XL (XLGLF) 10-K 23 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. 17, 2017	Jun. 30, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	XL GROUP LTD
Entity Central Index Key	875,159
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		264,971,941
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 9.1

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments:
Fixed maturities, at fair value (amortized cost: 2016 - $29,587,656; 2015 - $31,517,654)	$ 30,256,602	$ 32,257,589
Equity securities, at fair value (cost: 2016 - $996,610; 2015 - $834,079)	1,037,331	878,919
Short-term investments, at fair value (amortized cost: 2016 - $626,142; 2015 - $618,851)	625,193	617,390
Total investments available for sale	31,919,126	33,753,898
Fixed maturities, at fair value (amortized cost: 2016 - $1,548,178; 2015 - $1,263,609)	1,617,014	1,235,699
Short-term investments, at fair value (amortized cost: 2016 - $9,536; 2015 - $60,176)	9,563	60,330
Total investments trading	1,626,577	1,296,029
Investments in affiliates	2,177,645	1,708,899
Other investments	1,164,564	1,433,057
Total investments	36,887,912	38,191,883
Cash and cash equivalents	3,426,988	3,256,236
Restricted cash	153,504	154,992
Accrued investment income	284,366	312,667
Deferred acquisition costs and value of business acquired	946,721	890,568
Ceded unearned premiums	1,687,864	1,821,793
Premiums receivable	5,522,976	4,712,493
Reinsurance balances receivable	577,479	418,666
Unpaid losses and loss expenses recoverable	5,491,297	5,262,706
Receivable from investments sold	128,411	231,158
Goodwill and other intangible assets	2,203,653	2,210,266
Deferred tax asset	310,542	282,311
Other assets	812,389	937,199
Total assets	58,434,102	58,682,938
Liabilities:
Unpaid losses and loss expenses	25,939,571	25,439,744
Deposit liabilities	1,116,233	1,168,376
Future policy benefit reserves	3,506,047	4,163,500
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	998,968	914,629
Unearned premiums	7,293,028	7,043,358
Notes payable and debt	2,647,677	2,644,970
Reinsurance balances payable	2,451,717	2,117,727
Payable for investments purchased	226,009	130,060
Deferred tax liability	77,271	120,651
Other liabilities	1,216,902	1,285,460
Total liabilities	45,473,423	45,028,475
Commitments and Contingencies
Shareholders' Equity:
Common shares, 999,990,000 authorized, par value $0.01; issued and outstanding (2016 - 266,889,127; 2015 - 294,745,045)	2,669	2,947
Additional paid in capital	8,068,503	8,910,167
Accumulated other comprehensive income	715,546	686,616
Retained earnings	2,151,794	2,077,349
Shareholders' equity attributable to XL Group Ltd	10,938,512	11,677,079
Non-controlling interest in equity of consolidated subsidiaries	2,022,167	1,977,384
Total shareholders' equity	12,960,679	13,654,463
Total liabilities and shareholders' equity	$ 58,434,102	$ 58,682,938

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Amortized cost of fixed maturities, available for sale	$ 29,587,656	$ 31,517,654
Cost of equity securities, available for sale	996,610	834,079
Amortized cost of short-term investments, available for sale	626,142	618,851
Amortized cost of fixed maturities, trading	1,548,178	1,263,609
Amortized cost of short term investments, trading	9,536	60,176
Reinsurance recoverable from GCLR	$ 3,072,615	$ 3,719,131
Ordinary shares, shares authorized (in shares)	999,990,000	999,990,000
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Ordinary shares, shares issued (in shares)	266,889,127	294,745,045
Ordinary shares, shares outstanding (in shares)	266,889,127	294,745,045

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Net premiums earned	$ 9,777,934	$ 8,226,425	$ 5,895,070
Net investment income	827,133	872,370	918,625
Realized investment gains (losses):
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	372,138	202,178	107,462
Net realized and unrealized gains (losses) on derivative instruments	2,521	53,123	29,886
Income (loss) from investment fund affiliates	70,758	73,320	95,816
Fee income and other	35,692	33,201	43,630
Total revenues	10,546,086	9,308,926	6,602,267
Expenses:
Net losses and loss expenses incurred	6,072,835	4,766,200	3,258,393
Claims and policy benefits	28,244	115,997	242,963
Acquisition costs	1,620,671	1,317,448	738,118
Operating expenses	2,063,362	1,966,939	1,341,315
Foreign exchange (gains) losses	(9,578)	22,504	(37,568)
Loss (gain) sale of subsidiaries	(7,088)	0	666,423
Extinguishment of debt	0	5,592	0
Interest expense	209,763	205,215	134,106
Total expenses	9,978,209	8,399,895	6,343,750
Income (loss) before income tax and income (loss) from operating affiliates	567,877	909,031	258,517
Income (loss) from operating affiliates	44,397	44,740	107,218
Gain on sale of operating affiliate	0	340,407	0
Provision (benefit) for income tax	42,129	(19,161)	96,897
Net income (loss)	570,145	1,313,339	268,838
Non-controlling interests	129,177	106,187	80,498
Net income (loss) attributable to common shareholders	$ 440,968	$ 1,207,152	$ 188,340
Weighted average ordinary shares and ordinary share equivalents outstanding - basic (in shares)	278,957	286,194	267,103
Weighted average ordinary shares and ordinary share equivalents outstanding - diluted (in shares)	282,758	290,999	271,527
Earnings (loss) per ordinary share and ordinary share equivalent - basic (in dollars per share)	$ 1.58	$ 4.22	$ 0.71
Earnings (loss) per ordinary share and ordinary share equivalent - diluted (in dollars per share)	$ 1.56	$ 4.15	$ 0.69
Exclude Life Funds Withheld Assets
Revenues:
Net investment income	$ 672,382	$ 684,881	$ 789,050
Realized investment gains (losses):
Net realized gains (losses) on investments sold	191,247	102,957	158,733
Other-than-temporary impairments (OTTI) on investments	(78,997)	(81,987)	(33,508)
OTTI on investments transferred to (from) other comprehensive income	439	(973)	(2,234)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	112,689	19,997	122,991
Life Funds Withheld Assets
Revenues:
Net investment income	154,751	187,489	129,575
Realized investment gains (losses):
Net realized gains (losses) on investments sold	152,589	223,272	5,067
Other-than-temporary impairments (OTTI) on investments	(2,598)	(13,357)	(20,587)
Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets	109,458	(27,734)	(9)
Net realized and unrealized gains (losses) on derivative instruments	$ (540,090)	$ (151,691)	$ (488,222)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income (loss) attributable to common shareholders	$ 440,968	$ 1,207,152	$ 188,340
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	0	0	424,861
Cumulative adjustments recorded to value of future policy benefit reserves, amount	62,295	170,688	(400,456)
Change in net unrealized gains (losses) on affiliate and other investments, net of tax	(57,820)	(6,074)	35,143
Change in OTTI losses recognized in other comprehensive income, net of tax	6,550	18,545	13,143
Change in underfunded pension liability	(246)	(3,852)	(7,550)
Change in value of cash flow hedge	(182)	(200)	255
Foreign currency translation adjustments	95,473	(25,315)	(25,729)
Comprehensive income (loss)	469,898	409,310	936,141
Exclude Life Funds Withheld Assets
Change in net unrealized gains (losses) on investments, net of tax	(72,638)	(530,030)	434,051
Life Funds Withheld Assets
Change in net unrealized gains (losses) on investments, net of tax	$ (4,502)	$ (421,604)	$ 274,083

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Ordinary shares	Additional Paid in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Deficit)	Non-controlling Interest in Equity of Consolidated Subsidiaries	Exclude Life Funds Withheld Assets	Exclude Life Funds Withheld AssetsAccumulated Other Comprehensive Income (Loss)	Life Funds Withheld Assets	Life Funds Withheld AssetsAccumulated Other Comprehensive Income (Loss)
Balance, beginning of year at Dec. 31, 2013		$ 2,783	$ 7,994,100	$ 736,657	$ 1,264,093	$ 1,351,665
Issuance of ordinary shares		12	27
Buybacks of ordinary shares		(247)	(708,993)		(92,713)
Exercise of stock options		4
Exercise of stock options, net of tax			6,363
Share based compensation expense			67,605		0
Change in net unrealized gains (losses) on investments, net of tax							$ 434,051	$ 434,051	$ 274,083	$ 274,083
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	$ 424,861			424,861
Cumulative adjustments recorded to value of future policy benefit reserves, amount	(400,456)			(400,456)
Change in net unrealized gains (losses) on affiliate and other investments, net of tax	35,143			35,143
Change in OTTI losses recognized in other comprehensive income, net of tax	13,143			13,143
Change in underfunded pension liability	(7,550)			(7,550)
Change in value of cash flow hedge	255			255
Foreign currency translation adjustments	(25,729)			(25,729)
Net income (loss) attributable to common shareholders	188,340				188,340
Dividends on ordinary shares					(172,081)
Non-controlling interests – contributions						48,261
Non-controlling interests - distributions						(1,666)
Non-controlling interests - acquired						0
Non-controlling interests						3,755
Non-controlling interest share in change in accumulated other comprehensive income (loss)						0
Balance, end of year at Dec. 31, 2014	11,435,766	2,552	7,359,102	1,484,458	1,187,639	1,402,015
Issuance of ordinary shares		515	1,851,046
Buybacks of ordinary shares		(125)	(370,395)		(98,451)
Exercise of stock options		5
Exercise of stock options, net of tax			9,972
Share based compensation expense			60,442		(7,177)
Change in net unrealized gains (losses) on investments, net of tax							(530,030)	(530,030)	(421,604)	(421,604)
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	0			0
Cumulative adjustments recorded to value of future policy benefit reserves, amount	170,688			170,688
Change in net unrealized gains (losses) on affiliate and other investments, net of tax	(6,074)			(6,074)
Change in OTTI losses recognized in other comprehensive income, net of tax	18,545			18,545
Change in underfunded pension liability	(3,852)			(3,852)
Change in value of cash flow hedge	(200)			(200)
Foreign currency translation adjustments	(25,315)			(25,315)
Net income (loss) attributable to common shareholders	1,207,152				1,207,152
Dividends on ordinary shares					(211,814)
Non-controlling interests – contributions						23,610
Non-controlling interests - distributions						(19,001)
Non-controlling interests - acquired						562,285
Non-controlling interests						7,466
Non-controlling interest share in change in accumulated other comprehensive income (loss)						1,009
Balance, end of year at Dec. 31, 2015	13,654,463	2,947	8,910,167	686,616	2,077,349	1,977,384
Issuance of ordinary shares		16	31
Buybacks of ordinary shares	(1,051,000)	(302)	(912,282)		(138,466)
Exercise of stock options		8
Exercise of stock options, net of tax			9,845
Share based compensation expense			60,742		(3,646)
Change in net unrealized gains (losses) on investments, net of tax							$ (72,638)	$ (72,638)	$ (4,502)	$ (4,502)
Unrealized gains on held to maturity investment portfolio at time of transfer to available for sale, net of tax	0			0
Cumulative adjustments recorded to value of future policy benefit reserves, amount	62,295			62,295
Change in net unrealized gains (losses) on affiliate and other investments, net of tax	(57,820)			(57,820)
Change in OTTI losses recognized in other comprehensive income, net of tax	6,550			6,550
Change in underfunded pension liability	(246)			(246)
Change in value of cash flow hedge	(182)			(182)
Foreign currency translation adjustments	95,473			95,473
Net income (loss) attributable to common shareholders	440,968				440,968
Dividends on ordinary shares					(224,411)
Non-controlling interests – contributions						47,524
Non-controlling interests - distributions						(9,028)
Non-controlling interests - acquired						0
Non-controlling interests						7,309
Non-controlling interest share in change in accumulated other comprehensive income (loss)						(1,022)
Balance, end of year at Dec. 31, 2016	$ 12,960,679	$ 2,669	$ 8,068,503	$ 715,546	$ 2,151,794	$ 2,022,167

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows provided by (used in) operating activities:
Net income (loss)	$ 570,145	$ 1,313,339	$ 268,838
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Net realized (gains) losses on investments	(372,138)	(202,178)	(107,462)
Net realized and unrealized (gains) losses on derivative instruments	(2,521)	(53,123)	(29,886)
Amortization of premiums (discounts) on fixed maturities	193,482	194,824	153,849
(Income) loss from investment and operating affiliates	(67,802)	(46,072)	(129,915)
Loss (gain) sale of subsidiaries	(7,088)	0	666,423
Gain on sale of operating affiliate	0	(340,407)	0
Share based compensation	81,001	74,431	81,287
Depreciation and amortization	118,063	92,313	56,118
Accretion of deposit liabilities	43,984	43,633	11,195
Changes in:
Unpaid losses and loss expenses	1,073,313	(211,831)	(427,528)
Future policy benefit reserves	(162,096)	(278,818)	(229,204)
Funds withheld on life retrocession agreements, net	(223,516)	(210,943)	(218,144)
Unearned premiums	436,106	(528,214)	253,396
Premiums receivable	(1,084,432)	156,168	15,248
Unpaid losses and loss expenses recoverable	(360,223)	(439,548)	(44,688)
Ceded unearned premiums	70,529	237,017	(191,242)
Reinsurance balances receivable	(174,126)	2,319	(17,736)
Deferred acquisition costs and value of business acquired	(62,926)	126,455	303,998
Reinsurance balances payable	398,738	229,205	160,916
Deferred tax asset - net	(41,641)	(47,924)	(33,735)
Derivatives	119,038	185,300	42,187
Other assets	(26,673)	17,054	33,344
Other liabilities	(78,422)	123,897	(147,744)
Other	(65,548)	26,968	5,447
Total adjustments	345,192	(697,783)	694,346
Net cash provided by (used in) operating activities	915,337	615,556	963,184
Cash flows provided by (used in) investing activities:
Proceeds from sale of fixed maturities and short-term investments	12,757,580	16,868,228	4,896,112
Proceeds from redemption of fixed maturities and short-term investments	3,847,709	3,751,174	3,601,793
Proceeds from sale of equity securities	848,779	664,735	571,410
Purchases of fixed maturities and short term investments	(15,457,689)	(19,718,064)	(7,158,258)
Purchases of equity securities	(1,103,447)	(567,334)	(445,504)
Proceeds from sale of affiliates	397,091	748,575	240,785
Purchases of affiliates	(681,385)	(280,856)	(371,226)
Purchase of subsidiaries, net of acquired cash	(92,893)	(1,020,015)	0
Proceeds from sale of subsidiary	22,998	0	570,000
Change in restricted cash	1,488	(154,992)	0
Other, net	197,536	(155,019)	(193,491)
Net cash provided by (used in) investing activities	737,767	136,432	1,711,621
Cash flows provided by (used in) financing activities:
Proceeds from issuance of ordinary shares and exercise of stock options	9,854	9,976	6,367
Buybacks of ordinary shares	(1,051,050)	(468,971)	(801,953)
Dividends paid on ordinary shares	(222,761)	(208,516)	(169,620)
Distributions to non-controlling interests	(130,447)	(117,683)	(78,465)
Contributions from non-controlling interest	47,524	23,610	48,261
Proceeds from issuance of debt	0	980,600	0
Repayment of debt	(8,248)	(87,447)	(600,000)
Deposit liabilities	(69,482)	(84,758)	(268,298)
Net cash provided by (used in) financing activities	(1,424,610)	46,811	(1,863,708)
Effects of exchange rate changes on foreign currency cash	(57,742)	(64,377)	(90,115)
Increase (decrease) in cash and cash equivalents	170,752	734,422	720,982
Cash and cash equivalents – beginning of period	3,256,236	2,521,814	1,800,832
Cash and cash equivalents – end of period	3,426,988	3,256,236	2,521,814
Supplemental cash flow disclosures:
Net taxes paid	81,662	96,886	20,168
Interest paid on notes payable and debt	138,025	115,598	121,285
Life Funds Withheld Assets
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Net realized and unrealized (gains) losses on derivative instruments	$ 540,090	$ 151,691	$ 488,222

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Significant accounting policies	Significant Accounting Policies (a) Basis of Preparation and Consolidation XL Group Ltd, a Bermuda exempted company ("XL-Bermuda"), through its operating subsidiaries, is a leading provider of insurance and reinsurance coverages to industrial, commercial and professional firms, insurance companies and other enterprises on a worldwide basis. XL-Bermuda and its various subsidiaries operate globally in 29 countries, through the Company's two business segments: Insurance and Reinsurance. These segments are further discussed in Note 3, "Segment Information ." On July 25, 2016, XL Group plc, an Irish public limited company ("XL-Ireland"), and XL-Bermuda completed a scheme of arrangement under Irish law (the "Scheme of Arrangement") that effected a transaction (the "Redomestication") that resulted in the shareholders of XL-Ireland becoming shareholders of XL-Bermuda and XL-Ireland becoming a subsidiary of XL-Bermuda. In accordance with the terms of the Scheme of Arrangement, the following steps simultaneously occurred at the effective time of the Redomestication: (i) all of the existing XL-Ireland ordinary shares, par value $0.01 per share (the "XL-Ireland shares") (other than XL-Ireland shares held by XL-Bermuda) were canceled; (ii) the reserves created on cancellation of the XL-Ireland shares were used to issue XL-Ireland shares to XL-Bermuda; and (iii) in return for such issuance of XL-Ireland shares to XL-Bermuda, XL-Bermuda issued common shares, par value $0.01 per share (the "XL-Bermuda shares"). The XL-Bermuda shares issued in connection with the redomestication were issued in reliance upon an exemption from registration under the U.S. Securities Act of 1933, as amended (the "Securities Act") provided under Section 3(a)(10) of the Securities Act. Upon the Redomestication, XL-Bermuda became the successor issuer to XL-Ireland and succeeded XL-Ireland’s obligation to file reports, proxy statements and other information required of domestic registrants by the Securities Exchange Act of 1934, as amended (the "Exchange Act") with the U.S. Securities and Exchange Commission (the “SEC”). As the successor issuer, the XL-Bermuda shares were deemed to be registered under Section 12(b) of the Exchange Act. Further, XL-Bermuda is subject to the applicable listing standards of the New York Stock Exchange ("NYSE"), and reports its financial results in U.S. dollars and under U.S. generally accepted accounting principles, in addition to any reporting requirements under Bermuda law. XL-Bermuda's shares continue in place of the XL-Ireland shares to trade on the NYSE under the ticker symbol "XL". Additionally, upon completion of the Redomestication, XL-Bermuda fully and unconditionally guaranteed the majority of the outstanding debt issued by XLIT Ltd., an exempted company incorporated under the laws of the Cayman Islands ("XL-Cayman"). See Note 14, "Notes Payable and Debt and Financing Arrangements ," for more information regarding our outstanding debt. In connection with the Redomestication, on August 3, 2016, XL-Ireland distributed the ordinary shares of XL-Cayman, to XL-Bermuda (the “Distribution”), which was recorded on the share register of XL-Cayman on August 4, 2016. As a result of the Distribution, XL-Cayman is now a direct, wholly-owned subsidiary of XL-Bermuda. It is anticipated that XL-Ireland will be liquidated (via a solvent members voluntary liquidation which was initiated on August 2, 2016) in 2017. Prior to July 25, 2016, unless the context otherwise indicates, references herein to the "Company" are to, and these financial statements include the accounts of, XL-Ireland and its consolidated subsidiaries. On and subsequent to July 25, 2016, unless the context otherwise indicates, references herein to the "Company" are to, and these financial statements include the accounts of, XL-Bermuda and its consolidated subsidiaries. On May 1, 2015, the Company completed its acquisition (the "Catlin Acquisition") of Catlin Group Limited and its consolidated subsidiaries ("Catlin"). Catlin, through its wholly-owned subsidiaries, provided property, casualty and specialty insurance and reinsurance coverage on a worldwide basis. The Company's consolidated results of operations include those of Catlin from May 1, 2015. See Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," for additional information with respect to the acquisition of Catlin. These consolidated financial statements include the accounts of the Company and all of its subsidiaries. These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). To facilitate period-to-period comparisons, certain reclassifications have been made to prior year consolidated financial statement amounts to conform to the current year presentation. There was no effect on net income from this change in presentation. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amount 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. The Company’s most significant areas of estimation include: ▪ unpaid losses and loss expenses and unpaid losses and loss expenses recoverable; ▪ future policy benefit reserves; ▪ valuation and other-than-temporary impairments of investments; ▪ income taxes; ▪ reinsurance premium estimates; and ▪ carrying value of goodwill and intangible assets. While management believes that the amounts included in the consolidated financial statements reflect the Company’s best estimates and assumptions, actual results could differ from these estimates. (b) Fair Value Measurements Financial Instruments Subject to Fair Value Measurements Accounting guidance over fair value measurements requires that a fair value measurement reflect the assumptions market participants would use in pricing an asset or liability based on the best information available. Assumptions include the risks inherent in a particular valuation technique (such as a pricing model) and/or the risks inherent in the inputs to the model. The fair value of a financial instrument is the amount 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 (the "exit price"). Instruments that the Company owns ("long positions") are marked to bid prices and instruments that the Company has sold but not yet purchased ("short positions") are marked to offer prices. Fair value measurements are not adjusted for transaction costs. Basis of Fair Value Measurement Fair value measurements accounting guidance also establishes a fair value hierarchy that prioritizes the inputs to the respective valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). An asset or liability’s classification within the fair value hierarchy is based on the lowest level of significant input to its valuation. The three levels of the fair value hierarchy are described further below: ▪ Level 1 - Quoted prices in active markets for identical assets or liabilities (unadjusted); no blockage factors. ▪ Level 2 - Other observable inputs (quoted prices in markets that are not active or inputs that are observable either directly or indirectly)—include quoted prices for similar assets/liabilities (adjusted) other than quoted prices in Level 1; quoted prices in markets that are not active; or other inputs that are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. ▪ Level 3 - Unobservable inputs that are supported by little or no market activity and are significant to the fair value of the assets or liabilities. Unobservable inputs reflect the reporting entity’s own assumptions about the assumptions that market participants would use in pricing the asset or liability. Level 3 assets and liabilities include financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation. Details on assets and liabilities that have been included under the requirements of authoritative guidance on fair value measurements to illustrate the bases for determining the fair values of these items held by the Company are included in each respective section of this note. Fair values of investments and derivatives are based on published market values if available, estimates of fair values of similar issues, or estimates of fair values provided by independent pricing services and brokers. Fair values of financial instruments for which quoted market prices are not available or for which the Company believes current trading conditions represent distressed markets are based on estimates using present value or other valuation techniques. The fair values estimated using such techniques are significantly affected by the assumptions used, including the discount rates and the estimated amounts and timing of future cash flows. In such instances, the derived fair value estimates cannot be substantiated by comparison to independent markets and are not necessarily indicative of the amounts that would be realized in a current market exchange. (c) Investments Investments - Available For Sale Investments that are considered available for sale (comprised of fixed maturities, equity securities and short-term investments) are carried at fair value. The fair values for available for sale investments are generally sourced from third parties. The fair values of fixed income securities are based upon quoted market values where available, "evaluated bid" prices provided by third party pricing services ("pricing services") where quoted market values are not available, or by reference to broker or underwriter bid indications where pricing services do not provide coverage for a particular security. To the extent the Company believes current trading conditions represent distressed transactions, the Company may elect to utilize internally generated models. It is common industry practice to utilize pricing services as a source for determining the fair values of investments where the pricing services are able to obtain sufficient market-corroborating information to allow them to produce a valuation at a reporting date. In addition, in the majority of cases, although a value may be obtained from a particular pricing service for a security or class of similar securities, these values are corroborated against values provided by other pricing services. The pricing services use market approaches to valuations using primarily Level 2 inputs in the vast majority of valuations, or some form of discounted cash flow analysis, to obtain investment values for a small percentage of fixed income securities for which they provide a price. Standard inputs to the valuations provided by the pricing services listed in approximate order of priority for use when available include: reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data. The pricing services may prioritize inputs differently on any given day for any security, and not all inputs listed are available for use in the evaluation process on any given day for each security evaluation; however, the pricing services also monitor market indicators, customer feedback through a price challenge process and industry and economic events. Information of this nature is a trigger to acquire further corroborating market data. When these inputs are not available, they identify "buckets" of similar securities (allocated by asset class types, sectors, sub-sectors, contractual cash flows/structure, and credit rating characteristics) and apply some form of matrix or other modeled pricing to determine an appropriate security value which represents their best estimate as to what a buyer in the marketplace would pay for a security in a current sale. Prices provided by independent pricing services and independent broker quotes can vary widely even for the same security. The use of different methodologies and assumptions may have a material effect on the estimated fair value amounts. While the Company receives values for the majority of the investment securities it holds from pricing services, it is ultimately management’s responsibility to determine whether the values received and recorded in the financial statements are representative of appropriate fair value measurements. Broker/dealer quotations are used to value fixed maturities where prices are unavailable from pricing services due to factors specific to the security such as limited liquidity, lack of current transactions, or trades only taking place in privately negotiated transactions. These are considered Level 3 valuations, as significant inputs utilized by brokers may be difficult to corroborate with observable market data, or sufficient information regarding the specific inputs utilized by the broker was not available to support a Level 2 classification. Equity securities include investments in open-end mutual funds and shares of publicly traded hedge funds. The fair value of equity securities is based upon quoted market values (Level 1), or monthly net asset value statements provided by the investment managers upon which subscriptions and redemptions can be executed (Level 2). Short-term investments include investments due to mature within one year from the date of purchase and are valued using the same external factors and in the same manner as fixed income securities. Changes in the value of investments available for sale are reflected as unrealized gains or losses on investments, and are included in "accumulated other comprehensive income (loss)", on a net of tax basis. All investment transactions are recorded on a trade date basis. Realized gains and losses on sales of equities and fixed income investments are determined on a first-in, first-out basis. Investment income is recognized when earned and includes interest and dividend income together with the amortization of premium and discount on fixed maturities and short-term investments, and is recorded net of related investment expenses. Amortization of discounts on fixed maturities includes amortization to expected recovery values for investments that have previously been recorded as other than temporarily impaired. For mortgage-backed securities, and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and revised as necessary. Prepayment fees or call premiums that are only payable to the Company when a security is called prior to its maturity are earned when received and reflected in net investment income. Investments - Trading Investments for which the Company has elected the fair value option are classified as "trading". Trading securities are carried at fair value. All trading securities are held in support of the GreyCastle Life Retro Arrangements as defined in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ." Thus, changes in the fair value of trading securities are included in "Net unrealized gains (losses) on investments, trading securities - Life Funds Withheld Assets," and interest and dividend income from trading securities are included as a component of "Net investment income - Life Funds Withheld Assets". Investments Related to Life Retrocession Arrangements written on a Funds Withheld Basis Designated investments that support the GreyCastle Life Retro Arrangements, which were written on a funds withheld basis ("Life Funds Withheld Assets") and entered into in connection with the sale of our life reinsurance subsidiary, are classified as either available for sale or trading. Investment results for these assets - including interest income, unrealized gains and losses, and gains and losses from sales - are passed directly to the reinsurer pursuant to a contractual arrangement that is accounted for as a derivative. Changes in the fair value of the embedded derivative associated with the GreyCastle Life Retro Arrangements are recorded in "Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets" on the consolidated statements of income. The fair value of the embedded derivative is included within "Funds withheld on life retrocession arrangements, net of future policy benefit reserves recoverable" on the consolidated balance sheets. Investments In Affiliates Investments in which the Company has significant influence over the operating and financial policies of the investee are classified as investments in affiliates on the Company’s balance sheets and are accounted for under the equity method of accounting. Under this method, the Company records its proportionate share of income or loss from such investments in its results for the period as well as its portion of movements in certain of the investee shareholders’ equity balances. When financial statements of the affiliate are not available on a timely basis to record the Company’s share of income or loss for the same reporting periods as the Company, the most recently available financial statements are used. This lag in reporting is applied consistently. Distributions received from affiliates representing returns on invested capital are recorded as operating cash flows, while distributions representing returns of invested capital or proceeds upon sale of all or a portion of an affiliate are recorded as investing cash flows. The Company generally records its hedge fund and private investment fund affiliates on a one -month and three -month lag, respectively, and its operating affiliates on a three -month lag. Significant influence is considered on a case-by-case basis. Investments in affiliates are not subject to fair value measurement guidance as they are not considered to be fair value measured investments under GAAP. However, impairments associated with investments in affiliates that are deemed to be other-than-temporary are calculated in accordance with fair value measurement guidance and appropriate disclosures included within the financial statements during the period the losses are recorded. Other Investments Contained within this asset class are equity interests in investment funds, limited partnerships and unrated tranches of collateralized debt obligations for which the Company does not have sufficient rights or ownership interests to follow the equity method of accounting. Also included within other investments are structured transactions, which are carried at amortized cost. Fair values for other investments, principally other direct equity investments, investment funds and limited partnerships, are primarily based on the net asset value provided by the investment manager, the general partner or the respective entity, recent financial information, available market data and, in certain cases, management judgment, if required. These entities generally carry their trading positions and investments, the majority of which have underlying securities valued using Level 1 or Level 2 inputs, at fair value as determined by their respective investment managers; accordingly, these investments are generally classified as Level 2. Investments for which fair value is estimated using net asset value per share as a practical expedient are excluded from the fair value hierarchy. Private equity investments are classified as Level 3. The net unrealized gain or loss on investments, net of tax, is included in "Accumulated other comprehensive income (loss)." Any unrealized loss in value considered by management to be other-than-temporary is charged to income in the period in which it is determined. Overseas deposits include investments in private funds related to Lloyd’s syndicates in which the underlying instruments are primarily fixed maturities. The funds themselves do not trade on an exchange and therefore are not included within available for sale securities. Also included in overseas deposits are restricted balances held by Lloyd’s syndicates for solvency purposes which are primarily invested in cash and cash equivalents. Given the restricted nature of these balances, they are included in other investments on the balance sheets. Each of these investment types is considered a Level 2 valuation. The Company has historically participated in structured transactions. These have included providing cash loans supporting project finance transactions, and providing liquidity facility financing to structured project deals. The Company also invested in a payment obligation with an insurance company. The Company's policy is to value such transactions at amortized cost. For further details see Note 8, "Fair Value Measurements " and Note 6, "Other Investments ." (d) Premiums and Acquisition Costs Insurance premiums written are recorded in accordance with the terms of the underlying policies. Reinsurance premiums written are recorded at the inception of the policy and are estimated based upon information received from ceding companies and any subsequent differences arising on such estimates are recorded in the period they are determined. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term. Premiums are earned on a pro-rata basis over the period the coverage is provided. Unearned premiums represent the portion of premiums written applicable to the unexpired terms of policies in force. Net premiums earned are presented after deductions for reinsurance ceded, as applicable. Mandatory reinstatement premiums are recognized and earned at the time a loss event occurs. Life and annuity premiums from long duration contracts that transfer significant mortality or morbidity risks are recognized as revenue and earned when due from policyholders. Life and annuity premiums from long duration contracts that do not subject the Company to risks arising from policyholder mortality or morbidity are accounted for as investment contracts and presented within deposit liabilities. The Company has periodically written retroactive loss portfolio transfer contracts. These contracts are evaluated to determine whether they meet the established criteria for reinsurance accounting, and, if so, at inception, written premiums are fully earned and corresponding losses and loss expense recognized. The contracts can cause significant variances in gross premiums written, net premiums written, net premiums earned, and net incurred losses in the years in which they are written. Reinsurance contracts sold not meeting the established criteria for reinsurance accounting are recorded using the deposit method. Acquisition costs, which vary with and are directly related to the acquisition of policies, consist primarily of commissions paid to brokers and cedants, and are deferred and amortized over the period during which the premiums are earned. Acquisition costs are shown net of contractual commissions earned on reinsurance ceded. Future earned premiums, the anticipated losses and other costs (and in the case of a premium deficiency, investment income) related to those premiums, are also considered in determining the level of acquisition costs to be deferred. (e) Reinsurance In the normal course of business, the Company seeks to reduce the potential amount of loss arising from claims events by reinsuring certain levels of risk assumed in various areas of exposure with other insurers or reinsurers. Reinsurance premiums ceded are expensed (and any commissions recorded thereon are earned) on a monthly pro-rata basis over the period the reinsurance coverage is provided. Ceded unearned reinsurance premiums represent the portion of premiums ceded applicable to the unexpired term of policies in force. Mandatory reinstatement premiums ceded are recorded at the time a loss event occurs. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Provisions are made for estimated unrecoverable reinsurance. The Company enters into ceded reinsurance agreements with other companies in the normal course of business. All premium and loss-related balances related to reinsurance agreements are reported on a gross basis within our consolidated balance sheets, with the exception of the GreyCastle Life Retro Arrangements, which were written on a funds withheld basis. The future policy benefit reserves recoverable related to these retrocession arrangements are netted against the funds withheld liability owing to the counterparty on the consolidated balance sheets due to the contractual right of offset. During the year ended December 31, 2014, the Company recorded $20 million , net of tax, to premiums earned and associated tax accruals, related to reinstatement premiums due under assumed reinsurance contracts arising from unpaid losses and loss expenses reported in a prior period. We evaluated the quantitative and qualitative aspects of this correction and concluded that the impact of recognizing it during the third quarter of 2014 was not material to the consolidated financial statements, nor was it material to previously issued consolidated financial statements in prior periods. (f) Fee Income and Other Fee income and other includes fees received for insurance and product structuring services provided and is earned over the service period of the contract. Any adjustments to fees earned or the service period are reflected in income in the period when determined. (g) Other-Than-Temporary Impairments ("OTTI") of Available for Sale Securities The Company’s process for identifying declines in the fair value of investments that are other-than-temporary involves consideration of several factors. The primary factors include (i) an analysis of the liquidity, business prospects and financial condition of the issuer including consideration of credit ratings, (ii) the significance of the decline, (iii) an analysis of the collateral structure and other credit support, as applicable, of the securities in question, and (iv) for debt securities, whether the Company intends to sell such securities. In addition, the authoritative guidance requires that OTTI for certain asset-backed and mortgage-backed securities be recognized if the fair value of the security is less than its discounted cash flow value and there has been a decrease in the present value of the expected cash flows since the last reporting period. Where the Company’s analysis of the above factors results in the Company’s conclusion that declines in fair values are other-than-temporary, the cost of the security is written down to discounted cash flow and a portion of the previously unrealized loss is therefore realized in the period such determination is made. With respect to equity securities and other investments carried at fair value, we generally impair a security if its fair value is 50% or lower than its amortized cost or if the security is in a loss position for 11 or more consecutive months. If the Company intends to sell an impaired security, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis, the impairment is other-than-temporary and is recognized currently in earnings in an amount equal to the entire difference between fair value and amortized cost. In instances in which the Company determines that a credit loss exists but the Company does not intend to sell the security, and it is not more likely than not that the Company will be required to sell the security before the anticipated recovery of its remaining amortized cost basis, the OTTI is separated into (1) the amount of the total impairment related to the credit loss and (2) the amount of the total impairment related to all other factors (i.e. the noncredit portion). The amount of the total OTTI related to the credit loss is recognized in earnings and the amount of the total OTTI related to all other factors is recognized in accumulated other comprehensive loss. The total OTTI is presented in the income statement with an offset for the amount of the total OTTI that is recognized in accumulated other comprehensive income (loss). Absent the intent or requirement to sell a security, if a credit loss does not exist, any impairment is considered to be temporary. The noncredit portion of any OTTI losses on securities classified as available for sale is recorded as a component of other comprehensive income (loss) with an offsetting adjustment to the carrying value of the security. The fair value adjustment could increase or decrease the carrying value of the security. In periods subsequent to the recognition of an OTTI loss, the other-than-temporarily impaired debt security is accounted for as if it had been purchased on the measurement date of the OTTI at an amount equal to the previous amortized cost basis less the credit-related OTTI recognized in earnings. For debt securities for which credit-related OTTI is recognized in earnings, the difference between the new cost basis and the cash flows expected to be collected is accreted into interest income over the remaining life of the security in a prospective manner based on the estimated amount and timing of future estimated cash flows. With respect to securities where the decline in value is determined to be temporary and the security’s amortized cost is not written down, a subsequent decision may be made to sell that security and realize a loss. Subsequent decisions on security sales are made within the context of overall risk monitoring, changing information, market conditions generally and assessing value relative to other comparable securities. We have outsourced a significant portion of the day-to-day management of the Company’s investment portfolio to third party investment manager service providers. While these investment manager service providers may, at a given point in time, believe that the preferred course of action is to hold securities with unrealized losses that are considered temporary until such losses are recovered, the dynamic nature of the portfolio management may result in a subsequent decision to sell the security and realize the loss, based upon a change in market and other factors described above. The Company believes that subsequent decisions to sell such securities are consistent with the classification of the Company’s portfolio as available for sale. There are risks and uncertainties associated with determining whether declines in the fair value of investments are other-than-temporary. These include subsequent significant changes in general economic conditions as well as specific business conditions affecting particular issuers, subjective assessment of issue-specific factors (seniority of claims, collateral value, etc.), future financial market effects, stability of foreign governments and economies, future rating agency actions and significant disclosure of accounting, fraud or corporate governance issues that may adversely affect certain investments. In addition, significant assumptions and management judgment are involved in determining if the decline is other-than-temporary. If management determines that a decline in fair value is temporary, then a security’s value is not written down at that time. However, there are potential effects upon the Company’s future earnings and financial position should management later conclude that some of the current declines in the fair value of the investments are other-than-temporary declines. (h) Derivative Instruments The Company recognizes all derivatives as either assets or liabilities on the balance sheets and measures those instruments at fair value. Except for the embedded derivative associated with the GreyCastle Life Retro Arrangements discussed above within (c) "Investm

Acquisitions and Disposals

Acquisitions and Disposals	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Acquisitions and Disposals	Acquisitions and Disposals (a) Partial Sale of New Ocean Capital Management Limited On October 11, 2016, Fundamental Insurance Investment Ltd. a wholly-owned subsidiary of the Company, completed a partial sale of its common and preference shares in New Ocean Capital Management Limited ("New Ocean Capital Management") with other investors to an unrelated investor. Fundamental Insurance Investment Ltd. received $3.9 million in proceeds for the sale of 7.8% of common shares and 6.4% of preference shares. The Company recorded a pre-tax gain of $3.5 million as a result of this transaction. (b) Sale of XL Life Insurance and Annuity Company ("XLLIAC") On September 30, 2016, X.L. America, Inc. ("XL America") and XL Life and Annuity Holding Company ("XLLAHC"), both indirect wholly-owned subsidiaries of the Company, completed the previously announced sale of the Company's wholly-owned subsidiary XLLIAC to Mutual of Omaha Insurance Company ("Omaha") pursuant to the terms of the Stock Purchase Agreement with Omaha. XL America and XLLAHC received a closing date payment of $20.9 million in proceeds from the transaction, which was based upon the fair market value of the entity's investment assets and insurance licenses. The Company recorded a pre-tax gain of $3.7 million as a result of this transaction. (c) Brooklyn Acquisition On September 30, 2016, the Company's indirect, wholly-owned subsidiary, Catlin Holdings Limited, completed the acquisition ("Brooklyn Acquisition") of Brooklyn Underwriting Pty Limited and Brooklyn IT Pty Limited (collectively “Brooklyn”). Brooklyn is a specialty underwriting agency in Australia and Lloyd's-approved coverholder, serving brokers across Australia. The Company recorded definite-lived intangible assets of $22.9 million , which will be amortized over their estimated useful lives. See Note 9, "Goodwill and Other Intangible Assets ," for further information. (d) Allied Acquisition Overview On February 1, 2016, the Company's indirect, wholly-owned subsidiary, XL Reinsurance America Inc. ("XLRA"), completed the acquisition ("Allied Acquisition") of Allied International Holdings, Inc. ("Allied"). Allied is the holding company of Allied Specialty Insurance, Inc. and T.H.E. Insurance Company, an insurer of the outdoor entertainment industry in the U.S. Acquisition Consideration The Company made an initial payment of $75.7 million to acquire Allied. Additional contingent consideration will be paid based on production and underwriting profitability over a three year period subsequent to the acquisition date. The target payments of contingent consideration range from $7.5 million to $30.0 million . The Company currently believes the fair market value of these payments to be $15.0 million , resulting in total consideration of $90.7 million recorded for the acquisition. Fair Value of Net Assets Acquired and Liabilities Assumed The purchase price was allocated to the acquired assets and assumed liabilities of Allied based on estimated fair values on the acquisition date. The estimated fair value of the net assets acquired and liabilities assumed was $76.7 million , which includes indefinite-lived intangible assets of $8.0 million and other intangible assets of $6.0 million , which will be amortized over their estimated useful lives. Other adjustments to the historical carrying value of acquired assets and liabilities included: the estimated fair value of net loss and loss expense reserves at the present value of expected net loss and loss adjustment expense payments plus a risk premium, the estimated value of the business acquired at the present value of expected underwriting profits with net unearned premiums plus a risk margin less policy servicing costs, and the estimated fair value of real estate assets at appraised market values. In conjunction with the transaction, the Company recognized goodwill of $14.1 million , which is primarily attributable to the acquiree's underwriting expertise in a niche specialty risk business. The Company has allocated all of the $14.1 million of goodwill to its Insurance segment. See Note 8, "Goodwill and Other Intangible Assets ," for further information. The allocation of the purchase price is based on information that was available to management at the time the consolidated financial statements were prepared. The allocation may change as additional information becomes available within the measurement period, which cannot exceed 12 months from the acquisition date. The fair value recorded for these items may be subject to adjustments, which may impact the individual amounts recorded for assets acquired and liabilities assumed, as well as the residual goodwill. (e) New Energy On July 24, 2015, the Company purchased an additional 63.63% interest in New Energy Risk Inc. ("New Energy"), a provider of insurance risk management solutions within the alternative energy sector. A substantial portion of the additional shares was purchased directly from the family trusts of a Company employee who is responsible for managing the business generated by New Energy. Prior to the additional purchase, the Company held a 31.16% ownership interest in New Energy, which was accounted for as an equity method investment. The subsequent purchase raised the Company's ownership stake to 94.79% , which is deemed a controlling financial interest, and hence, the Company now consolidates New Energy. Subsequent to the additional purchase, the family trusts of the employee contributed their remaining 5.21% ownership interest in New Energy to XL Innovate Fund, LP ("XL Innovate Fund"), the entity that holds the Company's interest in New Energy, in partial satisfaction of the employee's aggregate 5.21% investment commitment to XL Innovate Fund. See Note 15, "Related Party Transactions ," for further details of these transactions. The Company paid approximately $8.8 million to acquire the additional interest in New Energy, and realized a gain of approximately $2.5 million , included within income from operating affiliates, in order to reflect the appropriate fair value adjustment to its existing investment previously accounted for under the equity method. The assets and liabilities of New Energy are now reflected in the consolidated financial statements of the Company based on their fair value as of the acquisition date, while goodwill of approximately $13.4 million was recorded in conjunction with the transaction. See Note 9, "Goodwill and Other Intangible Assets ," for a further discussion of the goodwill recorded in conjunction with the acquisition. (f) Catlin Acquisition Overview On May 1, 2015 (the "Acquisition Date"), XL-Ireland completed its acquisition (the "Catlin Acquisition") of the entire issued share capital of Catlin as contemplated by the Implementation Agreement, dated January 9, 2015 (the "Implementation Agreement"), by and among XL-Ireland, Green Holdings Limited, a wholly-owned subsidiary of the Company ("Green Holdings"), and Catlin. Pursuant to the terms of the Implementation Agreement, the Catlin Acquisition was implemented by way of a scheme of arrangement (the "Scheme") under Section 99 of the Companies Act 1981 of Bermuda, as amended (the "Companies Act"), and sanctioned by the Supreme Court of Bermuda (the "Court"). Immediately after such Court action, Catlin was merged with and into Green Holdings under Section 104H of the Companies Act, with Green Holdings as the surviving company, pursuant to the terms of that certain Merger Agreement, dated January 9, 2015 (the "Merger Agreement"), among XL-Ireland, Green Holdings and Catlin. Pursuant to the terms of the Implementation Agreement, XL-Ireland acquired each ordinary share of Catlin, par value $0.01 per share ("Catlin Shares"), for consideration per Catlin Share (the "Acquisition Consideration") equal to 388 pence in cash and 0.130 of an XL-Ireland ordinary share, par value $0.01 per share ("XL Shares"), subject to the mix and match facility set forth in the Implementation Agreement. The XL Shares issued in connection with the Catlin Acquisition are listed on the New York Stock Exchange. The XL Shares issued in connection with the Catlin Acquisition were issued in reliance upon the exemption from registration under the the Securities Act, provided by Section 3(a)(10) of the Securities Act. XL-Ireland issued approximately 49.9 million XL Shares and paid approximately £1.49 billion in cash to the holders of Catlin Shares as Acquisition Consideration pursuant to the terms of the Scheme. The foregoing description of the Implementation Agreement and the Merger Agreement is qualified in its entirety by reference to the full text of the Implementation Agreement and Merger Agreement, which are included as exhibits to this Form 10-K. In connection with the Catlin Acquisition, on January 9, 2015, the Company announced that it was relying on £1.6 billion of debt to be provided under a bridge facility entered into by XLIT Ltd., a wholly-owned subsidiary of the Company ("XL-Cayman"), and arranged by Morgan Stanley Senior Funding, Inc. and Goldman Sachs Bank USA (the "Bridge Facility") for the purposes of discharging the cash component of the Acquisition Consideration. The Company subsequently terminated the commitments under the Bridge Facility as of April 8, 2015, due to a sufficient amount in escrow to discharge the cash portion of the Acquisition Consideration. Costs related to maintaining the Bridge Facility are discussed in "Transaction-related Costs" below. In addition, on January 9, 2015, the Company entered into deal contingent deliverable foreign exchange forwards ("FX Forwards") with Morgan Stanley Capital Services LLC and Goldman Sachs International. The purpose of the FX Forwards was to mitigate risk of foreign currency exposure related to the Catlin Acquisition. Following the closing of the Catlin Acquisition, the FX Forwards were settled. Acquisition Consideration The calculation of the consideration transferred to acquire Catlin Shares is as follows: (In thousands, except per share data) Catlin Shares outstanding as of April 30, 2015 that received share consideration (including the dilutive effect of warrants) 384,118 Exchange ratio per the Implementation Agreement 0.130 XL Share issuance to Catlin shareholders 49,935 Closing price per XL share on April 30, 2015 (1) $ 37.08 XL Share issuance consideration $ 1,851,601 Catlin Shares outstanding as of April 30, 2015 that received cash consideration (including the dilutive effect of warrants) 384,118 Cash price component, per Catlin Share in GBP £ 3.88 Cash consideration, in GBP £ 1,490,377 Foreign exchange rate: GBP/USD on April 30, 2015 $ 1.5349 Cash consideration $ 2,287,579 Total acquisition consideration $ 4,139,180 ____________ (1) The closing market price of XL Shares on the Acquisition Date represents the fair value of XL shares issued as part of the Acquisition Consideration. The Company financed the $2.29 billion cash portion of the Acquisition Consideration by issuing $1.0 billion of subordinated debt, the proceeds (net of debt issuance costs) of which were $980.6 million , and the remaining $1.31 billion by using cash and cash equivalents on hand. See Note 14, "Notes Payable and Debt and Financing Arrangements ," for further information on the debt issuance. Fair Value of Net Assets Acquired and Liabilities Assumed The purchase price was allocated to the acquired assets and assumed liabilities of Catlin based on estimated fair values on the Acquisition Date. The Company recognized goodwill of $794.0 million which is primarily attributable to the synergies and economies of scale expected to result upon integration of Catlin into the Company's operations, including further diversification in geographic mix and product offerings and an increase in distribution strength. As of December 31, 2015, the allocation of the purchase price reflects an increase of $15.9 million in the amount recorded for current and deferred tax liabilities from the allocation initially reported at June 30, 2015 and a corresponding increase in the amount recorded for goodwill. See "Income Taxes" section below for further discussion of the change in the acquired current and deferred tax liabilities. The Company has allocated $466.1 million of this goodwill to its Insurance segment and $327.9 million to its Reinsurance segment. The Company also recognized indefinite lived intangible assets of $673.0 million and other intangible assets of $315.0 million , which will be amortized over their estimated useful lives. See Note 9, "Goodwill and Other Intangible Assets ," for further information. The following table summarizes the fair values of the assets acquired and liabilities assumed at the Acquisition Date: (U.S. dollars in thousands) ASSETS Fixed maturities, at fair value $ 6,266,489 Short-term investments, at fair value 634,599 Equity investments, at fair value 236,230 Investment in affiliates 216,843 Other investments 386,828 Total investments $ 7,740,989 Cash and cash equivalents (1) 1,267,565 Accrued investment income 35,063 Premiums receivable 2,545,188 Unpaid losses and loss expenses recoverable 1,493,267 Reinsurance balances receivable 299,579 Ceded unearned premiums 1,143,852 Deferred acquisition costs and value of business acquired 679,259 Intangible assets 988,000 Receivable from investments sold 9,633 Other assets (2) 306,686 Total assets $ 16,509,081 LIABILITIES Unpaid losses and loss expenses $ 6,933,144 Unearned premiums 3,742,234 Reinsurance balances payable 1,441,749 Notes payable and debt 82,066 Payable for investments purchased 34,149 Deferred tax liability (2) 82,783 Other liabilities (2) 285,481 Total liabilities $ 12,601,606 Net assets acquired before non-controlling interest $ 3,907,475 Non-controlling interest in equity of consolidated subsidiaries 562,285 Net assets acquired $ 3,345,190 Acquisition consideration $ 4,139,180 Goodwill (2) $ 793,990 ____________ (1) Includes restricted cash. (2) Includes an increase of $15.9 million to goodwill from the amount initially recorded at June 30, 2015, as a result of several tax-related adjustments, including a decrease in other assets of $7.5 million , a decrease in deferred tax liability of $11.3 million , and an increase in other liabilities of $19.8 million . See discussion of "Income Taxes" below for further information. An explanation of the significant adjustments to the components of fair value are as follows: • Deferred acquisition costs and value of business acquired - The adjustment consists of two components. The first adjustment is the elimination of Catlin's deferred acquisition costs asset. The second adjustment is the establishment of the value of business acquired asset, which represents the present value of the expected underwriting profit within the unearned premiums liability, net of reinsurance, less costs to service the related policies and a risk premium. This adjustment are being amortized to underwriting, acquisition and insurance expenses over approximately two years , as the contracts for business in-force as of the Acquisition Date expire. The Company has included $186.7 million and $471.0 million in acquisition expenses related to the amortization of the value of business acquired during the years ended December 31, 2016 and 2015 . • Intangible assets - Establish the estimated fair value of intangible assets related to Catlin. See Note 9, "Goodwill and Other Intangible Assets ," for further information. • Other assets - Establish the estimated fair value of Catlin's internally developed software. • Unpaid losses and loss adjustment expenses - Unpaid losses and loss adjustment expenses acquired include an increase to adjust the carrying value of Catlin's historical unpaid losses and loss adjustment expenses, net of related reinsurance recoverable, to fair value as of the Acquisition Date. The estimated fair value consists of the present value of the expected net loss and loss adjustment expense payments plus a risk premium. This adjustment is being amortized to losses and loss adjustment expenses over approximately 20 years , based on the estimated payout pattern of net reserves as of the Acquisition Date. • Net deferred tax liabilities - The adjustment to deferred tax liabilities is related to the deferred tax impact of the adjustments to fair value as noted above. This net increase of deferred tax liabilities is explained further in "Income Taxes" below. • Non-controlling interest - The fair value was determined based on the last trade price of preferred shares issued by Catlin Insurance Company Limited ("Catlin-Bermuda"). See Note 19, "Share Capital ," for further information. Income Taxes As noted above, during the measurement period within 2015, the Company recorded several tax-related adjustments. These adjustments resulted from analysis following the filing of Catlin's 2014 tax returns, and a refinement of the jurisdictional fair value allocations of certain assets and liabilities. Other assets decreased by $7.5 million , deferred tax liabilities decreased by $11.3 million , and other liabilities increased by $19.8 million as a result of these adjustments. The net impact was that Goodwill associated with the transaction increased by $15.9 million . Following these measurement period adjustments, the net deferred tax liability recorded by the Company as part of the allocation of the purchase price was $82.8 million . This is primarily comprised of $145.2 million of deferred tax liabilities related to intangible assets, partially offset by deferred tax assets of $62.4 million , which is net of a $90.0 million valuation allowance. Included in the total deferred tax assets are loss carryforwards of $85.8 million with a related $66.8 million valuation allowance. In order to align all U.S. regulated entities under XL America, XL America purchased 100% of the stock of Catlin Inc. from Catlin North America Holdings, Ltd, a U.K. holding company, on September 28, 2015. The transaction, which was contingent upon regulatory approval, resulted in a release of the $59.6 million valuation allowance previously held against the Catlin Inc. deferred tax asset as a benefit through the results of operations. Transaction-related Costs The Company incurred certain acquisition and financing costs associated with the Catlin Acquisition. The Company recorded $64.7 million of these costs in the year ended December 31, 2015 , of which $50.2 million has been included in Operating Expense and $14.5 million has been included in Interest Expense. Transaction costs included in Operating Expense for 2015 primarily consisted of due diligence, legal, advisory and investment banking costs. Transaction costs included in Interest Expense related to the maintenance of the Bridge Facility. Pursuant to the terms of the Implementation Agreement, Catlin was required to pay its own costs and expenses in relation to the negotiation, preparation, execution and implementation of the Catlin Acquisition. Costs incurred by Catlin were recorded and paid by Catlin prior to the Acquisition Date and are not included within the Company's consolidated statements of income and comprehensive income. As a part of the integration of Catlin's operations, the Company incurs costs associated with restructuring the systems, processes and workforce. These costs include such items as severance, retention, facilities and consulting and other costs. The Company separately identifies such costs and includes these expenses within Corporate and Other: (U.S. dollars in thousands) Severance related costs Retention and other compensation costs Facilities-related costs Consulting and other Total Liabilities at December 31, 2015 $ 16,127 $ 16,969 $ 818 $ 23,375 $ 57,289 Costs incurred in 2016 $ 57,098 $ 33,220 $ 30,236 $ 99,801 220,355 2016 payments 47,865 45,708 31,036 116,069 240,678 Liabilities at December 31, 2016 $ 25,360 $ 4,481 $ 18 $ 7,107 $ 36,966 Financial Results The following table summarizes the financial results of the acquired Catlin subsidiaries since the Acquisition Date that have been included within the Company's consolidated statements of income and comprehensive income as required by ASC 805-10-50-2(h) based on legal entity reporting. These results are not used as a part of management analysis of the financial results and performance of the Company's business. These results are adjusted, where possible, for transaction and integration related costs. These results involve a significant amount of estimates and are not indicative of future results of the acquired Catlin subsidiaries, which will be further impacted by potential changes in targeted business mix, investment management strategies, and synergies recognized from changes in the combined entity's operating structure, as well as the impact of changes in other business and capital management strategies. Since the Acquisition Date, a growing number of underlying policies have been underwritten onto different legal entities, staffing has been allocated to new divisions and activities, and reinsurance has been purchased to cover combined risks, only some of which would have been reflected in the underlying legacy Catlin infrastructure, systems and general ledgers of the acquired Catlin subsidiaries. In future quarters, the summary results of such subsidiaries will be increasingly impractical to produce and even less indicative of the results of the acquired Catlin operations given the significant estimates involved and the nature and pace of our integration activities which are intended to promote the operation of the consolidated group as a whole as quickly as possible. (U.S. dollars in thousands) May 1, 2015 to December 31, 2015 Total revenues - see comments above $ 2,791,789 Net income (loss) - see comments above $ 103,637 Supplemental Pro Forma Information The results of the acquired Catlin operations have been included in the Company's consolidated financial statements from the Acquisition Date to December 31, 2015. The following table presents unaudited pro forma consolidated information for the years ended December 31, 2015 and 2014 and assumes the Catlin Acquisition occurred on January 1, 2014. The pro forma financial information is presented for informational purposes only and does not necessarily reflect the results that would have occurred had the acquisition taken place on January 1, 2014, nor is it necessarily indicative of future results. Significant adjustments used to determine pro forma results include amortization of intangible assets and amortization of fair value adjustments discussed above, and the corresponding income tax effects. Non-recurring transaction related costs noted above have been included in the unaudited pro forma results for the years ended December 31, 2015 and 2014. Unaudited Pro Forma (In thousands, except per share data) 2015 2014 Total revenues $ 10,628,915 $ 10,938,216 Net income attributable to common shareholders 1,221,497 475,914 Earnings (loss) per common share and common share equivalent – basic 4.03 1.50 Earnings (loss) per common share and common share equivalent – diluted 3.97 1.48 (f) Sale of Operating Affiliate On April 1, 2015, XL Re Ltd ("XL Re", which in May 2016 amalgamated with XL Insurance (Bermuda) Ltd ("XLIB") to form a new entity, XL Bermuda Ltd), an indirect wholly-owned subsidiary of the Company, completed the sale of all of its shares in ARX Holding Corp. ("ARX") to The Progressive Corporation ("Progressive") pursuant to the terms of the Stock Purchase Agreement with Progressive. XL Re's shares in ARX represented approximately 40.6% of ARX's outstanding capital stock on a fully diluted basis at the time of the announcement. The carrying value of XL Re's shares in ARX was $220.2 million at the time of the sale. XL Re received $560.6 million in proceeds from the transaction, which was based upon the consolidated tangible net book value of ARX and its subsidiaries as of December 31, 2014, and certain other factors. Thus, the Company recorded a gain of $340.4 million as a result of this transaction. (g) Sale of Life Reinsurance Subsidiary The Company ceased writing new life reinsurance contracts in 2009 and since that time has been managing the run-off of its life reinsurance operations ("Run-Off Life Operations"). On May 30, 2014, we completed a transaction with GreyCastle Holdings Ltd ("GreyCastle") that resulted in the sale of our wholly-owned subsidiary, XL Life Reinsurance (SAC) Ltd ("XLLR"), to GreyCastle (subsequent to the transaction, XLLR changed its name to GreyCastle Life Reinsurance (SAC) Ltd ("GCLR")) and the retrocession of the majority of our life reinsurance business to GCLR through a 100% quota share reinsurance arrangement (the "GreyCastle Life Retro Arrangements"). The sale to GreyCastle was completed for $570 million in cash. The transaction included the retrocession of the majority of our life reinsurance business to GreyCastle through a 100% quota share reinsurance arrangement (the "GreyCastle Life Retro Arrangements"). This transaction covers a substantial portion of our life reinsurance reserves. The Run-Off Life Operations business, including the business subject to the transaction, was previously reported within the Company’s Life operations segment. Subsequent to the transaction, the Company no longer considers the Life operations to be a separate operating segment, and the results of the Run-Off Life Operations are reported within "Corporate and Other." See Note 3, "Segment Information " for further information. In addition, certain securities within fixed maturities were reclassified from held to maturity to available for sale in conjunction with this transaction. See Note 4, "Investments ," for further information. All of the reclassified securities are held by the Company and managed pursuant to agreed upon investment guidelines and are used to support the GreyCastle Life Retro Arrangements on a funds withheld basis ("Life Funds Withheld Assets"). All of the investment results associated with the Life Funds Withheld Assets ultimately accrue to GCLR. Because the Company no longer shares in the risks and rewards of the underlying performance of the supporting invested assets, disclosures within the financial statement notes included herein separate the Life Funds Withheld Assets from the rest of the Company's investments. Under the terms of the transaction, the Company continues to own, on a funds withheld basis, assets supporting the GreyCastle Life Retro Arrangements consisting of cash, fixed maturity securities and accrued interest. Based upon the right of offset, the funds withheld liability owing to GCLR is recorded net of future policy benefit reserves recoverable, and is included within "Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable)" on the consolidated balance sheets. The transaction resulted in an overall after-tax U.S. GAAP net loss of $621.3 million . See Note 7, "Derivative Instruments ," for further discussion of the impacts of the GreyCastle Life Retro Arrangements and Note 11, "Future Policy Benefit Reserves ," for a discussion of our future policy benefit reserves, the related future policy benefit reserves recoverable and information about the net funds withheld liability.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	Segment Information The Company is organized into two operating segments: Insurance and Reinsurance. Subsequent to the transaction described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," the underwriting results of the acquired businesses from the Acquisition Date through December 31, 2016 are included in the Company's Insurance or Reinsurance segment, as appropriate. The Company’s general investment and financing operations are reflected in "Corporate and Other." Subsequent to the transaction described in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ," GCLR reinsures the majority of the Company's life reinsurance business through the GreyCastle Life Retro Arrangements. The results of the run-off life operations not subject to the GreyCastle Life Retro Arrangements are also reported within "Corporate and Other." The Company evaluates the performance of both the Insurance and Reinsurance segments based on underwriting profit. Other items of revenues and expenditures of the Company are not evaluated at the segment level. In addition, the Company does not allocate investment assets used to support its Property and Casualty ("P&C") operations to the individual segments, except as noted below. Investment assets related to the Company’s Run-Off Life Operations and certain structured products included in the Insurance and Reinsurance segments are held in separately identified portfolios. As such, net investment income from these assets is included in the contribution from the applicable segment or in "Corporate and Other." The following tables summarize the segment results for the indicated years ended December 31, 2016, 2015, and 2014: Year Ended December 31, 2016 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate and Other (1) Total Gross premiums written $ 9,650,503 $ 3,975,106 $ 13,625,609 $ 265,315 $ 13,890,924 Net premiums written 6,715,969 3,514,667 10,230,636 12,047 10,242,683 Net premiums earned 6,651,495 3,114,392 9,765,887 12,047 9,777,934 Less: Net losses and loss expenses (2) 4,320,737 1,752,098 6,072,835 28,244 6,101,079 Less: Acquisition costs (2) 897,308 717,588 1,614,896 5,775 1,620,671 Less: Operating expenses (3) 1,224,233 283,270 1,507,503 1,356 1,508,859 Underwriting profit (loss) $ 209,217 $ 361,436 $ 570,653 $ (23,328 ) $ 547,325 Net investment income - excluding Life Funds Withheld Assets (4) 586,658 31,726 618,384 Net investment income - Life Funds Withheld Assets 154,751 154,751 Net results from structured products (5) 8,495 5,785 14,280 — 14,280 Net fee income and other (6) (18,506 ) 3,280 (15,226 ) 1,911 (13,315 ) Loss (gain) on sale of subsidiary — (7,088 ) (7,088 ) Net realized gains (losses) on investments - excluding Life Funds Withheld Assets 127,533 (14,844 ) 112,689 Net realized gains (losses) on investments and net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets (3 ) 259,452 259,449 Net realized and unrealized gains (losses) on derivative instruments — 2,521 2,521 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (540,090 ) (540,090 ) Net income (loss) from investment fund affiliates and operating affiliates — 115,155 115,155 Less: Exchange (gains) losses — (9,578 ) (9,578 ) Less: Corporate operating expenses — 505,483 505,483 Contribution from P&C and Corporate and Other 1,283,895 (501,563 ) 782,332 Less: Interest expense (7) 170,058 170,058 Less: Non-controlling interests 129,177 129,177 Less: Income tax expense 42,129 42,129 Net income (loss) attributable to common shareholders $ 440,968 Ratios – P&C operations: (8) Loss and loss expense ratio 65.0 % 56.3 % 62.2 % Underwriting expense ratio 31.9 % 32.1 % 32.0 % Combined ratio 96.9 % 88.4 % 94.2 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments. (3) Operating expenses of the segments exclude Corporate operating expenses, shown separately. (4) Net investment income - excluding Life Funds Withheld Assets does not include net investment income related to the net results from structured products. (5) The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million , respectively. (6) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (7) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (8) Ratios are based on net premiums earned from P&C operations. Year Ended December 31, 2015 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate & Other (1) Total Gross premiums written $ 8,395,846 $ 2,273,163 $ 10,669,009 $ 309,916 $ 10,978,925 Net premiums written 5,859,934 2,028,890 7,888,824 62,239 7,951,063 Net premiums earned 5,648,482 2,515,702 8,164,184 62,241 8,226,425 Less: Net losses and loss expenses (2) 3,614,048 1,152,152 4,766,200 115,997 4,882,197 Less: Acquisition costs (2) 704,364 602,290 1,306,654 10,794 1,317,448 Less: Operating expenses (3) 1,154,760 283,379 1,438,139 1,232 1,439,371 Underwriting profit (loss) $ 175,310 $ 477,881 $ 653,191 $ (65,782 ) $ 587,409 Net investment income - excluding Life Funds Withheld Assets (4) 583,871 40,569 624,440 Net investment income - Life Funds Withheld Assets 187,489 187,489 Net results from structured products (5) 12,185 5,806 17,991 — 17,991 Net fee income and other (6) (16,936 ) 2,958 (13,978 ) 622 (13,356 ) Net realized gains (losses) on investments 14,586 5,411 19,997 Net realized gains (losses) on investments - Life Funds Withheld Assets — 182,181 182,181 Net realized and unrealized gains (losses) on derivative instruments — 53,123 53,123 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (151,691 ) (151,691 ) Net income (loss) from investment fund affiliates and operating affiliates — 118,060 118,060 Gain on sale of operating affiliate 340,407 340,407 Less: Extinguishment of debt — 5,592 5,592 Less: Exchange (gains) losses — 22,504 22,504 Less: Corporate operating expenses — 480,755 480,755 Contribution from P&C and Corporate and Other 1,255,661 201,538 1,457,199 Less: Interest expense (7) 163,021 163,021 Less: Non-controlling interests 106,187 106,187 Less: Income tax expense (19,161 ) (19,161 ) Net income (loss) attributable to common shareholders $ 1,207,152 Ratios – P&C operations: (8) Loss and loss expense ratio 64.0 % 45.8 % 58.4 % Underwriting expense ratio 32.9 % 35.2 % 33.6 % Combined ratio 96.9 % 81.0 % 92.0 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments (3) Operating expenses of the segments exclude Corporate operating expenses, shown separately. (4) Net investment income does not include net investment income related to the net results from structured products. (5) The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million , respectively. (6) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (7) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (8) Ratios are based on net premiums earned from P&C operations. Year Ended December 31, 2014 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate and Other (1) Total Gross premiums written $ 5,976,011 $ 1,785,479 $ 7,761,490 $ 333,436 $ 8,094,926 Net premiums written 4,134,151 1,633,058 5,767,209 177,632 5,944,841 Net premiums earned 4,026,713 1,690,725 5,717,438 177,632 5,895,070 Less: Net losses and loss expenses 2,543,108 715,285 3,258,393 242,963 3,501,356 Less: Acquisition costs 393,319 330,684 724,003 14,115 738,118 Less: Operating expenses (2) 865,592 193,404 1,058,996 10,693 1,069,689 Underwriting profit (loss) $ 224,694 $ 451,352 $ 676,046 $ (90,139 ) $ 585,907 Net investment income (3) 574,458 146,558 721,016 Net investment income - Life Funds Withheld Assets 129,575 129,575 Net results from structured products (4) 43,710 10,499 54,209 — 54,209 Net fee income and other (5) (10,051 ) 2,800 (7,251 ) 360 (6,891 ) Loss (gain) on sale of subsidiary — 666,423 666,423 Net realized gains (losses) on investments 119,366 3,625 122,991 Net realized gains (losses) on investments - Life Funds Withheld Assets — (15,529 ) (15,529 ) Net realized and unrealized gains (losses) on derivative instruments — 29,886 29,886 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (488,222 ) (488,222 ) Net income (loss) from investment fund affiliates and operating affiliates — 203,034 203,034 Less: Exchange (gains) losses — (37,568 ) (37,568 ) Less: Corporate operating expenses — 220,165 220,165 Contribution from P&C and Corporate and Other 1,416,828 (929,872 ) 486,956 Less: Interest expense (6) 121,221 121,221 Less: Non-controlling interests 80,498 80,498 Less: Income tax expense 96,897 96,897 Net income (loss) attributable to common shareholders $ 188,340 Ratios – P&C operations: (7) Loss and loss expense ratio 63.2 % 42.3 % 57.0 % Underwriting expense ratio 31.2 % 31.0 % 31.2 % Combined ratio 94.4 % 73.3 % 88.2 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) Operating expenses exclude Corporate operating expenses, shown separately. (3) Net investment income does not include net investment income related to the net results from structured products. (4) The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million , respectively. (5) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (6) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (7) Ratios are based on net premiums earned from P&C operations. The following tables summarize the Company’s net premiums earned by line of business: Year Ended December 31, 2016 (U.S. dollars in thousands) Insurance (2) Reinsurance Corporate and Other Total P&C Operations: Professional $ 1,330,909 $ 163,157 $ — $ 1,494,066 Casualty 1,973,672 657,590 — 2,631,262 Property catastrophe — 792,445 — 792,445 Property 1,625,133 1,021,626 — 2,646,759 Specialty 1,711,344 174,477 — 1,885,821 Other (1) 10,437 305,097 — 315,534 Total P&C Operations $ 6,651,495 $ 3,114,392 $ — $ 9,765,887 Corporate and Other: Run-off life operations - Annuity — — 1 1 Run-off life operations - Other life — — 12,046 12,046 Total Corporate and Other $ — $ — $ 12,047 $ 12,047 Total $ 6,651,495 $ 3,114,392 $ 12,047 $ 9,777,934 Year Ended December 31, 2015 P&C Operations: Professional $ 1,164,446 $ 168,367 $ — $ 1,332,813 Casualty 1,805,563 468,286 — 2,273,849 Property catastrophe — 663,958 — 663,958 Property 1,257,383 869,286 — 2,126,669 Specialty 1,421,124 127,797 — 1,548,921 Other (1) (34 ) 218,008 — 217,974 Total P&C Operations $ 5,648,482 $ 2,515,702 $ — $ 8,164,184 Corporate and Other: Run-off life operations - Annuity $ — $ — $ 1 $ 1 Run-off life operations - Other life — — 62,240 62,240 Total Corporate and Other $ — $ — $ 62,241 $ 62,241 Total $ 5,648,482 $ 2,515,702 $ 62,241 $ 8,226,425 Year Ended December 31, 2014 P&C Operations: Professional $ 1,075,420 $ 181,223 $ — $ 1,256,643 Casualty 1,669,097 300,223 — 1,969,320 Property catastrophe — 433,602 — 433,602 Property 544,856 555,583 — 1,100,439 Specialty 737,281 95,745 — 833,026 Other (1) 59 124,349 — 124,408 Total P&C Operations $ 4,026,713 $ 1,690,725 $ — $ 5,717,438 Corporate and Other: Run-off life operations - Annuity $ — $ — $ 53,363 $ 53,363 Run-off life operations - Other life — — 124,269 124,269 Total Corporate and Other $ — $ — $ 177,632 $ 177,632 Total $ 4,026,713 $ 1,690,725 $ 177,632 $ 5,895,070 ____________ (1) Other within the Insurance segment includes surety, structured indemnity and certain other exited lines. Other within the Reinsurance segment includes: whole account contracts, accident and health and other lines. (2) Amounts from the prior year have been represented to reflect current mapping of underlying lines of business to be consistent with the manner in which they are reflected in the current period. The most significant movements include the following: Energy business previously shown under Specialty is now reflected in Property; Programs business formerly in Other is now reflected in Property or Casualty, depending upon the predominant line for each program; and Excess and Surplus is now reflected primarily in Casualty. The following table shows an analysis of the Company’s net premiums written by geographical location of the subsidiary where the premium is written for the years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 P&C Operations: Bermuda $ 1,267,613 $ 781,618 $ 636,109 United States 3,575,969 3,045,031 2,528,196 Europe 4,778,299 3,628,258 2,124,117 Other 608,755 433,917 478,787 Total P&C Operations $ 10,230,636 $ 7,888,824 $ 5,767,209 Corporate and Other: Bermuda $ 12,194 $ 62,276 $ 91,979 Europe (147 ) (37 ) 85,653 Total Corporate and Other $ 12,047 $ 62,239 $ 177,632

