charges (credits) to reconcile net income to cash flows (used for) provided from operations:
Net income, including noncontrolling interests									(49.9)	(47.8)	(284)
Undistributed earnings from subsidiaries									49.9	47.5	285
Net loss from discontinued operations									0	0	0
Net loss from sale of discontinued operations									0	0	0
Net realized and change in unrealized investment gains									0	4.2	(1.2)
Net other realized losses										0
Net realized gain on sale of business									0		0
Deferred income tax expense (benefit)									0	(0.2)	0.2
Dividends received from subsidiaries									(282.8)	(155.4)	(310)
Other operating items:
Net change in loss and LAE reserves									0	0	0
Net change in unearned premiums									0	0	0
Net change in ceded unearned premiums									0	0	0
Net change in premiums receivable									0	0	0
Net change in reinsurance recoverable on paid and unpaid losses									0	0	0
Net change in funds held under reinsurance contracts									0	0	0
Net change in funds held under insurance contracts									0	0	0
Net change in other assets and liabilities									0	(6.5)	0
Net cash provided from operations—continuing operations									(282.8)	(158.2)	(310)
Net cash used for operations—discontinued operations									0	0	0
Net cash provided from operations									(282.8)	(158.2)	(310)
Cash flows from investing activities:
Net maturities, purchases and sales of short-term investments									0	0	0
Maturities of fixed maturity investments									0	0	0
Sales of fixed maturity investments									183.3	(165.1)	(483.4)
Sales of common equity securities									0	0	0
Return of capital and distributions of other investments									0	0	0
Purchases of fixed maturity investments									(183.3)	139.2	483.4
Purchases of common equity securities									0	0	0
Contributions for other investments									0	0	0
Proceeds from sale of business											0
Net change in unsettled investment purchases and sales									0	0	0
Proceeds from sale of property and equipment									0
Net acquisitions of property and equipment									0	0	0
Capital contribution from parent									(7.7)	(140)	(250)
Net cash provided from (used for) investing activities—continuing operations									(7.7)	(165.9)	(250)
Net cash provided from investing activities—discontinued operations									0	0	0
Net cash provided from (used for) investing activities									(7.7)	(165.9)	(250)
Cash flows from financing activities:
Repurchases of debt										28.7
Cash dividends paid to common shareholders									0	0	0
Cash dividends paid to parent									282.8	155.4	310
Proceeds from Contributed Capital											250
Capital contribution to subsidiary									7.7	140
Repurchases and retirements of common stock									0	0
Payments on capital lease obligation									0	0	0
Net cash used for financing activities—continuing operations									290.5	324.1	560
Net cash used for financing activities—discontinued operations									0	0	0
Net cash used for financing activities									290.5	324.1	560
Cash balance at beginning of period				$ 0				$ 0	0	0	0
Net increase (decrease) before cash transferred with sale of business										0
Cash transferred with sale of business										0
Cash and Cash Equivalents, Period Increase (Decrease)									0	0	0
Cash balance at end of period	$ 0				$ 0				$ 0	$ 0	$ 0

Subsequent Event (Details)

Subsequent Event (Details)	Feb. 23, 2016$ / shares
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared (in dollars per share)	$ 0.21

