Allied World Assurance 10-K 28 Feb 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Feb. 22, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Entity Registrant Name	Allied World Assurance Co Holdings, AG
Entity Central Index Key	1,163,348
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		87,316,864
Entity Public Float			$ 3.1
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
ASSETS:
Fixed maturity investments trading, at fair value (amortized cost: 2016: $6,847.4; 2015: $7,290.6)	$ 6,737.7	$ 7,201.5
Equity securities trading, at fair value (cost: 2016: $235.0; 2015: $395.3)	243.9	403
Other invested assets	960.7	966.7
Total investments	7,942.3	8,571.2
Cash and cash equivalents	720.9	608
Restricted cash	76.5	60.6
Insurance balances receivable	784	745.9
Funds held	466.8	640.8
Prepaid reinsurance	486.4	392.3
Reinsurance recoverable	1,625	1,480
Reinsurance recoverable on paid losses	104.4	96.4
Accrued investment income	36	38.3
Net deferred acquisition costs	121.1	165.2
Goodwill	389.7	388.1
Intangible assets	104.7	116.6
Balances receivable on sale of investments	114.7	36.9
Net deferred tax assets	38.7	24.4
Other assets	167.8	147.2
Total assets	13,179	13,511.9
LIABILITIES:
Reserve for losses and loss expenses	6,639.2	6,456.2
Unearned premiums	1,688.1	1,683.3
Reinsurance balances payable	223.3	214.4
Balances due on purchases of investments	79.7	125.1
Senior notes:
Principal amount	800	1,300
Less unamortized discount and debt issuance costs	5.8	7.1
Senior notes, net of unamortized discount and debt issuance costs	794.2	1,292.9
Other long-term debt	22	23
Accounts payable and accrued liabilities	180.7	184.5
Total liabilities	9,627.2	9,979.4
SHAREHOLDERS’ EQUITY:
Common shares: 2016 and 2015: par value CHF 4.10 per share (2016: 93,586,418; 2015: 95,523,230 shares issued and 2016: 87,098,120; 2015: 90,959,635 shares outstanding)	378.8	386.7
Treasury shares, at cost (2016: 6,488,298; 2015: 4,563,595)	(233.8)	(155.1)
Accumulated other comprehensive loss	(11.6)	(9.3)
Retained earnings	3,418.4	3,310.2
Total shareholders’ equity	3,551.8	3,532.5
Total liabilities and shareholders’ equity	$ 13,179	$ 13,511.9

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) $ in Millions	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Fixed maturity investments trading, amortized cost | $	$ 6,847.4	$ 7,290.6
Equity securities trading - cost | $	$ 235	$ 395.3
Common stock, shares issued	93,586,418	95,523,230
Common stock, shares outstanding	87,098,120	90,959,635
Treasury stock (shares)	6,488,298	4,563,595

Consolidated Statements Of Oper

Consolidated Statements Of Operations And Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
REVENUES:
Gross premiums written	$ 671.7	$ 730.2	$ 800.3	$ 863.5	$ 632.3	$ 754.1	$ 826	$ 880.6	$ 3,065.8	$ 3,093	$ 2,935.4
Premiums ceded	(226.4)	(201.9)	(222.2)	(159.5)	(167.5)	(147.1)	(222.3)	(108.1)	(810)	(645)	(613.4)
Net premiums written	445.3	528.3	578.1	704	464.8	607	603.7	772.5	2,255.8	2,448	2,322
Change in unearned premiums	131.7	55.7	24.8	(123.9)	158	43.7	42.7	(204)	88.3	40.4	(139.3)
Net premiums earned	577	584	602.9	580.1	622.8	650.7	646.4	568.5	2,344.1	2,488.4	2,182.7
Net investment income	58.1	50.6	55.8	53.3	49.1	45.7	42.8	44.5	217.8	182.1	176.9
Net realized investment gains (losses)	(101.9)	10.7	74.5	18.9	(38.8)	(113.6)	(20.2)	45	2.1	(127.6)	89
Other income	4.8	1.8	5.2	0.6	1	0.7	0.9	0.9	12.4	3.5	2.1
Total revenue	538	647.1	738.4	652.9	634.1	583.5	669.9	658.9	2,576.4	2,546.4	2,450.7
EXPENSES:
Net losses and loss expenses	387.8	376.3	365.4	372.4	412.7	416.9	431.5	325.2	1,501.8	1,586.3	1,199.2
Acquisition costs	82	82	87.4	88.3	96	100.1	100.6	78.7	339.8	375.4	295.1
General and administrative expenses	106.1	104.2	104.7	96.4	95	105.8	108.4	97.1	411.5	406.3	365.7
Other expense	1.8	2.2	1.7	1.1	1.9	1.3	1.2	1.8	6.8	6.2	8.6
Amortization and impairment of intangible assets	3.2	2.5	2.5	2.5	3.7	2.7	2.8	0.6	10.7	9.8	2.5
Interest expense	10.4	13.5	19.9	20	18.1	14.5	14.5	14.3	63.7	61.4	57.8
Foreign exchange (gain) loss	0.8	1	(2.9)	(3)	0.9	(0.8)	1.3	9.9	(4.1)	11.3	1
Total expenses	592.1	581.7	578.7	577.7	628.3	640.5	660.3	527.6	2,330.2	2,456.7	1,929.9
Income before income taxes	(54.1)	65.4	159.7	75.2	5.8	(57)	9.6	131.3	246.2	89.7	520.8
Income tax (benefit) expense	(13.3)	(3.2)	6.3	1.1	4	(5.3)	0.1	7	(9.1)	5.8	30.5
NET INCOME	$ (40.8)	$ 68.6	$ 153.4	$ 74.1	$ 1.8	$ (51.7)	$ 9.5	$ 124.3	255.3	83.9	490.3
Other comprehensive loss: foreign currency translation adjustment									(2.3)	(9.3)	0
COMPREHENSIVE INCOME									$ 253	$ 74.6	$ 490.3
PER SHARE DATA
Basic earnings per share	$ (0.47)	$ 0.79	$ 1.73	$ 0.82	$ 0.02	$ (0.57)	$ 0.10	$ 1.30	$ 2.89	$ 0.91	$ 5.03
Diluted earnings per share	$ (0.47)	$ 0.77	$ 1.70	$ 0.81	$ 0.02	$ (0.57)	$ 0.10	$ 1.27	$ 2.84	$ 0.89	$ 4.92
Weighted average common shares outstanding	87,036,339	87,102,290	88,742,484	90,254,512	90,934,107	90,882,511	92,441,730	95,935,551	88,275,810	92,530,208	97,538,319
Weighted average common shares and common share equivalents outstanding	87,036,339	88,603,101	90,040,509	91,559,225	92,422,422	90,882,511	93,984,226	97,577,029	89,800,894	94,174,460	99,591,773
Dividends paid per share									$ 1.04	$ 1.23	$ 0.784

Consolidated Statements Of Shar

Consolidated Statements Of Shareholders' Equity - USD ($) $ in Millions	Total	Share Capital	Treasury Shares		Accumulated Other Comprehensive Loss	Retained Earnings
Balance, at beginning of period at Dec. 31, 2013		$ 419	$ (80)		$ 0	$ 3,180.8
Net income	$ 490.3					490.3
Dividends						(81.7)
Stock compensation			19.6	[1]		5.6
Share repurchases	(175.4)		(175.4)
Shares cancelled		(11)	92.7			(81.7)
Foreign currency translation adjustment	0				0
Balance, at end of period at Dec. 31, 2014	3,778.2	408	(143.1)		0	3,513.3
Net income	83.9					83.9
Dividends						(92.4)
Stock compensation			19.6	[1]		(2.2)
Share repurchases	(245.3)		(245.3)
Shares cancelled		(21.3)	213.7			(192.4)
Foreign currency translation adjustment	(9.3)				(9.3)
Balance, at end of period at Dec. 31, 2015	3,532.5	386.7	(155.1)		(9.3)	3,310.2
Net income	255.3					255.3
Dividends						(91.5)
Stock compensation			20.9	[1]		3.2
Share repurchases	(166.3)		(166.3)
Shares cancelled		(7.9)	66.7			(58.8)
Foreign currency translation adjustment	(2.3)				(2.3)
Balance, at end of period at Dec. 31, 2016	$ 3,551.8	$ 378.8	$ (233.8)		$ (11.6)	$ 3,418.4
[1]	Includes stock compensation expense for the period and shares issued out of treasury for awards exercised or vested. See note 2(o) to the notes to the consolidated financial statements.

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS PROVIDED BY OPERATING ACTIVITIES:
Net income	$ 255.3	$ 83.9	$ 490.3
Adjustments to reconcile net income to cash provided by operating activities:
Net realized gains on sales of investments	(38.1)	(73.9)	(145)
Mark to market adjustments	12.7	189.8	22
Stock compensation expense	16.4	15.8	14.2
Undistributed income of equity method investments	30.6	22.6	13.9
Changes in:
Reserve for losses and loss expenses, net of reinsurance recoverables	38.1	175.9	8.9
Unearned premiums, net of prepaid reinsurance	(89.2)	(43.9)	139.3
Insurance balances receivable	(39.4)	37	(76.8)
Reinsurance recoverable on paid losses	(7.9)	(10.4)	(8.5)
Funds held	174	83.2	(91.6)
Reinsurance balances payable	9	(5.6)	7
Net deferred acquisition costs	44.1	17	(24.9)
Net deferred tax assets	(14.3)	(2.7)	4.2
Accounts payable and accrued liabilities	(4.9)	(10.1)	8
Other items, net	12.9	34.2	55.9
Net cash provided by operating activities	399.3	512.8	416.9
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	(5,423.7)	(5,863.2)	(7,630)
Purchases of other invested assets	(119)	(126.7)	(307.9)
Sales of trading securities	5,929.9	5,328.8	7,536.9
Sales of other invested assets	96.3	161.3	267.9
Purchases of fixed assets	(3.5)	(31.8)	(59.7)
Net cash paid for acquisitions	(1.2)	(124.4)	(2.6)
Change in restricted cash	(15.9)	20.3	68.4
Net cash provided by (used in) investing activities	462.9	(635.7)	(127)
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	(91.5)	(114.1)	(76.7)
Share repurchases	(166.3)	(246.4)	(175.9)
Repayment of senior notes	(500)	0	0
Proceeds from the exercise of stock options	10.3	10.1	10
Proceeds from senior notes	0	496.7	0
Proceeds from other long-term debt	0	4	19.2
Repayment of other long-term debt	(0.3)	(0.2)	0
Net cash (used in) provided by used in financing activities	(747.8)	150.1	(223.4)
Effect of exchange rate changes on foreign currency cash	(1.5)	(8.5)	(9.1)
NET INCREASE IN CASH AND CASH EQUIVALENTS	112.9	18.7	57.4
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	608	589.3	531.9
CASH AND CASH EQUIVALENTS, END OF PERIOD	720.9	608	589.3
Supplemental disclosure of cash flow information:
Cash paid for income taxes	3.5	2.5	18.4
Cash paid for interest expense	$ 75.8	$ 54	$ 54

General

General	12 Months Ended
	Dec. 31, 2016
General [Abstract]
General	GENERAL Allied World Assurance Company Holdings, AG, a Swiss holding company (“Allied World Switzerland”), through its wholly-owned subsidiaries (collectively, the “Company”), provides property and casualty insurance and reinsurance on a worldwide basis. References to “$” are to the lawful currency of the United States and to “CHF” are to the lawful currency of Switzerland. On December 18, 2016, the Company entered into a merger agreement with Fairfax Financial Holdings Limited (“Fairfax”), whereby Fairfax will acquire all of the outstanding ordinary shares of Allied World Switzerland. Under the terms of the merger agreement, Allied World Switzerland shareholders will receive a combination of Fairfax subordinate voting shares and cash having a value equal to $54.00 per Allied World Switzerland share (based on the closing price of Fairfax’s subordinate voting shares on December 16, 2016). The merger agreement has been unanimously approved by both companies’ Board of Directors. The acquisition is expected to be consummated following the satisfaction of customary closing conditions. The acquisition is anticipated to close in the second quarter of 2017. There can be no assurances that the acquisition will occur.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Significant accounting policies	SIGNIFICANT ACCOUNTING POLICIES These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at 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. The significant estimates reflected in the Company’s financial statements include, but are not limited to: • The premium estimates for certain reinsurance agreements, • Recoverability of deferred acquisition costs, • The reserve for outstanding losses and loss expenses, • Valuation of ceded reinsurance recoverables, • Determination of impairment of goodwill and other intangible assets, and • Valuation of financial instruments. Intercompany accounts and transactions have been eliminated on consolidation and all entities meeting consolidation requirements have been included in the consolidated financial statements. To facilitate comparison of information across periods, certain reclassifications have been made to prior year amounts to conform to the current year's presentation. The significant accounting policies are as follows: a) Premiums and Acquisition Costs Premiums are recorded as written on the inception date of the policy. For certain types of business written by the Company, notably assumed reinsurance, the exact premium income may not be known at the policy inception date. In the case of quota share reinsurance treaties assumed by the Company, the underwriter makes an estimate of premium income at inception. The underwriter’s estimate is based on statistical data provided by reinsureds and the underwriter’s judgment and experience. Such estimations are refined over the reporting period of each treaty as actual written premium information is reported by ceding companies and intermediaries. Premiums resulting from changes in the estimate of the premium income are recorded in the period the estimate is changed. Certain insurance and reinsurance contracts may require that the premium be adjusted at the expiry of the contract to reflect the change in exposure or loss experience of the insured or reinsured. Premiums are recognized as earned over the period of policy coverage in proportion to the risks to which they relate. Reinsurance premiums under a losses-occurring reinsurance contract are earned over the coverage period. Reinsurance premiums under a risks-attaching reinsurance contract are earned over the same period as the underlying policies, or risks, covered by the contract. As a result, the earning pattern of a risks-attaching reinsurance contract may extend up to 24 months, reflecting the inception dates of the underlying policies. Premiums relating to the unexpired periods of coverage are recorded on the consolidated balance sheets as “unearned premiums”. Acquisition costs, comprised of commissions, brokerage fees and insurance taxes, are costs that are directly related to the successful acquisition of new and renewal business and are deferred. Although permitted under U.S. GAAP to defer certain internal costs that are directly related to the successful acquisition of new and renewal business, the Company does not defer such costs. Acquisition costs that are deferred, and carried on the balance sheets as an asset, are expensed as the premiums to which they relate are earned. Expected losses and loss expenses, other costs and anticipated investment income related to these unearned premiums are considered in determining the recoverability or deficiency of deferred acquisition costs. If it is determined that deferred acquisition costs are not recoverable, they are expensed. Further analysis is performed to determine if a liability is required to provide for losses which may exceed the related unearned premiums. Acquisition costs recorded in the consolidated statements of operations and comprehensive income (“consolidated income statements”) includes other acquisition-related costs such as profit commissions that are expensed as incurred and the amortization of insurance-related intangible assets. b) Reserve for Losses and Loss Expenses The reserve for losses and loss expenses is comprised of two main elements: outstanding loss reserves (“OSLR,” also known as case reserves) and reserves for losses incurred but not reported (“IBNR”). OSLR relate to known claims and represent management’s best estimate of the likely loss payment. Reserves for IBNR relates to reserves established by the Company for claims that have occurred but have not yet been reported to us as well as for changes in the values of claims that have been reported to us but are not yet settled. See note 7 for additional information. c) Ceded Reinsurance In the ordinary course of business, the Company uses both treaty and facultative reinsurance to minimize its net loss exposure to any one catastrophic loss event or to an accumulation of losses from a number of smaller events. Reinsurance premiums ceded are expensed and any commissions recorded thereon are earned over the period the reinsurance coverage is provided in proportion to the risks to which they relate. For reinsurance treaties that have contractual minimum premium provisions, premiums ceded are recorded at the inception of the treaty based on the minimum premiums. Prepaid reinsurance represents unearned premiums ceded to reinsurance companies. Any unearned ceding commission is included in “net deferred acquisitions costs” on the consolidated balance sheets and is recorded as a reduction to the overall net deferred acquisition cost balance. Reinsurance recoverable includes the balances due from those reinsurance companies under the terms of the Company’s reinsurance agreements for unpaid losses and loss reserves, including IBNR, and is presented net of a provision for uncollectible reinsurance. Amounts recoverable from reinsurers are estimated in a manner consistent with the estimated claim liability associated with the reinsured policy. The Company determines the portion of the IBNR liability that will be recoverable under its reinsurance contracts by reference to the terms of the reinsurance protection purchased. This determination is necessarily based on the estimate of IBNR and accordingly, is subject to the same uncertainties as the estimate of IBNR. The Company remains liable to the extent that its reinsurers do not meet their obligations under the reinsurance contracts; therefore, the Company regularly evaluates the financial condition of its reinsurers and monitors concentration of credit risk. d) Investments All fixed maturity investments and equity securities are classified as trading securities as the Company has elected the fair value option permitted under U.S. GAAP for these investments at the time each security was acquired. Trading securities are carried at fair value with any change in unrealized gains or losses recognized in the consolidated income statements and included in “net realized investment gains (losses)”. As a result of this investment classification, the Company does not record any change in unrealized gains or losses on investments as a separate component of accumulated other comprehensive income on the consolidated balance sheets. Other invested assets consist primarily of investments in hedge funds and private equity funds, which have been accounted for as trading securities as the Company has elected the fair value option as permitted under U.S. GAAP at the time each investment was acquired. In addition, included in the Company’s other invested assets are various investments which are accounted for using the equity method of accounting. Generally, the Company uses the equity method where it does not have a controlling interest and is not the primary beneficiary. Equity method investments are recorded at cost and adjusted for the Company’s proportionate share of earnings or losses on a quarterly lag basis. An other-than-temporary impairment charge related to the equity method investments is assessed when facts and circumstances exists that indicate an impairment may exist. An other-than-temporary impairment charge is recorded when it is determined that the carrying value of the equity method investment is below its fair value and the Company does not have the intent and ability to hold to recovery. See note 4(c) for additional information regarding an other-than-temporary impairment charge recorded in 2015 related to one of the Company's equity method investments. No equity method investment, individually or in the aggregate, was deemed significant to disclose summarized financial data. Other investments are recorded based on valuation techniques depending on the nature of the individual assets. At each measurement date, the Company estimates the fair value of the financial instruments using various valuation techniques. The Company utilizes, to the extent available, quoted market prices in active markets or observable market inputs in estimating the fair value of financial instruments. When quoted market prices or observable market inputs are not available, the Company may utilize valuation techniques that rely on unobservable inputs to estimate the fair value of financial instruments, which principally relates to non-binding broker-dealer quotes. The Company bases its determination of whether a market is active or inactive on the spread between what a seller is asking for a security and what a buyer is bidding for that security. Spreads that are significantly above historical spreads are considered inactive markets. The Company also considers the volume of trading activity in the determination of whether a market is active or inactive. See note 6 for additional information regarding the fair value of financial instruments. The Company utilizes independent pricing sources to obtain market quotations for securities that have quoted prices in active markets. In general, the independent pricing sources use observable market inputs including, but not limited to, investment yields, credit risks and spreads, benchmarking of like securities, reported trades and sector groupings to determine the fair value. For a majority of the portfolio, the Company obtained two or more prices per security as of December 31, 2016 . When multiple prices are obtained, a price source hierarchy is utilized to determine which price source is the best estimate of the fair value of the security. The price source hierarchy emphasizes more weighting to significant observable inputs such as index pricing and less weighting towards non-binding broker-dealer quotes. The Company will investigate any material differences, if any, between the multiple sources and determines which price best reflects the fair value of the individual security. There were no material differences between the prices obtained from the independent pricing sources and the prices obtained from the Company’s investment portfolio managers and other sources as of December 31, 2016 and 2015 . Investment securities are recorded on a trade date basis. Investment income is recognized when earned and includes the accrual of discount or amortization of premium on fixed maturity investments using the effective yield method and is net of related expenses. Interest income for fixed maturity investments is accrued and recognized based on the contractual terms of the fixed maturity investments and is included in “net investment income” in the consolidated income statements. For mortgage-backed and asset-backed securities and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and revised on a regular basis. Revised prepayment assumptions are applied to securities on a retrospective basis to the date of acquisition. The cumulative adjustments to amortized cost required due to these changes in effective yields and maturities are recognized in net investment income in the same period as the revision of the assumptions. The Company’s share of undistributed net income from equity method investments is included in net investment income. The return on investments is managed on a total financial statement portfolio return basis, which includes the undistributed net income from equity method investments, and as such have classified these amounts in net investment income. Realized gains and losses on the disposition of investments, which are based upon the first-in first-out method of identification, are included in “net realized investment gains (losses)” in the consolidated income statements. e) Variable Interest Entities The Company is involved in the normal course of business with variable interest entities (“VIEs”) as a passive investor in certain asset-backed securities issued by third-party VIEs and affiliated VIEs, as well as certain of its hedge fund and private equity fund investments. The Company performs a qualitative assessment at the date when it becomes initially involved in the VIE, followed by ongoing reassessments related to its involvement in VIEs. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company’s consolidated balance sheets and any unfunded commitments. As a result of the adoption of Accounting Standards Update 2015-02, “Amendments to the Consolidation Analysis”, which became effective January 1, 2016, certain limited partnership investments and similar legal entity investments were considered VIEs as there were no substantive kick-out or other participating rights. These VIEs will not be consolidated because the Company has determined it is not considered the primary beneficiary, as it does not have both the power to direct the activities that most significantly impact the economic performance of the entity and the obligation to absorb losses of the entity that could be potentially significant to the VIE or the right to receive benefits from the entity that could be potentially significant. As such, the Company continues to record its interests in these entities at fair value, with changes in fair value recorded in the consolidated income statements. The Company's interests in these entities are recorded in “other invested assets” in the consolidated balance sheets. The Company's maximum exposure to loss in these entities, which is the sum of the carrying value and the unfunded commitment, was $996.8 million as of December 31, 2016 . f) Translation of Foreign Currencies Transactions in currencies other than a foreign operation's functional currency are translated into the functional currency of the foreign operation. Foreign currency transaction gains and losses, including those arising from forward exchange contracts, are included in “foreign exchange (gain) loss” in the consolidated income statements. Functional currency assets and liabilities are translated into the reporting currency, U.S. dollars, using period-end exchange rates, and functional currency income statements are translated using average exchange rates with the related foreign currency translation adjustment recorded as a separate component of accumulated other comprehensive income or loss. g) Cash and Cash Equivalents and Restricted Cash Cash and cash equivalents include amounts held in banks, time deposits, commercial paper, discount notes and U.S. Treasury Bills with maturities of less than three months from the date of purchase. Restricted cash primarily relates to cash held in trust accounts in favor of cedents, other counterparties or government authorities, as well as accounts that are pledged as collateral for the Company's letter of credit facilities. h) Income Taxes Allied World Switzerland and certain of its subsidiaries operate in jurisdictions where they are subject to income taxation. Current and deferred income taxes are charged or credited to operations, or to shareholders' equity in certain cases, based upon enacted tax laws and rates applicable in the relevant jurisdiction in the period in which the tax becomes payable. Deferred income taxes are provided for all temporary differences between the bases of assets and liabilities used in the financial statements and those used in the various jurisdictional tax returns. It is the Company’s policy to recognize interest accrued related to unrecognized tax benefits in “interest expense” and penalties in “general and administrative expenses” in the consolidated income statements. The Company has not recorded any interest or penalties during the years ended December 31, 2016 , 2015 and 2014 and the Company has not accrued any payment of interest and penalties as of December 31, 2016 and 2015 . i) Employee Stock Option Compensation Plan The Company has an employee stock option plan, which is in run-off, in which the amount of Allied World Switzerland's common shares received as compensation through the issuance of stock options is determined by reference to the value of the shares. Compensation expense for stock options granted to employees is recorded on a straight-line basis over the option vesting period and is based on the fair value of the stock options on the grant date. The fair value of each stock option on the grant date is determined by using the Black-Scholes option-pricing model. j) Restricted Stock Units The Company has granted restricted stock units (“RSUs”) to certain employees. The compensation expense for the RSUs is based on the market value of Allied World Switzerland’s common shares on the grant date, and is recognized on a straight-line basis over the applicable vesting period. The Company has also granted cash-equivalent RSUs to certain employees that vest on a straight-line basis over the applicable vesting period. The amount payable per unit awarded will be equal to the price per share of Allied World Switzerland’s common shares and as such the Company measures the value of the award each reporting period based on the period ending share price. The effects of changes in the share price at each period end during the service period are recognized as increases or decreases in compensation expense over the service period. k) Performance-Based Equity Awards The Company has granted performance-based equity awards to key employees in order to promote the long-term growth and profitability of the Company. Each award represents the right to receive a number of common shares in the future, based upon the achievement of established performance criteria during the applicable performance period. These performance-based equity awards vest after a three-year performance period. The compensation expense for these awards is based on the market value of Allied World Switzerland’s common shares on the grant date, and is recognized on a straight-line basis over the applicable performance and vesting period. The Company will also adjust the compensation expense, as a cumulative adjustment, to the extent the Company's performance is above or below the targeted performance criteria. The Company has also granted cash-equivalent, performance-based awards to certain employees that vest based upon the achievement of established performance criteria during the applicable performance period. These cash-equivalent, performance-based awards vest after a three-year performance period. The amount payable per unit awarded will be equal to the price per share of Allied World Switzerland’s common shares, and as such the Company measures the value of the award each reporting period based on the period-ending share price. The effects of changes in the share price at each period end during the service period are recognized as changes in compensation expense over the service period. The Company will also adjust the compensation expense, as a cumulative adjustment, to the extent the Company's performance is above or below the targeted performance criteria. l) Goodwill and Intangible Assets The Company classifies its intangible assets into three categories: (1) intangible assets with finite lives subject to amortization, (2) intangible assets with indefinite lives not subject to amortization, and (3) goodwill. Intangible assets, other than goodwill, generally consist of customer renewal rights, distribution channels, internally generated software, non-compete covenants, trademarks, and insurance licenses. For intangible assets with finite lives, the value of the assets is amortized over their expected useful lives and the expense is included in “amortization and impairment of intangible assets” in the consolidated income statements. The Company tests assets for impairment if conditions exist that indicate the carrying value may not be recoverable. If, as a result of the evaluation, the Company determines that the value of the intangible assets is impaired, then the value of the assets will be written-down in the period in which the determination of the impairment is made. See note 10 for additional information regarding an impairment recorded for one of the Company's intangible assets with finite lives. For indefinite lived intangible assets the Company does not amortize the intangible asset but evaluates and compares the fair value of the assets to their carrying values on an annual basis or more frequently if circumstances warrant. If, as a result of the evaluation, the Company determines that the value of the intangible assets is impaired, then the value of the assets will be written-down in the period in which the determination of the impairment is made. Goodwill represents the excess of the cost of acquisitions over the fair value of net assets acquired and is not amortized. Goodwill is assigned at acquisition to the applicable reporting unit(s) based on the expected benefit to be received by the reporting units from the business combination. The Company determines the expected benefit based on several factors including the purpose of the business combination, the strategy of the Company subsequent to the business combination and structure of the acquired company subsequent to the business combination. A reporting unit is a component of the Company’s business that has discrete financial information that is reviewed by management. In determining the reporting unit, the Company analyzes the inputs, processes, outputs and overall operating performance of the reporting unit. The Company has several reporting units to which the goodwill is allocated to. For goodwill, the Company performs an annual impairment test, or more frequently if circumstances are warranted. The Company may first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. The results of the qualitative assessment will determine if an entity needs to proceed with the two-step goodwill impairment test. For the year ended December 31, 2016 , the Company elected to bypass the qualitative assessment and performed the first step of the goodwill impairment test. During the fourth quarter of 2015, the Company changed its annual impairment test date from September 30th to October 1st. The Company believes the change in impairment test date is preferable as it aligns to the quarter in which the Company performs the impairment test, which is during the fourth quarter of each year. This change does not result in any delay, acceleration or avoidance of impairment. The first step of the goodwill impairment test is to compare the fair value of the reporting unit with its carrying value, including goodwill. If the carrying amount of the reporting unit exceeds its fair value then the second step of the goodwill impairment test is performed. The second step of the goodwill impairment test compares the implied fair value of the reporting unit’s goodwill with the carrying amount of that goodwill in order to determine the amount of impairment to be recognized. The implied fair value of goodwill is determined by deducting the fair value of a reporting unit’s identifiable assets and liabilities from the fair value of the reporting unit as a whole. The excess of the carrying value of goodwill above the implied goodwill, if any, would be recognized as an impairment charge in the consolidated income statements. We recorded no goodwill impairments during the years ended December 31, 2016 , 2015 and 2014 . m) Derivative Instruments The Company utilizes derivative financial instruments as part of its overall risk management strategy. The Company recognizes all derivative financial instruments at fair value as either assets or liabilities on the consolidated balance sheets. The accounting for gains and losses associated with changes in the fair value of a derivative and the effect on the consolidated financial statements depends on its hedge designation and whether the hedge is highly effective in achieving offsetting changes in the fair value of the asset or liability hedged. The Company uses currency forward contracts and foreign currency swaps to manage currency exposure. The Company also utilizes various derivative instruments such as interest rate futures, interest rate swaps and index options, for the purpose of managing market exposures, interest rate volatility, portfolio duration, hedging certain investments, or enhancing investment performance. These derivatives are not designated as hedges and accordingly are carried at fair value on the consolidated balance sheets with realized and unrealized gains and losses included in the consolidated income statements. Refer to Note 5 for the Company’s related disclosure. In addition, the Company’s derivative instruments include insurance or reinsurance contracts that are required to be accounted for as derivatives. This will be the case when the insurance or reinsurance contract provides indemnification to the insured or cedent as a result of a change in a variable versus an identifiable insurable event. The Company considers these insurance and reinsurance contracts to be an extension of its overall insurance operations. The insurance and reinsurance derivative contracts are recorded at fair value, with net premiums received recognized in “Net premiums earned” over the period of policy coverage in proportion to the risk to which it relates, and other changes in the fair value of this contract is recorded in “other income” or “other expense” in the consolidated income statements. To the extent losses are incurred or ceded under these contracts, those net losses would be recorded in “net losses and loss expenses”. During the year ended December 31, 2016 , the Company recorded net premiums earned of $0.1 million , other income of $7.7 million , and other expense of $3.4 million related to these insurance and reinsurance derivative contracts. During the year ended December 31, 2015 , the Company recorded $1.0 million in “other expense” related to a single-trigger industry loss warranty (“ILW”). No losses were incurred during the years ended December 31, 2016 and 2015 . There were no insurance or reinsurance derivative contracts outstanding for the year ended December 31, 2014. n) Earnings Per Share Basic earnings per share is defined as net income available to common shareholders divided by the weighted average number of common shares outstanding for the period, giving no effect to dilutive securities. Diluted earnings per share is defined as net income available to common shareholders divided by the weighted average number of common and common share equivalents outstanding calculated using the treasury stock method for all potentially dilutive securities, including employee stock options, employee share repurchase plan awards, RSUs and performance-based awards. When the effect of dilutive securities would be anti-dilutive, these securities are excluded from the calculation of diluted earnings per share. o) Treasury Shares Common shares repurchased by the Company and not subsequently canceled are classified as “treasury shares” on the consolidated balance sheets and are recorded at cost. When shares are reissued from treasury the historical cost, based on the first-in, first-out method, is used to determine the cost of the reissued shares. The difference between the cost of the treasury shares and the par value of the common stock shall be first reflected as additional paid-in capital, but to the extent additional paid-in capital is exhausted the remainder shall reduce retained earnings. The issuance of shares out of treasury have been related to vesting equity-based compensation of the Company's employees and directors. p) New Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). ASU 2014-09 provides a framework, through a five-step process, for recognizing revenue from customers, improves comparability and consistency of recognizing revenue across entities, industries, jurisdictions and capital markets, and requires enhanced disclosures. Certain contracts with customers are specifically excluded from the scope of ASU 2014-09, including, among others, insurance contracts accounted for under Accounting Standard Codification 944, Financial Services - Insurance . ASU 2014-09 is effective on January 1, 2017 with retrospective adoption required for the comparative periods. With the issuance of Accounting Standards Update 2015-14, “Revenue from Contracts with Customers (Topic 606) - Deferral of the Effective Date”, this standard will be effective on January 1, 2018 with retrospective adoption required for the comparative periods. The Company does not expect the adoption of ASU 2014-09 to have a material impact on future financial statements and related disclosures. In January 2016, the FASB issued Accounting Standards Update 2016-01, “Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (“ASU 2016-01”). ASU 2016-01 changes current U.S. GAAP for public entities by requiring the following, among others: (1) equity securities, except those accounted for under the equity method of accounting, to be measured at fair value with changes in fair value recognized in net income; (2) the use of the exit price when measuring fair value of financial instruments for disclosure purposes; (3) an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value; and (4) separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or notes to the financial statements. ASU 2016-01 is effective for annual periods beginning after January 1, 2018, including interim periods. Early application is permitted. The Company does not expect the adoption of ASU 2016-01 to have a material impact on future financial statements and disclosures. In February 2016, the FASB issued Accounting Standards Update 2016-02, “Leases” (“ASU 2016-02”). ASU 2016-02 changes current U.S. GAAP for lessees to recognize lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under previous U.S. GAAP. ASU 2016-02 is effective for annual periods beginning after January 1, 2019, including interim periods. Early application is permitted. The Company is currently assessing the impact the adoption of ASU 2016-02 will have on future financial statements and disclosures. Specifically, the Company is still evaluating its existing leases to determine the appropriate classification under the new standard and whether it will adopt the practical expedients allowed under ASU 2016-02. I n March 2016, the FASB issued Accounting Standards Update 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”). ASU 2016-09 modifies U.S. GAAP by requiring the following, among others: (1) all excess tax benefits and tax deficiencies are to be recognized as income tax expense or benefit on the income statement (excess tax benefits are recognized regardless of whether the benefit reduces taxes payable in the current period); (2) excess tax benefits are to be classified along with other income tax cash flows as an operating

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Acquisitions	ACQUISITIONS a) Hong Kong and Singapore Branches of Royal & Sun Alliance Insurance plc On April 1, 2015, the Company completed its acquisitions of certain assets and assumed certain liabilities of the Hong Kong and Singapore operations of RSA to further expand its international insurance operations. The assets acquired and liabilities assumed constituted a business, and as such the Company accounted for the acquisitions of the RSA branches under the acquisition method in accordance with U.S. GAAP. The consideration for the branches was $176.5 million in cash, after receipt of cash for post-closing adjustments. The post-closing adjustments were based on the net asset value of the acquired branches at the date of acquisitions that resulted in the Company receiving $17.4 million in cash. The Company has incurred a cumulative total of $9.2 million in acquisition related expenses, mostly related to advisory, legal and valuation services rendered, which were recorded in “other expense” in the consolidated income statements in 2015 and 2014. The following table summarizes the consideration paid for the Hong Kong and Singapore branches of RSA and the preliminary amounts of the assets acquired and liabilities assumed at the acquisition date. Consideration: Fair Value Cash consideration $ 176.5 Recognized amounts of identifiable assets acquired and liabilities assumed: Fixed maturity investments 246.1 Cash and cash equivalents 47.1 Insurance balances receivable 114.4 Prepaid reinsurance 17.5 Reinsurance recoverable 58.9 Value of business acquired 28.9 Intangible assets 79.9 Other assets 9.9 Reserve for losses and loss expenses (314.1 ) Unearned premiums (150.5 ) Reinsurance balances payable (35.8 ) Net deferred tax liabilities (11.9 ) Accounts payable and accrued liabilities (20.1 ) Total identifiable net assets acquired 70.3 Goodwill 106.2 Total net assets acquired $ 176.5 Of the $106.2 million of goodwill acquired, $54.7 million and $51.5 million related to the Hong Kong and Singapore branches, respectively. None of the goodwill recorded was deductible for tax purposes. The Company recognized identifiable finite lived intangible assets, including an intangible asset for the value of businesses acquired (“VOBA”), which will be amortized over a weighted average period of 12 years . The Company also recorded an insurance-related intangible liability related to the reserve for loss and loss expenses of $8.3 million that will be amortized over a weighted average period of 8 years , and included in “net losses and loss expenses” in the consolidated income statements. The insurance-related intangible liability related to the reserve for loss and loss expenses was calculated as the additional risk margin less the impact related to discounting the net reserves for losses and loss expenses. Since the fair value adjustment increased the net reserve for losses and loss expenses, it has been recorded as an insurance-related intangible liability. The following is a breakdown of the intangible assets acquired. Singapore Branch Estimated Useful Life Hong Kong Branch Estimated Useful Life Total VOBA $ 17.8 2 years $ 11.1 1.5 years $ 28.9 Customer renewals 8.6 4 years 4.4 5 years 13.0 Distribution channels 47.7 18 years 19.2 18 years 66.9 $ 74.1 $ 34.7 $ 108.8 The following is an explanation of identifiable finite lived intangible assets acquired: • VOBA: Represents the difference between the expected future losses and expenses and the associated unearned premium reserve. This intangible asset will be amortized consistent with how the associated unearned premiums will be earned and will be recorded in “acquisition costs” in the consolidated income statements. • Customer renewals: The value of inforce policies renewing taking into consideration the net cash flows generated from these renewals. The amortization expense for this intangible asset will be recorded in “amortization and impairment of intangible assets” in the consolidated income statements. • Distribution channels: The value of access to contractual and non-contractual relationships (e.g., brokers and affinity relationships) taking into consideration the net cash flows generated from these relationships. The amortization expense for this intangible asset will be recorded in “amortization and impairment of intangible assets” in the consolidated income statements. The following summarizes the results of the Hong Kong and Singapore branches that have been included in the Company’s consolidated income statement since the acquisitions closed on April 1, 2015. From April 1, 2015 to December 31, 2015 Total revenue $ 155.3 Net loss $ (28.9 ) The following unaudited pro forma information presents the combined results of the Company and the acquired Hong Kong and Singapore RSA branches for the years ended December 31, 2015 and 2014, with pro forma adjustments related to the acquisition method of accounting as if the acquisitions had been consummated as of January 1, 2014. This unaudited pro forma information is not necessarily indicative of what would have occurred had the acquisitions and related transactions been made on the dates indicated, or of future results of the Company. Year Ended December 31, 2015 Year Ended December 31, 2014 Total revenue $ 2,594.2 $ 2,681.7 Net income $ 74.2 $ 505.9 b) Acquisition of Labuan branch of RSA On April 30, 2015, the Company also acquired the assets and assumed the liabilities of the Labuan operations of RSA for consideration of one British pound sterling. The Company recorded goodwill of $1.4 million related to this acquisition. c) Acquisition of Latin American Underwriters Holdings, Ltd. In January 2015, the Company acquired Latin American Underwriters Holdings Ltd. (“LAU”) for cash consideration of $5.1 million . LAU had previously underwritten trade credit insurance and political risk coverages solely for the Company since 2010. As part of the acquisition, the Company recorded goodwill of $2.5 million and customer renewal intangibles of $3.6 million , which have a three -year useful life. The Company also recorded $1.0 million of contingent consideration related to certain earn-out payments. During the third quarter of 2015, it was determined that LAU will not achieve any of the earn-out payments. As a result, the Company reduced the fair value of the contingent consideration to zero with the corresponding gain recorded as a reduction in “general and administrative expenses” in the consolidated income statements. See note 10 for additional information regarding an impairment recorded related to the customer renewal intangible asset.

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments [Abstract]
Investments	INVESTMENTS a) Trading Securities Securities accounted for at fair value with changes in fair value recognized in the consolidated income statements by category are as follows: December 31, 2016 December 31, 2015 Fair Value Amortized Cost Fair Value Amortized Cost U.S. government and government agencies $ 1,426.0 $ 1,454.5 $ 1,434.0 $ 1,437.9 Non-U.S. government and government agencies 469.9 496.5 556.8 579.2 States, municipalities and political subdivisions 354.1 355.8 413.5 396.0 Corporate debt: Financial institutions 1,032.7 1,033.6 1,275.4 1,277.3 Industrials 1,321.3 1,322.3 1,308.1 1,345.6 Utilities 140.0 140.7 118.9 125.4 Mortgage-backed: Agency mortgage-backed 614.5 612.5 751.8 745.4 Non-agency residential mortgage-backed 23.9 22.7 34.0 32.4 Commercial mortgage-backed 598.0 636.1 582.8 600.1 Asset-backed 757.3 772.6 726.2 751.1 Total fixed maturity investments, trading $ 6,737.7 $ 6,847.4 $ 7,201.5 $ 7,290.6 December 31, 2016 December 31, 2015 Fair Value Cost Fair Value Cost Equity securities $ 243.9 $ 235.0 $ 403.0 $ 395.3 Other invested assets 897.8 831.2 840.2 770.9 $ 1,141.7 $ 1,066.2 $ 1,243.2 $ 1,166.2 Other invested assets, included in the table above, include investments in private equity funds, hedge funds and a high yield loan fund that are accounted for at fair value, but excludes other private securities described below in Note 4(b) that are accounted for using the equity method of accounting. b) Other Invested Assets Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of December 31, 2016 and 2015 were as follows: Fund Type Carrying Value as of December 31, 2016 Investments with Redemption Restrictions Estimated Remaining Restriction Period Investments without Redemption Restrictions Redemption Frequency(1) Redemption Notice Period(1) Unfunded Commitments Private equity $ 281.0 $ 281.0 1 - 15 Years $ — $ 219.3 Levered credit 204.9 204.9 3 - 9 Years — 190.8 Real estate 68.9 68.9 6 - 8 Years — 191.6 Distressed 5.0 5.0 1 Year — 3.8 Total private equity 559.8 559.8 — 605.5 Distressed 175.3 — 175.3 Quarterly 60 Days — Relative value credit 84.8 — 84.8 Quarterly 60 Days — Equity long/short 67.9 — 67.9 Quarterly 45 Days — Fund of funds 10.0 — 10.0 Quarterly 60 Days — Total hedge funds 338.0 — 338.0 — Total other invested assets at fair value 897.8 559.8 338.0 605.5 Other private securities 62.9 — 62.9 — Total other invested assets $ 960.7 $ 559.8 $ 400.9 $ 605.5 Fund Type Carrying Value as of December 31, 2015 Investments Estimated Investments Redemption Redemption Unfunded Private equity $ 236.4 $ 236.4 1 - 7 Years $ — $ 231.0 Levered credit 205.9 205.9 4 - 8 Years — 179.0 Distressed 5.1 5.1 2 Years — 3.8 Real estate — — 7 - 9 Years — 200.0 Total private equity 447.4 447.4 — 613.8 Distressed 215.6 54.6 2 Years 161.0 Monthly 90 Days — Relative value credit 105.4 — 105.4 Quarterly 60 Days — Equity long/short 58.0 — 58.0 Quarterly 45 Days — Total hedge funds 379.0 54.6 324.4 — High yield loan fund 13.8 — 13.8 Monthly 30 days — Total other invested assets at fair value 840.2 502.0 338.2 613.8 Other private securities 126.5 — 126.5 — Total other invested assets $ 966.7 $ 502.0 $ 464.7 $ 613.8 (1) The redemption frequency and notice periods only apply to the investments without redemption restrictions. During the year ended December 31, 2016 , the Company sold a portion of one of its other private securities. As a result of the sale, the Company no longer maintained significant influence over the operations of this other private security and discontinued the use of the equity method of accounting for the remaining equity interest still owned by the Company. The Company recorded a realized gain of $21.7 million related to the equity interest sold and recorded an unrealized gain of $8.1 million related to the fair value of the remaining interest still owned by the Company. The Company will account for its remaining interest as a trading security, with any changes in fair value recorded as an unrealized gain or loss in the consolidated income statements. In general, the Company has invested in hedge funds that require at least 30 days' notice of redemption, and may be redeemed on a monthly, quarterly, semi-annual, annual or longer basis, depending on the fund. Certain hedge funds have lock-up periods ranging from one to three years from initial investment. A lock-up period refers to the initial amount of time an investor is contractually required to invest before having the ability to redeem. Funds that provide for periodic redemptions may, depending on the funds’ governing documents, have the ability to deny or delay a redemption request, called a “gate.” The fund may implement this restriction because the aggregate amount of redemption requests as of a particular date exceeds a specified level, generally ranging from 15% to 25% of the fund’s net assets. The gate is a method for executing an orderly redemption process to reduce the possibility of adversely affecting investors in the fund. Typically, the imposition of a gate delays a portion of the requested redemption, with the remaining portion settled in cash sometime after the redemption date. Certain funds may impose a redemption fee on early redemptions. Interests in private equity funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the fund. The following describes each investment type: • Private equity (primary and secondary): Primary equity funds include funds that may invest in companies and general partnership interests, as well as direct investments. Secondary funds buy limited partnership interests from existing limited partners of primary private equity funds. As owners of private equity, funds may seek liquidity by selling their existing interests, plus any remaining commitment, to secondary market participants. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the funds. • Levered credit (including mezzanine debt): Levered credit funds invest across the capital structures of upper middle market and middle market companies in connection with leveraged buyouts, mergers and acquisitions, recapitalizations, growth financings, refinancings and other corporate purposes. The most common position in the capital structure of mezzanine funds will be between the senior secured debt holder and the equity; however, the funds in which we are invested may include secured debt, subordinated debt, preferred stock and/or private equity. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the funds. • Real estate funds: Private real estate funds invest directly (through debt and equity) in commercial real estate (multifamily, industrial, office, student housing and retail) as well as residential property. Real estate managers have diversified portfolios that generally follow core, core-plus, value-added or opportunistic strategies. These funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the funds. • Distressed funds: In distressed debt investing, managers take positions in the debt of companies experiencing significant financial difficulties, including bankruptcy, or in certain positions of the capital structure of structured securities. The manager relies on the fundamental analysis of these securities, including the claims on the assets and the likely return to bondholders. Certain funds cannot be redeemed because the investments include restrictions that do not allow for redemption until termination of the funds. • Relative value credit funds: These funds seek to take exposure to credit-sensitive securities, long and/or short, based upon credit analysis of issuers and securities and credit market views. • Equity long/short funds: In equity long/short funds, managers take long positions in companies they deem to be undervalued and short positions in companies they deem to be overvalued. Long/short managers may invest in countries, regions or sectors and vary by their use of leverage and by their targeted net long position. • Fund of funds: Fund of funds allocate assets among multiple investment managers unaffiliated with the fund of funds sponsor employing a variety of proprietary investment strategies. Fund of funds strategies will invest in a portfolio of funds that primarily pursue the following investment strategies: equity, macro, event driven and credit. • Other private securities: These securities mostly include strategic non-controlling minority investments in private asset management companies and other insurance related investments that are accounted for using the equity method of accounting. • High yield loan fund: A long-only private mutual fund that invests in high yield fixed income securities. c) Net Investment Income Year Ended December 31, 2016 2015 2014 Fixed maturity investments $ 191.0 $ 164.2 $ 149.5 Equity securities 5.1 13.3 17.6 Other invested assets: hedge funds and private equity 23.4 19.6 12.6 Other invested assets: other private securities 13.7 2.8 13.3 Cash and cash equivalents 2.9 1.7 2.1 Expenses (18.3 ) (19.5 ) (18.2 ) Net investment income $ 217.8 $ 182.1 $ 176.9 Net investment income from other invested assets: other private securities included the undistributed net income from investments accounted for using the equity method of accounting. The income reported for other invested assets: other private securities for the year ended December 31, 2015 included an other-than-temporary impairment of $6.3 million recorded in the second quarter of 2015 related to one of the Company's equity method investments. The Company recorded the other-than-temporary impairment as the fair value of this investment was below its carrying value. The income reported for other invested assets: other private securities for the year ended December 31, 2014 included a loss of $9.3 million recorded for an equity method investment due to impairment charges that it recorded. At the time, the Company determined the fair value of this investment and concluded that the fair value exceeded the Company's carrying value and as such no other-than-temporary impairment was recorded. d) Components of Realized Gains and Losses Year Ended December 31, 2016 2015 2014 Gross realized gains on sale of invested assets $ 159.5 $ 180.3 $ 195.4 Gross realized losses on sale of invested assets (121.3 ) (106.4 ) (48.2 ) Net realized and unrealized losses on derivatives (19.6 ) (15.4 ) (39.0 ) Mark-to-market (losses) gains: Debt securities, trading (17.2 ) (126.3 ) (1.7 ) Equity securities, trading 5.8 (41.7 ) 0.4 Other invested assets, trading (5.1 ) (18.1 ) (17.9 ) Net realized investment gains (losses) $ 2.1 $ (127.6 ) $ 89.0 e) Pledged Assets As of December 31, 2016 and 2015 , $2,687.7 million and $2,748.9 million , respectively, of cash and cash equivalents and investments were deposited, pledged or held in trust accounts in favor of ceding companies and other counterparties or government authorities to comply with reinsurance contract provisions and insurance laws. In addition, as of December 31, 2016 and 2015 , a further $587.6 million and $579.3 million , respectively, of cash and cash equivalents and investments were pledged as collateral for the Company’s letter of credit facilities. See Note 11(g) for details on the Company’s credit facilities.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative instruments	DERIVATIVE INSTRUMENTS As of December 31, 2016 and 2015 , none of the Company’s derivatives were designated as hedges for accounting purposes. The following table summarizes information on the location and amounts of derivative fair values on the consolidated balance sheets: December 31, 2016 December 31, 2015 Asset Derivative Notional Amount Asset Derivative Fair Value Liability Derivative Notional Amount Liability Derivative Fair Value Asset Derivative Notional Amount Asset Derivative Fair Value Liability Derivative Notional Amount Liability Derivative Fair Value Foreign exchange contracts $ 103.2 $ 10.4 $ 4.1 $ 0.1 $ 41.1 $ 0.1 $ 244.8 $ 3.0 Interest rate swaps — — — — — — 328.2 0.5 Insurance contracts 225.0 7.4 — — — — — — Reinsurance contracts — — 110.0 4.0 — — — — Total derivatives $ 328.2 $ 17.8 $ 114.1 $ 4.1 $ 41.1 $ 0.1 $ 573.0 $ 3.5 Derivative assets and derivative liabilities are classified within “other assets” or “accounts payable and accrued liabilities” on the consolidated balance sheets. The following table provides the net realized and unrealized (losses) gains on derivatives not designated as hedges recorded on the consolidated income statements: Year Ended December 31, 2016 2015 2014 Foreign exchange contracts $ (2.2 ) $ (7.3 ) $ 0.9 Total included in foreign exchange (gain) loss (2.2 ) (7.3 ) 0.9 Put options — — 0.5 Foreign exchange contracts (11.9 ) 0.2 3.5 Interest rate swaps (6.8 ) (13.4 ) (45.4 ) Interest rate futures (0.9 ) (2.2 ) 2.4 Total included in net realized investment gains (losses) (19.6 ) (15.4 ) (39.0 ) Insurance contracts 7.4 — — Reinsurance contracts (3.1 ) — — Total included in other income (other expense) 4.3 — — Total realized and unrealized (losses) gains on derivatives $ (17.5 ) $ (22.7 ) $ (38.1 ) The foreign exchange contracts loss recorded during the year ended December 31, 2016 was due to hedging our investment exposure to the Euro and Japanese Yen. The losses related to interest rate swap contracts for the years ended December 31, 2015 and 2014 were the result of selling interest rate swap contracts to reduce the duration of the investment portfolio. Given the decrease in interest rates during those years, the Company recorded a loss related to these interest rate swap contracts. Derivative Instruments Not Designated as Hedging Instruments The Company is exposed to foreign currency risk in its investment portfolio. Accordingly, the fair values of the Company’s investment portfolio are partially influenced by the change in foreign exchange rates. These foreign currency hedging activities have not been designated as specific hedges for financial reporting purposes. The Company’s insurance and reinsurance subsidiaries and branches operate in various foreign countries and consequently the Company’s underwriting portfolio is exposed to foreign currency risk. The Company manages foreign currency risk by seeking to match liabilities under the insurance policies and reinsurance contracts that it writes and that are payable in foreign currencies with cash and investments that are denominated in such currencies. When necessary, the Company may also use derivatives to economically hedge unmatched foreign currency exposures, specifically forward contracts and currency options. For example, during 2014, the Company purchased a forward contract to economically hedge a portion of its foreign currency exposure related to the consideration to be paid for the Hong Kong and Singapore operations of RSA. The Company also purchases and sells interest rate future and interest rate swap contracts to actively manage the duration and yield curve positioning of its fixed income portfolio. Interest rate futures and interest rate swaps can efficiently increase or decrease the overall duration of the portfolio. Additionally, interest rate future and interest rate swap contracts can be utilized to obtain the desired position along the yield curve in order to protect against certain future yield curve shapes. The Company also purchases options to actively manage the Company’s equity portfolio. The Company also has entered into insurance and reinsurance contracts that are required to be accounted for as derivatives. This will be the case when the insurance or reinsurance contract provides indemnification to the insured or cedent as a result of a change in a variable versus an identifiable insurable event, such as a single-trigger ILW. The Company considers these insurance and reinsurance contracts to be an extension of its overall insurance operations.