Investments

Investments	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Investments	Investments (a) Fixed Maturities, Short-Term Investments and Equity Securities Amortized Cost and Fair Value Summary The cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains and gross unrealized (losses), including non-credit related OTTI recorded in AOCI of the Company’s AFS investments at December 31, 2016 and 2015 were as follows: Included in AOCI December 31, 2016 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - Available for Sale ("AFS") - Excluding Life Funds Withheld Assets U.S. Government and Government-Related/Supported ("U.S. Government") $ 3,874,038 $ 53,172 $ (32,822 ) $ 3,894,388 $ — Corporate - Financials 3,587,557 59,968 (25,235 ) 3,622,290 — Corporate - Non Financials 6,468,200 138,114 (93,875 ) 6,512,439 (36 ) Residential mortgage-backed securities - Agency ("RMBS – Agency") 4,213,845 49,913 (45,391 ) 4,218,367 — Residential mortgage-backed securities - Non-Agency ("RMBS – Non-Agency") 265,877 21,132 (12,751 ) 274,258 (47,879 ) Commercial mortgage-backed securities ("CMBS") 670,005 5,955 (10,774 ) 665,186 (1,191 ) Collateralized debt obligations ("CDO") 379,532 498 (2,539 ) 377,491 (1,208 ) Other asset-backed securities 872,903 12,697 (9,703 ) 875,897 (821 ) U.S. States and political subdivisions of the States 2,399,490 86,041 (7,419 ) 2,478,112 — Non-U.S. Sovereign Government, Provincial, Supranational and Government-Related/Supported ("Non-U.S. Government") 5,037,482 112,772 (120,122 ) 5,030,132 — Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 27,768,929 $ 540,262 $ (360,631 ) $ 27,948,560 $ (51,135 ) Total short-term investments - Excluding Life Funds Withheld Assets 626,142 227 (1,176 ) 625,193 — Total equity securities - Excluding Life Funds Withheld Assets 996,610 48,931 (8,210 ) 1,037,331 — Total investments - AFS - Excluding Life Funds Withheld Assets $ 29,391,681 $ 589,420 $ (370,017 ) $ 29,611,084 $ (51,135 ) Included in AOCI December 31, 2016 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government $ 8,468 $ 2,109 $ — $ 10,577 $ — Corporate - Financials 376,018 63,249 — 439,267 — Corporate - Non Financials 797,652 217,689 — 1,015,341 — RMBS – Agency 470 143 — 613 — RMBS – Non-Agency 19,121 2,646 — 21,767 — CMBS 77,762 16,478 — 94,240 — Other asset-backed securities 84,541 17,019 — 101,560 — Non--U.S. Government 454,695 169,982 — 624,677 — Total fixed maturities - AFS - Life Funds Withheld Assets $ 1,818,727 $ 489,315 $ — $ 2,308,042 $ — Total investments - AFS $ 31,210,408 $ 1,078,735 $ (370,017 ) $ 31,919,126 $ (51,135 ) ____________ (1) Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date. December 31, 2015 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ 5,047,621 $ 52,355 $ (34,339 ) $ 5,065,637 $ — Corporate - Financials 3,535,830 49,535 (23,456 ) 3,561,909 — Corporate - Non Financials 6,867,525 130,568 (97,646 ) 6,900,447 — RMBS – Agency 3,697,756 77,776 (17,561 ) 3,757,971 — RMBS – Non-Agency 319,876 25,644 (16,980 ) 328,540 (54,200 ) CMBS 401,713 7,933 (4,330 ) 405,316 (1,182 ) CDOs 41,679 4 (9,273 ) 32,410 (1,208 ) Other asset-backed securities 1,164,426 17,665 (13,519 ) 1,168,572 (1,144 ) U.S. States and political subdivisions of the States 2,514,048 125,395 (7,373 ) 2,632,070 — Non-U.S. Government 5,249,148 100,383 (97,917 ) 5,251,614 — Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 28,839,622 $ 587,258 $ (322,394 ) $ 29,104,486 $ (57,734 ) Total short-term investments - Excluding Life Funds Withheld Assets $ 618,851 $ 967 $ (2,428 ) $ 617,390 $ — Total equity securities - Excluding Life Funds Withheld Assets $ 834,079 $ 89,993 $ (45,153 ) $ 878,919 $ — Total investments - AFS - Excluding Life Funds Withheld Assets $ 30,292,552 $ 678,218 $ (369,975 ) $ 30,600,795 $ (57,734 ) Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government $ 10,721 $ 2,021 $ — $ 12,742 $ — Corporate - Financials 531,016 67,220 — 598,236 — Corporate - Non Financials 1,132,926 175,702 — 1,308,628 — RMBS – Agency 591 161 — 752 — RMBS – Non-Agency 24,401 2,552 — 26,953 — CMBS 107,968 14,513 — 122,481 — Other asset-backed securities 132,674 17,121 — 149,795 — Non-U.S. Government 737,735 195,781 — 933,516 — Total fixed maturities - AFS - Life Funds Withheld Assets $ 2,678,032 $ 475,071 $ — $ 3,153,103 $ — Total investments - AFS $ 32,970,584 $ 1,153,289 $ (369,975 ) $ 33,753,898 $ (57,734 ) ____________ (1) Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date. The cost (amortized cost for fixed maturities and short-term investments) and fair value of trading investments at December 31, 2016 and 2015 were as follows: December 31, 2016 (U.S. dollars in thousands) Amortized Fair Value Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ 14,361 $ 14,708 Corporate - Financials 450,990 468,175 Corporate - Non Financials 611,863 643,030 RMBS – Agency 835 852 RMBS – Non-Agency 101 109 CMBS 5,242 5,526 Other asset-backed securities 38,342 39,446 U.S. States and political subdivisions of the States 219 224 Non-U.S. Government 426,225 444,944 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,548,178 $ 1,617,014 Total short-term investments - Trading - Life Funds Withheld Assets $ 9,536 $ 9,563 Total investments - Trading - Life Funds Withheld Assets $ 1,557,714 $ 1,626,577 December 31, 2015 (U.S. dollars in thousands) Amortized Fair Value Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ 4,957 $ 4,990 Corporate - Financials 344,070 335,956 Corporate - Non Financials 509,441 493,621 RMBS – Agency 370 368 CMBS 4,874 4,803 Other asset-backed securities 26,405 25,700 Non-U.S. Government 373,492 370,261 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,263,609 $ 1,235,699 Total short-term investments - Trading - Life Funds Withheld Assets $ 60,176 $ 60,330 Total investments - Trading - Life Funds Withheld Assets $ 1,323,785 $ 1,296,029 At December 31, 2016 and 2015 , approximately 2.4% and 2.0% , respectively, of the Company's fixed income investment portfolio at fair value, excluding Life Funds Withheld Assets, was invested in securities that were below investment grade or not rated. Approximately 4.1% and 14.7% of the gross unrealized losses in the Company's fixed income investment portfolio, excluding Life Funds Withheld Assets, at December 31, 2016 and 2015 , respectively, related to securities that were below investment grade or not rated. Contractual Maturities Summary The contractual maturities of AFS and Trading fixed income securities at December 31, 2016 and 2015 are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. (U.S. dollars in thousands) December 31, 2016 December 31, 2015 Amortized Cost Fair Value Amortized Cost Fair Value Fixed maturities - AFS - Excluding Life Funds Withheld Assets Due less than one year $ 2,121,088 $ 2,135,262 $ 2,106,851 $ 2,104,106 Due after 1 through 5 years 12,400,798 12,463,844 14,051,494 14,143,461 Due after 5 through 10 years 5,509,194 5,531,402 5,680,830 5,740,954 Due after 10 years 1,335,687 1,406,853 1,374,997 1,423,156 $ 21,366,767 $ 21,537,361 $ 23,214,172 $ 23,411,677 (U.S. dollars in thousands) December 31, 2016 December 31, 2015 Amortized Cost Fair Value Amortized Cost Fair Value RMBS – Agency $ 4,213,845 $ 4,218,367 $ 3,697,756 $ 3,757,971 RMBS – Non-Agency 265,877 274,258 319,876 328,540 CMBS 670,005 665,186 401,713 405,316 CDO 379,532 377,491 41,679 32,410 Other asset-backed securities 872,903 875,897 1,164,426 1,168,572 Total mortgage and asset-backed securities $ 6,402,162 $ 6,411,199 $ 5,625,450 $ 5,692,809 Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 27,768,929 $ 27,948,560 $ 28,839,622 $ 29,104,486 Fixed maturities - AFS - Life Funds Withheld Assets Due less than one year $ 71,207 $ 80,749 $ 81,700 $ 92,921 Due after 1 through 5 years 289,710 318,605 386,810 416,743 Due after 5 through 10 years 274,727 324,759 491,621 558,805 Due after 10 years 1,001,189 1,365,749 1,452,267 1,784,653 $ 1,636,833 $ 2,089,862 $ 2,412,398 $ 2,853,122 RMBS – Agency $ 470 $ 613 $ 591 $ 752 RMBS – Non-Agency 19,121 21,767 24,401 26,953 CMBS 77,762 94,240 107,968 122,481 Other asset-backed securities 84,541 101,560 132,674 149,795 Total mortgage and asset-backed securities $ 181,894 $ 218,180 $ 265,634 $ 299,981 Total fixed maturities - AFS - Life Funds Withheld Assets $ 1,818,727 $ 2,308,042 $ 2,678,032 $ 3,153,103 Total fixed maturities - AFS $ 29,587,656 $ 30,256,602 $ 31,517,654 $ 32,257,589 Fixed maturities - Trading - Life Funds Withheld Assets Due less than one year $ 59,138 $ 59,553 $ 4,573 $ 5,096 Due after 1 through 5 years 322,574 328,997 278,163 272,220 Due after 5 through 10 years 507,631 521,505 280,487 277,920 Due after 10 years 614,315 661,026 668,737 649,592 $ 1,503,658 $ 1,571,081 $ 1,231,960 $ 1,204,828 RMBS – Agency 835 852 370 368 RMBS – Non-Agency 101 109 — — CMBS 5,242 5,526 4,874 4,803 Other asset-backed securities 38,342 39,446 26,405 25,700 Total mortgage and asset-backed securities 44,520 45,933 31,649 30,871 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,548,178 $ 1,617,014 $ 1,263,609 $ 1,235,699 Pledged Assets Certain of the Company's invested assets are held in trust and pledged in support of insurance and reinsurance liabilities as well as to collateralize our credit facilities. Such pledges are largely required by the Company's operating subsidiaries that are "non-admitted" under U.S. state insurance regulations, in order for the U.S. cedant to receive statutory credit for reinsurance. Also included in pledged assets are Life Funds Withheld Assets as noted in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ." Additionally, certain deposit liabilities and annuity contracts require the use of pledged assets. As of December 31, 2016 and December 31, 2015 , the Company had $17.1 billion and $18.3 billion in pledged assets, respectively. Classification of Fixed Income Securities On May 1, 2014, fixed maturities with a carrying value of $2.8 billion were reclassified from held to maturity ("HTM") to AFS in conjunction with the sale of XLLR as discussed in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ." Gross unrealized gains and gross unrealized losses, net of tax, of $424.9 million and nil , respectively, related to these securities were recognized in other comprehensive income on the date of transfer. For certain annuity contracts that are subject to the GreyCastle Life Retro Arrangements, policy benefit reserves were historically increased for the impact of changes in unrealized gains on investments supporting such contracts as if the gains had been realized, with a corresponding entry to other comprehensive income ("Shadow Adjustments"). In conjunction with the sale of XLLR and the related reclassification of securities from HTM to AFS, the Company recorded an additional gross charge of $440.5 million , net of tax, as a reduction of comprehensive income for such Shadow Adjustments on the date of the transfer. See Note 22, "Accumulated Other Comprehensive Income (Loss) ," for further information. All of the reclassified securities are included within the Life Funds Withheld Assets, along with certain other available for sale securities, as defined in the sale and purchase agreement. The Life Funds Withheld Assets are managed pursuant to agreed-upon investment guidelines that meet the contractual commitments of the XL ceding companies and applicable laws and regulations. All of the investment results associated with the Life Funds Withheld Assets ultimately accrue to GCLR. Because the Company no longer shares in the risks and rewards of the underlying performance of the Life Funds Withheld Assets, disclosures within the financial statements and accompanying notes included herein separate the Life Funds Withheld Assets from the rest of the Company's investments. (b) Gross Unrealized Losses The following is an analysis of how long the AFS securities at December 31, 2016 and 2015 had been in a continual unrealized loss position: December 31, 2016 (U.S. dollars in thousands) Less than 12 months Equal to or greater than 12 months Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturities and short-term investments - AFS U.S. Government $ 2,456,685 $ (30,640 ) $ 43,873 $ (2,237 ) Corporate - Financials 1,111,700 (19,010 ) 59,091 (6,227 ) Corporate - Non Financials 2,302,552 (62,584 ) 205,829 (31,368 ) RMBS – Agency 2,456,028 (40,989 ) 136,014 (4,402 ) RMBS – Non-Agency 3,517 (205 ) 166,796 (12,546 ) CMBS 467,757 (9,470 ) 9,665 (1,304 ) CDO 105,653 (58 ) 2,752 (2,481 ) Other asset-backed securities 671,782 (3,830 ) 34,783 (5,960 ) U.S. States and political subdivisions of the States 457,288 (6,983 ) 4,287 (437 ) Non-U.S. Government 1,797,405 (75,596 ) 288,490 (45,480 ) Total fixed maturities and short-term investments - AFS $ 11,830,367 $ (249,365 ) $ 951,580 $ (112,442 ) Total equity securities $ 130,487 $ (8,210 ) $ — $ — Less than 12 months Equal to or greater than 12 months December 31, 2015 (U.S. dollars in thousands) Fair Value Gross Unrealized Losses Fair Value Gross Fixed maturities and short-term investments - AFS U.S. Government $ 3,762,869 $ (29,339 ) $ 89,113 $ (5,044 ) Corporate – Financials 1,641,021 (13,280 ) 102,022 (10,192 ) Corporate – Non Financials 3,275,270 (73,069 ) 227,527 (24,706 ) RMBS – Agency 1,065,055 (10,046 ) 221,211 (7,515 ) RMBS – Non-Agency 19,614 (1,104 ) 180,146 (15,876 ) CMBS 118,605 (1,561 ) 78,651 (2,769 ) CDOs 12,311 (516 ) 20,096 (8,757 ) Other asset-backed securities 572,671 (5,252 ) 57,563 (8,268 ) U.S. States and political subdivisions of the States 565,055 (6,609 ) 12,259 (765 ) Non-U.S. Government 1,921,286 (53,440 ) 474,929 (46,714 ) Total fixed maturities and short-term investments - AFS $ 12,953,757 $ (194,216 ) $ 1,463,517 $ (130,606 ) Total equity securities $ 356,742 $ (45,153 ) $ — $ — The Company had gross unrealized losses totaling $370.0 million on 3,037 securities out of a total of 8,495 held at December 31, 2016 in its AFS Excluding Life Funds Withheld Assets portfolio, which either it considers to be temporarily impaired or with respect to which it reflects non-credit losses on other-than-temporarily impaired assets. Individual security positions comprising this balance have been evaluated by management, in conjunction with our investment managers, to determine the severity of these impairments and whether they should be considered other-than-temporary. Management believes it is more likely than not that the issuer will be able to fund sufficient principal and interest payments to support the current amortized cost. (c) Net Investment Income Net investment income for the years ended December 31 is derived from the following sources: (U.S. dollars in thousands) 2016 2015 2014 Fixed maturities, short term investments and cash equivalents - Excluding Life Funds Withheld Assets $ 713,237 $ 726,161 $ 809,964 Fixed maturities, short term investments and cash equivalents - Life Funds Withheld Assets 154,751 187,489 129,575 Equity securities and other investments 34,620 28,200 42,252 Interest on funds withheld 10,276 10,835 14,583 Total gross investment income $ 912,884 $ 952,685 $ 996,374 Investment expenses (85,751 ) (80,315 ) (77,749 ) Total net investment income $ 827,133 $ 872,370 $ 918,625 (d) Net Realized and Unrealized Gains (Losses) The following represents an analysis of net realized gains (losses), the change in unrealized gains (losses) on trading securities and net realized and unrealized gains (losses) on investment related derivative instruments for the years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 Fixed maturities, short term investments, cash and cash equivalents - Excluding Life Funds Withheld Assets: Gross realized gains $ 192,119 $ 187,523 $ 119,817 Gross realized losses on investments sold (151,013 ) (134,441 ) (66,892 ) OTTI on investments, net of amounts transferred to other comprehensive income (48,432 ) (54,346 ) (12,341 ) Net realized gains (losses) $ (7,326 ) $ (1,264 ) $ 40,584 Equity securities: Gross realized gains $ 140,864 $ 79,556 $ 96,260 Gross realized losses on investments sold (11,882 ) (49,223 ) (12,270 ) OTTI on investments, net of amounts transferred to other comprehensive income (30,126 ) (15,954 ) (10,944 ) Net realized gains (losses) $ 98,856 $ 14,379 $ 73,046 Other investments: Gross realized gains $ 37,596 $ 39,198 $ 31,830 Gross realized losses on investments sold (16,437 ) (19,656 ) (10,011 ) OTTI on investments, net of amounts transferred to other comprehensive income — (12,660 ) (12,458 ) Net realized gains (losses) $ 21,159 $ 6,882 $ 9,361 Net realized gains (losses) on investments - Excluding Life Funds Withheld Assets $ 112,689 $ 19,997 $ 122,991 Fixed maturities, short term investments, cash and cash equivalents - Life Funds Withheld Assets: Gross realized gains $ 185,487 $ 259,798 $ 7,926 Gross realized losses on investments sold (32,898 ) (36,526 ) (2,859 ) Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets 109,458 (27,734 ) (9 ) OTTI on investments, net of amounts transferred to other comprehensive income (2,598 ) (13,357 ) (20,587 ) Net realized gains (losses) on investments - Life Funds Withheld Assets $ 259,449 $ 182,181 $ (15,529 ) Net realized gains (losses) on investments $ 372,138 $ 202,178 $ 107,462 Net realized and unrealized gains (losses) on investment related derivative instruments $ 2,521 $ (8,616 ) $ 20,121 Net realized gains (losses) on investments and net realized and unrealized gains (losses) on investment related derivative instruments $ 374,659 $ 193,562 $ 127,583 (U.S. dollars in thousands) 2016 2015 2014 Change in unrealized gains (losses): Fixed maturities – AFS - Excluding Life Funds Withheld Assets $ (84,721 ) $ (486,140 ) $ 360,463 Fixed maturities - AFS - Life Funds Withheld Assets 14,244 (405,155 ) 880,226 Fixed maturities – HTM — — (272,540 ) Equity securities (4,119 ) (59,619 ) (32,577 ) Other investments (63,096 ) (6,072 ) 35,143 Net change in unrealized gains (losses) on investments $ (137,692 ) $ (956,986 ) $ 970,715 Total net realized gains (losses) on investments, net realized and unrealized gains (losses) on investment related derivative instruments, and net change in unrealized gains (losses) on investments $ 236,967 $ (763,424 ) $ 1,098,298 The components of OTTI charges of $78.6 million for the year ended December 31, 2016 , compared to $83.0 million and $35.7 million for the years ended December 31, 2015 and December 31, 2014 , respectively, as defined in Note 1(g), "Significant Accounting Policies - Other-Than-Temporary Impairments of Available for Sale ," for investments excluding Life Funds Withheld Assets were: ▪ $29.3 million related to investments that we no longer intend to hold for a period sufficient to recover their fair value to cost, compared to $29.4 million and $3.7 million for the years ended December 31, 2015 and December 31, 2014 , respectively. ▪ $16.4 million related to equity investments that were in a loss position for more than 11 months or impaired by more than 50%, compared to $20.0 million and $10.9 million for the years ended December 31, 2015 and December 31, 2014 , respectively. ▪ $3.0 million for structured securities where we determined that the likely recovery on these securities was below the carrying value and, accordingly, recorded an impairment of the securities to the discounted value of the cash flows expected to be received on these securities. The charges for the years ended December 31, 2015 and December 31, 2014 were $1.3 million and $4.3 million , respectively. ▪ Nil related to other investments, compared to $8.7 million and $12.5 million for the years ended December 31, 2015 and December 31, 2014 , respectively. ▪ $29.9 million related to foreign exchange losses, compared to $23.6 million and $4.3 million for the years ended December 31, 2015 and December 31, 2014 , respectively. The following table sets forth the amount of credit loss impairments on fixed income securities, for which a portion of the OTTI loss was recognized in OCI, held by the Company as of years ended December 31, 2016 and 2015 and the corresponding changes in such amounts. Credit Loss Impairments (U.S. dollars in thousands) 2016 2015 Opening balance at beginning of indicated period $ 73,469 $ 131,942 Credit loss impairment recognized in the current period on securities not previously impaired 12,867 9,698 Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period (18,178 ) (54,648 ) Credit loss impairments previously recognized on securities impaired to fair value during the period — (2,629 ) Additional credit loss impairments recognized in the current period on securities previously impaired 2,233 2,230 Accretion of credit loss impairments previously recognized due to an increase in cash flows expected to be collected (8,796 ) (13,124 ) Closing balance at end of indicated period $ 61,595 $ 73,469

Investments in Affiliates

Investments in Affiliates	12 Months Ended
	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Investments in affiliates	Investments in Affiliates Investments in affiliates comprised the following at December 31, 2016 and 2015 . See Note 1(c), "Significant Accounting Policies - Total Investments - Investments in Affiliates," for a description of our accounting policy for these assets: (U.S. dollars in thousands) 2016 2015 Investment fund affiliates $ 1,674,925 $ 1,386,837 Operating affiliates 502,720 322,062 Total investment affiliates $ 2,177,645 $ 1,708,899 (a) Investment Fund Affiliates The Company has invested in certain hedge funds, including funds managed by certain of its investment manager affiliates, and in certain private equity and private credit funds (collectively, "private investment funds") that are accounted for under the equity method due to our ownership percentages in the limited partnerships, LLCs or other similar investment vehicles that form the funds. Collectively, these investments in hedge funds and private investment funds are classified as "investment fund affiliates." At December 31, 2016 and 2015 , the hedge fund portfolio, accounted for as hedge fund affiliates, employed four strategies. The Company’s equity investment in investment fund affiliates and equity in net income (loss) from such affiliates as well as certain summarized financial information of the investee on a combined basis (shown as "Combined Funds") are included below: (U.S. dollars in thousands, except percentages) XL Group Investment Combined Carrying Equity in Weighted Total Net Assets Year Ended December 31, 2016 Hedge Funds: Arbitrage $ 165,633 $ 965 12.3 % $ 1,343,655 Directional 672,934 1,480 7.4 % 9,039,159 Event Driven (2) 297,836 9,676 2.6 % 11,341,870 Multi-Style 180,972 29,549 3.3 % 5,557,296 Total hedge funds $ 1,317,375 $ 41,670 4.8 % $ 27,281,980 Private Investment Funds: 357,550 29,088 10.8 % 3,318,073 Total Investment Fund Affiliates $ 1,674,925 $ 70,758 5.5 % $ 30,600,053 Year Ended December 31, 2015 Hedge Funds: Arbitrage $ 190,016 $ 612 8.6 % $ 2,202,112 Directional 551,262 31,012 7.2 % 7,643,134 Event Driven (2) 285,823 5,592 3.0 % 9,460,387 Multi-Style 57,097 5,452 3.6 % 1,600,959 Total hedge funds $ 1,084,198 $ 42,668 5.2 % $ 20,906,592 Private Investment Funds: 302,639 30,652 9.5 % 3,195,204 Total Investment Fund Affiliates $ 1,386,837 $ 73,320 5.8 % $ 24,101,796 ____________ (1) Total estimated net assets are generally as at November 30 for hedge fund affiliates and September 30 for private investment fund affiliates. (2) The Company accounts for its investment in certain funds using the equity method where the Company has significant influence over the related investment management company even though the ownership percentage is less than three percent. In general, the hedge funds in which the Company is invested require at least 30 days notice of redemption, and may be redeemed on a monthly, quarterly, semi-annual, annual or longer basis, depending upon the specific terms of each fund. Certain hedge funds have a lock-up period and/or may also have the ability to impose a redemption gate. A lock-up period refers to the initial amount of time an investor is contractually required to remain invested before having the ability to redeem. Typically, the imposition of a gate delays a portion of the requested redemption, with only the portion that is not gated settled in cash shortly after the redemption date. The carrying value of the Company’s holdings in hedge fund affiliates that are subject to lockups and/or that have redemption gate provisions in their governing documents at December 31, 2016 and 2015 was $553.2 million and $382.0 million , respectively. Certain hedge funds may be allowed to invest a portion of their assets in illiquid securities, such as private equity or private debt. In such cases, a common mechanism used is a side-pocket, whereby the illiquid security is assigned to a separate memorandum capital account or other designated account. Typically, the investor loses its redemption rights in the designated account. Only when the illiquid securities in the side-pocket are sold, or otherwise deemed liquid by the fund, may investors redeem that portion of their interest that has been "side-pocketed." At December 31, 2016 and 2015 , the carrying value of our hedge fund affiliates held in side-pockets was $23.5 million and $18.2 million , respectively. The underlying assets within these positions are generally expected to be liquidated over a period of approximately two to four years. (b) Operating Affiliates The Company has invested in strategic (re)insurance affiliates and investment management companies’ securities or other forms of direct ownership interests across the capital structure. Collectively, these investments are classified as "operating affiliates." The Company’s equity investment in operating affiliates and equity in net income (loss) from such affiliates as well as certain summarized financial information of the investee as a whole are included below: Year ended December 31, 2016 (U.S. dollars in thousands) XL Group Investment Combined Investee Summarized Carrying Equity in Total Total Total Net Income Strategic and other operating affiliates $ 446,695 $ 12,622 $ 5,353,905 $ 3,791,300 $ 1,030,859 $ 30,424 Investment manager affiliates (1) 56,025 31,775 752,336 72,114 337,782 257,004 Total operating affiliates $ 502,720 $ 44,397 $ 6,106,241 $ 3,863,414 $ 1,368,641 $ 287,428 Year ended December 31, 2015 Strategic and other operating affiliates 251,348 33,608 4,280,976 3,293,873 847,131 91,701 Investment manager affiliates (1) 70,714 11,132 708,605 95,826 206,672 90,491 Total operating affiliates $ 322,062 $ 44,740 $ 4,989,581 $ 3,389,699 $ 1,053,803 $ 182,192 ____________ (1) During the years ended December 31, 2016 and 2015 , the Company received distributions from its Investment Manager Affiliates of approximately $35.9 million and $25.3 million , respectively. In certain investments, the carrying value is different from the share of the investee’s underlying net assets. The differences represent goodwill on acquisition, OTTI recorded with respect to the investment, or differences in the retained capital accounts of the various equity holders (including the Company). See Note 18(c), "Commitments and Contingencies - Investments in Affiliates ," for further information regarding commitments related to investments in affiliates. Strategic and Other Operating Affiliates At December 31, 2016 , the Company’s larger strategic and other operating affiliates included Privilege Underwriters, Inc. and its affiliates ("PURE Group"), HighVista III, Ltd., Westaim HIIG LP ("Westaim HIIG"), Five Oaks Investment Corp ("Five Oaks") and CATGS I, LLC. The Company has an investment of $129.7 million related to an acquisition made in the fourth quarter of 2015 in the PURE Group, an insurance provider specializing in products for high net worth individuals. The PURE Group investments consist of: (i) a $77.5 million purchase of 9.9% of the ordinary common units and preferred units of Privilege Group Holdings LP, and 9.9% of the units of Privilege Group Holdings GP, LLC; and (ii) a total of $50.0 million purchases, at par value, of ten year surplus notes issued by Privilege Underwriters Reciprocal Exchange. Under the terms of an agreement between the parties, at December 31, 2016 , the PURE Group has the option to require the Company to purchase a remaining $25.0 million of ten year surplus note, at par, over a commitment period expiring no later than November 2020. The Company has an investment of $106.6 million , representing a 29.5% ownership interest in HighVista III, Ltd., an investment company with the objective to generate attractive, long-term risk-adjusted returns with an emphasis on capital preservation and diversification through active asset allocation. HighVista III, Ltd. seeks to achieve these goals through a range of exposures to global equities, sovereign bonds, credit markets, inflation-indexed bonds, and real assets through a hybrid and proprietary approach. The Company has an investment of $33.1 million , representing a 13.1% ownership interest in Westaim HIIG. The primary purpose of Westaim HIIG is to invest in interests of Houston International Insurance Group ("HIIG"), a specialty insurance provider. Westaim HIIG holds a majority interest in the common stock of HIIG. The Company has an investment of $25.5 million , representing a 23.1% ownership interest in Five Oaks, a mortgage real estate investment trust that is focused on investing in, financing and managing a leveraged portfolio of agency and non-agency residential mortgage-backed securities, residential mortgage loans and other mortgage-related investments. In addition, the Company holds warrants to purchase an additional 3.753 million shares at $13.11 per share, which would result in a total additional investment of $49.2 million by the Company should it exercise the warrants in full in the future. The warrants expire in September 2019. The Company has an investment of $17.5 million , representing a 50.0% ownership interest in CATGS I, LLC. The remaining 50.0% is held by one other investor. The Company does not control the entity, whose primary purpose is the purchase and leasing of equipment. On December 15, 2014, the Company announced it had entered into a Stock Purchase Agreement to sell its interests in one of its largest strategic and other operating affiliates, ARX, to The Progressive Corporation ("Progressive"). For further information, see Note 2(f), "Acquisitions and Disposals - Sale of Operating Affiliate ." Investment Manager Affiliates At December 31, 2016 , the Company’s larger investment manager affiliates included Highfields Capital, a global equity investment firm, and Polar Capital, an investment firm offering traditional and alternative products.

Other Investments

Other Investments	12 Months Ended
	Dec. 31, 2016
Investments, All Other Investments [Abstract]
Other investments	Other Investments Other investments comprised the following at December 31, 2016 and 2015 . See Note 1(c), "Significant Accounting Policies - Total Investments - Other Investments," for a description of our accounting policy for these assets: Year ended December 31, (U.S. dollars in thousands) 2016 2015 Hedge Funds: Arbitrage $ 165,053 $ 205,117 Directional 159,701 276,277 Event Driven 2,877 5,427 Multi-Style 4,341 57,249 Total hedge funds $ 331,972 $ 544,070 Private investment funds 175,579 244,576 Overseas deposits 493,594 479,187 Structured transactions 142,698 138,608 Other 20,721 26,616 Total other investments $ 1,164,564 $ 1,433,057 (a) Hedge Funds and Private Investment Funds At December 31, 2016 and 2015 , the hedge fund portfolio, accounted for as other investments, employed four strategies. In general, the funds in which the Company is invested require at least 30 days notice of redemption, and may be redeemed on a monthly, quarterly, semi-annual, annual or longer basis, depending upon the specific terms of each fund. Certain hedge funds have a lock-up period and/or may also have the ability to impose a redemption gate. A lock-up period refers to the initial amount of time an investor is contractually required to remain invested before having the ability to redeem. Typically, the imposition of a gate delays a portion of the requested redemption, with the remaining portion that is not gated settled in cash shortly after the redemption date. The fair value of the Company’s holdings in hedge funds that may be subject to lockups and/or that have redemption gate provisions in their governing documents at December 31, 2016 and 2015 was $223.3 million and $399.6 million , respectively. The Company did not have any holdings in funds where a redemption gate was imposed at December 31, 2016 or 2015 . Certain hedge funds may be allowed to invest a portion of their assets in illiquid securities, such as private equity or private debt. In such cases, a common mechanism used is a side-pocket, whereby the illiquid security is assigned to a separate memorandum capital account or other designated account. Typically, the investor loses its redemption rights in the designated account. Only when the illiquid securities in the side-pocket are sold, or otherwise deemed liquid by the fund, may investors redeem that portion of their interest that has been "side-pocketed". At December 31, 2016 and 2015 , the fair value of hedge funds held in side-pockets was $11.3 million and $26.0 million , respectively. The underlying assets within these positions are generally expected to be liquidated over a period of approximately two to four years . The following represents an analysis of the net realized gains for the indicated years ended December 31, and the net unrealized gains as of December 31, on the Company’s hedge funds and private investment funds: Year ended December 31, (U.S. dollars in thousands) Net Unrealized Gains Net Realized Gains (Losses) 2016 2015 2016 2015 2014 Hedge funds $ 134,114 $ 188,698 $ 12,212 $ 12,769 $ 6,685 Private investment funds 36,775 38,340 8,636 9,342 13,275 Total $ 170,889 $ 227,038 $ 20,848 $ 22,111 $ 19,960 (b) Overseas Deposits Overseas deposits include investments in private funds related to Lloyd’s syndicates in which the underlying instruments are primarily government and government-related/supported and corporate fixed income securities. The funds themselves do not trade on an exchange and therefore are not included within available for sale securities. Also included in overseas deposits are restricted cash and cash equivalent balances held by Lloyd’s syndicates for solvency purposes. Given the restricted nature of these cash balances, they are not included within the cash and cash equivalents category in the balance sheets. (c) Structured Transactions National Indemnity Endorsement On June 9, 2009, XL Specialty Insurance Company ("XL Specialty"), a wholly-owned subsidiary of the Company, entered into an agreement with National Indemnity Company, an insurance company subsidiary of Berkshire Hathaway Inc. ("National Indemnity"). Under the agreement, and a related reinsurance agreement, National Indemnity agreed to issue endorsements to certain directors and officers liability insurance policies known as "Side A" coverage policies underwritten by XL Specialty (the "Facility") during an eighteen month period that ended in December 31, 2011. In connection with the Facility, XLIB purchased a payment obligation (the "Obligation") in an aggregate principal amount of $150.0 million from National Indemnity. At December 31, 2016 , the outstanding Obligation was recorded in other investments at a carrying value of $140.6 million , pays a coupon of 3.5% , and is being accreted to $150.0 million over the 11.5 years term of the payment obligation. The difference between the estimated fair value of the Obligation and the cost of that Obligation at the time of the transaction was approximately $21.9 million and was recorded in Other Assets. This difference, together with fees of $2.5 million , was amortized in relation to the earning of the underlying policies written. Other Structured Transactions On July 17, 2009, XLIB purchased notes with an aggregate face amount of $155.0 million . On October 29, 2014, XLIB purchased notes with an aggregate face amount of $81.9 million . The issuer of both series of notes is a structured credit vehicle that holds corporate debt and preferred equity securities, including some securities issued by European financial institutions, as well as project finance debt securities, among other assets. During the year ended December 31, 2015 the Company recorded losses of $8.6 million due to other than temporary declines in value of these investments. During the fourth quarter of 2015, XLIB entered into transactions whereby it acquired the underlying corporate debt and preferred equity securities in return for the cancellation of the notes. The acquired securities are included in the available for sale fixed maturities and equity securities portfolios. In connection with the cancellation of the notes, the Company recorded realized investment losses of $6.7 million . See Note 18(b), "Commitments and Contingencies - Other Investments ," for further information regarding commitments related to other investments.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative instruments	Derivative Instruments The Company enters into derivative instruments for both risk management and investment purposes. The Company is exposed to potential loss from various market risks, and manages its market risks based on a comprehensive framework of investment decision authorities adopted ("Authorities Framework") by the Risk and Finance Committee of XL-Bermuda's Board of Directors ("RFC"), which is intended to align the risk profile of our investment portfolio to be consistent with management's risk tolerance, and other guidelines established by the RFC. The Company recognizes all derivatives as either assets or liabilities on the balance sheets and measures those instruments at fair value, with the changes in fair values of derivatives shown in the consolidated statement of income as "Net realized and unrealized gains (losses) on derivative instruments" unless the derivatives are designated as hedging instruments. The accounting for derivatives that are designated as hedging instruments is described in Note 1(h), "Significant Accounting Policies - Derivative Instruments ." The following table summarizes information on the location and gross amounts of derivative fair values contained in the consolidated balance sheets at December 31, 2016 and 2015 : 2016 2015 (U.S. dollars in thousands) Asset Derivative Notional Amount Asset Derivative Fair Value (1) Liability Derivative Notional Amount Liability Derivative Fair Value (1) Asset Derivative Notional Amount Asset Derivative Fair Value (1) Liability Derivative Notional Amount Liability Derivative Fair Value (1) Derivatives designated as hedging instruments: Foreign exchange contracts $ 1,396,801 $ 85,175 $ 583,722 $ 25,750 $ 1,667,585 $ 64,289 $ 674,976 $ 11,941 Total derivatives designated as hedging instruments $ 1,396,801 $ 85,175 $ 583,722 $ 25,750 $ 1,667,585 $ 64,289 $ 674,976 $ 11,941 Derivatives not designated as hedging instruments: Investment Related Derivatives: Foreign exchange exposure 10,049 190 273,767 12,137 102,234 2,888 144,707 1,702 Credit exposure 32,500 1,077 82,500 6,978 8,433 652 71,614 12,067 Financial market exposure 5 5 — — 37 77 26,500 417 Other Non-Investment Derivatives: Foreign exchange contracts 181,300 1,208 — — 194,566 2,009 — — Credit exposure — — 24,490 340 29,874 31 — — Guaranteed minimum income benefit contract 43,553 19,499 43,553 19,499 46,032 19,368 46,032 19,368 Modified coinsurance funds withheld contracts including life retrocession embedded derivative (2) 59,775 — 4,048,446 — 60,667 — 4,620,879 — Other 15,000 342 — — — — — — Total derivatives not designated as hedging instruments $ 342,182 $ 22,321 $ 4,472,756 $ 38,954 $ 441,843 $ 25,025 $ 4,909,732 $ 33,554 Total derivatives $ 107,496 $ 64,704 $ 89,314 $ 45,495 Counterparty netting (17,947 ) (17,947 ) (3,087 ) (3,087 ) Total derivatives net of counterparty netting (1) 89,549 46,757 86,227 42,408 Cash collateral held/paid (3) (36,980 ) (5,810 ) (30,958 ) — Total derivatives as recorded in the balance sheets $ 52,569 $ 40,947 $ 55,269 $ 42,408 ____________ (1) Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements. (2) The fair value movements in derivative assets and liabilities relating to modified coinsurance funds withheld contracts are included within the associated asset or liability at each period end on the face of the balance sheets. Notional amounts associated with reinsurance agreements under which the Company assumes reinsurance risk are recorded as asset derivative notional amounts. Included in the liability derivative notional amount as of December 31, 2016 is the cumulative net realized and unrealized loss on the life retrocession embedded derivative of $937.7 million . (3) As of December 31, 2016 , the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015 , the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis. (a) Derivative Instruments Designated as Hedges of a Net Investment in a Foreign Operation The Company utilizes foreign exchange contracts to hedge the fair value of certain net investments in foreign operations. During the year ended December 31, 2016 and 2015 , the Company entered into foreign exchange contracts that were formally designated as hedges of investments in foreign subsidiaries, the majority of which have functional currencies of either the British Pound or the Euro. There was no ineffectiveness in these transactions. The following table provides the weighted average U.S. dollar equivalent of foreign denominated net assets that were hedged and the resulting derivative gain (loss) that was recorded in the foreign currency translation adjustment, net of tax, account within AOCI for the years ended December 31, 2016 and 2015 . Derivative Instruments Designated as Hedges of a Net Investment in a Foreign Operation – Summary (U.S. dollars in thousands) 2016 2015 Weighted average of U.S. dollar equivalent of foreign denominated net assets $ 2,316,538 $ 1,769,106 Derivative gains (losses) (1) $ 130,365 $ 106,876 ____________ (1) Derivative gains (losses) from derivative instruments designated as hedges of the net investment in a foreign operation are recorded in the cumulative translation adjustment account within AOCI for each period. (b) Derivative Instruments Not Formally Designated As Hedging Instruments The following table provides the total impact on earnings relating to derivative instruments not formally designated as hedging instruments under authoritative accounting guidance. The impacts are all recorded through Net realized and unrealized gains (losses) on derivatives in the income statement for the years ended December 31, 2016, 2015 and 2014 : Net Realized and Unrealized Gains (Losses) on Derivative Instruments (U.S. dollars in thousands) 2016 2015 2014 Investment Related Derivatives: Interest rate exposure $ 781 $ (2,347 ) $ 15,959 Foreign exchange exposure (592 ) (1,542 ) 3,351 Credit exposure (1,539 ) (2,537 ) 400 Financial market exposure (2,494 ) (2,190 ) 411 Financial Operations Derivatives: Credit exposure — — 5,023 Other Non-Investment Derivatives: Foreign exchange exposure (1,701 ) 60,319 — Credit exposure 4,424 1,375 — Guaranteed minimum income benefit contract — — 2,257 Modified coinsurance funds withheld contract, including life retrocession embedded derivative 3,300 45 2,741 Other 342 — — Total derivatives not designated as hedging instruments $ 2,521 $ 53,123 $ 30,142 Amount of gain (loss) recognized in income from ineffective portion of fair value hedges — — (256 ) Net realized and unrealized gains (losses) on derivative instruments $ 2,521 $ 53,123 $ 29,886 Net realized and unrealized gains (losses on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets $ (540,090 ) $ (151,691 ) $ (488,222 ) The Company’s objectives in using these derivatives are explained below. Investment Related Derivatives The Company, either directly or through third party investment managers, may use derivative instruments within its investment portfolio, including interest rate swaps and options on interest rate swaps, total return swaps, credit derivatives (including single name and index credit default swaps and options on credit default swaps), equity options, forward contracts and future (including foreign exchange, bond and stock index, interest rate and commodity futures), primarily as a means of reducing investment risk by economically hedging exposures to interest rate, credit spread, equity price changes and foreign currency risk or, in limited instances, for efficient portfolio management. When using exchange traded or cleared over-the-counter derivatives, the Company is exposed to the credit risk of the applicable clearing house and of the Company's futures commission merchant. When using uncleared over-the-counter derivatives, the Company is exposed to credit risk in the event of non-performance by the counterparties to such derivative contracts. To manage this risk, the Company requires appropriate legal documentation with counterparties that has been reviewed and negotiated by legal counsel on behalf of the Company and complies with the Company’s documentation standards investment guidelines and policies. Investment Related Derivatives – Interest Rate Exposure The Company utilizes risk management and overlay strategies that incorporate the use of derivative financial instruments primarily to manage its fixed income portfolio duration and net economic exposure to interest rate risks. The Company may also use interest rate swaps to convert certain liabilities from a fixed rate to a variable rate of interest or use them to convert a variable rate of interest from one basis to another. Investment Related Derivatives – Foreign Exchange Exposure The Company has exposure to foreign currency exchange rate fluctuations through its operations and in its investment portfolio. The Company uses foreign exchange contracts to manage its exposure to the effects of fluctuating foreign currencies on the value of certain of its foreign currency fixed maturities. These contracts are not designated as specific hedges for financial reporting purposes and, therefore, realized and unrealized gains and losses on these contracts are recorded in income in the period in which they occur. These contracts generally have maturities of twelve months or less. In addition, certain of the Company's investment managers may, subject to investment guidelines, enter into forward contracts. Investment Related Derivatives – Credit Exposure Credit derivatives may be purchased within the Company's investment portfolio in the form of single name and basket credit default swaps and swaptions, which are used to mitigate credit exposure through a reduction in credit spread duration (i.e., macro credit strategies rather than single-name credit hedging) or exposure to securities of selected issuers. Credit derivatives may also be used to efficiently gain exposure to credit markets, subject to guidelines that prohibit the introduction of effective leverage. Investment Related Derivatives – Financial Market Exposure Stock index futures may be purchased within the Company's investment portfolio in order to create synthetic equity exposure and to add value to the portfolio with overlay strategies where market inefficiencies are believed to exist. Stock index futures may be sold to facilitate the timely and efficient reduction of equity exposure. Equity option strategies, including both purchases and sales of options, may be used to add value or reduce exposure with overlay or other strategies. From time to time, the Company may enter into other financial market exposure derivative contracts on various indices and other underlying financial instruments including, but not limited to, equity options, total return swaps, and commodity contracts. Financial Operations Derivatives – Credit Exposure During the fourth quarter of 2014, the remaining financial operations credit derivative exposure, which was written as part of the Company's previous financial lines business and is outside of the Company's investment portfolio, was terminated. The Company has no continuing financial operations derivative credit exposures. Other Non-Investment Derivatives Foreign Exchange Contracts On January 9, 2015, the Company entered into deal contingent deliverable Fx Forwards with Morgan Stanley Capital Services LLC and Goldman Sachs International. The purpose of the FX Forwards was to mitigate the risk of foreign currency exposure related to the Catlin Acquisition. Following the closing of the Catlin Acquisition, the FX Forwards were settled. In connection with the Catlin Acquisition and the FX Forwards, during the first quarter of 2015 certain foreign exchange contracts utilized to hedge the fair value of certain net investments in foreign operations were de-designated as hedging instruments; subsequently during the second quarter, the hedging relationships were then re-established. In the fourth quarter of 2015, the Company entered into an average rate option to mitigate the risk of foreign currency exposure to certain cash flows denominated in the British Pound. The option matured in the fourth quarter of 2016. Additionally, the Company has a small forward purchase to mitigate exposure to certain cash flows denominated in New Zealand dollars. Credit Exposure During the year ended December 31, 2016 , the Company entered into a non-investment-related credit derivative relating to a number of reference pool mortgage tranches associated with actual mortgage loans that were securitized into agency mortgage-backed securities and sold as Structured Agency Credit Risk Notes. As of December 31, 2016 , there was no reported event of default on this obligation. The credit derivative is recorded at fair value based upon models developed by the Company. Significant unobservable inputs considered in the valuation include the impact of changes in interest rates, future default, delinquency and prepayment rates, credit spreads, changes in credit quality, and other market factors. Guaranteed Minimum Income Benefit Contract The Company also has derivatives embedded in certain reinsurance contracts. For a certain life reinsurance contract, the Company pays the ceding company a fixed amount equal to the estimated present value of the excess of the guaranteed benefit over the account balance upon the policyholder's election to take the income benefit. The fair value of this derivative is determined based on the present value of expected cash flows. Modified Coinsurance and Funds Withheld Contracts, including Life Retrocession Embedded Derivative The Company has modified coinsurance and funds withheld reinsurance agreements that provide for a return to be paid to the Company based on a portfolio of fixed income securities. As such, the agreements contain an embedded derivative. The embedded derivative is bifurcated from the funds withheld balance and recorded at fair value with changes in fair value recognized in earnings through Net realized and unrealized gains (losses) on derivative instruments. In addition, the Company entered into the GreyCastle Life Retro Arrangements as described in Note 1(c), "Significant Accounting Policies - Total Investments - Investments Related to Life Retrocession Arrangements written on a Funds Withheld Basis," " Note 1(e), "Significant Accounting Policies - Reinsurance ," and Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ." The embedded derivative related to the GreyCastle Life Retro Arrangements is recorded at fair value with changes in fair value recognized in earnings through Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets. The impact of the GreyCastle Life Retro Arrangements on the Company's results for the years ended December 31, 2016 and 2015 and the period beginning from the completion of the transaction on May 30, 2014 through December 31, 2014 was as follows: Impact of GreyCastle Life Retro Arrangements (U.S. dollars in thousands) 2016 2015 2014 Underwriting profit (loss) (1) $ — $ 605 $ 11,649 Net investment income - Life Funds Withheld Assets 154,751 187,489 129,575 Net realized gains (losses) on investments sold - Life Funds Withheld Assets 152,589 223,272 5,067 Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets 109,458 (27,734 ) (9 ) OTTI on investments - Life Funds Withheld Assets (2,598 ) (13,357 ) (20,587 ) Exchange (gains) losses (8,988 ) 4,788 10,099 Other income and expenses (154 ) 2,280 (1,610 ) Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets (540,090 ) (151,691 ) (488,222 ) Net income (loss) $ (135,032 ) $ 225,652 $ (354,038 ) Change in net unrealized gains (losses) on investments - Life Funds Withheld Assets (4,502 ) (421,604 ) 274,083 Change in adjustments related to future policy benefit reserves 62,295 170,688 74,009 Change in cumulative translation adjustment - Life Funds Withheld Assets 77,239 25,869 17,595 Total changes to other comprehensive income as a result of GreyCastle Life Retro Arrangements $ 135,032 $ (225,047 ) $ 365,687 Comprehensive income (loss) $ — $ 605 $ 11,649 ____________ (1) The underwriting profit of $0.6 million in 2015 and $11.6 million in 2014 relate to premium adjustments relating to the GreyCastle Life Retro Arrangements transaction, which was completed on May 30, 2014. Excluding these transactions, the impact to comprehensive income relating to the GreyCastle Life Retro Arrangements was nil for the years ended December 31, 2016, 2015 and 2014 . As shown in the table above, although the Company's net income (loss) is subject to variability related to the GreyCastle Life Retro Arrangements, there is minimal net impact on the Company's comprehensive income in any period. The life retrocession embedded derivative value includes the interest income, unrealized gains and losses, and realized gains and losses from sales on the Life Funds Withheld Assets. The change in the value of the life retrocession embedded derivative, which includes the interest income, realized and unrealized gains and losses on Life Funds Withheld Assets and certain related expenses, is as follows: Components of Life Retrocession Embedded Derivative and Derivative Instruments - Life Funds Withheld Assets: (U.S. dollars in thousands) 2016 2015 Interest income - Life Funds Withheld Assets $ (161,887 ) $ (193,569 ) Realized and unrealized gains (losses) on Life Funds Withheld Assets (312,074 ) 180,134 Other 155 351 Net realized and unrealized gains (losses) on life retrocession embedded derivative $ (473,806 ) $ (13,084 ) Net adjustments related to future policy benefit reserves, net of tax $ (51,100 ) $ (125,747 ) Net realized and unrealized gains (losses) on derivative instruments - Life Funds Withheld Assets $ (15,184 ) $ (12,860 ) Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets $ (540,090 ) $ (151,691 ) Other The Company has entered into short term catastrophe derivative swap agreements as the fixed rate payer that provide for a return to be paid to the Company based the occurrence of certain industry catastrophe events. The derivatives are recorded at fair value with changes in fair value recognized in earnings through Net realized and unrealized gains (losses) on derivative instruments. (c) Derivative Instruments Designated as Fair Value Hedges The Company may designate certain of its derivative instruments as fair value hedges or cash flow hedges, in which case it formally and contemporaneously documents all relationships between the hedging instruments and hedged items and links the hedging derivative to specific assets and liabilities. The Company assesses the effectiveness of the hedge both at inception and on an on-going basis, and determines whether the hedge is highly effective in offsetting changes in fair value or cash flows of the linked hedged item. The Company uses foreign exchange contracts to hedge the fair value of certain fixed income securities. For the year ended December 31, 2016 , there is no exposure to fair value hedges. The following table provides the total impact on earnings relating to derivative instruments formally designated as fair value hedges along with the impacts of the related hedged items for the years indicated: Derivatives Designated as Fair Value Hedges (U.S. dollars in thousands) Hedged Items – Amount of Gain/(Loss) Recognized in Income Attributable to Risk Gain/(Loss) Recognized in Income on Derivative Fixed Maturity Investments Ineffective Portion of Hedging Relationship – Gain/(Loss) Year Ended December 31, 2016 Interest rate exposure $ — Foreign exchange exposure — Total $ — $ — $ — Year Ended December 31, 2015 Interest rate exposure $ — Foreign exchange exposure — Total $ — $ — $ — Year Ended December 31, 2014 Interest rate exposure $ — Foreign exchange exposure (15,663 ) Total $ (15,663 ) $ 15,407 $ (256 ) The gains (losses) recorded on both the derivative instruments and specific items designated as being hedged as part of the fair value hedging relationships outlined above, along with any associated ineffectiveness in the relationships, are recorded through Net realized and unrealized gains (losses) on derivative instruments in the income statement. Settlement of Fair Value Hedges During the fourth quarter of 2010 and the third quarter of 2012, the Company settled five interest rate contracts designated as fair value hedges of certain of the Company's structured indemnity contracts. The gain on settlement of these contracts, which represented the effective portion of the hedging relationship, was recorded as an increase in the carrying value of the deposit liabilities and is being amortized through interest expense over the remaining term of the structured indemnity contracts. During the second quarter of 2014, the Company negotiated the termination of one of these larger structured indemnity contracts. Upon the termination of the structured indemnity contract, the remaining fair value adjustment of the associated hedge in the amount of $47.0 million , which was being amortized as a reduction of interest expense over the remaining term of the contract, was reduced to zero and recorded as an adjustment to interest expense at the termination date. As a result of the termination, a net decrease of $28.7 million was recorded to interest expense reflecting the realization of the remaining balance of the fair value hedge adjustment, partially offset by an accretion rate adjustment due to changes in cash flows. A summary of these fair value hedges that have been terminated and their cumulative impact on results up to the indicated years ended December 31 as well as the remaining balance of the fair value hedges and average years remaining to maturity are shown below: Settlement of Fair Value Hedges – Summary (U.S. dollars in thousands, except years) Fair Value Hedges – Structured Indemnity Contracts December 31, 2016 2015 Cumulative reduction to interest expense $ 113,292 $ 103,742 Remaining balance $ 119,903 $ 129,454 Weighted average years remaining to maturity 20.1 21.6 (d) Contingent Credit Features Certain derivative agreements entered into by the Company or its subsidiaries contain credit rating downgrade provisions that permit early termination of the agreements by the counterparty if collateral is not posted following failure to maintain certain credit ratings from one or more of the principal credit rating agencies. If the Company were required to terminate such agreements early due to a credit rating downgrade, it could potentially be in a net liability position at the time of settlement of such agreements. The aggregate fair value of all derivative agreements containing such rating downgrade provisions that were in a liability position and any collateral posted under these agreements as of December 31 for the years indicated were as follows: Contingent Credit Features - Summary: (U.S. dollars in thousands) 2016 2015 Aggregate fair value of derivative agreements with downgrade provisions in a net liability position $ 14,130 $ 5,827 Collateral posted to counterparty $ 4,630 $ —