Selected Quarterly Financial114

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 296.2	$ 267.8	$ 314.2	$ 308.2	$ 332.4	$ 301.5	$ 326	$ 306.8	$ 1,186.4	$ 1,266.7	$ 1,244
Expenses	285.1	284.6	311.3	280.1	381.5	296.6	294.3	252	1,161.1	1,224.4	1,060.8
Pre-tax income (loss) from continuing operations	11.1	(16.8)	2.9	28.1	(49.1)	4.9	31.7	54.8	25.3	42.3	183.2
Tax (expense) benefit	11.9	3.5	0.9	(3.4)	24.2	1.1	(5.9)	(7.1)	12.9	12.3	(36.5)
Net income from continuing operations	23	(13.3)	3.8	24.7	(24.9)	6	25.8	47.7	38.2	54.6	146.7
Loss from discontinued operations, net of tax	(0.1)	(0.1)	(0.2)	(0.1)	(0.9)	(0.3)	(0.1)	(0.5)
(Loss) gain from sale of discontinued operations, net of tax	0	0	0.3	0	(11.3)	(7)	(0.5)	0	0.3	(18.8)	46.6
Net income, including noncontrolling interests	22.9	(13.4)	3.9	24.6	(37.1)	(1.3)	25.2	47.2	38	34	146.7
Less: Net income attributable to noncontrolling interests	(0.2)	0	(0.5)	(0.5)	(0.2)	0	(0.5)	(0.4)	(1.2)	(1.1)	(1)
Net income (loss) attributable to OneBeacon's common shareholders	$ 22.7	$ (13.4)	$ 3.4	$ 24.1	$ (37.3)	$ (1.3)	$ 24.7	$ 46.8	$ 36.8	$ 32.9	$ 145.7
Net income (loss) from continuing operations per share	$ 0.24	$ (0.14)	$ 0.03	$ 0.25	$ (0.26)	$ 0.05	$ 0.26	$ 0.50	$ 0.38	$ 0.55	$ 1.52
Net Loss from discontinued operations, net of tax, per share	0	0	0	0	(0.13)	(0.07)	0	(0.01)	0	(0.02)	(0.49)
Net income (loss) attributable to OneBeacon's common shareholders per share	$ 0.24	$ (0.14)	$ 0.03	$ 0.25	$ (0.39)	$ (0.02)	$ 0.26	$ 0.49	$ 0.38	$ 0.34	$ 1.52

SCHEDULE II CONDENSED FINANC115

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONDENSED BALANCE SHEETS) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Short-term investments, at amortized cost (which approximates fair value)	$ 69.2	$ 202.2
Equity Method Investments	0	0
Other assets	194.4	184.8
Total assets	3,604.5	3,578.2
Common equity securities, at fair value	298.7	320
Total liabilities	2,600	2,528.9
Total OneBeacon's common shareholders' equity	1,000.9	1,045.8
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	3,604.5	3,578.2
OneBeacon
Condensed Balance Sheet Statements, Captions [Line Items]
Short-term investments, at amortized cost (which approximates fair value)	4.4	18.4
Equity Method Investments	996.9	1,027.4
Other assets	0.5	0.3
Total assets	1,001.8	1,046.1
Common equity securities, at fair value	0	0
Total liabilities	0.9	0.3
Total OneBeacon's common shareholders' equity	1,000.9	1,045.8
Total liabilities, OneBeacon's common shareholders' equity and noncontrolling interests	$ 1,001.8	$ 1,046.1

SCHEDULE I SUMMARY OF INVEST116

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Total investment securities	$ 2,591.4	$ 2,525.8
Summary of Investments, Other than Investments in Related Parties, Cost	2,578.1
Summary of Investments, Other than Investments in Related Parties, Fair Value	2,591.4
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	2,591.4
U.S. Government and agency obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	85.4
Summary of Investments, Other than Investments in Related Parties, Fair Value	85.3
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	85.3
Debt securities issued by industrial corporations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1,845.9
Summary of Investments, Other than Investments in Related Parties, Fair Value	1,842.3
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1,842.3
Municipal obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	67.7
Summary of Investments, Other than Investments in Related Parties, Fair Value	69
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	69
Foreign government obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	1
Summary of Investments, Other than Investments in Related Parties, Fair Value	1.2
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	1.2
Preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	78.3
Summary of Investments, Other than Investments in Related Parties, Fair Value	82.7
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	82.7
Fixed maturity investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	2,078.3
Summary of Investments, Other than Investments in Related Parties, Fair Value	2,080.5
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	2,080.5
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	69.2
Summary of Investments, Other than Investments in Related Parties, Fair Value	69.2
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	69.2
Exchange Traded Funds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	189.7
Summary of Investments, Other than Investments in Related Parties, Fair Value	183.3
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	183.3
Banks, Trust and Insurance, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	3.5
Summary of Investments, Other than Investments in Related Parties, Fair Value	4.5
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	4.5
Industrial, Miscellaneous, and All Others [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	291.5
Summary of Investments, Other than Investments in Related Parties, Fair Value	294.2
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	294.2
Common equity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	295
Summary of Investments, Other than Investments in Related Parties, Fair Value	298.7
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	298.7
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Summary of Investments, Other than Investments in Related Parties, Cost	135.6
Summary of Investments, Other than Investments in Related Parties, Fair Value	143
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 143