Fair Value Of Financial Instrum

Fair Value Of Financial Instruments	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair value of financial instruments	FAIR VALUE OF FINANCIAL INSTRUMENTS In accordance with U.S. GAAP, 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 at the measurement date. There is a three-level valuation hierarchy for disclosure of fair value measurements. The valuation hierarchy is based upon whether the inputs to the valuation of an asset or liability are observable or unobservable in the market at the measurement date, with quoted market prices being the highest level (Level 1) and unobservable inputs being the lowest level (Level 3). A fair value measurement will fall within the level of the hierarchy based on the input that is significant to determining such measurement. The three levels are defined as follows: • Level 1 : Observable inputs to the valuation methodology that are quoted prices (unadjusted) for identical assets or liabilities in active markets. • Level 2 : Observable inputs to the valuation methodology other than quoted market prices (unadjusted) for identical assets or liabilities in active markets. Level 2 inputs include quoted prices for similar assets and liabilities in active markets, quoted prices for identical assets in markets that are not active and inputs other than quoted prices that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the asset or liability. • Level 3 : Inputs to the valuation methodology that are unobservable for the asset or liability. The following table shows the fair value of the Company’s financial instruments and where in the fair value hierarchy the fair value measurements are included as of the dates indicated below: December 31, 2016 Carrying amount Total fair value Level 1 Level 2 Level 3 ASSETS: Fixed maturity investments: U.S. government and government agencies $ 1,426.0 $ 1,426.0 $ 1,379.6 $ 46.4 $ — Non-U.S. government and government agencies 469.9 469.9 — 469.9 — States, municipalities and political subdivisions 354.1 354.1 — 354.1 — Corporate debt: Financial institutions 1,032.7 1,032.7 — 1,031.2 1.5 Industrials 1,321.3 1,321.3 — 1,321.3 — Utilities 140.0 140.0 — 140.0 — Mortgage-backed: Agency mortgage-backed 614.5 614.5 — 475.9 138.7 Non-agency residential mortgage-backed 23.9 23.9 — 23.9 — Commercial mortgage-backed 598.0 598.0 — 598.0 — Asset-backed 757.3 757.3 697.8 59.5 Total fixed maturity investments 6,737.7 6,737.7 1,379.6 5,158.5 199.7 Equity securities 243.9 243.9 219.2 — 24.7 Other invested assets (1) 897.8 897.8 — — — Total investments 7,879.4 7,879.4 1,598.8 5,158.5 224.4 Derivative assets: Foreign exchange contracts 10.4 10.4 — 10.4 — Insurance contracts 7.4 7.4 — — 7.4 LIABILITIES: Derivative liabilities: Foreign exchange contracts 0.1 0.1 — 0.1 — Reinsurance contracts 4.0 4.0 — — 4.0 Senior notes 794.2 827.1 — 827.1 — Other long-term debt $ 22.0 $ 26.7 $ — $ 26.7 $ — December 31, 2015 Carrying amount Total fair value Level 1 Level 2 Level 3 ASSETS: Fixed maturity investments: U.S. government and government agencies $ 1,434.0 $ 1,434.0 $ 1,396.4 $ 37.6 $ — Non-U.S. government and government agencies 556.8 556.8 — 556.8 — States, municipalities and political subdivisions 413.5 413.5 — 413.5 — Corporate debt Financial institutions 1,275.4 1,275.4 — 1,275.4 — Industrials 1,308.1 1,308.1 — 1,308.1 — Utilities 118.9 118.9 — 118.9 — Mortgage-backed Agency mortgage-backed 751.8 751.8 — 650.8 101.1 Non-agency residential mortgage-backed 34.0 34.0 — 29.0 5.0 Commercial mortgage-backed 582.8 582.8 — 582.8 — Asset-backed 726.2 726.2 — 663.2 63.0 Total fixed maturity investments 7,201.5 7,201.5 1,396.4 5,636.1 169.1 Equity securities 403.0 403.0 403.0 — — Other invested assets (1) 840.2 840.2 — — — Total investments 8,444.7 8,444.7 1,799.4 5,636.1 169.1 Derivative assets: Foreign exchange contracts 0.1 0.1 — 0.1 — LIABILITIES: Derivative liabilities: Foreign exchange contracts 3.0 3.0 — 3.0 — Interest rate swaps 0.5 0.5 — 0.5 — Senior notes 1,292.9 1,337.9 — 1,337.9 — Other long-term debt $ 23.0 $ 27.7 $ — $ 27.7 $ — (1) In accordance with U.S. GAAP, other invested assets, excluding other private securities, are measured at fair value using the net asset value per share (or its equivalent) practical expedient and have not been classified in the fair value hierarchy. The following describes the valuation techniques used by the Company to determine the fair value of financial instruments held as of the balance sheet date. Fair Value of Financial Instruments U.S. government and government agencies: Comprised primarily of bonds issued by the U.S. Treasury, the Federal Home Loan Bank, the Federal Home Loan Mortgage Corporation and the Federal National Mortgage Association. The fair values of the Company’s U.S. government securities are based on quoted market prices in active markets and are included in the Level 1 fair value hierarchy. The Company believes the market for U.S. Treasury securities is an actively traded market given the high level of daily trading volume. The fair values of U.S. government agency securities are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are included in the Level 2 fair value hierarchy. Non-U.S. government and government agencies: Comprised of fixed income obligations of non-U.S. governmental entities. The fair values of these securities are based on prices obtained from international indices and are included in the Level 2 fair value hierarchy. States, municipalities and political subdivisions: Comprised of fixed income obligations of U.S. domiciled state and municipality entities. The fair values of these securities are based on prices obtained from the new issue market, and are included in the Level 2 fair value hierarchy. Corporate debt: Comprised of bonds issued by or loan obligations of corporations that are diversified across a wide range of issuers and industries. The fair values of corporate debt that are short-term are priced using spread above the LIBOR yield curve, and the fair value of corporate debt that are long-term are priced using the spread above the risk-free yield curve. The spreads are sourced from broker-dealers, trade prices and the new issue market. As the significant inputs used to price corporate bonds are observable market inputs, the fair values of corporate debt are included in the Level 2 fair value hierarchy, unless the significant inputs used to price the corporate debt securities are broker-dealer quotes and the Company is not able to determine if those quotes are based on observable market inputs, in which case the fair value is included in the Level 3 hierarchy. Mortgage-backed: Primarily comprised of residential and commercial mortgages originated by both U.S. government agencies (such as the Federal National Mortgage Association) and non-U.S. government agencies. The fair values of mortgage-backed securities originated by U.S. government agencies and non-U.S. government agencies are based on a pricing model that incorporates prepayment speeds and spreads to determine appropriate average life of mortgage-backed securities. The spreads are sourced from broker-dealers, trade prices and the new issue market. As the significant inputs used to price the mortgage-backed securities are observable market inputs, the fair values of these securities are included in the Level 2 fair value hierarchy, unless the significant inputs used to price the mortgage-backed securities are broker-dealer quotes and the Company is not able to determine if those quotes are based on observable market inputs, in which case the fair value is included in the Level 3 hierarchy. Asset-backed: Principally comprised of bonds backed by pools of automobile loan receivables, home equity loans, credit card receivables and collateralized loan obligations originated by a variety of financial institutions. The fair values of asset-backed securities are priced using prepayment speed and spread inputs that are sourced from the new issue market or broker-dealer quotes. As the significant inputs used to price the asset-backed securities are observable market inputs, the fair values of these securities are included in the Level 2 fair value hierarchy, unless the significant inputs used to price the asset-backed securities are broker-dealer quotes and the Company is not able to determine if those quotes are based on observable market inputs, in which case the fair value is included in the Level 3 hierarchy. Equity securities: Comprised of U.S. and foreign common and preferred stocks and mutual funds. Equities are generally included in the Level 1 fair value hierarchy as prices are obtained from market exchanges in active markets. Non-U.S. mutual funds where the net asset value (“NAV”) is not provided on a daily basis are included in the Level 3 fair value hierarchy. Also, the Company's remaining equity interest in an equity security that it no longer accounts for under the equity method of accounting is included in the Level 3 fair value hierarchy as the fair value is based on the enterprise value of that security which is not a publicly traded company. Other invested assets: Comprised of funds invested in a range of diversified strategies. In accordance with U.S. GAAP, the fair values of the funds are based on the NAV of the funds as reported by the fund manager. The Company does not measure its investments that are accounted for using the equity method of accounting at fair value, unless an other-than-temporary impairment is recorded. Derivative instruments: The fair value of foreign exchange contracts and interest rate futures and swaps are priced from quoted market prices for similar exchange-traded derivatives and pricing valuation models that utilize independent market data inputs. The fair value of foreign exchange contracts and interest futures and swaps are included in the Level 2 fair value hierarchy. The fair value of the insurance and reinsurance contracts are based on an internal model that estimates the expected value based on multiple scenarios (i.e., Monte-Carlo simulation) and discounted back to current value. The key unobservable inputs are the discount rate, which was 10%, and the values of the underlying insured risks. Given the inputs to the internal model are unobservable, the fair value of the insurance and reinsurance contracts are included in the Level 3 fair value hierarchy. Senior notes: The fair value of the senior notes is based on reported trades. The fair value of the senior notes is included in the Level 2 fair value hierarchy. Other long-term debt: Comprised of the mortgage and credit facility associated with the purchase of office space in Switzerland. The fair value of the other long-term debt is based on the value of the debt using current interest rates. The fair value of the long-term debt is included in the Level 2 fair value hierarchy. Non-recurring Fair Value of Financial Instruments The Company measures the fair value of certain assets on a non-recurring basis, generally quarterly, annually, or when events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. These assets include investments accounted for using the equity method, goodwill and intangible assets. The Company uses a variety of techniques to measure the fair value of these assets when appropriate, as described below: Investments accounted for using the equity method: When the Company determines that the carrying value of these assets may not be recoverable, the Company records the assets at fair value with the loss recognized in income. In such cases, the Company measures the fair value of these assets using the techniques discussed above. Goodwill and intangible assets: The Company tests goodwill and intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable, but at least annually for goodwill and indefinite-lived intangibles. When the Company determines that goodwill and indefinite-lived intangible assets may be impaired, the Company uses various techniques, including discounted expected future cash flows and market multiple models, to measure fair value. Rollforward of Level 3 Financial Instruments The following is a rollforward of the beginning and ending balance of financial instruments using significant unobservable inputs (Level 3): Fair value measurements using significant unobservable inputs (Level 3): Corporate Debt - Financial Institutions Agency MBS Non-agency RMBS CMBS Asset-backed Equities Insurance contracts Reinsurance contracts Balance at December 31, 2014 $ — $ 180.1 $ — $ 1.7 $ 55.4 $ 43.3 $ — $ — Realized and unrealized gains (losses) included in net income — (1.0 ) (0.1 ) 0.1 (6.1 ) 3.5 — — Purchases — 17.7 5.2 1.8 18.4 — — — Sales — (95.7 ) (0.1 ) (3.6 ) (23.1 ) (46.8 ) — — Transfers into Level 3 from Level 2 — — — — 37.3 — — — Transfers out of Level 3 into Level 2 (1) — — — — (18.9 ) — — — Balance at December 31, 2015 $ — $ 101.1 $ 5.0 $ — $ 63.0 $ — $ — $ — Realized and unrealized gains (losses) included in net income — (6.4 ) — — 3.1 8.1 7.4 (4.0 ) Purchases 1.5 212.6 — — 31.2 16.6 — — Sales — (175.3 ) — — (27.2 ) — — — Transfers into Level 3 from Level 2 — 6.7 — — 8.0 — — — Transfers out of Level 3 into Level 2 (1) — — (5.0 ) — (18.6 ) — — — Balance at December 31, 2016 $ 1.5 $ 138.7 $ — $ — $ 59.5 $ 24.7 $ 7.4 $ (4.0 ) Realized and unrealized losses (gains) included in net income for investments still held as of December 31, 2016 $ — $ (6.4 ) $ — $ — $ 1.9 $ 8.1 $ 7.4 $ (4.0 ) Realized and unrealized gains (losses) included in net income for investments still held as of December 31, 2015 $ — $ (1.5 ) $ (0.1 ) $ — $ (0.3 ) $ — $ — $ — (1) Transfers out of Level 3 are primarily attributable to the availability of market observable information. The Company attempts to verify the significant inputs used by broker-dealers in determining the fair value of the securities priced by them. If the Company could not obtain sufficient information to determine if the broker-dealers were using significant observable inputs, such securities have been transferred to the Level 3 fair value hierarchy. The Company believes the prices obtained from the broker-dealers are the best estimate of fair value of the securities being priced as the broker-dealers are typically involved in the initial pricing of the security, and the Company has compared the price per the broker-dealer to other pricing sources and noted no material differences. The Company recognizes transfers between levels at the end of the reporting period. There were no transfers between Level 1 and Level 2 during the period. The Company’s external investment accounting service provider receives prices from internationally recognized independent pricing services to measure the fair values of its fixed maturity investments. Pricing sources are evaluated and selected in a manner to ensure that the most reliable sources are used. The independent pricing sources obtain market quotations and actual transaction prices for securities that have quoted prices in active markets. Each pricing service has its own proprietary method for determining the fair value of securities that are not actively traded. In general, these methods involve the use of “matrix pricing” in which the independent pricing service uses observable market inputs, including, but not limited to, reported trades, benchmark yields, broker-dealer quotes, interest rates, prepayment speeds, default rates and such other inputs as are available from market sources to determine a reasonable fair value. All of the Company’s fixed maturity investment securities classified as Level 3 are valued based on unadjusted broker-dealer quotes. This includes less liquid securities such as lower quality asset-backed securities, commercial mortgage-backed securities and residential mortgage-backed securities. The primary valuation inputs include monthly payment information, the probability of default, loss severity rates and estimated prepayment rates. Significant changes in these inputs in isolation would result in a significantly lower or higher fair value measurement. In general, a change in the assumption of the probability of default is accompanied by a directionally similar change in the assumption used for the loss severity in an event of default and prepayment rates. The Company records the unadjusted price provided and validates this price through a process that includes, but is not limited to monthly and/or quarterly: (i) comparison of prices between two independent sources, with significant differences requiring additional price sources; (ii) quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to their target benchmark, with significant differences identified and investigated); (iii) evaluation of methodologies used by external parties to calculate fair value, including a review of the inputs used for pricing; (iv) comparing the price to the Company’s knowledge of the current investment market; and (v) back-testing, which includes randomly selecting purchased or sold securities and comparing the executed prices to the fair value estimates from the pricing service. In addition to internal controls, management relies on the effectiveness of the valuation controls in place at the Company’s external investment accounting service provider (supported by a Statement on Standards for Attestation Engagements No. 16 report) in conjunction with regular discussion and analysis of the investment portfolio’s structure and performance.

Reserve For Losses And Loss Exp

Reserve For Losses And Loss Expenses	12 Months Ended
	Dec. 31, 2016
Insurance Loss Reserves [Abstract]
Reserve for losses and loss expenses	RESERVE FOR LOSSES AND LOSS EXPENSES a) Basis for estimating the reserves for losses and loss expenses The reserve for losses and loss expenses is comprised of two main elements: outstanding loss reserves (“OSLR,” also known as case reserves) and reserves for losses incurred but not reported (“IBNR”). OSLR relate to known claims and represent management’s best estimate of the likely loss settlement. IBNR reserves relate primarily to unreported events that, based on industry information, management’s experience and actuarial evaluation, can reasonably be expected to have occurred and are reasonably likely to result in a loss to the Company. IBNR reserves also relate to estimated development of reported events that based on industry information, management’s experience and actuarial evaluation, can reasonably be expected to reach the Company’s attachment point and are reasonably likely to result in a loss. The Company also includes in IBNR reserves changes in the values of claims that have been reported but are not yet settled. Each claim is settled individually based upon its merits and it is not unusual for a claim to take years after being reported to settle, especially if legal action is involved. As a result, reserves for losses and loss expenses include significant estimates for IBNR reserves. The reserve for IBNR is estimated by management for each line of business based on various factors, including underwriters’ expectations about loss experience, actuarial analysis, comparisons with the results of industry benchmarks and loss experience to date. The Company implicitly factors into IBNR reserves inflation by assuming an inflation rate consistent with historical trends. The IBNR reserves are calculated as the ultimate amount of losses and loss expenses less cumulative paid losses and loss expenses and OSLR. The Company’s actuaries employ generally accepted actuarial methodologies to determine estimated ultimate loss reserves. The Company believes that its current estimates of liabilities appropriately reflect its current knowledge of the business and the prevailing market, social, legal and economic conditions while giving due consideration to historical trends and volatility evidenced in the liabilities over the longer term. Although management believes that OSLR and the IBNR reserves are sufficient to cover losses assumed by the Company, there can be no assurance that losses will not deviate from the Company’s reserves, possibly by material amounts. The methodology of estimating loss reserves is periodically reviewed to ensure that the assumptions made continue to be appropriate. The Company recognizes any changes in its loss reserve estimates, including prior year loss reserve development, and the related reinsurance recoverables in the periods in which they are determined and are recorded in “net losses and loss expenses” in the consolidated income statements. The reserve for losses and loss expenses consists of the following: December 31, 2016 2015 Outstanding loss reserves $ 1,807.5 $ 1,678.5 Reserves for losses incurred but not reported 4,831.7 4,777.7 Reserve for losses and loss expenses $ 6,639.2 $ 6,456.2 b) Reserve for losses and loss expenses rollforward The table below is a reconciliation of the beginning and ending liability for unpaid losses and loss expenses. Losses incurred and paid are reflected net of reinsurance recoverables. Year Ended December 31, 2016 2015 2014 Gross liability at beginning of year $ 6,456.2 $ 5,881.2 $ 5,766.5 Reinsurance recoverable at beginning of year (1,480.0 ) (1,340.3 ) (1,234.5 ) Net liability at beginning of year 4,976.2 4,540.9 4,532.0 Acquisition of net reserves for losses and loss expenses — 259.3 — Net losses incurred related to: Current year 1,600.1 1,667.9 1,411.8 Prior years (98.3 ) (81.6 ) (212.6 ) Total incurred 1,501.8 1,586.3 1,199.2 Net paid losses related to: Current year 208.4 186.0 171.8 Prior years 1,238.6 1,201.6 1,001.5 Total paid 1,447.0 1,387.6 1,173.3 Foreign exchange revaluation and other (16.8 ) (22.7 ) (17.0 ) Net liability at end of year 5,014.2 4,976.2 4,540.9 Reinsurance recoverable at end of year 1,625.0 1,480.0 1,340.3 Gross liability at end of year $ 6,639.2 $ 6,456.2 $ 5,881.2 The net reserve for losses and loss expenses acquired of $259.3 million represents the net reserves acquired from the Hong Kong and Singapore branches of RSA of $255.2 million and the net reserves from the Labuan branch of RSA of $4.1 million . For the year ended December 31, 2016, the Company recorded net favorable prior year reserve development in each of its operating segments, primarily due to actual loss emergence being lower than initially expected. The net favorable prior year reserve development in the North American Insurance segment was primarily related to the professional liability line of business. The net favorable reserve development in the Global Markets Insurance segment was primarily related to the casualty and property lines of business, partially offset by unfavorable reserve development in the professional liability and other specialty lines of business . The net favorable prior year reserve development in the Reinsurance segment was primarily related to our property reinsurance and specialty reinsurance lines of business, partially offset by net unfavorable prior year reserve development in our casualty reinsurance line of business. For the year ended December 31, 2015, the Company recognized net favorable prior year reserve development primarily due to lower than expected loss emergence in the Global Markets Insurance and Reinsurance segments and net unfavorable prior year reserve development in the North American Insurance segment. The net favorable reserve development in the Global Markets Insurance segment was primarily due to net favorable loss reserve development in the property, professional liability and casualty lines of business, partially offset by unfavorable prior year reserve development in the specialty and other line of business from the 2013 loss year. The net favorable reserve development in the Reinsurance segment was primarily related to the property and casualty reinsurance lines of business. The net unfavorable prior year reserve development for the North American Insurance segment primarily related to net unfavorable prior year development in the healthcare and casualty lines of business mainly from the 2012 through 2014 loss years partially offset by favorable prior year reserve development in the professional liability, programs and property lines of business. For the year ended December 31, 2014, the Company recognized net favorable reserve development in each of its operating segments due to actual loss emergence being lower than initially expected. The net favorable prior year reserve development in the North American Insurance segment primarily related to the 2006, 2007, 2009 and 2010 loss years, partially offset by unfavorable reserve development from the 2011 to 2013 loss years. The net favorable prior year reserve development in the Global Markets Insurance segment was primarily due to favorable reserve development for the 2008 to 2010 loss years. The net favorable reserve development in the Reinsurance segment was primarily due to benign global property catastrophe activity for the 2013 loss year. The Company has not accrued any additional premiums or return premiums as a result of the net prior year reserve development during the years ended December 31, 2016, 2015 and 2014. Although the Company has experienced favorable development in its insurance and reinsurance lines, there is no assurance that conditions and trends that have affected the development of liabilities in the past will continue. It is not appropriate to extrapolate future redundancies based on prior years’ development. The methodology of estimating loss reserves is periodically reviewed to ensure that the key assumptions used in the actuarial models continue to be appropriate. c) Incurred and Paid Loss Development Triangles The following information presents the incurred and paid claims information as of December 31, 2016, net of reinsurance, as well as cumulative claim frequency and total IBNR reserves by accident year. The information about incurred and paid claims development presented for the years ended December 31, 2010 to December 31, 2015 is presented as supplementary information. The incurred and paid loss development triangles are presented based on the following: • Disaggregated based on lines of business within each operating segment. There are a total of 17 incurred and paid loss development triangles presented. Of the 17 incurred and paid loss development triangles presented, six relate to the North American Insurance segment, eight relate to the Global Markets Insurance segment and three relate to the Reinsurance segment. The 17 incurred and paid loss development triangles were selected to create categories that were relatively homogeneous yet were not so small as to have insufficient actuarial credibility, and are consistent with how the Company discloses gross premiums written and net premiums earned by line of business, as well as disaggregated to reflect the reserves acquired from the Hong Kong, Singapore and Labuan branches of RSA in 2015 on a prospective basis. The Company has lines of business that are 100% ceded that are not presented in the incurred and paid loss development triangles. • All incurred and paid loss development triangles are presented net of reinsurance. • All incurred and paid loss development triangles exclude unallocated loss adjustment expenses, allowance for uncollectible reinsurance recoverables, currency translation adjustments and fair value adjustments related to acquired reserves as those balances are not estimated for each accident year. • The incurred and paid loss development triangles include seven years of historical information. The Company has determined that it is impractical to provide incurred and paid loss development information at this disaggregated basis prior to accident year 2010 as all the necessary data prior to 2010 was not maintained at this disaggregated level. • Reserves for losses and loss expenses and paid losses that are not recorded in the United States dollar functional currency are revalued at the United States dollar conversion rate at the end of the period. • Acquisitions will be presented in the incurred and paid loss development triangles based on how the acquired reserves impact the nature, amount, timing and uncertainty of the cash flows related the settlement of the reserve for losses and loss expenses. As it relates to the reserves for losses and loss expenses acquired from RSA, those reserves are presented from the date in which they were acquired (April 1, 2015) as separate incurred and paid loss development triangles until such time when it is appropriate to combine with the equivalent Global Markets Insurance incurred and paid loss development triangles. The Company has made changes to how reserves are settled and estimated, and therefore the incurred and paid development information prior to the acquisition will no longer provide relevant information regarding the nature, amount, timing and uncertainty of how these reserves will settle in the future. Also, the Company does not have sufficient information at this disaggregated level to present the Global Markets Insurance incurred and paid loss development triangles on a retrospective basis, including the incurred and paid information from the acquired RSA reserves. • The ‘Total IBNR’ by accident year disclosed with the incurred and paid loss development triangles includes (1) IBNR reserves for unreported events and (2) changes in the values of claims that have been reported but are not yet settled. • Cumulative reported claims included in the tables below, which are reflected as the actual claim counts shown, consist of any reported indemnity claim by claimant (i.e., insured) as of December 31, 2016 with a reserve balance greater than one United States dollar (or equivalent foreign currency). By including only indemnity claims with reserves greater than one United States dollar (or equivalent foreign currency), the tables do not include any notifications of claims which may or may not result in an indemnity claim. The cumulative claim count information for the acquired RSA operations are higher, on a relative basis, than the other lines of business cumulative claim count information as the acquired RSA operations have a higher percentage of retail business. This will result in reporting, on average, higher frequency of reported claims with lower severity per claim. The Company has determined that it is impractical to provide cumulative reported claim information for the lines of business in the Reinsurance segment as this information is not provided to the Company from the cedents. The Company also does not believe cumulated reported claim counts for its Reinsurance segment provides any meaningful information related to the nature, amount, timing and uncertainty of the cash flows related to the settled of the reserve for losses and loss expenses. North American Insurance Segment Casualty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 133.8 $ 156.8 $ 158.4 $ 151.5 $ 149.3 $ 143.5 $ 127.3 $ 23.6 277 2011 120.7 140.7 145.1 143.0 136.7 144.2 36.8 347 2012 144.4 147.9 150.7 166.3 188.5 42.7 388 2013 184.0 192.4 208.9 237.4 90.3 638 2014 220.2 222.4 232.4 94.7 763 2015 288.0 279.1 214.8 820 2016 268.4 244.3 614 $ 1,477.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 0.6 $ 28.4 $ 65.9 $ 72.8 $ 83.0 $ 87.4 $ 96.8 2011 2.1 11.2 32.8 53.0 79.0 91.8 2012 6.5 25.9 53.2 85.4 114.0 2013 9.7 38.6 70.2 103.6 2014 8.5 58.3 103.9 2015 11.0 34.2 2016 10.0 $ 554.4 All outstanding liabilities before 2010, net of reinsurance $ 157.0 Liability for losses and loss expenses, net of reinsurance $ 1,079.9 Professional liability Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 189.4 $ 196.5 $ 190.5 $ 178.0 $ 169.3 $ 154.8 $ 152.3 $ 23.1 334 2011 182.5 206.4 228.7 235.4 214.4 210.7 24.4 474 2012 193.5 266.2 274.0 271.1 265.6 46.9 530 2013 220.9 226.8 225.8 240.4 77.3 534 2014 213.0 233.7 235.7 79.2 378 2015 254.2 258.9 165.7 269 2016 256.0 234.1 127 $ 1,619.5 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 7.9 $ 36.5 $ 57.0 $ 78.1 $ 91.3 $ 97.5 $ 118.2 2011 13.6 56.1 102.6 124.7 152.7 179.5 2012 15.8 62.5 98.0 146.5 181.1 2013 9.6 50.0 95.8 142.8 2014 11.7 69.8 125.6 2015 9.0 61.0 2016 9.5 $ 817.6 All outstanding liabilities before 2010, net of reinsurance $ 89.7 Liability for losses and loss expenses, net of reinsurance $ 891.6 Property Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 66.9 $ 54.0 $ 49.6 $ 47.7 $ 48.6 $ 48.8 $ 48.8 $ 0.7 330 2011 124.3 121.8 115.0 111.4 110.2 107.9 (0.1 ) 448 2012 157.7 146.9 140.5 136.9 136.3 0.3 599 2013 81.6 75.3 69.8 68.9 0.1 923 2014 97.0 96.0 88.9 0.3 1,344 2015 110.7 114.4 3.3 1,448 2016 101.3 11.8 1,502 $ 666.4 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 16.4 $ 34.2 $ 40.9 $ 45.7 $ 47.4 $ 47.9 $ 48.1 2011 24.6 69.8 98.6 106.2 107.4 108.1 2012 20.5 98.0 127.8 134.7 135.0 2013 25.4 56.3 64.6 67.8 2014 32.3 73.1 83.8 2015 51.6 98.5 2016 46.7 $ 587.9 All outstanding liabilities before 2010, net of reinsurance $ 0.5 Liability for losses and loss expenses, net of reinsurance $ 79.0 Programs Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 70.7 $ 72.5 $ 86.4 $ 80.8 $ 78.8 $ 75.5 $ 75.0 $ 2.6 479 2011 54.0 61.9 62.6 58.1 52.5 53.5 4.4 446 2012 56.7 60.5 62.4 59.6 58.9 5.7 496 2013 64.9 62.0 59.7 56.2 14.5 871 2014 74.9 73.9 70.0 28.8 1,201 2015 86.8 86.2 43.5 1,266 2016 113.6 72.3 1,281 $ 513.4 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.9 $ 17.9 $ 42.4 $ 52.3 $ 59.9 $ 63.4 $ 66.3 2011 3.8 15.2 26.7 34.7 41.3 45.3 2012 3.8 17.6 29.6 38.3 44.5 2013 5.7 15.8 24.4 33.0 2014 6.4 16.9 27.5 2015 9.3 26.3 2016 14.1 $ 257.0 All outstanding liabilities before 2010, net of reinsurance $ 9.4 Liability for losses and loss expenses, net of reinsurance $ 265.8 Healthcare Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 78.5 $ 76.4 $ 79.3 $ 79.8 $ 64.2 $ 63.4 $ 62.8 $ 6.8 156 2011 85.9 87.1 94.5 108.1 113.6 113.3 4.5 248 2012 87.9 91.4 99.4 113.7 113.7 8.5 260 2013 85.4 111.2 123.9 123.9 18.8 227 2014 84.4 92.5 92.5 46.4 150 2015 76.8 76.8 58.0 85 2016 51.1 47.6 17 $ 634.1 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 1.2 $ 6.4 $ 17.1 $ 28.9 $ 39.8 $ 48.5 $ 51.9 2011 0.5 10.9 42.5 69.6 84.0 99.9 2012 1.3 15.1 34.3 54.8 77.5 2013 2.6 12.6 56.9 84.6 2014 1.0 9.0 26.5 2015 0.6 8.5 2016 0.9 $ 349.7 All outstanding liabilities before 2010, net of reinsurance $ 16.8 Liability for losses and loss expenses, net of reinsurance $ 301.2 Other specialty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 0.9 $ 0.9 $ 0.9 $ 0.6 $ 0.5 $ 0.3 $ 0.4 $ — 9 2011 16.5 18.9 18.3 18.7 18.7 18.7 0.7 16 2012 21.2 21.2 22.5 21.3 21.2 2.3 19 2013 16.6 16.6 16.6 16.6 10.6 73 2014 30.6 33.6 34.3 12.1 331 2015 47.4 48.2 30.6 352 2016 70.1 62.4 520 $ 209.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ 0.1 $ 0.1 $ 0.1 $ 0.4 2011 4.0 11.2 14.5 15.1 15.9 16.7 2012 0.5 10.2 14.7 17.5 17.9 2013 0.8 2.3 3.2 4.4 2014 5.2 13.0 18.6 2015 4.1 13.4 2016 4.2 $ 75.6 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 134.0 Global Markets Insurance Segment: Casualty - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 14.2 $ 14.2 $ 14.2 $ 13.9 $ 10.3 $ 5.8 $ 4.2 $ 4.1 1 2011 9.8 9.6 15.4 16.5 15.8 15.5 5.4 10 2012 11.0 11.6 11.3 10.5 7.6 5.8 16 2013 9.3 9.3 8.1 7.3 6.5 25 2014 9.0 11.8 11.9 6.0 66 2015 16.6 19.5 6.5 111 2016 15.9 11.4 233 $ 81.9 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ 0.1 $ 0.1 $ 0.1 $ 0.1 2011 — 0.2 0.3 10.1 10.1 10.1 2012 — 0.6 0.9 1.0 1.6 2013 — 0.4 0.4 0.4 2014 0.4 0.7 1.1 2015 1.1 4.0 2016 0.4 $ 17.7 All outstanding liabilities before 2010, net of reinsurance $ 24.1 Liability for losses and loss expenses, net of reinsurance $ 88.3 Casualty - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 3.2 $ 2.7 $ 0.5 130 2011 — — — — 7.2 6.2 0.1 337 2012 — — — 19.3 17.9 0.4 496 2013 — — 53.6 43.2 3.1 1,302 2014 — 99.2 68.7 5.4 3,618 2015 98.3 78.0 15.4 9,095 2016 60.9 22.0 8,506 $ 277.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 1.0 $ 1.5 2011 — — — — 2.7 4.7 2012 — — — 8.2 14.2 2013 — — 13.2 28.2 2014 — 16.6 37.1 2015 12.0 31.1 2016 13.4 $ 130.1 All outstanding liabilities before 2010, net of reinsurance $ 1.1 Liability for losses and loss expenses, net of reinsurance $ 148.6 Professional liability - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 32.6 $ 32.6 $ 32.5 $ 30.3 $ 20.0 $ 13.8 $ 14.7 $ 5.7 15 2011 32.4 29.8 27.8 24.3 20.7 19.2 7.3 21 2012 32.4 30.7 37.9 39.2 37.3 10.7 34 2013 33.9 33.4 30.4 28.5 20.0 92 2014 39.6 39.2 40.5 29.4 125 2015 57.3 60.3 48.9 147 2016 53.5 48.9 150 $ 254.0 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ 0.1 $ 0.5 $ 2.6 $ 3.1 $ 8.6 2011 0.1 0.5 6.7 8.4 8.6 8.6 2012 0.2 1.6 10.5 13.6 21.3 2013 0.1 0.9 2.4 3.5 2014 0.5 2.6 4.8 2015 1.3 5.4 2016 1.9 $ 54.3 All outstanding liabilities before 2010, net of reinsurance $ 46.5 Liability for losses and loss expenses, net of reinsurance $ 246.2 Professional liability - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 0.8 $ 0.9 $ 0.1 11 2011 — — — — 1.5 1.0 — 12 2012 — — — 0.4 0.2 — 9 2013 — — 0.8 1.9 0.2 25 2014 — 2.1 1.5 0.3 48 2015 3.2 2.6 1.8 74 2016 1.0 1.0 32 $ 9.1 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.6 $ 0.7 2011 — — — — — 0.5 2012 — — — 0.1 0.1 2013 — — 0.2 0.4 2014 — 0.2 0.3 2015 — 0.1 2016 0.1 $ 2.3 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 6.8 Property - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 87.9 $ 102.3 $ 97.5 $ 96.6 $ 95.7 $ 96.5 $ 93.6 $ 0.1 249 2011 66.2 64.2 58.5 54.6 54.5 54.9 0.2 214 2012 25.2 21.9 18.6 17.3 18.2 0.8 161 2013 26.0 18.6 14.4 14.4 0.2 108 2014 29.0 23.3 21.1 0.6 164 2015 22.8 25.1 1.8 223 2016 29.3 12.3 282 $ 256.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 47.8 $ 75.0 $ 84.1 $ 90.5 $ 92.1 $ 92.5 $ 92.9 2011 10.6 28.4 43.3 52.2 52.8 53.6 2012 3.5 9.3 11.5 15.1 17.3 2013 4.0 9.0 12.5 12.9 2014 6.7 12.3 15.9 2015 3.7 15.4 2016 3.0 $ 211.1 All outstanding liabilities before 2010, net of reinsurance $ 2.3 Liability for losses and loss expenses, net of reinsurance $ 47.8 Property - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ — $ 0.1 $ — 54 2011 — — — — 0.9 0.5 — 122 2012 — — — 1.7 1.4 — 353 2013 — — 4.2 4.5 — 758 2014 — 14.0 14.3 0.5 1,332 2015 22.1 12.0 0.6 1,988 2016 20.6 7.4 1,190 $ 53.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.1 $ — 2011 — — — — 0.2 0.6 2012 — — — 0.5 1.3 2013 — — 1.6 3.1 2014 — 6.4 9.7 2015 2.8 8.1 2016 1.9 $ 24.8 All outstanding liabilities before 2010, net of reinsurance $ (3.5 ) Liability for losses and loss expenses, net of reinsurance $ 25.0 Other specialty - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ — $ — $ — $ — — 2011 1.0 1.0 1.0 — — — — 3 2012 4.3 4.3 1.7 1.6 1.7 — 5 2013 7.2 16.0 20.2 19.7 1.1 110 2014 31.9 41.4 52.1 3.2 750 2015 44.0 46.4 8.6 1,086 2016 55.1 19.1 1,049 $ 174.9 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ — $ — 2011 — — — — — — 2012 — 0.1 1.4 1.6 1.6 2013 0.2 4.8 16.6 18.4 2014 8.9 27.0 32.9 2015 12.7 29.3 2016 24.7 $ 107.0 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 67.9 Other specialty - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 1.1 $ 1.1 $ — 115 2011 — — — — 1.3 2.6 — 239 2012 — — — 2.4 2.6 (0.1 ) 411 2013 — — 7.0 7.0 0.2 857 2014 — 20.6 21.8 (0.9 ) 2,808 2015 39.0 41.5 0.9 14,366 2016 31.3 7.9 15,908 $ 107.8 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.1 $ 0.3 2011 — — — — 0.3 0.8 2012 — — — 0.4 1.4 2013 — — 2.1 3.2 2014 — 5.5 10.0 2015 7.2 19.1 2016 6.7 $ 41.5 All outstanding liabilities before 2010, net of reinsurance $ 0.4 Liability for losses and loss expenses, net of reinsurance $ 66.7 Reinsurance Segment: Property Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 80.3 $ 78.7 $ 73.0 $ 68.6 $ 68.0 $ 67.9 $ 67.0 $ 0.6 n/a 2011 219.8 223.9 207.2 199.4 197.8 199.2 1.2 n/a 2012 190.9 143.0 131.2 126.9 124.5 3.1 n/a 2013 176.3 143.7 133.6 123.1 2.9 n/a 2014 196.5 165.0 152.8 5.2 n/a 2015 202.1 174.4 26.3 n/a 2016 180.4 74.4 n/a $ 1,021.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 11.1 $ 38.2 $ 50.2 $ 57.6 $ 63.2 $ 64.8 $ 65.2 2011 53.4 116.6 162.9 182.1 190.5 193.9 2012 38.5 87.8 105.8 111.7 114.6 2013 29.7 84.8 110.6 115.7 2014 57.5 112.8 131.0 2015 53.9 104.2 2016 52.8 $ 777.5 All outstanding liabilities before 2010, net of reinsurance $ 1.9 Liability for losses and loss expenses, net of reinsurance $ 245.7 Casualty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 200.0 $ 222.1 $ 225.9 $ 223.2 $ 213.2 $ 197.9 $ 196.0 $ 48.4 n/a 2011 165.2 184.6 189.4 192.7 185.6 180.5 51.8 n/a 2012 190.5 214.7 216.9 223.8 231.2 68.9 n/a 2013 177.4 192.5 198.6 214.9 92.8 n/a 2014 167.2 179.5 182.0 120.0 n/a 2015 159.2 157.5 123.6 n/a 2016 130.2 120.5 n/a $ 1,292.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.6 $ 32.2 $ 58.6 $ 76.3 $ 97.9 $ 114.5 $ 126.8 2011 8.4 26.9 49.0 71.3 93.2 105.0 2012 12.6 39.2 57.3 92.5 127.5 2013 7.8 22.4 60.2 81.4 2014 1.7 12.5 31.0 2015 1.5 14.5 2016 1.8 $ 487.9 All outstanding liabilities before 2010, net of reinsurance $ 225.9 Liability for losses and loss expenses, net of reinsurance $ 1,030.3 Specialty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 11.3 $ 7.7 $ 9.0 $ 8.8 $ 8.6 $ 8.3 $ 8.1 $ 0.4 n/a 2011 30.0 26.9 21.9 22.7 22.1 21.4 1.5 n/a 2012 123.1 132.0 138.3 137.2 136.5 4.5 n/a 2013 111.6 106.7 100.3 102.0 4.2 n/a 2014 121.0 124.8 118.4 6.2 n/a 2015 130.0 128.0 23.9 n/a 2016 118.4 101.6 n/a $ 632.8 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.1 $ 4.1 $ 6.1 $ 6.5 $ 7.0 $ 7.1 $ 7.3 2011 3.2 12.7 16.3 17.5 18.4 19.0 2012 24.5 108.0 121.8 125.5 127.9 2013 3.3 75.7 92.0 93.3 2014 14.8 102.8 107.7 2015 7.2 95.3 2016 9.8 $ 460.4 All outstanding liabilities before 2010, net of reinsurance $ 3.3 Liability for losses and loss expenses, net of reinsurance $ 175.7 d) Reconciliation of incurred and paid loss development triangles to the reserve for losses and loss expenses The following table reconciles the net reserve for losses and loss expenses derived from the incurred and paid loss development triangles to the reserve for losses and loss expenses in the consolidated balance sheet as of December 31, 2016 December 31, 2016 Net reserve for losses and loss expenses per the loss development triangles: North American Insurance: Casualty $ 1,079.9 Professional liability 891.6 Property 79.0 Programs 265.8 Healthcare 301.2 Other specialty 134.0 Global Markets Insurance: Casualty 88.3 Casualty - RSA acquired reserves 148.6 Professional liability 246.2 Professional liability - RSA acquired reserves 6.8 Property 47.8 Property - RSA acquired reserves 25.0 Other specialty 67.9 Other specialty - RSA acquired reserves 66.7 Reinsurance: Property 245.7 Casualty 1,030.3 Specialty 175.7 Total net reserves for losses and loss expenses per the loss development triangles: $ 4,900.4 Reinsurance recoverable for each loss development triangle: North American Insurance: Casualty $ 605.9 Professional liability 352.7 Property 74.5 Programs 83.8 Healthcare 135.6 Other Specialty 55.6 Global Markets Insurance: Casualty 62.9 Casualty - RSA acquired reserves 5.0 Professional liability 111.9 Professional liability - RSA acquired reserves 1.0 Property 4.0 Property - RSA acquired reserves 15.3 Other specialty 30.7 Other specialty - RSA acquired reserves 31.5 Reinsurance: Property 3.8 Casualty — Specialty — Total reinsurance recoverables per the loss development triangles: $ 1,574.0 Total gross reserves for losses and loss expenses per the loss development triangles: $ 6,474.4 Other balances not included in the loss development triangles: Unallocated loss adjustment expenses 118.6 Other reserves not included in the loss development triangles 43.6 Fair value adjustment 6.0 Currency translation adjustment (3.0 ) Other (0.4 ) 164.8 Total gross reserves for losses and loss expenses $ 6,639.2 e) Methods for estimating the reserve for losses and loss expenses, including IBNR reserves, and changes in methodologies In general, the methods, and related assumptions, used for estimating the reserve for losses and loss expenses, including IBNR, are predicated on whether the line of business falls into one of the following two categories: short-tail line or long-tail line. In certain lines of

Ceded Reinsurance

Ceded Reinsurance	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Ceded reinsurance	CEDED REINSURANCE The Company purchases reinsurance from third-party reinsurance companies to reduce its net exposure to losses. Reinsurance provides for recovery of a portion of gross losses and loss expenses from these reinsurers. The Company remains liable to the extent that its reinsurers do not meet their obligations under the related reinsurance contracts. The Company therefore regularly evaluates the financial condition of its reinsurers and monitors concentration of credit risk. The Company believes that as of December 31, 2016 , its reinsurers are able to meet, and will meet, all of their obligations under the agreements. The provision for unrecoverable reinsurance was $1.2 million as of December 31, 2016 and 2015 . The amount of reinsurance recoverable is as follows: 2016 2015 OSLR recoverable $ 384.1 $ 254.6 IBNR recoverable 1,240.9 1,225.4 Reinsurance recoverable $ 1,625.0 $ 1,480.0 Reinsurance recoverable on paid losses $ 104.4 $ 96.4 Direct, assumed and ceded premiums written and earned and losses and loss expenses incurred are as follows: Premiums Written Premiums Earned Losses and Loss Expenses Year Ended December 31, 2016 Direct $ 2,359.6 $ 2,316.6 $ 1,539.2 Assumed 706.2 743.1 379.4 Ceded (810.0 ) (715.6 ) (416.8 ) $ 2,255.8 $ 2,344.1 $ 1,501.8 Year Ended December 31, 2015 Direct $ 2,291.6 $ 2,255.3 $ 1,471.6 Assumed 801.4 863.6 442.8 Ceded (645.0 ) (630.5 ) (328.1 ) $ 2,448.0 $ 2,488.4 $ 1,586.3 Year Ended December 31, 2014 Direct $ 1,996.8 $ 1,835.1 $ 1,031.3 Assumed 938.6 941.2 464.7 Ceded (613.4 ) (593.6 ) (296.8 ) $ 2,322.0 $ 2,182.7 $ 1,199.2 Of the premiums ceded during the years ended December 31, 2016 , 2015 and 2014 , approximately 44.4% , 41.1% and 42.3% , respectively, were ceded to four reinsurers. The Company actively manages its reinsurance exposures by generally selecting reinsurers having a credit rating of “A-” or higher and monitoring the overall credit quality of its reinsurers to ensure the recoverables will be collected. December 31, 2016 A.M. Best Reinsurance Recoverable Percentage of Total Prepaid Reinsurance (1) Percentage of Total Munich Re A+ $ 348.1 21.4 % $ 87.5 18.0 % Axis Capital A+ 160.4 9.9 % 58.5 12.0 % Swiss Re A+ 146.7 9.0 % 64.2 13.2 % Markel A 103.0 6.3 % 25.9 5.3 % Arch Re A+ 100.5 6.2 % 14.0 2.9 % Top five reinsurers 858.7 52.8 % 250.1 51.4 % Other reinsurers’ balances 766.3 47.2 % 236.3 48.6 % Total reinsurance recoverable $ 1,625.0 100.0 % $ 486.4 100.0 % December 31, 2015 A.M. Best Rating Reinsurance Recoverable Percentage of Total Prepaid Reinsurance (1) Percentage of Total Munich Re A+ $ 307.9 20.8 % $ 61.7 15.7 % Axis Capital A+ 150.8 10.2 % 32.2 8.2 % Arch Re A+ 115.3 7.8 % 16.0 4.1 % Swiss Re A+ 103.9 7.0 % 57.3 14.6 % RenaissanceRe A+ 94.0 6.4 % 8.0 2.0 % Top five reinsurers 771.9 52.2 % 175.2 44.6 % Other reinsurers’ balances 708.1 47.8 % 217.1 55.4 % Total reinsurance recoverable $ 1,480.0 100.0 % $ 392.3 100.0 % (1) Prepaid reinsurance represents unearned premiums ceded to reinsurance companies. Approximately 99% of ceded reserves were recoverable from reinsurers who had an A.M. Best rating of “A” or higher as of December 31, 2016 and 2015 .