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair value disclosures	Fair Value Measurements (a) Fair Value Summary The following tables set forth the Company’s assets and liabilities that were accounted for at fair value at December 31, 2016 and 2015 by level within the fair value hierarchy. For further information, see Note 1(b), "Significant Accounting Policies - Fair Value Measurements ": December 31, 2016 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2016 Assets Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ — $ 3,869,637 $ 24,751 $ — $ 3,894,388 Corporate - Financials — 3,612,006 10,284 — 3,622,290 Corporate - Non Financials — 6,502,638 9,801 — 6,512,439 RMBS - Agency — 4,218,367 — — 4,218,367 RMBS - Non-Agency — 274,258 — — 274,258 CMBS — 665,087 99 — 665,186 CDO — 377,490 1 — 377,491 Other asset-backed securities — 874,767 1,130 — 875,897 U.S. States and political subdivisions of the States — 2,478,112 — — 2,478,112 Non-U.S. Government — 5,030,132 — — 5,030,132 Total fixed maturities - AFS - Excluding Life Funds Withheld Assets, at fair value $ — $ 27,902,494 $ 46,066 $ — $ 27,948,560 Equity securities, at fair value 898,664 138,667 — — 1,037,331 Short-term investments, at fair value (1) — 625,193 — — 625,193 Total investments AFS - Excluding Life Funds Withheld Assets $ 898,664 $ 28,666,354 $ 46,066 $ — $ 29,611,084 Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government — 10,577 — — 10,577 Corporate - Financials — 439,267 — — 439,267 Corporate - Non Financials — 1,015,341 — — 1,015,341 RMBS - Agency — 613 — — 613 RMBS - Non-Agency — 21,767 — — 21,767 CMBS — 94,240 — — 94,240 Other asset-backed securities — 101,560 — — 101,560 Non-U.S. Government — 624,677 — — 624,677 Total fixed maturities - AFS - Life Funds Withheld Assets, at fair value — 2,308,042 — — 2,308,042 Total investments - AFS, at fair value 898,664 30,974,396 46,066 — 31,919,126 December 31, 2016 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2016 Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government — 14,708 — — 14,708 Corporate - Financials — 468,175 — — 468,175 Corporate - Non Financials — 643,030 — — 643,030 RMBS - Agency — 852 — — 852 RMBS - Non-Agency — 109 — — 109 CMBS — 5,526 — — 5,526 Other asset-backed securities — 39,446 — — 39,446 U.S. States and political subdivisions of the States — 224 — — 224 Non-U.S. Government — 444,944 — — 444,944 Total fixed maturities - Trading - Life Funds Withheld Assets, at fair value — 1,617,014 — — 1,617,014 Short-term investments, at fair value — 9,563 — — 9,563 Total investments, Trading — 1,626,577 — — 1,626,577 Cash equivalents (2) 573,398 1,096,254 — — 1,669,652 Cash equivalents - Life Funds Withheld Assets — 72,798 — — 72,798 Other investments (3) 493,874 205,528 — 699,402 Other assets (4) — 87,655 19,841 (17,947 ) 89,549 Total assets accounted for at fair value $ 1,472,062 $ 34,351,554 $ 271,435 $ (17,947 ) $ 36,077,104 Liabilities Funds withheld on GreyCastle Life Retro Arrangements (net of future policy benefit reserves recoverable) (5) $ — $ 937,721 $ — $ — $ 937,721 Other liabilities (4) — 44,865 19,839 (17,947 ) 46,757 Total liabilities accounted for at fair value $ — $ 982,586 $ 19,839 $ (17,947 ) $ 984,478 December 31, 2015 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2015 Assets Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ — $ 5,020,574 $ 45,063 $ — $ 5,065,637 Corporate - Financials — 3,508,224 53,685 — $ 3,561,909 Corporate - Non Financials — 6,900,259 188 — $ 6,900,447 RMBS - Agency — 3,754,894 3,077 — $ 3,757,971 RMBS - Non-Agency — 328,540 — — $ 328,540 CMBS — 405,316 — — $ 405,316 CDOs — 2 32,408 — $ 32,410 Other asset-backed securities — 1,150,715 17,857 — $ 1,168,572 U.S. States and political subdivisions of the States — 2,632,070 — — $ 2,632,070 Non-U.S. Government — 5,251,614 — — $ 5,251,614 Total fixed maturities - AFS - Excluding Funds Withheld Assets, at fair value $ — $ 28,952,208 $ 152,278 $ — $ 29,104,486 Equity securities, at fair value 528,581 350,338 — — 878,919 Short-term investments, at fair value (1) — 617,390 — — 617,390 Total investments AFS - Excluding Funds Withheld Assets $ 528,581 $ 29,919,936 $ 152,278 $ — $ 30,600,795 December 31, 2015 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2015 Fixed maturities - Life Funds Withheld Assets U.S. Government and Government-Related/Supported $ — $ 12,742 $ — $ — $ 12,742 Corporate - Financials — 598,236 — — $ 598,236 Corporate - Non Financials — 1,308,628 — — $ 1,308,628 RMBS – Agency — 752 — — $ 752 RMBS – Non-Agency — 26,953 — — $ 26,953 CMBS — 122,481 — — $ 122,481 Other asset-backed securities — 149,795 — — $ 149,795 Non-U.S. Government — 933,516 — — $ 933,516 Total fixed maturities - AFS - Life Funds Withheld Assets, at fair value $ — $ 3,153,103 $ — $ — $ 3,153,103 Total investments - AFS, at fair value $ 528,581 $ 33,073,039 $ 152,278 $ — $ 33,753,898 Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ — $ 4,990 $ — $ — $ 4,990 Corporate - Financials — 335,956 — — $ 335,956 Corporate - Non Financials — 493,621 — — $ 493,621 RMBS – Agency — 368 — — $ 368 CMBS — 4,803 — — $ 4,803 Other asset-backed securities — 25,700 — — $ 25,700 Non-U.S. Government — 370,261 — — $ 370,261 Total fixed maturities - Trading - Life Funds Withheld Assets, at fair value $ — $ 1,235,699 $ — $ — $ 1,235,699 Short-term investments, at fair value — 60,330 — — $ 60,330 Total investments, Trading $ — $ 1,296,029 $ — $ — $ 1,296,029 Cash equivalents (2) 437,742 830,924 — — $ 1,268,666 Cash equivalents - Life Funds Withheld Assets (2) 517 100,757 — — $ 101,274 Other investments (3) — 490,058 283,550 — $ 773,608 Other assets (4) — 69,914 19,400 (3,087 ) $ 86,227 Total assets accounted for at fair value $ 966,840 $ 35,860,721 $ 455,228 $ (3,087 ) $ 37,279,702 Liabilities Funds withheld on life retrocession arrangements (net of future policy benefit reserves recoverable) (5) $ — $ 463,915 $ — $ — $ 463,915 Financial instruments sold, but not yet purchased (6) 347 — — — $ 347 Other liabilities (4) — 16,304 29,191 (3,087 ) $ 42,408 Total liabilities accounted for at fair value $ 347 $ 480,219 $ 29,191 $ (3,087 ) $ 506,670 ____________ (1) Short-term investments consist primarily of Corporate securities and U.S. and Non-U.S. Government and Government-Related/ Supported securities. (2) Cash equivalents balances subject to fair value measurement include certificates of deposit and money market funds. Operating cash balances are not subject to recurring fair value measurement guidance. (3) Other Investments balance excludes $322.9 million and $518.1 million as of December 31, 2016 and December 31, 2015 , respectively, measured using Net Asset Value, based on new accounting guidance. In addition, the Other investments balance excludes a certain payment obligation. These investments, which totaled $142.3 million at December 31, 2016 and $141.3 million at December 31, 2015 , are carried at amortized cost. For further information, see Note 6, "Other Investments ." (4) Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy. For further details regarding derivative fair values and associated collateral received or paid see Note 7, "Derivative Instruments ." (5) Funds withheld on life retrocession arrangements (net of future policy benefit reserves recoverable) include balances related to the life retrocession embedded derivative, under which all investment results associated with the Life Funds Withheld Assets related to the GreyCastle Life Retro Arrangements described in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ", accrue to the benefit of GCLR. (6) Financial instruments sold, but not yet purchased, represent "short sales" and are included within "Payable for investments purchased" on the balance sheets. (b) Level 2 Asset Valuations U.S. Government, Corporate - Financials, Corporate - Non Financials and Non-U.S. Government Transaction activity inputs utilized in the valuation of fair value hierarchy Level 2 securities within these sub-categories include actual trades, dealer posts, results of bids-wanted, institutional secondary offerings, primary market offerings and Trade Reporting and Compliance Engine ("TRACE") trade feeds. As part of the evaluation process, transaction activity is compared to prior evaluations and necessary adjustments are made accordingly. Market-color inputs include actively quoted benchmark issues, buy-side/evaluator dialogue, sell-side/evaluator dialogue and credit derivative indices. RMBS - Agency, RMBS - Non-Agency, CMBS, CDO and Other asset-backed securities As part of the fair valuation process, Level 2 securities in these sub-categories are analyzed by collateral type, deal structure, deal performance and vintage. Market inputs into the valuation process for each sub-category include reported or observed trades, results of bids-wanted, buy-side/sell-side evaluator dialogue, dealer offering and market research reports. Cash flow inputs into the evaluation process include conditional prepayment rates, conditional decay rates, delinquency and loss severity rates. This assumptive data is reviewed and updated using third party reported information to reflect current market convention. U.S. States and political subdivisions of the States Transaction activity inputs utilized in the valuation of fair value hierarchy Level 2 securities within this sub-category include client and broker trades, dealer posts, results of bids-wanted, institutional secondary offerings, primary market offerings, and Municipal Securities Rulemaking trade feeds. As part of the evaluation process, transaction activity is compared to prior evaluations and necessary adjustments are made accordingly. Market-color inputs include bids, offerings, two-sided markets, buy-side/evaluator dialogue and sell-side/evaluator dialogue. Credit information inputs include issuer financial statements, default and material event notices, developer reports and liquidation and restructuring analysis. Equity securities and other investments Other investment securities generally include investments in thinly traded equity funds and hedge funds. Fair value is determined based upon the most recent net asset values (“NAV’) received from the fund administrators, the nature of the underlying investments in the funds and the frequency of subscriptions or redemptions as dictated by the fund’s governing documents. Other assets and other liabilities Other assets and other liabilities primarily include over-the-counter (“OTC”) derivatives, which are valued using market transactions and other market evidence whenever possible, including market-based inputs to models, model calibration to market clearing transactions, broker or dealer quotations or alternative independent pricing sources where an understanding of the inputs utilized in arriving at the valuations is obtained. Where models are used, the selection of a particular model to value an OTC derivative depends upon the contractual terms and specific risks inherent in the instrument as well as the availability of pricing information in the market. The Company generally uses similar models to value similar instruments. Valuation models require a variety of inputs, including contractual terms, market prices, yield curves, credit curves, measures of volatility, prepayment rates and correlations of such inputs. For OTC derivatives that trade in liquid markets, such as generic forwards, interest rate swaps and options, model inputs can generally be verified and model selection does not involve significant management judgment. (c) Level 3 Assets and Liabilities The tables below present additional information about assets and liabilities measured at fair value on a recurring basis and for which Level 3 inputs were utilized to determine fair value. The tables present a reconciliation of the beginning and ending balances for the years ended December 31, 2016 and 2015 for all financial assets and liabilities measured at fair value using significant unobservable inputs (Level 3) at December 31, 2016 and 2015 , respectively. The tables do not include gains or losses that were reported in Level 3 in prior periods for assets that were transferred out of Level 3 prior to December 31, 2016 and 2015 , respectively. Gains and losses for assets and liabilities classified within Level 3 in the table below may include changes in fair value that are attributable to both observable inputs (Levels 1 and 2) and unobservable inputs (Level 3). Further, it should be noted that the following tables do not take into consideration the effect of offsetting Level 1 and 2 financial instruments entered into by the Company that are either economically hedged by certain exposures to the Level 3 positions or that hedge the exposures in Level 3 positions. In general, Level 3 assets include securities for which values were obtained from brokers where either significant inputs were utilized in determining the values that were difficult to corroborate with observable market data, or sufficient information regarding the specific inputs utilized by the broker was not available to support a Level 2 classification. Transfers into or out of Level 3 primarily arise as a result of the valuations utilized by the Company changing between either those provided by independent pricing services that do not contain significant unobservable inputs and other valuations sourced from brokers that are considered Level 3. Fixed maturities and short-term investments The Company’s Level 3 assets consist primarily of U.S. Government and Government-Related/Supported, Corporates and CDOs, for which non-binding broker quotes are the primary source of the valuations. Sufficient information regarding the specific inputs utilized by the brokers was not available to support a Level 2 classification. The Company obtains the majority of broker quotes for these securities from third party investment managers who perform independent verifications of these valuations using pricing matrices based upon information gathered by market traders. In addition, for the majority of these securities, the Company compares the broker quotes to independent valuations obtained from third party pricing vendors, which may also consist of broker quotes, to assess if the prices received represent a reasonable estimate of the fair value. Although the Company does not have access to the specific unobservable inputs that may have been used in the fair value measurements of these securities provided by brokers, we would expect that the significant inputs considered are prepayment rates, probability of default, loss severity in the event of default, recovery rates, liquidity premium and reinvestment rates. Significant increases (decreases) in any of those inputs in isolation could result in a significantly different fair value measurement. Generally, a change in the assumption used for the probability of default is accompanied by a directionally similar change in the assumption used for the loss severity and a directionally opposite change in the assumption used for prepayment rates. The remainder of the Level 3 assets relate primarily to private investments (including funds) and certain derivative positions as described below. Other investments Included within the other investments component of the Company’s Level 3 valuations are private investments (including funds) and hedge funds where the Company is not deemed to have significant influence over the investee. The fair value of these investments is based upon net asset values received from the investment manager or general partner of the respective entity. The nature of the underlying investments held by the investee that form the basis of the net asset value include assets such as private business ventures and are such that significant Level 3 inputs are utilized in the determination of the individual underlying holding values and, accordingly, the fair value of the Company’s investment in each entity is classified within Level 3. The Company has not adjusted the net asset values received; however, management incorporates factors such as the most recent financial information received, annual audited financial statements and the values at which capital transactions with the investee take place when applying judgment regarding whether any adjustments should be made to the net asset value in recording the fair value of each position. Investments in hedge funds included in other investments utilize strategies including arbitrage, directional, event driven and multi-style. The funds potentially have lockup and gate provisions which may limit redemption liquidity. For further details regarding the nature of other investments and related features, see Note 6, "Other Investments ," for further details. Derivative instruments Derivative instruments recorded within other liabilities and classified within Level 3 include credit derivatives sold providing protection on senior tranches of structured finance transactions where the value is obtained directly from the investment bank counterparty and sufficient information regarding the inputs utilized in such valuation was not obtained to support a Level 2 classification and guaranteed minimum income benefits embedded within one reinsurance contract. The majority of inputs utilized in the valuations of these types of derivative contracts are considered Level 1 or Level 2; however, each valuation includes at least one Level 3 input that was significant to the valuation and, accordingly, the values are disclosed within Level 3. The calculation of the change in fair value of the embedded derivative associated with the Life Retro Arrangements includes the interest income, realized and unrealized gains and losses on Life Funds Withheld Assets and certain related expenses related to the Life Funds Withheld Assets. The fair value of the embedded derivative is included in “Funds withheld on life retrocession arrangements, net of future policy benefit reserves recoverable” on the consolidated balance sheets. The fair value of the embedded derivative is considered a Level 2 valuation. Level 3 Assets and Liabilities - Year Ended December 31, 2016 (U.S. dollars in thousands) Balance, beginning of period Realized gains (losses) Movement in unrealized gains (losses) Purchases and Issuances Sales Settlements Net transfers into (out of) Level 3 (2) Balance, end of period Movement in total gains (losses) relating to investments still held U.S. Government $ 45,063 $ 264 $ 687 $ — $ (19,101 ) $ (2,162 ) $ — $ 24,751 $ 886 Corporate - Financials 53,685 (2,991 ) 10 285 (30,420 ) — (10,285 ) 10,284 31 Corporate - Non-Financials 188 — 13 1,747 — (6 ) 7,859 9,801 14 RMBS - Agency 3,077 (3 ) 7 — — (229 ) (2,852 ) — — CMBS — — (3 ) — — — 102 99 (3 ) CDO 32,408 189 6,870 — — (23,030 ) (16,436 ) 1 6,152 Other asset-backed securities 17,857 479 (2,113 ) 1,072 — (14,190 ) (1,975 ) 1,130 (1,673 ) Other investments 283,550 18,097 (10,622 ) 47,998 (27,676 ) (43,607 ) (62,212 ) 205,528 2,454 Derivative Contracts - Net (9,791 ) — 9,793 — — — — 2 10 Total $ 426,037 $ 16,035 $ 4,642 $ 51,102 $ (77,197 ) $ (83,224 ) $ (85,799 ) $ 251,596 $ 7,871 Level 3 Assets and Liabilities - Year Ended December 31, 2015 (U.S. dollars in thousands) Balance, beginning of period Realized gains (losses) Movement in unrealized gains (losses) Purchases and Issuances (1) Sales Settlements Net transfers into (out of) Level 3 (2) Balance, end of period Movement in total gains (losses) relating to investments still held U.S. Government $ — $ — $ — $ 35,044 $ — $ — $ 10,019 $ 45,063 $ — Corporate - Financials — 9 (10 ) 53,686 — — — 53,685 (2 ) Corporate - Non-Financials 5,894 (186 ) (13 ) (123 ) — (316 ) (5,068 ) 188 (153 ) RMBS - Agency 1,910 — (3 ) 1,297 — (323 ) 196 3,077 (2 ) CDO 687,958 (8,658 ) 16,688 25,882 (366,633 ) (322,829 ) — 32,408 5,279 Other asset-backed securities 5,288 628 (599 ) 46,940 (7,269 ) (6,359 ) (20,772 ) 17,857 451 Other investments 185,083 15,270 (12,548 ) 117,143 (1,417 ) (19,981 ) — 283,550 2,724 Derivative Contracts - Net (9,764 ) — (27 ) — — — — (9,791 ) 80 Total $ 876,369 $ 7,063 $ 3,488 $ 279,869 $ (375,319 ) $ (349,808 ) $ (15,625 ) $ 426,037 $ 8,377 ____________ (1) Includes assets acquired as result of the transaction described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition " (2) Net transfers include both movement in and movement out of Level 3. Corporate - Non-Financials securities for 2016 includes $9.7 million of incoming transfers partially offset by $1.9 million outgoing transfers. Other asset-backed securities for 2016 includes $5.0 million of outgoing transfers partially offset by $3.0 million of incoming transfers, and 2015 includes $34.1 million of outgoing transfers partially offset by $13.3 million of incoming transfers. Other investments for 2016 includes $77.7 million of outgoing transfers partially offset by $15.5 million of incoming transfers. RMBS-Agency for 2015 includes $3.1 million of incoming transfers partially offset by $2.9 million of outgoing transfers. (d) Financial Instruments Not Carried at Fair Value Authoritative guidance over disclosures about the fair value of financial instruments requires additional disclosure of fair value information for financial instruments not carried at fair value in both interim and annual reporting periods. Certain financial instruments, particularly insurance contracts, are excluded from these fair value disclosure requirements. The carrying values of cash and cash equivalents, accrued investment income, net receivable from investments sold, other assets, net payable for investments purchased, other liabilities and other financial instruments not included below approximated their fair values. The following table includes financial instruments for which the carrying value differs from the estimated fair values at December 31, 2016 and 2015 . All of these fair value estimates are considered Level 2 fair value measurements. (U.S. dollars in thousands) 2016 2015 Carrying Value Fair Value Carrying Value Fair Value Financial Assets - Other investments, structured transactions $ 142,271 $ 153,173 $ 141,329 $ 154,065 Deposit liabilities $ 1,116,233 $ 1,337,406 $ 1,168,376 $ 1,436,210 Notes payable and debt 2,647,677 2,813,257 2,644,970 2,805,152 Financial Liabilities $ 3,763,910 $ 4,150,663 $ 3,813,346 $ 4,241,362 The Company historically participated in structured transactions. Our remaining structured transaction is an investment in a payment obligation with an insurance company. This transaction is carried at amortized cost. The fair value of this investment held by the Company is determined through use of an internal model utilizing benchmark yields, issuer spreads and reference data. Deposit liabilities include obligations under structured insurance and reinsurance transactions. For purposes of fair value disclosures, the Company determined the estimated fair value of the deposit liabilities by assuming a discount rate equal to the appropriate U.S. Treasury rate plus 50.0 basis points and 26.5 basis points at December 31, 2016 and 2015 , respectively. The discount rate incorporates the Company’s own credit risk into the determination of estimated fair value. The fair values of the Company’s notes payable and debt outstanding were determined based on quoted market prices. There are no significant concentrations of credit risk within the Company’s financial instruments as defined in the authoritative guidance over disclosures of fair value of financial instruments not carried at fair value, which excludes certain financial instruments, particularly insurance contracts.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and other intangible assets	Goodwill and Other Intangible Assets The following table presents an analysis of intangible assets broken down between goodwill, intangible assets with an indefinite life and intangible assets with a definite life for the years ended December 31, 2016, 2015 and 2014 : (U.S. dollars in thousands) Goodwill Intangible assets with an indefinite life Intangible assets with a definite life Total Balance at December 31, 2013 $ 396,245 $ 15,366 $ — $ 411,611 Additions 25,159 — 18,500 43,659 Amortization — — (1,850 ) (1,850 ) Foreign currency translation (5,468 ) — — (5,468 ) Balance at December 31, 2014 $ 415,936 $ 15,366 $ 16,650 $ 447,952 Additions 807,381 673,000 315,000 1,795,381 Amortization — — (15,517 ) (15,517 ) Foreign currency translation (9,687 ) (5,507 ) (2,356 ) (17,550 ) Balance at December 31, 2015 $ 1,213,630 $ 682,859 $ 313,777 $ 2,210,266 Additions 14,084 8,000 28,948 51,032 Amortization — — (22,422 ) (22,422 ) Foreign currency translation (14,190 ) (8,080 ) (12,953 ) (35,223 ) Balance at December 31, 2016 $ 1,213,524 $ 682,779 $ 307,350 $ 2,203,653 Goodwill At December 31, 2016 and 2015 , the Company had goodwill of $1.2 billion , with $483.6 million and $479.5 million , respectively allocated to the Insurance Segment and $730.0 million and $734.2 million , respectively, allocated to the Reinsurance Segment. In the first quarter of 2016, as a result of the transaction described in Note 2(c), "Acquisitions and Disposals - Allied Acquisition ," the Company recognized additional goodwill of approximately $14.1 million . The transaction was accounted for using the acquisition method under which the Company recorded the identifiable assets acquired, including indefinite-lived and definite-lived intangible assets, and liabilities assumed, at their Acquisition Date fair values, and recorded the excess of consideration transferred over the net assets acquired as goodwill. In the third quarter of 2015, as a result of the transaction described in Note 2(d), "Acquisitions and Disposals - New Energy Risk ," the Company recognized additional goodwill of approximately $13.4 million . The transaction was accounted for using the acquisition method under which the Company recorded the identifiable assets acquired and liabilities assumed at their acquisition date fair values, and recorded as goodwill the excess of the sum of a) over b) - in which a) represents the aggregate of: i) the consideration transferred, ii) the fair value of non-controlling interest in the acquiree, and iii) the acquisition-date fair value of the Company's previously held equity interest in the acquiree; and b) represents the net assets acquired in the transaction. In the second quarter of 2015, as a result of the transaction described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," the Company recognized additional goodwill and other intangible assets. The transaction was accounted for using the acquisition method under which the Company recorded the identifiable assets acquired, including indefinite-lived and definite-lived intangible assets, and liabilities assumed, at their Acquisition Date fair values, and recorded the excess of consideration transferred over the net assets acquired as goodwill. During the first quarter of 2014, Goodwill and Other Intangible Assets increased as a result of the completion of an acquisition. The transaction was accounted for using the acquisition method under which the Company recorded the identifiable assets and liabilities at their acquisition date fair values, and recorded the excess of consideration transferred over the net assets acquired as goodwill and intangible assets. The fair value of identifiable assets and liabilities acquired, as well as amounts recorded in the Company’s consolidated results since the acquisition date, are not material. The estimated fair values of the reporting units’ carried goodwill exceeded their estimated net book values at December 31, 2016 , and therefore no impairments were recorded during 2016 . At December 31, 2016 and 2015 , the ending goodwill balance is comprised of gross goodwill of $2.6 billion , offset by accumulated impairment charges of $1.4 billion at December 31, 2016 and 2015 . For further details regarding our impairment process, see Note 1(k), "Significant Accounting Policies - Goodwill, Intangibles and Other Long-Lived Assets ." Other Intangible Assets At December 31, 2016 and 2015 , the ending definite-lived intangible assets balance is comprised of $347.2 million and $333.5 million , respectively, of gross intangible assets, offset by accumulated amortization of $39.8 million and $17.4 million , respectively. Future amortization expenses are expected to be as follows: Year Ended December 31, 2017 $ 21,957 2018 20,291 2019 20,041 2020 19,957 2021 19,957 2022-2036 205,147 Total expected amortization expenses $ 307,350 In connection with the transaction described in Note 2(a), "Acquisitions and Disposals - Brooklyn Acquisition ," the Company acquired definite-lived intangible assets of $22.9 million , which will be amortized over their estimated useful lives. In connection with the transaction described in Note 2(c), "Acquisitions and Disposals - Allied Acquisition ," the Company acquired indefinite-lived intangible assets of $8.0 million and definite-lived intangible assets of $6.0 million , which will be amortized over their estimated useful lives. The following table summarizes the intangible assets and their related useful lives recorded in connection with the Catlin Acquisition, as described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," as of the Acquisition Date: (U.S. dollars in thousands) Amount Estimated Useful Life Lloyd's - Syndicate capacity $ 660,000 Indefinite Insurance licenses 13,000 Indefinite Total identified indefinite life intangible assets $ 673,000 Lloyd's - Managing agent contracts 15,000 15 years Distribution network 290,000 20 years Trademarks / Trade names 10,000 2 years Total identified definite life intangible assets $ 315,000 Total identified intangible assets $ 988,000 An explanation of the intangible assets is as follows: • Lloyd's - Syndicate capacity - This asset represents the syndicate capacity of two Lloyd's syndicates allowing the Company to write insurance business in the Lloyd's market globally and realize the profits from that business. The value of the syndicate capacity includes the reputational value of participation in the Lloyd's market, and the value of trade names and licenses associated with syndicate ownership. The syndicate capacity was valued using the Multi-Period Excess Earnings Method, an application of the Income Approach. Critical inputs into the valuation model used for this intangible included estimates of the future growth of syndicate authorized premium income limits (ie, capacity) and expected return on that capacity and discounting based on a weighted average cost of capital. • Insurance licenses - The insurance licenses owned by Catlin at the time of the Catlin Acquisition allow the Company to write insurance business in the United States. The insurance licenses were valued using the Market Approach. Critical inputs utilized in the valuation of this intangible were the number of licenses obtained by US state and an aggregate market value per license based on similar past market transactions. • Lloyd's - Managing agent contracts - As the managing agent for certain Lloyd's syndicates, the Company has contracts with the syndicate members to provide underwriting services for which it earns managing agent fees and a profit commission. The managing agent contracts were based on the Income Approach. Critical inputs utilized in the valuation of this intangible included expected contract fee and profit commission rates applied to future managed syndicate capacity, contract renewal probabilities over a time horizon and discounting based on a weighted average cost of capital. • Distribution network - This asset represents a network of hundreds of retail and wholesale brokers worldwide, including specialty and regional brokerages, which allow the Company to form closer relationships with clients and aids business retention. The distribution network was valued using the Multi-Period Excess Earnings Method, an application of the Income Approach. Critical inputs into the valuation model used for this intangible included projections of underwriting profitability and investment returns, supporting capital charges, and discounting based on a weighted average cost of capital. • Trademarks / Trade names - The Catlin trademarks / trade names are utilized to attract customers for the turnkey solutions provided under the Company's managing agent contracts and to generate premiums from the non-Lloyd's platform underwriting products for which the Catlin brand is known.The trademarks and trade names were based on the Relief-from-Royalty Method, an application of the Income Approach. Critical inputs used in the valuation of this intangible included industry-based market royalty rates on premium revenues to be generated through use of the trademarks/trade names, expected useful life over which the company expects to co-brand under the trademarks/trade names and discounting based on a weighted average cost of capital.

Losses and Loss Expenses

Losses and Loss Expenses	12 Months Ended
	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Abstract]
Losses and loss expenses	Losses and Loss Expenses The following table represents a reconciliation of the beginning and ending balances of unpaid losses and loss expenses, including an analysis of the Company’s paid and unpaid losses and loss expenses incurred for the years indicated: (U.S. dollars in thousands) 2016 2015 2014 Unpaid losses and loss expenses at the beginning of the year $ 25,439,744 $ 19,353,243 $ 20,481,065 Unpaid losses and loss expenses recoverable (1) 5,248,905 3,411,528 3,414,735 Net unpaid losses and loss expenses at the beginning of the year $ 20,190,839 $ 15,941,715 $ 17,066,330 Acquired reserves 101,315 5,439,876 — Increase (decrease) in net losses and loss expenses incurred in respect of losses occurring in: Current year 6,374,377 5,072,830 3,513,465 Prior year (301,542 ) (306,630 ) (255,072 ) Total net incurred losses and loss expenses 6,072,835 4,766,200 3,258,393 Exchange rate effects (571,198 ) (582,300 ) (561,673 ) Less net losses and loss expenses paid in respect of losses occurring in: Current year 1,444,251 1,047,277 381,008 Prior year 3,890,269 4,327,375 3,440,327 Total net paid losses $ 5,334,520 $ 5,374,652 $ 3,821,335 Net unpaid losses and loss expenses at the end of the year 20,459,271 20,190,839 15,941,715 Unpaid losses and loss expenses recoverable (1) 5,480,300 5,248,905 3,411,528 Unpaid losses and loss expenses at the end of the year $ 25,939,571 $ 25,439,744 $ 19,353,243 ____________ (1) Property and Casualty business only. See Note 12, "Reinsurance ," for further information. (a) Liability for Unpaid Losses and Loss Expenses As the Company earns premiums for the underwriting risks it assumes, an estimate of the expected ultimate losses related to the premium is established. Loss reserves for unpaid loss and loss expenses are established due to the significant periods of time that may elapse between the occurrence, reporting and settlement of a loss. The process of establishing reserves for unpaid P&C claims can be complex and is subject to considerable variability, as it requires the use of judgment to make informed estimates. These estimates are based on numerous factors, and may be revised as additional experience and other data become available and are reviewed, as new or improved methodologies are developed or as current laws change. Loss reserves include: • Case reserves - reserves for reported losses and loss expenses that have not yet been settled; and • IBNR reserves – reserves for incurred but not reported losses or for reported losses over and above the amount of case reserves. Case Reserves Case reserves for the Company's P&C operations are established by management based on amounts reported from insureds or ceding companies and consultation with legal counsel, and represent the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. The method of establishing case reserves for reported claims differs among the Company's operations. With respect to the Insurance segment, the Company is notified of insured losses and records a case reserve for the estimated amount of the settlement, if any. The estimate reflects the judgment of claims personnel based on general reserving practices, the experience and knowledge of such personnel regarding the nature of the specific claim and, where appropriate, advice of legal counsel. Reserves are also established to provide for the estimated expense of settling claims, including legal and other fees and the general expenses of administering the claims adjustment process. With respect to reinsurance operations, case reserves for reported claims are generally established based on reports received from ceding companies. Additional case reserves may be established by the Company to reflect the estimated ultimate cost of a loss. For reinsurers, uncertainty in the reserving process stems, in part, from timing lags inherent in reporting by the claimant to the primary insurer, and subsequently by the primary insurer to the reinsurer. As a predominantly broker market reinsurer for both excess-of-loss and proportional contracts, the Company is potentially subject to an additional timing lag in the receipt of information as the primary insurer reports to the broker who in turn reports to the Company. Since the Company relies on information regarding paid losses, case reserves and IBNR provided by ceding companies to estimate its liability for unpaid losses and loss adjustment expenses ("LAE"), certain procedures are maintained in order to help determine the completeness and accuracy of such information. Periodically, management assesses the reporting activities of its ceding companies on the basis of qualitative and quantitative criteria. In addition to conferring with ceding companies or brokers on claims matters, our claims personnel conduct periodic audits of specific claims and the overall claims procedures of ceding companies at their offices. The Company relies on its ability to effectively monitor the claims handling and claims reserving practices of ceding companies in order to help establish the proper reinsurance premium for reinsurance agreements and to establish proper loss reserves. Disputes with ceding companies have been rare and generally have been resolved through negotiation. In addition to information received from ceding companies on reported claims, the Company also utilizes information on the pattern of ceding company loss reporting and loss settlements from previous catastrophic events in order to estimate the ultimate liability related to catastrophic events such as hurricanes. Commercial catastrophe model analyses and zonal aggregate exposures are utilized to assess potential client loss before and after an event. Initial cedant loss reports are generally obtained shortly after a catastrophic event, with subsequent updates received as new information becomes available. The Company actively requests loss updates from cedants periodically while there is still considerable uncertainty for an event, often for the first year following an event. The Company's claim settlement processes also incorporate an update to the total loss reserve at the time a claim payment is made to a ceding company. While the reliance on loss reports from ceding companies may increase the level of uncertainty associated with the estimation of total loss reserves for property catastrophe reinsurance relative to direct property insurance, there are several factors which serve to reduce the uncertainty in loss reserve estimates for property catastrophe reinsurance. First, for large natural catastrophe events, aggregate limits in property catastrophe reinsurance contracts are in some cases fully exhausted by the loss reserve estimates. Second, as a reinsurer, the Company has access to information from a broad cross section of the insurance industry. The Company utilizes such information in order to perform consistency checks on the data provided by ceding companies and is able to identify trends in loss reporting and settlement activity and incorporate such information in the estimate of IBNR reserves. Finally, the Company also supplements the loss information received from cedants with loss estimates developed by market share techniques and/or from third party catastrophe models applied to exposure data supplied by cedants. IBNR Reserves IBNR reserves represent management’s best estimate, at a given point in time, of the amount in excess of case reserves that is needed for the future settlement and loss adjustment costs associated with claims incurred. It is possible that the ultimate liability may differ materially from these estimates. Because the ultimate amount of unpaid losses and LAE is uncertain, management believes that quantitative techniques to estimate these amounts are enhanced by professional and managerial judgment. Management reviews the IBNR estimates produced by its actuarial department and determines its best estimate of the liabilities to record in the financial statements. The Company considers this single point estimate to be the mean expected outcome. IBNR reserves are estimated by the Company's actuaries using several standard actuarial methodologies including the loss ratio method, the loss development or chain ladder method, the Bornhuetter-Ferguson ("BF") method and frequency and severity approaches. IBNR related to a specific event may be based on the estimated exposure to an industry loss and may include the use of catastrophe modeling software. On a quarterly basis, IBNR reserves are reviewed by the Company's actuaries, and are adjusted as new information becomes available. Any such adjustments are accounted for as changes in estimates and are reflected in the results of operations in the period in which they are made. The Company's actuaries use one set of assumptions in calculating the single point estimate, which includes actual loss data, loss development factors, loss ratios, reported claim frequency and severity. The actuarial reviews and documentation are completed in accordance with professional actuarial standards with reserves established on a basis consistent with GAAP. The selected assumptions reflect the actuary’s judgment based on historical data and experience combined with information concerning current underwriting, economic, judicial, regulatory and other influences on ultimate claim settlements. When estimating IBNR reserves, each insurance and reinsurance business unit segregates business into exposure classes. Within each class, the business is further segregated by either the year in which the contract incepted ("underwriting year"), the year in which the claim occurred ("accident year"), or the year in which the claim is reported ("report year"). Within the Insurance Segment, reviews are on an accident year, underwriting year, or report year basis depending on the nature of the business. The Reinsurance segment is reviewed on an underwriting year basis. In each case, management believes the selected method most accurately represents the economic condition of the business. Generally, initial actuarial estimates of IBNR reserves not related to a specific event are based on the loss ratio method applied to each class of business. Actual paid losses and case reserves ("reported losses") are subtracted from expected ultimate losses to determine IBNR reserves. Estimates of the initial expected ultimate losses involve management judgment and are based on historical information for that class of business, which includes loss ratios, market conditions, changes in pricing and conditions, underwriting changes, changes in claims emergence, and other factors that may influence expected ultimate losses. Over time, as greater numbers of claims are reported, actuarial estimates of IBNR are based on the BF method and loss development techniques. The BF method utilizes actual loss data and the expected patterns of loss emergence, combined with an initial expectation of ultimate losses to determine an estimate of ultimate losses. This method may be appropriate when there is limited actual loss data and a relatively less stable pattern of loss emergence. The chain ladder method utilizes actual loss and expected patterns of loss emergence to determine an estimate of ultimate losses that is independent of the initial expectation of ultimate losses. This method may be appropriate when there is a relatively stable pattern of loss emergence and a relatively larger number of reported claims. Multiple estimates of ultimate losses using a variety of actuarial methods are calculated for each class of business for each year of loss experience. The Company's actuaries look at each class and determine the most appropriate point estimate based on the characteristics of the particular class and other relevant factors, such as historical ultimate loss ratios, the presence of individual large losses, and known occurrences that have not yet resulted in reported losses. Once the actuaries make their determination of the most appropriate point estimate for each class, this information is aggregated and presented to management for review and approval. The pattern of loss emergence is determined using actuarial analysis and judgment and is based on the historical patterns of the recording of paid and reported losses, as well as industry information. Information that may cause historical patterns to differ from future patterns is considered and reflected in expected patterns as appropriate. For property, marine and aviation insurance, losses are generally reported within 2 to 3 years from the beginning of the accident year. For casualty insurance, loss emergence patterns can vary from 3 years to over 20 years depending on the type of business. For other insurance, loss emergence patterns generally fall within these ranges. For reinsurance business, loss reporting lags the corresponding insurance classes often by at least one quarter due to the need for loss information to flow from the ceding companies to us generally via reinsurance intermediaries. Such lags in loss reporting are reflected in the actuary’s selections of loss reporting patterns used in establishing our reserves. Such estimates are not precise because, among other things, they are based on predictions of future developments and estimates of future trends in claim severity, claim frequency and other issues. In the process of estimating IBNR reserves, provisions for economic inflation and changes in the social and legal environment are considered, but involve considerable judgment. When estimating IBNR reserves, more judgment is typically required for lines of business with longer loss emergence patterns. Due to the low frequency and high severity nature of some of the business the Company underwrites, our reserve estimates are highly dependent on actuarial and management judgment and are therefore uncertain. In property classes, there can be additional uncertainty in loss estimation related to large catastrophe events. With wind events, such as hurricanes, the damage assessment process may take more than a year. The cost of claims is subject to volatility due to supply shortages for construction materials and labor. In the case of earthquakes, the damage assessment process may take several years as buildings are discovered to have structural weaknesses not initially detected. The uncertainty inherent in IBNR reserve estimates is particularly pronounced for casualty coverages, such as excess liability, professional liability and workers’ compensation, where information emerges relatively slowly over time. The three types of property and casualty reserve exposure with the longest tails included in the Company's portfolio are: • high layer excess casualty insurance; • casualty reinsurance; and • discontinued asbestos and run-off environmental insurance and reinsurance liabilities. Certain aspects of casualty operations complicate the actuarial process for establishing reserves. Certain casualty business written by insurance operations is high layer excess casualty business, meaning that liability attaches after large deductibles, including self-insurance or insurance from other sources. The Company began writing this type of business in 1986 and issued policies in forms that were different from traditional policies used by the industry at that time. Initially, there was a lack of industry data available for this type of business. Consequently, the basis for establishing loss reserves for this type of business was largely based upon judgment and the Company's reported loss experience, which was used as a basis for determining ultimate losses and, therefore, IBNR reserves. Over time, the amount of available historical loss experience data has increased. As a result, there is a larger statistical base to assist in establishing reserves for these excess casualty insurance claims. High layer excess casualty insurance claims typically involve claims relating to (i) a "shock loss" such as an explosion or transportation accident causing severe damage to persons and/or property over a short period of time, (ii) a "non-shock" loss where a large number of claimants are exposed to injurious conditions over a longer period of time, such as exposure to chemicals or pharmaceuticals or (iii) a professional liability loss such as a medical malpractice claim. In each case, these claims are ultimately settled following extensive negotiations and legal proceedings. This process typically takes 5 to 15 years following the date of loss. Reinsurance operations by their nature add further complications to the reserving process, particularly for the casualty business written, in that there is an inherent lag in the timing and reporting of a loss event from an insured or ceding company to the reinsurer. This reporting lag creates an even longer period of time between the policy inception and when a claim is finally settled. As a result, more judgment is required to establish reserves for ultimate claims in reinsurance operations. Casualty reinsurance business involves reserving methods that generally include historical aggregated claim information as reported by ceding companies, combined with the results of claims and underwriting reviews of a sample of the ceding company’s claims and underwriting files. Therefore, we do not always receive detailed claim information for this line of business. Discontinued asbestos and run-off environmental liabilities are attached to certain policies previously written by NAC Re Corp. (now known as XL Reinsurance America Inc.), prior to being acquired by the Company; from business of Winterthur purchased by the Company from AXA Insurance in 2001; from a loss portfolio transfer in 2006; and acquired as a result of the Catlin Acquisition. At December 31, 2016 , total gross unpaid losses and loss expenses with respect to these businesses represented less than 1% of unpaid losses and loss expenses of the Company. Unpaid losses and loss expenses prior to reinsurance recoveries for the indicated years ended December 31 comprise the following: (U.S. dollars in thousands) 2016 2015 Reserve for reported losses and loss expenses $ 10,343,481 $ 10,293,448 Reserve for losses incurred but not reported 15,596,090 15,146,296 Unpaid losses and loss expenses $ 25,939,571 $ 25,439,744 Claims Development Management has determined that the appropriate level of disaggregation for the incurred and paid claims development information best falls into six categories within its two operating segments. This level of disaggregation is consistent with the Company's historical disclosure levels and provides groupings of the Company's insurance and reinsurance businesses of a credible size and with similar claim development characteristics, particularly payment patterns. It should be noted that when estimating IBNR reserves, the Company's Insurance and Reinsurance segments segregate business into exposure classes and over 250 classes are reviewed in total. Furthermore, large losses and catastrophe events are evaluated separately. As noted previously, reserve reviews are carried out on an accident year, underwriting year or report year basis depending on the nature of the business. Typically, reserve reviews are carried out gross of reinsurance with ceded reinsurance recoveries evaluated separately to arrive at net reserves. However, in accordance with accounting guidance, the disclosures presented herein are accident year triangles, presented net of reinsurance recoverables. Underwriting year triangles are converted to an accident year basis using assumptions consistent with the underlying premium earning profiles and considering large losses in their respective accident year. Similarly, ceded reinsurance recoverables are allocated to accident year and class of business in order to present net accident year triangles. While we have compiled the triangles on a best efforts basis, the allocation bases required to develop historical net accident year triangles should be viewed as approximations only. Within the Insurance segment, there are four business groups: Professional; Casualty and other; Energy, Property and Construction ("EPC"); and Specialty. Within the Reinsurance segment, all major products fall within two categories: Property and Other Short-Tail Lines, and Casualty and Other Long-Tail Lines. The Company has also provided aggregate triangles for the total Company and the Insurance and Reinsurance segments to reflect the levels at which the Company manages its business. The nature of the Company's high excess of loss liability and catastrophe business can result in loss events that are both irregular and significant. Similarly, adjustments to reserves for individual years can be irregular and significant. Such adjustments are part of the normal course of business of the Company. There is no assurance that conditions and trends that have affected the development of liabilities in the past will continue. Furthermore, changes in business mix over time, including discontinuation of certain classes of business and growth in others, can impact development patterns. Accordingly, it may not be appropriate to extrapolate future redundancies or deficiencies based on the Company's historical results. As discussed in further detail in part (c), except for certain workers’ compensation (including long term disability) liabilities and certain bodily injury liability claims, emanating from U.K. exposures, predominantly from the U.K. motor liability portfolio, the Company does not discount its unpaid losses and loss expenses. The development in the tables included herein is presented on a gross of discount basis, reflecting the undiscounted case reserves established using a tabular reserving methodology and the undiscounted IBNR. The amount of discount is then determined for both Case and IBNR reserves and booked accordingly. The amount of discount is included in the reconciliation of the reserves to the Consolidated Balance Sheet. As a result of the Catlin Acquisition in 2015 as noted in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition , the Company acquired approximately $5.4 billion of unpaid claims liability, net of reinsurance, as well as $101.3 million of unpaid claims liability, net of reinsurance due to the Allied Acquisition in 2016 as noted in Note 2(c), "Acquisitions and Disposals - Allied Acquisition ." For purposes of this disclosure, the Company has applied the retrospective method for these acquired reserves, including the combined companies' incurred and paid claim development histories throughout the tables. It should be noted that historical reserves for the acquired businesses were established by the respective companies using methods, assumptions and procedures then in effect which may differ from the Company's current reserving bases. Accordingly, it may not be appropriate to extrapolate future redundancies or deficiencies based on the aggregated historical results shown in the triangles. The Company has also revalued all historical data using exchange rates at December 31, 2016 in order to mitigate the effect of foreign exchange on the development throughout the triangles. Due to currency mix changes from one year end to the next, revaluation of incurred losses will result in different year-on-year movements within the triangles with each annual presentation. This approach for handling foreign exchange movements within the triangles differs somewhat from the underlying calculation of prior year development in our financial statements due the inclusion of historical loss payments as well as reserves and the level of granularity used in the calculation. The differences have been deemed not to be material. The number of reported claims is provided for the Insurance segment on a per claim basis and excludes those claims which closed with no payment. It should be noted that certain claims may eventually close with no payment in the future at which time the claims will be excluded on a prospective basis. The number of reported claims can vary over time due to changes in mix of business and policy terms and conditions. For the Reinsurance segment, the number of reported claims is not provided due to the common industry practice of cedants reporting loss information for proportional treaties on a bulk basis without comprehensive claim details. Therefore, it is impractical to provide meaningful claim count detail for our Reinsurance business. The Average Annual Percentage Payout of Incurred Losses for each age has been derived using a weighted average of all cumulative paid amounts as a percentage of 2016 incurred losses and allocated loss expenses. The average annual percentage payout can change over time due to changes in business mix, policy terms and conditions as well as ceded reinsurance arrangements. As previously noted, the process of establishing reserves for unpaid P&C claims can be complex and is subject to considerable variability, as it requires the use of judgment to make informed estimates. These estimates are based on numerous factors, and may be revised as additional experience and data become available, as new or improved methodologies are developed or as current laws change. In addition, there is no assurance that conditions and trends that have affected the development of liabilities in the past will continue. This variability may result in either favorable or adverse development in the Incurred Loss and Allocated Loss Expense triangles provided by the Company. The variability experienced to date has been in line with management’s expectations given the underlying business written by the Company. We have provided additional commentary for the individual categories below: For the Insurance Segment in total, while individual accident years have both favorable and adverse incremental development across the triangle, accident years 2007 to 2013 have all developed favorably since the first evaluation. The 2014 and 2015 accident years reflect modest adverse development due primarily to large loss activity in several lines that the Company does not view as a trend. In addition, the Company notes that these accident years are still relatively immature. For the Insurance EPC category, individual accident years have generally developed favorably as updated loss estimates were received and volatility in the loss estimates decreased. The 2014 accident year experienced adverse development from the 2014 evaluation to the 2015 evaluation due to development on a large fire loss which occurred in late December 2014. The 2014 accident year then developed favorably from the 2015 evaluation to the 2016 evaluation. The 2015 accident year experienced adverse development from the first evaluation in 2015 to the second evaluation in 2016 due to movements on several claims in the international property and construction businesses. For the Insurance Specialty category, individual accident years have generally developed favorably as updated loss estimates were received and volatility in the loss estimates decreased. This category includes a range of businesses with both short-tail and medium-tail exposures. Typically, development in the second year relates to short-tail lines with development on medium-tail business being reflected at subsequent evaluations. For the Insurance Professional category, individual accident years have both favorable and adverse development across the triangle. These developments relate to the complexity associated with claims in this class of business. In 2008, the Company strengthened its reserves for the 2007 report/accident year due to the developing subprime-credit crisis. Due to the claims-made nature of the underlying Professional policies, the subprime-credit crisis impacted the 2008 to 2012 report years and reserves were re-allocated from the 2007 report year to these later years as claims developed. The cumulative impact of the credit crisis and developing loss trends were more severe than originally expected for these years. The 2014 and 2015 report years have experienced modest adverse development due to large loss activity in the international financial lines management liability book and the discontinued design subcontractors default portfolio. For the Insurance Casualty category, individual accident years have both favorable and adverse development across the triangle. These developments relate to the complexity associated with claims in this class of business and the high level of attachment of the Company’s excess policies. The 2010 accident year experienced more adverse development than other accident years due to development on the Deepwater Horizon event. The 2013 to 2015 accident years reflect modest adverse development due to large loss activity relating to the excess casualty portfolio and strengthening of the excess and surplus portfolio and the newly acquired Allied business. For the Reinsurance Segment in total, while individual accident years have both favorable and adverse incremental development across the triangle, all accident years except for the 2010 accident year developed favorably since the first evaluation. The adverse development since the first evaluation for the 2010 accident year was very modest. For the Reinsurance Property and Other Short Tail category, individual accident years have generally developed favorably as updated loss estimates were received and volatility in the loss estimates decreased. The two outliers were the 2010 and 2012 accident years where there was modest adverse development related to large loss events from the business acquired in the Catlin Acquisition. Specifically, the 2010 adverse development relates to the Buncefield Explosion and the New Zealand Darfield Earthquake and the 2012 development relates to Costa Concordia and Superstorm Sandy. The favorable development on the 2011 year relates in part to reductions on the Japan Earthquake and Tsunami event also within the business acquired in the Catlin Acquisition. As noted earlier, the historical reserves for the acquired businesses were established by the respective companies using methods, assumptions and procedures then in effect which may differ from the Company's current reserving bases. For the Reinsurance Casualty and Other Long Tail category, the earlier years had modest favorable development and the later years had modest adverse development. The adverse development for the later accident years relates to changes in reserving methodology for certain long tailed lines of business that occurred in calendar years 2012 and 2015. In 2012, the Company changed its methodology to hold an explicit discount on loss reserves for U.K. bodily injury claims expected to settle via Periodical Payment Orders ("PPOs"). As these claims became more prevalent and costly, reserves were strengthened on an undiscounted basis. However, with the implementation of discounting, there was a minimal change in the loss reserves, net of the discount. Similarly, a significant portion of the increase in the Incurred Losses and Allocated Loss Expense, Net of Reinsurance for the 2015 calendar year is due to a change in the methodology used to determine the undiscounted ultimate losses for the reinsurance workers' compensation liabilities acquired in the Catlin Acquisition resulting in a large increase in the undiscounted losses but an insignificant change in the discounted losses. Total Property and Casualty (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 4,632,657 $ 4,806,850 $ 4,718,961 $ 4,684,540 $ 4,689,256 $ 4,569,019 $ 4,541,978 $ 4,519,599 $ 4,432,150 $ 4,390,981 $ 246,827 N/A 2008 5,504,796 5,575,015 5,503,422 5,524,325 5,479,907 5,449,364 5,417,072 5,357,648 5,322,204 307,738 N/A 2009 4,622,547 4,627,569 4,542,408 4,556,902 4,550,362 4,550,542 4,422,167 4,392,904 317,583 N/A 2010 4,983,044 5,111,634 5,002,061 5,026,101 4,974,782 4,957,474 4,981,939 464,306 N/A 2011 6,236,775 6,187,474 6,111,779 5,980,635 6,116,046 6,083,796 558,008 N/A 2012 5,697,958 5,660,616 5,640,576 5,754,387 5,663,926 715,827 N/A 2013 5,558,316 5,554,791 5,523,695 5,426,144 1,082,491 N/A 2014 5,183,056 5,369,393 5,397,264 1,396,883 N/A 2015 5,354,494 5,498,206 1,962,006 N/A 2016 6,005,506 3,425,518 N/A $ 53,162,870 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Ye

Future Policy Benefit Reserve

Future Policy Benefit Reserve	12 Months Ended
	Dec. 31, 2016
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Future policy benefit reserve	Future Policy Benefit Reserves Net future policy benefit reserves are comprised of the following: As of December 31 (U.S. dollars in thousands) 2016 2015 Traditional Life $ 737,252 $ 792,001 Annuities 2,768,795 3,371,499 Gross future policy benefit reserves $ 3,506,047 $ 4,163,500 Reinsurance recoverable - GreyCastle Life Retro Arrangements (3,072,615 ) (3,719,131 ) Reinsurance recoverable - U.S. Term Life Retro Arrangements (270,238 ) (284,481 ) Reinsurance recoverable - Other life retrocessions (10,997 ) (13,801 ) Net future policy benefit reserves $ 152,197 $ 146,087 The Company entered into long duration contracts that subject the Company to mortality and morbidity risks and that were accounted for as life premiums earned. Future policy benefit reserves were established using appropriate assumptions for investment yields, mortality, and expenses, including a provision for adverse deviation. At December 31, 2016 and 2015 , the average interest rate used for the determination of the future policy benefits for these contracts was 4.0% and 3.3% , respectively. Gross future policy benefit reserves for the years ended December 31, 2016 and 2015 were $3.5 billion and $4.2 billion , respectively. The decrease in gross future policy benefit reserves during 2016 was from normal course releases on single premium annuities in line with the benefits paid and mortality of underlying policyholders, as well as foreign exchange movements. Under the terms of the transaction described in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ," the Company has reinsured $3.1 billion and $3.7 billion at December 31, 2016 and 2015 , respectively, of its future policy benefit reserves under the GreyCastle Life Retro Arrangements. The Company continues to own, on a funds withheld basis, assets supporting the GreyCastle Life Retro Arrangements consisting of cash, fixed maturity securities and accrued interest. Based upon the contractual right of offset, the funds withheld liability owing to GCLR is recorded net of future policy benefit reserves recoverable, and is included within "Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable)" on the consolidated balance sheets, and is comprised of the following at December 31, 2016 and 2015 : (U.S. dollars in thousands) 2016 2015 Assets held on a funds withheld basis relating to the GreyCastle Life Retro Arrangements $ 4,071,583 $ 4,633,760 Reinsurance recoverable from GCLR (3,072,615 ) (3,719,131 ) Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable) $ 998,968 $ 914,629 The Company has also reinsured an additional $270.2 million and $284.5 million at December 31, 2016 and 2015 , respectively, of its U.S. Term Life future policy benefit reserves ("U.S. Term Life Retro Arrangements"). The Company continues to own, on a funds withheld basis, assets supporting the U.S. Term Life Retro Arrangements. Based upon the contractual right of offset, the funds withheld liability is recorded net of future policy benefit reserves recoverable, and is included within "Reinsurance balances payable" on the consolidated balance sheets.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The Company utilizes reinsurance and retrocession agreements principally to increase aggregate capacity and to reduce the risk of loss on business assumed. The Company’s reinsurance and retrocession agreements provide for recovery of a portion of losses and loss expenses from reinsurers, and reinsurance recoverables are recorded as assets. The Company is liable if the reinsurers are unable to satisfy their obligations under the agreements. Under its reinsurance security policy, the Company seeks to cede business to reinsurers generally with a financial strength rating of "A" or better. The Company considers reinsurers that are not rated or do not fall within the above rating categories and may grant exceptions to the Company’s general policy on a case-by-case basis. The effect of reinsurance and retrocessional activity on premiums written and earned from property and casualty operations is shown below: (U.S. dollars in thousands) Premiums Written Year Ended December 31, Premiums Earned Year Ended December 31, 2016 2015 2014 2016 2015 2014 Direct $ 9,166,627 $ 7,847,236 $ 5,450,868 $ 9,142,690 $ 7,717,173 $ 5,173,403 Assumed 4,458,981 2,821,771 2,310,621 4,074,817 3,465,421 2,343,329 Ceded (3,394,972 ) (2,780,183 ) (1,994,280 ) (3,451,620 ) (3,018,410 ) (1,799,294 ) Net $ 10,230,636 $ 7,888,824 $ 5,767,209 $ 9,765,887 $ 8,164,184 $ 5,717,438 The Company recorded reinsurance recoveries on losses and loss expenses incurred of $1.7 billion , $1.6 billion and $0.7 billion for the years ended December 31, 2016, 2015 and 2014 , respectively. The following table presents an analysis of total unpaid losses and loss expenses recoverable for the years ended December 31: (U.S. dollars in thousands) 2016 2015 P&C Operations $ 5,480,300 $ 5,248,905 Corporate and Other 10,997 13,801 Total unpaid losses and loss expenses recoverable $ 5,491,297 $ 5,262,706 The table above excludes a combined $3.1 billion and $0.3 billion of the Company's future policy benefit reserve recoverables under the GreyCastle Life Retro Arrangements and U.S. Term Life Retro Arrangements, as defined in Note 11, "Future Policy Benefit Reserves ," respectively, and are also excluded from the remainder of this disclosure. At December 31, 2016 and 2015 , the total reinsurance assets of $6.1 billion and $5.7 billion , respectively, included reinsurance balances receivable for paid losses and loss expenses of $577.5 million and $418.7 million , respectively, with $5.5 billion and $5.3 billion of unpaid losses and loss expenses recoverable, including ceded losses incurred but not reported for each year end. Although the contractual obligation of individual reinsurers to pay their reinsurance obligations is based on specific contract provisions, the collectibility of such amounts requires significant estimation by management. The majority of the balance the Company has accrued as recoverable will not be due for collection until sometime in the future. Over this period of time, economic conditions and operational performance of a particular reinsurer may impact its ability to meet these obligations and, while it may continue to acknowledge its contractual obligation to do so, it may not have the financial resources or willingness to fully meet its obligations to the Company. At December 31, 2016 and 2015 , the allowance for uncollectible reinsurance relating to both reinsurance balances receivable and unpaid losses and loss expenses recoverable was $62.8 million and $82.1 million , respectively. To estimate the provision for uncollectible reinsurance recoverable, the reinsurance recoverable must first be allocated to applicable reinsurers. As part of this process, ceded IBNR is allocated by reinsurer. The allocations are generally based on historical relationships between gross and ceded losses. If actual experience varies materially from historical experience, the allocation of reinsurance recoverable by reinsurer will change. The Company uses a default analysis to estimate uncollectible reinsurance recoverables. The primary components of the default analysis are reinsurance recoverable balances by reinsurer, net of collateral, and default factors used to determine the portion of a reinsurer’s balance deemed uncollectible. The definition of collateral for this purpose requires some judgment and is generally limited to assets held in trust, letters of credit, and liabilities held by the Company with the same legal entity for which the Company believes there is a right of offset. The Company is the beneficiary of letters of credit, trust accounts and funds withheld in the aggregate amount of $4.1 billion and $3.8 billion at December 31, 2016 and 2015 , respectively, collateralizing reinsurance recoverables with respect to certain reinsurers. Default factors require considerable judgment and are determined using the current financial strength rating, or rating equivalent, of each reinsurer as well as other key considerations and assumptions. The total allowance recorded relating to unpaid loss and loss expense recoverables was $42.1 million and $58.2 million at December 31, 2016 and 2015 , respectively. The Company uses an aging analysis to estimate uncollectible reinsurance balances receivable relating to paid losses in addition to recording allowances relating to any specific balances with known collectibility issues, irrespective of aging. The balances are aged from the date the expected recovery was billed to the reinsurer. Provisions are applied at specified percentages of the outstanding balances based upon the aging profile. Allowances otherwise required as a result of the aging process may not be recorded to the extent that specific facts and circumstances exist that lead management to believe that amounts will ultimately be collectible. The total allowance recorded relating to reinsurance balances receivable was $20.7 million and $23.9 million at December 31, 2016 and 2015 , respectively. At December 31, 2016 , the use of different assumptions within the model could have a material effect on the bad debt provision reflected in the Company’s Consolidated Financial Statements. To the extent the creditworthiness of the Company’s reinsurers was to deteriorate due to an adverse event affecting the reinsurance industry, such as a large number of major catastrophes, actual uncollectible amounts could be significantly greater than the Company’s bad debt provision. Such an event could have a material adverse effect on the Company’s financial condition, results of operations, and cash flows. At December 31, 2016 and 2015 , approximately 95% and 96% , respectively, of the total outstanding unpaid loss and loss expense recoverable and reinsurance balances receivable, net of collateral held, was due from reinsurers with a financial strength rating of "A" or better. The following is an analysis of the total recoverable and reinsurance balances receivable, net of collateral held, at December 31, 2016 , by reinsurers owing 3% or more of such total: Name of Reinsurer Reinsurer Financial Strength Rating % of Total Munich Reinsurance Co. AA-/Stable 25.6 % Lloyd's Syndicates A+/Stable 15.9 % Swiss Reinsurance Co. AA-/Stable 7.2 % Transatlantic Reinsurance Company A+/Stable 4.1 % Arch Reinsurance Company A+/Negative 3.7 % AXIS Reinsurance Co. A+/Stable 3.0 % The following table sets forth the ratings profile of the reinsurers that support the unpaid loss and loss expense recoverable and reinsurance balances receivable, net of collateral, at December 31, 2016 : Reinsurer Financial Strength Rating % of Total AAA 2.8 % AA 44.5 % A 48.1 % BBB 0.6 % BB and below 0.6 % Captives 3.3 % Not Rated 0.1 % Total 100.0 %

Deposit Liabilities

Deposit Liabilities	12 Months Ended
	Dec. 31, 2016
Deposit Contracts, Liabilities [Abstract]
Deposit liabilities	Deposit Liabilities The Company has entered into certain insurance and reinsurance policies that transfer insufficient risk under GAAP to be accounted for as insurance or reinsurance transactions and are recognized as deposits. These structured P&C agreements have been recorded as deposit liabilities and are initially matched by an equivalent amount of investments. The Company has investment risk related to its ability to generate sufficient investment income to enable the total invested assets to cover the payment of the ultimate liability. See Note 4, "Investments ," for further information relating to the Company’s net investment income as well as realized and unrealized investment (losses) gains. Each deposit liability accrues at a rate equal to the internal rate of return of the payment receipts and obligations due during the life of the agreement. Where the timing and/or amount of future payments are uncertain, cash flows reflecting the Company’s actuarially determined best estimates are utilized. Deposit liabilities are initially recorded at an amount equal to the assets received. At December 31, 2016 and 2015 , total deposit liabilities were $1.1 billion and $1.2 billion , respectively. For the years ended December 31, 2016, 2015 and 2014 , interest expense of $39.7 million , $42.2 million and $12.9 million , respectively, was recorded related to the accretion of deposit liabilities. During the second quarter of 2014, the Company negotiated the termination of one of its larger structured indemnity contracts and as a result a net decrease of $28.7 million was recorded to interest expense. See Note 7, "Derivative Instruments ," for further information.