SCHEDULE II CONDENSED FINANC117

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Income Statements, Captions [Line Items]
Revenues	$ 296.2	$ 267.8	$ 314.2	$ 308.2	$ 332.4	$ 301.5	$ 326	$ 306.8	$ 1,186.4	$ 1,266.7	$ 1,244
Total expenses	285.1	284.6	311.3	280.1	381.5	296.6	294.3	252	1,161.1	1,224.4	1,060.8
Pre-tax income (loss) from continuing operations	11.1	(16.8)	2.9	28.1	(49.1)	4.9	31.7	54.8	25.3	42.3	183.2
Tax (expense) benefit	11.9	3.5	0.9	(3.4)	24.2	1.1	(5.9)	(7.1)	12.9	12.3	(36.5)
Net income from continuing operations	23	(13.3)	3.8	24.7	(24.9)	6	25.8	47.7	38.2	54.6	146.7
Income (Loss) from Equity Method Investments									0	0	0
Net income (loss) attributable to OneBeacon's common shareholders	$ 22.7	$ (13.4)	$ 3.4	$ 24.1	$ (37.3)	$ (1.3)	$ 24.7	$ 46.8	36.8	32.9	145.7
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									36.8	20.9	166.3
OneBeacon
Condensed Income Statements, Captions [Line Items]
Revenues									0	0	0
Total expenses									4.8	5.1	5
Pre-tax income (loss) from continuing operations									(4.8)	(5.1)	(5)
Tax (expense) benefit									0	0	0.1
Net income from continuing operations									(4.8)	(5.1)	(4.9)
Income (Loss) from Equity Method Investments									41.6	38	150.6
Net income (loss) attributable to OneBeacon's common shareholders									36.8	32.9	145.7
Other Comprehensive Income (Loss), Net of Tax									0	(12)	20.6
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									$ 36.8	$ 20.9	$ 166.3

SCHEDULE II CONDENSED FINANC118

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONDENSED STATEMENTS OF CASH FLOWS) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to OneBeacon's common shareholders	$ 22.7	$ (13.4)	$ 3.4	$ 24.1	$ (37.3)	$ (1.3)	$ 24.7	$ 46.8	$ 36.8	$ 32.9	$ 145.7
Net income, including noncontrolling interests	22.9	$ (13.4)	$ 3.9	$ 24.6	(37.1)	$ (1.3)	$ 25.2	$ 47.2	38	34	146.7
Income (Loss) from Equity Method Investments									0	0	0
Dividends received from subsidiaries									0	0	0
Net change in other assets and liabilities									16.6	(56.1)	19.8
Net cash provided from operations									191.9	97.5	128.7
Net maturities, purchases and sales of short-term investments									133.1	(65.5)	72.2
Net cash (used for) provided from investing activities									(94.6)	(40.7)	81.4
Cash dividends paid to common shareholders									(80)	(80)	(80.2)
Repurchase and retirement of common shares									(3.7)	(1.8)
Net cash used for financing activities									(89.1)	(87.1)	(85.9)
Cash and Cash Equivalents, Period Increase (Decrease)									8.2	(81.1)	124.2
Cash	95.2				87				95.2	87	168.1	$ 43.9
OneBeacon
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to OneBeacon's common shareholders									36.8	32.9	145.7
Net income, including noncontrolling interests									36.8	32.9	145.7
Income (Loss) from Equity Method Investments									41.6	38	150.6
Dividends received from subsidiaries									72	90.4	92
Net change in other assets and liabilities									2.5	1.9	3.4
Net cash provided from operations									69.7	87.2	90.5
Net maturities, purchases and sales of short-term investments									14	(5.4)	(10.3)
Net cash (used for) provided from investing activities									14	(5.4)	(10.3)
Cash dividends paid to common shareholders									(80)	(80)	(80.2)
Repurchase and retirement of common shares									(3.7)	(1.8)	0
Net cash used for financing activities									(83.7)	(81.8)	(80.2)
Cash and Cash Equivalents, Period Increase (Decrease)									0	0	0
Cash	$ 0				$ 0				$ 0	$ 0	$ 0	$ 0