Funds Held

Funds Held	12 Months Ended
	Dec. 31, 2016
Other Insurance Industry Disclosures [Abstract]
Funds held	FUNDS HELD The Company has also entered into a collateralized property catastrophe quota share reinsurance contract with Aeolus Re, Ltd., a Bermuda-based property catastrophe reinsurer (“Aeolus Re”), whereby the Company assumes property catastrophe business underwritten by Aeolus Re. The Company provided a multi-year capital commitment to support the business being underwritten by Aeolus Re. To the extent that capital is not utilized to support the business being underwritten by Aeolus Re, as all obligations have been settled, the capital is returned to the Company. To the extent the losses are in excess of the premiums written, the capital is utilized to pay the claims. The capital commitment is recorded in “funds held” on the consolidated balance sheets. The funds held balance as of December 31, 2016 and 2015 was $442.0 million and $622.4 million , respectively. For the years ended December 31, 2016 , 2015 and 2014 , the premiums written assumed by the Company through the collateralized property catastrophe quota share reinsurance contract with Aeolus Re were $38.2 million , $76.3 million and $87.3 million , respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and intangible assets	GOODWILL AND INTANGIBLE ASSETS The following table shows the Company’s goodwill and intangible assets at December 31, 2016 and 2015 : Goodwill Indefinite-Lived Intangible Assets Finite-Lived Intangible Assets Net Carrying Value Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Balance at December 31, 2014 $ 278.3 $ 23.9 $ 41.3 $ (18.9 ) $ 22.4 Additions 110.1 — 83.5 — 83.5 Impairments — — (1.4 ) — (1.4 ) Amortization of intangible assets — — — (8.3 ) (8.3 ) Foreign currency translation adjustment (0.3 ) — (3.5 ) — (3.5 ) Balance at December 31, 2015 388.1 23.9 119.9 (27.2 ) 92.7 Additions 2.7 — — — — Impairments — — (0.9 ) — (0.9 ) Amortization of intangible assets — — — (9.8 ) (9.8 ) Foreign currency translation adjustment (1.1 ) — (1.2 ) — (1.2 ) Balance at December 31, 2016 $ 389.7 $ 23.9 $ 117.8 $ (37.0 ) $ 80.8 The additions to goodwill and finite-lived intangible assets during the year ended December 31, 2015 related to the acquisitions of the Hong Kong, Singapore and Labuan branches of RSA and the acquisition of LAU. The goodwill and finite-lived intangible assets related to these acquisitions have been allocated to the Global Markets Insurance segment. The additions to goodwill during the year ended December 31, 2016 related to the Company acquisition of the remaining interest in an insurance agency operation it did not own. The goodwill related to this acquisition has been allocated to the European direct insurance operations of the Global Markets Insurance segment. The impairment to the finite-lived intangible assets during the years ended December 31, 2016 and 2015 related to the customer renewal intangibles from the acquisition of LAU. The trade credit business that is underwritten by LAU has underperformed over the past several years due to increased frequency of reported losses and as a result the customer renewal intangible asset was impaired by $0.9 million and $1.4 million during the years ended December 31, 2016 and 2015 , respectively. The impairments were recorded in “amortization and impairment of intangible assets” in the consolidated income statements. As a result of these impairments recorded, the customer renewal intangible asset, related to the LAU acquisition, has a zero net carrying value as of December 31, 2016 . As of December 31, 2016 , goodwill of $274.3 million , $111.5 million and $3.9 million was allocated to the North American Insurance segment, Global Markets Insurance segment and Reinsurance segment, respectively. The impairment reviews for goodwill and indefinite-lived intangibles did not result in the recognition of impairment losses for the years ended December 31, 2016 , 2015 and 2014 . The net carrying value of the goodwill is net of accumulated impairment charges of $0.2 million that occurred prior to December 31, 2014 . As of December 31, 2016 , the net carrying value of the finite-lived intangible assets is net of accumulated impairment charges of $9.1 million . As of December 31, 2016 , the net carrying value of the finite-lived intangible assets is comprised of distribution network intangible assets of $73.7 million and customer renewal intangible assets of $7.1 million . As of December 31, 2015 , the net carrying value of the finite-lived intangible assets was comprised of distribution network intangible assets of $ 81.0 million and customer renewal intangible assets of $ 11.7 million . The remaining finite-lived intangible assets as of December 31, 2016 will be amortized over an expected remaining useful life of 13.0 years . The distribution network intangible asset will be amortized over an expected remaining useful life of 14.0 years , and the customer renewal intangible asset will be amortized over an expected remaining useful life of 2.7 years . The estimated amortization expense for each of the five succeeding fiscal years and thereafter related to the Company’s finite-lived intangible assets is as follows: Amount 2017 $ 8.8 2018 8.8 2019 7.3 2020 6.1 2021 5.9 2022 and thereafter 43.9 Total $ 80.8

Debt and Financing Arrangements

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt and financing arrangements	DEBT AND FINANCING ARRANGEMENTS a) Financing Structure The following table shows the Company’s financing structure: Outstanding (1) Unamortized discount and debt issuance costs Balance (2) December 31, 2016 2010 Senior notes due 2020 (discount is based on imputed interest rate of 2.80%) 300.0 1.8 298.2 2015 Senior notes due 2025 (discount is based on imputed interest rate of 2.18%) 500.0 4.0 496.0 Swiss office building mortgage 16.9 — 16.9 Swiss office building credit facility 5.1 — 5.1 $900 million Secured letter of credit facility — uncommitted 458.0 — — $200 million Secured letter of credit facility — committed — — — $ 1,280.0 $ 5.8 $ 816.2 December 31, 2015 2006 Senior notes due 2016 (discount is based on imputed interest rate of 3.77%) $ 500.0 $ 0.5 $ 499.5 2010 Senior notes due 2020 (discount is based on imputed interest rate of 2.78%) 300.0 2.3 297.7 2015 Senior notes due 2025 (discount is based on imputed interest rate of 2.18%) 500.0 4.3 495.7 Swiss office building mortgage 17.9 — 17.9 Swiss office building credit facility 5.1 — 5.1 $1,000 million Secured letter of credit facility — uncommitted 507.5 — — $150 million Secured letter of credit facility — committed — — — $ 1,830.5 $ 7.1 $ 1,315.9 (1) Indicates utilization of commitment amount, not drawn borrowings. (2) Represents the principal amount borrowed, net of unamortized discount and debt issuance costs. b) 2006 Senior Notes Due 2016 In 2006, Allied World Assurance Company Holdings, Ltd, a Bermuda company (“Allied World Bermuda”) issued $500.0 million aggregate principal amount of 7.50% Senior Notes due August 1, 2016 (the “2006 Senior Notes”), with interest payable semi-annually . The 2006 Senior Notes were fully repaid at maturity by Allied World Bermuda. c) 2010 Senior Notes Due 2020 In November 2010, Allied World Bermuda issued $300.0 million aggregate principal amount of 5.50% Senior Notes due November 15, 2020 (the “2010 Senior Notes”), with interest on the notes payable semi-annually . The 2010 Senior Notes are Allied World Bermuda’s unsecured and unsubordinated obligations and rank equally in right of payment with all existing and future unsecured and unsubordinated indebtedness. Allied World Bermuda may redeem the 2010 Senior Notes at any time or from time to time in whole or in part at a redemption price equal to the greater of the principal amount of the 2010 Senior Notes to be redeemed or a make-whole price, plus accrued and unpaid interest. Allied World Bermuda has no current expectations of redeeming the notes prior to maturity. The 2010 Senior Notes include covenants and events of default that are usual and customary, but do not contain any financial covenants. d) 2015 Senior Notes Due 2025 In October 2015, Allied World Bermuda issued $500.0 million aggregate principal amount of 4.35% Senior Notes due October 29, 2025 (the “2025 Senior Notes”), with interest on the notes payable semi-annually . Proceeds from these senior notes were used to refinance the 2006 Senior Notes which matured in August 2016. The 2025 Senior Notes are Allied World Bermuda’s unsecured and unsubordinated obligations and rank equally in right of payment with all existing and future unsecured and unsubordinated indebtedness. Allied World Bermuda may redeem the 2025 Senior Notes at any time or from time to time in whole or in part at a redemption price equal to the greater of the principal amount of the 2025 Senior Notes to be redeemed or a make-whole price, in each case, plus accrued and unpaid interest. Allied World Bermuda has no current expectations of redeeming the notes prior to maturity. The 2025 Senior Notes include covenants and events of default that are usual and customary, but do not contain any financial covenants. e) Swiss Office Building Mortgage In 2014, the Company entered into a 20 -year mortgage commitment with a Swiss bank for the construction of a company-used office building in Zug, Switzerland. The total proceeds received in 2014 under the mortgage were $14.2 million (CHF 14.0 million ) with a fixed annual interest rate of 3.2% payable quarterly. An additional $4.0 million (CHF 4.0 million ) of proceeds from the mortgage was drawn during the first quarter of 2015. The mortgage payments are $0.3 million (CHF 0.3 million ) per year, plus accrued interest, for the first 19 years with the remaining balance payable at the end of the mortgage. The outstanding balance of the mortgage is included in “other long-term debt” on the consolidated balance sheets. f) Swiss Office Building Credit Facility In conjunction with the above mortgage commitment, the Company entered into a three -year credit facility with a Swiss bank that provides up to $5.1 million (CHF 5.0 million ) for general corporate purposes, however the Company will use the proceeds from the credit facility to fund the purchase of the office building in Zug, Switzerland. The Company utilized the full commitment of the credit facility to finance the purchase of the Swiss office space. The interest rate for the credit facility is 2.5% . The outstanding balance of the credit facility is included in “other long-term debt” on the consolidated balance sheets. g) Credit Facilities In the normal course of its operations, the Company enters into agreements with financial institutions to obtain secured and unsecured credit facilities. Allied World Bermuda has a collateralized amended letter of credit facility with Citibank Europe plc. that has been and will continue to be used to issue standby letters of credit. The maximum aggregate amount available under this letter of credit facility as of December 31, 2016 and 2015 was $900.0 million and $1.0 billion , respectively on an uncommitted basis. On November 27, 2007 , Allied World Bermuda entered into an $800.0 million five -year senior credit facility (the “Credit Facility”) with a syndication of lenders. The Credit Facility consisted of a $400.0 million secured letter of credit facility for the issuance of standby letters of credit (the “Secured Facility”) and a $400.0 million unsecured facility for the making of revolving loans and for the issuance of standby letters of credit. On June 7, 2012 , Allied World Bermuda amended the Secured Facility. The amended $450.0 million four -year secured credit facility (the “Amended Secured Credit Facility”) is primarily used for the issuance of standby letters of credit to support obligations in connection with the insurance and reinsurance business of Allied World Bermuda and its subsidiaries. A portion of the facility may also be used for revolving loans for general corporate and working capital purposes, up to a maximum of $150.0 million . Allied World Bermuda may request that existing lenders under the Amended Secured Credit Facility make additional commitments from time to time, up to $150.0 million , subject to approval by the lenders. The Amended Secured Credit Facility contains representations, warranties and covenants customary for similar bank loan facilities, including certain covenants that, among other things, require the Company to maintain a certain leverage ratio and financial strength rating. On November 12, 2014, Allied World Bermuda gave irrevocable notice to the administrative agent under the Amended Secured Credit Facility to reduce the aggregate commitment from $450.0 million to $150.0 million . All other material items of the Amended Secured Credit Facility remain unchanged. On June 16, 2016, Allied World Bermuda entered into a Credit Agreement that provides for a $200 million five -year senior unsecured revolving credit facility (the “Facility”) for the making of revolving loans and short-term swingline loans to the Company. The aggregate commitment of $200 million under the Facility may be increased by up to $150 million upon the Company's request and upon the agreement of one or more Lenders or additional lenders. Borrowings in the form of swingline loans are subject to a sublimit of $25 million included within the $200 million aggregate commitment. Borrowings under the Credit Agreement may be used by the Company for general corporate purposes. Borrowings under the Credit Agreement bear interest at a rate selected by the Company and equal to either the Base Rate or LIBOR plus a margin, other than swingline loans, which will only bear interest at the Base Rate plus a margin. The Credit Agreement requires that all revolving loans be repaid in full no later than the fifth anniversary of the Closing Date and that any swingline loans be repaid in full no later than the earlier of (i) ten business days after such swingline loan is made and (ii) the fifth anniversary of the Closing Date. The Company has unconditionally guaranteed the obligations under the Facility. The Company will pay customary arrangement and administration fees under the Credit Agreement. There is an additional fee payable at an annual rate based upon the long-term senior unsecured debt ratings of Allied World Switzerland and the Company in effect from time to time on the average daily unutilized commitments of the Lenders. The Facility replaced the four-year senior secured credit facility under the Amended Secured Credit Facility, dated as of June 7, 2012, by and among the Company, the lenders party thereto, Citibank, N.A., as syndication agent, and Wells Fargo Bank, National Association, as administrative agent, fronting bank and letters of credit agent. h) Debt Maturities The following table reflects the Company’s debt maturities, which includes its senior notes and other long-term debt: Amount 2017 $ 5.4 2018 0.3 2019 0.3 2020 300.3 2021 0.3 2022 and thereafter 515.4 Total $ 822.0

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income taxes	INCOME TAXES Under Swiss law, a resident company is subject to income tax at the federal, cantonal and communal levels that is levied on net income. Income attributable to permanent establishments or real estate located abroad is excluded from the Swiss tax base. Allied World Switzerland is a holding company and, therefore, is exempt from cantonal and communal income tax. As a result, Allied World Switzerland is subject to Swiss income tax only at the federal level. Allied World Switzerland is resident of the Canton of Zug and, as such, is subject to an annual cantonal and communal capital tax on the taxable equity of Allied World Switzerland in Switzerland. Allied World Switzerland has a Swiss operating company resident in the Canton of Zug. The operating company is subject to federal, cantonal and communal income tax and to annual cantonal and communal capital tax. Under current Bermuda law, Allied World Bermuda and its Bermuda subsidiaries are not required to pay taxes in Bermuda on either income or capital gains. Allied World Bermuda and Allied World Assurance Company, Ltd have received an assurance from the Bermuda Minister of Finance under the Exempted Undertakings Tax Protection Act 1966 of Bermuda, that in the event of any such taxes being imposed, Allied World Bermuda and Allied World Assurance Company, Ltd will be exempted until March 2035. Certain subsidiaries of Allied World Switzerland file U.S. federal income tax returns and various U.S. state income tax returns, as well as income tax returns in Canada, Hong Kong, Ireland, Singapore, Switzerland and the United Kingdom. The Company has open tax years that are potentially subject to examinations by local tax authorities, in the following major tax jurisdictions: the U.S., 2011 to 2016 ; the United Kingdom, 2015 and 2016 ; Ireland, 2012 to 2016 ; Switzerland, 2013 to 2016 ; Hong Kong, 2010 to 2016 ; and Singapore, 2012 to 2016 . The U.S. Internal Revenue Service (the “IRS”) is currently conducting an audit of the 2014 tax return of the U.S. services company. The audit is ongoing and the Company is not aware of any findings from the audit thus far. During the year ended December 31, 2016 , the IRS completed its audit of the 2012 consolidated tax return of the Company's U.S. subsidiaries. There were no findings as a result of the audit. To the best of the Company’s knowledge, there are no other income tax examinations pending by any other tax authority. Management has deemed all material tax positions to have a greater than 50% likelihood of being sustained based on technical merits if challenged. The Company does not expect any material unrecognized tax benefits within 12 months of December 31, 2016 . The components of income tax expense are as follows: Year Ended December 31, 2016 2015 2014 Current income tax expense $ 5.1 $ 9.8 $ 26.8 Deferred income tax (benefit) expense (14.2 ) (4.0 ) 3.7 Income tax (benefit) expense $ (9.1 ) $ 5.8 $ 30.5 Our income or loss is primarily sourced from our Bermuda, U.S., European, including Switzerland, and Asia Pacific operations. The income (loss) before income taxes for these operations are as follows: Year Ended December 31, 2016 2015 2014 Switzerland $ (25.5 ) $ (15.7 ) $ (19.0 ) Bermuda 336.6 162.1 460.2 United States (27.5 ) 12.8 72.9 All other jurisdictions (37.4 ) (69.5 ) 6.7 Income before income taxes $ 246.2 $ 89.7 $ 520.8 Deferred income taxes reflect the tax impact of temporary differences between the carrying amounts of assets and liabilities for financial reporting and income tax purposes. The significant components of the net deferred tax assets are as follows: December 31, 2016 2015 Deferred tax assets: Reserve for losses and loss expenses $ 17.7 $ 22.2 Equity compensation 16.0 14.2 Unearned premium 17.1 18.1 Deferred acquisition costs 11.9 10.5 Mark-to-market losses 8.6 — Net loss carryforward 21.0 27.3 Total deferred tax assets 92.3 92.3 Deferred tax liabilities: Intangible assets (21.9 ) (23.3 ) Mark-to-market gains — (3.0 ) Depreciation (4.4 ) (6.4 ) Market discount on bonds (2.0 ) (1.2 ) Other (1.2 ) (5.2 ) Total deferred tax liabilities (29.5 ) (39.1 ) Net deferred taxes before valuation allowance 62.8 53.2 Valuation allowance (24.1 ) (28.8 ) Net deferred tax assets $ 38.7 $ 24.4 The valuation allowance reported in the current period relates to net operating loss carryforwards for the European and Asia Pacific operations as it is unlikely those operations will have sufficient income to utilize the net loss carryforwards in the near term. The valuation allowance decreased by $4.7 million during the year ended December 31, 2016 compared to the year ended December 31, 2015. The decrease in the valuation allowance was due to the decrease in the net loss carryforwards. The net loss carryforwards from the United Kingdom and Asia Pacific operations do not expire. The net loss carryforward in our Swiss operations expire in seven years. Current tax receivable and payable has been included in “other assets” and “accounts payable and accrued liabilities” on the consolidated balance sheets, respectively. Current taxes receivable or payable was as follows: December 31, 2016 2015 Current tax receivable $ 5.5 $ 5.5 Current tax payable $ 0.7 $ 2.5 The expected tax provision has been calculated using the pre-tax accounting income in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. The statutory tax rates for our Swiss, Bermuda, U.S., Canada, Hong Kong, Ireland, Singapore and the United Kingdom operations are 7.8% , 0% , 35% , 15% , 16.5% , 12.5% , 17% and 20% , respectively. The reconciliation between the Company’s effective tax rate on pre-tax accounting income and the expected tax rate is as follows: Year Ended December 31, 2016 2015 2014 Expected tax rate 7.8 % 7.8 % 7.8 % Income not subject to income tax (10.7 )% (14.2 )% (7.1 )% Valuation allowance 4.4 % 14.5 % 2.3 % Foreign taxes at local expected tax rates (4.6 )% (1.7 )% 4.4 % Disallowed expenses and capital allowances 0.4 % 3.2 % 0.2 % Prior year refunds and adjustments (0.3 )% — % 1.2 % Other (0.7 )% (3.2 )% (2.9 )% Effective tax rate (3.7 )% 6.4 % 5.9 % The Company recorded a negative effective tax rate for the year ended December 31, 2016, due to recording an income tax benefit in most of our jurisdictions, due to pre-tax losses, while most of our pre-tax income was generated in Bermuda, which is not subject to income tax. During the year ended December 31, 2016, the income from the Company’s Bermuda operations represented 137% of the Company’s consolidated ‘income before income taxes’. The ‘Income not subject to income tax’ noted in the table above related to the income from the Company’s Bermuda operations, which are not subject to income tax. The change in this line item noted in the effective tax rate reconciliation for the year ended December 31, 2015 compared to the year ended December 31, 2014 was due to the income from the Company’s Bermuda operations representing a higher percentage of the Company’s consolidated ‘Income before income taxes’ during the year ended December 31, 2015 compared to the year ended December 31, 2014. During the years ended December 31, 2015 and 2014, the income from the Company’s Bermuda operations represented 181% and 88% , respectively, of the Company’s consolidated ‘income before income taxes’.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Shareholders' equity	SHAREHOLDERS’ EQUITY a) Authorized shares The issued share capital consists of the following: December 31, 2016 2015 Common shares issued and fully paid, 2016 and 2015: CHF 4.10 per share 93,586,418 95,523,230 Share capital at end of year $ 378.8 $ 386.7 2016 2015 Shares issued at beginning of year 95,523,230 100,775,256 Shares canceled (1,936,812 ) (5,252,026 ) Total shares issued at end of year 93,586,418 95,523,230 Treasury shares issued at beginning of year 4,563,595 4,579,774 Shares repurchased 4,669,513 6,047,437 Shares issued out of treasury (807,998 ) (811,590 ) Shares canceled (1,936,812 ) (5,252,026 ) Total treasury shares at end of year 6,488,298 4,563,595 Total shares outstanding at end of year 87,098,120 90,959,635 During the years ended December 31, 2016 and 2015 , 1,936,812 and 5,252,026 voting shares repurchased and designated for cancellation, respectively, were constructively retired and canceled. As required under Swiss law, the Company cannot hold more than 10% of its registered capital in treasury shares, unless such shares have been acquired in connection with a restriction on transferability, in which case the foregoing threshold is 20% . b) Dividends As a holding company, Allied World Switzerland’s principal source of income is dividends or other sources of permitted payments from its subsidiaries. These funds provide the cash flow required for dividend payments to the Company’s shareholders. The ability of the Company's insurance and reinsurance subsidiaries to make dividend payments is limited by the applicable laws and regulations of the various states and countries in which they operate. The Company’s primary restrictions on net assets of subsidiaries consist of regulatory requirements placed upon the regulated insurance and reinsurance subsidiaries to hold minimum amounts of total statutory capital and surplus and there were no other material restrictions on net assets in place as of December 31, 2016 . Under Swiss law, distributions to shareholders may be paid only if the Company has sufficient distributable profits from previous fiscal years, or if the Company has freely distributable reserves, each as presented on the audited stand-alone statutory balance sheet. Distributions to shareholders out of the share and participation capital may be made by way of a capital reduction in the form of a reduction to par value to achieve a similar result as the payment of a dividend. Under Swiss law, if the Company’s general capital reserves amount to less than 20% of the share and participation capital recorded in the Swiss Commercial Register, then at least 5% of the Company’s annual profit must be retained as general reserves. On May 1, 2014, the shareholders approved the Company’s proposal to pay cash dividends in the form of a distribution out of general legal reserve from capital contributions. The distribution amounts were paid to shareholders in quarterly installments of $0.225 per share in July 2014, October 2014, January 2015 and April 2015. On April 30, 2015, the shareholders approved the Company's proposal to pay cash dividends in the form of a distribution out of general legal reserve from capital contributions. The distribution amounts were paid to shareholders in quarterly installments of $0.26 per share in July 2015, October 2015, December 2015 and April 2016. On April 19, 2016, the shareholders approved the Company's proposal to pay cash dividends in the form of a distribution out of general legal reserve from capital contributions. The distribution amounts are paid to shareholders in quarterly installments of $0.26 per share. The first three installments of the dividend were paid to shareholders on June 30, 2016, September 29, 2016 and December 29, 2016. The fourth dividend scheduled for March 2017 will, subject to approval by the Company's shareholders, be deferred in conjunction with the announced transaction with Fairfax. The Company paid the following dividends during the years ended December 31, 2016 , 2015 and 2014 : Dividend Paid Dividend Share Total Paid December 29, 2016 $ 0.260 $ 22.6 September 29, 2016 $ 0.260 $ 22.6 June 30, 2016 $ 0.260 $ 22.8 March 31, 2016 $ 0.260 $ 23.4 December 31, 2015 $ 0.260 $ 23.7 October 1, 2015 $ 0.260 $ 23.6 July 2, 2015 $ 0.260 $ 23.6 April 2, 2015 $ 0.225 $ 21.5 January 2, 2015 $ 0.225 $ 21.7 October 2, 2014 $ 0.225 $ 21.7 July 2, 2014 $ 0.225 $ 21.9 April 3, 2014 $ 0.167 $ 16.5 c) Share Repurchases On April 19, 2016, the shareholders approved a share repurchase program (the “2016 share repurchase program”) in order for the Company to repurchase up to $500.0 million of its common shares. The 2016 share repurchase program supersedes the 2014 share repurchase program and no further repurchases will be made under the 2014 share repurchase program. Repurchases may be effected from time to time through open market purchases, privately negotiated transactions, tender offers or otherwise. The timing, form and amount of the share repurchases under the 2016 share repurchase program will depend on a variety of factors, including market conditions, the Company’s capital position, legal requirements and other factors. Under the terms of this share repurchase program, the first three million of common shares repurchased will remain in treasury and will be used by the Company to satisfy share delivery obligations under its equity-based compensation plans. Any additional common shares repurchased will be designated for cancellation at acquisition and will be canceled upon shareholder approval. Shares repurchased and designated for cancellation are constructively retired and recorded as a share cancellation. The Company does not anticipate repurchasing any of its common shares pending the completion of the Fairfax transaction. Shares repurchased by the Company and not designated for cancellation are classified as “Treasury shares, at cost” on the consolidated balance sheets. The Company will issue shares out of treasury principally related to the Company’s employee benefit plans. Shares repurchased and designated for cancellation are constructively retired and recorded as a share cancellation. The Company’s share repurchases were as follows: Year Ended December 31, 2016 2015 2014 Common shares repurchased 4,669,513 6,047,437 4,906,785 Total cost of shares repurchased $ 166.3 $ 245.3 $ 175.4 Average price per share $ 35.61 $ 40.56 $ 35.74 On May 6, 2015, the Company repurchased 4,053,537 shares from Exor S.A. at a repurchase price of $40.546 per share, for an aggregate purchase price of $164.4 million . The repurchase was executed under the 2014 share repurchase program.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee benefit plans	EMPLOYEE BENEFIT PLANS The Company implemented the Allied World Assurance Company Holdings, AG 2012 Omnibus Incentive Compensation Plan (the “2012 Omnibus Plan”). Under the 2012 Omnibus Plan, up to 4,500,000 common shares may be issued, subject to adjustment. The 2012 Omnibus Plan provides for the grant of options intended to qualify as incentive stock options under the Internal Revenue Code, non-qualified stock options, stock appreciation rights, restricted shares, RSUs, deferred share units, cash incentive awards, performance-based compensation awards and other equity-based and equity-related awards. These awards generally vest pro rata over four years from the date of grant, except for the performance-based awards that will generally vest over a three -year period based on the achievement of certain performance conditions. The Allied World Assurance Company Holdings, AG Third Amended and Restated 2001 Employee Stock Option Plan (the “Plan”), the Allied World Assurance Company Holdings, AG Third Amended and Restated 2004 Stock Incentive Plan and the Allied World Assurance Company Holdings, AG Third Amended and Restated Long-Term Incentive Plan (the “LTIP”) were automatically terminated, replaced and superseded by the 2012 Omnibus Plan on May 3, 2012, except that any outstanding awards granted under such plans remain in effect pursuant to their terms. a) Employee option plan Options under the Plan are exercisable in certain limited conditions, expire after 10 years , and generally vest pro-rata over four years from the date of grant. The exercise price of options issued were approved by the Compensation Committee but were not less than the fair market value of the common shares of Allied World Switzerland on the date the option award is granted. The Company has not granted stock options since 2011. The following table summarizes the activity related to options granted and exercised: Year Ended December 31, 2016 2015 2014 Options granted — — — Weighted average grant date fair value $ — $ — $ — Options exercised (428,938 ) (454,602 ) (479,831 ) Total intrinsic value of options exercised $ 10.8 $ 12.0 $ 10.3 Proceeds from option exercises $ 10.3 $ 10.1 $ 10.0 The activity related to the Company’s stock options is as follows: Year Ended December 31, 2016 Options Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value Outstanding at beginning of year 1,968,607 $ 16.86 Exercised (428,938 ) (15.24 ) Forfeited (13,926 ) 10.31 Outstanding at end of year 1,525,743 17.36 3.3 years $ 55.5 Exercisable at end of year 1,525,743 $ 17.36 3.3 years $ 55.5 As of December 31, 2016 , there was no remaining unrecognized compensation expense related to stock options granted under the Plan. b) Restricted stock units and performance-based equity awards The RSUs vest pro-rata over four years from the date of grant. The compensation expense for the RSUs is based on the fair market value of Allied World Switzerland’s common shares at the date of grant. The Company estimates the expected forfeitures of RSUs at the date of grant and recognizes compensation expense only for those awards that the Company expects to vest. The forfeiture assumption is ultimately adjusted to the actual forfeiture rate. Each award for the performance-based RSUs represents the right to receive a number of shares in the future, based upon the achievement of established performance criteria during the applicable performance period. The compensation expense for the performance-based RSUs is based on the fair market value of Allied World Switzerland's common shares at the time of grant. For the performance-based RSUs granted in 2016 , 2015 and 2014 , the Company anticipates that the performance goals are likely to be achieved. Based on the performance goals, the performance-based RSUs granted in 2016 , 2015 and 2014 are expensed at 100% , 100% and 55% , respectively, of the fair market value of Allied World Switzerland’s common shares on the date of grant. The expense is recognized over the performance period. The activity related to the Company’s RSU awards is as follows: Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Outstanding at beginning of year 819,309 $ 37.33 RSUs granted 689,042 32.00 RSUs forfeited (123,307 ) (34.80 ) RSUs fully vested (251,115 ) (36.30 ) Outstanding at end of year 1,133,929 $ 34.56 $ 60.9 As of December 31, 2016 , there remained $28.9 million of total unrecognized compensation expense related to 1,133,929 unvested RSUs awarded. This expense is expected to be recognized over a weighted-average period of 1.7 years . The activity related to the Company’s performance-based equity awards is as follows: Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Outstanding at beginning of year 591,683 $ 34.78 Performance-based equity awards granted 200,730 31.95 Additional awards granted due to achievement of performance criteria 24,979 29.24 Performance-based equity awards forfeited (16,993 ) (36.71 ) Performance-based equity awards fully vested (216,958 ) (29.24 ) Outstanding at end of year 583,441 $ 35.57 $ 31.3 As of December 31, 2016 , there was remaining $7.3 million of total unrecognized compensation expense related to 583,441 unvested performance-based equity awarded. This expense is expected to be recognized over a weighted-average period of 1.6 years . The RSUs and performance-based equity awards vested in 2016 , 2015 and 2014 had aggregate intrinsic values of $14.0 million , $16.9 million and $14.4 million , respectively, at the time of vesting. c) Cash-equivalent stock awards As part of the Company’s annual year-end compensation awards, the Company granted both stock-based awards and cash-equivalent stock awards. The cash-equivalent awards were granted to employees who received RSU and performance-based awards and were granted in lieu of granting the full award as a stock-based award. The cash-equivalent RSU awards vest pro-rata over four years from the date of grant. The cash-equivalent performance-based awards vest after a three -year performance period. As the cash-equivalent awards are settled in cash, the Company establishes a liability equal to the product of the fair market value of Allied World Switzerland’s common shares as of the end of the reporting period and the total awards outstanding. At December 31, 2016 , the liability was $32.2 million , and payments for awards vesting in the period are typically settled within the first three months of the year. The liability is included in “accounts payable and accrued expenses” in the consolidated balance sheets and changes in the liability are recorded in “general and administrative expenses” in the consolidated income statements. The activity related to the Company's cash-equivalent RSUs and performance-based equity awards is as follows: RSU's Performance-based Awards Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Number of Awards Weighted Average Grant Date Fair Value Outstanding at beginning of year 1,277,083 $ 31.94 693,477 33.25 Granted 167,438 31.95 50,183 31.95 Additional awards granted due to achievement of performance criteria — — 37,434 29.24 Forfeited (90,245 ) (33.66 ) (18,104 ) (35.27 ) Fully vested (581,829 ) (29.14 ) (325,386 ) (29.24 ) Outstanding at end of year 772,447 $ 33.86 437,604 $ 35.65 d) Total Stock-Related Compensation Expense The following table shows the total stock-related compensation expense relating to the stock options, RSUs, LTIPs and cash equivalent awards. Year Ended December 31, 2016 2015 2014 Stock options $ — $ 0.3 $ 1.9 RSUs and performance-based equity awards 16.4 15.0 12.3 Cash-equivalent stock awards 21.9 34.4 37.8 Total $ 38.3 $ 49.7 $ 52.0 e) Pension Plans The Company provides defined contribution retirement plans for its employees and officers. Contributions are made by the Company, and in some locations, these contributions are supplemented by the local plan participants. Contributions are based on a percentage of the participant’s base salary depending upon competitive local market practice and vesting provisions meeting legal compliance standards. The amount that an individual employee or officer can contribute may also be subject to regulatory requirements relating to the country of which the individual is a citizen. The Company incurred expenses for these defined contribution arrangements of $13.7 million , $13.5 million and $10.6 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. f) Employee Share Purchase Plan Under the Allied World Assurance Company Holdings, AG Amended and Restated 2008 Employee Share Purchase Plan (“ESPP”), eligible employees of the Company may purchase common shares of the Company at a 15% discount from the fair market value of one common share on the last trading day of each offering period. Employees purchase a variable number of common shares through payroll deductions elected as of the beginning of the offering period. The Company may sell up to 3,000,000 common shares to eligible employees under the ESPP.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings per share	EARNINGS PER SHARE The following table sets forth the comparison of basic and diluted earnings per share: Year Ended December 31, 2016 2015 2014 Basic earnings per share: Net income $ 255.3 $ 83.9 $ 490.3 Weighted average common shares outstanding 88,275,810 92,530,208 97,538,319 Basic earnings per share $ 2.89 $ 0.91 $ 5.03 Year Ended December 31, 2016 2015 2014 Diluted earnings per share: Net income $ 255.3 $ 83.9 $ 490.3 Weighted average common shares outstanding 88,275,810 92,530,208 97,538,319 Share equivalents: Stock options 839,038 1,031,666 1,432,960 RSU and PU awards 677,033 591,773 605,808 Employee share purchase plan 9,013 20,813 14,686 Weighted average common shares and common share equivalents outstanding — diluted 89,800,894 94,174,460 99,591,773 Diluted earnings per share $ 2.84 $ 0.89 $ 4.92 For the years ended December 31, 2016 , 2015 and 2014 , a weighted average of 229,359 , 308,405 and nil RSUs were considered anti-dilutive and were therefore excluded from the calculation of the diluted earnings per share, respectively.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	COMMITMENTS AND CONTINGENCIES a) Concentrations of Credit Risk Credit risk arises out of the failure of a counterparty to perform according to the terms of the contract. The Company’s investment portfolio is managed pursuant to guidelines that follow prudent standards of diversification. The guidelines limit the allowable holdings of a single issue and issuers. The Company believes that there are no significant concentrations of credit risk associated with its investment portfolio. As of December 31, 2016 and 2015 , substantially all of the Company’s cash and investments were held with one custodian. Insurance balances receivable primarily consist of net premiums due from insureds and reinsureds. The Company believes that the counterparties to these receivables are able to meet, and will meet, all of their obligations. The Company’s credit risk is further reduced by the contractual right to offset loss obligations or unearned premiums against premiums receivable. The insurance balances receivable that are outstanding greater than 90 days was $20.0 million as of December 31, 2016 , which represented 2.5% of the total receivable balance. Given the trend of writing more retail business, the Company has recorded an allowance for doubtful accounts against insurance balances receivable of $3.0 million as of December 31, 2016 . b) Operating Leases The Company leases office space under operating leases expiring in various years through 2031. The following are future minimum rental payments as of December 31, 2016 : Amount 2017 $ 21.6 2018 20.7 2019 19.6 2020 17.8 2021 16.9 2021 and thereafter 116.2 $ 212.8 Total rent expense for the years ended December 31, 2016 , 2015 and 2014 was $26.5 million , $25.9 million and $19.0 million , respectively. The rent expense for the years ended December 31, 2016 , 2015 and 2014 are net of sublease income of $1.8 million , $0.7 million and $0.1 million , respectively. c) Producers The three largest individual producers as a percentage of gross premiums written are as follows: Year Ended December 31, 2016 2015 2014 Marsh & McLennan Companies, Inc. 21 % 24 % 25 % Aon Corporation 14 % 16 % 17 % Willis Group Holdings 9 % 11 % 10 % d) Legal Proceedings The Company, in common with the insurance industry in general, is subject to litigation and arbitration in the normal course of its business. These legal proceedings generally relate to claims asserted by or against the Company in the ordinary course of insurance or reinsurance operations. Estimated amounts payable under these proceedings are included in the reserve for losses and loss expenses in the Company’s consolidated balance sheets. As of December 31, 2016 , the Company was not a party to any material legal proceedings arising outside the ordinary course of business that management believes will have a material adverse effect on the Company’s results of operations, financial position or cash flow.

Statutory Capital and Surplus

Statutory Capital and Surplus	12 Months Ended
	Dec. 31, 2016
Disclosure Dividend Restrictions And Statutory Requirements [Abstract]
Statutory capital and surplus	STATUTORY CAPITAL AND SURPLUS Allied World Switzerland’s ability to pay dividends is subject to certain regulatory restrictions on the payment of dividends by its subsidiaries. The payment of such dividends is limited by applicable laws and statutory requirements of the jurisdictions in which Allied World Switzerland and its subsidiaries operate. The total amount of restricted net assets for the Company’s consolidated subsidiaries as of December 31, 2016 was $2,678.3 million . The minimum required statutory capital and surplus is the amount of statutory capital and surplus necessary to satisfy regulatory requirements based on the Company’s current operations. The statutory capital and surplus and minimum required statutory capital and surplus for the Company’s most significant regulatory jurisdictions at December 31, 2016 and 2015 were as follows: December 31, 2016 December 31, 2015 Statutory Capital and Surplus Minimum Required Statutory Capital and Surplus Statutory Capital and Surplus Minimum Required Statutory Capital and Surplus Bermuda $ 3,494.1 $ 800.2 $ 3,270.9 $ 853.2 United States 1,185.9 263.3 1,215.5 241.0 Ireland 395.5 84.7 414.0 26.9 Switzerland 327.5 218.2 183.6 17.7 United Kingdom 268.4 264.1 245.9 231.8 There were no state-prescribed or permitted regulatory accounting practices for any of our insurance entities that resulted in reported statutory surplus that differed from that which would have been reported under the prescribed practices of the respective regulatory authorities, including the National Association of Insurance Commissioners. Statutory accounting under the prescribed practices of the respective regulatory authorities differs from U.S. GAAP accounting in the treatment of various items, including reporting of investments, acquisition costs and deferred income taxes. The statutory net income (loss) for the Company’s most significant regulatory jurisdictions for the years ended December 31, 2016 , 2015 and 2014 was as follows: Year Ended December 31, 2016 2015 2014 Bermuda $ 366.4 $ 221.5 $ 487.1 United States 19.0 40.5 45.4 Ireland 10.1 3.2 3.2 Switzerland 11.0 10.7 7.4 United Kingdom (5.1 ) (39.4 ) (7.8 ) At December 31, 2016 , the maximum amount of ordinary dividends or distributions that can be paid, without prior regulatory approval, for the Company’s most significant regulatory jurisdictions, were as follows: December 31, 2016 Bermuda $ 873.5 United States — Ireland 35.5 Switzerland — United Kingdom 2.7 a) Bermuda The Company’s Bermuda subsidiary, Allied World Assurance Company, Ltd, is registered under the Bermuda Insurance Act 1978 and Related Regulations as amended. As a Class 4 insurer, Allied World Assurance Company, Ltd is required to maintain minimum solvency standards and to hold available statutory capital and surplus equal to or exceeding the enhanced capital requirements as determined by the Bermuda Monetary Authority under the Bermuda Solvency Capital Requirement model (“BSCR model”). The BSCR model is a risk-based capital model that provides a method for determining an insurer’s minimum required capital taking into account the risk characteristics of different aspects of the company’s business. In addition, this subsidiary is required to maintain a minimum liquidity ratio. As of December 31, 2016 and 2015 , this subsidiary met the requirements. b) United States The Company’s U.S. insurance subsidiaries are subject to the insurance laws and regulations of the states in which they are domiciled, and also states in which they are licensed or authorized to transact business. These laws also restrict the amount of ordinary shareholder dividends the subsidiaries can pay. The restrictions are generally based on statutory surplus and/or statutory net income as determined in accordance with the relevant statutory accounting requirements of the individual domiciliary states. The U.S. subsidiaries are required to file annual statements with insurance regulatory authorities prepared on an accounting basis prescribed or permitted by such authorities. The U.S. subsidiaries are also required to maintain minimum levels of solvency and liquidity as determined by law, and comply with capital requirements and licensing rules. As of December 31, 2016 and 2015 , the actual levels of solvency, liquidity and capital of each U.S. subsidiary were in excess of the minimum levels required. c) Ireland The Company’s Irish insurance subsidiary is regulated by the Central Bank of Ireland pursuant to the Insurance Acts 1909 to 2000, the Central Bank Acts 1942 to 2015 and all statutory instruments relating to insurance made or adopted under the European Communities Acts 1972 to 2014, including the European Union (Insurance and Reinsurance) Regulations, 2015. This subsidiary is required to maintain a minimum level of capital. As of December 31, 2016 and 2015 , these requirements were met. The amount of dividends that this subsidiary is permitted to distribute is restricted to accumulated realized profits that have not been capitalized or distributed, less accumulated realized losses that have not been written off. The solvency and capital requirements must still be met following any distribution. d) Switzerland The Company’s Swiss insurance subsidiary, Allied World Assurance Company, AG, is regulated by the Swiss Financial Market Supervisory Authority (“FINMA”) pursuant to the Insurance Supervisory Law. This subsidiary’s accounts are prepared in accordance with the Swiss Code of Obligations and the Insurance Supervisory Law. This subsidiary is obligated to maintain a minimum level of capital based on the Swiss Code of Obligation, a minimum of tied assets based on the Insurance Supervisory Law and a minimum solvency margin in accordance with the Swiss Solvency Test. As of December 31, 2016 and 2015 , this subsidiary met the requirements. The amount of dividends that this subsidiary is permitted to distribute is restricted to freely distributable reserves which consist of retained earnings, the current year profit and legal reserves to a certain extent. Any dividend requires approval of the shareholders and in case of the dividend exceeding the current year profit, approval is also required from FINMA. The solvency and capital requirements must still be met following any distribution. e) United Kingdom Allied World Capital (Europe) Limited is the sole corporate member of Syndicate 2232. Syndicate 2232 is managed by Allied World Managing Agency Limited, which is authorized and regulated by the Prudential Regulatory Authority ("PRA") and the Financial Conduct Authority. As a member of Lloyd’s, Allied World Capital (Europe) Limited is obliged to comply with Lloyd’s byelaws and regulations (made pursuant to the Lloyd’s Acts 1871 to 1982) and applicable provisions of the Financial and Services and Markets Act 2000. The Council of Lloyd’s has wide discretionary powers to regulate members’ underwriting at Lloyd’s and its exercise of these powers might affect the return on an investment of the corporate member in a given underwriting year. The capital required to support a Syndicate’s underwriting capacity, referred to as “funds at Lloyd’s”, is assessed annually and is determined by Lloyd’s in accordance with the capital adequacy rules established by the PRA. If a member of Lloyd’s is unable to pay its debts to policyholders, such debts may be payable from the Lloyd’s Central Fund, which in many respects acts as an equivalent to a state guaranty fund in the United States. The Company has provided capital to support the underwriting of Syndicate 2232 in the form of pledged assets provided by Allied World Assurance Company, Ltd. The amount which the Company provides as funds at Lloyd’s is not available for distribution to the Company for the payment of dividends. Lloyd’s is supervised by the PRA and required to implement certain rules prescribed by the PRA under the Lloyd’s Act of 1982 regarding the operation of the Lloyd’s market. With respect to managing agents and corporate members, Lloyd’s prescribes certain minimum standards relating to management and control, solvency and other requirements and monitors managing agents’ compliance with such standards. f) Branch Offices The Company’s insurance subsidiaries maintain branch offices in Australia, Bermuda, Canada, Hong Kong, Labuan, Singapore, Switzerland and the United Kingdom. As branch offices are not considered separate legal entities, the required and actual statutory capital and surplus amounts for each jurisdiction in the table above include amounts related to the branch offices. These branch offices are subject to additional minimum capital or asset requirements in their countries of domicile. At December 31, 2016 and 2015 , the actual capital and surplus for each of these branches exceeded the relevant local regulatory requirements.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment information	SEGMENT INFORMATION The determination of reportable segments is based on how the Company's chief operating decision maker, the Chief Executive Officer, monitors the Company’s underwriting operations. Management monitors the performance of its direct underwriting operations based on the geographic location of the Company’s offices, the markets and customers served and the type of accounts written. The Company is currently organized into three operating segments: North American Insurance, Global Markets Insurance and Reinsurance. All product lines fall within these classifications. The North American Insurance segment includes the Company’s specialty insurance operations in the United States, Bermuda and Canada, as well as the Company's claims administration services operation. This segment provides both property and specialty casualty insurance primarily to North American domiciled accounts. The Global Markets Insurance segment includes the Company’s specialty insurance operations in Europe and Asia Pacific, which includes offices in Dublin, Hong Kong, Labuan, London, Singapore, Sydney, and Zug, as well as the Company's insurance agency operation. This segment provides both property and casualty insurance primarily to non-North American domiciled accounts. The Reinsurance segment includes the Company’s reinsurance operations in Bermuda, Labuan, London, New York, Singapore, and Zug. This segment provides reinsurance of property, general casualty, professional liability, specialty lines and property catastrophe coverages written by insurance companies. The Company presently writes reinsurance on both a treaty and a facultative basis, targeting several niche reinsurance markets. Responsibility and accountability for the results of underwriting operations are assigned by major line of business within each segment. Because the Company does not manage its assets by segment, investment income, interest expense and total assets are not allocated to individual reportable segments. General and administrative expenses are allocated to segments based on various factors, including staff count and each segment’s proportional share of gross premiums written. The Company measures its segment income or loss as underwriting income or loss plus other insurance-related income and expenses, which may include the net earnings from the claims administration services operation, insurance agency operation, derivative insurance and reinsurance contracts and other income or expense that is not directly related to our underwriting operations. Management measures results of each segment's underwriting income or loss on the basis of the “loss and loss expense ratio,” “acquisition cost ratio,” “general and administrative expense ratio”, “expense ratio” and the “combined ratio.” The “loss and loss expense ratio” is derived by dividing net losses and loss expenses by net premiums earned. The “acquisition cost ratio” is derived by dividing acquisition costs by net premiums earned. The “general and administrative expense ratio” is derived by dividing general and administrative expenses by net premiums earned. The expense ratio is the sum of the “acquisition cost ratio” and the “general and administrative expense ratio”. The “combined ratio” is the sum of the “loss and loss expense ratio,” the “acquisition cost ratio” and the “general and administrative expense ratio.” The following tables provide a summary of the segment results: Year Ended December 31, 2016 North American Insurance Global Markets Insurance Reinsurance Total Gross premiums written $ 1,856.3 $ 503.3 $ 706.2 $ 3,065.8 Net premiums written 1,223.4 367.5 664.9 2,255.8 Net premiums earned 1,266.9 377.8 699.4 2,344.1 Net losses and loss expenses (862.2 ) (269.5 ) (370.1 ) (1,501.8 ) Acquisition costs (132.0 ) (66.5 ) (141.3 ) (339.8 ) General and administrative expenses (223.3 ) (123.7 ) (64.5 ) (411.5 ) Underwriting income (loss) 49.4 (81.9 ) 123.5 91.0 Other insurance-related revenue 6.7 1.4 4.3 12.4 Other insurance-related expenses (2.3 ) (1.1 ) (3.4 ) (6.8 ) Segment income (loss) 53.8 (81.6 ) 124.4 96.6 Net investment income 217.8 Net realized investment gains 2.1 Amortization and impairment of intangible assets (10.7 ) Interest expense (63.7 ) Foreign exchange gain 4.1 Income before income taxes $ 246.2 Loss and loss expense ratio 68.1 % 71.3 % 52.9 % 64.1 % Acquisition cost ratio 10.4 % 17.6 % 20.2 % 14.5 % General and administrative expense ratio 17.6 % 32.7 % 9.2 % 17.6 % Expense ratio 28.0 % 50.3 % 29.4 % 32.1 % Combined ratio 96.1 % 121.6 % 82.3 % 96.2 % Year Ended December 31, 2015 North American Insurance Global Markets Reinsurance Total Gross premiums written $ 1,815.3 $ 476.3 $ 801.4 $ 3,093.0 Net premiums written 1,358.1 324.1 765.8 2,448.0 Net premiums earned 1,301.4 366.8 820.2 2,488.4 Net losses and loss expenses (910.2 ) (240.3 ) (435.8 ) (1,586.3 ) Acquisition costs (139.6 ) (70.9 ) (164.9 ) (375.4 ) General and administrative expenses (224.6 ) (108.4 ) (73.3 ) (406.3 ) Underwriting income (loss) 27.0 (52.8 ) 146.2 120.4 Other insurance-related revenue 3.5 — — 3.5 Other insurance-related expenses (2.7 ) (2.5 ) (1.0 ) (6.2 ) Segment income (loss) 27.8 (55.3 ) 145.2 117.7 Net investment income 182.1 Net realized investment losses (127.6 ) Amortization and impairment of intangible assets (9.8 ) Interest expense (61.4 ) Foreign exchange loss (11.3 ) Income before income taxes $ 89.7 Loss and loss expense ratio 69.9 % 65.5 % 53.1 % 63.7 % Acquisition cost ratio 10.7 % 19.3 % 20.1 % 15.1 % General and administrative expense ratio 17.3 % 29.5 % 8.9 % 16.3 % Expense ratio 28.0 % 48.8 % 29.0 % 31.4 % Combined ratio 97.9 % 114.3 % 82.1 % 95.1 % Year Ended December 31, 2014 North American Insurance Global Markets Reinsurance Total Gross premiums written $ 1,716.3 $ 280.5 $ 938.6 $ 2,935.4 Net premiums written 1,230.8 188.0 903.2 2,322.0 Net premiums earned 1,111.1 162.6 909.0 2,182.7 Net losses and loss expenses (683.8 ) (61.1 ) (454.3 ) (1,199.2 ) Acquisition costs (105.9 ) (18.2 ) (171.0 ) (295.1 ) General and administrative expenses (219.6 ) (68.1 ) (78.0 ) (365.7 ) Underwriting income 101.8 15.2 205.7 322.7 Other insurance-related revenue 2.1 — — 2.1 Other insurance-related expenses (1.9 ) (6.7 ) — (8.6 ) Segment income 102.0 8.5 205.7 316.2 Net investment income 176.9 Net realized investment gains 89.0 Amortization of intangible assets (2.5 ) Interest expense (57.8 ) Foreign exchange loss (1.0 ) Income before income taxes $ 520.8 Loss and loss expense ratio 61.5 % 37.6 % 50.0 % 54.9 % Acquisition cost ratio 9.5 % 11.2 % 18.8 % 13.5 % General and administrative expense ratio 19.8 % 41.9 % 8.6 % 16.8 % Expense ratio 29.3 % 53.1 % 27.4 % 30.3 % Combined ratio 90.8 % 90.7 % 77.4 % 85.2 % The following table shows an analysis of the Company’s gross premiums written by geographic location of the Company’s subsidiaries. All intercompany premiums have been eliminated. Year Ended December 31, 2016 2015 2014 United States $ 1,903.4 $ 1,893.4 $ 1,795.6 Bermuda 495.4 543.6 640.9 Asia Pacific 352.2 313.1 167.3 Europe 296.3 326.9 318.6 Canada 18.5 16.0 13.0 Total gross premiums written $ 3,065.8 $ 3,093.0 $ 2,935.4 Gross premiums written attributable to Switzerland were $46.5 million , $58.2 million and $67.6 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. The following table shows the Company’s net premiums earned by line of business for each segment for the years ended December 31, 2016 , 2015 and 2014 . Year Ended December 31, 2016 2015 2014 North American Insurance: Casualty $ 396.7 $ 424.0 $ 334.6 Professional liability 388.5 385.3 276.1 Property 127.6 162.8 170.3 Healthcare 66.5 102.9 168.5 Programs 170.4 150.7 119.8 Specialty and other 117.2 75.6 41.9 Total 1,266.9 1,301.4 1,111.1 Global Markets Insurance: Property 67.9 106.7 34.0 Professional liability 96.2 102.5 69.1 Specialty and other 125.9 99.8 44.2 Casualty 87.8 57.8 15.3 Total 377.8 366.8 162.6 Reinsurance: Property 337.2 403.5 412.0 Casualty 183.7 224.4 175.5 Specialty 178.5 192.3 321.5 Total 699.4 820.2 909.0 Total net premiums earned $ 2,344.1 $ 2,488.4 $ 2,182.7