Notes Payable and Debt and Fina

Notes Payable and Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Notes payable and debt and financing arrangements	Notes Payable and Debt and Financing Arrangements (a) Notes Payable and Debt The following table presents the Company's outstanding notes payable and debt as of December 31: (U.S. dollars in thousands) 2016 2015 Commitment/ In Use/ Commitment/ In Use/ Debt: 2.30% Senior Notes due 2018 $ 300,000 $ 298,686 $ 300,000 $ 298,015 5.75% Senior Notes due 2021 400,000 397,953 400,000 397,523 6.375% Senior Notes due 2024 350,000 349,139 350,000 349,029 4.45% Subordinated Notes due 2025 500,000 493,329 500,000 492,521 6.25% Senior Notes due 2027 325,000 323,375 325,000 323,218 5.25% Senior Notes due 2043 300,000 296,427 300,000 296,294 5.5% Subordinated Notes due 2045 500,000 488,768 500,000 488,370 Total debt carrying value $ 2,675,000 $ 2,647,677 $ 2,675,000 $ 2,644,970 _______________ (1) Excluded from the table are certain credit facilities under which the Company is permitted to utilize up to $1.0 billion and $1.4 billion as of December 31, 2016 and December 31, 2015 , respectively, for revolving loans to support general operating and financing needs. However, as of December 31, 2016 and December 31, 2015 , $245 million and $527.1 million , respectively, were utilized under these facilities to issue letters of credit, leaving $755.0 million and $ 822.9 million , respectively, available to support other operating and financing needs. (2) "In Use/Outstanding" data represent December 31, 2016 and December 31, 2015 accreted values. All outstanding debt of the Company at December 31, 2016 and 2015 , which is identified in the table above, was issued by XL-Cayman, a 100% owned subsidiary of XL-Bermuda (or, prior to the Redomestication, XL-Ireland). XL-Cayman's outstanding debt, other than the Senior Notes due 2024 and due 2027, historically was fully and unconditionally guaranteed by XL-Ireland. Such debt is now fully and unconditionally guaranteed by XL-Bermuda. In connection with the Redomestication and XL-Ireland's distribution of the ordinary shares of XL-Cayman to XL-Bermuda, on August 3, 2016, XL-Ireland was released as a guarantor under each of the applicable indentures, including as guarantor of the obligations of XL-Cayman under the outstanding securities issued pursuant to such indentures. The ability of XL-Cayman, like that of the Company, to obtain funds from its subsidiaries to satisfy any of its obligations, including under guarantees, is subject to certain contractual restrictions, applicable laws and statutory requirements of the various countries in which the subsidiaries operate, including, among others, Bermuda, the United States, Ireland, Switzerland and the United Kingdom. For details of the required statutory capital and surplus for the principal operating subsidiaries of the Company, see Item 8, Note 24, "Statutory Financial Data ." On September 15, 2014, the $600 million principal amount outstanding on the 5.25% Senior Notes issued by XL-Cayman was repaid at maturity. On March 30, 2015, XL-Cayman issued $500 million of subordinated notes due March 2025, with a fixed coupon of 4.45% , that were originally guaranteed by XL-Ireland, and are now guaranteed by XL-Bermuda. The notes are listed on the New York Stock Exchange. The notes were issued at 99.633% of the face amount and net proceeds were $492.2 million . Related expenses of the offering amounted to approximately $5.9 million . These costs were deferred and will be amortized over the term of the subordinated notes. On March 30, 2015, XL-Cayman issued $500 million of subordinated notes due March 2045, with a fixed coupon of 5.5% , that were originally guaranteed by XL-Ireland, and are now guaranteed by XL-Bermuda. The notes are listed on the New York Stock Exchange. The notes were issued at 99.115% of the face amount and net proceeds were $488.4 million . Related expenses of the offering amounted to approximately $7.2 million . These costs were deferred and will be amortized over the term of the subordinated notes. As a result of the Allied Acquisition described in Note 2(c), "Acquisitions and Disposals - Allied Acquisition " the Company assumed, and subsequently redeemed on June 15, 2016, $8.2 million of trust preferred securities, which bore interest at three-month LIBOR plus 3.75%. As a result of the Catlin Acquisition, the Company had assumed the following liabilities of Catlin, all of which were redeemed at par and extinguished in December of 2015: • Variable rate unsecured subordinated notes in the amounts of €7 million and $27 million due March 2035 and March 2036, respectively, issued by Catlin Underwriting (formerly Wellington Underwriting plc) in May 2006. The notes were subordinated to the claims of all senior creditors, as defined in the agreement governing the notes. The notes paid interest at a floating rate based on the rate on three-month deposits in U.S. dollars plus a margin of 295 basis points and 317 basis points, respectively. Interest was payable quarterly in arrears. • Variable rate unsecured subordinated notes in the amounts of $31 million , $10 million and €11 million due September 2036, issued by Catlin Underwriting, in July 2006. The notes were subordinated to the claims of all senior creditors, as defined in the agreement governing the notes. The notes paid interest at a floating rate based on the rate on three-month deposits in U.S. dollars plus a margin of 310 basis points, 300 basis points and 300 basis points, respectively. Interest is payable quarterly in arrears. The Company recognized a $5.6 million loss on early extinguishment of debt for the year ended December 31, 2015 . XL-Cayman and the Company were in compliance with all covenants at December 31, 2016 and 2015 , and the Company currently remains in compliance with all covenants. (b) Letter of Credit Facilities and Other Sources of Collateral The Company has several credit facilities provided on both syndicated and bilateral bases from commercial banks. As described in more detail below, the Company may utilize the full capacity of these credit facilities to issue letters of credit in support of non-admitted insurance and reinsurance operations in the U.S., and to meet capital requirements at Lloyd’s. Alternatively, under certain of the credit arrangements, the Company instead may elect to utilize a stated portion of such facilities' capacity for revolving loans to support other operating or financing needs, which would reduce the amount available for letters of credit. XL-Bermuda and several of its wholly-owned subsidiaries provide guarantees, on a joint and several basis, for obligations of the Company under certain of these facilities. The Company’s available credit facilities at December 31 were as follows: (U.S. dollars in thousands) 2016 (1) 2015 (1) Total available credit facilities – commitments (2) $ 3,991,687 $ 4,463,041 Letters of credit – in use $ 2,345,293 $ 2,515,653 Collateralized by certain assets of the Company’s investment portfolio 48.6 % 50.9 % ____________ (1) As of December 31, 2016 and December 31, 2015 , there were fifteen available credit facilities. (2) As of December 31, 2016 and December 31, 2015 the stated portion of allowable credit facilities permitted to be utilized for revolving loans was $1.0 billion and $1.4 billion , respectively. However, as of December 31, 2016 and December 31, 2015 , $245.0 million and $527.1 million , respectively, of such facilities' limits were utilized to issue letters of credit, leaving $755.0 million and $822.9 million , respectively, available either to issue additional letters of credit or to support other operating or financing needs under these particular facilities. Funds at Lloyd's In November 2015, we entered into four bilateral unsecured credit agreements, each providing for $125 million of letters of credit for Funds at Lloyd’s purposes (FAL Facility I, FAL Facility II, FAL Facility III, and FAL Facility IV, collectively the "FAL Facilities") for an aggregate amount of $500 million . Each of the FAL Facilities expires in 2019. The FAL Facilities replaced four unsecured bilateral facilities available for utilization by Catlin-Bermuda for Funds at Lloyd's purposes that we terminated in November 2015. Citi USA Facility On June 10, 2015, XL-Cayman entered into the fifth amendment to the credit agreement with Citicorp USA, Inc., as administrative agent and issuing lender, and the lenders party thereto (as amended, the "2015 Citi Facility"). The 2015 Citi Facility and a continuing agreement for standby letters of credit with Citibank, N.A. were initially entered into on May 7, 2013. The 2015 Citi Facility and the continuing agreement for standby letters of credit provides for issuance of letters of credit and revolving credit loans in an aggregate amount of up to $250 million . XL-Cayman has the option to increase the maximum amount of letters of credit and revolving credit loans available under the 2015 Citi Facility with the lender's and issuing lender's consent. The commitments under the 2015 Citi Facility expire on, and such credit facility is available until, the earlier of (i) June 20, 2017 and (ii) the date of termination in whole of the commitments upon an optional termination or reduction of the commitments by the account parties or upon the occurrence of certain events of default. Goldman Sachs Facility On September 8, 2015, XL-Cayman entered into a new credit agreement with Goldman Sachs Mortgage Company, as administrative agent and issuing lender, and a continuing agreement for standby letters of credit with Goldman Sachs Bank USA. On September 9, 14, and 16, 2015, XL-Cayman entered into first, second and third amendments, respectively, to such credit agreement (as amended, the Goldman Facility"). XL-Cayman entered into the Goldman Facility to replace the letter of credit capacity under a credit agreement with Citicorp USA, Inc. initially entered into on August 6, 2013 that expired by its terms on September 20, 2015. The Goldman Facility and the continuing agreement for standby letters of credit provide for issuance of letters of credit in an aggregate amount of up to $200 million . XL-Cayman has the option to increase the maximum amount of letters of credit available under the Goldman Facility with the lender's and issuing lender's consent. The commitments under the Goldman Facility expire on, and such credit facility is available until, the earlier of (i) September 20, 2017 and (ii) the date of termination in whole of the commitments upon an optional termination or reduction of the commitments by the account parties or upon the occurrence of certain events of default. Citi EU Facility On December 30, 2014, XLIB reduced the capacity available under a continuous letter of credit facility between XL Insurance (Bermuda) Ltd. and Citibank Europe plc (the "Citi EU Facility") from $750 million to $600 million . The Citi EU Facility is collateralized by pledged financial assets. Syndicated Facilities On August 5, 2016, the Company entered into agreements with a banking syndicate to provide: (a) a new secured credit facility that provides for the issuance of letters of credit up to $750 million (the "Secured Syndicated Facility"), and (b) a new unsecured credit facility that provides for the issuance of letters of credit and revolving credit loans up to $750 million (the "Unsecured Syndicated Facility", and together with the Secured Syndicated Facility, the "Syndicated Facilities"). The Company has the option to increase the maximum amount of letters of credit available under the facilities by $500 million in aggregate across the facilities. In connection with the Syndicated Facilities, the Company's previous syndicated credit agreements originally entered into in November 2013, as well as certain related security arrangements, were terminated. The commitments under the Syndicated Facilities are available until, the earlier of (i) August 5, 2021 (unless extended by the parties), and (ii) the date of termination in whole of the commitments upon an optional termination or reduction of the commitments by the account parties or upon the occurrence of certain events of default. The availability of letters of credit under the Secured Syndicated Facility is subject to a borrowing base requirement, determined on the basis of specified percentages of the face value of eligible categories of assets varying by type of collateral. In the event that such credit support is insufficient, the Company could be required to provide alternative security to cedants. This could take the form of insurance trusts supported by the investment portfolio or funds withheld (amounts retained by ceding companies to collateralize loss or premium reserves) using the Company's cash resources or combinations thereof. The face amount of letters of credit required is driven by, among other things, loss development of existing reserves, the payment pattern of such reserves, the expansion of business written by the Company and the loss experience of such business. London Market Facility The Company continues to maintain $250 million of available capacity pursuant to a continuous credit agreement between XL Bermuda Ltd and Citibank N.A. (the "London Market Facility") originally entered into in 1993, that is collateralized by pledged financial assets. Credit Agricole Facilities In November and December of 2016, we entered into two credit agreements with Credit Agricole Corporate and Investment Bank (“Credit Agricole Facility I” and “Credit Agricole Facility II,” respectively, and collectively, the “Credit Agricole Facilities”). Each credit agreement provides for the issuance of letters of credit in an amount up to $125 million . The commitments under the Credit Agricole Facilities expire on, and such facilities are available until, the earlier of (i) December 15, 2019, provided that, if neither the Company nor the lender provides notice to the other not more than 90 days, but at least 30 days, prior to such date, the commitment termination date will be extended to December 15, 2020, and (ii) the date of termination in whole of the commitments upon an optional termination or reduction of the commitments by the account parties or upon the occurrence of certain events of default. Facilities Assumed Through Catlin Acquisition As a result of the Catlin Acquisition on May 1, 2015, the Company assumed, and may continue to access, the following letter of credit facilities: • A bilateral facility pursuant to a continuous credit agreement, available for utilization by Catlin-Bermuda, collateralized by pledged financial assets (the "CICL Facility"). As of December 31, 2016 , $180 million of capacity was available under this facility. • A bilateral facility pursuant to a continuous credit agreement, available for utilization by Catlin Re Switzerland Ltd, collateralized by pledged financial assets (the "CRCH Facility"). As of December 31, 2016 , $250 million of capacity was available under this facility. • A facility managed by Lloyd's, acting for Catlin Syndicate 2003 (the "Syndicate 2003 Facility"). As of December 31, 2016 , $12 million of letters of credit were issued under this facility. In addition to letters of credit, the Company has established insurance trusts in the U.S. that provide cedants with statutory relief required under state insurance regulation in the U.S. It is anticipated that the commercial facilities may be renewed on expiry but such renewals are subject to the availability of credit from banks utilized by the Company and may be renewed with materially different terms and conditions. In the event that such credit support is insufficient, the Company could be required to provide alternative security to cedants. This could take the form of additional insurance trusts supported by the Company’s investment portfolio or funds withheld using the Company’s cash resources. The value of letters of credit required is driven by, among other things, loss development of existing reserves, the payment pattern of such reserves, the expansion of business written by the Company and the loss experience of such business. The majority of the Company’s bank facilities, indentures and other documents relating to the Company’s outstanding indebtedness (collectively, the "Company’s Debt Documents"), which are described above, contain cross acceleration or cross default provisions to each other and the Company’s Debt Documents contain affirmative covenants. These covenants provide for, among other things, a maximum ratio of total consolidated debt plus consolidated net worth. In addition, the Company's Debt Documents contain other customary affirmative and negative covenants as well as certain customary events of default. Generally, each of the Company's Debt Documents provide for an event of default in the event of bankruptcy, insolvency or reorganization of the Company, and the majority of the Company's bank facilities provide an event of default if there is a change of control in the Company. Given that many of the Company’s Debt Documents contain cross acceleration or cross default provisions, a default by one of these subsidiaries may result in all holders declaring their debt due and payable and accelerating all debt due under those documents. If this were to occur, the Company may not have funds sufficient at that time to repay any or all of such indebtedness.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related party transactions	Related Party Transactions (a) Investment Manager Affiliates At December 31, 2016 and 2015 , the Company owned minority stakes in four and six independent investment management companies ("Investment Manager Affiliates"), respectively, that are actively managing client capital and seeking growth opportunities. The Company also invests in certain of the funds and limited partnerships and other legal entities managed by these affiliates and through these funds and partnerships pays management and performance fees to the Company's Investment Manager Affiliates. In addition, at December 31, 2016 and 2015 , the company owned minority stakes in one and two independent firms, respectively, that provide technology and other services to alternative asset managers and allocators, respectively, and the results of the Company's interests in these enterprises are included in Investment Manager Affiliates. The Company pays fees to these Investment Manager Affiliates in exchange for them providing their services to the Company. The results of Investment Manager Affiliates are included in the Statement of Income under "income (loss) from operating affiliates." See Note 5, "Investments in Affiliates ," included herein, for further information. (b) Assumed Reinsurance Contracts In the normal course of business, the Company enters into assumed reinsurance contracts with certain of its other strategic affiliates, or their subsidiaries. During the years ended December 31, 2016, 2015 and 2014 , these contracts resulted in reported net premiums, reported net losses, and reported net acquisition costs as summarized below. (U.S. dollars in thousands) 2016 2015 2014 Reported net premiums $ 94,358 $ 42,042 $ 91,261 Reported net losses $ 44,728 $ 13,246 $ 38,927 Reported net acquisition costs $ 39,131 $ 14,682 $ 35,711 Results through April 1, 2015 include amounts under an assumed reinsurance contract with a wholly-owned subsidiary of ARX, an insurance operating affiliate of the Company through that date. The Company disposed of its investment in ARX on April 1, 2015, and thus, after that date, all amounts under this contract are no longer reported as related party transactions. See Note 2(f), "Acquisitions and Disposals - Sale of Operating Affiliate ." (c) New Ocean Commencing in 2014, several of the Company’s wholly-owned subsidiaries retroceded assumed reinsurance business to special purpose reinsurers that receive capital from funds managed by the Company's subsidiary, New Ocean Capital Management, as discussed in Note 16, "Variable Interest Entities ." Underwriting administration services are provided to the special purpose reinsurers by other subsidiaries of the Company under service fee agreements, while investment advisory services are provided by New Ocean Capital Management. During the year ended December 31, 2016 , ceded premiums earned, ceded losses and loss expenses incurred, ceding commission income, and other fee income related to these retrocessional contracts were not material to the Company. (d) New Energy On July 24, 2015, as described in Note 2(d), "Acquisitions and Disposals - New Energy Risk ," the Company completed its acquisition of 63.63% of the additional shares of New Energy for approximately $8.8 million , increasing its ownership of the entity to a majority portion 94.79% . These shares are held within the XL Innovate Fund. A substantial portion of the additional shares were purchased at directly from the family trusts of a Company employee, based on a market valuation of New Energy performed by an independent third party provider. The remaining 5.21% of equity shares of New Energy held by the family trusts of the employee was then contributed in-kind to XL Innovate Fund based on the share price implied by the independent valuation. Such contribution was made in partial satisfaction of the employee's aggregate 5.21% investment commitment to the Fund and resulted in XL Innovate Fund owning 100% of the net equity of New Energy, and the family trusts of the employee owning a 5.21% non-controlling equity interest in XL Innovate Fund. The employee serves as a member of the board of directors of both New Energy and XL Innovate Fund, and maintains responsibility over the business generated by New Energy. There were no other material transactions between the Company and this employee for the year ended December 31, 2016 .

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2016
Variable Interest Entities Disclosure [Abstract]
Variable interest entities	Variable Interest Entities At times, the Company has utilized variable interest entities ("VIEs") both indirectly and directly in the ordinary course of the Company's business. Within its investment portfolio, the Company has holdings in hedge funds, private equity funds and other investment vehicles. A number of these vehicles are considered VIEs based on their legal from and the generally passive role of their investors. As the Company lacks the ability to control the activities which most significantly impact the economic performance of these VIEs, the Company is not considered the primary beneficiary and does not consolidate these entities. The activities of the entities are generally limited to holding investments. The exposure to loss from these investments is limited to the carrying value of the investments at the balance sheet date. During the third quarter of 2013, the Company, along with other investors, formed New Ocean Capital Management to act as an investment manager that focuses on providing third-party investors access to insurance-linked securities and other insurance and reinsurance capital markets products. The Company holds a majority voting interest in New Ocean Capital Management through its ownership of common shares and, accordingly, the financial statements of New Ocean Capital Management have been included in the consolidated financial statements of the Company. None of the assets, liabilities, revenues or net income of New Ocean Management were material to the Company during the current year. The equity interest attributable to third party investors in New Ocean Capital Management recorded in the Company’s Consolidated Balance Sheets as "Non-controlling interest in equity of consolidated subsidiaries" was $1.0 million and $0.4 million at December 31, 2016 and December 31, 2015 , respectively. During the fourth quarter of 2013, the Company, along with other investors, formed a new Bermuda-based company, New Ocean Focus Cat Fund Ltd. ("New Ocean FCFL"), which is considered a VIE under GAAP. During the second quarter of 2014, the company formed another Bermuda-based investment company, New Ocean Market Value Cat Funds, Ltd. ("New Ocean MVCFL"), which is also considered a VIE under GAAP. New Ocean MVCFL primarily invests in insurance-linked securities, with a current focus on catastrophe bonds. During the year ended December 31, 2014, New Ocean FCFL invested in a special purpose Bermuda reinsurer, Vector Reinsurance Ltd ("Vector Re"), which was formed for the purpose of underwriting collateralized excess of loss reinsurance with a focus on global property catastrophe risks. During the first quarter of 2015, New Ocean MVCFL also invested in Vector Re. Most of Vector Re’s current underwriting activity relates to reinsurance business assumed from the Company's subsidiaries. Underwriting administration and claims services are provided to Vector Re by the Company under service fee contracts, while investment advisory services are provided by New Ocean Capital Management. The Company currently holds majority equity interests, which are considered to be the controlling financial interests, in New Ocean FCFL and New Ocean MVCFL, and by extension, Vector Re. Accordingly, included in the consolidated financial statements of the Company are the total net assets of New Ocean FCFL, New Ocean MVCFL and Vector Re of $223.4 million and $175.8 million as of December 31, 2016 and December 31, 2015 , respectively. The Company’s shares of revenue and net income in these VIEs were not material to the Company for the twelve months ended December 31, 2016 . All inter-company transactions between the Company's entities have been eliminated in consolidation. The equity interest attributable to third party investors in New Ocean FCFL, New Ocean MVCFL and Vector Re that is reflected in the Company’s Consolidated Balance Sheets as "Non-controlling interest in equity of consolidated subsidiaries" was $112.1 million and $70.5 million as of December 31, 2016 and December 31, 2015 , respectively.

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Retirement plans	Retirement Plans The Company provides pension benefits to eligible employees through various defined contribution and defined benefit retirement plans sponsored by the Company, which vary for each subsidiary. Plan assets are invested principally in equity securities and fixed maturities. (a) Defined contribution plans The Company has qualified defined contribution plans that are managed externally and to which employees and the Company contribute a certain percentage of the employee’s pensionable salary each month. The Company’s contribution generally vests after an employee has been with the Company for five years. The Company’s expenses for its qualified contributory defined contribution retirement plans were $88.3 million , $87.5 million and $56.6 million at December 31, 2016, 2015 and 2014 , respectively. (b) Defined benefit plans The Company maintains defined benefit plans that cover certain employees as follows: U.S. Plan A qualified non-contributory defined benefit pension plan exists to cover a number of U.S. employees. The plan was curtailed in 2002 and was closed to new entrants at that time. Under the terms of the curtailment, existing plan participants were no longer entitled to earn additional defined benefits for future services performed after the curtailment date; however, accrued benefits are eligible for annual cost-of-living increases. This plan also includes a non-qualified supplemental defined benefit plan designed to compensate individuals to the extent that their benefits under the Company’s qualified plan are curtailed due to IRS Code limitations. Benefits are based on years of service and compensation, as defined in the plan, during the highest consecutive three years of the employee’s last ten years of employment. In addition, pursuant to agreements entered into by the Company, certain former employees have received benefit type guarantees, not formally a part of any established plan. The liability recorded with respect to these agreements at each of December 31, 2016 and 2015 was $2.3 million and $3.2 million respectively, representing the entire unfunded projected benefit obligations. U.K. Plans A contributory defined benefit pension plan exists in the U.K., but has been closed to new entrants since 1996. Benefits are based on length of service and compensation as defined in the trust deed and rules. In addition, during 2003, six individuals, three of whom are still employed by the Company in the U.K., transferred from a defined benefit plan into a defined contribution plan. These employees have a contractual agreement with the Company that provides a "no worse than final salary pension" guarantee in the event that they are employed by the Company until retirement, under which the Company guarantees to top-up their defined contribution pension to the level of pension that they would have been entitled to receive had they remained in the defined benefit scheme. The pension liability recorded with respect to these individuals was $4.1 million and $4.8 million at December 31, 2016 and 2015 , respectively, representing the entire unfunded projected obligation. In connection with the Catlin Acquisition described in Note 3(e), "Acquisitions and Disposals - Catlin Acquisition ," the Company assumed additional assets and liabilities associated with a further U.K. defined benefit plan within Catlin. This plan has been closed to new members since 1993. The current membership consists only of pensioners and deferred members. Benefits are based on length of service and compensation. Other European Plans Certain contributory defined benefit pension plans exist in several European countries, most notably Germany, which are closed to new entrants. Benefits are generally based on length of service and compensation defined in the related agreements. The Company acquired certain defined benefit pension liabilities with the acquisition of XL GAPS in 2007. The related balances are not included in the tables below as the liabilities are insured under an annuity type contract. Funded Status - All Plans The funded status by geographical region of all the Company’s retirement plans at December 31, 2016 and 2015 is as follows: Funded Status 2016 2015 U.S. $ (14,093 ) $ (16,306 ) U.K. (2,316 ) (4,650 ) Other European (26,377 ) (21,807 ) Funded status – end of year $ (42,786 ) $ (42,763 ) The status of all the Company’s retirement plans at December 31, 2016 and 2015 is as follows: Change in projected benefit obligation (U.S. dollars in thousands) 2016 2015 Projected benefit obligation – beginning of year $ 122,165 $ 93,124 Projected benefit obligation assumed due to Catlin Acquisition — 28,414 Service cost (1) 1,701 1,494 Interest cost 5,126 4,382 Actuarial (gain) / loss 7,948 2,821 Benefits and expenses paid (5,977 ) (3,747 ) Foreign currency (gains) / losses (10,248 ) (4,047 ) Settlements (677 ) (276 ) Projected benefit obligation – end of year $ 120,038 $ 122,165 (1) Service costs include cost of living adjustments on curtailed plans. Change in plan assets (U.S. dollars in thousands) 2016 2015 Fair value of plan assets – beginning of year $ 79,402 $ 49,281 Fair value of plan assets acquired due to Catlin Acquisition — 33,131 Actual return on plan assets 8,499 (119 ) Employer contributions 2,077 1,775 Benefits and expenses paid (4,577 ) (3,305 ) Foreign currency gains / (losses) (8,149 ) (1,361 ) Fair value of plan assets – end of year $ 77,252 $ 79,402 Funded status – end of year $ (42,786 ) $ (42,763 ) Accrued pension liability $ 42,786 $ 42,763 The components of the net benefit cost for the years ended December 31, 2016, 2015 and 2014 are as follows: Components of net benefit cost (U.S. dollars in thousands) 2016 2015 2014 Service cost $ 1,701 $ 1,494 $ 1,279 Interest cost 5,126 4,382 3,747 Expected return on plan assets (4,357 ) (3,903 ) (2,859 ) Amortization of net actuarial loss 1,705 1,617 812 Net benefit cost $ 4,175 $ 3,590 $ 2,979 Assumptions - All Plans Several assumptions and statistical variables are used in the models to calculate the expenses and liability related to the plans. The Company, in consultation with its actuaries, determines assumptions about the discount rate, the expected rate of return on plan assets and the rate of compensation increase. The table below includes disclosure of these rates on a weighted-average basis, for the years ended December 31 as indicated: 2016 2015 U.S. Plans U.K. Plans Other European Plans U.S. Plans U.K. Plans Other European Plans Net Benefit Cost – Weighted-average assumptions Discount rate 4.25 % 2.74 % 1.33 % 3.91 % 3.70 % 2.42 % Expected long-term rate of return on plan assets 6.00 % 2.77 % N/A 6.00 % 3.48 % N/A Rate of compensation increase N/A 3.62 % 2.50 % N/A 3.96 % 2.50 % Benefit Obligation – Weighted-average assumptions Discount rate 4.04 % 2.76 % 1.33 % 4.25 % 3.70 % 2.42 % Rate of compensation increase N/A 3.62 % 2.50 % N/A 3.96 % 2.50 % The expected long-term rate of return assumption is determined by adding expected inflation to the expected long-term real rates of various asset classes taking into account expected volatility and correlation between the various asset classes. Plan Assets - All Plans The U.S. Plan assets at December 31, 2016 and 2015 consist of three mutual funds. The first fund seeks long-term capital appreciation. The fund invests primarily in Equity, Large Capital and Large Company Portfolio securities as well as Emerging Markets Assets. The second fund invests primarily in quality corporate and U.S. governmental bonds. The fund employs a high total investment return through a combination of current income and capital appreciation. The third fund seeks to outperform longer-duration benchmarks without excess volatility by investing primarily in longer duration, investment grade corporate and sovereign bonds. The fair value of the U.S. Plan assets at December 31, 2016 and 2015 was $38.7 million and $36.7 million , respectively. As the investments of the retirement plan are mutual funds, they fall within Level 1 in the fair value hierarchy. The inputs and methodologies used in determining the fair value of these assets are consistent with those used to measure our assets as set out in Note 8, "Fair Value Measurements ." The U.K. pension plan assets, including those acquired as part of the Catlin Acquisition, are held in a separate trustee administered fund to meet long term liabilities to past and present employees. The table below shows the composition of the plans' assets and the fair value of each major category of plan assets at December 31, 2016 and 2015 , as well as the potential returns of the different asset classes. The totals of the asset values held in various externally managed portfolios are provided by third party pricing vendors. There is no significant concentration of risk within plan assets. The assets in the plans and the expected rates of return were as follows: (U.S. dollars in thousands, except percentages) Expected Return on Assets for 2016 Fair Value at December 31, 2016 Expected Return on Assets for 2015 Fair Value at December 31, 2015 Equities ad Growth funds 5.7 % $ 9,122 6.2 % $ 7,893 Gilts 2.4 % 15,459 2.4 % 17,856 Corporate Bonds 3.3 % 13,850 3.4 % 16,915 Other (cash) 0.5 % 89 1.8 % 52 Total market fair value of assets $ 38,520 $ 42,716 Funding / Expected Cash Flows - U.S. Plan Under the U.S. defined benefit plans, the Company’s policy is to make annual contributions to the plan that are deductible for federal income tax purposes and that meet the minimum funding standards required by law. The contribution level is determined by utilizing the projected unit credit cost method and different actuarial assumptions than those used for pension expense purposes. The Company’s funding policy provides that contributions to the plan shall be at least equal to the minimum funding requirements of the Employee Retirement Income Security Act of 1974 ("ERISA"), as amended by the Pension Protection Act of 2006. During the fiscal year beginning January 1, 2017, the U.S. defined benefit plans expect to make contributions of $1.4 million . The estimated future benefit payments with respect to the U.S. defined benefit pension plans are as follows: (U.S. dollars in thousands) Retirement Plan Benefits Equalization Plan Total 2017 $ 1,029 $ 353 $ 1,382 2018 $ 1,057 $ 353 $ 1,410 2019 $ 1,226 $ 450 $ 1,676 2020 $ 1,389 $ 467 $ 1,856 2021 $ 1,683 $ 502 $ 2,185 2022-2026 $ 10,753 $ 2,823 $ 13,576 Funding - U.K. Plan The Company's U.K. plan administered for employees who joined prior to the Catlin Acquisition is subject to triennial funding valuations, the most recent of which was conducted as of June 30, 2015 and was reported in 2016. The $1.0 million deficit (calculated on a realistic basis) is being funded over a 4 -year period. With respect to the U.K. plan assumed as part of the Catlin Acquisition, the most recent funding valuation was prepared as at October 1, 2013. No contributions were required following that valuation. During 2017, it is expected that no contributions will be paid to the plan.

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 The creditworthiness of any counterparty is evaluated by the Company, taking into account credit ratings assigned by rating agencies. The credit approval process involves an assessment of factors including, among others, the counterparty and country and industry credit exposure limits. Collateral may be required, at the discretion of the Company, on certain transactions based on the creditworthiness of the counterparty. The areas where significant concentrations of credit risk may exist include unpaid losses and loss expenses recoverable and reinsurance balances receivable (collectively, "reinsurance assets") and in the investment fixed income portfolio. Reinsurance Assets The Company’s reinsurance assets result from reinsurance arrangements in the course of its operations. A credit exposure exists with respect to reinsurance assets as they may be uncollectible. The Company manages its credit risk in its reinsurance relationships by transacting with reinsurers that it considers financially sound, and if necessary, the Company may hold collateral in the form of funds, trust accounts and/or irrevocable letters of credit. This collateral can be drawn on for amounts that remain unpaid beyond specified time periods on an individual reinsurer basis. For further details regarding the Company’s reinsurance assets, see Note 12, "Reinsurance ." Fixed Income Portfolio The Company did not have an aggregate direct investment in any single corporate issuer in excess of 5% of the Company's shareholders’ equity at December 31, 2016 and 2015 . Corporate issuers represent only direct exposure to fixed maturities and short-term investments of the parent issuer and its subsidiaries. These exposures exclude asset and mortgage backed securities that were issued, sponsored or serviced by the parent and government-guaranteed issues, but does include covered bonds. Broker credit risk In addition, the Company underwrites a significant amount of its insurance and reinsurance property and casualty business through brokers and a credit risk exists should any of these brokers be unable to fulfill their contractual obligations with respect to the payments of insurance and reinsurance balances to the Company. During the three years ended December 31, 2016, 2015 and 2014 , P&C gross written premiums generated from or placed by the below companies individually accounted for more than 10% of the Company’s consolidated gross written premiums from P&C operations, as follows: (Percentage of consolidated gross written premiums from P&C operations) 2016 2015 2014 AON Corporation and subsidiaries 18 % 18 % 18 % Marsh & McLennan Companies 18 % 19 % 20 % Willis Group and subsidiaries 11 % 13 % 11 % These brokers are large, well established companies and there are no indications that any of them are financially troubled. No other broker and no one insured or reinsured accounted for more than 10% of gross premiums written from P&C operations in any of the three years ended December 31, 2016, 2015 and 2014 . (b) Other Investments The Company has committed to invest in certain private equity and private credit limited partnerships, limited liability companies or similar structures. At December 31, 2016 , the Company has unfunded commitments with these entities totaling $59.3 million over a weighted average period of 4.8 years. (c) Investments in Affiliates The Company has committed to invest in certain private equity and private credit limited partnerships, limited liability companies or similar structures where it accounts for its holdings in these structures under the equity method. At December 31, 2016 , the Company has unfunded commitments with these entities totaling to $237.1 million over a weighted average period of 4.9 years. (d) Properties The Company rents space for certain of its offices under leases that expire through 2031. Total rent expense under operating leases for the years ended December 31, 2016, 2015 and 2014 was approximately $68.0 million , $71.1 million and $36.6 million , respectively. Future minimum rental commitments under existing operating leases are expected to be as follows: Year Ended December 31, (U.S. dollars in thousands) 2017 $ 70,359 2018 62,590 2019 57,030 2020 51,566 2021 47,738 2022-2031 96,602 Total minimum future rentals $ 385,885 In 2003, the Company entered into a purchase, sale and leaseback transaction to acquire new office space in London. The Company has recognized a capital lease asset net of accumulated depreciation, of $55.5 million and $73.4 million , a capital lease liability of $89.9 million and $113.8 million , and a deferred gain liability of $16.9 million and $22.3 million related to the sale and leaseback, at December 31, 2016 and 2015 , respectively. The gain is being amortized to income in line with the amortization of the asset. The future minimum lease payments annually for the next five years are noted in the following table, as well as the aggregate for beyond five years. The total future minimum lease payments in the aggregate are expected to be $131.3 million . Year Ended December 31, (U.S. dollars in thousands) 2017 $ 9,998 2018 10,248 2019 10,504 2020 10,767 2021 11,036 2022-2031 78,736 Total minimum future lease payments $ 131,289 (e) Tax Matters XL-Bermuda is a Bermudian corporation and, except as described below, neither it nor its non-U.S. subsidiaries have paid U.S. corporate income taxes on the basis that they are not engaged in a trade or business or otherwise subject to taxation in the United States. However, because definitive identification of activities that constitute being engaged in a trade or business in the United States is not provided by the Internal Revenue Code of 1986 ("IRS Code"), regulations or court decisions, there can be no assurance that the Internal Revenue Service will not contend that the Company or its non-U.S. subsidiaries are engaged in a trade or business or otherwise subject to taxation in the United States. If the Company or its non-U.S. subsidiaries were considered to be engaged in a trade or business in the United States (and, if the Company or such subsidiaries were to qualify for the benefits under the income tax treaty between the United States and Bermuda and other countries in which the Company operates, such businesses would be considered to be attributable to a "permanent establishment" in the United States), the Company or such subsidiaries could be subject to U.S. tax at regular tax rates on their respective taxable income that is effectively connected with their U.S. trade or business plus an additional "branch profits" tax (at a rate as high as 30% ) on such income remaining after the regular tax, in which case there could be a significant adverse effect on the Company’s results of operations and financial condition. (f) Letters of Credit At December 31, 2016 and 2015 , $2.3 billion and $2.5 billion of letters of credit were outstanding, of which 48.6% and 50.9% , respectively, were collateralized by the Company’s investment portfolios, primarily supporting U.S. non-admitted business and the Company’s Lloyd’s syndicates’ capital requirements. (g) Litigation The Company and its subsidiaries are subject to litigation and arbitration in the normal course of business. These lawsuits and arbitrations principally involve claims on policies of insurance and contracts of reinsurance and are typical for the Company and for the property and casualty insurance and reinsurance industry in general. Such claims proceedings are considered in connection with the Company's loss and loss expense reserves. Reserves in varying amounts may or may not be established in respect of particular claims proceedings based on many factors, including the legal merits thereof. In addition to litigation relating to insurance and reinsurance claims, the Company and its subsidiaries are subject to lawsuits and regulatory actions in the normal course of business that do not arise from or directly relate to claims on insurance or reinsurance policies. This category of business litigation typically involves, among other things, allegations of underwriting errors or misconduct, employment claims, regulatory activity, shareholder disputes or disputes arising from business ventures. The status of these legal actions is actively monitored by management. Legal actions are subject to inherent uncertainties, and future events could change management's assessment of the probability or estimated amount of potential losses from pending or threatened legal actions. Based on available information, it is the opinion of management that the ultimate resolution of pending or threatened legal actions other than claims proceedings, both individually and in the aggregate, will not result in losses having a material adverse effect on the Company's financial position or liquidity at December 31, 2016 . If management believes that, based on available information, it is at least reasonably possible that a material loss (or additional material loss in excess of any accrual) will be incurred in connection with any legal actions other than claims proceedings, the Company discloses an estimate of the possible loss or range of loss, either individually or in the aggregate, as appropriate, if such an estimate can be made, or discloses that an estimate cannot be made. Based on the Company's assessment at December 31, 2016 , no such disclosures were considered necessary. (h) Financial Guarantee Exposures The Company's outstanding financial guarantee contracts at December 31, 2016 provided credit support for a variety of collateral types with the exposures constituting an aggregate amount of $80.8 million notional financial guarantee on two notes backed by zero coupon long dated bonds and bank perpetual securities, including some issued by European financial institutions. At December 31, 2016 and December 31, 2015 , the total gross claim liability recorded was nil , and the contracts had a weighted average contractual term to maturity of 23.2 years and 24.2 years , respectively. In February 2017, the Company negotiated the termination of these final two exposures. The Company will not recognize any insurance costs and will not realize any security valuation losses as a result of these terminations.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Share capital	Share Capital (a) Authorized and Issued As a result of the Redomestication discussed in Note 1(a), "Significant Accounting Policies - Basis of Preparation and Consolidation ," prior to July 25, 2016, share information relates to the ordinary shares of XL-Ireland and its consolidated subsidiaries. On and subsequent to July 25, 2016, share information relates to the common shares of XL-Bermuda and its consolidated subsidiaries. The authorized share capital of XL-Bermuda is $9,999,900 , divided into: (i) 500,000,000 common shares, par value $0.01 each and (ii) 499,990,000 shares, par value $0.01 . Holders of common shares are entitled to one vote for each share. In connection with the Catlin Acquisition described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," the Company issued 49.9 million ordinary shares of XL-Ireland to Catlin shareholders, which had an aggregate value as of the Acquisition Date of $1.85 billion . Common Shares The following table is a summary of common shares issued and outstanding: (in thousands) 2016 2015 Balance – beginning of year 294,745 255,183 Exercise of options 802 480 Net issuance of restricted shares 1,598 1,581 Share buybacks (1) (30,256 ) (12,434 ) Issue of shares — 49,935 Balance – end of year 266,889 294,745 ____________ (1) Includes share buybacks associated with authorized share buyback programs as well as purchases related to satisfying tax withholding obligations of employees in connection with the vesting of restricted shares granted under the Company’s equity compensation programs. Buyback of Ordinary and Common Shares On August 6, 2015, XL-Ireland announced that its Board of Directors approved a new share buyback program, authorizing the purchase of up to $1.0 billion of shares (the "August 2015 Program"). During the year ended December 31, 2016 , the Company purchased and canceled 14.2 million common shares under the August 2015 Program for $499.3 million . On May 13, 2016, XL-Ireland announced that its Board of Directors approved a new share buyback program, authorizing the purchase of up to $1.0 billion of XL-Ireland shares (the "May 2016 Program"). This authorization also canceled approximately $204.1 million remaining under the August 2015 Program. As a result of the Redomestication, XL-Bermuda assumed the May 2016 Program. Buybacks made prior to July 25, 2016 were of XL-Ireland shares, and on and after July 25, 2016 were of XL-Bermuda shares. During the year ended December 31, 2016 , the Company purchased and canceled 16.0 million shares under the May 2016 Program for $550.7 million . Other share buybacks, primarily for purposes of settling employee withholding taxes incurred in connection with the vesting of share-based compensation awards, amounted to $1.1 million for the year ended December 31, 2016 . In total, the Company purchased and canceled 30.3 million XL-Ireland shares and XL-Bermuda shares, for approximately $1.051 billion during the year ended December 31, 2016 . As of December 31, 2016 , $449.3 million remained available for purchase under the May 2016 Program. All share buybacks were carried out in accordance with applicable law, including prior to July 25, 2016 by way of redemption in accordance with Irish law. All shares so redeemed were canceled upon redemption. (b) Non-controlling Interest in Equity of Consolidated Subsidiaries The Series D Preference Ordinary Shares and Series E Preference Ordinary Shares discussed in this section were issued by XL-Cayman and do not represent share capital of XL-Bermuda. XL-Bermuda has no preferred shares outstanding and has never issued any preferred shares. Series D Preference Ordinary Shares On October 15, 2011, XL-Cayman issued $350 million Series D Preference Ordinary Shares. Dividends on the Series D Preference Ordinary Shares are declared and paid quarterly at a floating rate of three-month LIBOR plus 3.120% on the liquidation preference. Series E Preference Ordinary Shares On March 15, 2007, XL-Cayman issued 1.0 million Fixed/Floating Series E Perpetual Non-Cumulative preference ordinary shares, par value $0.01 each, with liquidation preference value of $1,000 per share (the "Series E preference ordinary shares"). The Series E preference ordinary shares are perpetual securities with no fixed maturity date. Dividends on the Series E preference ordinary shares are declared and paid semi-annually at a rate of $32.50 per share. Until April 15, 2017 (the "Series E Fixed Rate Period"), dividends on the series E preference ordinary shares will be payable semi-annually on a non-cumulative basis, when, as and if declared by our board of directors on April 15 and October 15 of each year at a fixed rate equal to 6.500% per annum on the liquidation preference (the "Series E Fixed Rate"). From and after April 15, 2017 (the "Series E Floating Rate Period"), dividends on the Series E preference ordinary shares will be payable quarterly on a non-cumulative basis, when, as and if declared by our board of directors, on January 15, April 15, July 15 and October 15 of each year at a floating rate equal to three-month LIBOR plus 2.4575% (the "Series E Floating Rate"). Acquisition of Non-controlling Preferred Shares In connection with the Catlin Acquisition described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," the Company acquired 0.6 million non-cumulative perpetual preferred shares issued by Catlin-Bermuda, par value of $0.01 per share, with liquidation preference of $1,000 per share, plus declared and unpaid dividends ("CICL Prefs"). Dividends at a rate of 7.249 percent on the liquidation preference are payable semi-annually on January 19 and July 19 in arrears as and when declared up to but not including January 2017. Thereafter, if the CICL-Prefs have not yet been redeemed, dividends will be payable quarterly at a rate equal to 2.975 percent plus the three-month LIBOR rate of the liquidation preference. The fair value of the outstanding CICL-Prefs on the date of the Catlin Acquisition was $562.3 million , which was based on the last trading price of such securities prior to the Catlin Acquisition. (c) Stock Plans The Company’s performance incentive programs provide for grants of stock options, restricted stock, restricted stock units, performance units and stock appreciation rights. Share-based compensation granted by the Company generally contains a vesting period of three or four years, and certain awards also contain performance conditions. The Company records compensation expense related to each award over its vesting period, incorporating the best estimate of the expected outcome of performance conditions where applicable. Compensation expense is generally recorded on a straight line basis over the vesting period of an award. The Company currently maintains the following performance incentive programs: the NAC Re Corp. 1989 Stock Option Plan (the "1989 Plan"), the XL Group Ltd Amended and Restated 1991 Performance Incentive Program (the "1991 Program"), the XL Group Ltd Amended and Restated 1999 Performance Incentive Program for Employees (the "1999 Program"), the XL Group plc Directors Stock & Option Plan (the "Directors Plan"), the XL Group Ltd 2009 Cash Long-Term Incentive Program (the "2009 Program"), the XL Group Ltd Supplemental Deferred Compensation Plan (the "DC Plan," and together with the 1989 Plan, the 1991 Program, the 1999 Program, the Directors Plan and the 2009 Program, the "Programs"). The programs provide that the securities to be issued pursuant to each Program are of XL-Bermuda. (d) Options The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: 2016 2015 2014 Dividend yield 2.00 % 2.00 % 2.00 % Risk free interest rate 1.37 % 1.70 % 1.81 % Volatility 21.7 % 21.6 % 34.0 % Expected lives 6.0 years 6.0 years 6.0 years The risk free interest rate is based on U.S. Treasury rates. The expected lives are estimated using the historical exercise behavior of grant recipients. The expected volatility is determined based upon a combination of the historical volatility of the Company’s stock and the implied volatility derived from publicly traded options. The following is a summary of the activity in the stock option plans for the indicated years ended December 31: (In thousands except for weighted average grant date fair value) 2016 2015 2014 Options granted to purchase common shares under the Programs - in thousands 2,200 1,974 1,025 Weighted average grant date fair value $ 5.99 $ 6.51 $ 8.60 Total intrinsic value of stock options exercised $ 19,471 $ 8,546 $ 7,499 Options exercised during the year - in thousands 810 480 424 Compensation expense related to stock option plans $ 11,065 $ 8,961 $ 9,961 Estimated tax benefit (charge) related to stock option plans $ 355 $ — $ (2 ) The following is a summary of the stock options outstanding at December 31, 2016 , and related activity for the year then ended: Number of Shares ( in thousands ) Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in thousands) Outstanding – beginning of year 10,749 $ 28.59 5.4 years $ 121,085 Granted 2,200 34.64 Exercised (810 ) 12.35 Canceled/Expired (278 ) 60.83 Outstanding – end of year 11,861 $ 30.07 5.5 years $ 86,558 Options exercisable 8,002 $ 27.75 4.0 years $ 77,366 Available for grant (1) 8,355 ____________ (1) Available for grant includes shares that may be granted as either stock options, restricted stock, restricted stock units or performance units. The aggregate intrinsic value in the table above represents the total pre-tax intrinsic value (the difference between the Company’s closing stock price on the last trading day of the 2016 fiscal year and the exercise price, multiplied by the number of in-the-money-options) that would have been received by the option holders had all option holders exercised their options on December 31, 2016 . Total unrecognized stock-based compensation expense related to non-vested stock options was approximately $15.3 million at December 31, 2016 , which related to approximately 3.9 million options and is expected to be recognized over a weighted-average period of 1.3 years. (e) Restricted Stock, Restricted Stock Units and Performance Units Restricted Stock Restricted stock awards issued under the 1991 Performance Incentive Program and the Directors Stock and Option Plan vest as set forth in the applicable award agreements. Each restricted stock award represents the Company’s obligation to deliver to the holder one ordinary share. The employees and directors who are granted a restricted stock award have all the rights of a shareholder, including the right to vote and receive dividends, but the shares are subject to certain restrictions prior to vesting relating to, among other things, forfeiture in the event of termination of employment and transferability. A summary of the restricted stock awards issued under the 1991 Performance Incentive Program and the Directors Stock and Option Plan for the indicated years ended December 31 is as follows: (In thousands except for weighted average grant date fair value) 2016 2015 2014 Restricted ordinary shares granted 48 44 46 Weighted average grant date fair value $ 34.05 $ 37.11 $ 31.86 Aggregate grant date fair value $ 1,650 $ 1,613 $ 1,463 Compensation expense related to restricted stock awards $ 2,078 $ 3,889 $ 5,239 Estimated tax benefit related to restricted stock awards $ 129 $ 709 $ 1,233 Total unrecognized stock based compensation expense related to non-vested restricted stock awards was nil at December 31, 2016 , which is related to approximately 0.2 million restricted stock awards. Non-vested restricted stock awards at December 31, 2016 and for the year then ended were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 275 $ 41.90 Granted 48 $ 34.05 Vested (132 ) $ 36.35 Unvested at December 31, 2016 191 $ 43.72 Restricted Stock Units Each restricted stock unit represents the Company’s obligation to deliver to the holder one common share upon satisfaction of the three -year vesting term. Restricted stock units are granted at the closing market price on the day of grant and entitle the holder to receive dividends declared and paid in the form of additional common shares contingent upon vesting. A summary of the restricted stock units issued to officers of the Company and its subsidiaries for the indicated years ended December 31 is as follows: (In thousands) 2016 2015 2014 Restricted stock units granted 1,117 1,534 1,867 Aggregate grant date fair value $ 38,681 $ 55,540 $ 57,134 Compensation expense related to restricted stock units $ 46,209 $ 48,937 $ 41,879 Estimated tax benefit related to restricted stock units $ 12,701 $ 13,271 $ 11,607 Total unrecognized stock-based compensation expense related to non-vested restricted stock units was $49.9 million at December 31, 2016 , which is related to approximately 2.5 million restricted stock units and is expected to be recognized over 1.4 years. Non-vested restricted stock units at December 31, 2016 and for the year then ended were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 3,070 $ 32.99 Granted 1,117 $ 34.64 Vested (1,559 ) $ 31.83 Forfeited (137 ) $ 36.37 Unvested at December 31, 2016 2,491 $ 34.30 Performance Units The performance units issued in 2016 vest after approximately three years, subject to the achievement of stated market metrics, and entitle the holder to shares of the Company’s common shares. Each grant of performance units has a target number of shares, with final payouts ranging from 0% to 200% of the grant amount depending upon the achievement of stated market metrics along with each employee’s continued service through the vesting date. Performance units issued prior to 2016 have a similar vesting schedule and a similar target of shares, but vesting and payout are dependent upon the achievement of stated relative and absolute financial performance metrics along with each employee's continued service through the vesting date. Furthermore, performance units granted in 2016 were granted at the closing market price on the day of grant and entitle the holder to receive dividends declared and paid in the form of additional common shares contingent upon vesting. A summary of the performance units issued to certain employees of the Company for the indicated years ended December 31 is as follows: (In thousands) 2016 2015 2014 Performance units granted 738 781 572 Potential maximum share payout 1,477 1,563 1,144 Aggregate grant date fair value $ 25,578 $ 28,082 $ 16,345 Compensation expense related to performance units $ 21,647 $ 12,942 $ 24,089 Estimated tax benefit (charge) related to performance units $ 3,152 $ 1,459 $ 4,250 Total unrecognized stock-based compensation expense related to non-vested performance units was approximately $29.8 million at December 31, 2016 , which is related to approximately 1.4 million performance units and is expected to be recognized over 1.8 years. Non-vested restricted performance units as of December 31, 2016 were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 1,881 $ 31.02 Granted 738 $ 34.64 Vested (746 ) $ 27.00 Forfeited (28 ) $ 34.12 Performance driven addition (reduction) (477 ) $ 34.60 Unvested at December 31, 2016 1,368 $ 32.83 (f) Restricted Cash Units During the year ended December 31, 2016 , the Company granted approximately 1.8 million liability-classed stock units to certain employees with an aggregate grant date fair value of approximately $63.2 million . Each liability-classed restricted stock unit represents the Company's obligation to deliver to the holder a cash payment equivalent to the value of one common share. The grants may vest either in three equal installments upon the first, second and third anniversaries of the date of grant; or in two equal installments upon the first and second anniversaries of the date of grant. Liability-classed stock units are granted at the closing market price on the day of grant and entitle the holder to receive dividends declared and are paid in cash contingent upon vesting. (In thousands) 2016 2015 2014 Restricted cash units granted 1,826 2,559 — Aggregate grant date fair value $ 63,261 $ 94,525 $ — Compensation expense related to restricted cash units $ 39,433 $ 19,834 $ — Estimated tax benefit related to restricted cash units $ 8,543 $ 4,374 $ — Total unrecognized stock-based compensation expense related to non-vested restricted cash units was approximately $74.1 million at December 31, 2016 , which is related to approximately 2.6 million restricted cash units and is expected to be recognized over 1.5 years. Non-vested restricted cash units as of December 31, 2016 were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 2,006 $ 36.95 Granted 1,826 $ 34.64 Vested (892 ) $ 36.93 Forfeited (367 ) $ 36.27 Unvested at December 31, 2016 2,573 $ 35.41 (g) Voting XL-Bermuda’s Bye-laws restrict the voting power of any person to less than approximately 10% of the total voting power.

Computation of Earnings Per Ord

Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Computation of earnings per ordinary share and ordinary share equivalent	Computation of Earnings Per Common Share and Common Share Equivalent As a result of the Redomestication discussed in Note 1(a), "Significant Accounting Policies - Basis of Preparation and Consolidation ," prior to July 25, 2016, share information relates to the ordinary shares of XL-Ireland and its consolidated subsidiaries. On and subsequent to July 25, 2016, share information relates to the common shares of XL-Bermuda and its consolidated subsidiaries. The following table sets forth the computation of basic and diluted earnings per common share for the years ended December 31, 2016, 2015 and 2014 : (U.S. dollars in thousands, except per share amounts) 2016 2015 2014 Basic earnings per common share and common share equivalents outstanding: Net income (loss) attributable to common shareholders $ 440,968 $ 1,207,152 $ 188,340 Weighted average common shares outstanding 278,957 286,194 267,103 Basic earnings per common share and common share equivalents outstanding $ 1.58 $ 4.22 $ 0.71 Diluted earnings per common share and common share equivalents outstanding: Weighted average common shares outstanding – basic 278,957 286,194 267,103 Impact of share-based compensation 3,801 4,805 4,424 Weighted average common shares outstanding – diluted 282,758 290,999 271,527 Diluted earnings per common share & common share equivalents outstanding $ 1.56 $ 4.15 $ 0.69 Dividends per common share $ 0.80 $ 0.72 $ 0.64 For the years ended December 31, 2016, 2015 and 2014 , common shares available for issuance under share-based compensation plans of 6.8 million , 2.5 million and 5.5 million , respectively, were not included in the calculation of diluted earnings per share because the assumed exercise or issuance of such shares would be anti-dilutive.