SCHEDULE II CONDENSED FINANC119

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Dividends received from subsidiaries	$ 0	$ 0	$ 0
OneBeacon
Condensed Cash Flow Statements, Captions [Line Items]
Dividends received from subsidiaries	$ 72	$ 90.4	$ 92

SCHEDULE III SUPPLEMENTARY I120

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Specialty Industries
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	$ 51.1	$ 53.5	$ 50.1
Future policy benefits, losses, claims and loss expenses	597.2	519.6	446.5
Unearned premiums	272.2	284.7	269.5
Other policy claims and benefits payable	0	0	0
Earned Premiums	615.9	595	566.9
Net investment income(2)	0	0	0
Benefits, claims, losses, and settlement expenses	(390)	(357.2)	(309.8)
Amortization of policy acquisition expenses	(113.7)	(107.1)	(102.6)
Other operating expenses	(120.3)	(100.8)	(107.4)
Net written premiums	603.6	610	579
Specialty Products
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	49.6	49.7	53.6
Future policy benefits, losses, claims and loss expenses	772.2	798.8	607.8
Unearned premiums	288.1	303.6	275.4
Other policy claims and benefits payable	0	0	0
Earned Premiums	560.3	582.1	553.5
Net investment income(2)	0	0	0
Benefits, claims, losses, and settlement expenses	(310.7)	(457.9)	(312.3)
Amortization of policy acquisition expenses	(100.1)	(96.2)	(106.3)
Other operating expenses	(97.9)	(78.4)	(97.4)
Net written premiums	533	606.9	509.6
Investing, Financing and Corporate
Supplementary Insurance Information, by Segment [Line Items]
Deferred acquisition costs	0	0	0
Future policy benefits, losses, claims and loss expenses	20.4	23.8	0
Unearned premiums	0	0	0
Other policy claims and benefits payable	0	0	0
Earned Premiums	0	0	0
Net investment income(2)	45.9	43.4	43
Benefits, claims, losses, and settlement expenses	0	0	0
Amortization of policy acquisition expenses	0	0	0
Other operating expenses	0	0	0
Net written premiums	$ 0	$ 0	$ 0