Condensed Consolidated Guaranto

Condensed Consolidated Guarantor Financial Statements	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidated guarantor financial statements	CONDENSED CONSOLIDATED PARENT COMPANY AND GUARANTOR FINANCIAL STATEMENTS The following tables present condensed consolidating financial information as of December 31, 2016 and 2015 and for the years ended December 31, 2016 , 2015 and 2014 for Allied World Switzerland (the “Parent Guarantor”) and Allied World Bermuda (the “Subsidiary Issuer”). The Subsidiary Issuer is a direct 100% -owned subsidiary of the Parent Guarantor. Investments in subsidiaries are accounted for by the Parent Guarantor under the equity method for purposes of the supplemental consolidating presentation. Earnings of subsidiaries are reflected in the Parent Guarantor’s investment accounts and earnings. The Parent Guarantor fully and unconditionally guarantees the senior notes issued by the Subsidiary Issuer. Condensed Consolidating Balance Sheet: As of December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated ASSETS: Investments $ — $ — $ 7,942.3 $ — $ 7,942.3 Cash and cash equivalents 13.1 0.8 707.0 — 720.9 Insurance balances receivable — — 784.0 — 784.0 Funds held — — 466.8 — 466.8 Reinsurance recoverable — — 1,625.0 — 1,625.0 Reinsurance recoverable on paid losses — — 104.4 — 104.4 Net deferred acquisition costs — — 121.1 — 121.1 Goodwill and intangible assets — — 494.4 — 494.4 Balances receivable on sale of investments — — 114.7 — 114.7 Investments in subsidiaries 3,433.7 4,020.1 — (7,453.8 ) — Due from subsidiaries 115.6 — 29.9 (145.5 ) — Other assets 1.8 0.8 802.8 — 805.4 Total assets $ 3,564.2 $ 4,021.7 $ 13,192.4 $ (7,599.3 ) $ 13,179.0 LIABILITIES: Reserve for losses and loss expenses $ — $ — $ 6,639.2 $ — $ 6,639.2 Unearned premiums — — 1,688.1 — 1,688.1 Reinsurance balances payable — — 223.3 — 223.3 Balances due on purchases of investments — — 79.7 — 79.7 Senior notes — 794.2 — — 794.2 Other long-term debt — — 22.0 — 22.0 Due to subsidiaries 9.9 20.0 115.6 (145.5 ) — Other liabilities 2.5 5.7 172.6 — 180.7 Total liabilities 12.4 819.9 8,940.5 (145.5 ) 9,627.2 Total shareholders’ equity 3,551.8 3,201.8 4,251.9 (7,453.8 ) 3,551.8 Total liabilities and shareholders’ equity $ 3,564.2 $ 4,021.7 $ 13,192.4 $ (7,599.3 ) $ 13,179.0 As of December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated ASSETS: Investments $ — $ — $ 8,571.2 $ — $ 8,571.2 Cash and cash equivalents 21.8 1.0 585.2 — 608.0 Insurance balances receivable — — 745.9 — 745.9 Funds held — — 640.8 — 640.8 Reinsurance recoverable — — 1,480.0 — 1,480.0 Reinsurance recoverable on paid losses — — 96.4 — 96.4 Net deferred acquisition costs — — 165.2 — 165.2 Goodwill and intangible assets — — 504.7 — 504.7 Balances receivable on sale of investments — — 36.9 — 36.9 Investments in subsidiaries 3,347.0 4,396.3 — (7,743.3 ) — Due from subsidiaries 173.1 36.4 16.8 (226.3 ) — Other assets 1.8 0.1 660.9 — 662.8 Total assets $ 3,543.7 $ 4,433.8 $ 13,504.0 $ (7,969.6 ) $ 13,511.9 LIABILITIES: Reserve for losses and loss expenses $ — $ — $ 6,456.2 $ — $ 6,456.2 Unearned premiums — — 1,683.3 — 1,683.3 Reinsurance balances payable — — 214.4 — 214.4 Balances due on purchases of investments — — 125.1 — 125.1 Senior notes — 1,292.9 — — 1,292.9 Other long-term debt — — 23.0 — 23.0 Due to subsidiaries 8.5 8.3 209.5 (226.3 ) — Other liabilities 2.7 22.2 159.7 — 184.5 Total liabilities 11.2 1,323.4 8,871.2 (226.3 ) 9,979.4 Total shareholders’ equity 3,532.5 3,110.4 4,632.8 (7,743.3 ) 3,532.5 Total liabilities and shareholders’ equity $ 3,543.7 $ 4,433.8 $ 13,504.0 $ (7,969.6 ) $ 13,511.9 Condensed Consolidating Income Statement: Year Ended December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,344.1 $ — $ 2,344.1 Net investment income 0.1 0.1 217.6 — 217.8 Net realized investment losses — — 2.1 — 2.1 Other income — — 12.4 — 12.4 Net losses and loss expenses — — (1,501.8 ) — (1,501.8 ) Acquisition costs — — (339.8 ) — (339.8 ) General and administrative expenses (18.7 ) 0.2 (393.0 ) — (411.5 ) Other expense — — (6.8 ) — (6.8 ) Amortization of intangible assets — — (10.7 ) — (10.7 ) Interest expense — (61.6 ) (2.1 ) — (63.7 ) Foreign exchange gain (loss) — — 4.1 — 4.1 Income tax (expense) benefit (0.1 ) — 9.2 — 9.1 Equity in earnings of consolidated subsidiaries 274.0 341.9 — (615.9 ) — NET INCOME (LOSS) $ 255.3 $ 280.6 $ 335.3 $ (615.9 ) $ 255.3 Other comprehensive income (loss) (2.3 ) — (2.3 ) 2.3 (2.3 ) COMPREHENSIVE INCOME (LOSS) $ 253.0 $ 280.6 $ 333.0 $ (613.6 ) $ 253.0 Year Ended December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,488.4 $ — $ 2,488.4 Net investment income — 0.1 182.0 — 182.1 Net realized investment gains — — (127.6 ) — (127.6 ) Other income — — 3.5 — 3.5 Net losses and loss expenses — — (1,586.3 ) — (1,586.3 ) Acquisition costs — — (375.4 ) — (375.4 ) General and administrative expenses (36.7 ) (0.5 ) (369.1 ) — (406.3 ) Other expense — — (6.2 ) — (6.2 ) Amortization of intangible assets — — (9.8 ) — (9.8 ) Interest expense — (59.2 ) (2.2 ) — (61.4 ) Foreign exchange gain (loss) — — (11.3 ) — (11.3 ) Income tax (expense) benefit (0.1 ) — (5.7 ) — (5.8 ) Equity in earnings of consolidated subsidiaries 120.7 157.3 — (278.0 ) — NET INCOME (LOSS) $ 83.9 $ 97.7 $ 180.3 $ (278.0 ) $ 83.9 Other comprehensive income (loss) (9.3 ) — (9.3 ) 9.3 (9.3 ) COMPREHENSIVE INCOME (LOSS) $ 74.6 $ 97.7 $ 171.0 $ (268.7 ) $ 74.6 Year Ended December 31, 2014 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,182.7 $ — $ 2,182.7 Net investment income 0.1 — 176.8 — 176.9 Net realized investment gains — — 89.0 — 89.0 Other income — — 2.1 — 2.1 Net losses and loss expenses — — (1,199.2 ) — (1,199.2 ) Acquisition costs — — (295.1 ) — (295.1 ) General and administrative expenses (35.6 ) (3.1 ) (327.1 ) — (365.7 ) Other expense — — (8.6 ) — (8.6 ) Amortization of intangible assets — — (2.5 ) — (2.5 ) Interest expense — (55.4 ) (2.3 ) — (57.8 ) Foreign exchange gain (loss) — 0.1 (1.1 ) — (1.0 ) Income tax (expense) benefit (0.1 ) — (30.4 ) — (30.5 ) Equity in earnings of consolidated subsidiaries 525.9 564.6 — (1,090.5 ) — NET INCOME (LOSS) $ 490.3 $ 506.2 $ 584.3 $ (1,090.5 ) $ 490.3 Other comprehensive income (loss) — — — — — COMPREHENSIVE INCOME (LOSS) $ 490.3 $ 506.2 $ 584.3 $ (1,090.5 ) $ 490.3 Condensed Consolidating Statement of Cash Flows: Year Ended December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES $ 238.8 $ 506.4 $ 493.6 $ (841.0 ) $ 397.8 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases trading securities — — (5,423.7 ) — (5,423.7 ) Purchases of other invested assets — — (119.0 ) — (119.0 ) Sales of trading securities — — 5,929.9 — 5,929.9 Sales of other invested assets — — 96.3 — 96.3 Net cash paid for acquisitions — — (1.2 ) — (1.2 ) Return of investment in subsidiary — 250.0 — (250.0 ) — Other — — (19.4 ) — (19.4 ) Net cash provided by (used in) investing activities — 250.0 462.9 (250.0 ) 462.9 CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (91.5 ) — — — (91.5 ) Intercompany dividends paid — (256.6 ) (584.4 ) 841.0 — Proceeds to parent — — (250.0 ) 250.0 — Proceeds from the exercise of stock options 10.3 — — — 10.3 Share repurchases (166.3 ) — — — (166.3 ) Repayment of senior notes — (500.0 ) — — (500.0 ) Repayment of other long-term debt — — (0.3 ) — (0.3 ) Net cash provided by (used in) financing activities (247.5 ) (756.6 ) (834.7 ) 1,091.0 (747.8 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS (8.7 ) (0.2 ) 121.8 — 112.9 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 21.8 1.0 585.2 — 608.0 CASH AND CASH EQUIVALENTS, END OF YEAR $ 13.1 $ 0.8 $ 707.0 $ — $ 720.9 Year Ended December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES $ 339.6 $ 377.7 $ 598.1 $ (811.1 ) $ 504.3 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases of trading securities — — (5,863.2 ) — (5,863.2 ) Purchases of other invested assets — — (126.7 ) — (126.7 ) Sales of trading securities — — 5,328.8 — 5,328.8 Sales of other invested assets — — 161.3 — 161.3 Net cash paid for acquisitions — — (124.4 ) — (124.4 ) Capital contributions — (496.7 ) 496.7 — — Other — — (11.5 ) — (11.5 ) Net cash provided by (used in) investing activities — (496.7 ) (139.0 ) — (635.7 ) CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (114.1 ) — — — (114.1 ) Intercompany dividends paid — (378.4 ) (432.7 ) 811.1 — Proceeds from the exercise of stock options 10.1 — — — 10.1 Share repurchases (246.4 ) — — — (246.4 ) Proceeds from senior notes — 496.7 — — 496.7 Proceeds from other long-term debt — — 4.0 — 4.0 Repayment of other long-term debt — — (0.2 ) — (0.2 ) Net cash provided by (used in) financing activities (350.4 ) 118.3 (428.9 ) 811.1 150.1 NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS (10.8 ) (0.7 ) 30.2 — 18.7 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 32.6 1.7 555.0 — 589.3 CASH AND CASH EQUIVALENTS, END OF YEAR $ 21.8 $ 1.0 $ 585.2 $ — $ 608.0 Year Ended December 31, 2014 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES: $ 264.4 $ 292.9 $ 493.8 $ (643.3 ) $ 407.8 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases of trading securities — — (7,630.0 ) — (7,630.0 ) Purchases of other invested assets — — (307.9 ) — (307.9 ) Sales of trading securities — — 7,536.9 — 7,536.9 Sales of other invested assets — — 267.9 — 267.9 Net cash paid for acquisitions — — (2.6 ) — (2.6 ) Other — — 8.7 — 8.7 Net cash provided by (used in) investing activities — — (127.0 ) — (127.0 ) CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (76.7 ) — — — (76.7 ) Intercompany dividends paid — (294.0 ) (349.3 ) 643.3 — Proceeds from the exercise of stock options 10.0 — — — 10.0 Share repurchases (175.9 ) — — — (175.9 ) Proceeds from other long-term debt — — 19.2 — 19.2 Net cash provided by (used in) financing activities (242.6 ) (294.0 ) (330.1 ) 643.3 (223.4 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS 21.8 (1.1 ) 36.7 — 57.4 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 10.8 2.8 518.3 — 531.9 CASH AND CASH EQUIVALENTS, END OF YEAR $ 32.6 $ 1.7 $ 555.0 $ — $ 589.3 Notes to Parent Company Condensed Financial Information a) Dividends Allied World Switzerland received cash dividends from its subsidiaries of $256.6 million , $378.4 million and $294.0 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. Such dividends are included in “cash flows provided by (used in) operating activities” in the condensed consolidating statement of cash flows.

Unaudited Quarterly Financial D

Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Unaudited quarterly financial data	UNAUDITED QUARTERLY FINANCIAL DATA The following are the unaudited consolidated statements of income by quarter for the years ended December 31, 2016 and 2015 : Quarter Ended December 31, September 30, June 30, March 31, REVENUES: Gross premiums written $ 671.7 $ 730.2 $ 800.3 $ 863.5 Premiums ceded (226.4 ) (201.9 ) (222.2 ) (159.5 ) Net premiums written 445.3 528.3 578.1 704.0 Change in unearned premiums 131.7 55.7 24.8 (123.9 ) Net premiums earned 577.0 584.0 602.9 580.1 Net investment income 58.1 50.6 55.8 53.3 Net realized investment (losses) gains (101.9 ) 10.7 74.5 18.9 Other income 4.8 1.8 5.2 0.6 538.0 647.1 738.4 652.9 EXPENSES: Net losses and loss expenses 387.8 376.3 365.4 372.4 Acquisition costs 82.0 82.0 87.4 88.3 General and administrative expenses 106.1 104.2 104.7 96.4 Other expense 1.8 2.2 1.7 1.1 Amortization and impairment of intangible assets 3.2 2.5 2.5 2.5 Interest expense 10.4 13.5 19.9 20.0 Foreign exchange loss (gain) 0.8 1.0 (2.9 ) (3.0 ) 592.1 581.7 578.7 577.7 (Loss) income before income taxes (54.1 ) 65.4 159.7 75.2 Income tax (benefit) expense) (13.3 ) (3.2 ) 6.3 1.1 NET (LOSS) INCOME $ (40.8 ) $ 68.6 $ 153.4 $ 74.1 PER SHARE DATA Basic (loss) earnings per share $ (0.47 ) $ 0.79 $ 1.73 $ 0.82 Diluted (loss) earnings per share $ (0.47 ) $ 0.77 $ 1.70 $ 0.81 Weighted average common shares outstanding 87,036,339 87,102,290 88,742,484 90,254,512 Weighted average common shares and common share equivalents outstanding 87,036,339 88,603,101 90,040,509 91,559,225 Quarter Ended December 31, September 30, June 30, March 31, REVENUES: Gross premiums written $ 632.3 $ 754.1 $ 826.0 $ 880.6 Premiums ceded (167.5 ) (147.1 ) (222.3 ) (108.1 ) Net premiums written 464.8 607.0 603.7 772.5 Change in unearned premiums 158.0 43.7 42.7 (204.0 ) Net premiums earned 622.8 650.7 646.4 568.5 Net investment income 49.1 45.7 42.8 44.5 Net realized investment (losses) gains (38.8 ) (113.6 ) (20.2 ) 45.0 Other income 1.0 0.7 0.9 0.9 634.1 583.5 669.9 658.9 EXPENSES: Net losses and loss expenses 412.7 416.9 431.5 325.2 Acquisition costs 96.0 100.1 100.6 78.7 General and administrative expenses 95.0 105.8 108.4 97.1 Other expense 1.9 1.3 1.2 1.8 Amortization and impairment of intangible assets 3.7 2.7 2.8 0.6 Interest expense 18.1 14.5 14.5 14.3 Foreign exchange loss (gain) 0.9 (0.8 ) 1.3 9.9 628.3 640.5 660.3 527.6 Income (loss) before income taxes 5.8 (57.0 ) 9.6 131.3 Income tax expense (benefit) 4.0 (5.3 ) 0.1 7.0 NET INCOME (LOSS) $ 1.8 $ (51.7 ) $ 9.5 $ 124.3 PER SHARE DATA Basic earnings (loss) per share 0.02 (0.57 ) 0.10 1.30 Diluted earnings (loss) per share 0.02 (0.57 ) 0.10 1.27 Weighted average common shares outstanding 90,934,107 90,882,511 92,441,730 95,935,551 Weighted average common shares and common share equivalents outstanding 92,422,422 90,882,511 93,984,226 97,577,029

Schedule III - Supplementary In

Schedule III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2016
Supplementary Insurance Information [Abstract]
Schedule III - Supplementary insurance information	Schedule III ALLIED WORLD ASSURANCE COMPANY HOLDINGS, AG SUPPLEMENTARY INSURANCE INFORMATION (Expressed in thousands of United States dollars) Year Ended December 31, 2016 Net Deferred Acquisition Costs Reserve for Losses and Loss Expenses Unearned Premiums Net Premiums Earned Net Investment Income Losses and Loss Expenses Amortization of Deferred Acquisition Costs Other Operating Costs Net Premiums Written North American Insurance $ 40.7 $ 4,191.3 $ 1,118.2 $ 1,266.9 $ — $ 862.2 $ 132.0 $ 223.3 $ 1,223.4 Global Markets Insurance 21.5 983.6 312.8 377.8 — 269.5 66.5 123.7 367.5 Reinsurance 58.9 1,464.3 257.1 699.4 — 370.1 141.3 64.5 664.9 Corporate — — — — 217.8 — — — — Total $ 121.1 $ 6,639.2 $ 1,688.1 $ 2,344.1 $ 217.8 $ 1,501.8 $ 339.8 $ 411.5 $ 2,255.8 Year Ended December 31, 2015 Net Deferred Acquisition Costs Reserve for Losses and Loss Expenses Unearned Premiums Net Premiums Earned Net Investment Income Losses and Loss Expenses Amortization of Deferred Acquisition Costs Other Operating Costs Net Premiums Written North American Insurance $ 70.1 $ 3,998.2 $ 1,061.5 $ 1,301.4 $ — $ 910.2 $ 139.6 $ 224.6 $ 1,358.1 Global Markets Insurance 26.2 972.4 327.8 366.8 — 240.3 70.9 108.4 324.1 Reinsurance 68.9 1,485.6 294.0 820.2 — 435.8 164.9 73.3 765.8 Corporate — — — — 182.1 — — — — Total $ 165.2 $ 6,456.2 $ 1,683.3 $ 2,488.4 $ 182.1 $ 1,586.3 $ 375.4 $ 406.3 $ 2,448.0 Year Ended December 31, 2014 Net Deferred Acquisition Costs Reserve for Losses and Loss Expenses Unearned Premiums Net Premiums Earned Net Investment Income Losses and Loss Expenses Amortization of Deferred Acquisition Costs Other Operating Costs Net Premiums Written North American Insurance $ 55.7 $ 3,806.6 $ 1,003.1 $ 1,111.1 $ — $ 683.8 $ 105.9 $ 219.7 $ 1,230.8 Global Markets Insurance 23.3 568.2 223.4 162.6 — 61.1 18.2 68.1 188.0 Reinsurance 72.5 1,506.4 328.8 909.0 — 454.3 171.0 78.0 903.2 Corporate — — — — 176.9 — — — — Total $ 151.5 $ 5,881.2 $ 1,555.3 $ 2,182.7 $ 176.9 $ 1,199.2 $ 295.1 $ 365.7 $ 2,322.0

Schedule IV - Supplementary Rei

Schedule IV - Supplementary Reinsurance Information	12 Months Ended
	Dec. 31, 2016
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Schedule IV - Supplementary reinsurance information	Schedule IV ALLIED WORLD ASSURANCE COMPANY HOLDINGS, AG SUPPLEMENTARY REINSURANCE INFORMATION (Expressed in thousands of United States dollars) Property and Casualty: (a) Gross (b) Ceded to Other Companies (c) Assumed from Other Companies (d) Net Amount (a) - (b) + (c) Percentage of Amount Assumed to Net (c) / (d) Year Ended December 31, 2016 $ 2,359.6 $ 810.0 $ 706.2 $ 2,255.8 31% Year Ended December 31, 2015 $ 2,291.6 $ 645.0 $ 801.4 $ 2,448.0 33% Year Ended December 31, 2014 $ 1,996.8 $ 613.4 $ 938.6 $ 2,322.0 40%

Significant Accounting Polici29

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of accounting	These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”). Intercompany accounts and transactions have been eliminated on consolidation and all entities meeting consolidation requirements have been included in the consolidated financial statements. To facilitate comparison of information across periods, certain reclassifications have been made to prior year amounts to conform to the current year's presentation.
Use of estimates	The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at 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. The significant estimates reflected in the Company’s financial statements include, but are not limited to: • The premium estimates for certain reinsurance agreements, • Recoverability of deferred acquisition costs, • The reserve for outstanding losses and loss expenses, • Valuation of ceded reinsurance recoverables, • Determination of impairment of goodwill and other intangible assets, and • Valuation of financial instruments.
Premiums	Premiums are recorded as written on the inception date of the policy. For certain types of business written by the Company, notably assumed reinsurance, the exact premium income may not be known at the policy inception date. In the case of quota share reinsurance treaties assumed by the Company, the underwriter makes an estimate of premium income at inception. The underwriter’s estimate is based on statistical data provided by reinsureds and the underwriter’s judgment and experience. Such estimations are refined over the reporting period of each treaty as actual written premium information is reported by ceding companies and intermediaries. Premiums resulting from changes in the estimate of the premium income are recorded in the period the estimate is changed. Certain insurance and reinsurance contracts may require that the premium be adjusted at the expiry of the contract to reflect the change in exposure or loss experience of the insured or reinsured. Premiums are recognized as earned over the period of policy coverage in proportion to the risks to which they relate. Reinsurance premiums under a losses-occurring reinsurance contract are earned over the coverage period. Reinsurance premiums under a risks-attaching reinsurance contract are earned over the same period as the underlying policies, or risks, covered by the contract. As a result, the earning pattern of a risks-attaching reinsurance contract may extend up to 24 months, reflecting the inception dates of the underlying policies. Premiums relating to the unexpired periods of coverage are recorded on the consolidated balance sheets as “unearned premiums”.
Acquisition costs	Acquisition costs, comprised of commissions, brokerage fees and insurance taxes, are costs that are directly related to the successful acquisition of new and renewal business and are deferred. Although permitted under U.S. GAAP to defer certain internal costs that are directly related to the successful acquisition of new and renewal business, the Company does not defer such costs. Acquisition costs that are deferred, and carried on the balance sheets as an asset, are expensed as the premiums to which they relate are earned. Expected losses and loss expenses, other costs and anticipated investment income related to these unearned premiums are considered in determining the recoverability or deficiency of deferred acquisition costs. If it is determined that deferred acquisition costs are not recoverable, they are expensed. Further analysis is performed to determine if a liability is required to provide for losses which may exceed the related unearned premiums. Acquisition costs recorded in the consolidated statements of operations and comprehensive income (“consolidated income statements”) includes other acquisition-related costs such as profit commissions that are expensed as incurred and the amortization of insurance-related intangible assets.
Reserve for losses and loss expenses	The reserve for losses and loss expenses is comprised of two main elements: outstanding loss reserves (“OSLR,” also known as case reserves) and reserves for losses incurred but not reported (“IBNR”). OSLR relate to known claims and represent management’s best estimate of the likely loss payment. Reserves for IBNR relates to reserves established by the Company for claims that have occurred but have not yet been reported to us as well as for changes in the values of claims that have been reported to us but are not yet settled. See note 7 for additional information.
Ceded reinsurance	In the ordinary course of business, the Company uses both treaty and facultative reinsurance to minimize its net loss exposure to any one catastrophic loss event or to an accumulation of losses from a number of smaller events. Reinsurance premiums ceded are expensed and any commissions recorded thereon are earned over the period the reinsurance coverage is provided in proportion to the risks to which they relate. For reinsurance treaties that have contractual minimum premium provisions, premiums ceded are recorded at the inception of the treaty based on the minimum premiums. Prepaid reinsurance represents unearned premiums ceded to reinsurance companies. Any unearned ceding commission is included in “net deferred acquisitions costs” on the consolidated balance sheets and is recorded as a reduction to the overall net deferred acquisition cost balance. Reinsurance recoverable includes the balances due from those reinsurance companies under the terms of the Company’s reinsurance agreements for unpaid losses and loss reserves, including IBNR, and is presented net of a provision for uncollectible reinsurance. Amounts recoverable from reinsurers are estimated in a manner consistent with the estimated claim liability associated with the reinsured policy. The Company determines the portion of the IBNR liability that will be recoverable under its reinsurance contracts by reference to the terms of the reinsurance protection purchased. This determination is necessarily based on the estimate of IBNR and accordingly, is subject to the same uncertainties as the estimate of IBNR. The Company remains liable to the extent that its reinsurers do not meet their obligations under the reinsurance contracts; therefore, the Company regularly evaluates the financial condition of its reinsurers and monitors concentration of credit risk.
Investments	All fixed maturity investments and equity securities are classified as trading securities as the Company has elected the fair value option permitted under U.S. GAAP for these investments at the time each security was acquired. Trading securities are carried at fair value with any change in unrealized gains or losses recognized in the consolidated income statements and included in “net realized investment gains (losses)”. As a result of this investment classification, the Company does not record any change in unrealized gains or losses on investments as a separate component of accumulated other comprehensive income on the consolidated balance sheets. Other invested assets consist primarily of investments in hedge funds and private equity funds, which have been accounted for as trading securities as the Company has elected the fair value option as permitted under U.S. GAAP at the time each investment was acquired. In addition, included in the Company’s other invested assets are various investments which are accounted for using the equity method of accounting. Generally, the Company uses the equity method where it does not have a controlling interest and is not the primary beneficiary. Equity method investments are recorded at cost and adjusted for the Company’s proportionate share of earnings or losses on a quarterly lag basis. An other-than-temporary impairment charge related to the equity method investments is assessed when facts and circumstances exists that indicate an impairment may exist. An other-than-temporary impairment charge is recorded when it is determined that the carrying value of the equity method investment is below its fair value and the Company does not have the intent and ability to hold to recovery. See note 4(c) for additional information regarding an other-than-temporary impairment charge recorded in 2015 related to one of the Company's equity method investments. No equity method investment, individually or in the aggregate, was deemed significant to disclose summarized financial data. Other investments are recorded based on valuation techniques depending on the nature of the individual assets. Investment securities are recorded on a trade date basis. Investment income is recognized when earned and includes the accrual of discount or amortization of premium on fixed maturity investments using the effective yield method and is net of related expenses. Interest income for fixed maturity investments is accrued and recognized based on the contractual terms of the fixed maturity investments and is included in “net investment income” in the consolidated income statements. For mortgage-backed and asset-backed securities and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and revised on a regular basis. Revised prepayment assumptions are applied to securities on a retrospective basis to the date of acquisition. The cumulative adjustments to amortized cost required due to these changes in effective yields and maturities are recognized in net investment income in the same period as the revision of the assumptions. The Company’s share of undistributed net income from equity method investments is included in net investment income. The return on investments is managed on a total financial statement portfolio return basis, which includes the undistributed net income from equity method investments, and as such have classified these amounts in net investment income. Realized gains and losses on the disposition of investments, which are based upon the first-in first-out method of identification, are included in “net realized investment gains (losses)” in the consolidated income statements.
Fair value measurements	At each measurement date, the Company estimates the fair value of the financial instruments using various valuation techniques. The Company utilizes, to the extent available, quoted market prices in active markets or observable market inputs in estimating the fair value of financial instruments. When quoted market prices or observable market inputs are not available, the Company may utilize valuation techniques that rely on unobservable inputs to estimate the fair value of financial instruments, which principally relates to non-binding broker-dealer quotes. The Company bases its determination of whether a market is active or inactive on the spread between what a seller is asking for a security and what a buyer is bidding for that security. Spreads that are significantly above historical spreads are considered inactive markets. The Company also considers the volume of trading activity in the determination of whether a market is active or inactive. See note 6 for additional information regarding the fair value of financial instruments. The Company utilizes independent pricing sources to obtain market quotations for securities that have quoted prices in active markets. In general, the independent pricing sources use observable market inputs including, but not limited to, investment yields, credit risks and spreads, benchmarking of like securities, reported trades and sector groupings to determine the fair value. For a majority of the portfolio, the Company obtained two or more prices per security as of December 31, 2016 . When multiple prices are obtained, a price source hierarchy is utilized to determine which price source is the best estimate of the fair value of the security. The price source hierarchy emphasizes more weighting to significant observable inputs such as index pricing and less weighting towards non-binding broker-dealer quotes. The Company will investigate any material differences, if any, between the multiple sources and determines which price best reflects the fair value of the individual security. There were no material differences between the prices obtained from the independent pricing sources and the prices obtained from the Company’s investment portfolio managers and other sources as of December 31, 2016 and 2015 .
Variable interest entities	The Company is involved in the normal course of business with variable interest entities (“VIEs”) as a passive investor in certain asset-backed securities issued by third-party VIEs and affiliated VIEs, as well as certain of its hedge fund and private equity fund investments. The Company performs a qualitative assessment at the date when it becomes initially involved in the VIE, followed by ongoing reassessments related to its involvement in VIEs. The Company’s maximum exposure to loss with respect to these investments is limited to the investment carrying amounts reported in the Company’s consolidated balance sheets and any unfunded commitments. As a result of the adoption of Accounting Standards Update 2015-02, “Amendments to the Consolidation Analysis”, which became effective January 1, 2016, certain limited partnership investments and similar legal entity investments were considered VIEs as there were no substantive kick-out or other participating rights. These VIEs will not be consolidated because the Company has determined it is not considered the primary beneficiary, as it does not have both the power to direct the activities that most significantly impact the economic performance of the entity and the obligation to absorb losses of the entity that could be potentially significant to the VIE or the right to receive benefits from the entity that could be potentially significant. As such, the Company continues to record its interests in these entities at fair value, with changes in fair value recorded in the consolidated income statements. The Company's interests in these entities are recorded in “other invested assets” in the consolidated balance sheets.
Translation of foreign currencies	Transactions in currencies other than a foreign operation's functional currency are translated into the functional currency of the foreign operation. Foreign currency transaction gains and losses, including those arising from forward exchange contracts, are included in “foreign exchange (gain) loss” in the consolidated income statements. Functional currency assets and liabilities are translated into the reporting currency, U.S. dollars, using period-end exchange rates, and functional currency income statements are translated using average exchange rates with the related foreign currency translation adjustment recorded as a separate component of accumulated other comprehensive income or loss.
Cash and cash equivalents	Cash and cash equivalents include amounts held in banks, time deposits, commercial paper, discount notes and U.S. Treasury Bills with maturities of less than three months from the date of purchase. Restricted cash primarily relates to cash held in trust accounts in favor of cedents, other counterparties or government authorities, as well as accounts that are pledged as collateral for the Company's letter of credit facilities.
Income taxes	Allied World Switzerland and certain of its subsidiaries operate in jurisdictions where they are subject to income taxation. Current and deferred income taxes are charged or credited to operations, or to shareholders' equity in certain cases, based upon enacted tax laws and rates applicable in the relevant jurisdiction in the period in which the tax becomes payable. Deferred income taxes are provided for all temporary differences between the bases of assets and liabilities used in the financial statements and those used in the various jurisdictional tax returns. It is the Company’s policy to recognize interest accrued related to unrecognized tax benefits in “interest expense” and penalties in “general and administrative expenses” in the consolidated income statements. The Company has not recorded any interest or penalties during the years ended December 31, 2016 , 2015 and 2014 and the Company has not accrued any payment of interest and penalties as of December 31, 2016 and 2015 .
Employee stock options, restricted stock units and performance-based equity awards	The Company has an employee stock option plan, which is in run-off, in which the amount of Allied World Switzerland's common shares received as compensation through the issuance of stock options is determined by reference to the value of the shares. Compensation expense for stock options granted to employees is recorded on a straight-line basis over the option vesting period and is based on the fair value of the stock options on the grant date. The fair value of each stock option on the grant date is determined by using the Black-Scholes option-pricing model. The Company has granted restricted stock units (“RSUs”) to certain employees. The compensation expense for the RSUs is based on the market value of Allied World Switzerland’s common shares on the grant date, and is recognized on a straight-line basis over the applicable vesting period. The Company has also granted cash-equivalent RSUs to certain employees that vest on a straight-line basis over the applicable vesting period. The amount payable per unit awarded will be equal to the price per share of Allied World Switzerland’s common shares and as such the Company measures the value of the award each reporting period based on the period ending share price. The effects of changes in the share price at each period end during the service period are recognized as increases or decreases in compensation expense over the service period. The Company has granted performance-based equity awards to key employees in order to promote the long-term growth and profitability of the Company. Each award represents the right to receive a number of common shares in the future, based upon the achievement of established performance criteria during the applicable performance period. These performance-based equity awards vest after a three-year performance period. The compensation expense for these awards is based on the market value of Allied World Switzerland’s common shares on the grant date, and is recognized on a straight-line basis over the applicable performance and vesting period. The Company will also adjust the compensation expense, as a cumulative adjustment, to the extent the Company's performance is above or below the targeted performance criteria. The Company has also granted cash-equivalent, performance-based awards to certain employees that vest based upon the achievement of established performance criteria during the applicable performance period. These cash-equivalent, performance-based awards vest after a three-year performance period. The amount payable per unit awarded will be equal to the price per share of Allied World Switzerland’s common shares, and as such the Company measures the value of the award each reporting period based on the period-ending share price. The effects of changes in the share price at each period end during the service period are recognized as changes in compensation expense over the service period. The Company will also adjust the compensation expense, as a cumulative adjustment, to the extent the Company's performance is above or below the targeted performance criteria.
Goodwill and intangible assets	The Company classifies its intangible assets into three categories: (1) intangible assets with finite lives subject to amortization, (2) intangible assets with indefinite lives not subject to amortization, and (3) goodwill. Intangible assets, other than goodwill, generally consist of customer renewal rights, distribution channels, internally generated software, non-compete covenants, trademarks, and insurance licenses. For intangible assets with finite lives, the value of the assets is amortized over their expected useful lives and the expense is included in “amortization and impairment of intangible assets” in the consolidated income statements. The Company tests assets for impairment if conditions exist that indicate the carrying value may not be recoverable. If, as a result of the evaluation, the Company determines that the value of the intangible assets is impaired, then the value of the assets will be written-down in the period in which the determination of the impairment is made. See note 10 for additional information regarding an impairment recorded for one of the Company's intangible assets with finite lives. For indefinite lived intangible assets the Company does not amortize the intangible asset but evaluates and compares the fair value of the assets to their carrying values on an annual basis or more frequently if circumstances warrant. If, as a result of the evaluation, the Company determines that the value of the intangible assets is impaired, then the value of the assets will be written-down in the period in which the determination of the impairment is made. Goodwill represents the excess of the cost of acquisitions over the fair value of net assets acquired and is not amortized. Goodwill is assigned at acquisition to the applicable reporting unit(s) based on the expected benefit to be received by the reporting units from the business combination. The Company determines the expected benefit based on several factors including the purpose of the business combination, the strategy of the Company subsequent to the business combination and structure of the acquired company subsequent to the business combination. A reporting unit is a component of the Company’s business that has discrete financial information that is reviewed by management. In determining the reporting unit, the Company analyzes the inputs, processes, outputs and overall operating performance of the reporting unit. The Company has several reporting units to which the goodwill is allocated to. For goodwill, the Company performs an annual impairment test, or more frequently if circumstances are warranted. The Company may first assess qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. The results of the qualitative assessment will determine if an entity needs to proceed with the two-step goodwill impairment test. For the year ended December 31, 2016 , the Company elected to bypass the qualitative assessment and performed the first step of the goodwill impairment test. During the fourth quarter of 2015, the Company changed its annual impairment test date from September 30th to October 1st. The Company believes the change in impairment test date is preferable as it aligns to the quarter in which the Company performs the impairment test, which is during the fourth quarter of each year. This change does not result in any delay, acceleration or avoidance of impairment. The first step of the goodwill impairment test is to compare the fair value of the reporting unit with its carrying value, including goodwill. If the carrying amount of the reporting unit exceeds its fair value then the second step of the goodwill impairment test is performed. The second step of the goodwill impairment test compares the implied fair value of the reporting unit’s goodwill with the carrying amount of that goodwill in order to determine the amount of impairment to be recognized. The implied fair value of goodwill is determined by deducting the fair value of a reporting unit’s identifiable assets and liabilities from the fair value of the reporting unit as a whole. The excess of the carrying value of goodwill above the implied goodwill, if any, would be recognized as an impairment charge in the consolidated income statements. We recorded no goodwill impairments during the years ended December 31, 2016 , 2015 and 2014 .
Derivative instruments	The Company utilizes derivative financial instruments as part of its overall risk management strategy. The Company recognizes all derivative financial instruments at fair value as either assets or liabilities on the consolidated balance sheets. The accounting for gains and losses associated with changes in the fair value of a derivative and the effect on the consolidated financial statements depends on its hedge designation and whether the hedge is highly effective in achieving offsetting changes in the fair value of the asset or liability hedged. The Company uses currency forward contracts and foreign currency swaps to manage currency exposure. The Company also utilizes various derivative instruments such as interest rate futures, interest rate swaps and index options, for the purpose of managing market exposures, interest rate volatility, portfolio duration, hedging certain investments, or enhancing investment performance. These derivatives are not designated as hedges and accordingly are carried at fair value on the consolidated balance sheets with realized and unrealized gains and losses included in the consolidated income statements. Refer to Note 5 for the Company’s related disclosure. In addition, the Company’s derivative instruments include insurance or reinsurance contracts that are required to be accounted for as derivatives. This will be the case when the insurance or reinsurance contract provides indemnification to the insured or cedent as a result of a change in a variable versus an identifiable insurable event. The Company considers these insurance and reinsurance contracts to be an extension of its overall insurance operations. The insurance and reinsurance derivative contracts are recorded at fair value, with net premiums received recognized in “Net premiums earned” over the period of policy coverage in proportion to the risk to which it relates, and other changes in the fair value of this contract is recorded in “other income” or “other expense” in the consolidated income statements. To the extent losses are incurred or ceded under these contracts, those net losses would be recorded in “net losses and loss expenses”.
Earnings per share	Basic earnings per share is defined as net income available to common shareholders divided by the weighted average number of common shares outstanding for the period, giving no effect to dilutive securities. Diluted earnings per share is defined as net income available to common shareholders divided by the weighted average number of common and common share equivalents outstanding calculated using the treasury stock method for all potentially dilutive securities, including employee stock options, employee share repurchase plan awards, RSUs and performance-based awards. When the effect of dilutive securities would be anti-dilutive, these securities are excluded from the calculation of diluted earnings per share.
Treasury shares	Common shares repurchased by the Company and not subsequently canceled are classified as “treasury shares” on the consolidated balance sheets and are recorded at cost. When shares are reissued from treasury the historical cost, based on the first-in, first-out method, is used to determine the cost of the reissued shares. The difference between the cost of the treasury shares and the par value of the common stock shall be first reflected as additional paid-in capital, but to the extent additional paid-in capital is exhausted the remainder shall reduce retained earnings. The issuance of shares out of treasury have been related to vesting equity-based compensation of the Company's employees and directors.
New accounting pronouncements	In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). ASU 2014-09 provides a framework, through a five-step process, for recognizing revenue from customers, improves comparability and consistency of recognizing revenue across entities, industries, jurisdictions and capital markets, and requires enhanced disclosures. Certain contracts with customers are specifically excluded from the scope of ASU 2014-09, including, among others, insurance contracts accounted for under Accounting Standard Codification 944, Financial Services - Insurance . ASU 2014-09 is effective on January 1, 2017 with retrospective adoption required for the comparative periods. With the issuance of Accounting Standards Update 2015-14, “Revenue from Contracts with Customers (Topic 606) - Deferral of the Effective Date”, this standard will be effective on January 1, 2018 with retrospective adoption required for the comparative periods. The Company does not expect the adoption of ASU 2014-09 to have a material impact on future financial statements and related disclosures. In January 2016, the FASB issued Accounting Standards Update 2016-01, “Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (“ASU 2016-01”). ASU 2016-01 changes current U.S. GAAP for public entities by requiring the following, among others: (1) equity securities, except those accounted for under the equity method of accounting, to be measured at fair value with changes in fair value recognized in net income; (2) the use of the exit price when measuring fair value of financial instruments for disclosure purposes; (3) an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value; and (4) separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or notes to the financial statements. ASU 2016-01 is effective for annual periods beginning after January 1, 2018, including interim periods. Early application is permitted. The Company does not expect the adoption of ASU 2016-01 to have a material impact on future financial statements and disclosures. In February 2016, the FASB issued Accounting Standards Update 2016-02, “Leases” (“ASU 2016-02”). ASU 2016-02 changes current U.S. GAAP for lessees to recognize lease assets and lease liabilities on the balance sheet for those leases classified as operating leases under previous U.S. GAAP. ASU 2016-02 is effective for annual periods beginning after January 1, 2019, including interim periods. Early application is permitted. The Company is currently assessing the impact the adoption of ASU 2016-02 will have on future financial statements and disclosures. Specifically, the Company is still evaluating its existing leases to determine the appropriate classification under the new standard and whether it will adopt the practical expedients allowed under ASU 2016-02. I n March 2016, the FASB issued Accounting Standards Update 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”). ASU 2016-09 modifies U.S. GAAP by requiring the following, among others: (1) all excess tax benefits and tax deficiencies are to be recognized as income tax expense or benefit on the income statement (excess tax benefits are recognized regardless of whether the benefit reduces taxes payable in the current period); (2) excess tax benefits are to be classified along with other income tax cash flows as an operating activity in the statement of cash flows; (3) in the area of forfeitures, an entity can still follow the current U.S. GAAP practice of making an entity-wide accounting policy election to estimate the number of awards that are expected to vest or may instead account for forfeitures when they occur; and (4) classification as a financing activity in the statement of cash flows of cash paid by an employer to the taxing authorities when directly withholding shares for tax withholding purposes. ASU 2016-09 is effective for annual periods beginning after January 1, 2017, including interim periods. Although early adoption is permitted, the Company will not early adopt ASU 2016-09. The Company does not expect the adoption of ASU 2016-09 to have a material impact on future financial statements and disclosures. In June 2016, the FASB issued Accounting Standards Update 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” (“ASU 2016-13”). ASU 2016-13 modifies U.S. GAAP related to the recognition of credit losses by replacing the incurred loss impairment methodology in current U.S. GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 would apply to financial assets such as loans, debt securities, trade receivables, off-balance sheet credit exposures, reinsurance receivables, and other financial assets that have the contractual right to receive cash. The measurement of expected credit losses is based on relevant information about past events, including historical experience, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. The Company's invested assets are measured at fair value through net income, and therefore those invested assets would not be impacted by the adoption of ASU 2016-13. The Company has other financial assets, such as reinsurance recoverables, that could be impacted by the adoption of ASU 2016-13. ASU 2016-13 is effective for annual periods beginning after January 1, 2020, including interim periods. The Company is currently assessing the impact the adoption of ASU 2016-13 will have on future financial statements and disclosures. Specifically, the Company is developing a credit impairment methodology for its reinsurance recoverables based on the guidance in ASU 2016-13. In August 2016, the FASB issued Accounting Standards Update 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” (“ASU 2016-15”). ASU 2016-15 clarifies the classification of receipts and payments in the statement of cash flows. ASU 2016-15 provides guidance related to (1) settlement and payment of zero coupon debt instruments, (2) contingent consideration, (3) proceeds from settlement of insurance claims, (4) proceeds from settlement of corporate and bank owned life insurance policies, (5) distributions from equity method investees, (6) cash receipts from beneficial interests obtained by a transferor, and (7) general guidelines for cash receipts and payments that have more than one aspect of classification. ASU 2016-15 is effective for annual periods beginning after January 1, 2018, including interim periods. Early adoption is permitted. The Company is currently assessing the impact the adoption of ASU 2016-15 will have on future financial statements and disclosures. In October 2016, the FASB issued Accounting Standards Update 2016-16, “Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory” (“ASU 2016-16”). ASU 2016-16 requires entities to recognize the income tax consequences of intra-entity transfers of assets other than inventory when the transfers occur; this is a change from the current U.S. GAAP guidance which prohibits the recognition of current and deferred income taxes until the underlying assets have been sold to outside entities. ASU 2016-16 is effective for annual periods beginning after January 1, 2018, including interim periods. Early adoption is permitted. The Company is currently assessing the impact the adoption of ASU 2016-16 will have on future financial statements and disclosures. In November 2016, the FASB issued Accounting Standards Update 2016-18, “Statement of Cash Flows (Topic 230): Restricted Cash a consensus of the FASB Emerging Issues Task Force ” (“ASU 2016-18”). ASU 2016-18 changes existing U.S. GAAP by requiring the following, among others: (1) amounts generally described as restricted cash or restricted cash equivalents are to be included with the totals for cash and cash equivalents when reconciling the period change in cash and cash equivalents on the consolidated statements of cash flow, (2) in addition to the exchange rate impact on cash held in foreign currencies, entities must also include, as a component of this quantified amount, the impact on cash equivalents and amounts generally described as restricted cash or restricted cash equivalents as a separate component of the reconciliation referenced in (1) above, (3) when cash, cash equivalents, and amounts generally deemed as restricted cash or restricted cash equivalents are presented in more than one line item within the consolidated balance sheet, such line items must also be presented either on the face of the consolidated statements of cash flow or in the notes to the financial statements, (4) a disclosure of the nature of restrictions on an entity’s cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents, and (5) any applicable change in accounting principle disclosures in the first interim and annual period in which the update is adopted. ASU 2016-18 is effective for annual periods beginning after January 1, 2018, including interim periods, and is to be applied retrospectively to all periods presented. Early adoption is permitted. The Company is currently assessing the impact the adoption of ASU 2016-18 will have on future financial statements and disclosures. In January 2017, the FASB issued Accounting Standards Update 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment” (“ASU 2017-04”). ASU 2017-04 changes existing U.S. GAAP by requiring the following, among others: (1) the elimination of step 2 of the goodwill impairment test; entities will no longer utilize the implied fair value of their assets and liabilities for purposes of testing goodwill for impairment, (2) the quantitative portion of the goodwill impairment test will be performed by comparing the fair value of a reporting unit with its carrying amount; an impairment charge is to be recognized for the excess of carrying amount over fair value, but only to the extent of the amount of goodwill allocated to that reporting unit, and (3) foreign currency translation adjustments are not to be allocated to a reporting unit from an entity’s accumulated other comprehensive income; the reporting unit’s carrying amount should include only the currently translated balances of the assets and liabilities assigned to the reporting unit. ASU 2017-04 is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company plans to adopt ASU 2017-04 as of January 1, 2017.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Summary of consideration paid and amounts of assets acquired and liabilities assumed	The following table summarizes the consideration paid for the Hong Kong and Singapore branches of RSA and the preliminary amounts of the assets acquired and liabilities assumed at the acquisition date. Consideration: Fair Value Cash consideration $ 176.5 Recognized amounts of identifiable assets acquired and liabilities assumed: Fixed maturity investments 246.1 Cash and cash equivalents 47.1 Insurance balances receivable 114.4 Prepaid reinsurance 17.5 Reinsurance recoverable 58.9 Value of business acquired 28.9 Intangible assets 79.9 Other assets 9.9 Reserve for losses and loss expenses (314.1 ) Unearned premiums (150.5 ) Reinsurance balances payable (35.8 ) Net deferred tax liabilities (11.9 ) Accounts payable and accrued liabilities (20.1 ) Total identifiable net assets acquired 70.3 Goodwill 106.2 Total net assets acquired $ 176.5
Summary of intangible assets acquired	The following is a breakdown of the intangible assets acquired. Singapore Branch Estimated Useful Life Hong Kong Branch Estimated Useful Life Total VOBA $ 17.8 2 years $ 11.1 1.5 years $ 28.9 Customer renewals 8.6 4 years 4.4 5 years 13.0 Distribution channels 47.7 18 years 19.2 18 years 66.9 $ 74.1 $ 34.7 $ 108.8
Summary of results since acquisition	The following summarizes the results of the Hong Kong and Singapore branches that have been included in the Company’s consolidated income statement since the acquisitions closed on April 1, 2015. From April 1, 2015 to December 31, 2015 Total revenue $ 155.3 Net loss $ (28.9 )
Pro forma information	The following unaudited pro forma information presents the combined results of the Company and the acquired Hong Kong and Singapore RSA branches for the years ended December 31, 2015 and 2014, with pro forma adjustments related to the acquisition method of accounting as if the acquisitions had been consummated as of January 1, 2014. This unaudited pro forma information is not necessarily indicative of what would have occurred had the acquisitions and related transactions been made on the dates indicated, or of future results of the Company. Year Ended December 31, 2015 Year Ended December 31, 2014 Total revenue $ 2,594.2 $ 2,681.7 Net income $ 74.2 $ 505.9