Dividends

Dividends	12 Months Ended
	Dec. 31, 2016
Dividends Disclosure [Abstract]
Dividends	Dividends In 2016, four quarterly dividends of $0.20 per share were paid to all XL-Ireland ordinary shareholders of record at March 15 and June 15, and XL-Bermuda common shareholders of record at September 15 and December 15. In 2015, two quarterly dividends of $0.16 were paid to XL-Ireland ordinary shareholders of record at March 13 and June 15 and two quarterly dividends of $0.20 per share were paid to all XL-Ireland ordinary shareholders of record at September 15 and December 15. In 2014, four quarterly dividends of $0.16 per share were paid to all XL-Ireland ordinary shareholders of record at March 14, June 13, September 15 and December 15. XL-Cayman paid its preference shareholders for the indicated years ended December 31, as follows: (U.S. dollars in millions) 2016 2015 2014 Series D preference ordinary shares (1) (2) $ 12.9 $ 11.8 $ 11.7 Series E preference ordinary shares (3) $ 65.0 $ 65.1 $ 65.1 Non-cumulative perpetual preferred shares (4) $ 43.5 $ 21.8 $ — ____________ (1) On October 28, 2016 , the Company announced that the Board of Directors of XL-Cayman resolved to pay a dividend of $10.2222 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017 . On December 29, 2016, the Board of Directors of XL-Cayman also resolved to pay an additional one-time dividend of $0.3525 per share on XL-Cayman's Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017 . (2) On February 17, 2017 , the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $10.473 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017 . (3) On February 17, 2017 , the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $32.50 per share on XL-Cayman’s Series E Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017 . (4) On January 12, 2017 , the Board of Directors of Catlin-Bermuda resolved to pay a dividend in the aggregate amount of $21.8 million on CICL Prefs. The dividend was paid on January 19, 2017 to all shareholders of record at December 31, 2016 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2016
Comprehensive Income Loss Note [Abstract]
Accumulated other comprehensive income (loss)	Accumulated Other Comprehensive Income (Loss) The changes in AOCI, net of tax, by component for the indicated years ended December 31 are as follows: (U.S. dollars in thousands) Unrealized Gains (Losses) on Investments (1) OTTI Losses Recognized in AOCI Foreign Currency Translation Adjustments Underfunded Pension Liability Cash Flow Hedge Total Balance, net of tax, December 31, 2013 $ 822,432 $ (89,190 ) $ 14,541 $ (13,239 ) $ 2,113 $ 736,657 OCI before reclassifications 954,326 — (26,497 ) (10,877 ) — 916,952 Amounts reclassified from AOCI (143,330 ) 14,082 87 812 255 (128,094 ) Tax benefit (expense) (43,314 ) (939 ) 681 2,515 — (41,057 ) Net current period OCI - net of tax $ 767,682 $ 13,143 $ (25,729 ) $ (7,550 ) $ 255 $ 747,801 Balance, net of tax, December 31, 2014 $ 1,590,114 $ (76,047 ) $ (11,188 ) $ (20,789 ) $ 2,368 $ 1,484,458 OCI before reclassifications (474,304 ) — (33,690 ) (6,100 ) — (514,094 ) Amounts reclassified from AOCI (346,911 ) 18,987 — 1,145 (200 ) (326,979 ) Tax benefit (expense) 34,195 (442 ) 8,375 1,103 — 43,231 Net current period OCI - net of tax $ (787,020 ) $ 18,545 $ (25,315 ) $ (3,852 ) $ (200 ) $ (797,842 ) Balance, net of tax, December 31, 2015 $ 803,094 $ (57,502 ) $ (36,503 ) $ (24,641 ) $ 2,168 $ 686,616 OCI before reclassifications 254,333 — 102,772 (1,332 ) — 355,773 Amounts reclassified from AOCI (353,910 ) 6,599 — 3,100 (182 ) (344,393 ) Tax benefit (expense) 26,912 (49 ) (7,299 ) (2,014 ) — 17,550 Net current period OCI - net of tax $ (72,665 ) $ 6,550 $ 95,473 $ (246 ) $ (182 ) $ 28,930 Balance, net of tax, December 31, 2016 $ 730,429 $ (50,952 ) $ 58,970 $ (24,887 ) $ 1,986 $ 715,546 ____________ (1) Included in these amounts is the impact of Shadow Adjustments on future policy benefit reserves. As of December 31, 2015 , $274.4 million was recorded. During the year ended December 31, 2016 , additional net impacts of $(62.3) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $212.1 million at December 31, 2016 . The reclassifications out of AOCI along with the associated income statement line items affected by component, and the total related tax (expense) benefit for indicated years ended December 31, are as follows: Details About AOCI Components (U.S. dollars in thousands) 2016 2015 Affected Line Item in the Statement of Income Unrealized gains and losses on investments: Net realized gains (losses) on investments sold $ (350,875 ) $ (316,508 ) OTTI on investments 81,595 95,344 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets (51,100 ) (125,747 ) Income (loss) from investment fund affiliates (33,530 ) — Total before tax $ (353,910 ) $ (346,911 ) Provision (benefit) for income tax 10,084 7,597 Net of tax $ (343,826 ) $ (339,314 ) OTTI losses recognized in OCI: Net realized gains (losses) on investments sold $ 7,038 $ 18,014 OTTI on investments transferred to (from) OCI (439 ) 973 Total before tax $ 6,599 $ 18,987 Provision (benefit) for income tax (49 ) (32 ) Net of tax $ 6,550 $ 18,955 Underfunded Pension Liability: Operating Expenses $ 3,100 $ 1,145 Provision (benefit) for income tax (1,085 ) (401 ) Net of tax $ 2,015 $ 744 Gains and losses on cash flow hedges: Interest Expense $ (182 ) $ (200 ) Provision (benefit) for income tax — — Net of tax $ (182 ) $ (200 ) Total reclassifications for the period, gross of tax $ (344,393 ) $ (326,979 ) Tax (benefit) expense 8,950 7,164 Total reclassifications for the period, net of tax $ (335,443 ) $ (319,815 )

Taxation

Taxation	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Taxation	Taxation XL-Bermuda conducts global operations through its subsidiaries in various jurisdictions around the world, including but not limited to Bermuda, the U.S., the U.K., Switzerland, Ireland, Germany, Italy, Spain, and France. The Company is subject to tax in accordance with the relevant tax laws and regulations governing taxation in the jurisdictions in which it operates. XL-Bermuda, and its Bermuda subsidiaries, are not subject to any income or capital gains taxes under current Bermuda law. In the event that there is a change such that these taxes are imposed, the Bermuda subsidiaries would be exempted from any such tax until March 2035 pursuant to the Bermuda Exempted Undertakings Tax Protection Act 1966, and the Exempted Undertakings Tax Protection Amendment Act 2011. The Company’s U.S. subsidiaries are subject to federal, state and local corporate income taxes, as well as premium, excise and other taxes applicable to U.S. corporations. The U.S. related provision for federal income taxes has been determined under the principles of the consolidated tax provisions of the IRS Code and Regulations thereunder. With the exception of the U.S., deferred income taxes have not been accrued with respect to certain undistributed earnings of subsidiaries located outside of Bermuda. If the earnings were to be distributed, as dividends or otherwise, such amounts may be subject to withholding taxation in the jurisdiction of the paying entity. The Company does not assert that all earnings arising in the U.S. will be permanently reinvested in the U.S., and accordingly, the Company provides for withholding taxes arising in respect of current period U.S. earnings. No withholding taxes are accrued with respect to the earnings of the Company’s subsidiaries arising outside the U.S. However, if there is a change in tax law, interpretation of existing law, or change in way in which the Company conducts its business, then the company would accrue the required withholding tax. The Company's current corporate structure is such that distribution of earnings from subsidiaries located outside of the United States would not be subject to significant incremental taxation. It is not practicable to estimate the amount of additional withholding taxes that might be payable on such earnings due to a variety of factors, including the timing, extent and nature of any repatriation. The following table details the years that are the subject of open examinations, by major tax jurisdiction. While the Company cannot estimate with certainty the outcome of these examinations, the Company does not believe that adjustments from open tax years will result in a significant change to the Company's financial results. Jurisdiction Tax Years U.S. 2013-2015 Ireland 2008 - 2009 U.K. 2014 France 2013 - 2014 Spain 2011 - 2012 The following table details open tax years that are open to assessment by local tax authorities, in the following major tax jurisdictions. Jurisdiction Tax Years U.S. 2013 - 2016 Ireland 2008 - 2016 U.K. 2014 - 2016 Germany 2014 - 2016 Switzerland 2011 - 2016 France 2013 - 2016 Spain 2011 - 2016 Italy 2012 - 2016 The Company’s income (loss) before income tax and non-controlling interests, for the years ended December 31, 2016, 2015 and 2014 , was distributed between U.S. and non-U.S. jurisdictions as follows: Income (loss) before income tax: (U.S. dollars in thousands) 2016 2015 2014 U.S. $ 68,970 $ (5,931 ) $ 228,708 Non U.S. 543,304 1,300,109 137,027 Total $ 612,274 $ 1,294,178 $ 365,735 The income tax provisions for the years ended December 31, 2016, 2015 and 2014 are as follows: (U.S. dollars in thousands) 2016 2015 2014 Current expense (benefit): U.S. $ (12,201 ) $ (22,698 ) $ 45,598 Non U.S. 59,031 67,784 81,371 Total current expense (benefit) $ 46,830 $ 45,086 $ 126,969 Deferred expense (benefit): U.S. $ 8,502 $ (63,491 ) $ 8,572 Non U.S. (13,203 ) (756 ) (38,644 ) Total deferred expense (benefit) $ (4,701 ) $ (64,247 ) $ (30,072 ) Total tax expense (benefit) $ 42,129 $ (19,161 ) $ 96,897 The applicable statutory tax rates for the current year of the most significant jurisdictions contributing to the overall taxation of the Company are: Jurisdiction Applicable Statutory Corporate Income Tax Rates Ireland (1) 12.50 % Bermuda — % U.S. 35.00 % U.K. 20.00 % Switzerland (2) 21.15 % Germany (3) 15.00 % France (4) 33.33 % ____________ (1) The 12.5% statutory corporate income tax rate applies to active income from the conduct of a trade in Ireland. For passive income or income from other defined activities the rate increases to 25% . (2) Represents the combined federal and cantonal rate primarily applicable to XL Catlin Swiss entities. (3) The statutory corporate income tax rate is 15% . However, including applicable surcharges and local trade tax, which can vary by location, would increase the combined statutory rate to approximately 33% . (4) The statutory corporate income tax rate is 33.33%. However, with the mandatory social surcharge, the combined statutory rate would increase to 34.43% . The expected tax provision in the table below has been calculated using the pre-tax accounting income (loss) in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. A reconciliation of the difference between the provision for income taxes and the expected tax provision for the years ended December 31, 2016, 2015 and 2014 is provided below: (U.S. dollars in thousands) 2016 2015 2014 Expected tax (benefit) provision $ (31,080 ) $ (50,797 ) $ 132,775 Permanent differences: Non-taxable (income) loss (19,937 ) (23,036 ) (19,870 ) Revision to prior year estimates (24,121 ) 7,402 2,016 State, local and foreign taxes 23,157 27,499 47,078 Valuation allowance 1,197 9,517 (181 ) Net allocated investment income 5,990 (405 ) 3,399 Stock awards 543 (433 ) 411 Non-deductible expenses 48,206 42,839 22,556 Other investment related adjustments (905 ) 2,075 (2,916 ) Adjustments related to GreyCastle Life Retro Arrangements 21,682 (35,045 ) (99,535 ) Change in tax rates (6,233 ) (11,877 ) 3,974 Uncertain tax positions 23,630 13,100 7,190 Total tax expense (benefit) $ 42,129 $ (19,161 ) $ 96,897 Significant components of the Company’s deferred tax assets and liabilities at December 31, 2016 and 2015 were as follows: (U.S. dollars in thousands) 2016 2015 Deferred tax asset: Net unpaid loss reserve discount $ 96,357 $ 111,584 Net unearned premiums 95,676 80,434 Compensation liabilities 96,280 94,013 Net operating losses 323,716 181,295 Investment adjustments 14,030 14,399 Pension 6,817 10,370 Bad debt reserve 12,418 7,425 Amortizable goodwill 967 5,396 Net unrealized depreciation on investments 5,915 5,051 Stock options 7,249 16,192 Depreciation 26,525 13,299 Net realized capital losses 89,568 98,756 Deferred intercompany capital losses 18,221 26,164 Untaxed Lloyd's result — 3,769 Deferred acquisition costs 17,820 31,133 Currency translation adjustments — 6,280 Tax Credits 71,651 5,047 Other 34,708 19,930 Deferred tax asset, gross of valuation allowance $ 917,918 $ 730,537 Valuation allowance 367,366 276,301 Deferred tax asset, net of valuation allowance $ 550,552 $ 454,236 Deferred tax liability: Net unrealized appreciation on investments $ 21,500 $ 51,010 Unremitted earnings — 3,739 Deferred acquisition costs 10,858 8,308 Currency translation adjustments 12,813 1,210 Regulatory reserves 116,500 64,352 Net unearned premiums 4,380 — Investment adjustments 5,269 6,373 Untaxed Lloyd’s result 11,940 — Depreciation 15,601 11,500 Syndicate capacity 82,106 92,756 Intangible asset 32,508 40,126 Other 3,806 13,202 Deferred tax liability $ 317,281 $ 292,576 Net Deferred Tax Asset $ 233,271 $ 161,660 The deferred tax asset and deferred tax liability balances presented above represent the gross deferred tax asset and liability balances across each tax jurisdiction. As disclosed on the consolidated balance sheets, the deferred tax asset balances of $310.5 million and $282.3 million at December 31, 2016 and 2015 , respectively, and deferred tax liability balances of $77.3 million and $120.7 million at December 31, 2016 and 2015 , respectively, include netting of certain deferred tax assets and liabilities within a tax jurisdiction to the extent such netting is consistent with ASC 740 "Income Taxes". During 2016, the Company recorded net deferred tax assets related to certain branch operations that were previously deemed worthless and not disclosed. Due to changes in the global operating environment, the company now believes that, while unlikely, these net deferred tax assets may have future value. As such, the company has updated its year end deferred tax balances to reflect these net deferred tax assets with an offsetting valuation allowance. There is no net impact to equity or reported tax expense resulting from this change in disclosure. At December 31, 2016 and 2015 , the valuation allowance of $367.4 million and $276.3 million , respectively, related primarily to net operating loss and realized capital loss carryforwards in the following major tax jurisdictions: Jurisdiction (U.S. dollars in thousands) 2016 2015 Ireland $ 96,642 $ 93,396 U.S. 92,999 106,624 U.K. 32,528 46,732 Switzerland 15,025 7,818 Other 130,172 21,731 Valuation Allowance Total $ 367,366 $ 276,301 The increase in the valuation allowance in 2016 of $91.1 million was primarily driven by the valuation allowances recorded on branch operations, as noted above. This increase was partially offset by a decrease in the valuation allowance related to U.K. losses based on filing positions taken on the 2015 tax returns, and a reduction in the valuation allowance held against U.S. capital loss carry-forwards that expired in 2016. Management believes it is more likely than not that the tax benefit associated with the group's deferred tax assets, not offset by a valuation allowance, will be realized. At December 31, 2016 , the Company had total net operating loss carryforwards of $1.6 billion , with an associated net deferred tax asset of $117.1 million ( $323.7 million gross deferred tax asset with an offsetting valuation allowance of $206.6 million ). At December 31, 2016 , the Company had U.S. net operating loss carryforwards of $108.0 million , with an associated net deferred tax asset of $37.0 million ( $37.8 million gross deferred tax asset with an offsetting valuation allowance of $0.8 million ), which were primarily generated during 2015. Of this amount, approximately $47.0 million are subject to restrictions on timing and utilization under §382 of the IRS Code. Management has reviewed historical taxable income and future taxable income projections for its U.S. group and has determined that in its judgment, all of the U.S. net operating losses will more likely than not be realized as reductions to future taxable income prior to expiration through 2036. At December 31, 2016 , the Company had net operating loss carryforwards in the U.K. of $203.3 million , with an associated net deferred tax asset of $12.8 million ( $39.0 million gross deferred tax asset with an offsetting valuation allowance of $26.2 million ). These operating loss carryforward have no expiration. At December 31, 2016 , the Company had net operating loss carryforwards in Switzerland of $200.1 million , with an associated net deferred tax asset of $8.8 million ( $23.7 million gross deferred tax asset with an offsetting valuation allowance of $14.9 million ). Losses of $5.3 million and $4.0 million will expire in 2017 and 2018, respectively, with the remaining $190.8 million expiring through 2023. At December 31, 2016 , the Company had net operating loss carryforwards in Ireland of $484.9 million , with no associated net deferred tax asset ( $60.6 million gross deferred tax asset with an offsetting valuation allowance of $60.6 million ). These net operating loss carryforwards primarily relate to XL-Ireland and XL-Cayman, formerly an Irish tax resident company. Although these losses may be carried forward indefinitely, the companies are in the process of filing final Irish tax returns and are not expected to generate further taxable profits in Ireland. Therefore, a valuation allowance is being held with respect to these losses. The Company expects to receive tax clearance from the Irish taxing authority in 2017 and at that point will write-off any remaining deferred tax asset and related valuation allowance. At December 31, 2016 , the Company had net operating loss carryforwards in other jurisdictions of $629.1 million , with an associated net deferred tax asset of $58.5 million ( $162.6 million gross deferred tax asset with an offsetting valuation allowance of $104.1 million ). Losses of $609.1 million have no expiration date and the remaining losses will expire through 2028. At December 31, 2016 , the Company had capital loss carryforwards of $293.5 million , with no associated net deferred tax asset ( $89.6 million gross deferred tax asset with an offsetting valuation allowance of $89.6 million ). At December 31, 2016 , the Company had U.S. realized capital loss carryforwards of $165.5 million , with no associated net deferred tax asset ( $57.9 million gross deferred tax asset with an offsetting valuation allowance of $57.9 million ). The five year carryforward limitation for the utilization of realized capital losses applies to this balance. Losses of $59.1 million will expire at the end of 2018 with another $106.3 million of realized capital losses expiring in future years through 2021. At December 31, 2016 , the Company had capital loss carryforwards in Ireland of $122.1 million , with no associated net deferred tax asset ( $30.5 million gross deferred tax asset with an offsetting valuation allowance of $30.5 million ) and in the U.K of $5.9 million , with no associated net deferred tax asset ( $1.1 million gross deferred tax asset with an offsetting valuation allowance of $1.1 million ). Although these capital losses may be carried forward indefinitely, due to the uncertainty surrounding any future capital gain income generation within these specific entities, a full valuation allowance is held in respect of these losses. At December 31, 2016 , the Company had total tax credits of $71.7 million comprised of $32.3 million of U.S. Alternative Minimum Tax Credits, that do not expire, $5.6 million of U.S. foreign tax credits that expire through 2025, $3.1 million of U.S. Research and Development tax credits which expire through 2034, and $30.7 million of U.K. foreign tax credits that do not expire. Shareholders’ equity at December 31, 2016 and 2015 reflected cumulative tax benefits of $10.6 million and $9.2 million , respectively, related to the excess of tax deductions over book compensation expense for stock awards exercised/vested by the Company's U.S. subsidiaries. For the years ended December 31, 2016, 2015 and 2014 , the Company had unrecognized tax benefits of $97.8 million , $80.6 million and $37.2 million , respectively. If recognized, the full amount of these unrecognized tax benefits would decrease the annual effective tax rate. The Company does not currently anticipate any significant change in unrecognized tax benefits during 2017. The following table presents a reconciliation of the Company’s unrecognized tax benefits: (U.S. dollars in thousands) 2016 2015 2014 Unrecognized tax benefits, beginning of the year $ 80,590 $ 37,190 $ 30,000 Increases for tax positions taken during the year 25,250 20,370 12,182 Increases for tax positions taken in prior years 11,700 38,650 15,304 Decreases for tax positions taken in prior years (6,440 ) (4,850 ) (20,296 ) Decreases for lapse of the applicable statute of limitations (13,320 ) (10,770 ) — Unrecognized tax benefits, end of year $ 97,780 $ 80,590 $ 37,190 The Company’s policy is to recognize any interest and penalties related to unrecognized tax benefits as a component of tax expense. For the years ended December 31, 2016, 2015 and 2014 , the Company had accrued interest and penalties of $0.9 million , $0.4 million and $0.4 million , respectively.

Statutory Financial Data

Statutory Financial Data	12 Months Ended
	Dec. 31, 2016
Statutory Capital And Surplus Disclosure Text Block [Abstract]
Statutory financial data	Statutory Financial Data The Company’s ability to pay dividends or return capital from shareholders’ equity is limited by applicable laws and regulations of the various jurisdictions in which the Company’s principal operating subsidiaries operate, certain additional required regulatory approvals and financial covenants contained in the Company’s credit facilities. The payment of dividends to XL-Bermuda and XL-Cayman, the Company’s holding companies, and by the Company’s principal operating subsidiaries is regulated under the laws of various jurisdictions including Bermuda, the U.K., Ireland and Switzerland and certain insurance statutes of various U.S. states in which the principal operating subsidiaries are licensed to transact business and the other jurisdictions where the Company has regulated subsidiaries. The Bermuda Monetary Authority (the “BMA”) became group supervisor of XL-Bermuda following the completion of the Redomestication to Bermuda from Ireland in July 2016. The BMA’s group rules require an assessment of group capital and solvency and XL-Bermuda is required to meet the BMA’s group capital requirements. Statutory capital and surplus for the principal operating subsidiaries of the Company for the years ended December 31, 2016 and 2015 are summarized below: (U.S. dollars in thousands) Bermuda (1) U.S. (2) U.K., Europe and Other 2016 2015 2016 2015 2016 2015 Required statutory capital and surplus $ 6,351,874 $ 7,722,123 $ 822,651 $ 747,313 $ 4,320,140 $ 4,445,247 Actual statutory capital and surplus (3) $ 12,333,870 $ 11,112,176 $ 2,362,827 $ 2,234,767 $ 5,201,602 $ 6,054,122 ____________ (1) Required statutory capital and surplus at December 31, 2016 represents 100% Bermuda Solvency Capital Requirement ("BSCR") level for the top Bermuda operating subsidiary, XL Bermuda Ltd, calculated on a consolidated basis (and therefore includes a BSCR requirement for all regions). (2) Required statutory capital and surplus represents 100% Risk-Based Capital level for principal U.S. operating subsidiaries. (3) Statutory assets in Bermuda include investments in other U.S. and international subsidiaries reported separately herein. Statutory net income (loss) for the principal operating subsidiaries of the Company for the years ended December 31, 2016, 2015 and 2014 is summarized below: (U.S. dollars in thousands) 2016 2015 2014 Bermuda $ 724,711 $ 1,513,924 $ 361,022 U.S. $ 96,481 $ 17,574 $ 155,751 U.K., Europe and Other $ 366,708 $ (125,758 ) $ 215,787 The difference between statutory financial statements and statements prepared in accordance with GAAP varies by jurisdiction, however, the primary difference is that statutory financial statements do not reflect deferred policy acquisition costs, deferred income tax net assets, intangible assets, or unrealized appreciation on investments, but they do reflect any unauthorized/authorized reinsurance charges. Certain restrictions on the payment of dividends from retained earnings by the Company’s principal operating subsidiaries are further detailed below. Management has evaluated the group and principal operating subsidiaries’ ability to maintain adequate levels of statutory capital, liquidity and rating agency capital and believes they will be able to do so. In performing this analysis, management has considered the most recent statutory capital position of each of the principal operating subsidiaries as well as the group overall, through its holding companies as a result of BMA group regulation. In addition, management has evaluated the ability of the holding companies to allocate capital and liquidity around the group as and when needed. Bermuda Operations In early July 2008, the Insurance Amendment Act of 2008 was passed, which introduced a number of changes to the Bermuda Insurance Act 1978, such as allowing the BMA to prescribe standards for an enhanced capital requirement and a capital and solvency return with which insurers and reinsurers must comply. The BSCR employs a standard mathematical model that can relate more accurately the risks undertaken by (re)insurers to the capital that is dedicated to their business. Insurers and reinsurers may adopt the BSCR model or, where an insurer or reinsurer believes that its own internal model better reflects the inherent risk of its business, an in-house model approved by the BMA. Class 4 (re)insurers, such as the Company, were required to implement the new capital requirements under the BSCR model beginning with fiscal years ending on or after December 31, 2009. The Company’s capital requirements for its Bermuda principal operating subsidiaries, XLB and Catlin-Bermuda, under the BSCR are highlighted in the aggregate in the table above. In addition to the BSCR based requirements, the BMA also prescribes minimum liquidity standards which must be met. Under the Insurance Act 1978, amendments thereto and related regulations of Bermuda, Class 4 (re)insurers are prohibited from declaring or paying dividends of more than 25% of each of their prior year’s statutory capital and surplus unless they file with the BMA an affidavit stating that the dividend has not caused the Class 4 (re)insurer to fail to meet its relevant margins. At December 31, 2016 and 2015 , the maximum dividend that our Bermuda Class 4 (re)insurers could pay, without a signed affidavit, having met minimum levels of statutory capital and surplus and liquidity requirements, was approximately $3.2 billion and $2.8 billion , respectively. No Class 4 (re)insurer may reduce its total statutory capital by 15% or more unless it has received the prior approval of the BMA, and it must also submit an affidavit stating that the proposed reduction will not cause it to fail to meet its minimum solvency margin or minimum liquidity ratio. U.S. Operations The Company has two lead property and casualty subsidiaries in the U.S., XLRA and Catlin Specialty Insurance Company ("CSIC"), which are domiciled in the States of New York and Delaware, respectively. Both XLRA and CSIC are the lead companies in their respective insurance pools. Including the pool leaders, these insurance pools include seven and three P&C companies, respectively. The Company also has another property and casualty subsidiary, T.H.E. Insurance Company ("THE"), a Louisiana-domiciled insurer which was acquired as part of the transaction described in Note 3(c), "Acquisitions and Disposals - Allied Acquisition , and exists outside of the existing pools at December 31, 2016 . Unless permitted by the New York Superintendent of Financial Services, XLRA cannot declare or distribute any dividend to shareholders during any twelve month period that exceeds the lesser of 10 percent of XLRA’s statutory policyholders’ surplus or 100 percent of its "adjusted net investment income," as defined. The New York State insurance laws also provide that any distribution that is a dividend may only be paid out of statutory earned surplus. At December 31, 2016 and 2015 , XLRA had statutory earned surplus of $66.9 million and $31.7 million , respectively. At December 31, 2016 , XLRA’s statutory policyholders’ surplus was $2.1 billion , and the maximum amount of dividends XLRA can declare and pay in 2017 , without prior regulatory approval, is $66.9 million . At December 31, 2016 and 2015 , one and two , respectively, of the seven P&C members of the XLRA insurance pool had a statutory earned deficit. Unless permitted by the Insurance Commissioner of the State of Delaware, CSIC cannot declare or distribute any dividend to shareholders during any twelve month period that exceeds the greater of 10 percent of statutory policyholders' surplus or 100 percent of net income excluding realized gains. The Delaware State insurance laws also provide that any distribution that is a dividend may only be paid out of statutory earned surplus. At December 31, 2016 , CSIC had a statutory earned surplus of $3.4 million , and an earned deficit at December 31, 2015. At December 31, 2016 , CSIC's statutory policyholders' surplus was $234.2 million , and no dividends can be declared and paid in 2017 without prior regulatory approval. At December 31, 2016 , two of the P&C members of the CSIC insurance pool had a statutory earned deficit. Unless permitted by the Insurance Commissioner of the State of Louisiana, THE cannot declare or distribute any dividend to shareholders during any twelve month period that exceeds the greater of 10 percent of statutory policyholders' surplus or 100 percent of net income excluding realized gains. At December 31, 2016 , THE's statutory policyholders' surplus was $52.3 million , and no dividends can be declared and paid in 2017 without regulatory approval. International Operations The Company’s international principal operating subsidiaries prepare statutory financial statements based on local laws and regulations. Some jurisdictions impose enhanced regulatory requirements on insurance companies while other jurisdictions impose fewer requirements. In some countries, such subsidiaries must obtain licenses issued by governmental authorities to conduct local insurance business. These licenses may be subject to minimum reserves and minimum capital and solvency tests. Jurisdictions may impose fines, censure, and/or impose criminal sanctions for violation of regulatory requirements. The majority of the actual statutory capital outside of the U.S. and Bermuda is held in the U.K. ( $1.2 billion at December 31, 2016 ), Switzerland ( $1.5 billion at December 31, 2016 ) and Ireland ( $0.9 billion at December 31, 2016 ). The Company also has sufficient capital available to meet Funds at Lloyd's requirements of approximately $1.5 billion . Other Restrictions XL-Bermuda and XL-Cayman have no operations of their own and their assets consist primarily of investments in subsidiaries. Accordingly, XL-Bermuda’s and XL-Cayman’s future cash flows largely depend on the availability of dividends or other permissible payments from subsidiaries as noted above. XL-Bermuda is subject to certain legal constraints that affect its ability to pay dividends on or redeem or buyback its common shares. Under Bermuda law, XL-Bermuda may not declare or pay a dividend or make a distribution out of contributed surplus if there are reasonable grounds for believing that: (a) the company is, or would after the payment be, unable to pay its liabilities as they become due; or (b) the realizable value of the company’s assets would thereby be less than its liabilities. At December 31, 2016 , XL-Bermuda had $8.1 billion in contributed surplus. The ability to declare and pay dividends may also be restricted by the group-wide capital and solvency provisions imposed by the BMA described earlier. In addition, XL-Cayman is subject to certain constraints that affect its ability to pay dividends on its preferred shares. Under Cayman Islands law, XL-Cayman may not declare or pay a dividend if there are reasonable grounds for believing that XL-Cayman is, or would after the payment be, unable to pay its liabilities as they become due in the ordinary course of business. Also, the terms of XL-Cayman’s preferred shares prohibit declaring or paying dividends on the common shares unless full dividends have been declared and paid on the outstanding preferred shares. Full dividends have been declared and paid on the outstanding preferred shares at December 31, 2016 . At December 31, 2016 , XL-Bermuda and XL-Cayman held cash and investments, net of liabilities associated with cash sweeping arrangements, of $1.0 million and $0.7 billion , respectively, compared to $11.6 million and $0.9 billion , respectively, at December 31, 2015 . The ability to declare and pay dividends may also be restricted by financial covenants in the Company’s credit facilities. The Company was in compliance with all covenants at December 31, 2016 , and the Company remains in compliance as of the date of this Form 10-K.

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 is a summary of the unaudited quarterly financial data for 2016 and 2015 : (U.S. dollars in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter 2016 Net premiums earned – P&C operations $ 2,351,446 $ 2,528,704 $ 2,431,677 $ 2,454,060 Net premiums earned – Corporate and Other $ 3,164 $ 3,508 $ 2,360 $ 3,015 Underwriting profit (loss) – P&C operations $ 175,489 $ 101,893 $ 166,851 $ 126,420 Net income (loss) attributable to common shareholders $ 21,885 $ 43,782 $ 70,601 $ 304,700 Net income (loss) per common share and common equivalent – basic $ 0.07 $ 0.16 $ 0.26 $ 1.13 Net income (loss) per common share and common equivalent – diluted $ 0.07 $ 0.15 $ 0.25 $ 1.12 2015 Net premiums earned – P&C operations $ 1,319,494 $ 2,063,795 $ 2,405,740 $ 2,375,155 Net premiums earned – Corporate and Other $ 14,506 $ 18,258 $ 17,812 $ 11,665 Underwriting profit (loss) – P&C operations $ 146,836 $ 208,779 $ 114,118 $ 183,458 Net income (loss) attributable to common shareholders $ 36,281 $ 915,039 $ 27,282 $ 228,550 Net income (loss) per common share and common equivalent – basic $ 0.14 $ 3.16 $ 0.09 $ 0.77 Net income (loss) per common share and common equivalent – diluted $ 0.14 $ 3.11 $ 0.09 $ 0.76

Guarantor Financial Information

Guarantor Financial Information	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Statements [Text Block]	Guarantor Financial Information The following tables present condensed consolidating balance sheets at December 31, 2016 and December 31, 2015 , condensed consolidating statements of income and comprehensive income for the years ended December 31, 2016, 2015 and 2014 and condensed consolidating statements of cash flows for the years ended December 31, 2016, 2015 and 2014 for XL-Bermuda, XL-Cayman, a 100% owned subsidiary of XL-Bermuda, and XL-Bermuda's other subsidiaries (excluding XL-Ireland), which are all 100% directly or indirectly owned subsidiaries of XL-Cayman. For purposes of this disclosure, the 2016 results of XL-Ireland, which is currently in liquidation proceedings and whose assets are otherwise immaterial, have been included within the results of XL-Bermuda. See Note 1, "Significant Accounting Policies " for information regarding changes in the Company's organizational structure as a result of the Redomestication. For a discussion of debt instruments issued by XL-Cayman, a majority of which were fully and unconditionally guaranteed by XL-Ireland prior to the Redomestication, and which are now fully and unconditionally guaranteed by XL-Bermuda subsequent to the Redomestication, see Note 14(a), "Notes Payable and Debt and Financing Arrangements - Notes Payable and Debt ." December 31, 2016 Condensed Consolidating Balance Sheet (U.S. dollars in thousands, except share data) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated ASSETS Investments: Total investments available for sale $ — $ 638,236 $ 31,280,890 $ — $ 31,919,126 Total investments trading — — 1,626,577 — 1,626,577 Investments in affiliates — — 2,177,645 — 2,177,645 Other investments — 9 1,164,555 — 1,164,564 Total investments $ — $ 638,245 $ 36,249,667 $ — $ 36,887,912 Cash and cash equivalents 1,022 84,286 3,341,680 — 3,426,988 Restricted cash — — 153,504 — 153,504 Investments in subsidiaries 10,897,195 14,238,698 — (25,135,893 ) — Accrued investment income 55 2,981 281,385 (55 ) 284,366 Deferred acquisition costs and value of business acquired — — 946,721 — 946,721 Ceded unearned premiums — — 1,687,864 — 1,687,864 Premiums receivable — — 5,522,976 — 5,522,976 Reinsurance balances receivable — — 577,479 — 577,479 Unpaid losses and loss expenses recoverable — — 5,491,297 — 5,491,297 Receivable from investments sold — — 128,411 — 128,411 Goodwill and other intangible assets — — 2,203,653 — 2,203,653 Deferred tax asset — — 310,542 — 310,542 Amounts due from subsidiaries/parent 42,780 — 72,962 (115,742 ) — Other assets 15,188 40,108 757,093 — 812,389 Total assets $ 10,956,240 $ 15,004,318 $ 57,725,234 $ (25,251,690 ) $ 58,434,102 LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities: Unpaid losses and loss expenses $ — $ — $ 25,939,571 $ — $ 25,939,571 Deposit liabilities — — 1,116,233 — 1,116,233 Future policy benefit reserves — — 3,506,047 — 3,506,047 Funds withheld on GreyCastle life retrocession arrangements — — 998,968 — 998,968 Unearned premiums — — 7,293,028 — 7,293,028 Notes payable and debt — 2,647,677 — — 2,647,677 Reinsurance balances payable — — 2,451,717 — 2,451,717 Payable for investments purchased — — 226,009 — 226,009 Deferred tax liability — — 77,271 — 77,271 Amounts due to subsidiaries/parent — 72,962 42,780 (115,742 ) — Other liabilities 17,728 41,984 1,157,190 — 1,216,902 Total liabilities $ 17,728 $ 2,762,623 $ 42,808,814 $ (115,742 ) $ 45,473,423 Shareholders’ Equity: Shareholders’ equity attributable to XL Group Ltd $ 10,938,512 $ 10,897,195 $ 14,238,698 $ (25,135,893 ) $ 10,938,512 Non-controlling interest in equity of consolidated subsidiaries — 1,344,500 677,722 (55 ) 2,022,167 Total shareholders’ equity $ 10,938,512 $ 12,241,695 $ 14,916,420 $ (25,135,948 ) $ 12,960,679 Total liabilities and shareholders’ equity $ 10,956,240 $ 15,004,318 $ 57,725,234 $ (25,251,690 ) $ 58,434,102 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. December 31, 2015 Condensed Consolidating Balance Sheet (U.S. dollars in thousands, except share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated ASSETS Investments: Total investments available for sale $ — $ 516,425 $ 33,237,473 $ — $ 33,753,898 Total investments trading — — 1,296,029 — 1,296,029 Investments in affiliates — — 1,708,899 — 1,708,899 Other investments — 877 1,432,180 — 1,433,057 Total investments $ — $ 517,302 $ 37,674,581 $ — $ 38,191,883 Cash and cash equivalents 11,557 369,997 2,874,682 — 3,256,236 Restricted cash — — 154,992 — 154,992 Investments in subsidiaries 11,648,673 15,836,651 — (27,485,324 ) — Accrued investment income — 2,323 310,344 — 312,667 Deferred acquisition costs and value of business acquired — — 890,568 — 890,568 Ceded unearned premiums — — 1,821,793 — 1,821,793 Premiums receivable — — 4,712,493 — 4,712,493 Reinsurance balances receivable — — 418,666 — 418,666 Unpaid losses and loss expenses recoverable — — 5,262,706 — 5,262,706 Receivable from investments sold — — 231,158 — 231,158 Goodwill and other intangible assets — — 2,210,266 — 2,210,266 Deferred tax asset — — 282,311 — 282,311 Amounts due from subsidiaries/parent 33,417 — 1,054,177 (1,087,594 ) — Other assets 2,748 44,570 889,881 — 937,199 Total assets $ 11,696,395 $ 16,770,843 $ 58,788,618 $ (28,572,918 ) $ 58,682,938 LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities: Unpaid losses and loss expenses $ — $ — $ 25,439,744 $ — $ 25,439,744 Deposit liabilities — — 1,168,376 — 1,168,376 Future policy benefit reserves — — 4,163,500 — 4,163,500 Funds withheld on GreyCastle life retrocession arrangements — — 914,629 — 914,629 Unearned premiums — — 7,043,358 — 7,043,358 Notes payable and debt — 2,644,970 — — 2,644,970 Reinsurance balances payable — — 2,117,727 — 2,117,727 Payable for investments purchased — — 130,060 — 130,060 Deferred tax liability — — 120,651 — 120,651 Amounts due to subsidiaries/parent — 1,087,594 — (1,087,594 ) — Other liabilities 19,316 45,106 1,221,038 — 1,285,460 Total liabilities $ 19,316 $ 3,777,670 $ 42,319,083 $ (1,087,594 ) $ 45,028,475 Shareholders’ Equity: Shareholders’ equity attributable to XL Group plc $ 11,677,079 $ 11,648,673 $ 15,836,651 $ (27,485,324 ) $ 11,677,079 Non-controlling interest in equity of consolidated subsidiaries — 1,344,500 632,884 — 1,977,384 Total shareholders’ equity $ 11,677,079 $ 12,993,173 $ 16,469,535 $ (27,485,324 ) $ 13,654,463 Total liabilities and shareholders’ equity $ 11,696,395 $ 16,770,843 $ 58,788,618 $ (28,572,918 ) $ 58,682,938 Year Ended December 31, 2016 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated Revenues: Net premiums earned $ — $ — $ 9,777,934 $ — $ 9,777,934 Total net investment income 436 9,135 817,998 (436 ) 827,133 Total net realized gains (losses) on investments — 1,918 370,220 — 372,138 Net realized and unrealized gains (losses) on derivative instruments — — 2,521 — 2,521 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (540,090 ) — (540,090 ) Income (loss) from investment fund affiliates — — 70,758 — 70,758 Fee income and other — — 35,692 — 35,692 Total revenues $ 436 $ 11,053 $ 10,535,033 $ (436 ) $ 10,546,086 Expenses: Net losses and loss expenses incurred $ — $ — $ 6,072,835 $ — $ 6,072,835 Claims and policy benefits — — 28,244 — 28,244 Acquisition costs — — 1,620,671 — 1,620,671 Operating expenses 93,247 4,985 1,965,130 — 2,063,362 Exchange (gains) losses (1,106 ) (343 ) (8,129 ) — (9,578 ) Loss (Gain) on sale of subsidiary — — (7,088 ) — (7,088 ) Interest expense (4 ) 140,644 69,123 — 209,763 Total expenses $ 92,137 $ 145,286 $ 9,740,786 $ — $ 9,978,209 Income (loss) before income tax and income (loss) from operating affiliates $ (91,701 ) $ (134,233 ) $ 794,247 $ (436 ) $ 567,877 Income (loss) from operating affiliates — — 44,397 — 44,397 Equity in net earnings (losses) of subsidiaries 532,049 744,877 — (1,276,926 ) — Provision (benefit) for income tax (620 ) — 42,749 — 42,129 Net income (loss) $ 440,968 $ 610,644 $ 795,895 $ (1,277,362 ) $ 570,145 Non-controlling interests — 78,595 51,018 (436 ) 129,177 Net income (loss) attributable to common shareholders $ 440,968 $ 532,049 $ 744,877 $ (1,276,926 ) $ 440,968 Comprehensive income (loss) $ 469,898 $ 560,979 $ 773,807 $ (1,334,786 ) $ 469,898 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. Year Ended December 31, 2015 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Revenues: Net premiums earned $ — $ — $ 8,226,425 $ — $ 8,226,425 Total net investment income 169 9,363 859,002 3,836 872,370 Total net realized gains (losses) on investments — 13,814 197,129 (8,765 ) 202,178 Net realized and unrealized gains (losses) on derivative instruments — 12,363 40,760 — 53,123 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (151,691 ) — (151,691 ) Income (loss) from investment fund affiliates — — 73,320 — 73,320 Fee income and other — — 33,201 — 33,201 Total revenues $ 169 $ 35,540 $ 9,278,146 $ (4,929 ) $ 9,308,926 Expenses: Net losses and loss expenses incurred $ — $ — $ 4,766,200 $ — $ 4,766,200 Claims and policy benefits — — 115,997 — 115,997 Acquisition costs — — 1,317,448 — 1,317,448 Operating expenses 46,340 10,565 1,910,034 — 1,966,939 Exchange (gains) losses (345 ) 20 22,829 — 22,504 Extinguishment of debt — — 5,592 — 5,592 Interest expense 11 143,330 61,874 — 205,215 Total expenses $ 46,006 $ 153,915 $ 8,199,974 $ — $ 8,399,895 Income (loss) before income tax and income (loss) from operating affiliates $ (45,837 ) $ (118,375 ) $ 1,078,172 $ (4,929 ) $ 909,031 Income (loss) from operating affiliates — — 44,740 — 44,740 Gain on sale of operating affiliate — — 340,407 — 340,407 Equity in net earnings (losses) of subsidiaries 1,253,609 1,449,404 — (2,703,013 ) — Provision (benefit) for income tax 620 245 (20,026 ) — (19,161 ) Net income (loss) $ 1,207,152 $ 1,330,784 $ 1,483,345 $ (2,707,942 ) $ 1,313,339 Non-controlling interests — 77,175 29,012 — 106,187 Net income (loss) attributable to common shareholders $ 1,207,152 $ 1,253,609 $ 1,454,333 $ (2,707,942 ) $ 1,207,152 Comprehensive income (loss) $ 409,310 $ 455,767 $ 656,491 $ (1,112,258 ) $ 409,310 Year Ended December 31, 2014 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Revenues: Net premiums earned $ — $ — $ 5,895,070 $ — $ 5,895,070 Total net investment income 275 20,256 889,611 8,483 918,625 Total net realized gains (losses) on investments — 27,541 102,150 (22,229 ) 107,462 Net realized and unrealized gains (losses) on derivative instruments — — 29,886 — 29,886 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (488,222 ) — (488,222 ) Income (loss) from investment fund affiliates — — 95,816 — 95,816 Fee income and other — — 43,630 — 43,630 Total revenues $ 275 $ 47,797 $ 6,567,941 $ (13,746 ) $ 6,602,267 Expenses: Net losses and loss expenses incurred $ — $ — $ 3,258,393 $ — $ 3,258,393 Claims and policy benefits — — 242,963 — 242,963 Acquisition costs — — 738,118 — 738,118 Operating expenses 9,646 13,102 1,318,567 — 1,341,315 Exchange (gains) losses 127 168 (37,863 ) — (37,568 ) Loss (Gain) on sale of subsidiary — — 666,423 — 666,423 Interest expense 5 110,323 23,778 — 134,106 Total expenses $ 9,778 $ 123,593 $ 6,210,379 $ — $ 6,343,750 Income (loss) before income tax and income (loss) from operating affiliates $ (9,503 ) $ (75,796 ) $ 357,562 $ (13,746 ) $ 258,517 Income (loss) from operating affiliates — — 107,218 — 107,218 Equity in net earnings (losses) of subsidiaries 197,843 350,602 — (548,445 ) — Provision (benefit) for income tax — (212 ) 97,109 — 96,897 Net income (loss) $ 188,340 $ 275,018 $ 367,671 $ (562,191 ) $ 268,838 Non-controlling interests — 77,175 3,323 — 80,498 Net income (loss) attributable to common shareholders $ 188,340 $ 197,843 $ 364,348 $ (562,191 ) $ 188,340 Comprehensive income (loss) $ 936,141 $ 945,644 $ 1,112,149 $ (2,057,793 ) $ 936,141 Year Ended December 31, 2016 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 978,695 $ 775,100 $ 2,116,580 $ (2,955,038 ) $ 915,337 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 303,070 $ 13,037,976 $ (583,466 ) $ 12,757,580 Proceeds from redemption of fixed maturities and short-term investments — 97,168 3,750,541 — 3,847,709 Proceeds from sale of equity securities — — 848,779 — 848,779 Purchases of fixed maturities and short-term investments — (534,502 ) (15,506,653 ) 583,466 (15,457,689 ) Purchases of equity securities — — (1,103,447 ) — (1,103,447 ) Proceeds from sale of affiliates — 324 396,767 — 397,091 Purchases of affiliates — — (681,385 ) — (681,385 ) Purchase of subsidiaries, net of acquired cash — — (92,893 ) — (92,893 ) Proceeds from sale of subsidiary, net of cash sold — — 22,998 — 22,998 Returns of capital from subsidiaries 274,727 465,203 — (739,930 ) — Change in restricted cash — — 1,488 — 1,488 Other, net — — 197,536 — 197,536 Net cash provided by (used in) investing activities $ 274,727 $ 331,263 $ 871,707 $ (739,930 ) $ 737,767 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 9,854 $ — $ — $ — $ 9,854 Buybacks of common shares (1,051,050 ) — — — (1,051,050 ) Dividends paid on common shares (222,761 ) (1,039,253 ) (1,915,785 ) 2,955,038 (222,761 ) Return of capital — (274,727 ) (465,203 ) 739,930 — Distributions to non-controlling interests — (78,094 ) (52,353 ) — (130,447 ) Contributions from non-controlling interests — — 47,524 — 47,524 Repayment of debt — — (8,248 ) — (8,248 ) Deposit liabilities — — (69,482 ) — (69,482 ) Net cash provided by (used in) financing activities $ (1,263,957 ) $ (1,392,074 ) $ (2,463,547 ) $ 3,694,968 $ (1,424,610 ) Effects of exchange rate changes on foreign currency cash — — (57,742 ) — (57,742 ) Increase (decrease) in cash and cash equivalents $ (10,535 ) $ (285,711 ) $ 466,998 $ — $ 170,752 Cash and cash equivalents – beginning of period 11,557 369,997 2,874,682 — 3,256,236 Cash and cash equivalents – end of period $ 1,022 $ 84,286 $ 3,341,680 $ — $ 3,426,988 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. Year Ended December 31, 2015 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 561,468 $ 148,850 $ 669,515 $ (764,277 ) $ 615,556 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 1,482,875 $ 15,745,247 $ (359,894 ) $ 16,868,228 Proceeds from redemption of fixed maturities and short-term investments — 188,788 3,562,386 — 3,751,174 Proceeds from sale of equity securities — — 664,735 — 664,735 Purchases of fixed maturities and short-term investments — (1,296,980 ) (18,780,978 ) 359,894 (19,718,064 ) Purchases of equity securities — — (567,334 ) — (567,334 ) Proceeds from sale of affiliates — — 748,575 — 748,575 Purchases of affiliates — — (280,856 ) — (280,856 ) Purchase of subsidiaries, net of acquired cash (2,287,579 ) (2,317,699 ) 1,267,564 2,317,699 (1,020,015 ) Proceeds from sale of subsidiary, net of cash sold 2,317,699 — — (2,317,699 ) — Returns of capital from subsidiaries 65,037 2,047,000 — (2,112,037 ) — Change in restricted cash — — (154,992 ) — (154,992 ) Other, net — — (155,019 ) — (155,019 ) Net cash provided by (used in) investing activities $ 95,157 $ 103,984 $ 2,049,328 $ (2,112,037 ) $ 136,432 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 9,976 $ — $ — $ — $ 9,976 Buybacks of common shares (468,971 ) — — — (468,971 ) Dividends paid on common shares (208,516 ) (764,277 ) — 764,277 (208,516 ) Return of capital — (65,037 ) (2,047,000 ) 2,112,037 — Distributions to non-controlling interests — (77,093 ) (40,590 ) — (117,683 ) Contributions from non-controlling interests — — 23,610 — 23,610 Proceeds from issuance of debt — 980,600 — — 980,600 Repayment of debt — — (87,447 ) — (87,447 ) Net proceeds from affiliated notional cash pooling programs (1) — — — — — Deposit liabilities — — (84,758 ) — (84,758 ) Net cash provided by (used in) financing activities $ (667,511 ) $ 74,193 $ (2,236,185 ) $ 2,876,314 $ 46,811 Effects of exchange rate changes on foreign currency cash — — (64,377 ) — (64,377 ) Increase (decrease) in cash and cash equivalents $ (10,886 ) $ 327,027 $ 418,281 $ — $ 734,422 Cash and cash equivalents – beginning of period 22,443 42,970 2,456,401 — 2,521,814 Cash and cash equivalents – end of period $ 11,557 $ 369,997 $ 2,874,682 $ — $ 3,256,236 Year Ended December 31, 2014 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 895,854 $ 518,715 $ 407,136 $ (858,521 ) $ 963,184 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 574,673 $ 4,793,978 $ (472,539 ) $ 4,896,112 Proceeds from redemption of fixed maturities and short-term investments — 351,737 3,250,056 — 3,601,793 Proceeds from sale of equity securities — — 571,410 — 571,410 Purchases of fixed maturities and short-term investments — (307,830 ) (7,322,967 ) 472,539 (7,158,258 ) Purchases of equity securities — — (445,504 ) — (445,504 ) Proceeds from sale of affiliates — — 240,785 — 240,785 Purchases of affiliates — — (371,226 ) — (371,226 ) Proceeds from sale of subsidiary, net of cash sold — — 570,000 — 570,000 Returns of capital from subsidiaries 79,086 482,570 — (561,656 ) — Other, net — 1,920 (195,411 ) — (193,491 ) Net cash provided by (used in) investing activities $ 79,086 $ 1,103,070 $ 1,091,121 $ (561,656 ) $ 1,711,621 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 6,367 $ — $ — $ — $ 6,367 Buybacks of common shares (801,953 ) — — — (801,953 ) Dividends paid on common shares (169,620 ) (858,521 ) — 858,521 (169,620 ) Return of capital — (79,086 ) (482,570 ) 561,656 — Distributions to non-controlling interests — (77,002 ) (1,463 ) — (78,465 ) Contributions from non-controlling interests — — 48,261 — 48,261 Repayment of debt — (600,000 ) — — (600,000 ) Net proceeds from affiliated notional cash pooling programs (1) — — — — — Deposit liabilities — — (268,298 ) — (268,298 ) Net cash provided by (used in) financing activities $ (965,206 ) $ (1,614,609 ) $ (704,070 ) $ 1,420,177 $ (1,863,708 ) Effects of exchange rate changes on foreign currency cash — — (90,115 ) — (90,115 ) Increase (decrease) in cash and cash equivalents $ 9,734 $ 7,176 $ 704,072 $ — $ 720,982 Cash and cash equivalents – beginning of period 12,709 35,794 1,752,329 — 1,800,832 Cash and cash equivalents – end of period $ 22,443 $ 42,970 $ 2,456,401 $ — $ 2,521,814

Schedule IV - Reinsurance

Schedule IV - Reinsurance	12 Months Ended
	Dec. 31, 2016
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]
Schedule IV - Reinsurance	SCHEDULE IV REINSURANCE FOR THE YEARS ENDED DECEMBER 31, 2016, 2015 AND 2014 (U.S. dollars in thousands) Gross Amount Ceded to Other Companies Assumed from Other Companies Net Amount Percentage of Amount Assumed to Net 2016 Life reinsurance in force (1) $ — $ 51,176,725 $ 51,971,475 $ 794,750 N/M Premiums Earned: Property and casualty operations $ 9,142,690 $ 3,451,620 $ 4,074,817 $ 9,765,887 41.7 % Life operations — 253,268 265,315 12,047 N/M Total premiums earned $ 9,142,690 $ 3,704,888 $ 4,340,132 $ 9,777,934 44.4 % 2015 Life reinsurance in force (1) $ — $ 62,290,992 $ 63,158,304 $ 867,312 N/M Premiums Earned: Property and casualty operations $ 7,717,173 $ 3,018,410 $ 3,465,421 $ 8,164,184 42.4 % Life operations — 247,675 309,916 62,241 N/M Total premiums earned $ 7,717,173 $ 3,266,085 $ 3,775,337 $ 8,226,425 45.9 % 2014 Life reinsurance in force (1) $ — $ 46,947,677 $ 68,854,340 $ 21,906,663 N/M Premiums Earned: Property and casualty operations $ 5,173,403 $ 1,799,294 $ 2,343,329 $ 5,717,438 41.0 % Life operations — 155,804 333,436 177,632 N/M Total premiums earned $ 5,173,403 $ 1,955,098 $ 2,676,765 $ 5,895,070 45.4 % ____________ (1) Represents the sum face value outstanding of the in force life reinsurance policies. * N/M - Not Meaningful

Schedule VI - Supplementary Inf

Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations	12 Months Ended
	Dec. 31, 2016
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Schedule VI - Supplementary information concerning property/casualty (re)insurance operations	SCHEDULE VI SUPPLEMENTAL INFORMATION CONCERNING PROPERTY/CASUALTY (RE)INSURANCE OPERATIONS FOR THE YEARS ENDED DECEMBER 31, 2016, 2015 AND 2014 (U.S. dollars in thousands) Deferred Acquisition Costs and Value of Business Acquired Reserves for Losses and Loss Expenses Reserves for Unearned Premiums Net Earned Premiums Net Investment Income Losses and Loss Expenses incurred related to Net Paid Losses and Loss Expenses Amortization of Deferred Acquisition Costs Net Premiums Written Current Year Prior Year 2016 $ 947,702 $ 25,939,571 $ 7,292,593 $ 9,765,887 $ 640,656 $ 6,374,377 $ (301,542 ) $ 5,334,520 $ 1,614,896 $ 10,230,636 2015 $ 893,111 $ 25,439,744 $ 7,043,383 $ 8,164,184 $ 644,312 $ 5,072,830 $ (306,630 ) $ 5,374,652 $ 1,306,654 $ 7,888,824 2014 $ 357,067 $ 19,353,241 $ 3,973,159 $ 5,717,438 $ 642,492 $ 3,513,465 $ (255,072 ) $ 3,821,335 $ 724,003 $ 5,767,209