SCHEDULE IV REINSURANCE (Detail

SCHEDULE IV REINSURANCE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct	$ 1,298	$ 1,209.1	$ 1,043.3
Ceded	(167.7)	(102.9)	(71.4)
Assumed	45.9	70.9	148.5
Earned premiums	1,176.2	1,177.1	1,120.4
Continuing Operations [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct		1,209.1	1,043.3
Ceded		(102.9)	(71.4)
Assumed		70.9	148.5
Earned premiums	$ 1,176.2	$ 1,177.1	$ 1,120.4
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net (Deprecated 2013-01-31)	3.90%	6.00%	13.30%
Segment, Discontinued Operations
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct		$ (0.7)	$ 0.4
Ceded		0.7	0
Assumed		0.1	0.4
Earned premiums	$ 0	$ 0.1	$ 0.8
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net (Deprecated 2013-01-31)		100.00%	50.00%
Specialty Products
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written		$ 606.9
Unearned premiums	288.1	303.6	$ 275.4
Deferred acquisition costs	49.6	49.7	53.6
Reserves for Unpaid Claims and Claims Adjustment Expenses		798.8
Earned premiums	560.3
Earned Premiums	560.3	582.1	553.5
Specialty Products | Continuing Operations [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written			509.6
Unearned premiums			275.4
Deferred acquisition costs			53.6
Reserves for Unpaid Claims and Claims Adjustment Expenses			607.8
Earned Premiums			553.5
Investing, Financing and Corporate
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written	0	0
Unearned premiums	0	0	0
Deferred acquisition costs	0	0	0
Reserves for Unpaid Claims and Claims Adjustment Expenses	20.4	23.8
Earned Premiums	0	0	0
Investing, Financing and Corporate | Continuing Operations [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written			0
Unearned premiums			0
Deferred acquisition costs			0
Reserves for Unpaid Claims and Claims Adjustment Expenses			0
Earned Premiums			0
Specialty Industries
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written		610
Unearned premiums	272.2	284.7	269.5
Deferred acquisition costs	51.1	53.5	50.1
Reserves for Unpaid Claims and Claims Adjustment Expenses		519.6
Earned premiums	615.9
Earned Premiums	$ 615.9	$ 595	566.9
Specialty Industries | Continuing Operations [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Premiums written			579
Unearned premiums			269.5
Deferred acquisition costs			50.1
Reserves for Unpaid Claims and Claims Adjustment Expenses			446.5
Earned Premiums			$ 566.9

SCHEDULE V VALUATION AND QUA122

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Allowance for Doubtful Accounts Receivable	$ 0	$ 0	$ 0.1
Allowance for Reinsurance Recoverable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance	0.7	2.2	14.3	$ 25.6
Valuation Allowances and Reserves, Charged to Cost and Expense	(0.1)	(0.5)	0
Valuation Allowances and Reserves, Charged to Other Accounts	0	0	0
Valuation Allowances and Reserves, Deductions	(1.4)	(11.6)	(11.3)
Allowance for Uncollectible Premiums Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance	2	1.9	3.1	$ 4.4
Valuation Allowances and Reserves, Charged to Cost and Expense	0.8	(0.2)	0.3
Valuation Allowances and Reserves, Charged to Other Accounts	(0.7)	(1)	0
Valuation Allowances and Reserves, Deductions	$ 0	$ 0	(1.6)
Valuation Allowance for Reinsurance Balances			11.3
Runoff | Allowance for Uncollectible Premiums Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance			$ 0.1