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments [Abstract]
Schedule of trading securities	Securities accounted for at fair value with changes in fair value recognized in the consolidated income statements by category are as follows: December 31, 2016 December 31, 2015 Fair Value Amortized Cost Fair Value Amortized Cost U.S. government and government agencies $ 1,426.0 $ 1,454.5 $ 1,434.0 $ 1,437.9 Non-U.S. government and government agencies 469.9 496.5 556.8 579.2 States, municipalities and political subdivisions 354.1 355.8 413.5 396.0 Corporate debt: Financial institutions 1,032.7 1,033.6 1,275.4 1,277.3 Industrials 1,321.3 1,322.3 1,308.1 1,345.6 Utilities 140.0 140.7 118.9 125.4 Mortgage-backed: Agency mortgage-backed 614.5 612.5 751.8 745.4 Non-agency residential mortgage-backed 23.9 22.7 34.0 32.4 Commercial mortgage-backed 598.0 636.1 582.8 600.1 Asset-backed 757.3 772.6 726.2 751.1 Total fixed maturity investments, trading $ 6,737.7 $ 6,847.4 $ 7,201.5 $ 7,290.6 December 31, 2016 December 31, 2015 Fair Value Cost Fair Value Cost Equity securities $ 243.9 $ 235.0 $ 403.0 $ 395.3 Other invested assets 897.8 831.2 840.2 770.9 $ 1,141.7 $ 1,066.2 $ 1,243.2 $ 1,166.2
Schedule of other invested assets	Details regarding the carrying value, redemption characteristics and unfunded investment commitments of the other invested assets portfolio as of December 31, 2016 and 2015 were as follows: Fund Type Carrying Value as of December 31, 2016 Investments with Redemption Restrictions Estimated Remaining Restriction Period Investments without Redemption Restrictions Redemption Frequency(1) Redemption Notice Period(1) Unfunded Commitments Private equity $ 281.0 $ 281.0 1 - 15 Years $ — $ 219.3 Levered credit 204.9 204.9 3 - 9 Years — 190.8 Real estate 68.9 68.9 6 - 8 Years — 191.6 Distressed 5.0 5.0 1 Year — 3.8 Total private equity 559.8 559.8 — 605.5 Distressed 175.3 — 175.3 Quarterly 60 Days — Relative value credit 84.8 — 84.8 Quarterly 60 Days — Equity long/short 67.9 — 67.9 Quarterly 45 Days — Fund of funds 10.0 — 10.0 Quarterly 60 Days — Total hedge funds 338.0 — 338.0 — Total other invested assets at fair value 897.8 559.8 338.0 605.5 Other private securities 62.9 — 62.9 — Total other invested assets $ 960.7 $ 559.8 $ 400.9 $ 605.5 Fund Type Carrying Value as of December 31, 2015 Investments Estimated Investments Redemption Redemption Unfunded Private equity $ 236.4 $ 236.4 1 - 7 Years $ — $ 231.0 Levered credit 205.9 205.9 4 - 8 Years — 179.0 Distressed 5.1 5.1 2 Years — 3.8 Real estate — — 7 - 9 Years — 200.0 Total private equity 447.4 447.4 — 613.8 Distressed 215.6 54.6 2 Years 161.0 Monthly 90 Days — Relative value credit 105.4 — 105.4 Quarterly 60 Days — Equity long/short 58.0 — 58.0 Quarterly 45 Days — Total hedge funds 379.0 54.6 324.4 — High yield loan fund 13.8 — 13.8 Monthly 30 days — Total other invested assets at fair value 840.2 502.0 338.2 613.8 Other private securities 126.5 — 126.5 — Total other invested assets $ 966.7 $ 502.0 $ 464.7 $ 613.8 (1) The redemption frequency and notice periods only apply to the investments without redemption restrictions.
Schedule of net investment income	Year Ended December 31, 2016 2015 2014 Fixed maturity investments $ 191.0 $ 164.2 $ 149.5 Equity securities 5.1 13.3 17.6 Other invested assets: hedge funds and private equity 23.4 19.6 12.6 Other invested assets: other private securities 13.7 2.8 13.3 Cash and cash equivalents 2.9 1.7 2.1 Expenses (18.3 ) (19.5 ) (18.2 ) Net investment income $ 217.8 $ 182.1 $ 176.9
Components of realized gains and losses	Year Ended December 31, 2016 2015 2014 Gross realized gains on sale of invested assets $ 159.5 $ 180.3 $ 195.4 Gross realized losses on sale of invested assets (121.3 ) (106.4 ) (48.2 ) Net realized and unrealized losses on derivatives (19.6 ) (15.4 ) (39.0 ) Mark-to-market (losses) gains: Debt securities, trading (17.2 ) (126.3 ) (1.7 ) Equity securities, trading 5.8 (41.7 ) 0.4 Other invested assets, trading (5.1 ) (18.1 ) (17.9 ) Net realized investment gains (losses) $ 2.1 $ (127.6 ) $ 89.0

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Location and amounts of derivative fair values on the unaudited condensed consolidated balance sheets	The following table summarizes information on the location and amounts of derivative fair values on the consolidated balance sheets: December 31, 2016 December 31, 2015 Asset Derivative Notional Amount Asset Derivative Fair Value Liability Derivative Notional Amount Liability Derivative Fair Value Asset Derivative Notional Amount Asset Derivative Fair Value Liability Derivative Notional Amount Liability Derivative Fair Value Foreign exchange contracts $ 103.2 $ 10.4 $ 4.1 $ 0.1 $ 41.1 $ 0.1 $ 244.8 $ 3.0 Interest rate swaps — — — — — — 328.2 0.5 Insurance contracts 225.0 7.4 — — — — — — Reinsurance contracts — — 110.0 4.0 — — — — Total derivatives $ 328.2 $ 17.8 $ 114.1 $ 4.1 $ 41.1 $ 0.1 $ 573.0 $ 3.5
Unrealized and realized gains (losses) on derivatives recorded in the unaudited condensed consolidated income statements	The following table provides the net realized and unrealized (losses) gains on derivatives not designated as hedges recorded on the consolidated income statements: Year Ended December 31, 2016 2015 2014 Foreign exchange contracts $ (2.2 ) $ (7.3 ) $ 0.9 Total included in foreign exchange (gain) loss (2.2 ) (7.3 ) 0.9 Put options — — 0.5 Foreign exchange contracts (11.9 ) 0.2 3.5 Interest rate swaps (6.8 ) (13.4 ) (45.4 ) Interest rate futures (0.9 ) (2.2 ) 2.4 Total included in net realized investment gains (losses) (19.6 ) (15.4 ) (39.0 ) Insurance contracts 7.4 — — Reinsurance contracts (3.1 ) — — Total included in other income (other expense) 4.3 — — Total realized and unrealized (losses) gains on derivatives $ (17.5 ) $ (22.7 ) $ (38.1 )

Fair Value Of Financial Instr33

Fair Value Of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair value hierarchy and related disclosures	The following table shows the fair value of the Company’s financial instruments and where in the fair value hierarchy the fair value measurements are included as of the dates indicated below: December 31, 2016 Carrying amount Total fair value Level 1 Level 2 Level 3 ASSETS: Fixed maturity investments: U.S. government and government agencies $ 1,426.0 $ 1,426.0 $ 1,379.6 $ 46.4 $ — Non-U.S. government and government agencies 469.9 469.9 — 469.9 — States, municipalities and political subdivisions 354.1 354.1 — 354.1 — Corporate debt: Financial institutions 1,032.7 1,032.7 — 1,031.2 1.5 Industrials 1,321.3 1,321.3 — 1,321.3 — Utilities 140.0 140.0 — 140.0 — Mortgage-backed: Agency mortgage-backed 614.5 614.5 — 475.9 138.7 Non-agency residential mortgage-backed 23.9 23.9 — 23.9 — Commercial mortgage-backed 598.0 598.0 — 598.0 — Asset-backed 757.3 757.3 697.8 59.5 Total fixed maturity investments 6,737.7 6,737.7 1,379.6 5,158.5 199.7 Equity securities 243.9 243.9 219.2 — 24.7 Other invested assets (1) 897.8 897.8 — — — Total investments 7,879.4 7,879.4 1,598.8 5,158.5 224.4 Derivative assets: Foreign exchange contracts 10.4 10.4 — 10.4 — Insurance contracts 7.4 7.4 — — 7.4 LIABILITIES: Derivative liabilities: Foreign exchange contracts 0.1 0.1 — 0.1 — Reinsurance contracts 4.0 4.0 — — 4.0 Senior notes 794.2 827.1 — 827.1 — Other long-term debt $ 22.0 $ 26.7 $ — $ 26.7 $ — December 31, 2015 Carrying amount Total fair value Level 1 Level 2 Level 3 ASSETS: Fixed maturity investments: U.S. government and government agencies $ 1,434.0 $ 1,434.0 $ 1,396.4 $ 37.6 $ — Non-U.S. government and government agencies 556.8 556.8 — 556.8 — States, municipalities and political subdivisions 413.5 413.5 — 413.5 — Corporate debt Financial institutions 1,275.4 1,275.4 — 1,275.4 — Industrials 1,308.1 1,308.1 — 1,308.1 — Utilities 118.9 118.9 — 118.9 — Mortgage-backed Agency mortgage-backed 751.8 751.8 — 650.8 101.1 Non-agency residential mortgage-backed 34.0 34.0 — 29.0 5.0 Commercial mortgage-backed 582.8 582.8 — 582.8 — Asset-backed 726.2 726.2 — 663.2 63.0 Total fixed maturity investments 7,201.5 7,201.5 1,396.4 5,636.1 169.1 Equity securities 403.0 403.0 403.0 — — Other invested assets (1) 840.2 840.2 — — — Total investments 8,444.7 8,444.7 1,799.4 5,636.1 169.1 Derivative assets: Foreign exchange contracts 0.1 0.1 — 0.1 — LIABILITIES: Derivative liabilities: Foreign exchange contracts 3.0 3.0 — 3.0 — Interest rate swaps 0.5 0.5 — 0.5 — Senior notes 1,292.9 1,337.9 — 1,337.9 — Other long-term debt $ 23.0 $ 27.7 $ — $ 27.7 $ —
Fair value measurements using significant unobservable inputs (Level 3)	The following is a rollforward of the beginning and ending balance of financial instruments using significant unobservable inputs (Level 3): Fair value measurements using significant unobservable inputs (Level 3): Corporate Debt - Financial Institutions Agency MBS Non-agency RMBS CMBS Asset-backed Equities Insurance contracts Reinsurance contracts Balance at December 31, 2014 $ — $ 180.1 $ — $ 1.7 $ 55.4 $ 43.3 $ — $ — Realized and unrealized gains (losses) included in net income — (1.0 ) (0.1 ) 0.1 (6.1 ) 3.5 — — Purchases — 17.7 5.2 1.8 18.4 — — — Sales — (95.7 ) (0.1 ) (3.6 ) (23.1 ) (46.8 ) — — Transfers into Level 3 from Level 2 — — — — 37.3 — — — Transfers out of Level 3 into Level 2 (1) — — — — (18.9 ) — — — Balance at December 31, 2015 $ — $ 101.1 $ 5.0 $ — $ 63.0 $ — $ — $ — Realized and unrealized gains (losses) included in net income — (6.4 ) — — 3.1 8.1 7.4 (4.0 ) Purchases 1.5 212.6 — — 31.2 16.6 — — Sales — (175.3 ) — — (27.2 ) — — — Transfers into Level 3 from Level 2 — 6.7 — — 8.0 — — — Transfers out of Level 3 into Level 2 (1) — — (5.0 ) — (18.6 ) — — — Balance at December 31, 2016 $ 1.5 $ 138.7 $ — $ — $ 59.5 $ 24.7 $ 7.4 $ (4.0 ) Realized and unrealized losses (gains) included in net income for investments still held as of December 31, 2016 $ — $ (6.4 ) $ — $ — $ 1.9 $ 8.1 $ 7.4 $ (4.0 ) Realized and unrealized gains (losses) included in net income for investments still held as of December 31, 2015 $ — $ (1.5 ) $ (0.1 ) $ — $ (0.3 ) $ — $ — $ — (1) Transfers out of Level 3 are primarily attributable to the availability of market observable information.

Reserve For Losses And Loss E34

Reserve For Losses And Loss Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
Insurance Loss Reserves [Abstract]
Components of liabilty for unpaid losses and loss expenses	The reserve for losses and loss expenses consists of the following: December 31, 2016 2015 Outstanding loss reserves $ 1,807.5 $ 1,678.5 Reserves for losses incurred but not reported 4,831.7 4,777.7 Reserve for losses and loss expenses $ 6,639.2 $ 6,456.2
Reconciliation of beginning and ending liability for unpaid losses and loss expenses	The table below is a reconciliation of the beginning and ending liability for unpaid losses and loss expenses. Losses incurred and paid are reflected net of reinsurance recoverables. Year Ended December 31, 2016 2015 2014 Gross liability at beginning of year $ 6,456.2 $ 5,881.2 $ 5,766.5 Reinsurance recoverable at beginning of year (1,480.0 ) (1,340.3 ) (1,234.5 ) Net liability at beginning of year 4,976.2 4,540.9 4,532.0 Acquisition of net reserves for losses and loss expenses — 259.3 — Net losses incurred related to: Current year 1,600.1 1,667.9 1,411.8 Prior years (98.3 ) (81.6 ) (212.6 ) Total incurred 1,501.8 1,586.3 1,199.2 Net paid losses related to: Current year 208.4 186.0 171.8 Prior years 1,238.6 1,201.6 1,001.5 Total paid 1,447.0 1,387.6 1,173.3 Foreign exchange revaluation and other (16.8 ) (22.7 ) (17.0 ) Net liability at end of year 5,014.2 4,976.2 4,540.9 Reinsurance recoverable at end of year 1,625.0 1,480.0 1,340.3 Gross liability at end of year $ 6,639.2 $ 6,456.2 $ 5,881.2
(Incurred and Paid Loss Development Triangles)	North American Insurance Segment Casualty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 133.8 $ 156.8 $ 158.4 $ 151.5 $ 149.3 $ 143.5 $ 127.3 $ 23.6 277 2011 120.7 140.7 145.1 143.0 136.7 144.2 36.8 347 2012 144.4 147.9 150.7 166.3 188.5 42.7 388 2013 184.0 192.4 208.9 237.4 90.3 638 2014 220.2 222.4 232.4 94.7 763 2015 288.0 279.1 214.8 820 2016 268.4 244.3 614 $ 1,477.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 0.6 $ 28.4 $ 65.9 $ 72.8 $ 83.0 $ 87.4 $ 96.8 2011 2.1 11.2 32.8 53.0 79.0 91.8 2012 6.5 25.9 53.2 85.4 114.0 2013 9.7 38.6 70.2 103.6 2014 8.5 58.3 103.9 2015 11.0 34.2 2016 10.0 $ 554.4 All outstanding liabilities before 2010, net of reinsurance $ 157.0 Liability for losses and loss expenses, net of reinsurance $ 1,079.9 Professional liability Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 189.4 $ 196.5 $ 190.5 $ 178.0 $ 169.3 $ 154.8 $ 152.3 $ 23.1 334 2011 182.5 206.4 228.7 235.4 214.4 210.7 24.4 474 2012 193.5 266.2 274.0 271.1 265.6 46.9 530 2013 220.9 226.8 225.8 240.4 77.3 534 2014 213.0 233.7 235.7 79.2 378 2015 254.2 258.9 165.7 269 2016 256.0 234.1 127 $ 1,619.5 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 7.9 $ 36.5 $ 57.0 $ 78.1 $ 91.3 $ 97.5 $ 118.2 2011 13.6 56.1 102.6 124.7 152.7 179.5 2012 15.8 62.5 98.0 146.5 181.1 2013 9.6 50.0 95.8 142.8 2014 11.7 69.8 125.6 2015 9.0 61.0 2016 9.5 $ 817.6 All outstanding liabilities before 2010, net of reinsurance $ 89.7 Liability for losses and loss expenses, net of reinsurance $ 891.6 Property Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 66.9 $ 54.0 $ 49.6 $ 47.7 $ 48.6 $ 48.8 $ 48.8 $ 0.7 330 2011 124.3 121.8 115.0 111.4 110.2 107.9 (0.1 ) 448 2012 157.7 146.9 140.5 136.9 136.3 0.3 599 2013 81.6 75.3 69.8 68.9 0.1 923 2014 97.0 96.0 88.9 0.3 1,344 2015 110.7 114.4 3.3 1,448 2016 101.3 11.8 1,502 $ 666.4 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 16.4 $ 34.2 $ 40.9 $ 45.7 $ 47.4 $ 47.9 $ 48.1 2011 24.6 69.8 98.6 106.2 107.4 108.1 2012 20.5 98.0 127.8 134.7 135.0 2013 25.4 56.3 64.6 67.8 2014 32.3 73.1 83.8 2015 51.6 98.5 2016 46.7 $ 587.9 All outstanding liabilities before 2010, net of reinsurance $ 0.5 Liability for losses and loss expenses, net of reinsurance $ 79.0 Programs Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 70.7 $ 72.5 $ 86.4 $ 80.8 $ 78.8 $ 75.5 $ 75.0 $ 2.6 479 2011 54.0 61.9 62.6 58.1 52.5 53.5 4.4 446 2012 56.7 60.5 62.4 59.6 58.9 5.7 496 2013 64.9 62.0 59.7 56.2 14.5 871 2014 74.9 73.9 70.0 28.8 1,201 2015 86.8 86.2 43.5 1,266 2016 113.6 72.3 1,281 $ 513.4 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.9 $ 17.9 $ 42.4 $ 52.3 $ 59.9 $ 63.4 $ 66.3 2011 3.8 15.2 26.7 34.7 41.3 45.3 2012 3.8 17.6 29.6 38.3 44.5 2013 5.7 15.8 24.4 33.0 2014 6.4 16.9 27.5 2015 9.3 26.3 2016 14.1 $ 257.0 All outstanding liabilities before 2010, net of reinsurance $ 9.4 Liability for losses and loss expenses, net of reinsurance $ 265.8 Healthcare Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 78.5 $ 76.4 $ 79.3 $ 79.8 $ 64.2 $ 63.4 $ 62.8 $ 6.8 156 2011 85.9 87.1 94.5 108.1 113.6 113.3 4.5 248 2012 87.9 91.4 99.4 113.7 113.7 8.5 260 2013 85.4 111.2 123.9 123.9 18.8 227 2014 84.4 92.5 92.5 46.4 150 2015 76.8 76.8 58.0 85 2016 51.1 47.6 17 $ 634.1 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 1.2 $ 6.4 $ 17.1 $ 28.9 $ 39.8 $ 48.5 $ 51.9 2011 0.5 10.9 42.5 69.6 84.0 99.9 2012 1.3 15.1 34.3 54.8 77.5 2013 2.6 12.6 56.9 84.6 2014 1.0 9.0 26.5 2015 0.6 8.5 2016 0.9 $ 349.7 All outstanding liabilities before 2010, net of reinsurance $ 16.8 Liability for losses and loss expenses, net of reinsurance $ 301.2 Other specialty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 0.9 $ 0.9 $ 0.9 $ 0.6 $ 0.5 $ 0.3 $ 0.4 $ — 9 2011 16.5 18.9 18.3 18.7 18.7 18.7 0.7 16 2012 21.2 21.2 22.5 21.3 21.2 2.3 19 2013 16.6 16.6 16.6 16.6 10.6 73 2014 30.6 33.6 34.3 12.1 331 2015 47.4 48.2 30.6 352 2016 70.1 62.4 520 $ 209.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ 0.1 $ 0.1 $ 0.1 $ 0.4 2011 4.0 11.2 14.5 15.1 15.9 16.7 2012 0.5 10.2 14.7 17.5 17.9 2013 0.8 2.3 3.2 4.4 2014 5.2 13.0 18.6 2015 4.1 13.4 2016 4.2 $ 75.6 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 134.0 Global Markets Insurance Segment: Casualty - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 14.2 $ 14.2 $ 14.2 $ 13.9 $ 10.3 $ 5.8 $ 4.2 $ 4.1 1 2011 9.8 9.6 15.4 16.5 15.8 15.5 5.4 10 2012 11.0 11.6 11.3 10.5 7.6 5.8 16 2013 9.3 9.3 8.1 7.3 6.5 25 2014 9.0 11.8 11.9 6.0 66 2015 16.6 19.5 6.5 111 2016 15.9 11.4 233 $ 81.9 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ 0.1 $ 0.1 $ 0.1 $ 0.1 2011 — 0.2 0.3 10.1 10.1 10.1 2012 — 0.6 0.9 1.0 1.6 2013 — 0.4 0.4 0.4 2014 0.4 0.7 1.1 2015 1.1 4.0 2016 0.4 $ 17.7 All outstanding liabilities before 2010, net of reinsurance $ 24.1 Liability for losses and loss expenses, net of reinsurance $ 88.3 Casualty - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 3.2 $ 2.7 $ 0.5 130 2011 — — — — 7.2 6.2 0.1 337 2012 — — — 19.3 17.9 0.4 496 2013 — — 53.6 43.2 3.1 1,302 2014 — 99.2 68.7 5.4 3,618 2015 98.3 78.0 15.4 9,095 2016 60.9 22.0 8,506 $ 277.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 1.0 $ 1.5 2011 — — — — 2.7 4.7 2012 — — — 8.2 14.2 2013 — — 13.2 28.2 2014 — 16.6 37.1 2015 12.0 31.1 2016 13.4 $ 130.1 All outstanding liabilities before 2010, net of reinsurance $ 1.1 Liability for losses and loss expenses, net of reinsurance $ 148.6 Professional liability - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 32.6 $ 32.6 $ 32.5 $ 30.3 $ 20.0 $ 13.8 $ 14.7 $ 5.7 15 2011 32.4 29.8 27.8 24.3 20.7 19.2 7.3 21 2012 32.4 30.7 37.9 39.2 37.3 10.7 34 2013 33.9 33.4 30.4 28.5 20.0 92 2014 39.6 39.2 40.5 29.4 125 2015 57.3 60.3 48.9 147 2016 53.5 48.9 150 $ 254.0 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ 0.1 $ 0.5 $ 2.6 $ 3.1 $ 8.6 2011 0.1 0.5 6.7 8.4 8.6 8.6 2012 0.2 1.6 10.5 13.6 21.3 2013 0.1 0.9 2.4 3.5 2014 0.5 2.6 4.8 2015 1.3 5.4 2016 1.9 $ 54.3 All outstanding liabilities before 2010, net of reinsurance $ 46.5 Liability for losses and loss expenses, net of reinsurance $ 246.2 Professional liability - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 0.8 $ 0.9 $ 0.1 11 2011 — — — — 1.5 1.0 — 12 2012 — — — 0.4 0.2 — 9 2013 — — 0.8 1.9 0.2 25 2014 — 2.1 1.5 0.3 48 2015 3.2 2.6 1.8 74 2016 1.0 1.0 32 $ 9.1 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.6 $ 0.7 2011 — — — — — 0.5 2012 — — — 0.1 0.1 2013 — — 0.2 0.4 2014 — 0.2 0.3 2015 — 0.1 2016 0.1 $ 2.3 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 6.8 Property - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 87.9 $ 102.3 $ 97.5 $ 96.6 $ 95.7 $ 96.5 $ 93.6 $ 0.1 249 2011 66.2 64.2 58.5 54.6 54.5 54.9 0.2 214 2012 25.2 21.9 18.6 17.3 18.2 0.8 161 2013 26.0 18.6 14.4 14.4 0.2 108 2014 29.0 23.3 21.1 0.6 164 2015 22.8 25.1 1.8 223 2016 29.3 12.3 282 $ 256.6 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 47.8 $ 75.0 $ 84.1 $ 90.5 $ 92.1 $ 92.5 $ 92.9 2011 10.6 28.4 43.3 52.2 52.8 53.6 2012 3.5 9.3 11.5 15.1 17.3 2013 4.0 9.0 12.5 12.9 2014 6.7 12.3 15.9 2015 3.7 15.4 2016 3.0 $ 211.1 All outstanding liabilities before 2010, net of reinsurance $ 2.3 Liability for losses and loss expenses, net of reinsurance $ 47.8 Property - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ — $ 0.1 $ — 54 2011 — — — — 0.9 0.5 — 122 2012 — — — 1.7 1.4 — 353 2013 — — 4.2 4.5 — 758 2014 — 14.0 14.3 0.5 1,332 2015 22.1 12.0 0.6 1,988 2016 20.6 7.4 1,190 $ 53.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.1 $ — 2011 — — — — 0.2 0.6 2012 — — — 0.5 1.3 2013 — — 1.6 3.1 2014 — 6.4 9.7 2015 2.8 8.1 2016 1.9 $ 24.8 All outstanding liabilities before 2010, net of reinsurance $ (3.5 ) Liability for losses and loss expenses, net of reinsurance $ 25.0 Other specialty - Excluding RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 0.1 $ 0.1 $ 0.1 $ 0.1 $ — $ — $ — $ — — 2011 1.0 1.0 1.0 — — — — 3 2012 4.3 4.3 1.7 1.6 1.7 — 5 2013 7.2 16.0 20.2 19.7 1.1 110 2014 31.9 41.4 52.1 3.2 750 2015 44.0 46.4 8.6 1,086 2016 55.1 19.1 1,049 $ 174.9 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ — $ — 2011 — — — — — — 2012 — 0.1 1.4 1.6 1.6 2013 0.2 4.8 16.6 18.4 2014 8.9 27.0 32.9 2015 12.7 29.3 2016 24.7 $ 107.0 All outstanding liabilities before 2010, net of reinsurance $ — Liability for losses and loss expenses, net of reinsurance $ 67.9 Other specialty - RSA acquired reserves Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ — $ — $ — $ — $ — $ 1.1 $ 1.1 $ — 115 2011 — — — — 1.3 2.6 — 239 2012 — — — 2.4 2.6 (0.1 ) 411 2013 — — 7.0 7.0 0.2 857 2014 — 20.6 21.8 (0.9 ) 2,808 2015 39.0 41.5 0.9 14,366 2016 31.3 7.9 15,908 $ 107.8 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ — $ — $ — $ — $ — $ 0.1 $ 0.3 2011 — — — — 0.3 0.8 2012 — — — 0.4 1.4 2013 — — 2.1 3.2 2014 — 5.5 10.0 2015 7.2 19.1 2016 6.7 $ 41.5 All outstanding liabilities before 2010, net of reinsurance $ 0.4 Liability for losses and loss expenses, net of reinsurance $ 66.7 Reinsurance Segment: Property Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 80.3 $ 78.7 $ 73.0 $ 68.6 $ 68.0 $ 67.9 $ 67.0 $ 0.6 n/a 2011 219.8 223.9 207.2 199.4 197.8 199.2 1.2 n/a 2012 190.9 143.0 131.2 126.9 124.5 3.1 n/a 2013 176.3 143.7 133.6 123.1 2.9 n/a 2014 196.5 165.0 152.8 5.2 n/a 2015 202.1 174.4 26.3 n/a 2016 180.4 74.4 n/a $ 1,021.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 11.1 $ 38.2 $ 50.2 $ 57.6 $ 63.2 $ 64.8 $ 65.2 2011 53.4 116.6 162.9 182.1 190.5 193.9 2012 38.5 87.8 105.8 111.7 114.6 2013 29.7 84.8 110.6 115.7 2014 57.5 112.8 131.0 2015 53.9 104.2 2016 52.8 $ 777.5 All outstanding liabilities before 2010, net of reinsurance $ 1.9 Liability for losses and loss expenses, net of reinsurance $ 245.7 Casualty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 200.0 $ 222.1 $ 225.9 $ 223.2 $ 213.2 $ 197.9 $ 196.0 $ 48.4 n/a 2011 165.2 184.6 189.4 192.7 185.6 180.5 51.8 n/a 2012 190.5 214.7 216.9 223.8 231.2 68.9 n/a 2013 177.4 192.5 198.6 214.9 92.8 n/a 2014 167.2 179.5 182.0 120.0 n/a 2015 159.2 157.5 123.6 n/a 2016 130.2 120.5 n/a $ 1,292.3 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.6 $ 32.2 $ 58.6 $ 76.3 $ 97.9 $ 114.5 $ 126.8 2011 8.4 26.9 49.0 71.3 93.2 105.0 2012 12.6 39.2 57.3 92.5 127.5 2013 7.8 22.4 60.2 81.4 2014 1.7 12.5 31.0 2015 1.5 14.5 2016 1.8 $ 487.9 All outstanding liabilities before 2010, net of reinsurance $ 225.9 Liability for losses and loss expenses, net of reinsurance $ 1,030.3 Specialty Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2016 Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 Total IBNR Cumulative Reported Claims 2010 $ 11.3 $ 7.7 $ 9.0 $ 8.8 $ 8.6 $ 8.3 $ 8.1 $ 0.4 n/a 2011 30.0 26.9 21.9 22.7 22.1 21.4 1.5 n/a 2012 123.1 132.0 138.3 137.2 136.5 4.5 n/a 2013 111.6 106.7 100.3 102.0 4.2 n/a 2014 121.0 124.8 118.4 6.2 n/a 2015 130.0 128.0 23.9 n/a 2016 118.4 101.6 n/a $ 632.8 Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance Accident Year Unaudited 2010 Unaudited 2011 Unaudited 2012 Unaudited 2013 Unaudited 2014 Unaudited 2015 2016 2010 $ 2.1 $ 4.1 $ 6.1 $ 6.5 $ 7.0 $ 7.1 $ 7.3 2011 3.2 12.7 16.3 17.5 18.4 19.0 2012 24.5 108.0 121.8 125.5 127.9 2013 3.3 75.7 92.0 93.3 2014 14.8 102.8 107.7 2015 7.2 95.3 2016 9.8 $ 460.4 All outstanding liabilities before 2010, net of reinsurance $ 3.3 Liability for losses and loss expenses, net of reinsurance $ 175.7
(Reconciliation of incurred and paid loss development triangles to the reserve for losses and loss expenses)	The following table reconciles the net reserve for losses and loss expenses derived from the incurred and paid loss development triangles to the reserve for losses and loss expenses in the consolidated balance sheet as of December 31, 2016 December 31, 2016 Net reserve for losses and loss expenses per the loss development triangles: North American Insurance: Casualty $ 1,079.9 Professional liability 891.6 Property 79.0 Programs 265.8 Healthcare 301.2 Other specialty 134.0 Global Markets Insurance: Casualty 88.3 Casualty - RSA acquired reserves 148.6 Professional liability 246.2 Professional liability - RSA acquired reserves 6.8 Property 47.8 Property - RSA acquired reserves 25.0 Other specialty 67.9 Other specialty - RSA acquired reserves 66.7 Reinsurance: Property 245.7 Casualty 1,030.3 Specialty 175.7 Total net reserves for losses and loss expenses per the loss development triangles: $ 4,900.4 Reinsurance recoverable for each loss development triangle: North American Insurance: Casualty $ 605.9 Professional liability 352.7 Property 74.5 Programs 83.8 Healthcare 135.6 Other Specialty 55.6 Global Markets Insurance: Casualty 62.9 Casualty - RSA acquired reserves 5.0 Professional liability 111.9 Professional liability - RSA acquired reserves 1.0 Property 4.0 Property - RSA acquired reserves 15.3 Other specialty 30.7 Other specialty - RSA acquired reserves 31.5 Reinsurance: Property 3.8 Casualty — Specialty — Total reinsurance recoverables per the loss development triangles: $ 1,574.0 Total gross reserves for losses and loss expenses per the loss development triangles: $ 6,474.4 Other balances not included in the loss development triangles: Unallocated loss adjustment expenses 118.6 Other reserves not included in the loss development triangles 43.6 Fair value adjustment 6.0 Currency translation adjustment (3.0 ) Other (0.4 ) 164.8 Total gross reserves for losses and loss expenses $ 6,639.2
(Average historical claims duration)	Years 1 2 3 4 5 6 7 North American Insurance Casualty 3 % 13 % 18 % 13 % 14 % 6 % 7 % Professional liability 5 % 20 % 18 % 16 % 12 % 8 % 14 % Property 34 % 44 % 17 % 7 % 2 % 1 % — % Programs 9 % 20 % 21 % 15 % 11 % 6 % 4 % Healthcare 1 % 9 % 23 % 21 % 17 % 14 % 5 % Other specialty 8 % 23 % 13 % 9 % 3 % 3 % 66 % Global Markets Insurance - excluding the RSA acquired reserves Casualty 2 % 5 % 2 % 16 % 3 % — % — % Professional liability 1 % 4 % 13 % 6 % 12 % 2 % 38 % Property 25 % 34 % 18 % 11 % 5 % 1 % — % Other specialty 18 % 23 % 37 % 7 % — % — % — % Reinsurance Property 28 % 37 % 18 % 7 % 5 % 2 % 1 % Casualty 3 % 10 % 12 % 12 % 13 % 7 % 6 % Specialty 13 % 57 % 14 % 4 % 4 % 2 % 3 %

Ceded Reinsurance (Tables)

Ceded Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Components of reinsurance recoverable	The amount of reinsurance recoverable is as follows: 2016 2015 OSLR recoverable $ 384.1 $ 254.6 IBNR recoverable 1,240.9 1,225.4 Reinsurance recoverable $ 1,625.0 $ 1,480.0 Reinsurance recoverable on paid losses $ 104.4 $ 96.4
Effects of reinsurance	Direct, assumed and ceded premiums written and earned and losses and loss expenses incurred are as follows: Premiums Written Premiums Earned Losses and Loss Expenses Year Ended December 31, 2016 Direct $ 2,359.6 $ 2,316.6 $ 1,539.2 Assumed 706.2 743.1 379.4 Ceded (810.0 ) (715.6 ) (416.8 ) $ 2,255.8 $ 2,344.1 $ 1,501.8 Year Ended December 31, 2015 Direct $ 2,291.6 $ 2,255.3 $ 1,471.6 Assumed 801.4 863.6 442.8 Ceded (645.0 ) (630.5 ) (328.1 ) $ 2,448.0 $ 2,488.4 $ 1,586.3 Year Ended December 31, 2014 Direct $ 1,996.8 $ 1,835.1 $ 1,031.3 Assumed 938.6 941.2 464.7 Ceded (613.4 ) (593.6 ) (296.8 ) $ 2,322.0 $ 2,182.7 $ 1,199.2
Schedule of ceded credit risk by reinsurer	December 31, 2016 A.M. Best Reinsurance Recoverable Percentage of Total Prepaid Reinsurance (1) Percentage of Total Munich Re A+ $ 348.1 21.4 % $ 87.5 18.0 % Axis Capital A+ 160.4 9.9 % 58.5 12.0 % Swiss Re A+ 146.7 9.0 % 64.2 13.2 % Markel A 103.0 6.3 % 25.9 5.3 % Arch Re A+ 100.5 6.2 % 14.0 2.9 % Top five reinsurers 858.7 52.8 % 250.1 51.4 % Other reinsurers’ balances 766.3 47.2 % 236.3 48.6 % Total reinsurance recoverable $ 1,625.0 100.0 % $ 486.4 100.0 % December 31, 2015 A.M. Best Rating Reinsurance Recoverable Percentage of Total Prepaid Reinsurance (1) Percentage of Total Munich Re A+ $ 307.9 20.8 % $ 61.7 15.7 % Axis Capital A+ 150.8 10.2 % 32.2 8.2 % Arch Re A+ 115.3 7.8 % 16.0 4.1 % Swiss Re A+ 103.9 7.0 % 57.3 14.6 % RenaissanceRe A+ 94.0 6.4 % 8.0 2.0 % Top five reinsurers 771.9 52.2 % 175.2 44.6 % Other reinsurers’ balances 708.1 47.8 % 217.1 55.4 % Total reinsurance recoverable $ 1,480.0 100.0 % $ 392.3 100.0 % (1) Prepaid reinsurance represents unearned premiums ceded to reinsurance companies.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of goodwill and intangible assets	The following table shows the Company’s goodwill and intangible assets at December 31, 2016 and 2015 : Goodwill Indefinite-Lived Intangible Assets Finite-Lived Intangible Assets Net Carrying Value Net Carrying Value Gross Carrying Value Accumulated Amortization Net Carrying Value Balance at December 31, 2014 $ 278.3 $ 23.9 $ 41.3 $ (18.9 ) $ 22.4 Additions 110.1 — 83.5 — 83.5 Impairments — — (1.4 ) — (1.4 ) Amortization of intangible assets — — — (8.3 ) (8.3 ) Foreign currency translation adjustment (0.3 ) — (3.5 ) — (3.5 ) Balance at December 31, 2015 388.1 23.9 119.9 (27.2 ) 92.7 Additions 2.7 — — — — Impairments — — (0.9 ) — (0.9 ) Amortization of intangible assets — — — (9.8 ) (9.8 ) Foreign currency translation adjustment (1.1 ) — (1.2 ) — (1.2 ) Balance at December 31, 2016 $ 389.7 $ 23.9 $ 117.8 $ (37.0 ) $ 80.8
Schedule of estimated amortization expense	The estimated amortization expense for each of the five succeeding fiscal years and thereafter related to the Company’s finite-lived intangible assets is as follows: Amount 2017 $ 8.8 2018 8.8 2019 7.3 2020 6.1 2021 5.9 2022 and thereafter 43.9 Total $ 80.8

Debt and Financing Arrangemen37

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of financing structure	The following table shows the Company’s financing structure: Outstanding (1) Unamortized discount and debt issuance costs Balance (2) December 31, 2016 2010 Senior notes due 2020 (discount is based on imputed interest rate of 2.80%) 300.0 1.8 298.2 2015 Senior notes due 2025 (discount is based on imputed interest rate of 2.18%) 500.0 4.0 496.0 Swiss office building mortgage 16.9 — 16.9 Swiss office building credit facility 5.1 — 5.1 $900 million Secured letter of credit facility — uncommitted 458.0 — — $200 million Secured letter of credit facility — committed — — — $ 1,280.0 $ 5.8 $ 816.2 December 31, 2015 2006 Senior notes due 2016 (discount is based on imputed interest rate of 3.77%) $ 500.0 $ 0.5 $ 499.5 2010 Senior notes due 2020 (discount is based on imputed interest rate of 2.78%) 300.0 2.3 297.7 2015 Senior notes due 2025 (discount is based on imputed interest rate of 2.18%) 500.0 4.3 495.7 Swiss office building mortgage 17.9 — 17.9 Swiss office building credit facility 5.1 — 5.1 $1,000 million Secured letter of credit facility — uncommitted 507.5 — — $150 million Secured letter of credit facility — committed — — — $ 1,830.5 $ 7.1 $ 1,315.9 (1) Indicates utilization of commitment amount, not drawn borrowings. (2) Represents the principal amount borrowed, net of unamortized discount and debt issuance costs.
Schedule of debt maturities	The following table reflects the Company’s debt maturities, which includes its senior notes and other long-term debt: Amount 2017 $ 5.4 2018 0.3 2019 0.3 2020 300.3 2021 0.3 2022 and thereafter 515.4 Total $ 822.0

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of components of income tax expense	The components of income tax expense are as follows: Year Ended December 31, 2016 2015 2014 Current income tax expense $ 5.1 $ 9.8 $ 26.8 Deferred income tax (benefit) expense (14.2 ) (4.0 ) 3.7 Income tax (benefit) expense $ (9.1 ) $ 5.8 $ 30.5
Schedule of sources of income before income tax	Our income or loss is primarily sourced from our Bermuda, U.S., European, including Switzerland, and Asia Pacific operations. The income (loss) before income taxes for these operations are as follows: Year Ended December 31, 2016 2015 2014 Switzerland $ (25.5 ) $ (15.7 ) $ (19.0 ) Bermuda 336.6 162.1 460.2 United States (27.5 ) 12.8 72.9 All other jurisdictions (37.4 ) (69.5 ) 6.7 Income before income taxes $ 246.2 $ 89.7 $ 520.8
Schedule of significant components of net deferred tax assets	The significant components of the net deferred tax assets are as follows: December 31, 2016 2015 Deferred tax assets: Reserve for losses and loss expenses $ 17.7 $ 22.2 Equity compensation 16.0 14.2 Unearned premium 17.1 18.1 Deferred acquisition costs 11.9 10.5 Mark-to-market losses 8.6 — Net loss carryforward 21.0 27.3 Total deferred tax assets 92.3 92.3 Deferred tax liabilities: Intangible assets (21.9 ) (23.3 ) Mark-to-market gains — (3.0 ) Depreciation (4.4 ) (6.4 ) Market discount on bonds (2.0 ) (1.2 ) Other (1.2 ) (5.2 ) Total deferred tax liabilities (29.5 ) (39.1 ) Net deferred taxes before valuation allowance 62.8 53.2 Valuation allowance (24.1 ) (28.8 ) Net deferred tax assets $ 38.7 $ 24.4
Schedule of current taxes receivable or payable	Current taxes receivable or payable was as follows: December 31, 2016 2015 Current tax receivable $ 5.5 $ 5.5 Current tax payable $ 0.7 $ 2.5
Schedule of reconciliation between effective and expected tax rate	The reconciliation between the Company’s effective tax rate on pre-tax accounting income and the expected tax rate is as follows: Year Ended December 31, 2016 2015 2014 Expected tax rate 7.8 % 7.8 % 7.8 % Income not subject to income tax (10.7 )% (14.2 )% (7.1 )% Valuation allowance 4.4 % 14.5 % 2.3 % Foreign taxes at local expected tax rates (4.6 )% (1.7 )% 4.4 % Disallowed expenses and capital allowances 0.4 % 3.2 % 0.2 % Prior year refunds and adjustments (0.3 )% — % 1.2 % Other (0.7 )% (3.2 )% (2.9 )% Effective tax rate (3.7 )% 6.4 % 5.9 %