Significant Accounting Polici36

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of preparation	These consolidated financial statements include the accounts of the Company and all of its subsidiaries. These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). To facilitate period-to-period comparisons, certain reclassifications have been made to prior year consolidated financial statement amounts to conform to the current year presentation. There was no effect on net income from this change in presentation.
Use of estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amount 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. The Company’s most significant areas of estimation include: ▪ unpaid losses and loss expenses and unpaid losses and loss expenses recoverable; ▪ future policy benefit reserves; ▪ valuation and other-than-temporary impairments of investments; ▪ income taxes; ▪ reinsurance premium estimates; and ▪ carrying value of goodwill and intangible assets. While management believes that the amounts included in the consolidated financial statements reflect the Company’s best estimates and assumptions, actual results could differ from these estimates.
Basis of fair value measurement	Financial Instruments Subject to Fair Value Measurements Accounting guidance over fair value measurements requires that a fair value measurement reflect the assumptions market participants would use in pricing an asset or liability based on the best information available. Assumptions include the risks inherent in a particular valuation technique (such as a pricing model) and/or the risks inherent in the inputs to the model. The fair value of a financial instrument is the amount 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 (the "exit price"). Instruments that the Company owns ("long positions") are marked to bid prices and instruments that the Company has sold but not yet purchased ("short positions") are marked to offer prices. Fair value measurements are not adjusted for transaction costs. Basis of Fair Value Measurement Fair value measurements accounting guidance also establishes a fair value hierarchy that prioritizes the inputs to the respective valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). An asset or liability’s classification within the fair value hierarchy is based on the lowest level of significant input to its valuation. The three levels of the fair value hierarchy are described further below: ▪ Level 1 - Quoted prices in active markets for identical assets or liabilities (unadjusted); no blockage factors. ▪ Level 2 - Other observable inputs (quoted prices in markets that are not active or inputs that are observable either directly or indirectly)—include quoted prices for similar assets/liabilities (adjusted) other than quoted prices in Level 1; quoted prices in markets that are not active; or other inputs that are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. ▪ Level 3 - Unobservable inputs that are supported by little or no market activity and are significant to the fair value of the assets or liabilities. Unobservable inputs reflect the reporting entity’s own assumptions about the assumptions that market participants would use in pricing the asset or liability. Level 3 assets and liabilities include financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation. Details on assets and liabilities that have been included under the requirements of authoritative guidance on fair value measurements to illustrate the bases for determining the fair values of these items held by the Company are included in each respective section of this note. Fair values of investments and derivatives are based on published market values if available, estimates of fair values of similar issues, or estimates of fair values provided by independent pricing services and brokers. Fair values of financial instruments for which quoted market prices are not available or for which the Company believes current trading conditions represent distressed markets are based on estimates using present value or other valuation techniques. The fair values estimated using such techniques are significantly affected by the assumptions used, including the discount rates and the estimated amounts and timing of future cash flows. In such instances, the derived fair value estimates cannot be substantiated by comparison to independent markets and are not necessarily indicative of the amounts that would be realized in a current market exchange.
Investments	Investments - Available For Sale Investments that are considered available for sale (comprised of fixed maturities, equity securities and short-term investments) are carried at fair value. The fair values for available for sale investments are generally sourced from third parties. The fair values of fixed income securities are based upon quoted market values where available, "evaluated bid" prices provided by third party pricing services ("pricing services") where quoted market values are not available, or by reference to broker or underwriter bid indications where pricing services do not provide coverage for a particular security. To the extent the Company believes current trading conditions represent distressed transactions, the Company may elect to utilize internally generated models. It is common industry practice to utilize pricing services as a source for determining the fair values of investments where the pricing services are able to obtain sufficient market-corroborating information to allow them to produce a valuation at a reporting date. In addition, in the majority of cases, although a value may be obtained from a particular pricing service for a security or class of similar securities, these values are corroborated against values provided by other pricing services. The pricing services use market approaches to valuations using primarily Level 2 inputs in the vast majority of valuations, or some form of discounted cash flow analysis, to obtain investment values for a small percentage of fixed income securities for which they provide a price. Standard inputs to the valuations provided by the pricing services listed in approximate order of priority for use when available include: reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data. The pricing services may prioritize inputs differently on any given day for any security, and not all inputs listed are available for use in the evaluation process on any given day for each security evaluation; however, the pricing services also monitor market indicators, customer feedback through a price challenge process and industry and economic events. Information of this nature is a trigger to acquire further corroborating market data. When these inputs are not available, they identify "buckets" of similar securities (allocated by asset class types, sectors, sub-sectors, contractual cash flows/structure, and credit rating characteristics) and apply some form of matrix or other modeled pricing to determine an appropriate security value which represents their best estimate as to what a buyer in the marketplace would pay for a security in a current sale. Prices provided by independent pricing services and independent broker quotes can vary widely even for the same security. The use of different methodologies and assumptions may have a material effect on the estimated fair value amounts. While the Company receives values for the majority of the investment securities it holds from pricing services, it is ultimately management’s responsibility to determine whether the values received and recorded in the financial statements are representative of appropriate fair value measurements. Broker/dealer quotations are used to value fixed maturities where prices are unavailable from pricing services due to factors specific to the security such as limited liquidity, lack of current transactions, or trades only taking place in privately negotiated transactions. These are considered Level 3 valuations, as significant inputs utilized by brokers may be difficult to corroborate with observable market data, or sufficient information regarding the specific inputs utilized by the broker was not available to support a Level 2 classification. Equity securities include investments in open-end mutual funds and shares of publicly traded hedge funds. The fair value of equity securities is based upon quoted market values (Level 1), or monthly net asset value statements provided by the investment managers upon which subscriptions and redemptions can be executed (Level 2). Short-term investments include investments due to mature within one year from the date of purchase and are valued using the same external factors and in the same manner as fixed income securities. Changes in the value of investments available for sale are reflected as unrealized gains or losses on investments, and are included in "accumulated other comprehensive income (loss)", on a net of tax basis. All investment transactions are recorded on a trade date basis. Realized gains and losses on sales of equities and fixed income investments are determined on a first-in, first-out basis. Investment income is recognized when earned and includes interest and dividend income together with the amortization of premium and discount on fixed maturities and short-term investments, and is recorded net of related investment expenses. Amortization of discounts on fixed maturities includes amortization to expected recovery values for investments that have previously been recorded as other than temporarily impaired. For mortgage-backed securities, and any other holdings for which there is a prepayment risk, prepayment assumptions are evaluated and revised as necessary. Prepayment fees or call premiums that are only payable to the Company when a security is called prior to its maturity are earned when received and reflected in net investment income. Investments - Trading Investments for which the Company has elected the fair value option are classified as "trading". Trading securities are carried at fair value. All trading securities are held in support of the GreyCastle Life Retro Arrangements as defined in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ." Thus, changes in the fair value of trading securities are included in "Net unrealized gains (losses) on investments, trading securities - Life Funds Withheld Assets," and interest and dividend income from trading securities are included as a component of "Net investment income - Life Funds Withheld Assets". Investments Related to Life Retrocession Arrangements written on a Funds Withheld Basis Designated investments that support the GreyCastle Life Retro Arrangements, which were written on a funds withheld basis ("Life Funds Withheld Assets") and entered into in connection with the sale of our life reinsurance subsidiary, are classified as either available for sale or trading. Investment results for these assets - including interest income, unrealized gains and losses, and gains and losses from sales - are passed directly to the reinsurer pursuant to a contractual arrangement that is accounted for as a derivative. Changes in the fair value of the embedded derivative associated with the GreyCastle Life Retro Arrangements are recorded in "Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets" on the consolidated statements of income. The fair value of the embedded derivative is included within "Funds withheld on life retrocession arrangements, net of future policy benefit reserves recoverable" on the consolidated balance sheets. Investments In Affiliates Investments in which the Company has significant influence over the operating and financial policies of the investee are classified as investments in affiliates on the Company’s balance sheets and are accounted for under the equity method of accounting. Under this method, the Company records its proportionate share of income or loss from such investments in its results for the period as well as its portion of movements in certain of the investee shareholders’ equity balances. When financial statements of the affiliate are not available on a timely basis to record the Company’s share of income or loss for the same reporting periods as the Company, the most recently available financial statements are used. This lag in reporting is applied consistently. Distributions received from affiliates representing returns on invested capital are recorded as operating cash flows, while distributions representing returns of invested capital or proceeds upon sale of all or a portion of an affiliate are recorded as investing cash flows. The Company generally records its hedge fund and private investment fund affiliates on a one -month and three -month lag, respectively, and its operating affiliates on a three -month lag. Significant influence is considered on a case-by-case basis. Investments in affiliates are not subject to fair value measurement guidance as they are not considered to be fair value measured investments under GAAP. However, impairments associated with investments in affiliates that are deemed to be other-than-temporary are calculated in accordance with fair value measurement guidance and appropriate disclosures included within the financial statements during the period the losses are recorded. Other Investments Contained within this asset class are equity interests in investment funds, limited partnerships and unrated tranches of collateralized debt obligations for which the Company does not have sufficient rights or ownership interests to follow the equity method of accounting. Also included within other investments are structured transactions, which are carried at amortized cost. Fair values for other investments, principally other direct equity investments, investment funds and limited partnerships, are primarily based on the net asset value provided by the investment manager, the general partner or the respective entity, recent financial information, available market data and, in certain cases, management judgment, if required. These entities generally carry their trading positions and investments, the majority of which have underlying securities valued using Level 1 or Level 2 inputs, at fair value as determined by their respective investment managers; accordingly, these investments are generally classified as Level 2. Investments for which fair value is estimated using net asset value per share as a practical expedient are excluded from the fair value hierarchy. Private equity investments are classified as Level 3. The net unrealized gain or loss on investments, net of tax, is included in "Accumulated other comprehensive income (loss)." Any unrealized loss in value considered by management to be other-than-temporary is charged to income in the period in which it is determined. Overseas deposits include investments in private funds related to Lloyd’s syndicates in which the underlying instruments are primarily fixed maturities. The funds themselves do not trade on an exchange and therefore are not included within available for sale securities. Also included in overseas deposits are restricted balances held by Lloyd’s syndicates for solvency purposes which are primarily invested in cash and cash equivalents. Given the restricted nature of these balances, they are included in other investments on the balance sheets. Each of these investment types is considered a Level 2 valuation. The Company has historically participated in structured transactions. These have included providing cash loans supporting project finance transactions, and providing liquidity facility financing to structured project deals. The Company also invested in a payment obligation with an insurance company. The Company's policy is to value such transactions at amortized cost.
Premiums	Insurance premiums written are recorded in accordance with the terms of the underlying policies. Reinsurance premiums written are recorded at the inception of the policy and are estimated based upon information received from ceding companies and any subsequent differences arising on such estimates are recorded in the period they are determined. For multi-year reinsurance treaties which are payable in annual installments, generally, only the initial annual installment is included as premiums written at policy inception due to the ability of the reinsured to commute or cancel coverage during the term of the policy. The remaining annual installments are included as premiums written at each successive anniversary date within the multi-year term. Premiums are earned on a pro-rata basis over the period the coverage is provided. Unearned premiums represent the portion of premiums written applicable to the unexpired terms of policies in force. Net premiums earned are presented after deductions for reinsurance ceded, as applicable. Mandatory reinstatement premiums are recognized and earned at the time a loss event occurs. Life and annuity premiums from long duration contracts that transfer significant mortality or morbidity risks are recognized as revenue and earned when due from policyholders. Life and annuity premiums from long duration contracts that do not subject the Company to risks arising from policyholder mortality or morbidity are accounted for as investment contracts and presented within deposit liabilities. The Company has periodically written retroactive loss portfolio transfer contracts. These contracts are evaluated to determine whether they meet the established criteria for reinsurance accounting, and, if so, at inception, written premiums are fully earned and corresponding losses and loss expense recognized. The contracts can cause significant variances in gross premiums written, net premiums written, net premiums earned, and net incurred losses in the years in which they are written. Reinsurance contracts sold not meeting the established criteria for reinsurance accounting are recorded using the deposit method.
Acquisition costs	Acquisition costs, which vary with and are directly related to the acquisition of policies, consist primarily of commissions paid to brokers and cedants, and are deferred and amortized over the period during which the premiums are earned. Acquisition costs are shown net of contractual commissions earned on reinsurance ceded. Future earned premiums, the anticipated losses and other costs (and in the case of a premium deficiency, investment income) related to those premiums, are also considered in determining the level of acquisition costs to be deferred.
Reinsurance	In the normal course of business, the Company seeks to reduce the potential amount of loss arising from claims events by reinsuring certain levels of risk assumed in various areas of exposure with other insurers or reinsurers. Reinsurance premiums ceded are expensed (and any commissions recorded thereon are earned) on a monthly pro-rata basis over the period the reinsurance coverage is provided. Ceded unearned reinsurance premiums represent the portion of premiums ceded applicable to the unexpired term of policies in force. Mandatory reinstatement premiums ceded are recorded at the time a loss event occurs. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policy. Provisions are made for estimated unrecoverable reinsurance. The Company enters into ceded reinsurance agreements with other companies in the normal course of business. All premium and loss-related balances related to reinsurance agreements are reported on a gross basis within our consolidated balance sheets, with the exception of the GreyCastle Life Retro Arrangements, which were written on a funds withheld basis. The future policy benefit reserves recoverable related to these retrocession arrangements are netted against the funds withheld liability owing to the counterparty on the consolidated balance sheets due to the contractual right of offset. During the year ended December 31, 2014, the Company recorded $20 million , net of tax, to premiums earned and associated tax accruals, related to reinstatement premiums due under assumed reinsurance contracts arising from unpaid losses and loss expenses reported in a prior period. We evaluated the quantitative and qualitative aspects of this correction and concluded that the impact of recognizing it during the third quarter of 2014 was not material to the consolidated financial statements, nor was it material to previously issued consolidated financial statements in prior periods.
Fee income and other	Fee income and other includes fees received for insurance and product structuring services provided and is earned over the service period of the contract. Any adjustments to fees earned or the service period are reflected in income in the period when determined.
Other-than-temporary impairments ("OTTI") of available for sale and held to maturity securities	The Company’s process for identifying declines in the fair value of investments that are other-than-temporary involves consideration of several factors. The primary factors include (i) an analysis of the liquidity, business prospects and financial condition of the issuer including consideration of credit ratings, (ii) the significance of the decline, (iii) an analysis of the collateral structure and other credit support, as applicable, of the securities in question, and (iv) for debt securities, whether the Company intends to sell such securities. In addition, the authoritative guidance requires that OTTI for certain asset-backed and mortgage-backed securities be recognized if the fair value of the security is less than its discounted cash flow value and there has been a decrease in the present value of the expected cash flows since the last reporting period. Where the Company’s analysis of the above factors results in the Company’s conclusion that declines in fair values are other-than-temporary, the cost of the security is written down to discounted cash flow and a portion of the previously unrealized loss is therefore realized in the period such determination is made. With respect to equity securities and other investments carried at fair value, we generally impair a security if its fair value is 50% or lower than its amortized cost or if the security is in a loss position for 11 or more consecutive months. If the Company intends to sell an impaired security, or it is more likely than not that it will be required to sell the security before recovery of its amortized cost basis, the impairment is other-than-temporary and is recognized currently in earnings in an amount equal to the entire difference between fair value and amortized cost. In instances in which the Company determines that a credit loss exists but the Company does not intend to sell the security, and it is not more likely than not that the Company will be required to sell the security before the anticipated recovery of its remaining amortized cost basis, the OTTI is separated into (1) the amount of the total impairment related to the credit loss and (2) the amount of the total impairment related to all other factors (i.e. the noncredit portion). The amount of the total OTTI related to the credit loss is recognized in earnings and the amount of the total OTTI related to all other factors is recognized in accumulated other comprehensive loss. The total OTTI is presented in the income statement with an offset for the amount of the total OTTI that is recognized in accumulated other comprehensive income (loss). Absent the intent or requirement to sell a security, if a credit loss does not exist, any impairment is considered to be temporary. The noncredit portion of any OTTI losses on securities classified as available for sale is recorded as a component of other comprehensive income (loss) with an offsetting adjustment to the carrying value of the security. The fair value adjustment could increase or decrease the carrying value of the security. In periods subsequent to the recognition of an OTTI loss, the other-than-temporarily impaired debt security is accounted for as if it had been purchased on the measurement date of the OTTI at an amount equal to the previous amortized cost basis less the credit-related OTTI recognized in earnings. For debt securities for which credit-related OTTI is recognized in earnings, the difference between the new cost basis and the cash flows expected to be collected is accreted into interest income over the remaining life of the security in a prospective manner based on the estimated amount and timing of future estimated cash flows. With respect to securities where the decline in value is determined to be temporary and the security’s amortized cost is not written down, a subsequent decision may be made to sell that security and realize a loss. Subsequent decisions on security sales are made within the context of overall risk monitoring, changing information, market conditions generally and assessing value relative to other comparable securities. We have outsourced a significant portion of the day-to-day management of the Company’s investment portfolio to third party investment manager service providers. While these investment manager service providers may, at a given point in time, believe that the preferred course of action is to hold securities with unrealized losses that are considered temporary until such losses are recovered, the dynamic nature of the portfolio management may result in a subsequent decision to sell the security and realize the loss, based upon a change in market and other factors described above. The Company believes that subsequent decisions to sell such securities are consistent with the classification of the Company’s portfolio as available for sale. There are risks and uncertainties associated with determining whether declines in the fair value of investments are other-than-temporary. These include subsequent significant changes in general economic conditions as well as specific business conditions affecting particular issuers, subjective assessment of issue-specific factors (seniority of claims, collateral value, etc.), future financial market effects, stability of foreign governments and economies, future rating agency actions and significant disclosure of accounting, fraud or corporate governance issues that may adversely affect certain investments. In addition, significant assumptions and management judgment are involved in determining if the decline is other-than-temporary. If management determines that a decline in fair value is temporary, then a security’s value is not written down at that time. However, there are potential effects upon the Company’s future earnings and financial position should management later conclude that some of the current declines in the fair value of the investments are other-than-temporary declines.
Derivative instruments	The Company recognizes all derivatives as either assets or liabilities on the balance sheets and measures those instruments at fair value. Except for the embedded derivative associated with the GreyCastle Life Retro Arrangements discussed above within (c) "Investments Related to Life Retrocession Arrangements written on a Funds Withheld Basis," the changes in fair value of derivatives are shown in the consolidated statements of income as "net realized and unrealized gains and losses on derivative instruments," unless the derivatives are designated as hedging instruments. The accounting for derivatives that are designated as hedging instruments is discussed below. Changes in the fair value of derivatives may create volatility in the Company’s results of operations from period to period. Amounts recognized for the right to reclaim cash collateral (a receivable) or the obligation to return cash collateral (a payable) are offset against net fair value amounts recognized in the consolidated balance sheets for derivative instruments executed with the same counterparty under the same netting arrangement to the extent that the Company intends to settle the amounts on a net basis. Derivative contracts can be exchange-traded or over-the-counter ("OTC"). Exchange-traded derivatives (futures and options) typically fall within Level 1 of the fair value hierarchy depending on whether they are deemed to be actively traded or not. OTC derivatives are valued using market transactions and other market evidence whenever possible, including market-based inputs to models, model calibration to market clearing transactions, broker or dealer quotations or alternative pricing sources where an understanding of the inputs utilized in arriving at the valuations is obtained. Where models are used, the selection of a particular model to value an OTC derivative depends upon the contractual terms and specific risks inherent in the instrument as well as the availability of pricing information in the market. The Company generally uses similar models to value similar instruments. Valuation models require a variety of inputs, including contractual terms, market prices, yield curves, credit curves, measures of volatility, prepayment rates and correlations of such inputs. For OTC derivatives that trade in liquid markets, such as generic forwards, interest rate swaps and options, model inputs can generally be verified and model selection does not involve significant management judgment. Such instruments comprise the majority of derivatives held by the Company and are typically classified within Level 2 of the fair value hierarchy. Certain OTC derivatives trade in less liquid markets with limited pricing information, or required model inputs that are not directly market corroborated, which causes the determination of fair value for these derivatives to be inherently more subjective. Accordingly, such derivatives are classified within Level 3 of the fair value hierarchy. The valuations of less standard or less liquid OTC derivatives are typically based on Level 1 and/or Level 2 inputs that can be observed in the market, as well as unobservable Level 3 inputs. Level 1 and Level 2 inputs are regularly updated to reflect observable market changes. Level 3 inputs are only changed when corroborated by evidence such as similar market transactions, pricing services and/or broker or dealer quotations. The Company conducts its non-hedging derivatives activities in three main areas: investment related derivatives, credit derivatives and other non-investment related derivatives. The Company uses derivative instruments, primarily interest rate swaps, to manage the interest rate exposure associated with certain assets and liabilities. These derivatives are recorded at fair value. On the date the derivative contract is entered into, the Company may designate the derivative as: a hedge of the fair value of a recognized asset or liability ("fair value" hedge); a hedge of the variability in cash flows of a forecasted transaction or of amounts to be received or paid related to a recognized asset or liability ("cash flow" hedge); or a hedge of a net investment in a foreign operation. Alternatively, the Company may not designate any hedging relationship for a derivative contract. Fair Value Hedges Changes in the fair value of a derivative that is designated and qualifies as a fair value hedge, along with the changes in the fair value of the hedged asset or liability that is attributable to the hedged risk, are recorded in current period earnings (through "net realized and unrealized gains and losses on derivative instruments") with any differences between the net change in fair value of the derivative and the hedged item representing the hedge ineffectiveness. Periodic derivative net coupon settlements are recorded in net investment income with the exception of hedges of Company-issued debt, which are recorded in interest expense. The Company may designate fair value hedging relationships where interest rate swaps are used to hedge the changes in the fair value of certain fixed rate liabilities and fixed maturity securities due to changes in the designated benchmark interest rate. Cash Flow Hedges Changes in the fair value of a derivative that is designated and qualifies as a cash flow hedge are recorded in accumulated other comprehensive income ("AOCI") and are reclassified into earnings when the variability of the cash flow of the hedged item impacts earnings. Gains and losses on derivative contracts that are reclassified from AOCI to current period earnings are included in the line item in the consolidated statements of operations in which the cash flows of the hedged item are recorded. Any hedge ineffectiveness is recorded immediately in current period earnings as "net realized and unrealized gains and losses on derivative instruments." Periodic derivative net coupon settlements are recorded in net investment income. The Company may designate cash flow hedging relationships where interest rate swaps are used to mitigate interest rate risk associated with anticipated issuances of debt or other forecasted transactions. Hedges of the Net Investment in a Foreign Operation Changes in the fair value of a derivative used as a hedge of a net investment in a foreign operation, to the extent effective as a hedge, are recorded in the foreign currency translation adjustments account within AOCI. Cumulative changes in fair value recorded in AOCI are reclassified into earnings upon the sale or complete or substantially complete liquidation of the foreign entity. Any hedge ineffectiveness is recorded immediately in current period earnings as "net realized and unrealized gains and losses on derivative instruments." Hedge Documentation and Effectiveness Testing To qualify for hedge accounting treatment, a derivative must be highly effective in mitigating the designated changes in value or cash flow of the hedged item. At hedge inception, the Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objective and strategy for undertaking each hedge transaction. The documentation process includes linking derivatives that are designated as fair value, cash flow, or net investment hedges to specific assets or liabilities on the balance sheet or to specific forecasted transactions. The Company also formally assesses, both at the hedge’s inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in fair values or cash flows of hedged items. In addition, certain hedging relationships are considered highly effective if the changes in the fair value or discounted cash flows of the hedging instrument are within a ratio of 80-125% of the inverse changes in the fair value or discounted cash flows of the hedged item. Hedge ineffectiveness is measured using qualitative and quantitative methods. Qualitative methods may include comparison of critical terms of the derivative to the hedged item. Depending on the hedging strategy, quantitative methods may include the "Change in Variable Cash Flows Method," the "Change in Fair Value Method," the "Hypothetical Derivative Method" or the "Dollar Offset Method." Discontinuance of Hedge Accounting The Company discontinues hedge accounting prospectively when it determines that the derivative is no longer highly effective in offsetting changes in the fair value or cash flows of a hedged item; the derivative is dedesignated as a hedging instrument; or the derivative expires or is sold, terminated or exercised. When hedge accounting is discontinued because it is determined that the derivative no longer qualifies as an effective fair-value hedge, the derivative continues to be carried at fair value on the balance sheets with changes in its fair value recognized in current period earnings through "net realized and unrealized gains and losses on derivative instruments." When hedge accounting is discontinued because the Company becomes aware that it is not probable that the forecasted transaction will occur, the derivative continues to be carried on the balance sheets at its fair value, and gains and losses that were accumulated in AOCI are recognized immediately in earnings.
Cash equivalents	Cash equivalents include fixed interest deposits placed with a maturity of under 90 days when purchased. Bank deposits are not considered to be fair value measurements and as such are not subject to the authoritative guidance on fair value measurement disclosures. Money market funds are classified as Level 1, as these instruments are considered actively traded; however, certificates of deposit are classified as Level 2.
Restricted cash	Restricted cash represents cash and cash equivalents that the Company is a) holding for the benefit of a third party and is legally or contractually restricted as to withdrawal or usage for general corporate purposes; and b) not replaceable by another type of asset other than cash or cash equivalents, under the terms of the Company's contractual arrangements with such third parties.
Foreign currency translation	Assets and liabilities of foreign operations whose functional currency is not the U.S. dollar are translated at prevailing year-end exchange rates. Revenue and expenses of such foreign operations are translated at monthly average exchange rates during the year. The net effect of the translation adjustments for foreign operations, net of applicable deferred income taxes, as well as any gains or losses on intercompany balances for which settlement is not planned or anticipated in the foreseeable future, are included in "accumulated other comprehensive income (loss)." Monetary assets and liabilities denominated in currencies other than the functional currency of the applicable entity are revalued at the exchange rate in effect at the balance sheet date and revenues and expenses are translated at the exchange rate on the date the transaction occurs with the resulting foreign exchange gains and losses on settlement or revaluation recognized in income.
Goodwill and other intangible assets	The Company has recorded goodwill in connection with various acquisitions in the current and prior years. Goodwill represents the excess of the purchase price over the fair value of the net assets acquired. In accordance with GAAP, the Company tests goodwill for potential impairment annually as of June 30, and between annual tests if an event occurs or circumstances change that may indicate that potential exists for the fair value of a reporting unit to be reduced to a level below its carrying amount. The Company tests for impairment at the reporting unit level in accordance with the authoritative guidance on intangibles and goodwill. The Company has organized its goodwill into two reporting units, reflecting its two segments. The Company’s indefinite-lived intangible assets consist primarily of Lloyd's syndicate capacity plus acquired insurance and reinsurance licenses. These assets are deemed to have indefinite useful lives and are therefore not subject to amortization. In accordance with GAAP, the Company tests non-amortized intangible assets for potential impairment annually, or more frequently if events or changes in circumstances indicate that the asset might be impaired. If the carrying value of a non-amortized intangible asset is in excess of its fair value, the asset must be written down to its fair value through the recognition of an impairment charge to earnings. All of the Company’s depreciable or amortizable intangible and other long-lived assets such as trade names, distribution networks, premises, equipment, agency relationships, and acquired or internally-developed software, are carried at net book value, and are depreciated or amortized on a straight-line basis over their estimated useful lives. The amortization periods approximate the period over which the Company expects to generate future net cash inflows from the use of these assets. All of these assets are subject to impairment testing in accordance with authoritative guidance for the impairment or disposal of long-lived assets when events or conditions indicate that the carrying value of an asset may not be fully recoverable from future cash flows.
Variable interest entities ('VIEs')	Investments or other interests that absorb portions of an entity’s expected losses or receive portions of the entity’s expected residual returns are called variable interests. Entities in which the equity investors, as a group, do not have the characteristic of a controlling financial interest, or that do not have sufficient equity at risk to allow them to finance their own activities without additional financial support are referred to as VIEs. A VIE must be consolidated by its primary beneficiary, which is the variable interest holder that is determined to have the controlling financial interest in the entity. This is the entity that has both: a) the power to direct the VIE’s activities that most significantly impact its economic performance, and b) the obligation to absorb losses or receive benefits of the VIE that could potentially be significant to it.
Non-controlling interests	Non-controlling shareholders' interests are presented separately in the Company's Consolidated Balance Sheets and Consolidated Statements of Shareholders' Equity as required under GAAP. The net loss (income) attributable to non-controlling interests is presented separately in the Company's Consolidated Statements of Comprehensive Income.
Losses and loss expenses	Unpaid losses and loss expenses include reserves for reported unpaid losses and loss expenses and for losses incurred but not reported. The reserve for reported unpaid losses and loss expenses for the Company’s property and casualty ("P&C") operations is established by management based on claims reported from insureds or amounts reported from ceding companies, and represent the estimated ultimate cost of events or conditions that have been reported to or specifically identified by the Company. The reserve for losses incurred but not reported is estimated by management based on loss development patterns determined by reference to the Company’s underwriting practices, the policy form, type of program and historical experience. The Company’s actuaries employ a variety of generally accepted methodologies to determine estimated ultimate loss reserves, including the "Bornhuetter-Ferguson incurred loss method" and frequency and severity approaches. Certain workers’ compensation and certain U.K. bodily injury liabilities are considered fixed and determinable and are discounted. Management believes that the reserves for unpaid losses and loss expenses are sufficient to cover losses that fall within coverages assumed by the Company. However, there can be no assurance that losses will not exceed the Company’s total reserves. The methodology of estimating loss reserves is periodically reviewed to ensure that the assumptions made continue to be appropriate and any adjustments resulting from such reviews are reflected in income in the year in which the adjustments are made.
Deposit liabilities	Contracts entered into by the Company that are not deemed to transfer significant underwriting risk and/or timing risk are accounted for as deposits, whereby liabilities are initially recorded at an amount equal to the assets received. The Company uses a portfolio rate of return of equivalent duration to the liabilities in determining risk transfer. An initial accretion rate is established based on actuarial estimates whereby the deposit liability is increased to the estimated amount payable over the term of the contract. The deposit accretion rate is the rate of return required to fund expected future payment obligations (this is equivalent to the "best estimate" of future cash flows), which are determined actuarially based upon the nature of the underlying indemnifiable losses. Accretion of the liability is recorded as interest expense. The Company periodically reassesses the estimated ultimate liability. Any changes to this liability are reflected as adjustments to interest expense to reflect the cumulative effect of the period the contract has been in force, and by an adjustment to the future accretion rate of the liability over the remaining estimated contract term.
Future policy benefit reserves	The Company estimates the present value of future policy benefits related to long duration contracts using assumptions for investment yields, mortality, and expenses, including a provision for adverse deviation. The assumptions used to determine future policy benefit reserves are best estimate assumptions that are determined at the inception of the contracts and are locked-in throughout the life of the contract unless a premium deficiency develops. As the experience on the contracts emerges, the assumptions are reviewed. If such review would produce reserves in excess of those currently held, then the locked-in assumptions will be revised and a claim and policy benefit is recognized at that time. The Company includes the cost of reinsurance in its premium deficiency considerations. Certain life insurance and annuity contracts provide the holder with a guarantee that the benefit received upon death will be no less than a minimum prescribed amount. The contracts are accounted for in accordance with GAAP, which requires that the best estimate of future experience be combined with actual experience to determine the benefit ratio used to calculate the policy benefit reserve.
Income taxes	The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, we determine deferred tax assets and liabilities on the basis of the differences between the financial statement and tax bases of assets and liabilities by using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes deferred tax assets to the extent that we believe that these assets are more likely than not to be realized. In making such a determination, we consider all available positive and negative evidence, including future reversals of existing temporary differences, projected future taxable income, tax planning strategies, and taxable income in prior years that may be available for carryback. A valuation allowance will be established for any portion of a deferred tax asset that we believe will not be realized, and the impact will be included in the provision for income taxes. The Company records uncertain tax positions in accordance with ASC 740 on the basis of a two- step process in which (1) we determine whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more likely than not recognition threshold, we recognize the largest amount of tax benefit that is more than 50 percent likely to be realized upon settlement with the tax authority. The Company recognizes interest and penalties on underpaid tax as a component of income tax expense. The Company’s investment income is allocated to applicable branch operations and is taxable in certain jurisdictions. The method of allocating this income may be different for tax reporting as compared to GAAP. The Company records the tax effects of this allocation entirely through operations.
Stock plans	At December 31, 2016 , the Company had several stock-based performance incentive programs, which are described more fully in Note 19, "Share Capital ." Stock-based compensation issued under these plans generally has a life of not longer than ten years and vests as set forth at the time of grant. Awards generally vest annually over three or four years from the date of grant. The Company recognizes compensation costs for stock-based awards on a straight-line basis over the requisite service period (usually the vesting period) for each award. Share-based payments to employees classified as equity awards, including grants of employee stock options, are recognized in the financial statements over the vesting period based on their grant date fair values. Share-based payments to employees classified as liability awards, including grants of restricted cash units, are recognized in the financial statements over the vesting period based on their fair values which are remeasured each reporting period until the awards are settled. Authoritative guidance requires that compensation costs be recognized for unvested stock-based compensation awards over the period through the date that the employee is no longer required to provide future services to earn the award, rather than over the explicit service period. Accordingly, the Company follows a policy of recognizing compensation cost to coincide with the date that the employee is eligible to retire, rather than the actual retirement date, for all stock-based compensation granted.
Per share data	Basic earnings per common share is based on weighted average common shares outstanding excluding any dilutive effects of potential share issuances under share-based compensation awards. Diluted earnings per common share assumes the exercise of all dilutive share-based compensation awards has occurred.
Recent accounting pronouncements	Recently Issued Accounting Standards Adopted in 2016 ASU 2014-15 Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In August 2014, the Financial Accounting Standards Board ("FASB") issued an accounting standards update concerning the evaluation of an entity's ability to continue as a going concern. Under this new guidance, in connection with preparing financial statements for each annual and interim reporting period, an entity's management should evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity's ability to continue as a going concern within one year after the date that the financial statements are issued. Management's evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. Substantial doubt exists when it is probable that the entity will be unable to meet its obligations as they become due. When management identifies conditions or events that raise substantial doubt about an entity's ability to continue as a going concern, management should consider whether its plans that are intended to mitigate those conditions or events will alleviate the substantial doubt. The mitigating effect of management's plans should be considered only to the extent that it is probable that the plans will be implemented, and if implemented, it is probable that the plans will be effective. If conditions or events raise substantial doubt, the entity should disclose the conditions or events, management's evaluation of their significance in relation to the ability to meet its obligations, and management's plans to mitigate the conditions or events along with whether substantial doubt has been alleviated. The Company adopted this guidance in 2016. There was no impact on its financial condition, results of operations, or cash flows, nor were any additional disclosures required. ASU 2015-02 Amendments to the Consolidation Analysis In February 2015, the FASB issued an accounting standards update concerning consolidation of certain legal entities. Under this new guidance, all legal entities are required to evaluate whether they should consolidate certain legal entities. The guidance: (1) modifies the evaluation of whether limited partnerships and similar legal entities are VIEs or voting interest entities; (2) eliminates the presumption that a general partner should consolidate a limited partnership; (3) affects the consolidation analysis of reporting entities that are involved with VIEs, particularly those that have fee arrangements and related party relationships; and (4) provides a scope exception from consolidation guidance for certain reporting entities. Upon adoption of the new guidance, differing requirements for performing a consolidation analysis under existing GAAP will be eliminated, and all reporting entities will now fall within the scope of the Accounting Standards Codification Subtopic 810-10, Consolidation-Overall , unless a specific exception applies. Under this Subtopic, there are only two primary models for determining whether consolidation is appropriately a voting interest entity model, and a variable interest entity model. The Company adopted this guidance in 2016. There was no impact on its financial condition, results of operations, or cash flows. The disclosure in Item 8, Note 16, "Variable Interest Entities ," was updated as a result of the adoption of this update. ASU 2015-07 Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent) In May 2015, the FASB issued an accounting standards update concerning investments for which management estimates fair value using net asset value per share (or its equivalent) as a practical expedient. Under the guidance, such investments will no longer be reported within the fair value hierarchy. Removing those investments from the fair value hierarchy not only eliminates the diversity in practice resulting from the way in which investments measured at net asset value per share (or its equivalent) with future redemption dates are classified, but also ensures that all investments categorized in the fair value hierarchy are classified using a consistent approach. Investments that calculate net asset value per share (or its equivalent), but for which the practical expedient is not applied, will continue to be included in the fair value hierarchy. A reporting entity should continue to disclose information on investments for which fair value is measured at net asset value (or its equivalent) as a practical expedient to help users understand the nature and risks of the investments and whether the investments, if sold, are probable of being sold at amounts different from net asset value. The Company adopted this guidance in 2016. As this guidance is disclosure related only, there was no impact on the Company's financial condition, results of operations, or cash flows. The disclosures in Item 8, Note 8, "Fair Value Measurements ," were updated as a result of the adoption of this update. ASU 2015-09 Disclosures about Short-Duration Contracts In May 2015, the FASB issued an accounting standards update concerning the annual disclosure regarding the liability for unpaid claims and claims adjustment expenses for insurance entities. The guidance requires: (1) incurred and paid claims development information by accident year, on a net basis after reinsurance, for the number of years for which claims incurred typically remain outstanding, including the most recent reporting period, which need not exceed 10 years; (2) a reconciliation of incurred and paid claims development information to the aggregate carrying amount of the liability for unpaid claims and claim adjustment expenses, with separate disclosure of reinsurance recoverable on unpaid claims for each period presented in the statement of financial position; (3) for each accident year for which incurred claims development information is presented, the total of incurred but not reported ("IBNR") liabilities plus expected development on reported claims included in the liability for unpaid claims and claims adjustment expenses, accompanied by a description of reserving methodologies; (4) for each accident year for which incurred claims development information is presented, quantitative information about claim frequency (unless it is impracticable to do so) accompanied by a qualitative description of methodologies used for determining claim frequency information; and (5) for all claims, the average annual percentage payout of incurred claims by age for the same number of accident years as the disclosure for IBNR. The guidance recommends that insurance entities aggregate or disaggregate those disclosures so that useful information is not obscured by either the inclusion of a large amount of insignificant detail or the aggregation of items that have significantly different characteristics. The amendments also require insurance entities to disclose information about significant changes in methodologies and assumptions used to calculate the liability for unpaid claims and claim adjustment expenses, including reasons for the change and the effects on the financial statements. Additionally, the amendments require insurance entities to disclose for annual and interim reporting periods a rollforward of the liability for unpaid claims and claims adjustment expenses. Additional disclosures about liabilities for unpaid claims and claim adjustment expenses reported at present value include: (1) for each period presented in the statement of financial position, the aggregate amount of discount for the time value of money deducted to derive the liability for unpaid claims and claim adjustment expenses; (2) for each period presented in the statement of income, the amount of interest accretion recognized; and (3) the line items in the statement of income in which interest accretion is classified. The Company adopted this guidance in 2016. There was no impact on its financial condition, results of operations, or cash flows. The additional disclosures required by this update have been included in Item 8, Note 10, "Losses and Loss Expenses ." ASU 2016-07 Simplifying the Transition to the Equity Method of Accounting In March 2016, the FASB issued an accounting standards update concerning the accounting for equity method investments. The amendments in this update require an investor to increase its current basis in an investment by the cost of the acquisition of an additional interest in the investee when the investment qualifies for use of the equity method as a result of such increase in the level of ownership interest or degree of influence and adopt the equity method of accounting as of that date. Additionally, if the investment was previously accounted for as an available-for-sale ("AFS") security, an entity also should immediately recognize through earnings the unrealized holding gain or loss in AOCI as of that date. Thus, this new treatment is eliminating existing GAAP rules requiring retroactive adjustment of an entity’s investments, results of operations and retained earnings when an existing investment qualifies for the equity method of accounting. The guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016, applied prospectively upon its effective date. However, the Company elected to early adopt this guidance during the third quarter of 2016, as was permitted under the standard's transition rules, and recognized approximately $33.5 million in 2016 earnings as a result of the adoption. Recently Issued Accounting Standards Not Yet Adopted ASU 2016-01 Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, the FASB issued an accounting standards update concerning the accounting for financial instruments. The guidance retains the basic existing framework for accounting for financial instruments under GAAP, while achieving limited convergence with IFRS in this area. The guidance: (1) requires equity investments (except consolidated entities and 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) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment; (3) eliminates the requirement to disclose the fair value of financial instruments measured at amortized cost for non-public business entities; (4) eliminates the requirement to disclose the method(s) and significant assumptions used to estimate the fair value of financial instruments measured at amortized cost on the balance sheet; (5) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; (6) requires 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 in accordance with the fair value option for financial statements; (7) requires separate presentation of financial assets and financial liabilities by measurement category and form of asset in the financial statements; and (8) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to AFS securities in combination with the entity's other deferred tax assets. The guidance will be effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. Early adoption is permitted at the beginning of the fiscal year of adoption only, and should be applied by means of a cumulative effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption, except the amendments related to impairment of equity securities without readily determinable fair values. The Company is currently evaluating the impact of this guidance, but expects that it will have an effect on results of operations as mark to market movements will prospectively impact net income. It is not expected to have a material impact on the Company's financial condition or cash flows. ASU 2016-02 Leases In February 2016, the FASB issued an accounting standards update concerning the accounting for leases. The most significant change to existing GAAP created by this standard will be the lessee recognition of lease assets and lease liabilities for those leases classified as operating. The core principle of this guidance stipulates that a lessee should recognize in the statement of financial position, initially measured at the present value of the lease payments, both a liability for contractual payments due under the lease, and an asset representing its right to use the underlying leased asset for the lease term ("right-of-use asset"). For financing leases, interest on the lease liability should be recognized separately from the amortization of the right-of-use asset in the statement of comprehensive income. Additionally, as regards the presentation of financing lease activities within the statement of cash flows, repayments of the principal portion of the lease liability should be classified within financing activities, while payments of interest on the lease liability should be classified within operating activities. For operating leases, a single net lease cost should be recognized over the lease term, generally on a straight-line basis, and all cash payments related to the lease should be classified within operating activities in the statement of cash flows. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities, and therefore recognize lease expense for such leases on a straight-line basis over the lease term. The guidance will be effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach, which includes a number of optional practical expedients that entities may elect to apply. An entity that elects to apply the practical expedients will substantively continue to account for leases that commence before the effective date in accordance with existing GAAP, except that a right-of-use asset and a lease liability must be recorded for all operating leases at each reporting date based on the present value of the remaining minimum rental payments that were previously tracked and disclosed. The Company is currently evaluating the impact of this guidance, but expects that it will have an effect on the Company's financial condition as new assets and liabilities related to operating leases are likely to be recorded as a result of adoption. The Company does not expect this new guidance to have a material impact on the Company's results of operations or cash flows. ASU 2016-09 Improvements to Employee Share-Based Payment Accounting In March 2016, as part of its simplification initiative, the FASB issued an accounting standards update concerning the accounting for several aspects of employee share-based payment awards including: income tax consequences, classification of awards as either equity or liabilities, classification of items in the statement of cash flows, and certain expedients that entities can now elect regarding estimates and assumptions in this area. Regarding the accounting for income taxes, all excess tax benefits and tax deficiencies, including tax benefits of dividends on share-based payment awards, should be recognized as income tax expense or benefit (regardless of whether the benefit reduces taxes payable in the current period) in the income statement, as opposed to additional paid-in capital as current GAAP prescribes. The tax effects of exercised or vested awards should be treated as discrete items in the reporting period in which they occur. Regarding the classification of awards, the update changes the threshold to qualify for equity classification from the employer's minimum statutory withholding requirements to the maximum statutory tax rates in the applicable jurisdictions. Regarding the classification of cash flows, excess tax benefits should be classified along with other income tax cash flows as an operating activity, while cash paid by an employer when directly withholding shares for tax-withholding purposes should be classified as a financing activity. As regards new expedients which can be elected related to estimates and assumptions in this area of accounting, the only one allowable for public business entities is that they may now make an entity-wide accounting policy election to either estimate the number of share-based payment awards that are expected to vest (which is current GAAP) or account for forfeitures as they occur. The guidance will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2016 with early adoption permitted so long as all the amendments in the update are adopted in the same period. The amendments within the guidance related to the recognition of excess tax benefits and tax deficiencies in the income statement as opposed to in paid-in capital should be applied prospectively. The amendments related to the statement of cash flows presentation of excess tax benefits may be adopted either prospectively or retrospectively, while the amendments related to the presentation of employee taxes paid must be applied retrospectively. The remaining amendments - relating to the timing of when excess tax benefits are recognized, the change in the threshold for equity versus liability classification of certain awards, and the allowable policy election regarding forfeitures - should be applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity as of the beginning of the period in which the guidance is adopted. The Company is currently evaluating the impact of this guidance, but expects that it will have an impact on the Company's financial position, results of operations and cash flows upon adoption. ASU 2016-13 Measurement of Credit Loss on Financial Instruments In June 2016, the FASB issued an accounting standards update concerning the measurement of credit losses on financial instruments. The amendments in this update affect the measurement of various financial assets, including loans, debt securities, trade receivables, reinsurance receivables and net investments in leases. For assets measured at amortized cost, the amendments in this update require presentation at the net amount expected to be collected. This results in an allowance for all expected credit losses over an asset’s entire life, with no threshold for recognition. This allowance should be maintained in a valuation account that is deducted from the amortized cost of the asset to result in the net amount for presentation purposes. Credit loss allowances for newly created financial assets and subsequent movements in these allowances will be recognized in the income statement, except for the initial credit losses on assets that are purchased in an already credit-impaired state, which will be added to the purchase price of such assets. For AFS debt securities, credit losses should also be recorded through an allowance. The allowance for credit losses is restricted to the difference between the fair value and amortized cost of the relevant asset. The guidance will be effective for fiscal years, and interim periods within those fiscal years beginning after December 15, 2019. Early adoption is permitted for fiscal years, and interim periods within those fiscal years beginning after December 15, 2018. The updates should be adopted in a modified-retrospective approach, by means of a cumulative-effect adjustment to retained earnings at the beginning of the first reporting period in which the guidance is effective. For securities with an existing other-than-temporary impairment or securities previously acquired with deteriorated quality the relevant provisions should be adopted prospectively. The Company is currently evaluating the impact of this guidance and expects that it will have an impact on the Company’s financial position and results of operations, but not the Company’s cash flows. ASU 2016-15 Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB issued an accounting standards update concerning the presentation and classification of certain cash receipts and cash payments in the statement of cash flows. The amendments in this update are intended to address areas where GAAP is unclear and diversity in practice exists. The following areas are covered in this update: (1) debt prepayment or debt extinguishment costs; (2) settlement of zero-coupon debt instruments; (3) contingent consideration payments following a business combination; (4) proceeds from settlement of insurance claims; (5) proceeds from settlement of corporate-owned life insurance policies; (6) distributions received from equity method investees; (7) beneficial interests in securitization transactions; and (8) separation of cash flows. The guidance will be effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. If an entity adopts this update during an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. An entity that elects early adoption must adopt all of the amendments in the same period. The amendments should be applied using a retrospective transition method to the period presented, unless it is impractical to do so. The Company is currently evaluating the impact of this guidance on our statement of cash flows and does not expect any material impact on the Company's financial position, or results of operations. ASU 2016-16 Income Taxes: Intra-Entity Transfers of Assets Other Than Inventory In October 2016, the FASB issued an accounting standards update concerning the tax effects of intra-entity asset transfers within a group. The new guidance requires an entity to reflect the income tax consequences of an intra-entity transfer of an asset other than inventory when that transfer occurs. This is a departure from current GAAP, which prohibits recognition of tax on such transfers until the asset has been sold to an external party or otherwise realized. The amendments are effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. Early adoption is permitted as of the beginning of an annual reporting period for which no financial statements (either interim or annual) have been issued or made available for issuance. The amendments should be applied on a modified retrospective basis through a cumulative-effect adjustment directly to retained earnings as of the beginning of the period of adoption. The Company is currently evaluating the impact of this guidance. ASU 2016-17 Consolidation: Interests Held through Related Parties That Are under Common Control In October 2016, the FASB issued an accounting standards update concerning the evaluation of indirect interests held through related parties during the assessment of variable interest entities (“VIEs”). When identifying the primary beneficiary of a VIE, this update requires a reporting entity that acts as the single decision maker of that VIE to include, on a proportionate basis, those interests held through related parties under common control when assessing whether it holds a variable interest in that VIE. This is a change from previous GAAP, which required such indirect interests to be included in their entirety during this assessment. In the event that a reporting entity is not considered to be the primary beneficiary of the VIE following this assessment, the update does not change the requirement to assess whether the entity and its related parties under common control as a group possess the characteristics of a primary beneficiary. The guidance will be effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. If an entity early adopts the amendments in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. When adopted, the amendments in this update must be applied retrospectively to all periods since Accounting Standards Update 2015-02 was adopted, which for the Company was the first quarter of 2016. The Company is currently evaluating the impact of this guidance, but does not expect any material impact on the Company’s financial position, results of operations or cash flows. ASU 2016-18 Statement of Cash Flows: Restricted Cash In November 2016, the FASB issued an accounting standards update concerning the presentation of restricted cash within the statement of cash flows. Existing GAAP does not provide guidance on the presentation or classification of movements in restricted cash. The update requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period to total amounts shown on the statement of cash flows. The guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. If an entity early adopts the amendments in an interim period, any adjustments should be reflected as of the beginning of the fiscal year that includes that interim period. When adopted, the guidance must be applied retrospectively to all periods presented. The Company is current evaluating the impact of this guidance on our statement of cash flows and does not expect any material impact on the Company's financial position or results of operations. ASU 2017-04 Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued an accounting standards update concerning impairment testing of goodwill. The main provision of this guidance removes the existing “Step 2” required under current testing procedures. Under the existing Step 2, an entity had to perform procedures to determine the fair value at the impairment testing date of its assets and liabilities (including unrecognized assets and liabilities) following the procedures that would be required in determining the fair value of assets acquired and liabilities assumed in a business combination. Instead, under the revised guidance, an entity‘s annual goodwill impairment review would include a “quantitative impairment test” in which it would compare the fair value of a reporting unit with its carrying amount. If the carrying amount exceeds the fair value then the entity should record an impairment charge for this difference, limited to the total goodwill allocated to the reporting unit (an entity would still have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary). The update should be applied on a prospective basis. Disclosure of the nature of and reason for the change in accounting principle is required upon transition. This guidance is effective for goodwill impairment testing performed in fiscal years beginning after December 15, 2019. Early adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company is currently evaluating the impact of this guidance. The guidance will change the Company’s goodwill impairment procedures and may impact the Company’s financial position and results of operations, but only in the event of a goodwill impairment. There will be no impact on the statement of cash flows.

Acquisitions and Disposals (Tab

Acquisitions and Disposals (Tables)	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Calculation of the consideration transferred in acquisition	The calculation of the consideration transferred to acquire Catlin Shares is as follows: (In thousands, except per share data) Catlin Shares outstanding as of April 30, 2015 that received share consideration (including the dilutive effect of warrants) 384,118 Exchange ratio per the Implementation Agreement 0.130 XL Share issuance to Catlin shareholders 49,935 Closing price per XL share on April 30, 2015 (1) $ 37.08 XL Share issuance consideration $ 1,851,601 Catlin Shares outstanding as of April 30, 2015 that received cash consideration (including the dilutive effect of warrants) 384,118 Cash price component, per Catlin Share in GBP £ 3.88 Cash consideration, in GBP £ 1,490,377 Foreign exchange rate: GBP/USD on April 30, 2015 $ 1.5349 Cash consideration $ 2,287,579 Total acquisition consideration $ 4,139,180 ____________ (1) The closing market price of XL Shares on the Acquisition Date represents the fair value of XL shares issued as part of the Acquisition Consideration.
Schedule of assets acquired and liabilities assumed	The following table summarizes the fair values of the assets acquired and liabilities assumed at the Acquisition Date: (U.S. dollars in thousands) ASSETS Fixed maturities, at fair value $ 6,266,489 Short-term investments, at fair value 634,599 Equity investments, at fair value 236,230 Investment in affiliates 216,843 Other investments 386,828 Total investments $ 7,740,989 Cash and cash equivalents (1) 1,267,565 Accrued investment income 35,063 Premiums receivable 2,545,188 Unpaid losses and loss expenses recoverable 1,493,267 Reinsurance balances receivable 299,579 Ceded unearned premiums 1,143,852 Deferred acquisition costs and value of business acquired 679,259 Intangible assets 988,000 Receivable from investments sold 9,633 Other assets (2) 306,686 Total assets $ 16,509,081 LIABILITIES Unpaid losses and loss expenses $ 6,933,144 Unearned premiums 3,742,234 Reinsurance balances payable 1,441,749 Notes payable and debt 82,066 Payable for investments purchased 34,149 Deferred tax liability (2) 82,783 Other liabilities (2) 285,481 Total liabilities $ 12,601,606 Net assets acquired before non-controlling interest $ 3,907,475 Non-controlling interest in equity of consolidated subsidiaries 562,285 Net assets acquired $ 3,345,190 Acquisition consideration $ 4,139,180 Goodwill (2) $ 793,990 ____________ (1) Includes restricted cash. (2) Includes an increase of $15.9 million to goodwill from the amount initially recorded at June 30, 2015, as a result of several tax-related adjustments, including a decrease in other assets of $7.5 million , a decrease in deferred tax liability of $11.3 million , and an increase in other liabilities of $19.8 million . See discussion of "Income Taxes" below for further information.
Schedule of restructuring costs	As a part of the integration of Catlin's operations, the Company incurs costs associated with restructuring the systems, processes and workforce. These costs include such items as severance, retention, facilities and consulting and other costs. The Company separately identifies such costs and includes these expenses within Corporate and Other: (U.S. dollars in thousands) Severance related costs Retention and other compensation costs Facilities-related costs Consulting and other Total Liabilities at December 31, 2015 $ 16,127 $ 16,969 $ 818 $ 23,375 $ 57,289 Costs incurred in 2016 $ 57,098 $ 33,220 $ 30,236 $ 99,801 220,355 2016 payments 47,865 45,708 31,036 116,069 240,678 Liabilities at December 31, 2016 $ 25,360 $ 4,481 $ 18 $ 7,107 $ 36,966
Results since acquisition	(U.S. dollars in thousands) May 1, 2015 to December 31, 2015 Total revenues - see comments above $ 2,791,789 Net income (loss) - see comments above $ 103,637
Pro Forma information	The following table presents unaudited pro forma consolidated information for the years ended December 31, 2015 and 2014 and assumes the Catlin Acquisition occurred on January 1, 2014. The pro forma financial information is presented for informational purposes only and does not necessarily reflect the results that would have occurred had the acquisition taken place on January 1, 2014, nor is it necessarily indicative of future results. Significant adjustments used to determine pro forma results include amortization of intangible assets and amortization of fair value adjustments discussed above, and the corresponding income tax effects. Non-recurring transaction related costs noted above have been included in the unaudited pro forma results for the years ended December 31, 2015 and 2014. Unaudited Pro Forma (In thousands, except per share data) 2015 2014 Total revenues $ 10,628,915 $ 10,938,216 Net income attributable to common shareholders 1,221,497 475,914 Earnings (loss) per common share and common share equivalent – basic 4.03 1.50 Earnings (loss) per common share and common share equivalent – diluted 3.97 1.48

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Schedule of segment reporting, by segment	The following tables summarize the segment results for the indicated years ended December 31, 2016, 2015, and 2014: Year Ended December 31, 2016 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate and Other (1) Total Gross premiums written $ 9,650,503 $ 3,975,106 $ 13,625,609 $ 265,315 $ 13,890,924 Net premiums written 6,715,969 3,514,667 10,230,636 12,047 10,242,683 Net premiums earned 6,651,495 3,114,392 9,765,887 12,047 9,777,934 Less: Net losses and loss expenses (2) 4,320,737 1,752,098 6,072,835 28,244 6,101,079 Less: Acquisition costs (2) 897,308 717,588 1,614,896 5,775 1,620,671 Less: Operating expenses (3) 1,224,233 283,270 1,507,503 1,356 1,508,859 Underwriting profit (loss) $ 209,217 $ 361,436 $ 570,653 $ (23,328 ) $ 547,325 Net investment income - excluding Life Funds Withheld Assets (4) 586,658 31,726 618,384 Net investment income - Life Funds Withheld Assets 154,751 154,751 Net results from structured products (5) 8,495 5,785 14,280 — 14,280 Net fee income and other (6) (18,506 ) 3,280 (15,226 ) 1,911 (13,315 ) Loss (gain) on sale of subsidiary — (7,088 ) (7,088 ) Net realized gains (losses) on investments - excluding Life Funds Withheld Assets 127,533 (14,844 ) 112,689 Net realized gains (losses) on investments and net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets (3 ) 259,452 259,449 Net realized and unrealized gains (losses) on derivative instruments — 2,521 2,521 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (540,090 ) (540,090 ) Net income (loss) from investment fund affiliates and operating affiliates — 115,155 115,155 Less: Exchange (gains) losses — (9,578 ) (9,578 ) Less: Corporate operating expenses — 505,483 505,483 Contribution from P&C and Corporate and Other 1,283,895 (501,563 ) 782,332 Less: Interest expense (7) 170,058 170,058 Less: Non-controlling interests 129,177 129,177 Less: Income tax expense 42,129 42,129 Net income (loss) attributable to common shareholders $ 440,968 Ratios – P&C operations: (8) Loss and loss expense ratio 65.0 % 56.3 % 62.2 % Underwriting expense ratio 31.9 % 32.1 % 32.0 % Combined ratio 96.9 % 88.4 % 94.2 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments. (3) Operating expenses of the segments exclude Corporate operating expenses, shown separately. (4) Net investment income - excluding Life Funds Withheld Assets does not include net investment income related to the net results from structured products. (5) The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million , respectively. (6) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (7) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (8) Ratios are based on net premiums earned from P&C operations. Year Ended December 31, 2015 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate & Other (1) Total Gross premiums written $ 8,395,846 $ 2,273,163 $ 10,669,009 $ 309,916 $ 10,978,925 Net premiums written 5,859,934 2,028,890 7,888,824 62,239 7,951,063 Net premiums earned 5,648,482 2,515,702 8,164,184 62,241 8,226,425 Less: Net losses and loss expenses (2) 3,614,048 1,152,152 4,766,200 115,997 4,882,197 Less: Acquisition costs (2) 704,364 602,290 1,306,654 10,794 1,317,448 Less: Operating expenses (3) 1,154,760 283,379 1,438,139 1,232 1,439,371 Underwriting profit (loss) $ 175,310 $ 477,881 $ 653,191 $ (65,782 ) $ 587,409 Net investment income - excluding Life Funds Withheld Assets (4) 583,871 40,569 624,440 Net investment income - Life Funds Withheld Assets 187,489 187,489 Net results from structured products (5) 12,185 5,806 17,991 — 17,991 Net fee income and other (6) (16,936 ) 2,958 (13,978 ) 622 (13,356 ) Net realized gains (losses) on investments 14,586 5,411 19,997 Net realized gains (losses) on investments - Life Funds Withheld Assets — 182,181 182,181 Net realized and unrealized gains (losses) on derivative instruments — 53,123 53,123 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (151,691 ) (151,691 ) Net income (loss) from investment fund affiliates and operating affiliates — 118,060 118,060 Gain on sale of operating affiliate 340,407 340,407 Less: Extinguishment of debt — 5,592 5,592 Less: Exchange (gains) losses — 22,504 22,504 Less: Corporate operating expenses — 480,755 480,755 Contribution from P&C and Corporate and Other 1,255,661 201,538 1,457,199 Less: Interest expense (7) 163,021 163,021 Less: Non-controlling interests 106,187 106,187 Less: Income tax expense (19,161 ) (19,161 ) Net income (loss) attributable to common shareholders $ 1,207,152 Ratios – P&C operations: (8) Loss and loss expense ratio 64.0 % 45.8 % 58.4 % Underwriting expense ratio 32.9 % 35.2 % 33.6 % Combined ratio 96.9 % 81.0 % 92.0 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments (3) Operating expenses of the segments exclude Corporate operating expenses, shown separately. (4) Net investment income does not include net investment income related to the net results from structured products. (5) The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million , respectively. (6) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (7) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (8) Ratios are based on net premiums earned from P&C operations. Year Ended December 31, 2014 (U.S. dollars in thousands, except ratios) Insurance Reinsurance Total P&C Corporate and Other (1) Total Gross premiums written $ 5,976,011 $ 1,785,479 $ 7,761,490 $ 333,436 $ 8,094,926 Net premiums written 4,134,151 1,633,058 5,767,209 177,632 5,944,841 Net premiums earned 4,026,713 1,690,725 5,717,438 177,632 5,895,070 Less: Net losses and loss expenses 2,543,108 715,285 3,258,393 242,963 3,501,356 Less: Acquisition costs 393,319 330,684 724,003 14,115 738,118 Less: Operating expenses (2) 865,592 193,404 1,058,996 10,693 1,069,689 Underwriting profit (loss) $ 224,694 $ 451,352 $ 676,046 $ (90,139 ) $ 585,907 Net investment income (3) 574,458 146,558 721,016 Net investment income - Life Funds Withheld Assets 129,575 129,575 Net results from structured products (4) 43,710 10,499 54,209 — 54,209 Net fee income and other (5) (10,051 ) 2,800 (7,251 ) 360 (6,891 ) Loss (gain) on sale of subsidiary — 666,423 666,423 Net realized gains (losses) on investments 119,366 3,625 122,991 Net realized gains (losses) on investments - Life Funds Withheld Assets — (15,529 ) (15,529 ) Net realized and unrealized gains (losses) on derivative instruments — 29,886 29,886 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — (488,222 ) (488,222 ) Net income (loss) from investment fund affiliates and operating affiliates — 203,034 203,034 Less: Exchange (gains) losses — (37,568 ) (37,568 ) Less: Corporate operating expenses — 220,165 220,165 Contribution from P&C and Corporate and Other 1,416,828 (929,872 ) 486,956 Less: Interest expense (6) 121,221 121,221 Less: Non-controlling interests 80,498 80,498 Less: Income tax expense 96,897 96,897 Net income (loss) attributable to common shareholders $ 188,340 Ratios – P&C operations: (7) Loss and loss expense ratio 63.2 % 42.3 % 57.0 % Underwriting expense ratio 31.2 % 31.0 % 31.2 % Combined ratio 94.4 % 73.3 % 88.2 % ____________ (1) Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations. (2) Operating expenses exclude Corporate operating expenses, shown separately. (3) Net investment income does not include net investment income related to the net results from structured products. (4) The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million , respectively. (5) Net fee income and other includes operating expenses from the Company's loss prevention consulting services business. (6) Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments. (7) Ratios are based on net premiums earned from P&C operations.
Schedule of net premiums earned by line of business	The following tables summarize the Company’s net premiums earned by line of business: Year Ended December 31, 2016 (U.S. dollars in thousands) Insurance (2) Reinsurance Corporate and Other Total P&C Operations: Professional $ 1,330,909 $ 163,157 $ — $ 1,494,066 Casualty 1,973,672 657,590 — 2,631,262 Property catastrophe — 792,445 — 792,445 Property 1,625,133 1,021,626 — 2,646,759 Specialty 1,711,344 174,477 — 1,885,821 Other (1) 10,437 305,097 — 315,534 Total P&C Operations $ 6,651,495 $ 3,114,392 $ — $ 9,765,887 Corporate and Other: Run-off life operations - Annuity — — 1 1 Run-off life operations - Other life — — 12,046 12,046 Total Corporate and Other $ — $ — $ 12,047 $ 12,047 Total $ 6,651,495 $ 3,114,392 $ 12,047 $ 9,777,934 Year Ended December 31, 2015 P&C Operations: Professional $ 1,164,446 $ 168,367 $ — $ 1,332,813 Casualty 1,805,563 468,286 — 2,273,849 Property catastrophe — 663,958 — 663,958 Property 1,257,383 869,286 — 2,126,669 Specialty 1,421,124 127,797 — 1,548,921 Other (1) (34 ) 218,008 — 217,974 Total P&C Operations $ 5,648,482 $ 2,515,702 $ — $ 8,164,184 Corporate and Other: Run-off life operations - Annuity $ — $ — $ 1 $ 1 Run-off life operations - Other life — — 62,240 62,240 Total Corporate and Other $ — $ — $ 62,241 $ 62,241 Total $ 5,648,482 $ 2,515,702 $ 62,241 $ 8,226,425 Year Ended December 31, 2014 P&C Operations: Professional $ 1,075,420 $ 181,223 $ — $ 1,256,643 Casualty 1,669,097 300,223 — 1,969,320 Property catastrophe — 433,602 — 433,602 Property 544,856 555,583 — 1,100,439 Specialty 737,281 95,745 — 833,026 Other (1) 59 124,349 — 124,408 Total P&C Operations $ 4,026,713 $ 1,690,725 $ — $ 5,717,438 Corporate and Other: Run-off life operations - Annuity $ — $ — $ 53,363 $ 53,363 Run-off life operations - Other life — — 124,269 124,269 Total Corporate and Other $ — $ — $ 177,632 $ 177,632 Total $ 4,026,713 $ 1,690,725 $ 177,632 $ 5,895,070 ____________ (1) Other within the Insurance segment includes surety, structured indemnity and certain other exited lines. Other within the Reinsurance segment includes: whole account contracts, accident and health and other lines. (2) Amounts from the prior year have been represented to reflect current mapping of underlying lines of business to be consistent with the manner in which they are reflected in the current period. The most significant movements include the following: Energy business previously shown under Specialty is now reflected in Property; Programs business formerly in Other is now reflected in Property or Casualty, depending upon the predominant line for each program; and Excess and Surplus is now reflected primarily in Casualty.
Schedule of net premiums written by geographic location	The following table shows an analysis of the Company’s net premiums written by geographical location of the subsidiary where the premium is written for the years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 P&C Operations: Bermuda $ 1,267,613 $ 781,618 $ 636,109 United States 3,575,969 3,045,031 2,528,196 Europe 4,778,299 3,628,258 2,124,117 Other 608,755 433,917 478,787 Total P&C Operations $ 10,230,636 $ 7,888,824 $ 5,767,209 Corporate and Other: Bermuda $ 12,194 $ 62,276 $ 91,979 Europe (147 ) (37 ) 85,653 Total Corporate and Other $ 12,047 $ 62,239 $ 177,632

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Amortized cost and fair value summary - AFS	The cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains and gross unrealized (losses), including non-credit related OTTI recorded in AOCI of the Company’s AFS investments at December 31, 2016 and 2015 were as follows: Included in AOCI December 31, 2016 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - Available for Sale ("AFS") - Excluding Life Funds Withheld Assets U.S. Government and Government-Related/Supported ("U.S. Government") $ 3,874,038 $ 53,172 $ (32,822 ) $ 3,894,388 $ — Corporate - Financials 3,587,557 59,968 (25,235 ) 3,622,290 — Corporate - Non Financials 6,468,200 138,114 (93,875 ) 6,512,439 (36 ) Residential mortgage-backed securities - Agency ("RMBS – Agency") 4,213,845 49,913 (45,391 ) 4,218,367 — Residential mortgage-backed securities - Non-Agency ("RMBS – Non-Agency") 265,877 21,132 (12,751 ) 274,258 (47,879 ) Commercial mortgage-backed securities ("CMBS") 670,005 5,955 (10,774 ) 665,186 (1,191 ) Collateralized debt obligations ("CDO") 379,532 498 (2,539 ) 377,491 (1,208 ) Other asset-backed securities 872,903 12,697 (9,703 ) 875,897 (821 ) U.S. States and political subdivisions of the States 2,399,490 86,041 (7,419 ) 2,478,112 — Non-U.S. Sovereign Government, Provincial, Supranational and Government-Related/Supported ("Non-U.S. Government") 5,037,482 112,772 (120,122 ) 5,030,132 — Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 27,768,929 $ 540,262 $ (360,631 ) $ 27,948,560 $ (51,135 ) Total short-term investments - Excluding Life Funds Withheld Assets 626,142 227 (1,176 ) 625,193 — Total equity securities - Excluding Life Funds Withheld Assets 996,610 48,931 (8,210 ) 1,037,331 — Total investments - AFS - Excluding Life Funds Withheld Assets $ 29,391,681 $ 589,420 $ (370,017 ) $ 29,611,084 $ (51,135 ) Included in AOCI December 31, 2016 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government $ 8,468 $ 2,109 $ — $ 10,577 $ — Corporate - Financials 376,018 63,249 — 439,267 — Corporate - Non Financials 797,652 217,689 — 1,015,341 — RMBS – Agency 470 143 — 613 — RMBS – Non-Agency 19,121 2,646 — 21,767 — CMBS 77,762 16,478 — 94,240 — Other asset-backed securities 84,541 17,019 — 101,560 — Non--U.S. Government 454,695 169,982 — 624,677 — Total fixed maturities - AFS - Life Funds Withheld Assets $ 1,818,727 $ 489,315 $ — $ 2,308,042 $ — Total investments - AFS $ 31,210,408 $ 1,078,735 $ (370,017 ) $ 31,919,126 $ (51,135 ) ____________ (1) Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date. December 31, 2015 (U.S. dollars in thousands) Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Non-credit Related OTTI (1) Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ 5,047,621 $ 52,355 $ (34,339 ) $ 5,065,637 $ — Corporate - Financials 3,535,830 49,535 (23,456 ) 3,561,909 — Corporate - Non Financials 6,867,525 130,568 (97,646 ) 6,900,447 — RMBS – Agency 3,697,756 77,776 (17,561 ) 3,757,971 — RMBS – Non-Agency 319,876 25,644 (16,980 ) 328,540 (54,200 ) CMBS 401,713 7,933 (4,330 ) 405,316 (1,182 ) CDOs 41,679 4 (9,273 ) 32,410 (1,208 ) Other asset-backed securities 1,164,426 17,665 (13,519 ) 1,168,572 (1,144 ) U.S. States and political subdivisions of the States 2,514,048 125,395 (7,373 ) 2,632,070 — Non-U.S. Government 5,249,148 100,383 (97,917 ) 5,251,614 — Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 28,839,622 $ 587,258 $ (322,394 ) $ 29,104,486 $ (57,734 ) Total short-term investments - Excluding Life Funds Withheld Assets $ 618,851 $ 967 $ (2,428 ) $ 617,390 $ — Total equity securities - Excluding Life Funds Withheld Assets $ 834,079 $ 89,993 $ (45,153 ) $ 878,919 $ — Total investments - AFS - Excluding Life Funds Withheld Assets $ 30,292,552 $ 678,218 $ (369,975 ) $ 30,600,795 $ (57,734 ) Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government $ 10,721 $ 2,021 $ — $ 12,742 $ — Corporate - Financials 531,016 67,220 — 598,236 — Corporate - Non Financials 1,132,926 175,702 — 1,308,628 — RMBS – Agency 591 161 — 752 — RMBS – Non-Agency 24,401 2,552 — 26,953 — CMBS 107,968 14,513 — 122,481 — Other asset-backed securities 132,674 17,121 — 149,795 — Non-U.S. Government 737,735 195,781 — 933,516 — Total fixed maturities - AFS - Life Funds Withheld Assets $ 2,678,032 $ 475,071 $ — $ 3,153,103 $ — Total investments - AFS $ 32,970,584 $ 1,153,289 $ (369,975 ) $ 33,753,898 $ (57,734 ) ____________ (1) Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date.
Amortized cost and fair value summary - Trading	The cost (amortized cost for fixed maturities and short-term investments) and fair value of trading investments at December 31, 2016 and 2015 were as follows: December 31, 2016 (U.S. dollars in thousands) Amortized Fair Value Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ 14,361 $ 14,708 Corporate - Financials 450,990 468,175 Corporate - Non Financials 611,863 643,030 RMBS – Agency 835 852 RMBS – Non-Agency 101 109 CMBS 5,242 5,526 Other asset-backed securities 38,342 39,446 U.S. States and political subdivisions of the States 219 224 Non-U.S. Government 426,225 444,944 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,548,178 $ 1,617,014 Total short-term investments - Trading - Life Funds Withheld Assets $ 9,536 $ 9,563 Total investments - Trading - Life Funds Withheld Assets $ 1,557,714 $ 1,626,577 December 31, 2015 (U.S. dollars in thousands) Amortized Fair Value Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ 4,957 $ 4,990 Corporate - Financials 344,070 335,956 Corporate - Non Financials 509,441 493,621 RMBS – Agency 370 368 CMBS 4,874 4,803 Other asset-backed securities 26,405 25,700 Non-U.S. Government 373,492 370,261 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,263,609 $ 1,235,699 Total short-term investments - Trading - Life Funds Withheld Assets $ 60,176 $ 60,330 Total investments - Trading - Life Funds Withheld Assets $ 1,323,785 $ 1,296,029
Contractual maturities summary	The contractual maturities of AFS and Trading fixed income securities at December 31, 2016 and 2015 are shown below. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. (U.S. dollars in thousands) December 31, 2016 December 31, 2015 Amortized Cost Fair Value Amortized Cost Fair Value Fixed maturities - AFS - Excluding Life Funds Withheld Assets Due less than one year $ 2,121,088 $ 2,135,262 $ 2,106,851 $ 2,104,106 Due after 1 through 5 years 12,400,798 12,463,844 14,051,494 14,143,461 Due after 5 through 10 years 5,509,194 5,531,402 5,680,830 5,740,954 Due after 10 years 1,335,687 1,406,853 1,374,997 1,423,156 $ 21,366,767 $ 21,537,361 $ 23,214,172 $ 23,411,677 (U.S. dollars in thousands) December 31, 2016 December 31, 2015 Amortized Cost Fair Value Amortized Cost Fair Value RMBS – Agency $ 4,213,845 $ 4,218,367 $ 3,697,756 $ 3,757,971 RMBS – Non-Agency 265,877 274,258 319,876 328,540 CMBS 670,005 665,186 401,713 405,316 CDO 379,532 377,491 41,679 32,410 Other asset-backed securities 872,903 875,897 1,164,426 1,168,572 Total mortgage and asset-backed securities $ 6,402,162 $ 6,411,199 $ 5,625,450 $ 5,692,809 Total fixed maturities - AFS - Excluding Life Funds Withheld Assets $ 27,768,929 $ 27,948,560 $ 28,839,622 $ 29,104,486 Fixed maturities - AFS - Life Funds Withheld Assets Due less than one year $ 71,207 $ 80,749 $ 81,700 $ 92,921 Due after 1 through 5 years 289,710 318,605 386,810 416,743 Due after 5 through 10 years 274,727 324,759 491,621 558,805 Due after 10 years 1,001,189 1,365,749 1,452,267 1,784,653 $ 1,636,833 $ 2,089,862 $ 2,412,398 $ 2,853,122 RMBS – Agency $ 470 $ 613 $ 591 $ 752 RMBS – Non-Agency 19,121 21,767 24,401 26,953 CMBS 77,762 94,240 107,968 122,481 Other asset-backed securities 84,541 101,560 132,674 149,795 Total mortgage and asset-backed securities $ 181,894 $ 218,180 $ 265,634 $ 299,981 Total fixed maturities - AFS - Life Funds Withheld Assets $ 1,818,727 $ 2,308,042 $ 2,678,032 $ 3,153,103 Total fixed maturities - AFS $ 29,587,656 $ 30,256,602 $ 31,517,654 $ 32,257,589 Fixed maturities - Trading - Life Funds Withheld Assets Due less than one year $ 59,138 $ 59,553 $ 4,573 $ 5,096 Due after 1 through 5 years 322,574 328,997 278,163 272,220 Due after 5 through 10 years 507,631 521,505 280,487 277,920 Due after 10 years 614,315 661,026 668,737 649,592 $ 1,503,658 $ 1,571,081 $ 1,231,960 $ 1,204,828 RMBS – Agency 835 852 370 368 RMBS – Non-Agency 101 109 — — CMBS 5,242 5,526 4,874 4,803 Other asset-backed securities 38,342 39,446 26,405 25,700 Total mortgage and asset-backed securities 44,520 45,933 31,649 30,871 Total fixed maturities - Trading - Life Funds Withheld Assets $ 1,548,178 $ 1,617,014 $ 1,263,609 $ 1,235,699
Gross unrealized losses	The following is an analysis of how long the AFS securities at December 31, 2016 and 2015 had been in a continual unrealized loss position: December 31, 2016 (U.S. dollars in thousands) Less than 12 months Equal to or greater than 12 months Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fixed maturities and short-term investments - AFS U.S. Government $ 2,456,685 $ (30,640 ) $ 43,873 $ (2,237 ) Corporate - Financials 1,111,700 (19,010 ) 59,091 (6,227 ) Corporate - Non Financials 2,302,552 (62,584 ) 205,829 (31,368 ) RMBS – Agency 2,456,028 (40,989 ) 136,014 (4,402 ) RMBS – Non-Agency 3,517 (205 ) 166,796 (12,546 ) CMBS 467,757 (9,470 ) 9,665 (1,304 ) CDO 105,653 (58 ) 2,752 (2,481 ) Other asset-backed securities 671,782 (3,830 ) 34,783 (5,960 ) U.S. States and political subdivisions of the States 457,288 (6,983 ) 4,287 (437 ) Non-U.S. Government 1,797,405 (75,596 ) 288,490 (45,480 ) Total fixed maturities and short-term investments - AFS $ 11,830,367 $ (249,365 ) $ 951,580 $ (112,442 ) Total equity securities $ 130,487 $ (8,210 ) $ — $ — Less than 12 months Equal to or greater than 12 months December 31, 2015 (U.S. dollars in thousands) Fair Value Gross Unrealized Losses Fair Value Gross Fixed maturities and short-term investments - AFS U.S. Government $ 3,762,869 $ (29,339 ) $ 89,113 $ (5,044 ) Corporate – Financials 1,641,021 (13,280 ) 102,022 (10,192 ) Corporate – Non Financials 3,275,270 (73,069 ) 227,527 (24,706 ) RMBS – Agency 1,065,055 (10,046 ) 221,211 (7,515 ) RMBS – Non-Agency 19,614 (1,104 ) 180,146 (15,876 ) CMBS 118,605 (1,561 ) 78,651 (2,769 ) CDOs 12,311 (516 ) 20,096 (8,757 ) Other asset-backed securities 572,671 (5,252 ) 57,563 (8,268 ) U.S. States and political subdivisions of the States 565,055 (6,609 ) 12,259 (765 ) Non-U.S. Government 1,921,286 (53,440 ) 474,929 (46,714 ) Total fixed maturities and short-term investments - AFS $ 12,953,757 $ (194,216 ) $ 1,463,517 $ (130,606 ) Total equity securities $ 356,742 $ (45,153 ) $ — $ —
Net investment income	Net investment income for the years ended December 31 is derived from the following sources: (U.S. dollars in thousands) 2016 2015 2014 Fixed maturities, short term investments and cash equivalents - Excluding Life Funds Withheld Assets $ 713,237 $ 726,161 $ 809,964 Fixed maturities, short term investments and cash equivalents - Life Funds Withheld Assets 154,751 187,489 129,575 Equity securities and other investments 34,620 28,200 42,252 Interest on funds withheld 10,276 10,835 14,583 Total gross investment income $ 912,884 $ 952,685 $ 996,374 Investment expenses (85,751 ) (80,315 ) (77,749 ) Total net investment income $ 827,133 $ 872,370 $ 918,625
Net realized gains (losses)	The following represents an analysis of net realized gains (losses), the change in unrealized gains (losses) on trading securities and net realized and unrealized gains (losses) on investment related derivative instruments for the years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 Fixed maturities, short term investments, cash and cash equivalents - Excluding Life Funds Withheld Assets: Gross realized gains $ 192,119 $ 187,523 $ 119,817 Gross realized losses on investments sold (151,013 ) (134,441 ) (66,892 ) OTTI on investments, net of amounts transferred to other comprehensive income (48,432 ) (54,346 ) (12,341 ) Net realized gains (losses) $ (7,326 ) $ (1,264 ) $ 40,584 Equity securities: Gross realized gains $ 140,864 $ 79,556 $ 96,260 Gross realized losses on investments sold (11,882 ) (49,223 ) (12,270 ) OTTI on investments, net of amounts transferred to other comprehensive income (30,126 ) (15,954 ) (10,944 ) Net realized gains (losses) $ 98,856 $ 14,379 $ 73,046 Other investments: Gross realized gains $ 37,596 $ 39,198 $ 31,830 Gross realized losses on investments sold (16,437 ) (19,656 ) (10,011 ) OTTI on investments, net of amounts transferred to other comprehensive income — (12,660 ) (12,458 ) Net realized gains (losses) $ 21,159 $ 6,882 $ 9,361 Net realized gains (losses) on investments - Excluding Life Funds Withheld Assets $ 112,689 $ 19,997 $ 122,991 Fixed maturities, short term investments, cash and cash equivalents - Life Funds Withheld Assets: Gross realized gains $ 185,487 $ 259,798 $ 7,926 Gross realized losses on investments sold (32,898 ) (36,526 ) (2,859 ) Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets 109,458 (27,734 ) (9 ) OTTI on investments, net of amounts transferred to other comprehensive income (2,598 ) (13,357 ) (20,587 ) Net realized gains (losses) on investments - Life Funds Withheld Assets $ 259,449 $ 182,181 $ (15,529 ) Net realized gains (losses) on investments $ 372,138 $ 202,178 $ 107,462 Net realized and unrealized gains (losses) on investment related derivative instruments $ 2,521 $ (8,616 ) $ 20,121 Net realized gains (losses) on investments and net realized and unrealized gains (losses) on investment related derivative instruments $ 374,659 $ 193,562 $ 127,583 (U.S. dollars in thousands) 2016 2015 2014 Change in unrealized gains (losses): Fixed maturities – AFS - Excluding Life Funds Withheld Assets $ (84,721 ) $ (486,140 ) $ 360,463 Fixed maturities - AFS - Life Funds Withheld Assets 14,244 (405,155 ) 880,226 Fixed maturities – HTM — — (272,540 ) Equity securities (4,119 ) (59,619 ) (32,577 ) Other investments (63,096 ) (6,072 ) 35,143 Net change in unrealized gains (losses) on investments $ (137,692 ) $ (956,986 ) $ 970,715 Total net realized gains (losses) on investments, net realized and unrealized gains (losses) on investment related derivative instruments, and net change in unrealized gains (losses) on investments $ 236,967 $ (763,424 ) $ 1,098,298
Credit loss impairments	The following table sets forth the amount of credit loss impairments on fixed income securities, for which a portion of the OTTI loss was recognized in OCI, held by the Company as of years ended December 31, 2016 and 2015 and the corresponding changes in such amounts. Credit Loss Impairments (U.S. dollars in thousands) 2016 2015 Opening balance at beginning of indicated period $ 73,469 $ 131,942 Credit loss impairment recognized in the current period on securities not previously impaired 12,867 9,698 Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period (18,178 ) (54,648 ) Credit loss impairments previously recognized on securities impaired to fair value during the period — (2,629 ) Additional credit loss impairments recognized in the current period on securities previously impaired 2,233 2,230 Accretion of credit loss impairments previously recognized due to an increase in cash flows expected to be collected (8,796 ) (13,124 ) Closing balance at end of indicated period $ 61,595 $ 73,469

Investments in Affiliates (Tabl

Investments in Affiliates (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	Investments in affiliates comprised the following at December 31, 2016 and 2015 . See Note 1(c), "Significant Accounting Policies - Total Investments - Investments in Affiliates," for a description of our accounting policy for these assets: (U.S. dollars in thousands) 2016 2015 Investment fund affiliates $ 1,674,925 $ 1,386,837 Operating affiliates 502,720 322,062 Total investment affiliates $ 2,177,645 $ 1,708,899
Operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	The Company’s equity investment in operating affiliates and equity in net income (loss) from such affiliates as well as certain summarized financial information of the investee as a whole are included below: Year ended December 31, 2016 (U.S. dollars in thousands) XL Group Investment Combined Investee Summarized Carrying Equity in Total Total Total Net Income Strategic and other operating affiliates $ 446,695 $ 12,622 $ 5,353,905 $ 3,791,300 $ 1,030,859 $ 30,424 Investment manager affiliates (1) 56,025 31,775 752,336 72,114 337,782 257,004 Total operating affiliates $ 502,720 $ 44,397 $ 6,106,241 $ 3,863,414 $ 1,368,641 $ 287,428 Year ended December 31, 2015 Strategic and other operating affiliates 251,348 33,608 4,280,976 3,293,873 847,131 91,701 Investment manager affiliates (1) 70,714 11,132 708,605 95,826 206,672 90,491 Total operating affiliates $ 322,062 $ 44,740 $ 4,989,581 $ 3,389,699 $ 1,053,803 $ 182,192 ____________ (1) During the years ended December 31, 2016 and 2015 , the Company received distributions from its Investment Manager Affiliates of approximately $35.9 million and $25.3 million , respectively.
Investment fund affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	The Company’s equity investment in investment fund affiliates and equity in net income (loss) from such affiliates as well as certain summarized financial information of the investee on a combined basis (shown as "Combined Funds") are included below: (U.S. dollars in thousands, except percentages) XL Group Investment Combined Carrying Equity in Weighted Total Net Assets Year Ended December 31, 2016 Hedge Funds: Arbitrage $ 165,633 $ 965 12.3 % $ 1,343,655 Directional 672,934 1,480 7.4 % 9,039,159 Event Driven (2) 297,836 9,676 2.6 % 11,341,870 Multi-Style 180,972 29,549 3.3 % 5,557,296 Total hedge funds $ 1,317,375 $ 41,670 4.8 % $ 27,281,980 Private Investment Funds: 357,550 29,088 10.8 % 3,318,073 Total Investment Fund Affiliates $ 1,674,925 $ 70,758 5.5 % $ 30,600,053 Year Ended December 31, 2015 Hedge Funds: Arbitrage $ 190,016 $ 612 8.6 % $ 2,202,112 Directional 551,262 31,012 7.2 % 7,643,134 Event Driven (2) 285,823 5,592 3.0 % 9,460,387 Multi-Style 57,097 5,452 3.6 % 1,600,959 Total hedge funds $ 1,084,198 $ 42,668 5.2 % $ 20,906,592 Private Investment Funds: 302,639 30,652 9.5 % 3,195,204 Total Investment Fund Affiliates $ 1,386,837 $ 73,320 5.8 % $ 24,101,796 ____________ (1) Total estimated net assets are generally as at November 30 for hedge fund affiliates and September 30 for private investment fund affiliates. (2) The Company accounts for its investment in certain funds using the equity method where the Company has significant influence over the related investment management company even though the ownership percentage is less than three percent.