SCHEDULE VI SUPPLEMENTAL INF123

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs	$ 103.2		$ 100.7	$ 103.2
Earned premiums			1,176.2	1,177.1	$ 1,120.4
Net investment income			45.9	43.4	43
Claims and Claims Adjustment Expenses Incurred Related to	33.7		702.5	725.3	622.1
Claims and Claims Adjustment Expenses Incurred Related to Prior Year	$ (75.5)	$ (14.3)	1.8	(89.8)	0
Net written premiums			$ 1,136.6	$ 1,216.9	$ 1,088.6
Interest rate at which discount computed	2.50%		2.50%	2.50%	3.50%
Liability for Claims and Claims Adjustment Expense	$ 1,342.2		$ 1,389.8	$ 1,342.2	$ 1,054.3	$ 1,000
Unearned premiums	588.3		560.3	588.3
Specialty Industries
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs			51.1
Deferred acquisition costs	53.5		51.1	53.5	50.1
Reserves for Unpaid Claims and Claims Adjustment Expenses	519.6			519.6
Discount, if any, deducted in Column C(3)	1		1.1	1
Unearned premiums	284.7		272.2	284.7	269.5
Earned premiums			615.9
Earned Premiums			615.9	595	566.9
Net investment income			0	0
Claims and Claims Adjustment Expenses Incurred Related to			368.2	329.2
Claims and Claims Adjustment Expenses Incurred Related to Prior Year			(21.8)	(28)
Amortization of policy acquisition expenses			(113.7)	(107.1)	(102.6)
Paid Claims and Claims Adjustment Expenses			322.7	277.3
Net written premiums			603.6
Premiums written				610
Liability for Claims and Claims Adjustment Expense			597.2
Unearned premiums			272.2
Specialty Products
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs			49.6
Deferred acquisition costs	49.7		49.6	49.7	53.6
Reserves for Unpaid Claims and Claims Adjustment Expenses	798.8			798.8
Discount, if any, deducted in Column C(3)	0		0	0
Unearned premiums	303.6		288.1	303.6	275.4
Earned premiums			560.3
Earned Premiums			560.3	582.1	553.5
Net investment income			0	0
Claims and Claims Adjustment Expenses Incurred Related to			334.3	396.1
Claims and Claims Adjustment Expenses Incurred Related to Prior Year			23.6	(61.8)
Amortization of policy acquisition expenses			(100.1)	(96.2)	(106.3)
Paid Claims and Claims Adjustment Expenses			354.8	331.3
Net written premiums			533
Premiums written				606.9
Liability for Claims and Claims Adjustment Expense			772.2
Unearned premiums			288.1
Investing, Financing and Corporate
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs	0		0	0	0
Reserves for Unpaid Claims and Claims Adjustment Expenses	23.8		20.4	23.8
Discount, if any, deducted in Column C(3)	0		0	0
Unearned premiums	$ 0		0	0	0
Earned Premiums			0	0	0
Net investment income			45.9	43.4
Claims and Claims Adjustment Expenses Incurred Related to			0	0
Claims and Claims Adjustment Expenses Incurred Related to Prior Year			0	0
Amortization of policy acquisition expenses			0	0	0
Paid Claims and Claims Adjustment Expenses			0	0
Premiums written			0	0
Continuing Operations [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Earned premiums			1,176.2	1,177.1	1,120.4
Continuing Operations [Member] | Specialty Industries
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs					50.1
Reserves for Unpaid Claims and Claims Adjustment Expenses					446.5
Discount, if any, deducted in Column C(3)					2.8
Unearned premiums					269.5
Earned Premiums					566.9
Net investment income					0
Claims and Claims Adjustment Expenses Incurred Related to					315.7
Claims and Claims Adjustment Expenses Incurred Related to Prior Year					5.9
Amortization of policy acquisition expenses					(102.6)
Paid Claims and Claims Adjustment Expenses					268.5
Premiums written					579
Continuing Operations [Member] | Specialty Products
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs					53.6
Reserves for Unpaid Claims and Claims Adjustment Expenses					607.8
Discount, if any, deducted in Column C(3)					0.2
Unearned premiums					275.4
Earned Premiums					553.5
Net investment income					0
Claims and Claims Adjustment Expenses Incurred Related to					306.4
Claims and Claims Adjustment Expenses Incurred Related to Prior Year					(5.9)
Amortization of policy acquisition expenses					(106.3)
Paid Claims and Claims Adjustment Expenses					272.2
Premiums written					509.6
Continuing Operations [Member] | Investing, Financing and Corporate
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs					0
Reserves for Unpaid Claims and Claims Adjustment Expenses					0
Discount, if any, deducted in Column C(3)					0
Unearned premiums					0
Earned Premiums					0
Net investment income					43
Claims and Claims Adjustment Expenses Incurred Related to					0
Claims and Claims Adjustment Expenses Incurred Related to Prior Year					0
Amortization of policy acquisition expenses					0
Paid Claims and Claims Adjustment Expenses					0
Premiums written					0
Segment, Discontinued Operations
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Earned premiums			0	0.1	0.8
Claims and Claims Adjustment Expenses Incurred Related to Prior Year				(7.4)
Net written premiums			$ 0	$ (0.1)	$ 0.4