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Issued share capital	The issued share capital consists of the following: December 31, 2016 2015 Common shares issued and fully paid, 2016 and 2015: CHF 4.10 per share 93,586,418 95,523,230 Share capital at end of year $ 378.8 $ 386.7
Schedule of common stock outstanding roll forward	2016 2015 Shares issued at beginning of year 95,523,230 100,775,256 Shares canceled (1,936,812 ) (5,252,026 ) Total shares issued at end of year 93,586,418 95,523,230 Treasury shares issued at beginning of year 4,563,595 4,579,774 Shares repurchased 4,669,513 6,047,437 Shares issued out of treasury (807,998 ) (811,590 ) Shares canceled (1,936,812 ) (5,252,026 ) Total treasury shares at end of year 6,488,298 4,563,595 Total shares outstanding at end of year 87,098,120 90,959,635
Dividends paid	The Company paid the following dividends during the years ended December 31, 2016 , 2015 and 2014 : Dividend Paid Dividend Share Total Paid December 29, 2016 $ 0.260 $ 22.6 September 29, 2016 $ 0.260 $ 22.6 June 30, 2016 $ 0.260 $ 22.8 March 31, 2016 $ 0.260 $ 23.4 December 31, 2015 $ 0.260 $ 23.7 October 1, 2015 $ 0.260 $ 23.6 July 2, 2015 $ 0.260 $ 23.6 April 2, 2015 $ 0.225 $ 21.5 January 2, 2015 $ 0.225 $ 21.7 October 2, 2014 $ 0.225 $ 21.7 July 2, 2014 $ 0.225 $ 21.9 April 3, 2014 $ 0.167 $ 16.5
Share repurchases	The Company’s share repurchases were as follows: Year Ended December 31, 2016 2015 2014 Common shares repurchased 4,669,513 6,047,437 4,906,785 Total cost of shares repurchased $ 166.3 $ 245.3 $ 175.4 Average price per share $ 35.61 $ 40.56 $ 35.74

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of activity related to options	The following table summarizes the activity related to options granted and exercised: Year Ended December 31, 2016 2015 2014 Options granted — — — Weighted average grant date fair value $ — $ — $ — Options exercised (428,938 ) (454,602 ) (479,831 ) Total intrinsic value of options exercised $ 10.8 $ 12.0 $ 10.3 Proceeds from option exercises $ 10.3 $ 10.1 $ 10.0 The activity related to the Company’s stock options is as follows: Year Ended December 31, 2016 Options Weighted Average Exercise Price Weighted Average Contractual Term Aggregate Intrinsic Value Outstanding at beginning of year 1,968,607 $ 16.86 Exercised (428,938 ) (15.24 ) Forfeited (13,926 ) 10.31 Outstanding at end of year 1,525,743 17.36 3.3 years $ 55.5 Exercisable at end of year 1,525,743 $ 17.36 3.3 years $ 55.5
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of compensation expense by type of award	The following table shows the total stock-related compensation expense relating to the stock options, RSUs, LTIPs and cash equivalent awards. Year Ended December 31, 2016 2015 2014 Stock options $ — $ 0.3 $ 1.9 RSUs and performance-based equity awards 16.4 15.0 12.3 Cash-equivalent stock awards 21.9 34.4 37.8 Total $ 38.3 $ 49.7 $ 52.0
Rsus Other Than Performance Based Rsus
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of activity related to equity based awards granted and exercised	The activity related to the Company’s RSU awards is as follows: Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Outstanding at beginning of year 819,309 $ 37.33 RSUs granted 689,042 32.00 RSUs forfeited (123,307 ) (34.80 ) RSUs fully vested (251,115 ) (36.30 ) Outstanding at end of year 1,133,929 $ 34.56 $ 60.9
Performance Based Rsus
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of activity related to equity based awards granted and exercised	The activity related to the Company’s performance-based equity awards is as follows: Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Outstanding at beginning of year 591,683 $ 34.78 Performance-based equity awards granted 200,730 31.95 Additional awards granted due to achievement of performance criteria 24,979 29.24 Performance-based equity awards forfeited (16,993 ) (36.71 ) Performance-based equity awards fully vested (216,958 ) (29.24 ) Outstanding at end of year 583,441 $ 35.57 $ 31.3
Cash-equivalent stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of activity related to cash-equivalent equity awards	The activity related to the Company's cash-equivalent RSUs and performance-based equity awards is as follows: RSU's Performance-based Awards Year Ended December 31, 2016 Number of Awards Weighted Average Grant Date Fair Value Number of Awards Weighted Average Grant Date Fair Value Outstanding at beginning of year 1,277,083 $ 31.94 693,477 33.25 Granted 167,438 31.95 50,183 31.95 Additional awards granted due to achievement of performance criteria — — 37,434 29.24 Forfeited (90,245 ) (33.66 ) (18,104 ) (35.27 ) Fully vested (581,829 ) (29.14 ) (325,386 ) (29.24 ) Outstanding at end of year 772,447 $ 33.86 437,604 $ 35.65

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Comparison of basic and diluted earnings per share	The following table sets forth the comparison of basic and diluted earnings per share: Year Ended December 31, 2016 2015 2014 Basic earnings per share: Net income $ 255.3 $ 83.9 $ 490.3 Weighted average common shares outstanding 88,275,810 92,530,208 97,538,319 Basic earnings per share $ 2.89 $ 0.91 $ 5.03 Year Ended December 31, 2016 2015 2014 Diluted earnings per share: Net income $ 255.3 $ 83.9 $ 490.3 Weighted average common shares outstanding 88,275,810 92,530,208 97,538,319 Share equivalents: Stock options 839,038 1,031,666 1,432,960 RSU and PU awards 677,033 591,773 605,808 Employee share purchase plan 9,013 20,813 14,686 Weighted average common shares and common share equivalents outstanding — diluted 89,800,894 94,174,460 99,591,773 Diluted earnings per share $ 2.84 $ 0.89 $ 4.92

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Summary of future minimum rental payments on operating leases	The Company leases office space under operating leases expiring in various years through 2031. The following are future minimum rental payments as of December 31, 2016 : Amount 2017 $ 21.6 2018 20.7 2019 19.6 2020 17.8 2021 16.9 2021 and thereafter 116.2 $ 212.8
Summary of three largest individual producers	The three largest individual producers as a percentage of gross premiums written are as follows: Year Ended December 31, 2016 2015 2014 Marsh & McLennan Companies, Inc. 21 % 24 % 25 % Aon Corporation 14 % 16 % 17 % Willis Group Holdings 9 % 11 % 10 %

Statutory Capital and Surplus (

Statutory Capital and Surplus (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure Dividend Restrictions And Statutory Requirements [Abstract]
Schedule of statutory capital	The statutory capital and surplus and minimum required statutory capital and surplus for the Company’s most significant regulatory jurisdictions at December 31, 2016 and 2015 were as follows: December 31, 2016 December 31, 2015 Statutory Capital and Surplus Minimum Required Statutory Capital and Surplus Statutory Capital and Surplus Minimum Required Statutory Capital and Surplus Bermuda $ 3,494.1 $ 800.2 $ 3,270.9 $ 853.2 United States 1,185.9 263.3 1,215.5 241.0 Ireland 395.5 84.7 414.0 26.9 Switzerland 327.5 218.2 183.6 17.7 United Kingdom 268.4 264.1 245.9 231.8
Schedule of statutory net income loss	The statutory net income (loss) for the Company’s most significant regulatory jurisdictions for the years ended December 31, 2016 , 2015 and 2014 was as follows: Year Ended December 31, 2016 2015 2014 Bermuda $ 366.4 $ 221.5 $ 487.1 United States 19.0 40.5 45.4 Ireland 10.1 3.2 3.2 Switzerland 11.0 10.7 7.4 United Kingdom (5.1 ) (39.4 ) (7.8 )
Schedule of allowable dividends by jurisdiction	At December 31, 2016 , the maximum amount of ordinary dividends or distributions that can be paid, without prior regulatory approval, for the Company’s most significant regulatory jurisdictions, were as follows: December 31, 2016 Bermuda $ 873.5 United States — Ireland 35.5 Switzerland — United Kingdom 2.7

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Summary of segment results	The following tables provide a summary of the segment results: Year Ended December 31, 2016 North American Insurance Global Markets Insurance Reinsurance Total Gross premiums written $ 1,856.3 $ 503.3 $ 706.2 $ 3,065.8 Net premiums written 1,223.4 367.5 664.9 2,255.8 Net premiums earned 1,266.9 377.8 699.4 2,344.1 Net losses and loss expenses (862.2 ) (269.5 ) (370.1 ) (1,501.8 ) Acquisition costs (132.0 ) (66.5 ) (141.3 ) (339.8 ) General and administrative expenses (223.3 ) (123.7 ) (64.5 ) (411.5 ) Underwriting income (loss) 49.4 (81.9 ) 123.5 91.0 Other insurance-related revenue 6.7 1.4 4.3 12.4 Other insurance-related expenses (2.3 ) (1.1 ) (3.4 ) (6.8 ) Segment income (loss) 53.8 (81.6 ) 124.4 96.6 Net investment income 217.8 Net realized investment gains 2.1 Amortization and impairment of intangible assets (10.7 ) Interest expense (63.7 ) Foreign exchange gain 4.1 Income before income taxes $ 246.2 Loss and loss expense ratio 68.1 % 71.3 % 52.9 % 64.1 % Acquisition cost ratio 10.4 % 17.6 % 20.2 % 14.5 % General and administrative expense ratio 17.6 % 32.7 % 9.2 % 17.6 % Expense ratio 28.0 % 50.3 % 29.4 % 32.1 % Combined ratio 96.1 % 121.6 % 82.3 % 96.2 % Year Ended December 31, 2015 North American Insurance Global Markets Reinsurance Total Gross premiums written $ 1,815.3 $ 476.3 $ 801.4 $ 3,093.0 Net premiums written 1,358.1 324.1 765.8 2,448.0 Net premiums earned 1,301.4 366.8 820.2 2,488.4 Net losses and loss expenses (910.2 ) (240.3 ) (435.8 ) (1,586.3 ) Acquisition costs (139.6 ) (70.9 ) (164.9 ) (375.4 ) General and administrative expenses (224.6 ) (108.4 ) (73.3 ) (406.3 ) Underwriting income (loss) 27.0 (52.8 ) 146.2 120.4 Other insurance-related revenue 3.5 — — 3.5 Other insurance-related expenses (2.7 ) (2.5 ) (1.0 ) (6.2 ) Segment income (loss) 27.8 (55.3 ) 145.2 117.7 Net investment income 182.1 Net realized investment losses (127.6 ) Amortization and impairment of intangible assets (9.8 ) Interest expense (61.4 ) Foreign exchange loss (11.3 ) Income before income taxes $ 89.7 Loss and loss expense ratio 69.9 % 65.5 % 53.1 % 63.7 % Acquisition cost ratio 10.7 % 19.3 % 20.1 % 15.1 % General and administrative expense ratio 17.3 % 29.5 % 8.9 % 16.3 % Expense ratio 28.0 % 48.8 % 29.0 % 31.4 % Combined ratio 97.9 % 114.3 % 82.1 % 95.1 % Year Ended December 31, 2014 North American Insurance Global Markets Reinsurance Total Gross premiums written $ 1,716.3 $ 280.5 $ 938.6 $ 2,935.4 Net premiums written 1,230.8 188.0 903.2 2,322.0 Net premiums earned 1,111.1 162.6 909.0 2,182.7 Net losses and loss expenses (683.8 ) (61.1 ) (454.3 ) (1,199.2 ) Acquisition costs (105.9 ) (18.2 ) (171.0 ) (295.1 ) General and administrative expenses (219.6 ) (68.1 ) (78.0 ) (365.7 ) Underwriting income 101.8 15.2 205.7 322.7 Other insurance-related revenue 2.1 — — 2.1 Other insurance-related expenses (1.9 ) (6.7 ) — (8.6 ) Segment income 102.0 8.5 205.7 316.2 Net investment income 176.9 Net realized investment gains 89.0 Amortization of intangible assets (2.5 ) Interest expense (57.8 ) Foreign exchange loss (1.0 ) Income before income taxes $ 520.8 Loss and loss expense ratio 61.5 % 37.6 % 50.0 % 54.9 % Acquisition cost ratio 9.5 % 11.2 % 18.8 % 13.5 % General and administrative expense ratio 19.8 % 41.9 % 8.6 % 16.8 % Expense ratio 29.3 % 53.1 % 27.4 % 30.3 % Combined ratio 90.8 % 90.7 % 77.4 % 85.2 %
Analysis of gross premiums written by geographic location	The following table shows an analysis of the Company’s gross premiums written by geographic location of the Company’s subsidiaries. All intercompany premiums have been eliminated. Year Ended December 31, 2016 2015 2014 United States $ 1,903.4 $ 1,893.4 $ 1,795.6 Bermuda 495.4 543.6 640.9 Asia Pacific 352.2 313.1 167.3 Europe 296.3 326.9 318.6 Canada 18.5 16.0 13.0 Total gross premiums written $ 3,065.8 $ 3,093.0 $ 2,935.4
Premiums earned by segment and line of business	The following table shows the Company’s net premiums earned by line of business for each segment for the years ended December 31, 2016 , 2015 and 2014 . Year Ended December 31, 2016 2015 2014 North American Insurance: Casualty $ 396.7 $ 424.0 $ 334.6 Professional liability 388.5 385.3 276.1 Property 127.6 162.8 170.3 Healthcare 66.5 102.9 168.5 Programs 170.4 150.7 119.8 Specialty and other 117.2 75.6 41.9 Total 1,266.9 1,301.4 1,111.1 Global Markets Insurance: Property 67.9 106.7 34.0 Professional liability 96.2 102.5 69.1 Specialty and other 125.9 99.8 44.2 Casualty 87.8 57.8 15.3 Total 377.8 366.8 162.6 Reinsurance: Property 337.2 403.5 412.0 Casualty 183.7 224.4 175.5 Specialty 178.5 192.3 321.5 Total 699.4 820.2 909.0 Total net premiums earned $ 2,344.1 $ 2,488.4 $ 2,182.7

Condensed Consolidated Guaran45

Condensed Consolidated Guarantor Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of condensed consolidating balance sheet	Condensed Consolidating Balance Sheet: As of December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated ASSETS: Investments $ — $ — $ 7,942.3 $ — $ 7,942.3 Cash and cash equivalents 13.1 0.8 707.0 — 720.9 Insurance balances receivable — — 784.0 — 784.0 Funds held — — 466.8 — 466.8 Reinsurance recoverable — — 1,625.0 — 1,625.0 Reinsurance recoverable on paid losses — — 104.4 — 104.4 Net deferred acquisition costs — — 121.1 — 121.1 Goodwill and intangible assets — — 494.4 — 494.4 Balances receivable on sale of investments — — 114.7 — 114.7 Investments in subsidiaries 3,433.7 4,020.1 — (7,453.8 ) — Due from subsidiaries 115.6 — 29.9 (145.5 ) — Other assets 1.8 0.8 802.8 — 805.4 Total assets $ 3,564.2 $ 4,021.7 $ 13,192.4 $ (7,599.3 ) $ 13,179.0 LIABILITIES: Reserve for losses and loss expenses $ — $ — $ 6,639.2 $ — $ 6,639.2 Unearned premiums — — 1,688.1 — 1,688.1 Reinsurance balances payable — — 223.3 — 223.3 Balances due on purchases of investments — — 79.7 — 79.7 Senior notes — 794.2 — — 794.2 Other long-term debt — — 22.0 — 22.0 Due to subsidiaries 9.9 20.0 115.6 (145.5 ) — Other liabilities 2.5 5.7 172.6 — 180.7 Total liabilities 12.4 819.9 8,940.5 (145.5 ) 9,627.2 Total shareholders’ equity 3,551.8 3,201.8 4,251.9 (7,453.8 ) 3,551.8 Total liabilities and shareholders’ equity $ 3,564.2 $ 4,021.7 $ 13,192.4 $ (7,599.3 ) $ 13,179.0 As of December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated ASSETS: Investments $ — $ — $ 8,571.2 $ — $ 8,571.2 Cash and cash equivalents 21.8 1.0 585.2 — 608.0 Insurance balances receivable — — 745.9 — 745.9 Funds held — — 640.8 — 640.8 Reinsurance recoverable — — 1,480.0 — 1,480.0 Reinsurance recoverable on paid losses — — 96.4 — 96.4 Net deferred acquisition costs — — 165.2 — 165.2 Goodwill and intangible assets — — 504.7 — 504.7 Balances receivable on sale of investments — — 36.9 — 36.9 Investments in subsidiaries 3,347.0 4,396.3 — (7,743.3 ) — Due from subsidiaries 173.1 36.4 16.8 (226.3 ) — Other assets 1.8 0.1 660.9 — 662.8 Total assets $ 3,543.7 $ 4,433.8 $ 13,504.0 $ (7,969.6 ) $ 13,511.9 LIABILITIES: Reserve for losses and loss expenses $ — $ — $ 6,456.2 $ — $ 6,456.2 Unearned premiums — — 1,683.3 — 1,683.3 Reinsurance balances payable — — 214.4 — 214.4 Balances due on purchases of investments — — 125.1 — 125.1 Senior notes — 1,292.9 — — 1,292.9 Other long-term debt — — 23.0 — 23.0 Due to subsidiaries 8.5 8.3 209.5 (226.3 ) — Other liabilities 2.7 22.2 159.7 — 184.5 Total liabilities 11.2 1,323.4 8,871.2 (226.3 ) 9,979.4 Total shareholders’ equity 3,532.5 3,110.4 4,632.8 (7,743.3 ) 3,532.5 Total liabilities and shareholders’ equity $ 3,543.7 $ 4,433.8 $ 13,504.0 $ (7,969.6 ) $ 13,511.9
Schedule of condensed consolidating income statement	Condensed Consolidating Income Statement: Year Ended December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,344.1 $ — $ 2,344.1 Net investment income 0.1 0.1 217.6 — 217.8 Net realized investment losses — — 2.1 — 2.1 Other income — — 12.4 — 12.4 Net losses and loss expenses — — (1,501.8 ) — (1,501.8 ) Acquisition costs — — (339.8 ) — (339.8 ) General and administrative expenses (18.7 ) 0.2 (393.0 ) — (411.5 ) Other expense — — (6.8 ) — (6.8 ) Amortization of intangible assets — — (10.7 ) — (10.7 ) Interest expense — (61.6 ) (2.1 ) — (63.7 ) Foreign exchange gain (loss) — — 4.1 — 4.1 Income tax (expense) benefit (0.1 ) — 9.2 — 9.1 Equity in earnings of consolidated subsidiaries 274.0 341.9 — (615.9 ) — NET INCOME (LOSS) $ 255.3 $ 280.6 $ 335.3 $ (615.9 ) $ 255.3 Other comprehensive income (loss) (2.3 ) — (2.3 ) 2.3 (2.3 ) COMPREHENSIVE INCOME (LOSS) $ 253.0 $ 280.6 $ 333.0 $ (613.6 ) $ 253.0 Year Ended December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,488.4 $ — $ 2,488.4 Net investment income — 0.1 182.0 — 182.1 Net realized investment gains — — (127.6 ) — (127.6 ) Other income — — 3.5 — 3.5 Net losses and loss expenses — — (1,586.3 ) — (1,586.3 ) Acquisition costs — — (375.4 ) — (375.4 ) General and administrative expenses (36.7 ) (0.5 ) (369.1 ) — (406.3 ) Other expense — — (6.2 ) — (6.2 ) Amortization of intangible assets — — (9.8 ) — (9.8 ) Interest expense — (59.2 ) (2.2 ) — (61.4 ) Foreign exchange gain (loss) — — (11.3 ) — (11.3 ) Income tax (expense) benefit (0.1 ) — (5.7 ) — (5.8 ) Equity in earnings of consolidated subsidiaries 120.7 157.3 — (278.0 ) — NET INCOME (LOSS) $ 83.9 $ 97.7 $ 180.3 $ (278.0 ) $ 83.9 Other comprehensive income (loss) (9.3 ) — (9.3 ) 9.3 (9.3 ) COMPREHENSIVE INCOME (LOSS) $ 74.6 $ 97.7 $ 171.0 $ (268.7 ) $ 74.6 Year Ended December 31, 2014 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated Net premiums earned $ — $ — $ 2,182.7 $ — $ 2,182.7 Net investment income 0.1 — 176.8 — 176.9 Net realized investment gains — — 89.0 — 89.0 Other income — — 2.1 — 2.1 Net losses and loss expenses — — (1,199.2 ) — (1,199.2 ) Acquisition costs — — (295.1 ) — (295.1 ) General and administrative expenses (35.6 ) (3.1 ) (327.1 ) — (365.7 ) Other expense — — (8.6 ) — (8.6 ) Amortization of intangible assets — — (2.5 ) — (2.5 ) Interest expense — (55.4 ) (2.3 ) — (57.8 ) Foreign exchange gain (loss) — 0.1 (1.1 ) — (1.0 ) Income tax (expense) benefit (0.1 ) — (30.4 ) — (30.5 ) Equity in earnings of consolidated subsidiaries 525.9 564.6 — (1,090.5 ) — NET INCOME (LOSS) $ 490.3 $ 506.2 $ 584.3 $ (1,090.5 ) $ 490.3 Other comprehensive income (loss) — — — — — COMPREHENSIVE INCOME (LOSS) $ 490.3 $ 506.2 $ 584.3 $ (1,090.5 ) $ 490.3
Schedule of condensed consolidating statement of cash flows	Condensed Consolidating Statement of Cash Flows: Year Ended December 31, 2016 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES $ 238.8 $ 506.4 $ 493.6 $ (841.0 ) $ 397.8 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases trading securities — — (5,423.7 ) — (5,423.7 ) Purchases of other invested assets — — (119.0 ) — (119.0 ) Sales of trading securities — — 5,929.9 — 5,929.9 Sales of other invested assets — — 96.3 — 96.3 Net cash paid for acquisitions — — (1.2 ) — (1.2 ) Return of investment in subsidiary — 250.0 — (250.0 ) — Other — — (19.4 ) — (19.4 ) Net cash provided by (used in) investing activities — 250.0 462.9 (250.0 ) 462.9 CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (91.5 ) — — — (91.5 ) Intercompany dividends paid — (256.6 ) (584.4 ) 841.0 — Proceeds to parent — — (250.0 ) 250.0 — Proceeds from the exercise of stock options 10.3 — — — 10.3 Share repurchases (166.3 ) — — — (166.3 ) Repayment of senior notes — (500.0 ) — — (500.0 ) Repayment of other long-term debt — — (0.3 ) — (0.3 ) Net cash provided by (used in) financing activities (247.5 ) (756.6 ) (834.7 ) 1,091.0 (747.8 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS (8.7 ) (0.2 ) 121.8 — 112.9 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 21.8 1.0 585.2 — 608.0 CASH AND CASH EQUIVALENTS, END OF YEAR $ 13.1 $ 0.8 $ 707.0 $ — $ 720.9 Year Ended December 31, 2015 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES $ 339.6 $ 377.7 $ 598.1 $ (811.1 ) $ 504.3 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases of trading securities — — (5,863.2 ) — (5,863.2 ) Purchases of other invested assets — — (126.7 ) — (126.7 ) Sales of trading securities — — 5,328.8 — 5,328.8 Sales of other invested assets — — 161.3 — 161.3 Net cash paid for acquisitions — — (124.4 ) — (124.4 ) Capital contributions — (496.7 ) 496.7 — — Other — — (11.5 ) — (11.5 ) Net cash provided by (used in) investing activities — (496.7 ) (139.0 ) — (635.7 ) CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (114.1 ) — — — (114.1 ) Intercompany dividends paid — (378.4 ) (432.7 ) 811.1 — Proceeds from the exercise of stock options 10.1 — — — 10.1 Share repurchases (246.4 ) — — — (246.4 ) Proceeds from senior notes — 496.7 — — 496.7 Proceeds from other long-term debt — — 4.0 — 4.0 Repayment of other long-term debt — — (0.2 ) — (0.2 ) Net cash provided by (used in) financing activities (350.4 ) 118.3 (428.9 ) 811.1 150.1 NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS (10.8 ) (0.7 ) 30.2 — 18.7 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 32.6 1.7 555.0 — 589.3 CASH AND CASH EQUIVALENTS, END OF YEAR $ 21.8 $ 1.0 $ 585.2 $ — $ 608.0 Year Ended December 31, 2014 Allied World Switzerland (Parent Guarantor) Allied World Bermuda (Subsidiary Issuer) Other Allied World Subsidiaries Consolidating Adjustments Allied World Switzerland Consolidated CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES: $ 264.4 $ 292.9 $ 493.8 $ (643.3 ) $ 407.8 CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES: Purchases of trading securities — — (7,630.0 ) — (7,630.0 ) Purchases of other invested assets — — (307.9 ) — (307.9 ) Sales of trading securities — — 7,536.9 — 7,536.9 Sales of other invested assets — — 267.9 — 267.9 Net cash paid for acquisitions — — (2.6 ) — (2.6 ) Other — — 8.7 — 8.7 Net cash provided by (used in) investing activities — — (127.0 ) — (127.0 ) CASH FLOWS PROVIDED BY (USED IN) FINANCING ACTIVITIES: Dividends paid (76.7 ) — — — (76.7 ) Intercompany dividends paid — (294.0 ) (349.3 ) 643.3 — Proceeds from the exercise of stock options 10.0 — — — 10.0 Share repurchases (175.9 ) — — — (175.9 ) Proceeds from other long-term debt — — 19.2 — 19.2 Net cash provided by (used in) financing activities (242.6 ) (294.0 ) (330.1 ) 643.3 (223.4 ) NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS 21.8 (1.1 ) 36.7 — 57.4 CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR 10.8 2.8 518.3 — 531.9 CASH AND CASH EQUIVALENTS, END OF YEAR $ 32.6 $ 1.7 $ 555.0 $ — $ 589.3

Unaudited Quarterly Financial46

Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of unaudited consolidated statements of income by quarter	The following are the unaudited consolidated statements of income by quarter for the years ended December 31, 2016 and 2015 : Quarter Ended December 31, September 30, June 30, March 31, REVENUES: Gross premiums written $ 671.7 $ 730.2 $ 800.3 $ 863.5 Premiums ceded (226.4 ) (201.9 ) (222.2 ) (159.5 ) Net premiums written 445.3 528.3 578.1 704.0 Change in unearned premiums 131.7 55.7 24.8 (123.9 ) Net premiums earned 577.0 584.0 602.9 580.1 Net investment income 58.1 50.6 55.8 53.3 Net realized investment (losses) gains (101.9 ) 10.7 74.5 18.9 Other income 4.8 1.8 5.2 0.6 538.0 647.1 738.4 652.9 EXPENSES: Net losses and loss expenses 387.8 376.3 365.4 372.4 Acquisition costs 82.0 82.0 87.4 88.3 General and administrative expenses 106.1 104.2 104.7 96.4 Other expense 1.8 2.2 1.7 1.1 Amortization and impairment of intangible assets 3.2 2.5 2.5 2.5 Interest expense 10.4 13.5 19.9 20.0 Foreign exchange loss (gain) 0.8 1.0 (2.9 ) (3.0 ) 592.1 581.7 578.7 577.7 (Loss) income before income taxes (54.1 ) 65.4 159.7 75.2 Income tax (benefit) expense) (13.3 ) (3.2 ) 6.3 1.1 NET (LOSS) INCOME $ (40.8 ) $ 68.6 $ 153.4 $ 74.1 PER SHARE DATA Basic (loss) earnings per share $ (0.47 ) $ 0.79 $ 1.73 $ 0.82 Diluted (loss) earnings per share $ (0.47 ) $ 0.77 $ 1.70 $ 0.81 Weighted average common shares outstanding 87,036,339 87,102,290 88,742,484 90,254,512 Weighted average common shares and common share equivalents outstanding 87,036,339 88,603,101 90,040,509 91,559,225 Quarter Ended December 31, September 30, June 30, March 31, REVENUES: Gross premiums written $ 632.3 $ 754.1 $ 826.0 $ 880.6 Premiums ceded (167.5 ) (147.1 ) (222.3 ) (108.1 ) Net premiums written 464.8 607.0 603.7 772.5 Change in unearned premiums 158.0 43.7 42.7 (204.0 ) Net premiums earned 622.8 650.7 646.4 568.5 Net investment income 49.1 45.7 42.8 44.5 Net realized investment (losses) gains (38.8 ) (113.6 ) (20.2 ) 45.0 Other income 1.0 0.7 0.9 0.9 634.1 583.5 669.9 658.9 EXPENSES: Net losses and loss expenses 412.7 416.9 431.5 325.2 Acquisition costs 96.0 100.1 100.6 78.7 General and administrative expenses 95.0 105.8 108.4 97.1 Other expense 1.9 1.3 1.2 1.8 Amortization and impairment of intangible assets 3.7 2.7 2.8 0.6 Interest expense 18.1 14.5 14.5 14.3 Foreign exchange loss (gain) 0.9 (0.8 ) 1.3 9.9 628.3 640.5 660.3 527.6 Income (loss) before income taxes 5.8 (57.0 ) 9.6 131.3 Income tax expense (benefit) 4.0 (5.3 ) 0.1 7.0 NET INCOME (LOSS) $ 1.8 $ (51.7 ) $ 9.5 $ 124.3 PER SHARE DATA Basic earnings (loss) per share 0.02 (0.57 ) 0.10 1.30 Diluted earnings (loss) per share 0.02 (0.57 ) 0.10 1.27 Weighted average common shares outstanding 90,934,107 90,882,511 92,441,730 95,935,551 Weighted average common shares and common share equivalents outstanding 92,422,422 90,882,511 93,984,226 97,577,029

General General (Details)

General General (Details)	Dec. 18, 2016$ / shares
Fairfax
Business Acquisition [Line Items]
Cash value per share	$ 54

Significant Accounting Polici48

Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncement, Early Adoption [Line Items]
Net premiums earned	$ 577	$ 584	$ 602.9	$ 580.1	$ 622.8	$ 650.7	$ 646.4	$ 568.5	$ 2,344.1	$ 2,488.4	$ 2,182.7
Other income	4.8	1.8	5.2	0.6	1	0.7	0.9	0.9	12.4	3.5	2.1
Other expense	1.8	$ 2.2	$ 1.7	$ 1.1	$ 1.9	$ 1.3	$ 1.2	$ 1.8	6.8	6.2	$ 8.6
Variable Interest Entity, Not Primary Beneficiary
New Accounting Pronouncement, Early Adoption [Line Items]
VIE, maximum exposure to loss	$ 996.8								996.8
Derivative
New Accounting Pronouncement, Early Adoption [Line Items]
Net premiums earned									0.1
Other income									7.7
Other expense									$ 3.4	$ 1

Acquisitions (Consideration Tra

Acquisitions (Consideration Transferred and Recognized Amounts of Identifiable Assets and Liabilities) (Details) - USD ($) $ in Millions	Apr. 02, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 389.7	$ 388.1	$ 278.3
Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Consideration:
Cash consideration	$ 176.5
Recognized amounts of identifiable assets acquired and liabilities assumed:
Fixed maturity investments	246.1
Cash and cash equivalents	47.1
Insurance balances receivable	114.4
Prepaid reinsurance	17.5
Reinsurance recoverable	58.9
Value of business acquired	28.9
Intangible assets	79.9
Other assets	9.9
Reserve for losses and loss expenses	(314.1)
Unearned premiums	(150.5)
Reinsurance balances payable	(35.8)
Net deferred tax liabilities	(11.9)
Accounts payable and accrued liabilities	(20.1)
Total identifiable net assets acquired	70.3
Goodwill	106.2
Total net assets acquired	$ 176.5

Acquisitions (Summary of Intang

Acquisitions (Summary of Intangible Assets Acquired) (Details) - Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc $ in Millions	Apr. 02, 2015USD ($)
Business Acquisition [Line Items]
Intangible assets acquired	$ 108.8
VOBA
Business Acquisition [Line Items]
Intangible assets acquired	28.9
Customer renewals
Business Acquisition [Line Items]
Intangible assets acquired	13
Distribution channels
Business Acquisition [Line Items]
Intangible assets acquired	66.9
SINGAPORE
Business Acquisition [Line Items]
Intangible assets acquired	74.1
SINGAPORE | VOBA
Business Acquisition [Line Items]
Intangible assets acquired	$ 17.8
Estimated useful life	2 years
SINGAPORE | Customer renewals
Business Acquisition [Line Items]
Intangible assets acquired	$ 8.6
Estimated useful life	4 years
SINGAPORE | Distribution channels
Business Acquisition [Line Items]
Intangible assets acquired	$ 47.7
Estimated useful life	18 years
HONG KONG
Business Acquisition [Line Items]
Intangible assets acquired	$ 34.7
HONG KONG | VOBA
Business Acquisition [Line Items]
Intangible assets acquired	$ 11.1
Estimated useful life	1 year 6 months
HONG KONG | Customer renewals
Business Acquisition [Line Items]
Intangible assets acquired	$ 4.4
Estimated useful life	5 years
HONG KONG | Distribution channels
Business Acquisition [Line Items]
Intangible assets acquired	$ 19.2
Estimated useful life	18 years

Acquisitions (Results Since Acq

Acquisitions (Results Since Acquisition and Pro Forma Information) (Details) - Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 155.3
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	$ (28.9)
Business Acquisition, Pro Forma Revenue		$ 2,594.2	$ 2,681.7
Business Acquisition, Pro Forma Net Income (Loss)		$ 74.2	$ 505.9

Acquisitions (Other Details) (D

Acquisitions (Other Details) (Details) - USD ($)	Apr. 02, 2015	Jan. 31, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Apr. 30, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill			$ 388,100,000	$ 389,700,000	$ 388,100,000			$ 278,300,000
Finite-lived Intangible Assets Acquired				$ 0	$ 83,500,000
Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Business Acquisition [Line Items]
Cash consideration	$ 176,500,000
Cash Acquired from Acquisition			17,400,000
Business Combination, Acquisition Related Costs			$ 9,200,000
Goodwill	106,200,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				12 years
Insurance Related Intangible Liability				$ 8,300,000
Insurance Related Intangible Liability Amortization Period				8 years
Latin American Underwriters Holdings Ltd [Member]
Business Acquisition [Line Items]
Cash consideration		$ 5,100,000
Goodwill		2,500,000
Finite-lived Intangible Assets Acquired		$ 3,600,000
Estimated useful life		3 years
Business Combination, Contingent Consideration, Liability		$ 1,000,000				$ 0
HONG KONG | Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Business Acquisition [Line Items]
Goodwill	54,700,000
SINGAPORE | Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Business Acquisition [Line Items]
Goodwill	$ 51,500,000
LABUAN | Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Business Acquisition [Line Items]
Goodwill							$ 1,400,000

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other private securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Realized gain on disposal	$ 21.7
Unrealized gain on change in method of accounting	$ 8.1
Other invested assets
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Income (loss) from equity method investments		$ (6.3)	$ (9.3)
Minimum | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption restriction, lock-up period	1 year
Minimum | Investments without redemption restrictions | Hedge funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	30 days
Gate trigger, percentage	15.00%
Maximum | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption restriction, lock-up period	3 years
Maximum | Investments without redemption restrictions | Hedge funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Gate trigger, percentage	25.00%

Investments (Schedule Of Tradin

Investments (Schedule Of Trading Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Equity securities and other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	$ 1,141.7	$ 1,243.2
Trading securities, Amortized Cost	1,066.2	1,166.2
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	243.9	403
Trading securities, Amortized Cost	235	395.3
Other invested assets
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	897.8	840.2
Trading securities, Amortized Cost	831.2	770.9
Fixed Maturities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	6,737.7	7,201.5
Trading securities, Amortized Cost	6,847.4	7,290.6
U.S. Government and Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,426	1,434
Trading securities, Amortized Cost	1,454.5	1,437.9
Non-U.S. Government and Government Agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	469.9	556.8
Trading securities, Amortized Cost	496.5	579.2
States, municipalities and political subdivisions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	354.1	413.5
Trading securities, Amortized Cost	355.8	396
Corporate debt: financial institutions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,032.7	1,275.4
Trading securities, Amortized Cost	1,033.6	1,277.3
Corporate debt: Industrials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,321.3	1,308.1
Trading securities, Amortized Cost	1,322.3	1,345.6
Corporate debt: utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	140	118.9
Trading securities, Amortized Cost	140.7	125.4
Agency mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	614.5	751.8
Trading securities, Amortized Cost	612.5	745.4
Non-agency residential mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	23.9	34
Trading securities, Amortized Cost	22.7	32.4
Commercial mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	598	582.8
Trading securities, Amortized Cost	636.1	600.1
Asset-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	757.3	726.2
Trading securities, Amortized Cost	$ 772.6	$ 751.1

Investments (Schedule Of Other

Investments (Schedule Of Other Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 960.7	$ 966.7
Unfunded commitments		605.5	613.8
Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		559.8	502
Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 400.9	464.7
Hedge funds | Investments without redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period		30 days
Total Fair Value
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 897.8	840.2
Unfunded commitments		605.5	613.8
Total Fair Value | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		559.8	502
Total Fair Value | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		338	338.2
Total Fair Value | Private equity funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		559.8	447.4
Unfunded commitments		605.5	613.8
Total Fair Value | Private equity funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		559.8	447.4
Total Fair Value | Private equity funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value | Private equity (primary and secondary)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		281	236.4
Unfunded commitments		219.3	231
Total Fair Value | Private equity (primary and secondary) | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 281	$ 236.4
Total Fair Value | Private equity (primary and secondary) | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		1 year	1 year
Total Fair Value | Private equity (primary and secondary) | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		15 years	7 years
Total Fair Value | Private equity (primary and secondary) | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Total Fair Value | Levered credit
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		204.9	205.9
Unfunded commitments		190.8	179
Total Fair Value | Levered credit | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 204.9	$ 205.9
Total Fair Value | Levered credit | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		3 years	4 years
Total Fair Value | Levered credit | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		9 years	8 years
Total Fair Value | Levered credit | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Total Fair Value | Distressed
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		5	5.1
Unfunded commitments		3.8	3.8
Total Fair Value | Distressed | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 5	$ 5.1
Estimated remaining restriction period		1 year	2 years
Total Fair Value | Distressed | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Total Fair Value | Real estate
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		68.9	0
Unfunded commitments		191.6	200
Total Fair Value | Real estate | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 68.9	$ 0
Total Fair Value | Real estate | Investments with redemption restrictions | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		6 years	7 years
Total Fair Value | Real estate | Investments with redemption restrictions | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		8 years	9 years
Total Fair Value | Real estate | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Total Fair Value | Hedge funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		338	379
Unfunded commitments		0	0
Total Fair Value | Hedge funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	54.6
Total Fair Value | Hedge funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		338	324.4
Total Fair Value | Distressed funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		175.3	215.6
Unfunded commitments		0	0
Total Fair Value | Distressed funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	$ 54.6
Estimated remaining restriction period			2 years
Total Fair Value | Distressed funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 175.3	$ 161
Redemption frequency	[1]	Quarterly	Monthly
Redemption notice period	[1]	60 days	90 days
Total Fair Value | Relative value credit
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 84.8	$ 105.4
Unfunded commitments		0	0
Total Fair Value | Relative value credit | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value | Relative value credit | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 84.8	$ 105.4
Redemption frequency	[1]	Quarterly	Quarterly
Redemption notice period	[1]	60 days	60 days
Total Fair Value | Equity long/short
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 67.9	$ 58
Unfunded commitments		0	0
Total Fair Value | Equity long/short | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value | Equity long/short | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 67.9	$ 58
Redemption frequency	[1]	Quarterly	Quarterly
Redemption notice period	[1]	45 days	45 days
Total Fair Value | Fund of funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 10
Unfunded commitments		0
Total Fair Value | Fund of funds | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0
Total Fair Value | Fund of funds | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 10
Redemption frequency	[1]	Quarterly
Redemption notice period	[1]	60 days
Total Fair Value | High yield loan fund
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			$ 13.8
Unfunded commitments			0
Total Fair Value | High yield loan fund | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			0
Total Fair Value | High yield loan fund | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			$ 13.8
Redemption frequency	[1]		Monthly
Redemption notice period	[1]		30 days
Carrying Value | Other private securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 62.9	$ 126.5
Unfunded commitments		0	0
Carrying Value | Other private securities | Investments with redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Carrying Value | Other private securities | Investments without redemption restrictions
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 62.9	$ 126.5
[1]	The redemption frequency and notice periods only apply to the investments without redemption restrictions.

Investments (Schedule Of Net In

Investments (Schedule Of Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	$ 58.1	$ 50.6	$ 55.8	$ 53.3	$ 49.1	$ 45.7	$ 42.8	$ 44.5	$ 217.8	$ 182.1	$ 176.9
Fixed maturity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									191	164.2	149.5
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									5.1	13.3	17.6
Other invested assets: hedge funds and private equity
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									23.4	19.6	12.6
Other invested assets: other private securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									13.7	2.8	13.3
Cash and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									2.9	1.7	2.1
Expenses
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income									$ (18.3)	$ (19.5)	$ (18.2)

Investments (Components Of Real

Investments (Components Of Realized Gains And Losses) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gain (Loss) on Investments [Line Items]
Gross realized gains on sale of invested assets									$ 159.5	$ 180.3	$ 195.4
Gross realized losses on sale of invested assets									(121.3)	(106.4)	(48.2)
Net realized and unrealized losses on derivatives									(19.6)	(15.4)	(39)
Net realized investment gains (losses)	$ (101.9)	$ 10.7	$ 74.5	$ 18.9	$ (38.8)	$ (113.6)	$ (20.2)	$ 45	2.1	(127.6)	89
Debt securities
Gain (Loss) on Investments [Line Items]
Mark-to-market changes									(17.2)	(126.3)	(1.7)
Equity securities
Gain (Loss) on Investments [Line Items]
Mark-to-market changes									5.8	(41.7)	0.4
Other invested assets
Gain (Loss) on Investments [Line Items]
Mark-to-market changes									$ (5.1)	$ (18.1)	$ (17.9)

Investments (Pledged Assets) (D

Investments (Pledged Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
In favor of ceding companies, other counterparties, or government authorities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 2,687.7	$ 2,748.9
Pledged as collateral for letter of credity facility
Schedule of Trading Securities and Other Trading Assets [Line Items]
Restricted cash, cash equivalents and investments	$ 587.6	$ 579.3

Derivative Instruments (Locatio

Derivative Instruments (Location and Amounts of Derivative Fair Values On The Condensed Consolidated Balance Sheets) (Details) - Not designated as hedging instruments - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	$ 328.2	$ 41.1
Asset Derivative Fair Value	17.8	0.1
Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	114.1	573
Liability Derivative Fair Value	4.1	3.5
Foreign exchange contracts | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	103.2	41.1
Asset Derivative Fair Value	10.4	0.1
Foreign exchange contracts | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	4.1	244.8
Liability Derivative Fair Value	0.1	3
Interest rate swaps | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	0	0
Asset Derivative Fair Value	0	0
Interest rate swaps | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	0	328.2
Liability Derivative Fair Value	0	0.5
Insurance contract | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	225	0
Asset Derivative Fair Value	7.4	0
Insurance contract | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	0	0
Liability Derivative Fair Value	0	0
Reinsurance contract | Other assets
Derivatives, Fair Value [Line Items]
Asset Derivative Notional Amount	0	0
Asset Derivative Fair Value	0	0
Reinsurance contract | Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Notional Amount	110	0
Liability Derivative Fair Value	$ 4	$ 0

Derivative Instruments (Locat60

Derivative Instruments (Location and Amounts of Unrealized And Realized Gains (Losses) On Derivatives Recorded In The Condensed Consolidated Income Statements) (Details) - Not designated as hedging instruments - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	$ (17.5)	$ (22.7)	$ (38.1)
Foreign exchange gain (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(2.2)	(7.3)	0.9
Foreign exchange gain (loss) | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(2.2)	(7.3)	0.9
Net realized investment gains (losses)
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(19.6)	(15.4)	(39)
Net realized investment gains (losses) | Put options
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	0	0	0.5
Net realized investment gains (losses) | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(11.9)	0.2	3.5
Net realized investment gains (losses) | Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(6.8)	(13.4)	(45.4)
Net realized investment gains (losses) | Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	(0.9)	(2.2)	2.4
Other income (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	4.3	0	0
Other income (loss) | Insurance contract
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	7.4	0	0
Other income (loss) | Reinsurance contract
Derivative Instruments, Gain (Loss) [Line Items]
Total realized and unrealized losses (gains) on derivatives	$ (3.1)	$ 0	$ 0

Fair Value Of Financial Instr61

Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$ 6,737.7	$ 7,201.5
Equity securities	243.9	403
Other invested assets	960.7	966.7
Total investments	7,942.3	8,571.2
Senior notes, net of unamortized discount and debt issuance costs	794.2	1,292.9
Other long-term debt	22	23
Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	897.8	840.2
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,737.7	7,201.5
Equity securities	243.9	403
Other invested assets	897.8	840.2
Total investments	7,879.4	8,444.7
Senior notes, net of unamortized discount and debt issuance costs	794.2	1,292.9
Other long-term debt	22	23
Fair Value, Measurements, Recurring | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	10.4	0.1
Derivative liabilities	0.1	3
Fair Value, Measurements, Recurring | Insurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	7.4
Fair Value, Measurements, Recurring | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0.5
Fair Value, Measurements, Recurring | Reinsurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	4
Fair Value, Measurements, Recurring | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,426	1,434
Fair Value, Measurements, Recurring | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	469.9	556.8
Fair Value, Measurements, Recurring | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	354.1	413.5
Fair Value, Measurements, Recurring | Corporate debt: financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,032.7	1,275.4
Fair Value, Measurements, Recurring | Corporate debt: Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,321.3	1,308.1
Fair Value, Measurements, Recurring | Corporate debt: utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	140	118.9
Fair Value, Measurements, Recurring | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	614.5	751.8
Fair Value, Measurements, Recurring | Non-agency residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	23.9	34
Fair Value, Measurements, Recurring | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	598	582.8
Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	757.3	726.2
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,379.6	1,396.4
Equity securities	219.2	403
Other invested assets	0	0
Total investments	1,598.8	1,799.4
Senior notes, net of unamortized discount and debt issuance costs	0	0
Other long-term debt	0	0
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Insurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0
Fair Value, Measurements, Recurring | Level 1 | Reinsurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Fair Value, Measurements, Recurring | Level 1 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,379.6	1,396.4
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt: financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt: Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt: utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Non-agency residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	5,158.5	5,636.1
Equity securities	0	0
Other invested assets	0	0
Total investments	5,158.5	5,636.1
Senior notes, net of unamortized discount and debt issuance costs	827.1	1,337.9
Other long-term debt	26.7	27.7
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	10.4	0.1
Derivative liabilities	0.1	3
Fair Value, Measurements, Recurring | Level 2 | Insurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0
Fair Value, Measurements, Recurring | Level 2 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0.5
Fair Value, Measurements, Recurring | Level 2 | Reinsurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	0
Fair Value, Measurements, Recurring | Level 2 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	46.4	37.6
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	469.9	556.8
Fair Value, Measurements, Recurring | Level 2 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	354.1	413.5
Fair Value, Measurements, Recurring | Level 2 | Corporate debt: financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,031.2	1,275.4
Fair Value, Measurements, Recurring | Level 2 | Corporate debt: Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,321.3	1,308.1
Fair Value, Measurements, Recurring | Level 2 | Corporate debt: utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	140	118.9
Fair Value, Measurements, Recurring | Level 2 | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	475.9	650.8
Fair Value, Measurements, Recurring | Level 2 | Non-agency residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	23.9	29
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	598	582.8
Fair Value, Measurements, Recurring | Level 2 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	697.8	663.2
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	199.7	169.1
Equity securities	24.7	0
Other invested assets	0	0
Total investments	224.4	169.1
Senior notes, net of unamortized discount and debt issuance costs	0	0
Other long-term debt	0	0
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Insurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	7.4
Fair Value, Measurements, Recurring | Level 3 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0
Fair Value, Measurements, Recurring | Level 3 | Reinsurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	4
Fair Value, Measurements, Recurring | Level 3 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt: financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1.5	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt: Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt: utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	138.7	101.1
Fair Value, Measurements, Recurring | Level 3 | Non-agency residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	5
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	59.5	63
Fair Value, Measurements, Recurring | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,737.7	7,201.5
Equity securities	243.9	403
Other invested assets	897.8	840.2
Total investments	7,879.4	8,444.7
Senior notes, net of unamortized discount and debt issuance costs	827.1	1,337.9
Other long-term debt	26.7	27.7
Fair Value, Measurements, Recurring | Total Fair Value | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	10.4	0.1
Derivative liabilities	0.1	3
Fair Value, Measurements, Recurring | Total Fair Value | Insurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	7.4
Fair Value, Measurements, Recurring | Total Fair Value | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0.5
Fair Value, Measurements, Recurring | Total Fair Value | Reinsurance contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	4
Fair Value, Measurements, Recurring | Total Fair Value | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,426	1,434
Fair Value, Measurements, Recurring | Total Fair Value | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	469.9	556.8
Fair Value, Measurements, Recurring | Total Fair Value | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	354.1	413.5
Fair Value, Measurements, Recurring | Total Fair Value | Corporate debt: financial institutions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,032.7	1,275.4
Fair Value, Measurements, Recurring | Total Fair Value | Corporate debt: Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,321.3	1,308.1
Fair Value, Measurements, Recurring | Total Fair Value | Corporate debt: utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	140	118.9
Fair Value, Measurements, Recurring | Total Fair Value | Agency mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	614.5	751.8
Fair Value, Measurements, Recurring | Total Fair Value | Non-agency residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	23.9	34
Fair Value, Measurements, Recurring | Total Fair Value | Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	598	582.8
Fair Value, Measurements, Recurring | Total Fair Value | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$ 757.3	$ 726.2

Fair Value Of Financial Instr62

Fair Value Of Financial Instruments (Schedule Of Fair Value Measurement Using Significant Unobservable Inputs Level Three) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Corporate debt: financial institutions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		$ 0	$ 0
Realized and unrealized gains (losses) included in net income		0	0
Purchases		1.5	0
Sales		0	0
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2		0	0
Ending balance		1.5	0
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		0	0
Agency mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		101.1	180.1
Realized and unrealized gains (losses) included in net income		(6.4)	(1)
Purchases		212.6	17.7
Sales		(175.3)	(95.7)
Transfers into Level 3 from Level 2		6.7	0
Transfers out of Level 3 to Level 2	[1]	0	0
Ending balance		138.7	101.1
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		(6.4)	(1.5)
Non-agency residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		5	0
Realized and unrealized gains (losses) included in net income		0	(0.1)
Purchases		0	5.2
Sales		0	(0.1)
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2	[1]	(5)	0
Ending balance		0	5
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		0	(0.1)
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		0	1.7
Realized and unrealized gains (losses) included in net income		0	0.1
Purchases		0	1.8
Sales		0	(3.6)
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2	[1]	0	0
Ending balance		0	0
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		0	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		63	55.4
Realized and unrealized gains (losses) included in net income		3.1	(6.1)
Purchases		31.2	18.4
Sales		(27.2)	(23.1)
Transfers into Level 3 from Level 2		8	37.3
Transfers out of Level 3 to Level 2	[1]	(18.6)	(18.9)
Ending balance		59.5	63
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		1.9	(0.3)
Equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		0	43.3
Realized and unrealized gains (losses) included in net income		8.1	3.5
Purchases		16.6	0
Sales		0	(46.8)
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2	[1]	0	0
Ending balance		24.7	0
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		8.1	0
Insurance contract
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		0	0
Realized and unrealized gains (losses) included in net income		7.4	0
Purchases		0	0
Sales		0	0
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2	[1]	0	0
Ending balance		7.4	0
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		7.4	0
Reinsurance contract
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance		0	0
Realized and unrealized gains (losses) included in net income		(4)	0
Purchases		0	0
Sales		0	0
Transfers into Level 3 from Level 2		0	0
Transfers out of Level 3 to Level 2	[1]	0	0
Ending balance		(4)	0
Realized and unrealized gains (losses) included in net income for investments still held as of balance sheet date		$ (4)	$ 0
[1]	Transfers out of Level 3 are primarily attributable to the availability of market observable information.