Other Investments (Tables)

Other Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Investments, All Other Investments [Abstract]
Components of other investments	Other investments comprised the following at December 31, 2016 and 2015 . See Note 1(c), "Significant Accounting Policies - Total Investments - Other Investments," for a description of our accounting policy for these assets: Year ended December 31, (U.S. dollars in thousands) 2016 2015 Hedge Funds: Arbitrage $ 165,053 $ 205,117 Directional 159,701 276,277 Event Driven 2,877 5,427 Multi-Style 4,341 57,249 Total hedge funds $ 331,972 $ 544,070 Private investment funds 175,579 244,576 Overseas deposits 493,594 479,187 Structured transactions 142,698 138,608 Other 20,721 26,616 Total other investments $ 1,164,564 $ 1,433,057
Analysis of net realized and unrealized gains	The following represents an analysis of the net realized gains for the indicated years ended December 31, and the net unrealized gains as of December 31, on the Company’s hedge funds and private investment funds: Year ended December 31, (U.S. dollars in thousands) Net Unrealized Gains Net Realized Gains (Losses) 2016 2015 2016 2015 2014 Hedge funds $ 134,114 $ 188,698 $ 12,212 $ 12,769 $ 6,685 Private investment funds 36,775 38,340 8,636 9,342 13,275 Total $ 170,889 $ 227,038 $ 20,848 $ 22,111 $ 19,960

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of location and gross amounts of derivative fair values in the consolidated balance sheets	The following table summarizes information on the location and gross amounts of derivative fair values contained in the consolidated balance sheets at December 31, 2016 and 2015 : 2016 2015 (U.S. dollars in thousands) Asset Derivative Notional Amount Asset Derivative Fair Value (1) Liability Derivative Notional Amount Liability Derivative Fair Value (1) Asset Derivative Notional Amount Asset Derivative Fair Value (1) Liability Derivative Notional Amount Liability Derivative Fair Value (1) Derivatives designated as hedging instruments: Foreign exchange contracts $ 1,396,801 $ 85,175 $ 583,722 $ 25,750 $ 1,667,585 $ 64,289 $ 674,976 $ 11,941 Total derivatives designated as hedging instruments $ 1,396,801 $ 85,175 $ 583,722 $ 25,750 $ 1,667,585 $ 64,289 $ 674,976 $ 11,941 Derivatives not designated as hedging instruments: Investment Related Derivatives: Foreign exchange exposure 10,049 190 273,767 12,137 102,234 2,888 144,707 1,702 Credit exposure 32,500 1,077 82,500 6,978 8,433 652 71,614 12,067 Financial market exposure 5 5 — — 37 77 26,500 417 Other Non-Investment Derivatives: Foreign exchange contracts 181,300 1,208 — — 194,566 2,009 — — Credit exposure — — 24,490 340 29,874 31 — — Guaranteed minimum income benefit contract 43,553 19,499 43,553 19,499 46,032 19,368 46,032 19,368 Modified coinsurance funds withheld contracts including life retrocession embedded derivative (2) 59,775 — 4,048,446 — 60,667 — 4,620,879 — Other 15,000 342 — — — — — — Total derivatives not designated as hedging instruments $ 342,182 $ 22,321 $ 4,472,756 $ 38,954 $ 441,843 $ 25,025 $ 4,909,732 $ 33,554 Total derivatives $ 107,496 $ 64,704 $ 89,314 $ 45,495 Counterparty netting (17,947 ) (17,947 ) (3,087 ) (3,087 ) Total derivatives net of counterparty netting (1) 89,549 46,757 86,227 42,408 Cash collateral held/paid (3) (36,980 ) (5,810 ) (30,958 ) — Total derivatives as recorded in the balance sheets $ 52,569 $ 40,947 $ 55,269 $ 42,408 ____________ (1) Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements. (2) The fair value movements in derivative assets and liabilities relating to modified coinsurance funds withheld contracts are included within the associated asset or liability at each period end on the face of the balance sheets. Notional amounts associated with reinsurance agreements under which the Company assumes reinsurance risk are recorded as asset derivative notional amounts. Included in the liability derivative notional amount as of December 31, 2016 is the cumulative net realized and unrealized loss on the life retrocession embedded derivative of $937.7 million . (3) As of December 31, 2016 , the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015 , the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.
Weighted average US dollar equivalent of foreign denominated net assets that were hedge and resultant gain (loss)	The following table provides the weighted average U.S. dollar equivalent of foreign denominated net assets that were hedged and the resulting derivative gain (loss) that was recorded in the foreign currency translation adjustment, net of tax, account within AOCI for the years ended December 31, 2016 and 2015 . Derivative Instruments Designated as Hedges of a Net Investment in a Foreign Operation – Summary (U.S. dollars in thousands) 2016 2015 Weighted average of U.S. dollar equivalent of foreign denominated net assets $ 2,316,538 $ 1,769,106 Derivative gains (losses) (1) $ 130,365 $ 106,876 ____________ (1) Derivative gains (losses) from derivative instruments designated as hedges of the net investment in a foreign operation are recorded in the cumulative translation adjustment account within AOCI for each period.
Total impact on earnings related to derivative instruments	The following table provides the total impact on earnings relating to derivative instruments formally designated as fair value hedges along with the impacts of the related hedged items for the years indicated: Derivatives Designated as Fair Value Hedges (U.S. dollars in thousands) Hedged Items – Amount of Gain/(Loss) Recognized in Income Attributable to Risk Gain/(Loss) Recognized in Income on Derivative Fixed Maturity Investments Ineffective Portion of Hedging Relationship – Gain/(Loss) Year Ended December 31, 2016 Interest rate exposure $ — Foreign exchange exposure — Total $ — $ — $ — Year Ended December 31, 2015 Interest rate exposure $ — Foreign exchange exposure — Total $ — $ — $ — Year Ended December 31, 2014 Interest rate exposure $ — Foreign exchange exposure (15,663 ) Total $ (15,663 ) $ 15,407 $ (256 )
Impact of Life Retro arrangements	The impact of the GreyCastle Life Retro Arrangements on the Company's results for the years ended December 31, 2016 and 2015 and the period beginning from the completion of the transaction on May 30, 2014 through December 31, 2014 was as follows: Impact of GreyCastle Life Retro Arrangements (U.S. dollars in thousands) 2016 2015 2014 Underwriting profit (loss) (1) $ — $ 605 $ 11,649 Net investment income - Life Funds Withheld Assets 154,751 187,489 129,575 Net realized gains (losses) on investments sold - Life Funds Withheld Assets 152,589 223,272 5,067 Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets 109,458 (27,734 ) (9 ) OTTI on investments - Life Funds Withheld Assets (2,598 ) (13,357 ) (20,587 ) Exchange (gains) losses (8,988 ) 4,788 10,099 Other income and expenses (154 ) 2,280 (1,610 ) Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets (540,090 ) (151,691 ) (488,222 ) Net income (loss) $ (135,032 ) $ 225,652 $ (354,038 ) Change in net unrealized gains (losses) on investments - Life Funds Withheld Assets (4,502 ) (421,604 ) 274,083 Change in adjustments related to future policy benefit reserves 62,295 170,688 74,009 Change in cumulative translation adjustment - Life Funds Withheld Assets 77,239 25,869 17,595 Total changes to other comprehensive income as a result of GreyCastle Life Retro Arrangements $ 135,032 $ (225,047 ) $ 365,687 Comprehensive income (loss) $ — $ 605 $ 11,649 ____________ (1) The underwriting profit of $0.6 million in 2015 and $11.6 million in 2014 relate to premium adjustments relating to the GreyCastle Life Retro Arrangements transaction, which was completed on May 30, 2014. Excluding these transactions, the impact to comprehensive income relating to the GreyCastle Life Retro Arrangements was nil for the years ended December 31, 2016, 2015 and 2014 .
Components of life retrocession embedded derivatives	The change in the value of the life retrocession embedded derivative, which includes the interest income, realized and unrealized gains and losses on Life Funds Withheld Assets and certain related expenses, is as follows: Components of Life Retrocession Embedded Derivative and Derivative Instruments - Life Funds Withheld Assets: (U.S. dollars in thousands) 2016 2015 Interest income - Life Funds Withheld Assets $ (161,887 ) $ (193,569 ) Realized and unrealized gains (losses) on Life Funds Withheld Assets (312,074 ) 180,134 Other 155 351 Net realized and unrealized gains (losses) on life retrocession embedded derivative $ (473,806 ) $ (13,084 ) Net adjustments related to future policy benefit reserves, net of tax $ (51,100 ) $ (125,747 ) Net realized and unrealized gains (losses) on derivative instruments - Life Funds Withheld Assets $ (15,184 ) $ (12,860 ) Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets $ (540,090 ) $ (151,691 )
Total impact on earnings relating to derivative instruments not formally designated as hedging	The following table provides the total impact on earnings relating to derivative instruments not formally designated as hedging instruments under authoritative accounting guidance. The impacts are all recorded through Net realized and unrealized gains (losses) on derivatives in the income statement for the years ended December 31, 2016, 2015 and 2014 : Net Realized and Unrealized Gains (Losses) on Derivative Instruments (U.S. dollars in thousands) 2016 2015 2014 Investment Related Derivatives: Interest rate exposure $ 781 $ (2,347 ) $ 15,959 Foreign exchange exposure (592 ) (1,542 ) 3,351 Credit exposure (1,539 ) (2,537 ) 400 Financial market exposure (2,494 ) (2,190 ) 411 Financial Operations Derivatives: Credit exposure — — 5,023 Other Non-Investment Derivatives: Foreign exchange exposure (1,701 ) 60,319 — Credit exposure 4,424 1,375 — Guaranteed minimum income benefit contract — — 2,257 Modified coinsurance funds withheld contract, including life retrocession embedded derivative 3,300 45 2,741 Other 342 — — Total derivatives not designated as hedging instruments $ 2,521 $ 53,123 $ 30,142 Amount of gain (loss) recognized in income from ineffective portion of fair value hedges — — (256 ) Net realized and unrealized gains (losses) on derivative instruments $ 2,521 $ 53,123 $ 29,886 Net realized and unrealized gains (losses on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets $ (540,090 ) $ (151,691 ) $ (488,222 )
Summary of fair value hedges that have been settled and their impact on results during the year	A summary of these fair value hedges that have been terminated and their cumulative impact on results up to the indicated years ended December 31 as well as the remaining balance of the fair value hedges and average years remaining to maturity are shown below: Settlement of Fair Value Hedges – Summary (U.S. dollars in thousands, except years) Fair Value Hedges – Structured Indemnity Contracts December 31, 2016 2015 Cumulative reduction to interest expense $ 113,292 $ 103,742 Remaining balance $ 119,903 $ 129,454 Weighted average years remaining to maturity 20.1 21.6
Summary of contingent credit features	The aggregate fair value of all derivative agreements containing such rating downgrade provisions that were in a liability position and any collateral posted under these agreements as of December 31 for the years indicated were as follows: Contingent Credit Features - Summary: (U.S. dollars in thousands) 2016 2015 Aggregate fair value of derivative agreements with downgrade provisions in a net liability position $ 14,130 $ 5,827 Collateral posted to counterparty $ 4,630 $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Summary of assets and liabilities that were accounted for at fair value	The following tables set forth the Company’s assets and liabilities that were accounted for at fair value at December 31, 2016 and 2015 by level within the fair value hierarchy. For further information, see Note 1(b), "Significant Accounting Policies - Fair Value Measurements ": December 31, 2016 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2016 Assets Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ — $ 3,869,637 $ 24,751 $ — $ 3,894,388 Corporate - Financials — 3,612,006 10,284 — 3,622,290 Corporate - Non Financials — 6,502,638 9,801 — 6,512,439 RMBS - Agency — 4,218,367 — — 4,218,367 RMBS - Non-Agency — 274,258 — — 274,258 CMBS — 665,087 99 — 665,186 CDO — 377,490 1 — 377,491 Other asset-backed securities — 874,767 1,130 — 875,897 U.S. States and political subdivisions of the States — 2,478,112 — — 2,478,112 Non-U.S. Government — 5,030,132 — — 5,030,132 Total fixed maturities - AFS - Excluding Life Funds Withheld Assets, at fair value $ — $ 27,902,494 $ 46,066 $ — $ 27,948,560 Equity securities, at fair value 898,664 138,667 — — 1,037,331 Short-term investments, at fair value (1) — 625,193 — — 625,193 Total investments AFS - Excluding Life Funds Withheld Assets $ 898,664 $ 28,666,354 $ 46,066 $ — $ 29,611,084 Fixed maturities - AFS - Life Funds Withheld Assets U.S. Government — 10,577 — — 10,577 Corporate - Financials — 439,267 — — 439,267 Corporate - Non Financials — 1,015,341 — — 1,015,341 RMBS - Agency — 613 — — 613 RMBS - Non-Agency — 21,767 — — 21,767 CMBS — 94,240 — — 94,240 Other asset-backed securities — 101,560 — — 101,560 Non-U.S. Government — 624,677 — — 624,677 Total fixed maturities - AFS - Life Funds Withheld Assets, at fair value — 2,308,042 — — 2,308,042 Total investments - AFS, at fair value 898,664 30,974,396 46,066 — 31,919,126 December 31, 2016 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2016 Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government — 14,708 — — 14,708 Corporate - Financials — 468,175 — — 468,175 Corporate - Non Financials — 643,030 — — 643,030 RMBS - Agency — 852 — — 852 RMBS - Non-Agency — 109 — — 109 CMBS — 5,526 — — 5,526 Other asset-backed securities — 39,446 — — 39,446 U.S. States and political subdivisions of the States — 224 — — 224 Non-U.S. Government — 444,944 — — 444,944 Total fixed maturities - Trading - Life Funds Withheld Assets, at fair value — 1,617,014 — — 1,617,014 Short-term investments, at fair value — 9,563 — — 9,563 Total investments, Trading — 1,626,577 — — 1,626,577 Cash equivalents (2) 573,398 1,096,254 — — 1,669,652 Cash equivalents - Life Funds Withheld Assets — 72,798 — — 72,798 Other investments (3) 493,874 205,528 — 699,402 Other assets (4) — 87,655 19,841 (17,947 ) 89,549 Total assets accounted for at fair value $ 1,472,062 $ 34,351,554 $ 271,435 $ (17,947 ) $ 36,077,104 Liabilities Funds withheld on GreyCastle Life Retro Arrangements (net of future policy benefit reserves recoverable) (5) $ — $ 937,721 $ — $ — $ 937,721 Other liabilities (4) — 44,865 19,839 (17,947 ) 46,757 Total liabilities accounted for at fair value $ — $ 982,586 $ 19,839 $ (17,947 ) $ 984,478 December 31, 2015 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2015 Assets Fixed maturities - AFS - Excluding Life Funds Withheld Assets U.S. Government $ — $ 5,020,574 $ 45,063 $ — $ 5,065,637 Corporate - Financials — 3,508,224 53,685 — $ 3,561,909 Corporate - Non Financials — 6,900,259 188 — $ 6,900,447 RMBS - Agency — 3,754,894 3,077 — $ 3,757,971 RMBS - Non-Agency — 328,540 — — $ 328,540 CMBS — 405,316 — — $ 405,316 CDOs — 2 32,408 — $ 32,410 Other asset-backed securities — 1,150,715 17,857 — $ 1,168,572 U.S. States and political subdivisions of the States — 2,632,070 — — $ 2,632,070 Non-U.S. Government — 5,251,614 — — $ 5,251,614 Total fixed maturities - AFS - Excluding Funds Withheld Assets, at fair value $ — $ 28,952,208 $ 152,278 $ — $ 29,104,486 Equity securities, at fair value 528,581 350,338 — — 878,919 Short-term investments, at fair value (1) — 617,390 — — 617,390 Total investments AFS - Excluding Funds Withheld Assets $ 528,581 $ 29,919,936 $ 152,278 $ — $ 30,600,795 December 31, 2015 (U.S. dollars in thousands) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Other Unobservable Inputs (Level 3) Collateral and Counterparty Netting Balance at December 31, 2015 Fixed maturities - Life Funds Withheld Assets U.S. Government and Government-Related/Supported $ — $ 12,742 $ — $ — $ 12,742 Corporate - Financials — 598,236 — — $ 598,236 Corporate - Non Financials — 1,308,628 — — $ 1,308,628 RMBS – Agency — 752 — — $ 752 RMBS – Non-Agency — 26,953 — — $ 26,953 CMBS — 122,481 — — $ 122,481 Other asset-backed securities — 149,795 — — $ 149,795 Non-U.S. Government — 933,516 — — $ 933,516 Total fixed maturities - AFS - Life Funds Withheld Assets, at fair value $ — $ 3,153,103 $ — $ — $ 3,153,103 Total investments - AFS, at fair value $ 528,581 $ 33,073,039 $ 152,278 $ — $ 33,753,898 Fixed maturities - Trading - Life Funds Withheld Assets U.S. Government $ — $ 4,990 $ — $ — $ 4,990 Corporate - Financials — 335,956 — — $ 335,956 Corporate - Non Financials — 493,621 — — $ 493,621 RMBS – Agency — 368 — — $ 368 CMBS — 4,803 — — $ 4,803 Other asset-backed securities — 25,700 — — $ 25,700 Non-U.S. Government — 370,261 — — $ 370,261 Total fixed maturities - Trading - Life Funds Withheld Assets, at fair value $ — $ 1,235,699 $ — $ — $ 1,235,699 Short-term investments, at fair value — 60,330 — — $ 60,330 Total investments, Trading $ — $ 1,296,029 $ — $ — $ 1,296,029 Cash equivalents (2) 437,742 830,924 — — $ 1,268,666 Cash equivalents - Life Funds Withheld Assets (2) 517 100,757 — — $ 101,274 Other investments (3) — 490,058 283,550 — $ 773,608 Other assets (4) — 69,914 19,400 (3,087 ) $ 86,227 Total assets accounted for at fair value $ 966,840 $ 35,860,721 $ 455,228 $ (3,087 ) $ 37,279,702 Liabilities Funds withheld on life retrocession arrangements (net of future policy benefit reserves recoverable) (5) $ — $ 463,915 $ — $ — $ 463,915 Financial instruments sold, but not yet purchased (6) 347 — — — $ 347 Other liabilities (4) — 16,304 29,191 (3,087 ) $ 42,408 Total liabilities accounted for at fair value $ 347 $ 480,219 $ 29,191 $ (3,087 ) $ 506,670 ____________ (1) Short-term investments consist primarily of Corporate securities and U.S. and Non-U.S. Government and Government-Related/ Supported securities. (2) Cash equivalents balances subject to fair value measurement include certificates of deposit and money market funds. Operating cash balances are not subject to recurring fair value measurement guidance. (3) Other Investments balance excludes $322.9 million and $518.1 million as of December 31, 2016 and December 31, 2015 , respectively, measured using Net Asset Value, based on new accounting guidance. In addition, the Other investments balance excludes a certain payment obligation. These investments, which totaled $142.3 million at December 31, 2016 and $141.3 million at December 31, 2015 , are carried at amortized cost. For further information, see Note 6, "Other Investments ." (4) Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy. For further details regarding derivative fair values and associated collateral received or paid see Note 7, "Derivative Instruments ." (5) Funds withheld on life retrocession arrangements (net of future policy benefit reserves recoverable) include balances related to the life retrocession embedded derivative, under which all investment results associated with the Life Funds Withheld Assets related to the GreyCastle Life Retro Arrangements described in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary ", accrue to the benefit of GCLR. (6) Financial instruments sold, but not yet purchased, represent "short sales" and are included within "Payable for investments purchased" on the balance sheets.
Additional information about assets and liabilities measured at fair value on a recurring basis - Level 3	Level 3 Assets and Liabilities - Year Ended December 31, 2016 (U.S. dollars in thousands) Balance, beginning of period Realized gains (losses) Movement in unrealized gains (losses) Purchases and Issuances Sales Settlements Net transfers into (out of) Level 3 (2) Balance, end of period Movement in total gains (losses) relating to investments still held U.S. Government $ 45,063 $ 264 $ 687 $ — $ (19,101 ) $ (2,162 ) $ — $ 24,751 $ 886 Corporate - Financials 53,685 (2,991 ) 10 285 (30,420 ) — (10,285 ) 10,284 31 Corporate - Non-Financials 188 — 13 1,747 — (6 ) 7,859 9,801 14 RMBS - Agency 3,077 (3 ) 7 — — (229 ) (2,852 ) — — CMBS — — (3 ) — — — 102 99 (3 ) CDO 32,408 189 6,870 — — (23,030 ) (16,436 ) 1 6,152 Other asset-backed securities 17,857 479 (2,113 ) 1,072 — (14,190 ) (1,975 ) 1,130 (1,673 ) Other investments 283,550 18,097 (10,622 ) 47,998 (27,676 ) (43,607 ) (62,212 ) 205,528 2,454 Derivative Contracts - Net (9,791 ) — 9,793 — — — — 2 10 Total $ 426,037 $ 16,035 $ 4,642 $ 51,102 $ (77,197 ) $ (83,224 ) $ (85,799 ) $ 251,596 $ 7,871 Level 3 Assets and Liabilities - Year Ended December 31, 2015 (U.S. dollars in thousands) Balance, beginning of period Realized gains (losses) Movement in unrealized gains (losses) Purchases and Issuances (1) Sales Settlements Net transfers into (out of) Level 3 (2) Balance, end of period Movement in total gains (losses) relating to investments still held U.S. Government $ — $ — $ — $ 35,044 $ — $ — $ 10,019 $ 45,063 $ — Corporate - Financials — 9 (10 ) 53,686 — — — 53,685 (2 ) Corporate - Non-Financials 5,894 (186 ) (13 ) (123 ) — (316 ) (5,068 ) 188 (153 ) RMBS - Agency 1,910 — (3 ) 1,297 — (323 ) 196 3,077 (2 ) CDO 687,958 (8,658 ) 16,688 25,882 (366,633 ) (322,829 ) — 32,408 5,279 Other asset-backed securities 5,288 628 (599 ) 46,940 (7,269 ) (6,359 ) (20,772 ) 17,857 451 Other investments 185,083 15,270 (12,548 ) 117,143 (1,417 ) (19,981 ) — 283,550 2,724 Derivative Contracts - Net (9,764 ) — (27 ) — — — — (9,791 ) 80 Total $ 876,369 $ 7,063 $ 3,488 $ 279,869 $ (375,319 ) $ (349,808 ) $ (15,625 ) $ 426,037 $ 8,377 ____________ (1) Includes assets acquired as result of the transaction described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition " (2) Net transfers include both movement in and movement out of Level 3. Corporate - Non-Financials securities for 2016 includes $9.7 million of incoming transfers partially offset by $1.9 million outgoing transfers. Other asset-backed securities for 2016 includes $5.0 million of outgoing transfers partially offset by $3.0 million of incoming transfers, and 2015 includes $34.1 million of outgoing transfers partially offset by $13.3 million of incoming transfers. Other investments for 2016 includes $77.7 million of outgoing transfers partially offset by $15.5 million of incoming transfers. RMBS-Agency for 2015 includes $3.1 million of incoming transfers partially offset by $2.9 million of outgoing transfers.
Financial instruments for which the carrying values differs from the estimated fair value	The following table includes financial instruments for which the carrying value differs from the estimated fair values at December 31, 2016 and 2015 . All of these fair value estimates are considered Level 2 fair value measurements. (U.S. dollars in thousands) 2016 2015 Carrying Value Fair Value Carrying Value Fair Value Financial Assets - Other investments, structured transactions $ 142,271 $ 153,173 $ 141,329 $ 154,065 Deposit liabilities $ 1,116,233 $ 1,337,406 $ 1,168,376 $ 1,436,210 Notes payable and debt 2,647,677 2,813,257 2,644,970 2,805,152 Financial Liabilities $ 3,763,910 $ 4,150,663 $ 3,813,346 $ 4,241,362

Goodwill and Other Intangible44

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of goodwill & intangible assets	The following table presents an analysis of intangible assets broken down between goodwill, intangible assets with an indefinite life and intangible assets with a definite life for the years ended December 31, 2016, 2015 and 2014 : (U.S. dollars in thousands) Goodwill Intangible assets with an indefinite life Intangible assets with a definite life Total Balance at December 31, 2013 $ 396,245 $ 15,366 $ — $ 411,611 Additions 25,159 — 18,500 43,659 Amortization — — (1,850 ) (1,850 ) Foreign currency translation (5,468 ) — — (5,468 ) Balance at December 31, 2014 $ 415,936 $ 15,366 $ 16,650 $ 447,952 Additions 807,381 673,000 315,000 1,795,381 Amortization — — (15,517 ) (15,517 ) Foreign currency translation (9,687 ) (5,507 ) (2,356 ) (17,550 ) Balance at December 31, 2015 $ 1,213,630 $ 682,859 $ 313,777 $ 2,210,266 Additions 14,084 8,000 28,948 51,032 Amortization — — (22,422 ) (22,422 ) Foreign currency translation (14,190 ) (8,080 ) (12,953 ) (35,223 ) Balance at December 31, 2016 $ 1,213,524 $ 682,779 $ 307,350 $ 2,203,653
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	Future amortization expenses are expected to be as follows: Year Ended December 31, 2017 $ 21,957 2018 20,291 2019 20,041 2020 19,957 2021 19,957 2022-2036 205,147 Total expected amortization expenses $ 307,350
Schedule Of Acquired Intangible Assets By Major Class [Table Text Block]	The following table summarizes the intangible assets and their related useful lives recorded in connection with the Catlin Acquisition, as described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition ," as of the Acquisition Date: (U.S. dollars in thousands) Amount Estimated Useful Life Lloyd's - Syndicate capacity $ 660,000 Indefinite Insurance licenses 13,000 Indefinite Total identified indefinite life intangible assets $ 673,000 Lloyd's - Managing agent contracts 15,000 15 years Distribution network 290,000 20 years Trademarks / Trade names 10,000 2 years Total identified definite life intangible assets $ 315,000 Total identified intangible assets $ 988,000

Losses and Loss Expenses (Table

Losses and Loss Expenses (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting Information [Line Items]
Reserve roll forward	The following table represents a reconciliation of the beginning and ending balances of unpaid losses and loss expenses, including an analysis of the Company’s paid and unpaid losses and loss expenses incurred for the years indicated: (U.S. dollars in thousands) 2016 2015 2014 Unpaid losses and loss expenses at the beginning of the year $ 25,439,744 $ 19,353,243 $ 20,481,065 Unpaid losses and loss expenses recoverable (1) 5,248,905 3,411,528 3,414,735 Net unpaid losses and loss expenses at the beginning of the year $ 20,190,839 $ 15,941,715 $ 17,066,330 Acquired reserves 101,315 5,439,876 — Increase (decrease) in net losses and loss expenses incurred in respect of losses occurring in: Current year 6,374,377 5,072,830 3,513,465 Prior year (301,542 ) (306,630 ) (255,072 ) Total net incurred losses and loss expenses 6,072,835 4,766,200 3,258,393 Exchange rate effects (571,198 ) (582,300 ) (561,673 ) Less net losses and loss expenses paid in respect of losses occurring in: Current year 1,444,251 1,047,277 381,008 Prior year 3,890,269 4,327,375 3,440,327 Total net paid losses $ 5,334,520 $ 5,374,652 $ 3,821,335 Net unpaid losses and loss expenses at the end of the year 20,459,271 20,190,839 15,941,715 Unpaid losses and loss expenses recoverable (1) 5,480,300 5,248,905 3,411,528 Unpaid losses and loss expenses at the end of the year $ 25,939,571 $ 25,439,744 $ 19,353,243 ____________ (1) Property and Casualty business only. See Note 12, "Reinsurance ," for further information.
Components of reserves	Unpaid losses and loss expenses prior to reinsurance recoveries for the indicated years ended December 31 comprise the following: (U.S. dollars in thousands) 2016 2015 Reserve for reported losses and loss expenses $ 10,343,481 $ 10,293,448 Reserve for losses incurred but not reported 15,596,090 15,146,296 Unpaid losses and loss expenses $ 25,939,571 $ 25,439,744
Incurred and paid claims development	Total Property and Casualty (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 4,632,657 $ 4,806,850 $ 4,718,961 $ 4,684,540 $ 4,689,256 $ 4,569,019 $ 4,541,978 $ 4,519,599 $ 4,432,150 $ 4,390,981 $ 246,827 N/A 2008 5,504,796 5,575,015 5,503,422 5,524,325 5,479,907 5,449,364 5,417,072 5,357,648 5,322,204 307,738 N/A 2009 4,622,547 4,627,569 4,542,408 4,556,902 4,550,362 4,550,542 4,422,167 4,392,904 317,583 N/A 2010 4,983,044 5,111,634 5,002,061 5,026,101 4,974,782 4,957,474 4,981,939 464,306 N/A 2011 6,236,775 6,187,474 6,111,779 5,980,635 6,116,046 6,083,796 558,008 N/A 2012 5,697,958 5,660,616 5,640,576 5,754,387 5,663,926 715,827 N/A 2013 5,558,316 5,554,791 5,523,695 5,426,144 1,082,491 N/A 2014 5,183,056 5,369,393 5,397,264 1,396,883 N/A 2015 5,354,494 5,498,206 1,962,006 N/A 2016 6,005,506 3,425,518 N/A $ 53,162,870 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 521,083 $ 1,289,961 $ 2,055,288 $ 2,587,918 $ 3,126,834 $ 3,397,370 $ 3,612,934 $ 3,744,872 $ 3,822,207 $ 3,894,280 2008 788,760 1,994,235 2,857,474 3,446,415 3,947,203 4,240,640 4,450,875 4,582,409 4,700,567 2009 638,179 1,530,295 2,192,791 2,655,163 3,117,922 3,366,917 3,551,474 3,663,224 2010 840,030 1,855,407 2,645,868 3,144,278 3,521,163 3,851,827 4,084,244 2011 1,246,596 2,872,319 3,664,970 4,242,053 4,737,827 5,021,000 2012 952,158 2,256,973 3,149,842 3,802,042 4,199,766 2013 976,023 2,194,912 3,049,907 3,614,076 2014 957,525 2,250,446 3,090,343 2015 970,277 2,152,569 2016 1,192,137 $ 35,612,206 All outstanding liabilities prior to 2007, net of reinsurance 2,501,779 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 20,052,443
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 17 % 22 % 15 % 10 % 9 % 6 % 3 % 3 % 3 % 1 %
Reconciliation of claims development to liability	Reconciliation (U.S. dollars in thousands) December 31, 2016 Net outstanding liabilities Insurance Segment EPC $ 1,235,716 Specialty 1,801,962 Professional 3,951,383 Casualty and other 6,354,077 Reinsurance Segment Property and Other Short-Tail lines 2,201,173 Casualty and Other Long-Tail lines 4,508,132 Subtotal, disaggregated triangles $ 20,052,443 Unallocated loss expenses 482,680 Discount (1) (413,522 ) Provision for uncollectible reinsurance 42,119 Other 295,551 Total net liability for unpaid losses and loss expenses 20,459,271 Reinsurance recoverable on unpaid losses Insurance Segment EPC $ 486,595 Specialty 524,545 Professional 1,195,720 Casualty 2,836,800 Reinsurance Segment Property and Other Short-Tail lines 242,845 Casualty and Other Long-Tail lines 122,190 Other 71,605 Total recoverable on unpaid losses and loss expenses $ 5,480,300 Unpaid losses and loss expenses $ 25,939,571 ____________ (1) As noted in Note 10(c), "Losses and Loss Expenses - Loss Reserve Discounting ," the Company discounts only certain workers’ compensation (including long term disability) liabilities and certain bodily injury liability claims, emanating from U.K. exposures, predominantly from the U.K. motor liability portfolio.
Components of incurred losses and loss expenses	Net losses and loss expenses incurred for the years indicated are comprised of: (U.S. dollars in thousands) 2016 2015 2014 Loss and loss expenses payments $ 6,828,012 $ 6,505,075 $ 4,499,642 Change in unpaid losses and loss expenses 976,401 (168,263 ) (514,406 ) Change in unpaid losses and loss expenses recoverable (238,086 ) (440,189 ) (48,536 ) Paid loss recoveries (1,493,492 ) (1,130,423 ) (678,307 ) Net losses and loss expenses incurred $ 6,072,835 $ 4,766,200 $ 3,258,393
Schedule of causes of increase (decrease) in liability for unpaid claims and claims adjustment expense [Table Text Block]	The following table presents the net (favorable) adverse prior year loss development of the Company’s loss and loss expense reserves for its property and casualty operations by operating segment for each of the years indicated: (U.S. dollars in thousands) 2016 2015 2014 Insurance segment $ (91,459 ) $ (65,030 ) $ (99,758 ) Reinsurance segment (210,083 ) (241,600 ) (155,314 ) Total $ (301,542 ) $ (306,630 ) $ (255,072 )
Asbestos and environmental related claims rollforward	A reconciliation of the opening and closing unpaid losses and loss expenses related to discontinued asbestos and run-off environmental exposure claims for the years indicated is as follows: Year ended December 31, (U.S. dollars in thousands) 2016 2015 2014 Net unpaid losses and loss expenses at beginning of year $ 93,704 $ 81,416 $ 80,435 Net incurred losses and loss expenses 9,042 15,663 8,903 Less net paid losses and loss expenses 9,912 9,087 7,922 Net increase (decrease) in unpaid losses and loss expenses $ (870 ) $ 6,576 $ 981 Acquired reserves — 5,712 — Net unpaid losses and loss expenses at end of year 92,834 93,704 81,416 Unpaid losses and loss expenses recoverable at end of year 83,430 93,688 100,537 Gross unpaid losses and loss expenses at end of year $ 176,264 $ 187,392 $ 181,953
Schedule of open claims files for potential asbestos and environmental claims	The development of the number of open claim files for potential discontinued asbestos and run-off environmental claims, including precautionary claims, is as follows: Asbestos Claims Environmental Claims Total number of claims outstanding at December 31, 2013 1,097 338 New claims reported in 2014 456 190 Claims resolved in 2014 (154 ) (69 ) Total number of claims outstanding at December 31, 2014 1,399 459 New claims reported in 2015 272 67 Claims resolved in 2015 (246 ) (96 ) Reserves acquired in 2015 1,166 — Total number of claims outstanding at December 31, 2015 2,591 430 New claims reported in 2016 579 69 Claims resolved in 2016 (753 ) (41 ) Total number of claims outstanding at December 31, 2016 2,417 458
Insurance Segment
Segment Reporting Information [Line Items]
Incurred and paid claims development	Insurance Segment (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 3,258,668 $ 3,490,955 $ 3,426,696 $ 3,431,600 $ 3,442,331 $ 3,329,848 $ 3,317,676 $ 3,318,423 $ 3,274,775 $ 3,246,355 $ 158,351 45.542 2008 3,891,682 3,969,259 3,935,499 3,974,071 3,918,450 3,889,538 3,857,758 3,822,133 3,786,671 186,723 54.952 2009 3,472,222 3,499,124 3,458,320 3,480,715 3,483,027 3,500,575 3,369,614 3,346,817 190,193 54.896 2010 3,702,458 3,809,102 3,699,234 3,735,809 3,688,045 3,661,919 3,697,761 313,815 61.416 2011 4,014,389 3,986,420 4,009,166 3,921,559 4,026,511 4,001,271 379,349 65.437 2012 3,870,871 3,799,876 3,800,046 3,921,415 3,851,259 468,002 70.919 2013 3,942,360 4,003,359 3,978,956 3,924,048 802,611 78.018 2014 3,748,154 3,917,364 3,978,436 1,052,314 87.491 2015 3,849,731 4,039,203 1,418,476 94.229 2016 4,160,269 2,358,172 65.684 $ 38,032,090 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 367,171 $ 930,428 $ 1,462,857 $ 1,884,318 $ 2,333,047 $ 2,549,256 $ 2,715,861 $ 2,822,610 $ 2,896,977 $ 2,943,144 2008 461,606 1,339,577 1,973,577 2,427,033 2,843,188 3,069,812 3,234,869 3,337,607 3,415,212 2009 462,090 1,140,796 1,666,673 2,043,196 2,432,021 2,634,783 2,787,167 2,865,558 2010 607,658 1,377,513 1,978,027 2,370,062 2,685,015 2,914,856 3,072,546 2011 649,690 1,617,155 2,216,640 2,653,619 3,062,399 3,290,213 2012 634,043 1,471,761 2,079,400 2,578,639 2,886,674 2013 657,753 1,509,232 2,141,332 2,597,422 2014 669,745 1,597,123 2,263,643 2015 691,253 1,563,019 2016 861,429 $ 25,758,860 All outstanding liabilities prior to 2007, net of reinsurance 1,069,908 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 13,343,138
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 16 % 21 % 16 % 11 % 10 % 6 % 4 % 3 % 3 % 1 %
Components of prior year development	The following table summarizes the net (favorable) adverse prior year development by business group relating to the Insurance segment for the indicated years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 EPC $ (38,366 ) $ (6,447 ) $ (57,465 ) Specialty (5,655 ) (93,043 ) (82,756 ) Professional $ 10,813 $ 5,740 $ 17,092 Casualty and other (58,251 ) 28,720 23,371 Total $ (91,459 ) $ (65,030 ) $ (99,758 )
Insurance Segment | Professional lines
Segment Reporting Information [Line Items]
Incurred and paid claims development	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 3 % 13 % 16 % 16 % 15 % 9 % 6 % 4 % 4 % 1 %
Average annual percentage payout of incurred losses by age	Professional (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 911,695 $ 1,130,926 $ 1,106,630 $ 1,061,995 $ 1,070,028 $ 995,364 $ 993,007 $ 1,000,256 $ 944,024 $ 928,677 $ 68,144 4.371 2008 1,033,982 1,087,436 1,131,685 1,221,906 1,195,931 1,174,486 1,167,289 1,136,720 1,114,924 60,568 5.187 2009 968,336 1,036,140 1,094,824 1,158,091 1,196,078 1,202,994 1,169,232 1,164,825 77,399 5.589 2010 989,432 984,780 957,486 1,035,571 996,024 1,016,013 1,061,340 113,635 5.418 2011 967,386 960,895 1,012,458 1,027,504 1,104,107 1,111,524 162,147 5.253 2012 976,450 976,593 1,011,363 1,124,437 1,117,970 212,997 5,320 2013 965,875 963,634 942,022 922,634 339,380 5.595 2014 747,671 799,952 843,003 371,270 5.969 2015 755,087 800,568 493,667 6.391 2016 730,198 654,395 3.704 $ 9,795,663 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 25,207 $ 111,289 $ 240,287 $ 421,654 $ 540,255 $ 612,498 $ 692,492 $ 738,301 $ 776,445 $ 801,141 2008 17,987 185,149 346,923 516,426 697,071 782,381 853,405 911,634 969,698 2009 22,350 161,125 337,568 507,629 745,836 838,990 922,453 948,015 2010 21,803 155,845 324,580 480,475 623,975 735,626 803,916 2011 28,625 144,365 315,130 480,248 683,043 815,129 2012 44,486 195,088 378,059 591,820 713,165 2013 36,582 152,052 304,503 457,890 2014 17,042 138,832 312,548 2015 22,521 139,345 2016 23,462 $ 5,984,309 All outstanding liabilities prior to 2007, net of reinsurance 140,029 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 3,951,383
Insurance Segment | Casualty and other
Segment Reporting Information [Line Items]
Incurred and paid claims development	Casualty and other (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 1,082,033 $ 1,112,540 $ 1,087,608 $ 1,166,693 $ 1,175,846 $ 1,159,030 $ 1,163,024 $ 1,179,115 $ 1,171,058 $ 1,162,152 $ 85,633 17.237 2008 1,140,247 1,112,464 1,112,589 1,106,258 1,093,984 1,105,909 1,102,780 1,085,898 1,078,619 111,716 18.669 2009 1,116,831 1,101,930 1,089,006 1,083,830 1,064,751 1,089,350 1,048,630 1,041,605 104,475 20.836 2010 1,112,521 1,250,384 1,258,380 1,253,471 1,276,555 1,233,729 1,230,374 193,273 23.029 2011 1,092,125 1,139,829 1,160,676 1,134,783 1,160,467 1,138,849 175,768 24.942 2012 1,195,390 1,212,625 1,235,541 1,258,868 1,217,096 229,162 26.613 2013 1,295,006 1,344,357 1,403,279 1,375,254 407,549 29.179 2014 1,351,268 1,417,460 1,463,809 607,888 30.254 2015 1,335,856 1,399,039 722,174 31.862 2016 1,395,154 1,088,868 18.283 $ 12,501,951 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 22,680 $ 142,855 $ 315,942 $ 470,594 $ 751,437 $ 855,446 $ 917,798 $ 961,739 $ 993,114 $ 1,011,066 2008 46,589 175,724 384,593 557,222 673,130 771,029 843,167 886,979 898,297 2009 43,912 237,264 414,586 535,197 638,617 727,782 771,855 818,732 2010 101,673 292,403 516,383 649,167 759,673 862,584 937,451 2011 115,807 258,861 418,204 594,047 748,537 818,838 2012 117,735 297,186 471,949 644,936 775,521 2013 124,226 307,950 533,465 710,905 2014 133,592 335,216 555,967 2015 109,217 282,670 2016 103,727 $ 6,913,174 All outstanding liabilities prior to 2007, net of reinsurance 765,300 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 6,354,077
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 7 % 14 % 16 % 13 % 13 % 8 % 5 % 4 % 3 % 3 %
Insurance Segment | EPC
Segment Reporting Information [Line Items]
Incurred and paid claims development	EPC (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 439,938 $ 394,730 $ 385,373 $ 365,395 $ 364,454 $ 361,632 $ 358,820 $ 357,009 $ 356,106 $ 355,709 $ (213 ) 5,380 2008 841,913 834,562 806,976 782,005 777,476 769,906 774,108 768,610 767,031 10,701 9.013 2009 400,045 382,644 364,526 356,069 349,819 345,668 344,108 342,072 6,549 7.596 2010 596,340 611,917 589,119 571,375 565,494 574,091 568,574 (5,681 ) 8.532 2011 979,353 911,684 890,820 857,510 846,315 842,481 7,165 10.172 2012 689,032 660,128 635,712 636,896 626,132 6,086 11.131 2013 740,573 715,909 690,102 684,578 9,763 12.141 2014 703,860 735,789 723,382 6,921 14.609 2015 791,724 812,247 64,949 16.424 2016 969,709 228,630 15.279 $ 6,691,915 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 69,288 $ 208,210 $ 298,622 $ 316,321 $ 329,883 $ 341,442 $ 347,421 $ 348,059 $ 350,602 $ 351,151 2008 152,946 467,537 604,163 653,749 730,513 748,607 752,294 747,374 750,022 2009 84,638 190,194 254,420 287,809 311,335 313,434 328,222 331,246 2010 166,353 380,649 476,832 526,375 543,985 542,011 547,486 2011 211,176 610,086 744,330 784,418 813,298 815,694 2012 161,117 389,827 531,299 574,467 593,981 2013 165,460 452,805 586,539 636,623 2014 180,735 504,925 645,682 2015 224,497 484,431 2016 324,575 $ 5,480,891 All outstanding liabilities prior to 2007, net of reinsurance 24,692 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 1,235,716
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 26 % 38 % 20 % 6 % 5 % 1 % 1 % — % 1 % 1 %
Insurance Segment | Specialty
Segment Reporting Information [Line Items]
Incurred and paid claims development	Specialty (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 825,002 $ 852,759 $ 847,085 $ 837,517 $ 832,003 $ 813,822 $ 802,825 $ 782,043 $ 803,587 $ 799,817 $ 4,787 18.554 2008 875,540 934,797 884,249 863,902 851,059 839,237 813,581 830,905 826,097 3,738 22.083 2009 987,010 978,410 909,964 882,725 872,379 862,563 807,644 798,315 1,770 20.875 2010 1,004,165 962,021 894,249 875,392 849,972 838,086 837,473 12,588 24.437 2011 975,525 974,012 945,212 901,762 915,622 908,417 34,269 25,070 2012 1,009,999 950,530 917,430 901,214 890,061 19,757 27.855 2013 940,906 979,459 943,553 941,582 45,919 31.103 2014 945,355 964,163 948,242 66,235 36.659 2015 967,064 1,027,349 137,686 39.552 2016 1,065,208 386,279 28.418 $ 9,042,561 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 249,996 $ 468,074 $ 608,006 $ 675,749 $ 711,472 $ 739,870 $ 758,150 $ 774,511 $ 776,816 $ 779,786 2008 244,084 511,167 637,898 699,636 742,474 767,795 786,003 791,620 797,195 2009 311,190 552,213 660,099 712,561 736,233 754,577 764,637 767,565 2010 317,829 548,616 660,232 714,045 757,382 774,635 783,693 2011 294,082 603,843 738,976 794,906 817,521 840,552 2012 310,705 589,660 698,093 767,416 804,007 2013 331,485 596,425 716,825 792,004 2014 338,376 618,150 749,446 2015 335,018 656,573 2016 409,665 $ 7,380,486 All outstanding liabilities prior to 2007, net of reinsurance 139,887 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 1,801,962
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 35 % 30 % 14 % 7 % 4 % 3 % 2 % 1 % 1 % 1 %
Reinsurance Segment
Segment Reporting Information [Line Items]
Incurred and paid claims development	Reinsurance Segment (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 1,373,989 $ 1,315,895 $ 1,292,265 $ 1,252,940 $ 1,246,925 $ 1,239,171 $ 1,224,302 $ 1,201,176 $ 1,157,375 $ 1,144,626 $ 88,476 N/A 2008 1,613,114 1,605,756 1,567,923 1,550,254 1,561,457 1,559,826 1,559,314 1,535,515 1,535,533 121,015 N/A 2009 1,150,325 1,128,445 1,084,088 1,076,187 1,067,335 1,049,967 1,052,553 1,046,087 127,390 N/A 2010 1,280,586 1,302,532 1,302,827 1,290,292 1,286,737 1,295,555 1,284,178 150,491 N/A 2011 2,222,386 2,201,054 2,102,613 2,059,076 2,089,535 2,082,525 178,659 N/A 2012 1,827,087 1,860,740 1,840,530 1,832,972 1,812,667 247,825 N/A 2013 1,615,956 1,551,432 1,544,739 1,502,096 279,880 N/A 2014 1,434,902 1,452,029 1,418,828 344,569 N/A 2015 1,504,763 1,459,003 543,530 N/A 2016 1,845,237 1,067,346 N/A $ 15,130,780 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 153,912 $ 359,533 $ 592,431 $ 703,600 $ 793,787 $ 848,114 $ 897,073 $ 922,262 $ 925,230 $ 951,136 2008 327,154 654,658 883,897 1,019,382 1,104,015 1,170,828 1,216,006 1,244,802 1,285,355 2009 176,089 389,499 526,118 611,967 685,901 732,134 764,307 797,666 2010 232,372 477,894 667,841 774,216 836,148 936,971 1,011,698 2011 596,906 1,255,164 1,448,330 1,588,434 1,675,428 1,730,787 2012 318,115 785,212 1,070,442 1,223,403 1,313,092 2013 318,270 685,680 908,575 1,016,654 2014 287,780 653,323 826,700 2015 279,024 589,550 2016 330,708 $ 9,853,346 All outstanding liabilities prior to 2007, net of reinsurance 1,431,871 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 6,709,305
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 20 % 24 % 15 % 8 % 5 % 4 % 1 % 2 % 3 % 1 %
Components of prior year development	The following table summarizes the net (favorable) adverse prior year development by line of business relating to the Reinsurance segment for the indicated years ended December 31: (U.S. dollars in thousands) 2016 2015 2014 Property and Other Short-Tail Lines $ (134,440 ) $ (173,754 ) $ (85,324 ) Casualty and Other Long-Tail Lines (75,643 ) (67,846 ) (69,990 ) Total $ (210,083 ) $ (241,600 ) $ (155,314 )
Reinsurance Segment | Property and other short-tail lines
Segment Reporting Information [Line Items]
Incurred and paid claims development	Property and Other Short-tail Lines (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 655,785 $ 612,847 $ 591,325 $ 576,823 $ 556,160 $ 543,586 $ 542,517 $ 531,757 $ 505,908 $ 504,777 $ 9,948 N/A 2008 922,391 913,108 893,143 870,757 855,385 851,340 855,891 849,351 856,596 22,281 N/A 2009 574,748 541,926 507,488 488,419 479,539 474,526 468,240 472,758 4,958 N/A 2010 821,119 842,728 846,563 852,550 857,788 840,206 840,582 26,847 N/A 2011 1,728,879 1,697,826 1,617,499 1,589,207 1,593,064 1,585,694 42,172 N/A 2012 1,268,108 1,294,768 1,285,569 1,255,565 1,243,866 69,188 N/A 2013 1,068,975 1,011,548 975,565 939,295 45,977 N/A 2014 865,668 855,081 814,558 57,491 N/A 2015 878,711 829,691 163,854 N/A 2016 1,140,759 531,843 N/A $ 9,228,576 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 128,299 $ 274,682 $ 427,810 $ 470,765 $ 487,471 $ 491,862 $ 503,233 $ 497,701 $ 478,062 $ 483,023 2008 291,995 541,613 693,174 757,091 784,005 801,027 805,951 803,919 816,877 2009 145,413 307,294 389,835 421,579 441,032 445,905 445,861 453,626 2010 215,463 429,578 577,128 639,012 665,932 734,453 783,155 2011 581,324 1,196,404 1,344,405 1,432,899 1,472,992 1,493,813 2012 293,705 713,154 933,717 1,028,319 1,068,475 2013 291,534 604,497 768,385 819,523 2014 250,708 556,548 658,511 2015 236,009 472,543 2016 265,695 $ 7,315,241 All outstanding liabilities prior to 2007, net of reinsurance 287,838 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 2,201,173
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 29 % 34 % 17 % 7 % 3 % 4 % 2 % 1 % (1 )% 1 %
Reinsurance Segment | Casualty and Other Long-Tail Lines
Segment Reporting Information [Line Items]
Incurred and paid claims development	Casualty and Other Long-Tail Lines (in thousands) Incurred Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, As of Dec 31, 2016 Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 IBNR (1) Number of Claims 2007 $ 718,204 $ 703,048 $ 700,940 $ 676,117 $ 690,765 $ 695,585 $ 681,785 $ 669,419 $ 651,467 $ 639,849 $ 78,528 N/A 2008 690,723 692,648 674,780 679,497 706,072 708,486 703,423 686,164 678,937 98,734 N/A 2009 575,577 586,519 576,600 587,768 587,796 575,441 584,313 573,329 122,432 N/A 2010 459,467 459,804 456,264 437,742 428,949 455,349 443,596 123,644 N/A 2011 493,507 503,228 485,114 469,869 496,471 496,831 136,487 N/A 2012 558,979 565,972 554,961 577,407 568,801 178,637 N/A 2013 546,981 539,884 569,174 562,801 233,903 N/A 2014 569,234 596,948 604,270 287,078 N/A 2015 626,052 629,312 379,676 N/A 2016 704,478 535,503 N/A $ 5,902,204 Total Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance For the Years Ended December 31, Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Unaudited Accident Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2007 $ 25,613 $ 84,851 $ 164,621 $ 232,835 $ 306,316 $ 356,252 $ 393,840 $ 424,561 $ 447,168 $ 468,113 2008 35,159 113,045 190,723 262,291 320,010 369,801 410,055 440,883 468,478 2009 30,676 82,205 136,283 190,388 244,869 286,229 318,446 344,040 2010 16,909 48,316 90,713 135,204 170,216 202,518 228,543 2011 15,582 58,760 103,925 155,535 202,436 236,974 2012 24,410 72,058 136,725 195,084 244,617 2013 26,736 81,183 140,190 197,131 2014 37,072 96,775 168,189 2015 43,015 117,007 2016 65,013 $ 2,538,105 All outstanding liabilities prior to 2007, net of reinsurance 1,144,033 Liabilities for unpaid losses and loss expenses, net of reinsurance $ 4,508,132
Average annual percentage payout of incurred losses by age	Average Annual Percentage Payout of Incurred Losses by Age, Net of Reinsurance Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 5 % 9 % 10 % 10 % 9 % 7 % 7 % 6 % 6 % 4 %

Future Policy Benefit Reserve (

Future Policy Benefit Reserve (Tables)	12 Months Ended
	Dec. 31, 2016
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Components of future policy benefit reserve	Net future policy benefit reserves are comprised of the following: As of December 31 (U.S. dollars in thousands) 2016 2015 Traditional Life $ 737,252 $ 792,001 Annuities 2,768,795 3,371,499 Gross future policy benefit reserves $ 3,506,047 $ 4,163,500 Reinsurance recoverable - GreyCastle Life Retro Arrangements (3,072,615 ) (3,719,131 ) Reinsurance recoverable - U.S. Term Life Retro Arrangements (270,238 ) (284,481 ) Reinsurance recoverable - Other life retrocessions (10,997 ) (13,801 ) Net future policy benefit reserves $ 152,197 $ 146,087
Funds withheld on Life Retro arrangements	Based upon the contractual right of offset, the funds withheld liability owing to GCLR is recorded net of future policy benefit reserves recoverable, and is included within "Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable)" on the consolidated balance sheets, and is comprised of the following at December 31, 2016 and 2015 : (U.S. dollars in thousands) 2016 2015 Assets held on a funds withheld basis relating to the GreyCastle Life Retro Arrangements $ 4,071,583 $ 4,633,760 Reinsurance recoverable from GCLR (3,072,615 ) (3,719,131 ) Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable) $ 998,968 $ 914,629

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Effect of reinsurance	The effect of reinsurance and retrocessional activity on premiums written and earned from property and casualty operations is shown below: (U.S. dollars in thousands) Premiums Written Year Ended December 31, Premiums Earned Year Ended December 31, 2016 2015 2014 2016 2015 2014 Direct $ 9,166,627 $ 7,847,236 $ 5,450,868 $ 9,142,690 $ 7,717,173 $ 5,173,403 Assumed 4,458,981 2,821,771 2,310,621 4,074,817 3,465,421 2,343,329 Ceded (3,394,972 ) (2,780,183 ) (1,994,280 ) (3,451,620 ) (3,018,410 ) (1,799,294 ) Net $ 10,230,636 $ 7,888,824 $ 5,767,209 $ 9,765,887 $ 8,164,184 $ 5,717,438
Analysis of losses, loss expenses and future policy benefit reserves recoverables	The following table presents an analysis of total unpaid losses and loss expenses recoverable for the years ended December 31: (U.S. dollars in thousands) 2016 2015 P&C Operations $ 5,480,300 $ 5,248,905 Corporate and Other 10,997 13,801 Total unpaid losses and loss expenses recoverable $ 5,491,297 $ 5,262,706
Ceded credit risk by reinsurer	The following is an analysis of the total recoverable and reinsurance balances receivable, net of collateral held, at December 31, 2016 , by reinsurers owing 3% or more of such total: Name of Reinsurer Reinsurer Financial Strength Rating % of Total Munich Reinsurance Co. AA-/Stable 25.6 % Lloyd's Syndicates A+/Stable 15.9 % Swiss Reinsurance Co. AA-/Stable 7.2 % Transatlantic Reinsurance Company A+/Stable 4.1 % Arch Reinsurance Company A+/Negative 3.7 % AXIS Reinsurance Co. A+/Stable 3.0 %
Ratings profile of reinsurers	The following table sets forth the ratings profile of the reinsurers that support the unpaid loss and loss expense recoverable and reinsurance balances receivable, net of collateral, at December 31, 2016 : Reinsurer Financial Strength Rating % of Total AAA 2.8 % AA 44.5 % A 48.1 % BBB 0.6 % BB and below 0.6 % Captives 3.3 % Not Rated 0.1 % Total 100.0 %