Reserve For Losses And Loss E63

Reserve For Losses And Loss Expenses (Schedule Of Reserve For Losses And Loss Expenses) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Insurance Loss Reserves [Abstract]
Outstanding loss reserves	$ 1,807.5	$ 1,678.5
Reserves for losses incurred but not reported	4,831.7	4,777.7
Reserve for losses and loss expenses	$ 6,639.2	$ 6,456.2	$ 5,881.2	$ 5,766.5

Reserve For Losses And Loss E64

Reserve For Losses And Loss Expenses (Schedule Of Reconciliation Of Unpaid Losses And Loss Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Gross liability at beginning of year	$ 6,456.2	$ 5,881.2	$ 5,766.5
Reinsurance recoverable at beginning of year	(1,480)	(1,340.3)	(1,234.5)
Net liability at beginning of year	4,976.2	4,540.9	4,532
Acquisition of net reserves for losses and loss expenses	0	259.3	0
Net losses incurred related to:
Current year	1,600.1	1,667.9	1,411.8
Prior years	(98.3)	(81.6)	(212.6)
Total incurred	1,501.8	1,586.3	1,199.2
Net paid losses related to:
Current year	208.4	186	171.8
Prior years	1,238.6	1,201.6	1,001.5
Total paid	1,447	1,387.6	1,173.3
Foreign exchange revaluation	(16.8)	(22.7)	(17)
Net liability at end of year	5,014.2	4,976.2	4,540.9
Reinsurance recoverable at end of year	1,625	1,480	1,340.3
Gross liability at end of year	$ 6,639.2	6,456.2	$ 5,881.2
Hong Kong And Singapore Operations Of Royal Sun Alliance Insurance Plc
Business Acquisition [Line Items]
Acquisition of net reserves for losses and loss expenses		255.2
Labuan Operations of Royal Sun Alliance
Business Acquisition [Line Items]
Acquisition of net reserves for losses and loss expenses		$ 4.1

Reserve For Losses And Loss E65

Reserve For Losses And Loss Expenses (Claims Development - North American Insurance) (Details) $ in Millions	Dec. 31, 2016USD ($)Claims	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)
Claims Development [Line Items]
Other reserves not included in the loss development triangles	$ 43.6
Liability for losses and loss expenses, net of reinsurance	4,900.4
North American Insurance | General casualty
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	1,477.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	554.4
Other reserves not included in the loss development triangles	157
Liability for losses and loss expenses, net of reinsurance	1,079.9
North American Insurance | General casualty | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	268.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	10
Total IBNR	$ 244.3
Cumulative Reported Claims | Claims	614
North American Insurance | General casualty | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 279.1	$ 288
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	34.2	11
Total IBNR	$ 214.8
Cumulative Reported Claims | Claims	820
North American Insurance | General casualty | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 232.4	222.4	$ 220.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	103.9	58.3	8.5
Total IBNR	$ 94.7
Cumulative Reported Claims | Claims	763
North American Insurance | General casualty | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 237.4	208.9	192.4	$ 184
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	103.6	70.2	38.6	9.7
Total IBNR	$ 90.3
Cumulative Reported Claims | Claims	638
North American Insurance | General casualty | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 188.5	166.3	150.7	147.9	$ 144.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	114	85.4	53.2	25.9	6.5
Total IBNR	$ 42.7
Cumulative Reported Claims | Claims	388
North American Insurance | General casualty | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 144.2	136.7	143	145.1	140.7	$ 120.7
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	91.8	79	53	32.8	11.2	2.1
Total IBNR	$ 36.8
Cumulative Reported Claims | Claims	347
North American Insurance | General casualty | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 127.3	143.5	149.3	151.5	158.4	156.8	$ 133.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	96.8	87.4	83	72.8	65.9	28.4	0.6
Total IBNR	$ 23.6
Cumulative Reported Claims | Claims	277
North American Insurance | Professional liability
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1,619.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	817.6
Other reserves not included in the loss development triangles	89.7
Liability for losses and loss expenses, net of reinsurance	891.6
North American Insurance | Professional liability | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	256
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	9.5
Total IBNR	$ 234.1
Cumulative Reported Claims | Claims	127
North American Insurance | Professional liability | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 258.9	254.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	61	9
Total IBNR	$ 165.7
Cumulative Reported Claims | Claims	269
North American Insurance | Professional liability | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 235.7	233.7	213
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	125.6	69.8	11.7
Total IBNR	$ 79.2
Cumulative Reported Claims | Claims	378
North American Insurance | Professional liability | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 240.4	225.8	226.8	220.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	142.8	95.8	50	9.6
Total IBNR	$ 77.3
Cumulative Reported Claims | Claims	534
North American Insurance | Professional liability | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 265.6	271.1	274	266.2	193.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	181.1	146.5	98	62.5	15.8
Total IBNR	$ 46.9
Cumulative Reported Claims | Claims	530
North American Insurance | Professional liability | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 210.7	214.4	235.4	228.7	206.4	182.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	179.5	152.7	124.7	102.6	56.1	13.6
Total IBNR	$ 24.4
Cumulative Reported Claims | Claims	474
North American Insurance | Professional liability | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 152.3	154.8	169.3	178	190.5	196.5	189.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	118.2	97.5	91.3	78.1	57	36.5	7.9
Total IBNR	$ 23.1
Cumulative Reported Claims | Claims	334
North American Insurance | General property
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 666.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	587.9
Other reserves not included in the loss development triangles	0.5
Liability for losses and loss expenses, net of reinsurance	79
North American Insurance | General property | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	101.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	46.7
Total IBNR	$ 11.8
Cumulative Reported Claims | Claims	1,502
North American Insurance | General property | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 114.4	110.7
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	98.5	51.6
Total IBNR	$ 3.3
Cumulative Reported Claims | Claims	1,448
North American Insurance | General property | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 88.9	96	97
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	83.8	73.1	32.3
Total IBNR	$ 0.3
Cumulative Reported Claims | Claims	1,344
North American Insurance | General property | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 68.9	69.8	75.3	81.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	67.8	64.6	56.3	25.4
Total IBNR	$ 0.1
Cumulative Reported Claims | Claims	923
North American Insurance | General property | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 136.3	136.9	140.5	146.9	157.7
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	135	134.7	127.8	98	20.5
Total IBNR	$ 0.3
Cumulative Reported Claims | Claims	599
North American Insurance | General property | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 107.9	110.2	111.4	115	121.8	124.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	108.1	107.4	106.2	98.6	69.8	24.6
Total IBNR	$ (0.1)
Cumulative Reported Claims | Claims	448
North American Insurance | General property | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 48.8	48.8	48.6	47.7	49.6	54	66.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	48.1	47.9	47.4	45.7	40.9	34.2	16.4
Total IBNR	$ 0.7
Cumulative Reported Claims | Claims	330
North American Insurance | Programs
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 513.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	257
Other reserves not included in the loss development triangles	9.4
Liability for losses and loss expenses, net of reinsurance	265.8
North American Insurance | Programs | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	113.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	14.1
Total IBNR	$ 72.3
Cumulative Reported Claims | Claims	1,281
North American Insurance | Programs | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 86.2	86.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	26.3	9.3
Total IBNR	$ 43.5
Cumulative Reported Claims | Claims	1,266
North American Insurance | Programs | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 70	73.9	74.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	27.5	16.9	6.4
Total IBNR	$ 28.8
Cumulative Reported Claims | Claims	1,201
North American Insurance | Programs | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 56.2	59.7	62	64.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	33	24.4	15.8	5.7
Total IBNR	$ 14.5
Cumulative Reported Claims | Claims	871
North American Insurance | Programs | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 58.9	59.6	62.4	60.5	56.7
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	44.5	38.3	29.6	17.6	3.8
Total IBNR	$ 5.7
Cumulative Reported Claims | Claims	496
North American Insurance | Programs | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 53.5	52.5	58.1	62.6	61.9	54
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	45.3	41.3	34.7	26.7	15.2	3.8
Total IBNR	$ 4.4
Cumulative Reported Claims | Claims	446
North American Insurance | Programs | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 75	75.5	78.8	80.8	86.4	72.5	70.7
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	66.3	63.4	59.9	52.3	42.4	17.9	2.9
Total IBNR	$ 2.6
Cumulative Reported Claims | Claims	479
North American Insurance | Healthcare
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 634.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	349.7
Other reserves not included in the loss development triangles	16.8
Liability for losses and loss expenses, net of reinsurance	301.2
North American Insurance | Healthcare | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	51.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.9
Total IBNR	$ 47.6
Cumulative Reported Claims | Claims	17
North American Insurance | Healthcare | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 76.8	76.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	8.5	0.6
Total IBNR	$ 58
Cumulative Reported Claims | Claims	85
North American Insurance | Healthcare | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 92.5	92.5	84.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	26.5	9	1
Total IBNR	$ 46.4
Cumulative Reported Claims | Claims	150
North American Insurance | Healthcare | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 123.9	123.9	111.2	85.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	84.6	56.9	12.6	2.6
Total IBNR	$ 18.8
Cumulative Reported Claims | Claims	227
North American Insurance | Healthcare | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 113.7	113.7	99.4	91.4	87.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	77.5	54.8	34.3	15.1	1.3
Total IBNR	$ 8.5
Cumulative Reported Claims | Claims	260
North American Insurance | Healthcare | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 113.3	113.6	108.1	94.5	87.1	85.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	99.9	84	69.6	42.5	10.9	0.5
Total IBNR	$ 4.5
Cumulative Reported Claims | Claims	248
North American Insurance | Healthcare | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 62.8	63.4	64.2	79.8	79.3	76.4	78.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	51.9	48.5	39.8	28.9	17.1	6.4	1.2
Total IBNR	$ 6.8
Cumulative Reported Claims | Claims	156
North American Insurance | Specialty
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 209.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	75.6
Other reserves not included in the loss development triangles	0
Liability for losses and loss expenses, net of reinsurance	134
North American Insurance | Specialty | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	70.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	4.2
Total IBNR	$ 62.4
Cumulative Reported Claims | Claims	520
North American Insurance | Specialty | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 48.2	47.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	13.4	4.1
Total IBNR	$ 30.6
Cumulative Reported Claims | Claims	352
North American Insurance | Specialty | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 34.3	33.6	30.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	18.6	13	5.2
Total IBNR	$ 12.1
Cumulative Reported Claims | Claims	331
North American Insurance | Specialty | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 16.6	16.6	16.6	16.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	4.4	3.2	2.3	0.8
Total IBNR	$ 10.6
Cumulative Reported Claims | Claims	73
North American Insurance | Specialty | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 21.2	21.3	22.5	21.2	21.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	17.9	17.5	14.7	10.2	0.5
Total IBNR	$ 2.3
Cumulative Reported Claims | Claims	19
North American Insurance | Specialty | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 18.7	18.7	18.7	18.3	18.9	16.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	16.7	15.9	15.1	14.5	11.2	4
Total IBNR	$ 0.7
Cumulative Reported Claims | Claims	16
North American Insurance | Specialty | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0.4	0.3	0.5	0.6	0.9	0.9	0.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.4	$ 0.1	$ 0.1	$ 0.1	$ 0	$ 0	$ 0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	9

Reserve For Losses And Loss E66

Reserve For Losses And Loss Expenses (Claims Development - Global Markets Insurance) (Details) $ in Millions	Dec. 31, 2016USD ($)Claims	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)
Claims Development [Line Items]
Other reserves not included in the loss development triangles	$ 43.6
Liability for losses and loss expenses, net of reinsurance	4,900.4
Global Markets Insurance | General casualty | Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	277.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	130.1
Other reserves not included in the loss development triangles	1.1
Liability for losses and loss expenses, net of reinsurance	148.6
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	60.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	13.4
Total IBNR	$ 22
Cumulative Reported Claims | Claims	8,506
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 78	$ 98.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	31.1	12
Total IBNR	$ 15.4
Cumulative Reported Claims | Claims	9,095
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 68.7	99.2	$ 0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	37.1	16.6	0
Total IBNR	$ 5.4
Cumulative Reported Claims | Claims	3,618
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 43.2	53.6	0	$ 0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	28.2	13.2	0	0
Total IBNR	$ 3.1
Cumulative Reported Claims | Claims	1,302
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 17.9	19.3	0	0	$ 0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	14.2	8.2	0	0	0
Total IBNR	$ 0.4
Cumulative Reported Claims | Claims	496
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 6.2	7.2	0	0	0	$ 0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	4.7	2.7	0	0	0	0
Total IBNR	$ 0.1
Cumulative Reported Claims | Claims	337
Global Markets Insurance | General casualty | Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 2.7	3.2	0	0	0	0	$ 0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.5	1	0	0	0	0	0
Total IBNR	$ 0.5
Cumulative Reported Claims | Claims	130
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 81.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	17.7
Other reserves not included in the loss development triangles	24.1
Liability for losses and loss expenses, net of reinsurance	88.3
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	15.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.4
Total IBNR	$ 11.4
Cumulative Reported Claims | Claims	233
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 19.5	16.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	4	1.1
Total IBNR	$ 6.5
Cumulative Reported Claims | Claims	111
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 11.9	11.8	9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.1	0.7	0.4
Total IBNR	$ 6
Cumulative Reported Claims | Claims	66
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 7.3	8.1	9.3	9.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.4	0.4	0.4	0
Total IBNR	$ 6.5
Cumulative Reported Claims | Claims	25
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 7.6	10.5	11.3	11.6	11
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.6	1	0.9	0.6	0
Total IBNR	$ 5.8
Cumulative Reported Claims | Claims	16
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 15.5	15.8	16.5	15.4	9.6	9.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	10.1	10.1	10.1	0.3	0.2	0
Total IBNR	$ 5.4
Cumulative Reported Claims | Claims	10
Global Markets Insurance | General casualty | Excluding Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 4.2	5.8	10.3	13.9	14.2	14.2	14.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.1	0.1	0.1	0.1	0	0	0
Total IBNR	$ 4.1
Cumulative Reported Claims | Claims	1
Global Markets Insurance | Professional liability | Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 9.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	2.3
Other reserves not included in the loss development triangles	0
Liability for losses and loss expenses, net of reinsurance	6.8
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.1
Total IBNR	$ 1
Cumulative Reported Claims | Claims	32
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 2.6	3.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.1	0
Total IBNR	$ 1.8
Cumulative Reported Claims | Claims	74
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1.5	2.1	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.3	0.2	0
Total IBNR	$ 0.3
Cumulative Reported Claims | Claims	48
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1.9	0.8	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.4	0.2	0	0
Total IBNR	$ 0.2
Cumulative Reported Claims | Claims	25
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0.2	0.4	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.1	0.1	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	9
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1	1.5	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.5	0	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	12
Global Markets Insurance | Professional liability | Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0.9	0.8	0	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.7	0.6	0	0	0	0	0
Total IBNR	$ 0.1
Cumulative Reported Claims | Claims	11
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 254
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	54.3
Other reserves not included in the loss development triangles	46.5
Liability for losses and loss expenses, net of reinsurance	246.2
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	53.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.9
Total IBNR	$ 48.9
Cumulative Reported Claims | Claims	150
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 60.3	57.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	5.4	1.3
Total IBNR	$ 48.9
Cumulative Reported Claims | Claims	147
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 40.5	39.2	39.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	4.8	2.6	0.5
Total IBNR	$ 29.4
Cumulative Reported Claims | Claims	125
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 28.5	30.4	33.4	33.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	3.5	2.4	0.9	0.1
Total IBNR	$ 20
Cumulative Reported Claims | Claims	92
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 37.3	39.2	37.9	30.7	32.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	21.3	13.6	10.5	1.6	0.2
Total IBNR	$ 10.7
Cumulative Reported Claims | Claims	34
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 19.2	20.7	24.3	27.8	29.8	32.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	8.6	8.6	8.4	6.7	0.5	0.1
Total IBNR	$ 7.3
Cumulative Reported Claims | Claims	21
Global Markets Insurance | Professional liability | Excluding Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 14.7	13.8	20	30.3	32.5	32.6	32.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	8.6	3.1	2.6	0.5	0.1	0	0
Total IBNR	$ 5.7
Cumulative Reported Claims | Claims	15
Global Markets Insurance | General property | Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 53.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	24.8
Other reserves not included in the loss development triangles	(3.5)
Liability for losses and loss expenses, net of reinsurance	25
Global Markets Insurance | General property | Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	20.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.9
Total IBNR	$ 7.4
Cumulative Reported Claims | Claims	1,190
Global Markets Insurance | General property | Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 12	22.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	8.1	2.8
Total IBNR	$ 0.6
Cumulative Reported Claims | Claims	1,988
Global Markets Insurance | General property | Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 14.3	14	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	9.7	6.4	0
Total IBNR	$ 0.5
Cumulative Reported Claims | Claims	1,332
Global Markets Insurance | General property | Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 4.5	4.2	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	3.1	1.6	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	758
Global Markets Insurance | General property | Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1.4	1.7	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.3	0.5	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	353
Global Markets Insurance | General property | Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0.5	0.9	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.6	0.2	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	122
Global Markets Insurance | General property | Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0.1	0	0	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0	0.1	0	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	54
Global Markets Insurance | General property | Excluding Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 256.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	211.1
Other reserves not included in the loss development triangles	2.3
Liability for losses and loss expenses, net of reinsurance	47.8
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	29.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	3
Total IBNR	$ 12.3
Cumulative Reported Claims | Claims	282
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 25.1	22.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	15.4	3.7
Total IBNR	$ 1.8
Cumulative Reported Claims | Claims	223
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 21.1	23.3	29
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	15.9	12.3	6.7
Total IBNR	$ 0.6
Cumulative Reported Claims | Claims	164
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 14.4	14.4	18.6	26
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	12.9	12.5	9	4
Total IBNR	$ 0.2
Cumulative Reported Claims | Claims	108
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 18.2	17.3	18.6	21.9	25.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	17.3	15.1	11.5	9.3	3.5
Total IBNR	$ 0.8
Cumulative Reported Claims | Claims	161
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 54.9	54.5	54.6	58.5	64.2	66.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	53.6	52.8	52.2	43.3	28.4	10.6
Total IBNR	$ 0.2
Cumulative Reported Claims | Claims	214
Global Markets Insurance | General property | Excluding Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 93.6	96.5	95.7	96.6	97.5	102.3	87.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	92.9	92.5	92.1	90.5	84.1	75	47.8
Total IBNR	$ 0.1
Cumulative Reported Claims | Claims	249
Global Markets Insurance | Specialty | Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 107.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	41.5
Other reserves not included in the loss development triangles	0.4
Liability for losses and loss expenses, net of reinsurance	66.7
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	31.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	6.7
Total IBNR	$ 7.9
Cumulative Reported Claims | Claims	15,908
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 41.5	39
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	19.1	7.2
Total IBNR	$ 0.9
Cumulative Reported Claims | Claims	14,366
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 21.8	20.6	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	10	5.5	0
Total IBNR	$ (0.9)
Cumulative Reported Claims | Claims	2,808
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 7	7	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	3.2	2.1	0	0
Total IBNR	$ 0.2
Cumulative Reported Claims | Claims	857
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 2.6	2.4	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.4	0.4	0	0	0
Total IBNR	$ (0.1)
Cumulative Reported Claims | Claims	411
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 2.6	1.3	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.8	0.3	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	239
Global Markets Insurance | Specialty | Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1.1	1.1	0	0	0	0	0
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0.3	0.1	0	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	115
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member]
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 174.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	107
Other reserves not included in the loss development triangles	0
Liability for losses and loss expenses, net of reinsurance	67.9
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	55.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	24.7
Total IBNR	$ 19.1
Cumulative Reported Claims | Claims	1,049
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 46.4	44
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	29.3	12.7
Total IBNR	$ 8.6
Cumulative Reported Claims | Claims	1,086
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 52.1	41.4	31.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	32.9	27	8.9
Total IBNR	$ 3.2
Cumulative Reported Claims | Claims	750
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 19.7	20.2	16	7.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	18.4	16.6	4.8	0.2
Total IBNR	$ 1.1
Cumulative Reported Claims | Claims	110
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 1.7	1.6	1.7	4.3	4.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.6	1.6	1.4	0.1	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	5
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0	0	0	1	1	1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0	0	0	0	0	0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	3
Global Markets Insurance | Specialty | Excluding Acquired Reserves [Member] | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	$ 0	0	0	0.1	0.1	0.1	0.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Total IBNR	$ 0
Cumulative Reported Claims | Claims	0

Reserve For Losses And Loss E67

Reserve For Losses And Loss Expenses (Claims Development - Reinsurance) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Claims Development [Line Items]
Other reserves not included in the loss development triangles	$ 43.6
Liability for losses and loss expenses, net of reinsurance	4,900.4
Reinsurance | Property
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	1,021.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	777.5
Other reserves not included in the loss development triangles	1.9
Liability for losses and loss expenses, net of reinsurance	245.7
Reinsurance | Property | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	180.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	52.8
Total IBNR	74.4
Reinsurance | Property | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	174.4	$ 202.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	104.2	53.9
Total IBNR	26.3
Reinsurance | Property | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	152.8	165	$ 196.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	131	112.8	57.5
Total IBNR	5.2
Reinsurance | Property | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	123.1	133.6	143.7	$ 176.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	115.7	110.6	84.8	29.7
Total IBNR	2.9
Reinsurance | Property | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	124.5	126.9	131.2	143	$ 190.9
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	114.6	111.7	105.8	87.8	38.5
Total IBNR	3.1
Reinsurance | Property | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	199.2	197.8	199.4	207.2	223.9	$ 219.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	193.9	190.5	182.1	162.9	116.6	53.4
Total IBNR	1.2
Reinsurance | Property | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	67	67.9	68	68.6	73	78.7	$ 80.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	65.2	64.8	63.2	57.6	50.2	38.2	11.1
Total IBNR	0.6
Reinsurance | Casualty
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	1,292.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	487.9
Other reserves not included in the loss development triangles	225.9
Liability for losses and loss expenses, net of reinsurance	1,030.3
Reinsurance | Casualty | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	130.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	1.8
Total IBNR	120.5
Reinsurance | Casualty | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	157.5	159.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	14.5	1.5
Total IBNR	123.6
Reinsurance | Casualty | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	182	179.5	167.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	31	12.5	1.7
Total IBNR	120
Reinsurance | Casualty | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	214.9	198.6	192.5	177.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	81.4	60.2	22.4	7.8
Total IBNR	92.8
Reinsurance | Casualty | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	231.2	223.8	216.9	214.7	190.5
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	127.5	92.5	57.3	39.2	12.6
Total IBNR	68.9
Reinsurance | Casualty | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	180.5	185.6	192.7	189.4	184.6	165.2
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	105	93.2	71.3	49	26.9	8.4
Total IBNR	51.8
Reinsurance | Casualty | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	196	197.9	213.2	223.2	225.9	222.1	200
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	126.8	114.5	97.9	76.3	58.6	32.2	2.6
Total IBNR	48.4
Reinsurance | Specialty and other
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	632.8
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	460.4
Other reserves not included in the loss development triangles	3.3
Liability for losses and loss expenses, net of reinsurance	175.7
Reinsurance | Specialty and other | 2016
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	118.4
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	9.8
Total IBNR	101.6
Reinsurance | Specialty and other | 2015
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	128	130
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	95.3	7.2
Total IBNR	23.9
Reinsurance | Specialty and other | 2014
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	118.4	124.8	121
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	107.7	102.8	14.8
Total IBNR	6.2
Reinsurance | Specialty and other | 2013
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	102	100.3	106.7	111.6
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	93.3	92	75.7	3.3
Total IBNR	4.2
Reinsurance | Specialty and other | 2012
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	136.5	137.2	138.3	132	123.1
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	127.9	125.5	121.8	108	24.5
Total IBNR	4.5
Reinsurance | Specialty and other | 2011
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	21.4	22.1	22.7	21.9	26.9	30
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	19	18.4	17.5	16.3	12.7	3.2
Total IBNR	1.5
Reinsurance | Specialty and other | 2010
Claims Development [Line Items]
Incurred Claims and Loss Adjustment Expenses, Net of Reinsurance	8.1	8.3	8.6	8.8	9	7.7	11.3
Cumulative Paid Claims and Loss Adjustment Expenses, Net of Reinsurance	7.3	$ 7.1	$ 7	$ 6.5	$ 6.1	$ 4.1	$ 2.1
Total IBNR	$ 0.4

Reserve For Losses And Loss E68

Reserve For Losses And Loss Expenses (Summary of Claims Development and Reinsurance Recoverable) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	$ 4,900.4
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	1,574
Total gross reserves for losses and loss expenses per the loss development triangles:	6,474.4
Unallocated loss adjustment expenses	118.6
Other reserves not included in the loss development triangles	43.6
Fair value adjustment	6
Currency translation adjustment	(3)
Other	(0.4)
Other balances not included in the loss development triangles	164.8
Reserve for losses and loss expenses	6,639.2	$ 6,456.2	$ 5,881.2	$ 5,766.5
General casualty | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	1,079.9
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	605.9
Other reserves not included in the loss development triangles	157
Professional liability | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	891.6
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	352.7
Other reserves not included in the loss development triangles	89.7
General property | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	79
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	74.5
Other reserves not included in the loss development triangles	0.5
Programs | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	265.8
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	83.8
Other reserves not included in the loss development triangles	9.4
Healthcare | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	301.2
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	135.6
Other reserves not included in the loss development triangles	16.8
Specialty | North American Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	134
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	55.6
Other reserves not included in the loss development triangles	0
Property | Reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	245.7
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	3.8
Other reserves not included in the loss development triangles	1.9
Casualty | Reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	1,030.3
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	0
Other reserves not included in the loss development triangles	225.9
Specialty and other | Reinsurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	175.7
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	0
Other reserves not included in the loss development triangles	3.3
Excluding Acquired Reserves [Member] | General casualty | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	88.3
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	62.9
Other reserves not included in the loss development triangles	24.1
Excluding Acquired Reserves [Member] | Professional liability | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	246.2
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	111.9
Other reserves not included in the loss development triangles	46.5
Excluding Acquired Reserves [Member] | General property | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	47.8
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	4
Other reserves not included in the loss development triangles	2.3
Excluding Acquired Reserves [Member] | Specialty | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	67.9
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	30.7
Other reserves not included in the loss development triangles	0
Acquired Reserves [Member] | General casualty | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	148.6
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	5
Other reserves not included in the loss development triangles	1.1
Acquired Reserves [Member] | Professional liability | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	6.8
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	1
Other reserves not included in the loss development triangles	0
Acquired Reserves [Member] | General property | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	25
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	15.3
Other reserves not included in the loss development triangles	(3.5)
Acquired Reserves [Member] | Specialty | Global Markets Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for losses and loss expenses, net of reinsurance	66.7
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	31.5
Other reserves not included in the loss development triangles	$ 0.4

Reserve For Losses And Loss E69

Reserve For Losses And Loss Expenses (Historical Claims Duration) (Details)	Dec. 31, 2016
North American Insurance | General casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	3.00%
Year Two	13.00%
Year Three	18.00%
Year Four	13.00%
Year Five	14.00%
Year Six	6.00%
Year Seven	7.00%
North American Insurance | Professional liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	5.00%
Year Two	20.00%
Year Three	18.00%
Year Four	16.00%
Year Five	12.00%
Year Six	8.00%
Year Seven	14.00%
North American Insurance | General property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	34.00%
Year Two	44.00%
Year Three	17.00%
Year Four	7.00%
Year Five	2.00%
Year Six	1.00%
Year Seven	0.00%
North American Insurance | Programs
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	9.00%
Year Two	20.00%
Year Three	21.00%
Year Four	15.00%
Year Five	11.00%
Year Six	6.00%
Year Seven	4.00%
North American Insurance | Healthcare
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	1.00%
Year Two	9.00%
Year Three	23.00%
Year Four	21.00%
Year Five	17.00%
Year Six	14.00%
Year Seven	5.00%
North American Insurance | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	8.00%
Year Two	23.00%
Year Three	13.00%
Year Four	9.00%
Year Five	3.00%
Year Six	3.00%
Year Seven	66.00%
Global Markets Insurance | General casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	2.00%
Year Two	5.00%
Year Three	2.00%
Year Four	16.00%
Year Five	3.00%
Year Six	0.00%
Year Seven	0.00%
Global Markets Insurance | Professional liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	1.00%
Year Two	4.00%
Year Three	13.00%
Year Four	6.00%
Year Five	12.00%
Year Six	2.00%
Year Seven	38.00%
Global Markets Insurance | General property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	25.00%
Year Two	34.00%
Year Three	18.00%
Year Four	11.00%
Year Five	5.00%
Year Six	1.00%
Year Seven	0.00%
Global Markets Insurance | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	18.00%
Year Two	23.00%
Year Three	37.00%
Year Four	7.00%
Year Five	0.00%
Year Six	0.00%
Year Seven	0.00%
Reinsurance | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	28.00%
Year Two	37.00%
Year Three	18.00%
Year Four	7.00%
Year Five	5.00%
Year Six	2.00%
Year Seven	1.00%
Reinsurance | Casualty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	3.00%
Year Two	10.00%
Year Three	12.00%
Year Four	12.00%
Year Five	13.00%
Year Six	7.00%
Year Seven	6.00%
Reinsurance | Specialty and other
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	13.00%
Year Two	57.00%
Year Three	14.00%
Year Four	4.00%
Year Five	4.00%
Year Six	2.00%
Year Seven	3.00%

Reserve For Losses And Loss E70

Reserve For Losses And Loss Expenses (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
Effect of Change in Valuation Method, Loss Reserves	$ (20.1)	$ (92.6)	$ (159.7)

Ceded Reinsurance (Narrative) (

Ceded Reinsurance (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)reinsurers	Dec. 31, 2015USD ($)	Dec. 31, 2014
Concentration Risk [Line Items]
Reinsurance Recoverables, Allowance | $	$ 1.2	$ 1.2
Reinsurance recoverable
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%
Credit concentration risk | Premiums ceded
Concentration Risk [Line Items]
Number of ceded reinsurers | reinsurers	4
Concentration risk, percentage	44.40%	41.10%	42.30%
Credit concentration risk | Reinsurance recoverable | A or better rating
Concentration Risk [Line Items]
Concentration risk, percentage	99.00%	99.00%

Ceded Reinsurance (Components o

Ceded Reinsurance (Components of Reinsurance) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reinsurance Disclosures [Abstract]
OSLR recoverable	$ 384.1	$ 254.6
IBNR recoverable	1,240.9	1,225.4
Reinsurance recoverable	1,625	1,480	$ 1,340.3	$ 1,234.5
Reinsurance recoverable on paid losses	$ 104.4	$ 96.4

Ceded Reinsurance (Effects of R

Ceded Reinsurance (Effects of Reinsurance) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Direct premiums written									$ 2,359.6	$ 2,291.6	$ 1,996.8
Assumed premiums written									706.2	801.4	938.6
Ceded premiums written	$ (226.4)	$ (201.9)	$ (222.2)	$ (159.5)	$ (167.5)	$ (147.1)	$ (222.3)	$ (108.1)	(810)	(645)	(613.4)
Net premiums written	445.3	528.3	578.1	704	464.8	607	603.7	772.5	2,255.8	2,448	2,322
Direct premiums earned									2,316.6	2,255.3	1,835.1
Assumed premiums earned									743.1	863.6	941.2
Ceded premiums earned									(715.6)	(630.5)	(593.6)
Net premiums earned	577	584	602.9	580.1	622.8	650.7	646.4	568.5	2,344.1	2,488.4	2,182.7
Direct losses and loss expenses									1,539.2	1,471.6	1,031.3
Assumed losses and loss expenses									379.4	442.8	464.7
Ceded losses and loss expenses									(416.8)	(328.1)	(296.8)
Net losses and loss expenses	$ 387.8	$ 376.3	$ 365.4	$ 372.4	$ 412.7	$ 416.9	$ 431.5	$ 325.2	$ 1,501.8	$ 1,586.3	$ 1,199.2

Ceded Reinsurance (Credit Risk

Ceded Reinsurance (Credit Risk by Reinsurer) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 1,625	$ 1,480	$ 1,340.3	$ 1,234.5
Prepaid reinsurance		486.4	392.3
Reinsurance recoverable
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 1,625	$ 1,480
Percentage of total		100.00%	100.00%
Reinsurance recoverable | Top five reinsurers
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 858.7	$ 771.9
Percentage of total		52.80%	52.20%
Reinsurance recoverable | Top five reinsurers | A plus | Munich Re
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 348.1	$ 307.9
Percentage of total		21.40%	20.80%
Reinsurance recoverable | Top five reinsurers | A plus | Axis Capital
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 160.4	$ 150.8
Percentage of total		9.90%	10.20%
Reinsurance recoverable | Top five reinsurers | A plus | Swiss Re
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 146.7	$ 103.9
Percentage of total		9.00%	7.00%
Reinsurance recoverable | Top five reinsurers | A plus | Arch Re
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 100.5	$ 115.3
Percentage of total		6.20%	7.80%
Reinsurance recoverable | Top five reinsurers | A plus | RenaissanceRe
Ceded Credit Risk [Line Items]
Reinsurance recoverable			$ 94
Percentage of total			6.40%
Reinsurance recoverable | Top five reinsurers | A rating | Markel
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 103
Percentage of total		6.30%
Reinsurance recoverable | Other reinsurers' balances
Ceded Credit Risk [Line Items]
Reinsurance recoverable		$ 766.3	$ 708.1
Percentage of total		47.20%	47.80%
Prepaid Reinsurance [Member]
Ceded Credit Risk [Line Items]
Prepaid reinsurance		$ 486.4	$ 392.3
Percentage of total		100.00%	100.00%
Prepaid Reinsurance [Member] | Top five reinsurers
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 250.1	$ 175.2
Percentage of total		51.40%	44.60%
Prepaid Reinsurance [Member] | Top five reinsurers | A plus | Munich Re
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 87.5	$ 61.7
Percentage of total		18.00%	15.70%
Prepaid Reinsurance [Member] | Top five reinsurers | A plus | Axis Capital
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 58.5	$ 32.2
Percentage of total		12.00%	8.20%
Prepaid Reinsurance [Member] | Top five reinsurers | A plus | Swiss Re
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 64.2	$ 57.3
Percentage of total		13.20%	14.60%
Prepaid Reinsurance [Member] | Top five reinsurers | A plus | Arch Re
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 14	$ 16
Percentage of total		2.90%	4.10%
Prepaid Reinsurance [Member] | Top five reinsurers | A plus | RenaissanceRe
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]		$ 8
Percentage of total			2.00%
Prepaid Reinsurance [Member] | Top five reinsurers | A rating | Markel
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 25.9
Percentage of total		5.30%
Prepaid Reinsurance [Member] | Other reinsurers' balances
Ceded Credit Risk [Line Items]
Prepaid reinsurance	[1]	$ 236.3	$ 217.1
Percentage of total		48.60%	55.40%
[1]	Prepaid reinsurance represents unearned premiums ceded to reinsurance companies.

Funds Held (Details)

Funds Held (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effects of Reinsurance [Line Items]
Funds held	$ 466.8	$ 640.8
Assumed premiums written	706.2	801.4	$ 938.6
Aeolus Capital Management [Member]
Effects of Reinsurance [Line Items]
Funds held	442	622.4
Assumed premiums written	$ 38.2	$ 76.3	$ 87.3

Goodwill and Intangible Asset76

Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Goodwill And Intangible Assets [Line Items]
Goodwill, beginning of year	$ 388.1	$ 278.3
Additions	2.7	110.1
Foreign currency translation adjustment	(1.1)	(0.3)
Goodwill, end of year	389.7	388.1
Indefinite-lived intangible assets, net carrying value, beginning of year	23.9	23.9
Indefinite-lived intangible assets, net carrying value, end of year	23.9	23.9
Finite-Lived Intangible Assets, Net [Abstract]
Gross carrying value	117.8	119.9	$ 41.3
Additions	0	83.5
Impairments	(0.9)	(1.4)
Accumulated amortization	(37)	(27.2)	(18.9)
Amortization of intangible assets	(9.8)	(8.3)
Foreign currency translation adjustment	(1.2)	(3.5)
Net carrying value	80.8	92.7	22.4
Goodwill, accumulated impairment loss			$ 0.2
Intangible assets, accumulated impairment loss	$ 9.1
Expected remaining useful life	13 years
North American Insurance
Schedule Of Goodwill And Intangible Assets [Line Items]
Goodwill, end of year	$ 274.3
Global Markets Insurance
Schedule Of Goodwill And Intangible Assets [Line Items]
Goodwill, end of year	111.5
Reinsurance
Schedule Of Goodwill And Intangible Assets [Line Items]
Goodwill, end of year	3.9
Distribution channels
Finite-Lived Intangible Assets, Net [Abstract]
Net carrying value	$ 73.7	81
Expected remaining useful life	14 years
Customer renewals
Finite-Lived Intangible Assets, Net [Abstract]
Net carrying value	$ 7.1	$ 11.7
Expected remaining useful life	2 years 8 months 12 days

Goodwill and Intangible Asset77

Goodwill and Intangible Assets (Future amortization expense) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,017	$ 8.8
2,018	8.8
2,019	7.3
2,020	6.1
2,021	5.9
2022 and thereafter	43.9
Net carrying value	$ 80.8	$ 92.7	$ 22.4

Debt and Financing Arrangemen78

Debt and Financing Arrangements (Financing Structure) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015	Nov. 12, 2014
Components of financing structure:
Unamortized discount and debt issuance costs		$ 5.8	$ 7.1
Outstanding, total	[1]	1,280	1,830.5
Balance, debt	[2]	816.2	1,315.9
2006 Senior notes due 2016
Components of financing structure:
Outstanding, debt	[1]		500
Unamortized discount and debt issuance costs			0.5
Balance, debt	[2]		$ 499.5
Imputed interest rate on debt			3.77%
2010 Senior notes due 2020
Components of financing structure:
Outstanding, debt	[1]	300	$ 300
Unamortized discount and debt issuance costs		1.8	2.3
Balance, debt	[2]	$ 298.2	$ 297.7
Imputed interest rate on debt		2.80%	2.78%
2015 Senior notes Due 2025
Components of financing structure:
Outstanding, debt	[1]	$ 500	$ 500
Unamortized discount and debt issuance costs		4	4.3
Balance, debt	[2]	$ 496	$ 495.7
Imputed interest rate on debt		2.18%	2.18%
Swiss office building mortgage
Components of financing structure:
Outstanding, debt	[1]	$ 16.9	$ 17.9
Unamortized discount and debt issuance costs		0	0
Balance, debt	[2]	16.9	17.9
Swiss office building credit facility
Components of financing structure:
Outstanding, credit facility	[1]	5.1	5.1
Unamortized discount and debt issuance costs		0	0
Balance, credit facility	[2]	5.1	5.1
$900,000 secured letter of credit facility - uncommitted
Components of financing structure:
Outstanding, credit facility	[1]	458	507.5
Unamortized discount and debt issuance costs		0	0
Credit facility, maximum borrowing capacity		900	1,000
$150,000 secured letter of credit facility - committed
Components of financing structure:
Outstanding, credit facility	[1]	0	0
Unamortized discount and debt issuance costs		0	0
Allied World Bermuda (Subsidiary Issuer) | $900,000 secured letter of credit facility - uncommitted
Components of financing structure:
Credit facility, maximum borrowing capacity		900	1,000
Allied World Bermuda (Subsidiary Issuer) | $150,000 secured letter of credit facility - committed
Components of financing structure:
Credit facility, maximum borrowing capacity		$ 150	$ 150	$ 450
[1]	Indicates utilization of commitment amount, not drawn borrowings.
[2]	Represents the principal amount borrowed, net of unamortized discount and debt issuance costs.

Debt and Financing Arrangemen79

Debt and Financing Arrangements (Debt Maturities) (Details) $ in Millions	Dec. 31, 2016USD ($)
Maturities of Long-term Debt [Abstract]
2,017	$ 5.4
2,018	0.3
2,019	0.3
2,020	300.3
2,021	0.3
2022 and thereafter	515.4
Total	$ 822

Debt and Financing Arrangemen80

Debt and Financing Arrangements (Narrative) (Details) SFr in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2016CHF (SFr)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016CHF (SFr)	Nov. 12, 2014USD ($)
Debt Instrument [Line Items]
Principal amount	$ 800		$ 1,300
Proceeds from other long-term debt	0		4	$ 19.2
Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Proceeds from other long-term debt			0	$ 0
2006 Senior notes due 2016 | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Principal amount	$ 500
Debt Instrument, interest rate	7.50%				7.50%
Senior Notes, maturity date	Aug. 1, 2016	Aug. 1, 2016
Senior Notes, frequency of periodic payment	semi-annually	semi-annually
2010 Senior notes due 2020 | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Principal amount	$ 300
Debt Instrument, interest rate	5.50%				5.50%
Senior Notes, maturity date	Nov. 15, 2020	Nov. 15, 2020
2015 Senior notes Due 2025 | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Principal amount	$ 500
Debt Instrument, interest rate	4.35%				4.35%
Senior Notes, maturity date	Oct. 29, 2025	Oct. 29, 2025
Senior Notes, frequency of periodic payment	semi-annually	semi-annually
$900,000 secured letter of credit facility - uncommitted
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 900		1,000
$900,000 secured letter of credit facility - uncommitted | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 900		1,000
$800,000 secured letter of credit facility [Member] | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Initiation Date	Nov. 27, 2007	Nov. 27, 2007
Line of Credit Facility, Maximum Borrowing Capacity	$ 800
Debt instrument term	5 years	5 years
$400,000 secured letter of credit facility (pre-amendment) | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 400
$400,000 unsecured letter of credit facility | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 400
$150,000 secured letter of credit facility | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Initiation Date	Jun. 7, 2012	Jun. 7, 2012
Line of Credit Facility, Maximum Borrowing Capacity	$ 150		$ 150			$ 450
Debt instrument term	4 years	4 years
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases	$ 150
Additional commitments subject to lender approval	150
$200,000 unsecured revolving credit facility | Allied World Bermuda (Subsidiary Issuer)
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200
Debt instrument term	5 years	5 years
Additional commitments subject to lender approval	$ 150
Line of Credit Sublimit for Swingline Loans	$ 25
Repayment Of Swingline Loans Period	10 days	10 days
Switzerland
Debt Instrument [Line Items]
Number of annual principal payments required	19 years	19 years
Switzerland | Swiss office building mortgage
Debt Instrument [Line Items]
Debt Instrument, interest rate	3.20%				3.20%
Proceeds from other long-term debt	$ 14.2	SFr 14
Additional borrowing capacity	4				SFr 4
Annual principal payment	$ 0.3				SFr 0.3
Debt instrument term	20 years	20 years
Switzerland | Swiss office building credit facility
Debt Instrument [Line Items]
Debt Instrument, interest rate	2.50%				2.50%
Line of Credit Facility, Maximum Borrowing Capacity	$ 5.1				SFr 5
Debt instrument term	3 years	3 years

Income Taxes (Components of Inc

Income Taxes (Components of Income Taxes) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current income tax expense									$ 5.1	$ 9.8	$ 26.8
Deferred income tax (benefit) expense									(14.2)	(4)	3.7
Income tax expense	$ (13.3)	$ (3.2)	$ 6.3	$ 1.1	$ 4	$ (5.3)	$ 0.1	$ 7	$ (9.1)	$ 5.8	$ 30.5

Income Taxes (Sources of Income

Income Taxes (Sources of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Before Income Tax Domestic And Foreign [Line Items]
Income before income taxes	$ (54.1)	$ 65.4	$ 159.7	$ 75.2	$ 5.8	$ (57)	$ 9.6	$ 131.3	$ 246.2	$ 89.7	$ 520.8
Switzerland
Income Before Income Tax Domestic And Foreign [Line Items]
Income before income taxes									(25.5)	(15.7)	(19)
Bermuda
Income Before Income Tax Domestic And Foreign [Line Items]
Income before income taxes									336.6	162.1	460.2
United States
Income Before Income Tax Domestic And Foreign [Line Items]
Income before income taxes									(27.5)	12.8	72.9
All other jurisdictions
Income Before Income Tax Domestic And Foreign [Line Items]
Income before income taxes									$ (37.4)	$ (69.5)	$ 6.7

Income Taxes (Deferred Tax Comp

Income Taxes (Deferred Tax Components) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Decrease in valuation allowance	$ (4.7)
Deferred tax assets:
Reserve for losses and loss expenses	17.7	$ 22.2
Equity compensation	16	14.2
Unearned premium	17.1	18.1
Deferred acquisition costs	11.9	10.5
Mark-to-market losses	8.6	0
Net loss carryforward	21	27.3
Total deferred tax assets	92.3	92.3
Deferred tax liabilities:
Intangible assets	(21.9)	(23.3)
Mark-to-market gains	0	(3)
Depreciation	(4.4)	(6.4)
Market discount on bonds	(2)	(1.2)
Other	(1.2)	(5.2)
Total deferred tax liabilities	(29.5)	(39.1)
Net deferred taxes before valuation allowance	62.8	53.2
Valuation allowance	(24.1)	(28.8)
Net deferred tax assets	$ 38.7	$ 24.4

Income Taxes (Current Taxes) (D

Income Taxes (Current Taxes) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current tax receivable	$ 5.5	$ 5.5
Current tax payable	$ 0.7	$ 2.5

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of Effective Tax Rate) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Expected tax rate	7.80%	7.80%	7.80%
Income not subject to income tax	(10.70%)	(14.20%)	(7.10%)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent	4.40%	14.50%	2.30%
Foreign taxes at local expected tax rates	(4.60%)	(1.70%)	4.40%
Disallowed expenses and capital allowances	0.40%	3.20%	0.20%
Prior year refunds and adjustments	(0.30%)	0.00%	1.20%
Other	(0.70%)	(3.20%)	(2.90%)
Effective tax rate	(3.70%)	6.40%	5.90%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	7.80%	7.80%	7.80%
Switzerland
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	7.80%
Bermuda
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	0.00%
Percentage of income before income taxes	137.00%	181.00%	88.00%
United States
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	35.00%
Canada
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	15.00%
HONG KONG
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	16.50%
Ireland
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	12.50%
SINGAPORE
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	17.00%
United Kingdom
Income Before Income Tax Domestic And Foreign [Line Items]
Statutory tax rate	20.00%

Shareholders' Equity (Narrative

Shareholders' Equity (Narrative) (Details) - $ / shares	Apr. 19, 2016	Apr. 30, 2015	May 01, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Stock Repurchased and Retired During Period, Shares				1,936,812	5,252,026
Treasury Stock, Shares, Acquired				4,669,513	6,047,437	4,906,785
Common stock, shares outstanding				87,098,120	90,959,635
Shares cancelled, shares				1,936,812	5,252,026
Allied World Switzerland (Parent Guarantor)
Class of Stock [Line Items]
Threshold for dividend restrictions				20.00%
Minimum Annual Profit Percentage Required				5.00%
Common shares
Class of Stock [Line Items]
Dividends declared per share	$ 0.26	$ 0.26	$ 0.225
Minimum
Class of Stock [Line Items]
Maximum percentage of registered capital in treasury shares				10.00%
Maximum
Class of Stock [Line Items]
Maximum percentage of registered capital in treasury shares				20.00%

Shareholders' Equity (Issued Sh

Shareholders' Equity (Issued Share Capital) (Details) $ in Millions	Dec. 31, 2016USD ($)shares	Dec. 31, 2016SFr / shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2015SFr / shares	Dec. 31, 2014shares
Stockholders' Equity Note [Abstract]
Common shares issued and fully paid, 2016 and 2015: CHF 4.10 per share | shares	93,586,418		95,523,230		100,775,256
Common shares, par value | SFr / shares		SFr 4.1		SFr 4.1
Total share capital | $	$ 378.8		$ 386.7

Shareholders' Equity (Schedule

Shareholders' Equity (Schedule Of Common Stock Outstanding Roll Forward) (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Stock Repurchased and Retired During Period, Shares	(1,936,812)	(5,252,026)
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares issued at beginning of year	95,523,230	100,775,256
Shares cancelled, shares	(1,936,812)	(5,252,026)
Shares issued at end of year	93,586,418	95,523,230	100,775,256
Treasury Stock Transactions, Excluding Value of Shares Reissued [Abstract]
Treasury shares issued at beginning of year	4,563,595	4,579,774
Shares repurchased, shares	4,669,513	6,047,437	4,906,785
Shares issued out of treasury	(807,998)	(811,590)
Shares cancelled, shares	(1,936,812)	(5,252,026)
Total treasury shares at end of year	6,488,298	4,563,595	4,579,774
Total shares outstanding at end of year	87,098,120	90,959,635

Shareholders' Equity (Schedul90

Shareholders' Equity (Schedule Of Dividends Paid) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 29, 2016	Sep. 29, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Oct. 01, 2015	Jul. 02, 2015	Apr. 02, 2015	Jan. 02, 2015	Oct. 02, 2014	Jul. 02, 2014	Apr. 03, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends, Common Stock [Abstract]
Dividends paid per common share													$ 1.04	$ 1.23	$ 0.784
Common shares
Dividends, Common Stock [Abstract]
Dividends paid per common share	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 0.225	$ 0.225	$ 0.225	$ 0.225	$ 0.1666666667
Payment of quarterly dividends	$ 22.6	$ 22.6	$ 22.8	$ 23.4	$ 23.7	$ 23.6	$ 23.6	$ 21.5	$ 21.7	$ 21.7	$ 21.9	$ 16.5

Shareholders' Equity (Schedul91

Shareholders' Equity (Schedule Of Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	May 06, 2015	May 01, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Stock repurchase program, authorized amount		$ 500
Treasury shares reserved for issuance under stock compensation plans		3,000,000
Shares repurchased, shares			4,669,513	6,047,437	4,906,785
Cost of shares repurchased			$ 166.3	$ 245.3	$ 175.4
Shares repurchased, average price per share			$ 35.61	$ 40.56	$ 35.74
Exor SA
Class of Stock [Line Items]
Shares repurchased, shares	4,053,537
Cost of shares repurchased	$ 164.4
Shares repurchased, average price per share	$ 40.546

Employee Benefit Plans (Options

Employee Benefit Plans (Options) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning of year	1,968,607
Granted	0	0	0
Exercised	(428,938)	(454,602)	(479,831)
Forfeited	(13,926)
Outstanding, end of year	1,525,743	1,968,607
Exercisable, end of year	1,525,743
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, beginning of year - weighted average exercise price	$ 16.86
Exercised - weighted average exercise price	(15.24)
Forfeited - weighted average exercise price	(10.31)
Outstanding, end of year - weighted average exercise price	17.36	$ 16.86
Exercisable, end of year - weighted average exercise price	$ 17.36
Additional disclosures:
Outstanding, end of year, weighted average contractual term	3 years 3 months 18 days
Exercisable, end of year, weighted average contractual term	3 years 3 months 18 days
Outstanding, end of year, aggregate intrinsic value	$ 55.5
Exercisable, end of year, aggregate intrinsic value	$ 55.5
Weighted average grant date fair value	$ 0	$ 0	$ 0
Total intrinsic value of options exercised	$ 10.8	$ 12	$ 10.3
Proceeds from option exercises	$ 10.3	$ 10.1	$ 10
Stock options
Additional disclosures:
Life of award	10 years
Vesting period	4 years

Employee Benefit Plans (Restric

Employee Benefit Plans (Restricted Stock Units) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
RSUs and performance-based equity awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Aggregate intrinsic value of vested awards	$ 14	$ 16.9	$ 14.4
Vesting period	4 years
Rsus Other Than Performance Based Rsus
Activity:
Outstanding, beginning of year	819,309
Granted, shares	689,042
Forfeited, shares	(123,307)
Fully vested, shares	(251,115)
Outstanding, end of year	1,133,929	819,309
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$ 37.33
Granted - weighted average grant date fair value	32
Forfeited - weighted average grant date fair value	(34.80)
Vested - weighted average grant date fair value	(36.30)
Outstanding, end of year - weighted average grant date fair value	$ 34.56	$ 37.33
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Aggregate intrinsic value	$ 60.9
Total compensation cost not yet recognized	$ 28.9
Compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Performance Based Rsus
Activity:
Outstanding, beginning of year	591,683
Granted, shares	200,730
Additional awards granted due to achievement of performance criteria, shares	24,979
Forfeited, shares	(16,993)
Fully vested, shares	(216,958)
Outstanding, end of year	583,441	591,683
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$ 34.78
Granted - weighted average grant date fair value	31.95
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	29.24
Forfeited - weighted average grant date fair value	(36.71)
Vested - weighted average grant date fair value	(29.24)
Outstanding, end of year - weighted average grant date fair value	$ 35.57	$ 34.78
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Aggregate intrinsic value	$ 31.3
Total compensation cost not yet recognized	$ 7.3
Compensation cost not yet recognized, period for recognition	1 year 7 months 2 days
The rate at which performance awards are expensed	100.00%	100.00%	55.00%

Employee Benefit Plans (Cash-Eq

Employee Benefit Plans (Cash-Equivalent Stock Awards) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Accounts payable and accrued liabilities	$ 180.7	$ 184.5
Cash-equivalent stock awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Accounts payable and accrued liabilities	$ 32.2
Cash Equivalent Stock Awards Rsus [Member]
Activity:
Outstanding, beginning of year	1,277,083
Granted, shares	167,438
Additional awards granted due to achievement of performance criteria, shares	0
Forfeited, shares	(90,245)
Fully vested, shares	(581,829)
Outstanding, end of year	772,447
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$ 31.94
Granted - weighted average grant date fair value	31.95
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	0
Forfeited - weighted average grant date fair value	(33.66)
Vested - weighted average grant date fair value	(29.14)
Outstanding, end of year - weighted average grant date fair value	$ 33.86
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vesting period	4 years
Cash Equivalent Stock Awards Performance Based [Member]
Activity:
Outstanding, beginning of year	693,477
Granted, shares	50,183
Additional awards granted due to achievement of performance criteria, shares	37,434
Forfeited, shares	(18,104)
Fully vested, shares	(325,386)
Outstanding, end of year	437,604
Weighted average grant date fair value:
Outstanding, beginning of year - weighted average grant date fair value	$ 33.25
Granted - weighted average grant date fair value	31.95
Additional awards granted due to achievement of performance criteria - weighted average grant date fair value	29.24
Forfeited - weighted average grant date fair value	(35.27)
Vested - weighted average grant date fair value	(29.24)
Outstanding, end of year - weighted average grant date fair value	$ 35.65
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]
Vesting period	3 years

Employee Benefit Plans (Other D

Employee Benefit Plans (Other Details) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 38.3	$ 49.7	$ 52
Expense related to defined contribution arrangements	13.7	13.5	10.6
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 0	0.3	1.9
Vesting period	4 years
RSUs and performance-based equity awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 16.4	15	12.3
Vesting period	4 years
Cash-equivalent stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 21.9	$ 34.4	$ 37.8
2012 Omnibus Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	4,500,000
2012 Omnibus Plan | Awards other than performance-based
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2012 Omnibus Plan | Performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share purchase plan, discount from fair market value	15.00%
Number of shares authorized	3,000,000

Earnings Per Share (Narrative)

Earnings Per Share (Narrative) (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee stock options and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	229,359	308,405	0

Earnings Per Share (Comparison

Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic earnings per share:
Net income	$ (40.8)	$ 68.6	$ 153.4	$ 74.1	$ 1.8	$ (51.7)	$ 9.5	$ 124.3	$ 255.3	$ 83.9	$ 490.3
Weighted average common shares outstanding	87,036,339	87,102,290	88,742,484	90,254,512	90,934,107	90,882,511	92,441,730	95,935,551	88,275,810	92,530,208	97,538,319
Basic earnings per share	$ (0.47)	$ 0.79	$ 1.73	$ 0.82	$ 0.02	$ (0.57)	$ 0.10	$ 1.30	$ 2.89	$ 0.91	$ 5.03
Diluted earnings per share:
Net income	$ (40.8)	$ 68.6	$ 153.4	$ 74.1	$ 1.8	$ (51.7)	$ 9.5	$ 124.3	$ 255.3	$ 83.9	$ 490.3
Weighted average common shares outstanding	87,036,339	87,102,290	88,742,484	90,254,512	90,934,107	90,882,511	92,441,730	95,935,551	88,275,810	92,530,208	97,538,319
Share equivalents:
Warrants and options									839,038	1,031,666	1,432,960
RSUs and LTIP awards									677,033	591,773	605,808
Employee share purchase plan									9,013	20,813	14,686
Weighted average common shares and common share equivalents outstanding - diluted	87,036,339	88,603,101	90,040,509	91,559,225	92,422,422	90,882,511	93,984,226	97,577,029	89,800,894	94,174,460	99,591,773
Diluted earnings per share	$ (0.47)	$ 0.77	$ 1.70	$ 0.81	$ 0.02	$ (0.57)	$ 0.10	$ 1.27	$ 2.84	$ 0.89	$ 4.92

Commitments And Contingencies98

Commitments And Contingencies (Operating Leases) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	$ 21.6
2,018	20.7
2,019	19.6
2,020	17.8
2,021	16.9
2022 and thereafter	116.2
Total	212.8
Other details:
Total rent expense	26.5	$ 25.9	$ 19
Sublease income	$ 1.8	$ 0.7	$ 0.1

Commitments And Contingencies99

Commitments And Contingencies (Credit Concentration Disclosure) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)Custodian	Dec. 31, 2015Custodian	Dec. 31, 2014
Concentration Risk [Line Items]
Number of custodians | Custodian	1	1
Insurance balances receivable over 90 days	$ 20
Allowance for doubtful accounts	$ 3
Total receivable balance | Credit concentration risk
Concentration Risk [Line Items]
Concentration risk, percentage	2.50%
Gross written premium | Credit concentration risk | Marsh & McLennan Companies, Inc.
Concentration Risk [Line Items]
Concentration risk, percentage	21.00%	24.00%	25.00%
Gross written premium | Credit concentration risk | Aon Corporation
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	16.00%	17.00%
Gross written premium | Credit concentration risk | Willis Group Holdings
Concentration Risk [Line Items]
Concentration risk, percentage	9.00%	11.00%	10.00%

Statutory Capital and Surplu100

Statutory Capital and Surplus (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statutory Accounting Practices [Line Items]
Amount of restricted net assets for the Company's consolidated subsidiaries	$ 2,678.3
Bermuda
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	3,494.1	$ 3,270.9
Minimum Required Statutory Capital and Surplus	800.2	853.2
Statutory Net Income (Loss)	366.4	221.5	$ 487.1
Statutory Amount Available for Dividend Payments	873.5
United States
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	1,185.9	1,215.5
Minimum Required Statutory Capital and Surplus	263.3	241
Statutory Net Income (Loss)	19	40.5	45.4
Statutory Amount Available for Dividend Payments	0
Ireland
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	395.5	414
Minimum Required Statutory Capital and Surplus	84.7	26.9
Statutory Net Income (Loss)	10.1	3.2	3.2
Statutory Amount Available for Dividend Payments	35.5
Switzerland
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	327.5	183.6
Minimum Required Statutory Capital and Surplus	218.2	17.7
Statutory Net Income (Loss)	11	10.7	7.4
Statutory Amount Available for Dividend Payments	0
United Kingdom
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus	268.4	245.9
Minimum Required Statutory Capital and Surplus	264.1	231.8
Statutory Net Income (Loss)	(5.1)	$ (39.4)	$ (7.8)
Statutory Amount Available for Dividend Payments	$ 2.7

Segment Information (Summary Of

Segment Information (Summary Of Segment Results) (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2016USD ($)segments	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Segment Reporting Information [Line Items]
Gross premiums written	$ 671.7	$ 730.2	$ 800.3	$ 863.5	$ 632.3	$ 754.1	$ 826	$ 880.6	$ 3,065.8	$ 3,093	$ 2,935.4
Net premiums written	445.3	528.3	578.1	704	464.8	607	603.7	772.5	2,255.8	2,448	2,322
Net premiums earned	577	584	602.9	580.1	622.8	650.7	646.4	568.5	2,344.1	2,488.4	2,182.7
Net losses and loss expenses	(387.8)	(376.3)	(365.4)	(372.4)	(412.7)	(416.9)	(431.5)	(325.2)	(1,501.8)	(1,586.3)	(1,199.2)
Acquisition costs	(82)	(82)	(87.4)	(88.3)	(96)	(100.1)	(100.6)	(78.7)	(339.8)	(375.4)	(295.1)
General and administrative expenses	(106.1)	(104.2)	(104.7)	(96.4)	(95)	(105.8)	(108.4)	(97.1)	(411.5)	(406.3)	(365.7)
Underwriting income									91	120.4	322.7
Other insurance-related revenue	4.8	1.8	5.2	0.6	1	0.7	0.9	0.9	12.4	3.5	2.1
Other insurance-related expenses	(1.8)	(2.2)	(1.7)	(1.1)	(1.9)	(1.3)	(1.2)	(1.8)	(6.8)	(6.2)	(8.6)
Segment income									96.6	117.7	316.2
Net investment income	58.1	50.6	55.8	53.3	49.1	45.7	42.8	44.5	217.8	182.1	176.9
Net realized investment gains (losses)	(101.9)	10.7	74.5	18.9	(38.8)	(113.6)	(20.2)	45	2.1	(127.6)	89
Amortization of intangible assets	(3.2)	(2.5)	(2.5)	(2.5)	(3.7)	(2.7)	(2.8)	(0.6)	(10.7)	(9.8)	(2.5)
Interest expense	(10.4)	(13.5)	(19.9)	(20)	(18.1)	(14.5)	(14.5)	(14.3)	(63.7)	(61.4)	(57.8)
Foreign exchange (loss) gain	(0.8)	(1)	2.9	3	(0.9)	0.8	(1.3)	(9.9)	4.1	(11.3)	(1)
Income before income taxes	$ (54.1)	$ 65.4	$ 159.7	$ 75.2	$ 5.8	$ (57)	$ 9.6	$ 131.3	$ 246.2	$ 89.7	$ 520.8
Loss and loss expense ratio									64.10%	63.70%	54.90%
Acquisition cost ratio									14.50%	15.10%	13.50%
General and administrative expense ratio									17.60%	16.30%	16.80%
Expense ratio									32.10%	31.40%	30.30%
Combined ratio									96.20%	95.10%	85.20%
Number of operating segments | segments									3
Operating segments | North American Insurance
Segment Reporting Information [Line Items]
Gross premiums written									$ 1,856.3	$ 1,815.3	$ 1,716.3
Net premiums written									1,223.4	1,358.1	1,230.8
Net premiums earned									1,266.9	1,301.4	1,111.1
Net losses and loss expenses									(862.2)	(910.2)	(683.8)
Acquisition costs									(132)	(139.6)	(105.9)
General and administrative expenses									(223.3)	(224.6)	(219.6)
Underwriting income									49.4	27	101.8
Other insurance-related revenue									6.7	3.5	2.1
Other insurance-related expenses									(2.3)	(2.7)	(1.9)
Segment income									$ 53.8	$ 27.8	$ 102
Loss and loss expense ratio									68.10%	69.90%	61.50%
Acquisition cost ratio									10.40%	10.70%	9.50%
General and administrative expense ratio									17.60%	17.30%	19.80%
Expense ratio									28.00%	28.00%	29.30%
Combined ratio									96.10%	97.90%	90.80%
Operating segments | Global Markets Insurance
Segment Reporting Information [Line Items]
Gross premiums written									$ 503.3	$ 476.3	$ 280.5
Net premiums written									367.5	324.1	188
Net premiums earned									377.8	366.8	162.6
Net losses and loss expenses									(269.5)	(240.3)	(61.1)
Acquisition costs									(66.5)	(70.9)	(18.2)
General and administrative expenses									(123.7)	(108.4)	(68.1)
Underwriting income									(81.9)	(52.8)	15.2
Other insurance-related revenue									1.4	0	0
Other insurance-related expenses									(1.1)	(2.5)	(6.7)
Segment income									$ (81.6)	$ (55.3)	$ 8.5
Loss and loss expense ratio									71.30%	65.50%	37.60%
Acquisition cost ratio									17.60%	19.30%	11.20%
General and administrative expense ratio									32.70%	29.50%	41.90%
Expense ratio									50.30%	48.80%	53.10%
Combined ratio									121.60%	114.30%	90.70%
Operating segments | Reinsurance
Segment Reporting Information [Line Items]
Gross premiums written									$ 706.2	$ 801.4	$ 938.6
Net premiums written									664.9	765.8	903.2
Net premiums earned									699.4	820.2	909
Net losses and loss expenses									(370.1)	(435.8)	(454.3)
Acquisition costs									(141.3)	(164.9)	(171)
General and administrative expenses									(64.5)	(73.3)	(78)
Underwriting income									123.5	146.2	205.7
Other insurance-related revenue									4.3	0	0
Other insurance-related expenses									(3.4)	(1)	0
Segment income									$ 124.4	$ 145.2	$ 205.7
Loss and loss expense ratio									52.90%	53.10%	50.00%
Acquisition cost ratio									20.20%	20.10%	18.80%
General and administrative expense ratio									9.20%	8.90%	8.60%
Expense ratio									29.40%	29.00%	27.40%
Combined ratio									82.30%	82.10%	77.40%

Segment Information (Gross Prem

Segment Information (Gross Premiums Written By Geographic Location) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written	$ 671.7	$ 730.2	$ 800.3	$ 863.5	$ 632.3	$ 754.1	$ 826	$ 880.6	$ 3,065.8	$ 3,093	$ 2,935.4
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									1,903.4	1,893.4	1,795.6
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									495.4	543.6	640.9
Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									296.3	326.9	318.6
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									352.2	313.1	167.3
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									18.5	16	13
Switzerland
Revenues from External Customers and Long-Lived Assets [Line Items]
Gross premiums written									$ 46.5	$ 58.2	$ 67.6

Segment Information (Net Premiu

Segment Information (Net Premiums Earned by Line of Business) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net premiums earned	$ 577	$ 584	$ 602.9	$ 580.1	$ 622.8	$ 650.7	$ 646.4	$ 568.5	$ 2,344.1	$ 2,488.4	$ 2,182.7
Operating segments | North American Insurance
Segment Reporting Information [Line Items]
Net premiums earned									1,266.9	1,301.4	1,111.1
Operating segments | North American Insurance | General casualty
Segment Reporting Information [Line Items]
Net premiums earned									396.7	424	334.6
Operating segments | North American Insurance | Professional liability
Segment Reporting Information [Line Items]
Net premiums earned									388.5	385.3	276.1
Operating segments | North American Insurance | General property
Segment Reporting Information [Line Items]
Net premiums earned									127.6	162.8	170.3
Operating segments | North American Insurance | Healthcare
Segment Reporting Information [Line Items]
Net premiums earned									66.5	102.9	168.5
Operating segments | North American Insurance | Programs
Segment Reporting Information [Line Items]
Net premiums earned									170.4	150.7	119.8
Operating segments | North American Insurance | Specialty and other
Segment Reporting Information [Line Items]
Net premiums earned									117.2	75.6	41.9
Operating segments | Global Markets Insurance
Segment Reporting Information [Line Items]
Net premiums earned									377.8	366.8	162.6
Operating segments | Global Markets Insurance | General casualty
Segment Reporting Information [Line Items]
Net premiums earned									87.8	57.8	15.3
Operating segments | Global Markets Insurance | Professional liability
Segment Reporting Information [Line Items]
Net premiums earned									96.2	102.5	69.1
Operating segments | Global Markets Insurance | General property
Segment Reporting Information [Line Items]
Net premiums earned									67.9	106.7	34
Operating segments | Global Markets Insurance | Specialty and other
Segment Reporting Information [Line Items]
Net premiums earned									125.9	99.8	44.2
Operating segments | Reinsurance
Segment Reporting Information [Line Items]
Net premiums earned									699.4	820.2	909
Operating segments | Reinsurance | Property
Segment Reporting Information [Line Items]
Net premiums earned									337.2	403.5	412
Operating segments | Reinsurance | Casualty
Segment Reporting Information [Line Items]
Net premiums earned									183.7	224.4	175.5
Operating segments | Reinsurance | Specialty
Segment Reporting Information [Line Items]
Net premiums earned									$ 178.5	$ 192.3	$ 321.5

Condensed Consolidated Guara104

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS:
Investments	$ 7,942.3	$ 8,571.2
Cash and cash equivalents	720.9	608	$ 589.3	$ 531.9
Insurance balances receivable	784	745.9
Funds held	466.8	640.8
Reinsurance recoverable	1,625	1,480	1,340.3	1,234.5
Reinsurance recoverable on paid losses	104.4	96.4
Net deferred acquisition costs	121.1	165.2
Goodwill and intangible assets	494.4	504.7
Balances receivable on sale of investments	114.7	36.9
Investments in subsidiaries	0	0
Due from subsidiaries	0	0
Other assets	805.4	662.8
Total assets	13,179	13,511.9
LIABILITIES:
Reserve for losses and loss expenses	6,639.2	6,456.2	5,881.2	5,766.5
Unearned premiums	1,688.1	1,683.3
Reinsurance balances payable	223.3	214.4
Balances due on purchases of investments	79.7	125.1
Senior notes, net of unamortized discount and debt issuance costs	794.2	1,292.9
Other long-term debt	22	23
Due to subsidiaries	0	0
Other liabilities	180.7	184.5
Total liabilities	9,627.2	9,979.4
Total shareholders' equity	3,551.8	3,532.5	3,778.2
Total liabilities and shareholders' equity	13,179	13,511.9
Consolidating Adjustments
ASSETS:
Investments	0	0
Cash and cash equivalents	0	0	0	0
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	(7,453.8)	(7,743.3)
Due from subsidiaries	(145.5)	(226.3)
Other assets	0	0
Total assets	(7,599.3)	(7,969.6)
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes, net of unamortized discount and debt issuance costs	0	0
Other long-term debt	0	0
Due to subsidiaries	(145.5)	(226.3)
Other liabilities	0	0
Total liabilities	(145.5)	(226.3)
Total shareholders' equity	(7,453.8)	(7,743.3)
Total liabilities and shareholders' equity	(7,599.3)	(7,969.6)
Allied World Switzerland (Parent Guarantor)
ASSETS:
Investments	0	0
Cash and cash equivalents	13.1	21.8	32.6	10.8
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	3,433.7	3,347
Due from subsidiaries	115.6	173.1
Other assets	1.8	1.8
Total assets	3,564.2	3,543.7
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes, net of unamortized discount and debt issuance costs	0	0
Other long-term debt	0	0
Due to subsidiaries	9.9	8.5
Other liabilities	2.5	2.7
Total liabilities	12.4	11.2
Total shareholders' equity	3,551.8	3,532.5
Total liabilities and shareholders' equity	3,564.2	3,543.7
Allied World Bermuda (Subsidiary Issuer)
ASSETS:
Investments	0	0
Cash and cash equivalents	0.8	1	1.7	2.8
Insurance balances receivable	0	0
Funds held	0	0
Reinsurance recoverable	0	0
Reinsurance recoverable on paid losses	0	0
Net deferred acquisition costs	0	0
Goodwill and intangible assets	0	0
Balances receivable on sale of investments	0	0
Investments in subsidiaries	4,020.1	4,396.3
Due from subsidiaries	0	36.4
Other assets	0.8	0.1
Total assets	4,021.7	4,433.8
LIABILITIES:
Reserve for losses and loss expenses	0	0
Unearned premiums	0	0
Reinsurance balances payable	0	0
Balances due on purchases of investments	0	0
Senior notes, net of unamortized discount and debt issuance costs	794.2	1,292.9
Other long-term debt	0	0
Due to subsidiaries	20	8.3
Other liabilities	5.7	22.2
Total liabilities	819.9	1,323.4
Total shareholders' equity	3,201.8	3,110.4
Total liabilities and shareholders' equity	4,021.7	4,433.8
Other Allied World Subsidiaries
ASSETS:
Investments	7,942.3	8,571.2
Cash and cash equivalents	707	585.2	$ 555	$ 518.3
Insurance balances receivable	784	745.9
Funds held	466.8	640.8
Reinsurance recoverable	1,625	1,480
Reinsurance recoverable on paid losses	104.4	96.4
Net deferred acquisition costs	121.1	165.2
Goodwill and intangible assets	494.4	504.7
Balances receivable on sale of investments	114.7	36.9
Investments in subsidiaries	0	0
Due from subsidiaries	29.9	16.8
Other assets	802.8	660.9
Total assets	13,192.4	13,504
LIABILITIES:
Reserve for losses and loss expenses	6,639.2	6,456.2
Unearned premiums	1,688.1	1,683.3
Reinsurance balances payable	223.3	214.4
Balances due on purchases of investments	79.7	125.1
Senior notes, net of unamortized discount and debt issuance costs	0	0
Other long-term debt	22	23
Due to subsidiaries	115.6	209.5
Other liabilities	172.6	159.7
Total liabilities	8,940.5	8,871.2
Total shareholders' equity	4,251.9	4,632.8
Total liabilities and shareholders' equity	$ 13,192.4	$ 13,504

Condensed Consolidated Guara105

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Net premiums earned	$ 577	$ 584	$ 602.9	$ 580.1	$ 622.8	$ 650.7	$ 646.4	$ 568.5	$ 2,344.1	$ 2,488.4	$ 2,182.7
Net investment income	58.1	50.6	55.8	53.3	49.1	45.7	42.8	44.5	217.8	182.1	176.9
Net realized investment gains (losses)	(101.9)	10.7	74.5	18.9	(38.8)	(113.6)	(20.2)	45	2.1	(127.6)	89
Other income	4.8	1.8	5.2	0.6	1	0.7	0.9	0.9	12.4	3.5	2.1
Net losses and loss expenses	(387.8)	(376.3)	(365.4)	(372.4)	(412.7)	(416.9)	(431.5)	(325.2)	(1,501.8)	(1,586.3)	(1,199.2)
Acquisition costs	(82)	(82)	(87.4)	(88.3)	(96)	(100.1)	(100.6)	(78.7)	(339.8)	(375.4)	(295.1)
General and administrative expenses	(106.1)	(104.2)	(104.7)	(96.4)	(95)	(105.8)	(108.4)	(97.1)	(411.5)	(406.3)	(365.7)
Other expense	(1.8)	(2.2)	(1.7)	(1.1)	(1.9)	(1.3)	(1.2)	(1.8)	(6.8)	(6.2)	(8.6)
Amortization of intangible assets	(3.2)	(2.5)	(2.5)	(2.5)	(3.7)	(2.7)	(2.8)	(0.6)	(10.7)	(9.8)	(2.5)
Interest expense	(10.4)	(13.5)	(19.9)	(20)	(18.1)	(14.5)	(14.5)	(14.3)	(63.7)	(61.4)	(57.8)
Foreign exchange (loss) gain	(0.8)	(1)	2.9	3	(0.9)	0.8	(1.3)	(9.9)	4.1	(11.3)	(1)
Income tax (expense) benefit	13.3	3.2	(6.3)	(1.1)	(4)	5.3	(0.1)	(7)	9.1	(5.8)	(30.5)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME	$ (40.8)	$ 68.6	$ 153.4	$ 74.1	$ 1.8	$ (51.7)	$ 9.5	$ 124.3	255.3	83.9	490.3
Other comprehensive loss									(2.3)	(9.3)	0
COMPREHENSIVE INCOME (LOSS)									253	74.6	490.3
Consolidating Adjustments
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									0	0	0
Net realized investment gains (losses)									0	0	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									0	0	0
Other expense									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									0	0	0
Foreign exchange (loss) gain									0	0	0
Income tax (expense) benefit									0	0	0
Equity in earnings of consolidated subsidiaries									(615.9)	(278)	(1,090.5)
NET INCOME									(615.9)	(278)	(1,090.5)
Other comprehensive loss									2.3	9.3	0
COMPREHENSIVE INCOME (LOSS)									(613.6)	(268.7)	(1,090.5)
Allied World Switzerland (Parent Guarantor)
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									0.1	0	0.1
Net realized investment gains (losses)									0	0	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									(18.7)	(36.7)	(35.6)
Other expense									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									0	0	0
Foreign exchange (loss) gain									0	0	0
Income tax (expense) benefit									(0.1)	(0.1)	(0.1)
Equity in earnings of consolidated subsidiaries									274	120.7	525.9
NET INCOME									255.3	83.9	490.3
Other comprehensive loss									(2.3)	(9.3)	0
COMPREHENSIVE INCOME (LOSS)									253	74.6	490.3
Allied World Bermuda (Subsidiary Issuer)
Condensed Income Statements, Captions [Line Items]
Net premiums earned									0	0	0
Net investment income									0.1	0.1	0
Net realized investment gains (losses)									0	0	0
Other income									0	0	0
Net losses and loss expenses									0	0	0
Acquisition costs									0	0	0
General and administrative expenses									0.2	(0.5)	(3.1)
Other expense									0	0	0
Amortization of intangible assets									0	0	0
Interest expense									(61.6)	(59.2)	(55.4)
Foreign exchange (loss) gain									0	0	0.1
Income tax (expense) benefit									0	0	0
Equity in earnings of consolidated subsidiaries									341.9	157.3	564.6
NET INCOME									280.6	97.7	506.2
Other comprehensive loss									0	0	0
COMPREHENSIVE INCOME (LOSS)									280.6	97.7	506.2
Other Allied World Subsidiaries
Condensed Income Statements, Captions [Line Items]
Net premiums earned									2,344.1	2,488.4	2,182.7
Net investment income									217.6	182	176.8
Net realized investment gains (losses)									2.1	(127.6)	89
Other income									12.4	3.5	2.1
Net losses and loss expenses									(1,501.8)	(1,586.3)	(1,199.2)
Acquisition costs									(339.8)	(375.4)	(295.1)
General and administrative expenses									(393)	(369.1)	(327.1)
Other expense									(6.8)	(6.2)	(8.6)
Amortization of intangible assets									(10.7)	(9.8)	(2.5)
Interest expense									(2.1)	(2.2)	(2.3)
Foreign exchange (loss) gain									4.1	(11.3)	(1.1)
Income tax (expense) benefit									9.2	(5.7)	(30.4)
Equity in earnings of consolidated subsidiaries									0	0	0
NET INCOME									335.3	180.3	584.3
Other comprehensive loss									(2.3)	(9.3)	0
COMPREHENSIVE INCOME (LOSS)									$ 333	$ 171	$ 584.3

Condensed Consolidated Guara106

Condensed Consolidated Guarantor Financial Statements (Schedule Of Condensed Consolidating Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	$ 397.8	$ 504.3	$ 407.8
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	(5,423.7)	(5,863.2)	(7,630)
Purchases of other invested assets	(119)	(126.7)	(307.9)
Sales of trading securities	5,929.9	5,328.8	7,536.9
Sales of other invested assets	96.3	161.3	267.9
Net cash paid for acquisitions	(1.2)	(124.4)	(2.6)
Return of investment in subsidiary	0
Capital contributions		0
Other	(19.4)	(11.5)	8.7
Net cash provided by (used in) investing activities	462.9	(635.7)	(127)
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	(91.5)	(114.1)	(76.7)
Intercompany dividends paid	0	0	0
Proceeds to parent	0
Proceeds from the exercise of stock options	10.3	10.1	10
Share repurchases	(166.3)	(246.4)	(175.9)
Proceeds from senior notes	0	496.7	0
Proceeds from other long-term debt	0	4	19.2
Repayment of other long-term debt	(0.3)	(0.2)	0
Repayment of senior notes	(500)	0	0
Net cash (used in) provided by used in financing activities	(747.8)	150.1	(223.4)
NET INCREASE IN CASH AND CASH EQUIVALENTS	112.9	18.7	57.4
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	608	589.3	531.9
CASH AND CASH EQUIVALENTS, END OF PERIOD	720.9	608	589.3
Consolidating Adjustments
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	(841)	(811.1)	(643.3)
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Net cash paid for acquisitions	0	0	0
Return of investment in subsidiary	(250)
Capital contributions		0
Other	0	0	0
Net cash provided by (used in) investing activities	(250)	0	0
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	0	0	0
Intercompany dividends paid	841	811.1	643.3
Proceeds to parent	250
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Proceeds from senior notes		0
Proceeds from other long-term debt		0	0
Repayment of other long-term debt	0	0
Repayment of senior notes	0
Net cash (used in) provided by used in financing activities	1,091	811.1	643.3
NET INCREASE IN CASH AND CASH EQUIVALENTS	0	0	0
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	0	0	0
CASH AND CASH EQUIVALENTS, END OF PERIOD	0	0	0
Allied World Switzerland (Parent Guarantor)
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	238.8	339.6	264.4
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Net cash paid for acquisitions	0	0	0
Return of investment in subsidiary	0
Capital contributions		0
Other	0	0	0
Net cash provided by (used in) investing activities	0	0	0
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	(91.5)	(114.1)	(76.7)
Intercompany dividends paid	0	0	0
Proceeds to parent	0
Proceeds from the exercise of stock options	10.3	10.1	10
Share repurchases	(166.3)	(246.4)	(175.9)
Proceeds from senior notes		0
Proceeds from other long-term debt		0	0
Repayment of other long-term debt	0	0
Repayment of senior notes	0
Net cash (used in) provided by used in financing activities	(247.5)	(350.4)	(242.6)
NET INCREASE IN CASH AND CASH EQUIVALENTS	(8.7)	(10.8)	21.8
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	21.8	32.6	10.8
CASH AND CASH EQUIVALENTS, END OF PERIOD	13.1	21.8	32.6
Allied World Bermuda (Subsidiary Issuer)
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	506.4	377.7	292.9
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	0	0	0
Purchases of other invested assets	0	0	0
Sales of trading securities	0	0	0
Sales of other invested assets	0	0	0
Net cash paid for acquisitions	0	0	0
Return of investment in subsidiary	250
Capital contributions		(496.7)
Other	0	0	0
Net cash provided by (used in) investing activities	250	(496.7)	0
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	0	0	0
Intercompany dividends paid	(256.6)	(378.4)	(294)
Proceeds to parent	0
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Proceeds from senior notes		496.7
Proceeds from other long-term debt		0	0
Repayment of other long-term debt	0	0
Repayment of senior notes	(500)
Net cash (used in) provided by used in financing activities	(756.6)	118.3	(294)
NET INCREASE IN CASH AND CASH EQUIVALENTS	(0.2)	(0.7)	(1.1)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	1	1.7	2.8
CASH AND CASH EQUIVALENTS, END OF PERIOD	0.8	1	1.7
Other Allied World Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
CASH FLOWS PROVIDED BY (USED IN) OPERATING ACTIVITIES:	493.6	598.1	493.8
CASH FLOWS PROVIDED BY (USED IN) INVESTING ACTIVITIES:
Purchases of trading securities	(5,423.7)	(5,863.2)	(7,630)
Purchases of other invested assets	(119)	(126.7)	(307.9)
Sales of trading securities	5,929.9	5,328.8	7,536.9
Sales of other invested assets	96.3	161.3	267.9
Net cash paid for acquisitions	(1.2)	(124.4)	(2.6)
Return of investment in subsidiary	0
Capital contributions		496.7
Other	(19.4)	(11.5)	8.7
Net cash provided by (used in) investing activities	462.9	(139)	(127)
CASH FLOWS (USED IN) PROVIDED BY FINANCING ACTIVITIES:
Dividends paid	0	0	0
Intercompany dividends paid	(584.4)	(432.7)	(349.3)
Proceeds to parent	(250)
Proceeds from the exercise of stock options	0	0	0
Share repurchases	0	0	0
Proceeds from senior notes		0
Proceeds from other long-term debt		4	19.2
Repayment of other long-term debt	(0.3)	(0.2)
Repayment of senior notes	0
Net cash (used in) provided by used in financing activities	(834.7)	(428.9)	(330.1)
NET INCREASE IN CASH AND CASH EQUIVALENTS	121.8	30.2	36.7
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	585.2	555	518.3
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 707	$ 585.2	$ 555

Condensed Consolidated Guara107

Condensed Consolidated Guarantor Financial Statements (Notes to Consolidated Guarantor Financial Statements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Subsidiary Investee Percentage Ownership	100.00%
Allied World Switzerland (Parent Guarantor)
Condensed Financial Statements, Captions [Line Items]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	$ 256.6	$ 378.4	$ 294

Unaudited Quarterly Financia108

Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
REVENUES:
Gross premiums written	$ 671.7	$ 730.2	$ 800.3	$ 863.5	$ 632.3	$ 754.1	$ 826	$ 880.6	$ 3,065.8	$ 3,093	$ 2,935.4
Premiums ceded	(226.4)	(201.9)	(222.2)	(159.5)	(167.5)	(147.1)	(222.3)	(108.1)	(810)	(645)	(613.4)
Net premiums written	445.3	528.3	578.1	704	464.8	607	603.7	772.5	2,255.8	2,448	2,322
Change in unearned premiums	131.7	55.7	24.8	(123.9)	158	43.7	42.7	(204)	88.3	40.4	(139.3)
Net premiums earned	577	584	602.9	580.1	622.8	650.7	646.4	568.5	2,344.1	2,488.4	2,182.7
Net investment income	58.1	50.6	55.8	53.3	49.1	45.7	42.8	44.5	217.8	182.1	176.9
Net realized investment gains (losses)	(101.9)	10.7	74.5	18.9	(38.8)	(113.6)	(20.2)	45	2.1	(127.6)	89
Other income	4.8	1.8	5.2	0.6	1	0.7	0.9	0.9	12.4	3.5	2.1
Total revenue	538	647.1	738.4	652.9	634.1	583.5	669.9	658.9	2,576.4	2,546.4	2,450.7
EXPENSES:
Net losses and loss expenses	387.8	376.3	365.4	372.4	412.7	416.9	431.5	325.2	1,501.8	1,586.3	1,199.2
Acquisition costs	82	82	87.4	88.3	96	100.1	100.6	78.7	339.8	375.4	295.1
General and administrative expenses	106.1	104.2	104.7	96.4	95	105.8	108.4	97.1	411.5	406.3	365.7
Other expense	1.8	2.2	1.7	1.1	1.9	1.3	1.2	1.8	6.8	6.2	8.6
Amortization and impairment of intangible assets	3.2	2.5	2.5	2.5	3.7	2.7	2.8	0.6	10.7	9.8	2.5
Interest expense	10.4	13.5	19.9	20	18.1	14.5	14.5	14.3	63.7	61.4	57.8
Foreign exchange (gain) loss	0.8	1	(2.9)	(3)	0.9	(0.8)	1.3	9.9	(4.1)	11.3	1
Total expenses	592.1	581.7	578.7	577.7	628.3	640.5	660.3	527.6	2,330.2	2,456.7	1,929.9
Income before income taxes	(54.1)	65.4	159.7	75.2	5.8	(57)	9.6	131.3	246.2	89.7	520.8
Income tax (benefit) expense	(13.3)	(3.2)	6.3	1.1	4	(5.3)	0.1	7	(9.1)	5.8	30.5
Net income	$ (40.8)	$ 68.6	$ 153.4	$ 74.1	$ 1.8	$ (51.7)	$ 9.5	$ 124.3	$ 255.3	$ 83.9	$ 490.3
PER SHARE DATA
Basic earnings (loss) per share	$ (0.47)	$ 0.79	$ 1.73	$ 0.82	$ 0.02	$ (0.57)	$ 0.10	$ 1.30	$ 2.89	$ 0.91	$ 5.03
Diluted earnings (loss) per share	$ (0.47)	$ 0.77	$ 1.70	$ 0.81	$ 0.02	$ (0.57)	$ 0.10	$ 1.27	$ 2.84	$ 0.89	$ 4.92
Weighted average common shares outstanding	87,036,339	87,102,290	88,742,484	90,254,512	90,934,107	90,882,511	92,441,730	95,935,551	88,275,810	92,530,208	97,538,319
Weighted average common shares and common share equivalents outstanding	87,036,339	88,603,101	90,040,509	91,559,225	92,422,422	90,882,511	93,984,226	97,577,029	89,800,894	94,174,460	99,591,773

Schedule III - Supplementary109

Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Net deferred acquisition costs	$ 121.1	$ 165.2	$ 151.5
Reserves for losses and loss expenses	6,639.2	6,456.2	5,881.2
Unearned premiums	1,688.1	1,683.3	1,555.3
Net premiums earned	2,344.1	2,488.4	2,182.7
Net investment income	217.8	182.1	176.9
Losses and loss expenses	1,501.8	1,586.3	1,199.2
Amortization of deferred acquisition costs	339.8	375.4	295.1
Other operating costs	411.5	406.3	365.7
Net premiums written	2,255.8	2,448	2,322
North American Insurance
Supplementary Insurance Information, by Segment [Line Items]
Net deferred acquisition costs	40.7	70.1	55.7
Reserves for losses and loss expenses	4,191.3	3,998.2	3,806.6
Unearned premiums	1,118.2	1,061.5	1,003.1
Net premiums earned	1,266.9	1,301.4	1,111.1
Net investment income	0	0	0
Losses and loss expenses	862.2	910.2	683.8
Amortization of deferred acquisition costs	132	139.6	105.9
Other operating costs	223.3	224.6	219.7
Net premiums written	1,223.4	1,358.1	1,230.8
Global Markets Insurance
Supplementary Insurance Information, by Segment [Line Items]
Net deferred acquisition costs	21.5	26.2	23.3
Reserves for losses and loss expenses	983.6	972.4	568.2
Unearned premiums	312.8	327.8	223.4
Net premiums earned	377.8	366.8	162.6
Net investment income	0	0	0
Losses and loss expenses	269.5	240.3	61.1
Amortization of deferred acquisition costs	66.5	70.9	18.2
Other operating costs	123.7	108.4	68.1
Net premiums written	367.5	324.1	188
Reinsurance
Supplementary Insurance Information, by Segment [Line Items]
Net deferred acquisition costs	58.9	68.9	72.5
Reserves for losses and loss expenses	1,464.3	1,485.6	1,506.4
Unearned premiums	257.1	294	328.8
Net premiums earned	699.4	820.2	909
Net investment income	0	0	0
Losses and loss expenses	370.1	435.8	454.3
Amortization of deferred acquisition costs	141.3	164.9	171
Other operating costs	64.5	73.3	78
Net premiums written	664.9	765.8	903.2
Corporate
Supplementary Insurance Information, by Segment [Line Items]
Net deferred acquisition costs	0	0	0
Reserves for losses and loss expenses	0	0	0
Unearned premiums	0	0	0
Net premiums earned	0	0	0
Net investment income	217.8	182.1	176.9
Losses and loss expenses	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other operating costs	0	0	0
Net premiums written	$ 0	$ 0	$ 0

Schedule IV - Supplementary 110

Schedule IV - Supplementary Reinsurance Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount [Abstract]
Gross									$ 2,359.6	$ 2,291.6	$ 1,996.8
Ceded to other companies	$ 226.4	$ 201.9	$ 222.2	$ 159.5	$ 167.5	$ 147.1	$ 222.3	$ 108.1	810	645	613.4
Assumed from other companies									706.2	801.4	938.6
Net amount	$ 445.3	$ 528.3	$ 578.1	$ 704	$ 464.8	$ 607	$ 603.7	$ 772.5	2,255.8	2,448	2,322
Property and casualty
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount [Abstract]
Gross									2,359.6	2,291.6	1,996.8
Ceded to other companies									810	645	613.4
Assumed from other companies									706.2	801.4	938.6
Net amount									$ 2,255.8	$ 2,448	$ 2,322
Percentage of amount assumed to net									31.00%	33.00%	40.00%