Notes Payable and Debt and Fi48

Notes Payable and Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Financing structure	The following table presents the Company's outstanding notes payable and debt as of December 31: (U.S. dollars in thousands) 2016 2015 Commitment/ In Use/ Commitment/ In Use/ Debt: 2.30% Senior Notes due 2018 $ 300,000 $ 298,686 $ 300,000 $ 298,015 5.75% Senior Notes due 2021 400,000 397,953 400,000 397,523 6.375% Senior Notes due 2024 350,000 349,139 350,000 349,029 4.45% Subordinated Notes due 2025 500,000 493,329 500,000 492,521 6.25% Senior Notes due 2027 325,000 323,375 325,000 323,218 5.25% Senior Notes due 2043 300,000 296,427 300,000 296,294 5.5% Subordinated Notes due 2045 500,000 488,768 500,000 488,370 Total debt carrying value $ 2,675,000 $ 2,647,677 $ 2,675,000 $ 2,644,970 _______________ (1) Excluded from the table are certain credit facilities under which the Company is permitted to utilize up to $1.0 billion and $1.4 billion as of December 31, 2016 and December 31, 2015 , respectively, for revolving loans to support general operating and financing needs. However, as of December 31, 2016 and December 31, 2015 , $245 million and $527.1 million , respectively, were utilized under these facilities to issue letters of credit, leaving $755.0 million and $ 822.9 million , respectively, available to support other operating and financing needs. (2) "In Use/Outstanding" data represent December 31, 2016 and December 31, 2015 accreted values.
Credit facilities	The Company’s available credit facilities at December 31 were as follows: (U.S. dollars in thousands) 2016 (1) 2015 (1) Total available credit facilities – commitments (2) $ 3,991,687 $ 4,463,041 Letters of credit – in use $ 2,345,293 $ 2,515,653 Collateralized by certain assets of the Company’s investment portfolio 48.6 % 50.9 % ____________ (1) As of December 31, 2016 and December 31, 2015 , there were fifteen available credit facilities. (2) As of December 31, 2016 and December 31, 2015 the stated portion of allowable credit facilities permitted to be utilized for revolving loans was $1.0 billion and $1.4 billion , respectively. However, as of December 31, 2016 and December 31, 2015 , $245.0 million and $527.1 million , respectively, of such facilities' limits were utilized to issue letters of credit, leaving $755.0 million and $822.9 million , respectively, available either to issue additional letters of credit or to support other operating or financing needs under these particular facilities.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Summary of related party transactions	During the years ended December 31, 2016, 2015 and 2014 , these contracts resulted in reported net premiums, reported net losses, and reported net acquisition costs as summarized below. (U.S. dollars in thousands) 2016 2015 2014 Reported net premiums $ 94,358 $ 42,042 $ 91,261 Reported net losses $ 44,728 $ 13,246 $ 38,927 Reported net acquisition costs $ 39,131 $ 14,682 $ 35,711

Retirement Plans (Tables)

Retirement Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Funded status by geographical region	The funded status by geographical region of all the Company’s retirement plans at December 31, 2016 and 2015 is as follows: Funded Status 2016 2015 U.S. $ (14,093 ) $ (16,306 ) U.K. (2,316 ) (4,650 ) Other European (26,377 ) (21,807 ) Funded status – end of year $ (42,786 ) $ (42,763 )
Change in projected benefit obligation	Change in projected benefit obligation (U.S. dollars in thousands) 2016 2015 Projected benefit obligation – beginning of year $ 122,165 $ 93,124 Projected benefit obligation assumed due to Catlin Acquisition — 28,414 Service cost (1) 1,701 1,494 Interest cost 5,126 4,382 Actuarial (gain) / loss 7,948 2,821 Benefits and expenses paid (5,977 ) (3,747 ) Foreign currency (gains) / losses (10,248 ) (4,047 ) Settlements (677 ) (276 ) Projected benefit obligation – end of year $ 120,038 $ 122,165 (1) Service costs include cost of living adjustments on curtailed plans.
Change in plan assets	Change in plan assets (U.S. dollars in thousands) 2016 2015 Fair value of plan assets – beginning of year $ 79,402 $ 49,281 Fair value of plan assets acquired due to Catlin Acquisition — 33,131 Actual return on plan assets 8,499 (119 ) Employer contributions 2,077 1,775 Benefits and expenses paid (4,577 ) (3,305 ) Foreign currency gains / (losses) (8,149 ) (1,361 ) Fair value of plan assets – end of year $ 77,252 $ 79,402 Funded status – end of year $ (42,786 ) $ (42,763 ) Accrued pension liability $ 42,786 $ 42,763
Components of net benefit cost	The components of the net benefit cost for the years ended December 31, 2016, 2015 and 2014 are as follows: Components of net benefit cost (U.S. dollars in thousands) 2016 2015 2014 Service cost $ 1,701 $ 1,494 $ 1,279 Interest cost 5,126 4,382 3,747 Expected return on plan assets (4,357 ) (3,903 ) (2,859 ) Amortization of net actuarial loss 1,705 1,617 812 Net benefit cost $ 4,175 $ 3,590 $ 2,979
Weighted average assumptions used	The table below includes disclosure of these rates on a weighted-average basis, for the years ended December 31 as indicated: 2016 2015 U.S. Plans U.K. Plans Other European Plans U.S. Plans U.K. Plans Other European Plans Net Benefit Cost – Weighted-average assumptions Discount rate 4.25 % 2.74 % 1.33 % 3.91 % 3.70 % 2.42 % Expected long-term rate of return on plan assets 6.00 % 2.77 % N/A 6.00 % 3.48 % N/A Rate of compensation increase N/A 3.62 % 2.50 % N/A 3.96 % 2.50 % Benefit Obligation – Weighted-average assumptions Discount rate 4.04 % 2.76 % 1.33 % 4.25 % 3.70 % 2.42 % Rate of compensation increase N/A 3.62 % 2.50 % N/A 3.96 % 2.50 %
Allocation of plan assets - UK pension	The assets in the plans and the expected rates of return were as follows: (U.S. dollars in thousands, except percentages) Expected Return on Assets for 2016 Fair Value at December 31, 2016 Expected Return on Assets for 2015 Fair Value at December 31, 2015 Equities ad Growth funds 5.7 % $ 9,122 6.2 % $ 7,893 Gilts 2.4 % 15,459 2.4 % 17,856 Corporate Bonds 3.3 % 13,850 3.4 % 16,915 Other (cash) 0.5 % 89 1.8 % 52 Total market fair value of assets $ 38,520 $ 42,716
Estimated future benefit payments	The estimated future benefit payments with respect to the U.S. defined benefit pension plans are as follows: (U.S. dollars in thousands) Retirement Plan Benefits Equalization Plan Total 2017 $ 1,029 $ 353 $ 1,382 2018 $ 1,057 $ 353 $ 1,410 2019 $ 1,226 $ 450 $ 1,676 2020 $ 1,389 $ 467 $ 1,856 2021 $ 1,683 $ 502 $ 2,185 2022-2026 $ 10,753 $ 2,823 $ 13,576

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Broker credit risk	During the three years ended December 31, 2016, 2015 and 2014 , P&C gross written premiums generated from or placed by the below companies individually accounted for more than 10% of the Company’s consolidated gross written premiums from P&C operations, as follows: (Percentage of consolidated gross written premiums from P&C operations) 2016 2015 2014 AON Corporation and subsidiaries 18 % 18 % 18 % Marsh & McLennan Companies 18 % 19 % 20 % Willis Group and subsidiaries 11 % 13 % 11 %
Future minimum lease payments - operating	Future minimum rental commitments under existing operating leases are expected to be as follows: Year Ended December 31, (U.S. dollars in thousands) 2017 $ 70,359 2018 62,590 2019 57,030 2020 51,566 2021 47,738 2022-2031 96,602 Total minimum future rentals $ 385,885
Future minimum lease payments - capital lease	The future minimum lease payments annually for the next five years are noted in the following table, as well as the aggregate for beyond five years. The total future minimum lease payments in the aggregate are expected to be $131.3 million . Year Ended December 31, (U.S. dollars in thousands) 2017 $ 9,998 2018 10,248 2019 10,504 2020 10,767 2021 11,036 2022-2031 78,736 Total minimum future lease payments $ 131,289

Share Capital (Tables)

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Summary of ordinary shares issued and outstanding	The following table is a summary of common shares issued and outstanding: (in thousands) 2016 2015 Balance – beginning of year 294,745 255,183 Exercise of options 802 480 Net issuance of restricted shares 1,598 1,581 Share buybacks (1) (30,256 ) (12,434 ) Issue of shares — 49,935 Balance – end of year 266,889 294,745 ____________ (1) Includes share buybacks associated with authorized share buyback programs as well as purchases related to satisfying tax withholding obligations of employees in connection with the vesting of restricted shares granted under the Company’s equity compensation programs.
Weighted average option pricing assumptions	The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions: 2016 2015 2014 Dividend yield 2.00 % 2.00 % 2.00 % Risk free interest rate 1.37 % 1.70 % 1.81 % Volatility 21.7 % 21.6 % 34.0 % Expected lives 6.0 years 6.0 years 6.0 years
Summary of options and options activity	The following is a summary of the activity in the stock option plans for the indicated years ended December 31: (In thousands except for weighted average grant date fair value) 2016 2015 2014 Options granted to purchase common shares under the Programs - in thousands 2,200 1,974 1,025 Weighted average grant date fair value $ 5.99 $ 6.51 $ 8.60 Total intrinsic value of stock options exercised $ 19,471 $ 8,546 $ 7,499 Options exercised during the year - in thousands 810 480 424 Compensation expense related to stock option plans $ 11,065 $ 8,961 $ 9,961 Estimated tax benefit (charge) related to stock option plans $ 355 $ — $ (2 ) The following is a summary of the stock options outstanding at December 31, 2016 , and related activity for the year then ended: Number of Shares ( in thousands ) Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in thousands) Outstanding – beginning of year 10,749 $ 28.59 5.4 years $ 121,085 Granted 2,200 34.64 Exercised (810 ) 12.35 Canceled/Expired (278 ) 60.83 Outstanding – end of year 11,861 $ 30.07 5.5 years $ 86,558 Options exercisable 8,002 $ 27.75 4.0 years $ 77,366 Available for grant (1) 8,355 ____________ (1) Available for grant includes shares that may be granted as either stock options, restricted stock, restricted stock units or performance units.
Summary of restricted stock and non-vested restricted stock activity	A summary of the restricted stock awards issued under the 1991 Performance Incentive Program and the Directors Stock and Option Plan for the indicated years ended December 31 is as follows: (In thousands except for weighted average grant date fair value) 2016 2015 2014 Restricted ordinary shares granted 48 44 46 Weighted average grant date fair value $ 34.05 $ 37.11 $ 31.86 Aggregate grant date fair value $ 1,650 $ 1,613 $ 1,463 Compensation expense related to restricted stock awards $ 2,078 $ 3,889 $ 5,239 Estimated tax benefit related to restricted stock awards $ 129 $ 709 $ 1,233 Total unrecognized stock based compensation expense related to non-vested restricted stock awards was nil at December 31, 2016 , which is related to approximately 0.2 million restricted stock awards. Non-vested restricted stock awards at December 31, 2016 and for the year then ended were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 275 $ 41.90 Granted 48 $ 34.05 Vested (132 ) $ 36.35 Unvested at December 31, 2016 191 $ 43.72
Summary of restricted stock units and restricted stock unit activity	A summary of the restricted stock units issued to officers of the Company and its subsidiaries for the indicated years ended December 31 is as follows: (In thousands) 2016 2015 2014 Restricted stock units granted 1,117 1,534 1,867 Aggregate grant date fair value $ 38,681 $ 55,540 $ 57,134 Compensation expense related to restricted stock units $ 46,209 $ 48,937 $ 41,879 Estimated tax benefit related to restricted stock units $ 12,701 $ 13,271 $ 11,607 Total unrecognized stock-based compensation expense related to non-vested restricted stock units was $49.9 million at December 31, 2016 , which is related to approximately 2.5 million restricted stock units and is expected to be recognized over 1.4 years. Non-vested restricted stock units at December 31, 2016 and for the year then ended were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 3,070 $ 32.99 Granted 1,117 $ 34.64 Vested (1,559 ) $ 31.83 Forfeited (137 ) $ 36.37 Unvested at December 31, 2016 2,491 $ 34.30
Summary of performance units and performance units activity	A summary of the performance units issued to certain employees of the Company for the indicated years ended December 31 is as follows: (In thousands) 2016 2015 2014 Performance units granted 738 781 572 Potential maximum share payout 1,477 1,563 1,144 Aggregate grant date fair value $ 25,578 $ 28,082 $ 16,345 Compensation expense related to performance units $ 21,647 $ 12,942 $ 24,089 Estimated tax benefit (charge) related to performance units $ 3,152 $ 1,459 $ 4,250 Total unrecognized stock-based compensation expense related to non-vested performance units was approximately $29.8 million at December 31, 2016 , which is related to approximately 1.4 million performance units and is expected to be recognized over 1.8 years. Non-vested restricted performance units as of December 31, 2016 were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 1,881 $ 31.02 Granted 738 $ 34.64 Vested (746 ) $ 27.00 Forfeited (28 ) $ 34.12 Performance driven addition (reduction) (477 ) $ 34.60 Unvested at December 31, 2016 1,368 $ 32.83
Summary of nonvested restricted cash units	(In thousands) 2016 2015 2014 Restricted cash units granted 1,826 2,559 — Aggregate grant date fair value $ 63,261 $ 94,525 $ — Compensation expense related to restricted cash units $ 39,433 $ 19,834 $ — Estimated tax benefit related to restricted cash units $ 8,543 $ 4,374 $ — Total unrecognized stock-based compensation expense related to non-vested restricted cash units was approximately $74.1 million at December 31, 2016 , which is related to approximately 2.6 million restricted cash units and is expected to be recognized over 1.5 years. Non-vested restricted cash units as of December 31, 2016 were as follows: (In thousands except for weighted average grant date fair value) Number of Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2015 2,006 $ 36.95 Granted 1,826 $ 34.64 Vested (892 ) $ 36.93 Forfeited (367 ) $ 36.27 Unvested at December 31, 2016 2,573 $ 35.41

Computation of Earnings Per O53

Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Computation of basic and diluted earnings per share	The following table sets forth the computation of basic and diluted earnings per common share for the years ended December 31, 2016, 2015 and 2014 : (U.S. dollars in thousands, except per share amounts) 2016 2015 2014 Basic earnings per common share and common share equivalents outstanding: Net income (loss) attributable to common shareholders $ 440,968 $ 1,207,152 $ 188,340 Weighted average common shares outstanding 278,957 286,194 267,103 Basic earnings per common share and common share equivalents outstanding $ 1.58 $ 4.22 $ 0.71 Diluted earnings per common share and common share equivalents outstanding: Weighted average common shares outstanding – basic 278,957 286,194 267,103 Impact of share-based compensation 3,801 4,805 4,424 Weighted average common shares outstanding – diluted 282,758 290,999 271,527 Diluted earnings per common share & common share equivalents outstanding $ 1.56 $ 4.15 $ 0.69 Dividends per common share $ 0.80 $ 0.72 $ 0.64

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Dec. 31, 2016
Dividends Disclosure [Abstract]
Schedule of dividends paid	XL-Cayman paid its preference shareholders for the indicated years ended December 31, as follows: (U.S. dollars in millions) 2016 2015 2014 Series D preference ordinary shares (1) (2) $ 12.9 $ 11.8 $ 11.7 Series E preference ordinary shares (3) $ 65.0 $ 65.1 $ 65.1 Non-cumulative perpetual preferred shares (4) $ 43.5 $ 21.8 $ — ____________ (1) On October 28, 2016 , the Company announced that the Board of Directors of XL-Cayman resolved to pay a dividend of $10.2222 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017 . On December 29, 2016, the Board of Directors of XL-Cayman also resolved to pay an additional one-time dividend of $0.3525 per share on XL-Cayman's Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017 . (2) On February 17, 2017 , the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $10.473 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017 . (3) On February 17, 2017 , the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $32.50 per share on XL-Cayman’s Series E Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017 . (4) On January 12, 2017 , the Board of Directors of Catlin-Bermuda resolved to pay a dividend in the aggregate amount of $21.8 million on CICL Prefs. The dividend was paid on January 19, 2017 to all shareholders of record at December 31, 2016 .

Accumulated Other Comprehensi55

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2016
Comprehensive Income Loss Note [Abstract]
Components of acculumated other comprehensive income (loss)	The changes in AOCI, net of tax, by component for the indicated years ended December 31 are as follows: (U.S. dollars in thousands) Unrealized Gains (Losses) on Investments (1) OTTI Losses Recognized in AOCI Foreign Currency Translation Adjustments Underfunded Pension Liability Cash Flow Hedge Total Balance, net of tax, December 31, 2013 $ 822,432 $ (89,190 ) $ 14,541 $ (13,239 ) $ 2,113 $ 736,657 OCI before reclassifications 954,326 — (26,497 ) (10,877 ) — 916,952 Amounts reclassified from AOCI (143,330 ) 14,082 87 812 255 (128,094 ) Tax benefit (expense) (43,314 ) (939 ) 681 2,515 — (41,057 ) Net current period OCI - net of tax $ 767,682 $ 13,143 $ (25,729 ) $ (7,550 ) $ 255 $ 747,801 Balance, net of tax, December 31, 2014 $ 1,590,114 $ (76,047 ) $ (11,188 ) $ (20,789 ) $ 2,368 $ 1,484,458 OCI before reclassifications (474,304 ) — (33,690 ) (6,100 ) — (514,094 ) Amounts reclassified from AOCI (346,911 ) 18,987 — 1,145 (200 ) (326,979 ) Tax benefit (expense) 34,195 (442 ) 8,375 1,103 — 43,231 Net current period OCI - net of tax $ (787,020 ) $ 18,545 $ (25,315 ) $ (3,852 ) $ (200 ) $ (797,842 ) Balance, net of tax, December 31, 2015 $ 803,094 $ (57,502 ) $ (36,503 ) $ (24,641 ) $ 2,168 $ 686,616 OCI before reclassifications 254,333 — 102,772 (1,332 ) — 355,773 Amounts reclassified from AOCI (353,910 ) 6,599 — 3,100 (182 ) (344,393 ) Tax benefit (expense) 26,912 (49 ) (7,299 ) (2,014 ) — 17,550 Net current period OCI - net of tax $ (72,665 ) $ 6,550 $ 95,473 $ (246 ) $ (182 ) $ 28,930 Balance, net of tax, December 31, 2016 $ 730,429 $ (50,952 ) $ 58,970 $ (24,887 ) $ 1,986 $ 715,546 ____________ (1) Included in these amounts is the impact of Shadow Adjustments on future policy benefit reserves. As of December 31, 2015 , $274.4 million was recorded. During the year ended December 31, 2016 , additional net impacts of $(62.3) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $212.1 million at December 31, 2016 .
Reclassifications out of AOCI	The reclassifications out of AOCI along with the associated income statement line items affected by component, and the total related tax (expense) benefit for indicated years ended December 31, are as follows: Details About AOCI Components (U.S. dollars in thousands) 2016 2015 Affected Line Item in the Statement of Income Unrealized gains and losses on investments: Net realized gains (losses) on investments sold $ (350,875 ) $ (316,508 ) OTTI on investments 81,595 95,344 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets (51,100 ) (125,747 ) Income (loss) from investment fund affiliates (33,530 ) — Total before tax $ (353,910 ) $ (346,911 ) Provision (benefit) for income tax 10,084 7,597 Net of tax $ (343,826 ) $ (339,314 ) OTTI losses recognized in OCI: Net realized gains (losses) on investments sold $ 7,038 $ 18,014 OTTI on investments transferred to (from) OCI (439 ) 973 Total before tax $ 6,599 $ 18,987 Provision (benefit) for income tax (49 ) (32 ) Net of tax $ 6,550 $ 18,955 Underfunded Pension Liability: Operating Expenses $ 3,100 $ 1,145 Provision (benefit) for income tax (1,085 ) (401 ) Net of tax $ 2,015 $ 744 Gains and losses on cash flow hedges: Interest Expense $ (182 ) $ (200 ) Provision (benefit) for income tax — — Net of tax $ (182 ) $ (200 ) Total reclassifications for the period, gross of tax $ (344,393 ) $ (326,979 ) Tax (benefit) expense 8,950 7,164 Total reclassifications for the period, net of tax $ (335,443 ) $ (319,815 )

Taxation (Tables)

Taxation (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Summary of income tax examinations	The following table details the years that are the subject of open examinations, by major tax jurisdiction. While the Company cannot estimate with certainty the outcome of these examinations, the Company does not believe that adjustments from open tax years will result in a significant change to the Company's financial results. Jurisdiction Tax Years U.S. 2013-2015 Ireland 2008 - 2009 U.K. 2014 France 2013 - 2014 Spain 2011 - 2012 The following table details open tax years that are open to assessment by local tax authorities, in the following major tax jurisdictions. Jurisdiction Tax Years U.S. 2013 - 2016 Ireland 2008 - 2016 U.K. 2014 - 2016 Germany 2014 - 2016 Switzerland 2011 - 2016 France 2013 - 2016 Spain 2011 - 2016 Italy 2012 - 2016
Distribution of income (loss) before income tax, by jurisdiction	The Company’s income (loss) before income tax and non-controlling interests, for the years ended December 31, 2016, 2015 and 2014 , was distributed between U.S. and non-U.S. jurisdictions as follows: Income (loss) before income tax: (U.S. dollars in thousands) 2016 2015 2014 U.S. $ 68,970 $ (5,931 ) $ 228,708 Non U.S. 543,304 1,300,109 137,027 Total $ 612,274 $ 1,294,178 $ 365,735
Components of income tax expense	The income tax provisions for the years ended December 31, 2016, 2015 and 2014 are as follows: (U.S. dollars in thousands) 2016 2015 2014 Current expense (benefit): U.S. $ (12,201 ) $ (22,698 ) $ 45,598 Non U.S. 59,031 67,784 81,371 Total current expense (benefit) $ 46,830 $ 45,086 $ 126,969 Deferred expense (benefit): U.S. $ 8,502 $ (63,491 ) $ 8,572 Non U.S. (13,203 ) (756 ) (38,644 ) Total deferred expense (benefit) $ (4,701 ) $ (64,247 ) $ (30,072 ) Total tax expense (benefit) $ 42,129 $ (19,161 ) $ 96,897
Applicable statutory tax rates by jurisdiction	The applicable statutory tax rates for the current year of the most significant jurisdictions contributing to the overall taxation of the Company are: Jurisdiction Applicable Statutory Corporate Income Tax Rates Ireland (1) 12.50 % Bermuda — % U.S. 35.00 % U.K. 20.00 % Switzerland (2) 21.15 % Germany (3) 15.00 % France (4) 33.33 % ____________ (1) The 12.5% statutory corporate income tax rate applies to active income from the conduct of a trade in Ireland. For passive income or income from other defined activities the rate increases to 25% . (2) Represents the combined federal and cantonal rate primarily applicable to XL Catlin Swiss entities. (3) The statutory corporate income tax rate is 15% . However, including applicable surcharges and local trade tax, which can vary by location, would increase the combined statutory rate to approximately 33% . (4) The statutory corporate income tax rate is 33.33%. However, with the mandatory social surcharge, the combined statutory rate would increase to 34.43% .
Reconciliation of effective tax rate	A reconciliation of the difference between the provision for income taxes and the expected tax provision for the years ended December 31, 2016, 2015 and 2014 is provided below: (U.S. dollars in thousands) 2016 2015 2014 Expected tax (benefit) provision $ (31,080 ) $ (50,797 ) $ 132,775 Permanent differences: Non-taxable (income) loss (19,937 ) (23,036 ) (19,870 ) Revision to prior year estimates (24,121 ) 7,402 2,016 State, local and foreign taxes 23,157 27,499 47,078 Valuation allowance 1,197 9,517 (181 ) Net allocated investment income 5,990 (405 ) 3,399 Stock awards 543 (433 ) 411 Non-deductible expenses 48,206 42,839 22,556 Other investment related adjustments (905 ) 2,075 (2,916 ) Adjustments related to GreyCastle Life Retro Arrangements 21,682 (35,045 ) (99,535 ) Change in tax rates (6,233 ) (11,877 ) 3,974 Uncertain tax positions 23,630 13,100 7,190 Total tax expense (benefit) $ 42,129 $ (19,161 ) $ 96,897
Components of net deferred tax assets	Significant components of the Company’s deferred tax assets and liabilities at December 31, 2016 and 2015 were as follows: (U.S. dollars in thousands) 2016 2015 Deferred tax asset: Net unpaid loss reserve discount $ 96,357 $ 111,584 Net unearned premiums 95,676 80,434 Compensation liabilities 96,280 94,013 Net operating losses 323,716 181,295 Investment adjustments 14,030 14,399 Pension 6,817 10,370 Bad debt reserve 12,418 7,425 Amortizable goodwill 967 5,396 Net unrealized depreciation on investments 5,915 5,051 Stock options 7,249 16,192 Depreciation 26,525 13,299 Net realized capital losses 89,568 98,756 Deferred intercompany capital losses 18,221 26,164 Untaxed Lloyd's result — 3,769 Deferred acquisition costs 17,820 31,133 Currency translation adjustments — 6,280 Tax Credits 71,651 5,047 Other 34,708 19,930 Deferred tax asset, gross of valuation allowance $ 917,918 $ 730,537 Valuation allowance 367,366 276,301 Deferred tax asset, net of valuation allowance $ 550,552 $ 454,236 Deferred tax liability: Net unrealized appreciation on investments $ 21,500 $ 51,010 Unremitted earnings — 3,739 Deferred acquisition costs 10,858 8,308 Currency translation adjustments 12,813 1,210 Regulatory reserves 116,500 64,352 Net unearned premiums 4,380 — Investment adjustments 5,269 6,373 Untaxed Lloyd’s result 11,940 — Depreciation 15,601 11,500 Syndicate capacity 82,106 92,756 Intangible asset 32,508 40,126 Other 3,806 13,202 Deferred tax liability $ 317,281 $ 292,576 Net Deferred Tax Asset $ 233,271 $ 161,660
Summary of valuation allowance	At December 31, 2016 and 2015 , the valuation allowance of $367.4 million and $276.3 million , respectively, related primarily to net operating loss and realized capital loss carryforwards in the following major tax jurisdictions: Jurisdiction (U.S. dollars in thousands) 2016 2015 Ireland $ 96,642 $ 93,396 U.S. 92,999 106,624 U.K. 32,528 46,732 Switzerland 15,025 7,818 Other 130,172 21,731 Valuation Allowance Total $ 367,366 $ 276,301
Reconciliation of unrecognized tax benefits	The following table presents a reconciliation of the Company’s unrecognized tax benefits: (U.S. dollars in thousands) 2016 2015 2014 Unrecognized tax benefits, beginning of the year $ 80,590 $ 37,190 $ 30,000 Increases for tax positions taken during the year 25,250 20,370 12,182 Increases for tax positions taken in prior years 11,700 38,650 15,304 Decreases for tax positions taken in prior years (6,440 ) (4,850 ) (20,296 ) Decreases for lapse of the applicable statute of limitations (13,320 ) (10,770 ) — Unrecognized tax benefits, end of year $ 97,780 $ 80,590 $ 37,190

Statutory Financial Data (Table

Statutory Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Statutory Capital And Surplus Disclosure Text Block [Abstract]
Schedule of statutory capital	Statutory capital and surplus for the principal operating subsidiaries of the Company for the years ended December 31, 2016 and 2015 are summarized below: (U.S. dollars in thousands) Bermuda (1) U.S. (2) U.K., Europe and Other 2016 2015 2016 2015 2016 2015 Required statutory capital and surplus $ 6,351,874 $ 7,722,123 $ 822,651 $ 747,313 $ 4,320,140 $ 4,445,247 Actual statutory capital and surplus (3) $ 12,333,870 $ 11,112,176 $ 2,362,827 $ 2,234,767 $ 5,201,602 $ 6,054,122 ____________ (1) Required statutory capital and surplus at December 31, 2016 represents 100% Bermuda Solvency Capital Requirement ("BSCR") level for the top Bermuda operating subsidiary, XL Bermuda Ltd, calculated on a consolidated basis (and therefore includes a BSCR requirement for all regions). (2) Required statutory capital and surplus represents 100% Risk-Based Capital level for principal U.S. operating subsidiaries. (3) Statutory assets in Bermuda include investments in other U.S. and international subsidiaries reported separately herein.
Schedule of statutory net income loss	Statutory net income (loss) for the principal operating subsidiaries of the Company for the years ended December 31, 2016, 2015 and 2014 is summarized below: (U.S. dollars in thousands) 2016 2015 2014 Bermuda $ 724,711 $ 1,513,924 $ 361,022 U.S. $ 96,481 $ 17,574 $ 155,751 U.K., Europe and Other $ 366,708 $ (125,758 ) $ 215,787

Unaudited Quarterly Financial58

Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly financial data	The following is a summary of the unaudited quarterly financial data for 2016 and 2015 : (U.S. dollars in thousands, except per share amounts) First Quarter Second Quarter Third Quarter Fourth Quarter 2016 Net premiums earned – P&C operations $ 2,351,446 $ 2,528,704 $ 2,431,677 $ 2,454,060 Net premiums earned – Corporate and Other $ 3,164 $ 3,508 $ 2,360 $ 3,015 Underwriting profit (loss) – P&C operations $ 175,489 $ 101,893 $ 166,851 $ 126,420 Net income (loss) attributable to common shareholders $ 21,885 $ 43,782 $ 70,601 $ 304,700 Net income (loss) per common share and common equivalent – basic $ 0.07 $ 0.16 $ 0.26 $ 1.13 Net income (loss) per common share and common equivalent – diluted $ 0.07 $ 0.15 $ 0.25 $ 1.12 2015 Net premiums earned – P&C operations $ 1,319,494 $ 2,063,795 $ 2,405,740 $ 2,375,155 Net premiums earned – Corporate and Other $ 14,506 $ 18,258 $ 17,812 $ 11,665 Underwriting profit (loss) – P&C operations $ 146,836 $ 208,779 $ 114,118 $ 183,458 Net income (loss) attributable to common shareholders $ 36,281 $ 915,039 $ 27,282 $ 228,550 Net income (loss) per common share and common equivalent – basic $ 0.14 $ 3.16 $ 0.09 $ 0.77 Net income (loss) per common share and common equivalent – diluted $ 0.14 $ 3.11 $ 0.09 $ 0.76

Guarantor Financial Informati59

Guarantor Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed consolidating balance sheet	December 31, 2016 Condensed Consolidating Balance Sheet (U.S. dollars in thousands, except share data) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated ASSETS Investments: Total investments available for sale $ — $ 638,236 $ 31,280,890 $ — $ 31,919,126 Total investments trading — — 1,626,577 — 1,626,577 Investments in affiliates — — 2,177,645 — 2,177,645 Other investments — 9 1,164,555 — 1,164,564 Total investments $ — $ 638,245 $ 36,249,667 $ — $ 36,887,912 Cash and cash equivalents 1,022 84,286 3,341,680 — 3,426,988 Restricted cash — — 153,504 — 153,504 Investments in subsidiaries 10,897,195 14,238,698 — (25,135,893 ) — Accrued investment income 55 2,981 281,385 (55 ) 284,366 Deferred acquisition costs and value of business acquired — — 946,721 — 946,721 Ceded unearned premiums — — 1,687,864 — 1,687,864 Premiums receivable — — 5,522,976 — 5,522,976 Reinsurance balances receivable — — 577,479 — 577,479 Unpaid losses and loss expenses recoverable — — 5,491,297 — 5,491,297 Receivable from investments sold — — 128,411 — 128,411 Goodwill and other intangible assets — — 2,203,653 — 2,203,653 Deferred tax asset — — 310,542 — 310,542 Amounts due from subsidiaries/parent 42,780 — 72,962 (115,742 ) — Other assets 15,188 40,108 757,093 — 812,389 Total assets $ 10,956,240 $ 15,004,318 $ 57,725,234 $ (25,251,690 ) $ 58,434,102 LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities: Unpaid losses and loss expenses $ — $ — $ 25,939,571 $ — $ 25,939,571 Deposit liabilities — — 1,116,233 — 1,116,233 Future policy benefit reserves — — 3,506,047 — 3,506,047 Funds withheld on GreyCastle life retrocession arrangements — — 998,968 — 998,968 Unearned premiums — — 7,293,028 — 7,293,028 Notes payable and debt — 2,647,677 — — 2,647,677 Reinsurance balances payable — — 2,451,717 — 2,451,717 Payable for investments purchased — — 226,009 — 226,009 Deferred tax liability — — 77,271 — 77,271 Amounts due to subsidiaries/parent — 72,962 42,780 (115,742 ) — Other liabilities 17,728 41,984 1,157,190 — 1,216,902 Total liabilities $ 17,728 $ 2,762,623 $ 42,808,814 $ (115,742 ) $ 45,473,423 Shareholders’ Equity: Shareholders’ equity attributable to XL Group Ltd $ 10,938,512 $ 10,897,195 $ 14,238,698 $ (25,135,893 ) $ 10,938,512 Non-controlling interest in equity of consolidated subsidiaries — 1,344,500 677,722 (55 ) 2,022,167 Total shareholders’ equity $ 10,938,512 $ 12,241,695 $ 14,916,420 $ (25,135,948 ) $ 12,960,679 Total liabilities and shareholders’ equity $ 10,956,240 $ 15,004,318 $ 57,725,234 $ (25,251,690 ) $ 58,434,102 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. December 31, 2015 Condensed Consolidating Balance Sheet (U.S. dollars in thousands, except share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated ASSETS Investments: Total investments available for sale $ — $ 516,425 $ 33,237,473 $ — $ 33,753,898 Total investments trading — — 1,296,029 — 1,296,029 Investments in affiliates — — 1,708,899 — 1,708,899 Other investments — 877 1,432,180 — 1,433,057 Total investments $ — $ 517,302 $ 37,674,581 $ — $ 38,191,883 Cash and cash equivalents 11,557 369,997 2,874,682 — 3,256,236 Restricted cash — — 154,992 — 154,992 Investments in subsidiaries 11,648,673 15,836,651 — (27,485,324 ) — Accrued investment income — 2,323 310,344 — 312,667 Deferred acquisition costs and value of business acquired — — 890,568 — 890,568 Ceded unearned premiums — — 1,821,793 — 1,821,793 Premiums receivable — — 4,712,493 — 4,712,493 Reinsurance balances receivable — — 418,666 — 418,666 Unpaid losses and loss expenses recoverable — — 5,262,706 — 5,262,706 Receivable from investments sold — — 231,158 — 231,158 Goodwill and other intangible assets — — 2,210,266 — 2,210,266 Deferred tax asset — — 282,311 — 282,311 Amounts due from subsidiaries/parent 33,417 — 1,054,177 (1,087,594 ) — Other assets 2,748 44,570 889,881 — 937,199 Total assets $ 11,696,395 $ 16,770,843 $ 58,788,618 $ (28,572,918 ) $ 58,682,938 LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities: Unpaid losses and loss expenses $ — $ — $ 25,439,744 $ — $ 25,439,744 Deposit liabilities — — 1,168,376 — 1,168,376 Future policy benefit reserves — — 4,163,500 — 4,163,500 Funds withheld on GreyCastle life retrocession arrangements — — 914,629 — 914,629 Unearned premiums — — 7,043,358 — 7,043,358 Notes payable and debt — 2,644,970 — — 2,644,970 Reinsurance balances payable — — 2,117,727 — 2,117,727 Payable for investments purchased — — 130,060 — 130,060 Deferred tax liability — — 120,651 — 120,651 Amounts due to subsidiaries/parent — 1,087,594 — (1,087,594 ) — Other liabilities 19,316 45,106 1,221,038 — 1,285,460 Total liabilities $ 19,316 $ 3,777,670 $ 42,319,083 $ (1,087,594 ) $ 45,028,475 Shareholders’ Equity: Shareholders’ equity attributable to XL Group plc $ 11,677,079 $ 11,648,673 $ 15,836,651 $ (27,485,324 ) $ 11,677,079 Non-controlling interest in equity of consolidated subsidiaries — 1,344,500 632,884 — 1,977,384 Total shareholders’ equity $ 11,677,079 $ 12,993,173 $ 16,469,535 $ (27,485,324 ) $ 13,654,463 Total liabilities and shareholders’ equity $ 11,696,395 $ 16,770,843 $ 58,788,618 $ (28,572,918 ) $ 58,682,938
Condensed consolidating statement of income and comprehensive income	Year Ended December 31, 2016 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated Revenues: Net premiums earned $ — $ — $ 9,777,934 $ — $ 9,777,934 Total net investment income 436 9,135 817,998 (436 ) 827,133 Total net realized gains (losses) on investments — 1,918 370,220 — 372,138 Net realized and unrealized gains (losses) on derivative instruments — — 2,521 — 2,521 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (540,090 ) — (540,090 ) Income (loss) from investment fund affiliates — — 70,758 — 70,758 Fee income and other — — 35,692 — 35,692 Total revenues $ 436 $ 11,053 $ 10,535,033 $ (436 ) $ 10,546,086 Expenses: Net losses and loss expenses incurred $ — $ — $ 6,072,835 $ — $ 6,072,835 Claims and policy benefits — — 28,244 — 28,244 Acquisition costs — — 1,620,671 — 1,620,671 Operating expenses 93,247 4,985 1,965,130 — 2,063,362 Exchange (gains) losses (1,106 ) (343 ) (8,129 ) — (9,578 ) Loss (Gain) on sale of subsidiary — — (7,088 ) — (7,088 ) Interest expense (4 ) 140,644 69,123 — 209,763 Total expenses $ 92,137 $ 145,286 $ 9,740,786 $ — $ 9,978,209 Income (loss) before income tax and income (loss) from operating affiliates $ (91,701 ) $ (134,233 ) $ 794,247 $ (436 ) $ 567,877 Income (loss) from operating affiliates — — 44,397 — 44,397 Equity in net earnings (losses) of subsidiaries 532,049 744,877 — (1,276,926 ) — Provision (benefit) for income tax (620 ) — 42,749 — 42,129 Net income (loss) $ 440,968 $ 610,644 $ 795,895 $ (1,277,362 ) $ 570,145 Non-controlling interests — 78,595 51,018 (436 ) 129,177 Net income (loss) attributable to common shareholders $ 440,968 $ 532,049 $ 744,877 $ (1,276,926 ) $ 440,968 Comprehensive income (loss) $ 469,898 $ 560,979 $ 773,807 $ (1,334,786 ) $ 469,898 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. Year Ended December 31, 2015 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Revenues: Net premiums earned $ — $ — $ 8,226,425 $ — $ 8,226,425 Total net investment income 169 9,363 859,002 3,836 872,370 Total net realized gains (losses) on investments — 13,814 197,129 (8,765 ) 202,178 Net realized and unrealized gains (losses) on derivative instruments — 12,363 40,760 — 53,123 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (151,691 ) — (151,691 ) Income (loss) from investment fund affiliates — — 73,320 — 73,320 Fee income and other — — 33,201 — 33,201 Total revenues $ 169 $ 35,540 $ 9,278,146 $ (4,929 ) $ 9,308,926 Expenses: Net losses and loss expenses incurred $ — $ — $ 4,766,200 $ — $ 4,766,200 Claims and policy benefits — — 115,997 — 115,997 Acquisition costs — — 1,317,448 — 1,317,448 Operating expenses 46,340 10,565 1,910,034 — 1,966,939 Exchange (gains) losses (345 ) 20 22,829 — 22,504 Extinguishment of debt — — 5,592 — 5,592 Interest expense 11 143,330 61,874 — 205,215 Total expenses $ 46,006 $ 153,915 $ 8,199,974 $ — $ 8,399,895 Income (loss) before income tax and income (loss) from operating affiliates $ (45,837 ) $ (118,375 ) $ 1,078,172 $ (4,929 ) $ 909,031 Income (loss) from operating affiliates — — 44,740 — 44,740 Gain on sale of operating affiliate — — 340,407 — 340,407 Equity in net earnings (losses) of subsidiaries 1,253,609 1,449,404 — (2,703,013 ) — Provision (benefit) for income tax 620 245 (20,026 ) — (19,161 ) Net income (loss) $ 1,207,152 $ 1,330,784 $ 1,483,345 $ (2,707,942 ) $ 1,313,339 Non-controlling interests — 77,175 29,012 — 106,187 Net income (loss) attributable to common shareholders $ 1,207,152 $ 1,253,609 $ 1,454,333 $ (2,707,942 ) $ 1,207,152 Comprehensive income (loss) $ 409,310 $ 455,767 $ 656,491 $ (1,112,258 ) $ 409,310 Year Ended December 31, 2014 Condensed Consolidating Statement of Income and Comprehensive Income (U.S. dollars in thousands, except per share data) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Revenues: Net premiums earned $ — $ — $ 5,895,070 $ — $ 5,895,070 Total net investment income 275 20,256 889,611 8,483 918,625 Total net realized gains (losses) on investments — 27,541 102,150 (22,229 ) 107,462 Net realized and unrealized gains (losses) on derivative instruments — — 29,886 — 29,886 Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets — — (488,222 ) — (488,222 ) Income (loss) from investment fund affiliates — — 95,816 — 95,816 Fee income and other — — 43,630 — 43,630 Total revenues $ 275 $ 47,797 $ 6,567,941 $ (13,746 ) $ 6,602,267 Expenses: Net losses and loss expenses incurred $ — $ — $ 3,258,393 $ — $ 3,258,393 Claims and policy benefits — — 242,963 — 242,963 Acquisition costs — — 738,118 — 738,118 Operating expenses 9,646 13,102 1,318,567 — 1,341,315 Exchange (gains) losses 127 168 (37,863 ) — (37,568 ) Loss (Gain) on sale of subsidiary — — 666,423 — 666,423 Interest expense 5 110,323 23,778 — 134,106 Total expenses $ 9,778 $ 123,593 $ 6,210,379 $ — $ 6,343,750 Income (loss) before income tax and income (loss) from operating affiliates $ (9,503 ) $ (75,796 ) $ 357,562 $ (13,746 ) $ 258,517 Income (loss) from operating affiliates — — 107,218 — 107,218 Equity in net earnings (losses) of subsidiaries 197,843 350,602 — (548,445 ) — Provision (benefit) for income tax — (212 ) 97,109 — 96,897 Net income (loss) $ 188,340 $ 275,018 $ 367,671 $ (562,191 ) $ 268,838 Non-controlling interests — 77,175 3,323 — 80,498 Net income (loss) attributable to common shareholders $ 188,340 $ 197,843 $ 364,348 $ (562,191 ) $ 188,340 Comprehensive income (loss) $ 936,141 $ 945,644 $ 1,112,149 $ (2,057,793 ) $ 936,141
Condensed consolidating statement of cash flows	Year Ended December 31, 2016 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Bermuda (1) XL-Cayman Other XL-Bermuda Subsidiaries Consolidating Adjustments and Eliminations XL-Bermuda Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 978,695 $ 775,100 $ 2,116,580 $ (2,955,038 ) $ 915,337 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 303,070 $ 13,037,976 $ (583,466 ) $ 12,757,580 Proceeds from redemption of fixed maturities and short-term investments — 97,168 3,750,541 — 3,847,709 Proceeds from sale of equity securities — — 848,779 — 848,779 Purchases of fixed maturities and short-term investments — (534,502 ) (15,506,653 ) 583,466 (15,457,689 ) Purchases of equity securities — — (1,103,447 ) — (1,103,447 ) Proceeds from sale of affiliates — 324 396,767 — 397,091 Purchases of affiliates — — (681,385 ) — (681,385 ) Purchase of subsidiaries, net of acquired cash — — (92,893 ) — (92,893 ) Proceeds from sale of subsidiary, net of cash sold — — 22,998 — 22,998 Returns of capital from subsidiaries 274,727 465,203 — (739,930 ) — Change in restricted cash — — 1,488 — 1,488 Other, net — — 197,536 — 197,536 Net cash provided by (used in) investing activities $ 274,727 $ 331,263 $ 871,707 $ (739,930 ) $ 737,767 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 9,854 $ — $ — $ — $ 9,854 Buybacks of common shares (1,051,050 ) — — — (1,051,050 ) Dividends paid on common shares (222,761 ) (1,039,253 ) (1,915,785 ) 2,955,038 (222,761 ) Return of capital — (274,727 ) (465,203 ) 739,930 — Distributions to non-controlling interests — (78,094 ) (52,353 ) — (130,447 ) Contributions from non-controlling interests — — 47,524 — 47,524 Repayment of debt — — (8,248 ) — (8,248 ) Deposit liabilities — — (69,482 ) — (69,482 ) Net cash provided by (used in) financing activities $ (1,263,957 ) $ (1,392,074 ) $ (2,463,547 ) $ 3,694,968 $ (1,424,610 ) Effects of exchange rate changes on foreign currency cash — — (57,742 ) — (57,742 ) Increase (decrease) in cash and cash equivalents $ (10,535 ) $ (285,711 ) $ 466,998 $ — $ 170,752 Cash and cash equivalents – beginning of period 11,557 369,997 2,874,682 — 3,256,236 Cash and cash equivalents – end of period $ 1,022 $ 84,286 $ 3,341,680 $ — $ 3,426,988 ____________ (1) Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies ." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation. Year Ended December 31, 2015 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 561,468 $ 148,850 $ 669,515 $ (764,277 ) $ 615,556 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 1,482,875 $ 15,745,247 $ (359,894 ) $ 16,868,228 Proceeds from redemption of fixed maturities and short-term investments — 188,788 3,562,386 — 3,751,174 Proceeds from sale of equity securities — — 664,735 — 664,735 Purchases of fixed maturities and short-term investments — (1,296,980 ) (18,780,978 ) 359,894 (19,718,064 ) Purchases of equity securities — — (567,334 ) — (567,334 ) Proceeds from sale of affiliates — — 748,575 — 748,575 Purchases of affiliates — — (280,856 ) — (280,856 ) Purchase of subsidiaries, net of acquired cash (2,287,579 ) (2,317,699 ) 1,267,564 2,317,699 (1,020,015 ) Proceeds from sale of subsidiary, net of cash sold 2,317,699 — — (2,317,699 ) — Returns of capital from subsidiaries 65,037 2,047,000 — (2,112,037 ) — Change in restricted cash — — (154,992 ) — (154,992 ) Other, net — — (155,019 ) — (155,019 ) Net cash provided by (used in) investing activities $ 95,157 $ 103,984 $ 2,049,328 $ (2,112,037 ) $ 136,432 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 9,976 $ — $ — $ — $ 9,976 Buybacks of common shares (468,971 ) — — — (468,971 ) Dividends paid on common shares (208,516 ) (764,277 ) — 764,277 (208,516 ) Return of capital — (65,037 ) (2,047,000 ) 2,112,037 — Distributions to non-controlling interests — (77,093 ) (40,590 ) — (117,683 ) Contributions from non-controlling interests — — 23,610 — 23,610 Proceeds from issuance of debt — 980,600 — — 980,600 Repayment of debt — — (87,447 ) — (87,447 ) Net proceeds from affiliated notional cash pooling programs (1) — — — — — Deposit liabilities — — (84,758 ) — (84,758 ) Net cash provided by (used in) financing activities $ (667,511 ) $ 74,193 $ (2,236,185 ) $ 2,876,314 $ 46,811 Effects of exchange rate changes on foreign currency cash — — (64,377 ) — (64,377 ) Increase (decrease) in cash and cash equivalents $ (10,886 ) $ 327,027 $ 418,281 $ — $ 734,422 Cash and cash equivalents – beginning of period 22,443 42,970 2,456,401 — 2,521,814 Cash and cash equivalents – end of period $ 11,557 $ 369,997 $ 2,874,682 $ — $ 3,256,236 Year Ended December 31, 2014 Condensed Consolidating Statement of Cash Flows (U.S. dollars in thousands) XL- Ireland XL-Cayman Other XL-Ireland Subsidiaries Consolidating Adjustments and Eliminations XL-Ireland Consolidated Cash flows provided by (used in) operating activities: Net cash provided by (used in) operating activities $ 895,854 $ 518,715 $ 407,136 $ (858,521 ) $ 963,184 Cash flows provided by (used in) investing activities: Proceeds from sale of fixed maturities and short-term investments $ — $ 574,673 $ 4,793,978 $ (472,539 ) $ 4,896,112 Proceeds from redemption of fixed maturities and short-term investments — 351,737 3,250,056 — 3,601,793 Proceeds from sale of equity securities — — 571,410 — 571,410 Purchases of fixed maturities and short-term investments — (307,830 ) (7,322,967 ) 472,539 (7,158,258 ) Purchases of equity securities — — (445,504 ) — (445,504 ) Proceeds from sale of affiliates — — 240,785 — 240,785 Purchases of affiliates — — (371,226 ) — (371,226 ) Proceeds from sale of subsidiary, net of cash sold — — 570,000 — 570,000 Returns of capital from subsidiaries 79,086 482,570 — (561,656 ) — Other, net — 1,920 (195,411 ) — (193,491 ) Net cash provided by (used in) investing activities $ 79,086 $ 1,103,070 $ 1,091,121 $ (561,656 ) $ 1,711,621 Cash flows provided by (used in) financing activities: Proceeds from issuance of common shares and exercise of stock options $ 6,367 $ — $ — $ — $ 6,367 Buybacks of common shares (801,953 ) — — — (801,953 ) Dividends paid on common shares (169,620 ) (858,521 ) — 858,521 (169,620 ) Return of capital — (79,086 ) (482,570 ) 561,656 — Distributions to non-controlling interests — (77,002 ) (1,463 ) — (78,465 ) Contributions from non-controlling interests — — 48,261 — 48,261 Repayment of debt — (600,000 ) — — (600,000 ) Net proceeds from affiliated notional cash pooling programs (1) — — — — — Deposit liabilities — — (268,298 ) — (268,298 ) Net cash provided by (used in) financing activities $ (965,206 ) $ (1,614,609 ) $ (704,070 ) $ 1,420,177 $ (1,863,708 ) Effects of exchange rate changes on foreign currency cash — — (90,115 ) — (90,115 ) Increase (decrease) in cash and cash equivalents $ 9,734 $ 7,176 $ 704,072 $ — $ 720,982 Cash and cash equivalents – beginning of period 12,709 35,794 1,752,329 — 1,800,832 Cash and cash equivalents – end of period $ 22,443 $ 42,970 $ 2,456,401 $ — $ 2,521,814

Significant Accounting Polici60

Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)segmentscountry$ / shares	Dec. 31, 2015USD ($)$ / shares	Dec. 31, 2014USD ($)
Significant Accounting Policies [Line Items]
Number of Reporting Units | segments	2
Number of Countries in which Entity Operates | country	29
Premiums Earned and Associated Tax Accruals Adjustment Amount | $			$ 20,000
Options, life of award	10 years
Number of Operating Segments | segments	2
Common shares, par value (in dollars per share)	$ 0.01	$ 0.01
Hedge funds
Significant Accounting Policies [Line Items]
Alternative investments, timelag for reporting	1 month
Private investment funds
Significant Accounting Policies [Line Items]
Alternative investments, timelag for reporting	3 months
Operating affiliates
Significant Accounting Policies [Line Items]
Alternative investments, timelag for reporting	3 months
Maximum
Significant Accounting Policies [Line Items]
Vesting period required	4 years
Minimum
Significant Accounting Policies [Line Items]
Vesting period required	3 years
XL Group Ltd
Significant Accounting Policies [Line Items]
Common shares, par value (in dollars per share)	$ 0.01
XL Ireland [Member]
Significant Accounting Policies [Line Items]
Common shares, par value (in dollars per share)	$ 0.01
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Investments
Significant Accounting Policies [Line Items]
Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Investments Transferred From Available for sale To Equity Method | $	$ 33,530	$ 0

Acquisitions and Disposals - Br

Acquisitions and Disposals - Brooklyn Acquisition narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired		$ 28,948	$ 315,000	$ 18,500
Brooklyn Underwriting Pty Limited and Brooklyn IT Pty Limited [Member]
Business Acquisition [Line Items]
Finite-lived Intangible Assets Acquired	$ 22,900

Acquisitions and Disposals - Sa

Acquisitions and Disposals - Sale of Subsidiaries (Details) - USD ($) $ in Millions	Oct. 11, 2016	Sep. 30, 2016
New Ocean Capital Management Ltd
Business Acquisition [Line Items]
Disposal Group, Including Discontinued Operation, Consideration	$ 3.9
Sale of Subsidiary Stock, Percentage	7.80%
Sale of Subsidiary Preferred Stock, Percentage	6.40%
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	$ 3.5
XL Life Insurance and Annuity Company
Business Acquisition [Line Items]
Disposal Group, Including Discontinued Operation, Consideration		$ 20.9
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal		$ 3.7

Acquisitions and Disposals - Al

Acquisitions and Disposals - Allied Acquisition (Details) - USD ($) $ in Thousands	Feb. 01, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 8,000	$ 673,000	$ 0
Finite-lived Intangible Assets Acquired		28,948	315,000	18,500
Goodwill, acquired during period		$ 14,084	$ 807,381	$ 25,159
Allied International Holdings, Inc.
Business Acquisition [Line Items]
Cash consideration	$ 75,700
Contingent Consideration Measurement Period	3 years
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low	$ 7,500
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	30,000
Business Combination, Contingent Consideration, Liability	15,000
Acquisition consideration	90,700
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	76,700
Indefinite-lived Intangible Assets Acquired	8,000
Finite-lived Intangible Assets Acquired	6,000
Goodwill, acquired during period	14,100
Insurance Segment | Allied International Holdings, Inc.
Business Acquisition [Line Items]
Goodwill, acquired during period	$ 14,100

Acquisitions and Disposals - Ne

Acquisitions and Disposals - New Energy Risk narrative (Details) - USD ($) $ in Thousands	Jul. 24, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill, acquired during period		$ 14,084	$ 807,381	$ 25,159
New Energy Risk Inc. [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired	63.63%
Business combination, step acquisition, equity interest in acquiree, percentage	31.16%
Business combination, step acquisition, equity interest in acquiree, including subsequent acquisition, percentage	94.79%
Noncontrolling interest, ownership percentage by noncontrolling owners	5.21%
Cash consideration	$ 8,800
Business combination, step acquisition, equity interest in acquiree, remeasurement gain	2,500
Goodwill, acquired during period	$ 13,400

Acquisitions and Disposals - Ca

Acquisitions and Disposals - Catlin Acquisition narrative (Details) £ / shares in Units, $ / shares in Units, £ in Thousands, $ in Thousands		Sep. 28, 2015USD ($)	May 01, 2015USD ($)shares$ / shares	May 01, 2015GBP (£)shares£ / shares	Dec. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)$ / shares	Dec. 31, 2014USD ($)	Mar. 30, 2015USD ($)	Jan. 08, 2015GBP (£)
Business Acquisition [Line Items]
Ordinary shares, par value (in dollars per share) | $ / shares					$ 0.01	$ 0.01
Debt instrument, face amount					$ 2,675,000	$ 2,675,000
Goodwill, acquired during period					14,084	807,381	$ 25,159
Indefinite-lived Intangible Assets Acquired					8,000	673,000	0
Finite-lived Intangible Assets Acquired					28,948	315,000	$ 18,500
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount					$ (91,100)
Catlin Group Limited [Member]
Business Acquisition [Line Items]
Ordinary shares, par value (in dollars per share) | $ / shares			$ 0.01
Cash price component, per Catlin Share in GBP | £ / shares				£ 3.88
Exchange ratio per the Implementation Agreement | shares			0.13	0.13
XL Share issuance to Catlin shareholders | shares			49,935,000	49,935,000
Cash consideration			$ 2,287,579	£ 1,490,377
Debt instrument, face amount								$ 1,000,000
Goodwill, acquired during period	[1]		793,990
Goodwill, Purchase Accounting Adjustments						15,900
Indefinite-lived Intangible Assets Acquired			673,000
Finite-lived Intangible Assets Acquired			315,000
Value of Business Acquired Adjustment, Amortization Period					2 years
Intangibles Assets Arising from Insurance Contracts Acquired in Business Combination, Amortization Expense					$ 186,700	471,000
Unpaid Losses And Loss Expenses Adjustment Amortization Period					20 years
Business Combination Initial Accounting Incomplete Other Assets						(7,500)
Business Combination Initial Accounting Incomplete Deferred Tax Liabilities						(11,300)
Business Combination Initial Accounting Incomplete Other Liabilities						19,800
Deferred tax liability	[1]		82,783
Business Combination, Acquisition Related Costs						64,700
Catlin Inc [Member]
Business Acquisition [Line Items]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ (59,600)
XL Cayman | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Available letter of credit facilities - commitments | £									£ 1,600,000
XL Ireland [Member]
Business Acquisition [Line Items]
Ordinary shares, par value (in dollars per share) | $ / shares					$ 0.01
XL Ireland [Member] | Catlin Inc [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired		100.00%
Proceeds From Debt [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Cash consideration			980,600
Cash and Cash Equivalents [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Cash consideration			1,310,000
Net Deferred Tax Liability Excluding Valuation Allowance [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Deferred tax liability			145,200
Deferred Tax Asset Net of Valuation Allowance [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets			62,400
Valuation Allowance of Deferred Tax Assets [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Deferred tax liability			90,000
Loss Carryforwards [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets			85,800
Valuation Allowance, Operating Loss Carryforwards [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Deferred tax liability			66,800
Operating expense | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs						50,200
Interest expense | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs						$ 14,500
Insurance Segment | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Goodwill, acquired during period	[1]		466,100
Reinsurance Segment | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Goodwill, acquired during period	[1]		$ 327,900
[1]	ncludes an increase of $15.9 million to goodwill from the amount initially recorded at June 30, 2015, as a result of several tax-related adjustments, including a decrease in other assets of $7.5 million, a decrease in deferred tax liability of $11.3 million, and an increase in other liabilities of $19.8 million.

Acquisitions and Disposals - 66

Acquisitions and Disposals - Catlin Acquisition consideration (Details) £ / shares in Units, $ / shares in Units, £ in Thousands, $ in Thousands	May 01, 2015USD ($)shares$ / shares		May 01, 2015GBP (£)shares£ / shares
Business Acquisition [Line Items]
Closing price per XL share on April 30, 2015 | $ / shares	$ 37.08	[1]
Catlin Group Limited [Member]
Business Acquisition [Line Items]
Catlin Shares outstanding as of April 30, 2015 that received share consideration (including the dilutive effect of warrants)	384,118,000
Exchange ratio per the Implementation Agreement	0.13		0.13
XL Share issuance to Catlin shareholders	49,935,000		49,935,000
XL Share issuance consideration | $	$ 1,851,601
Cash price component, per Catlin Share in GBP | £ / shares			£ 3.88
Cash consideration	$ 2,287,579		£ 1,490,377
Foreign exchange rate: GBP/USD on April 30, 2015	1.5349
Acquisition consideration | $	$ 4,139,180
[1]	The closing market price of XL Shares on the Acquisition Date represents the fair value of XL shares issued as part of the Acquisition Consideration.

Acquisitions and Disposals - Fa

Acquisitions and Disposals - Fair Value of Assets and Liabilities Acquired - Catlin (Details) - USD ($) $ in Thousands		May 01, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill, acquired during period			$ 14,084	$ 807,381	$ 25,159
Catlin Group Limited [Member]
Business Acquisition [Line Items]
Fixed maturities, at fair value		$ 6,266,489
Short-term investments, at fair value		634,599
Equity investments, at fair value		236,230
Investment in affiliates		216,843
Other investments		386,828
Total investments		7,740,989
Cash and cash equivalents		1,267,565
Unpaid losses and loss expenses recoverable		1,493,267
Reinsurance balances receivable		299,579
Ceded unearned premiums		1,143,852
Deferred acquisition costs and value of business acquired		679,259
Intangible assets		988,000
Other assets		306,686
Total assets		16,509,081
Unpaid losses and loss expenses		6,933,144
Unearned premiums		3,742,234
Reinsurance balances payable		1,441,749
Notes payable and debt		82,066
Payable for investments purchased		34,149
Deferred tax liability	[1]	82,783
Other liabilities		285,481
Total liabilities		12,601,606
Net assets acquired before non-controlling interest		3,907,475
Non-controlling interest in equity of consolidated subsidiaries		562,285
Net assets acquired		3,345,190
Acquisition consideration		4,139,180
Goodwill, acquired during period	[1]	793,990
Accrued Income Receivable [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Acquired receivables		35,063
Premiums Receivable [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Acquired receivables		2,545,188
Receivable From Investments Sold [Member] | Catlin Group Limited [Member]
Business Acquisition [Line Items]
Acquired receivables		$ 9,633
[1]	ncludes an increase of $15.9 million to goodwill from the amount initially recorded at June 30, 2015, as a result of several tax-related adjustments, including a decrease in other assets of $7.5 million, a decrease in deferred tax liability of $11.3 million, and an increase in other liabilities of $19.8 million.

Acquisitions and Disposals - Tr

Acquisitions and Disposals - Transaction Related Costs - Catlin (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Liabilities at December 31, 2015	$ 57,289
Costs incurred in 2016	220,355
2016 payments	240,678
Liabilities at December 31, 2016	36,966
Severance related costs
Business Acquisition [Line Items]
Liabilities at December 31, 2015	16,127
Costs incurred in 2016	57,098
2016 payments	47,865
Liabilities at December 31, 2016	25,360
Retention and other compensation costs
Business Acquisition [Line Items]
Liabilities at December 31, 2015	16,969
Costs incurred in 2016	33,220
2016 payments	45,708
Liabilities at December 31, 2016	4,481
Facilities-related costs
Business Acquisition [Line Items]
Liabilities at December 31, 2015	818
Costs incurred in 2016	30,236
2016 payments	31,036
Liabilities at December 31, 2016	18
Consulting and other
Business Acquisition [Line Items]
Liabilities at December 31, 2015	23,375
Costs incurred in 2016	99,801
2016 payments	116,069
Liabilities at December 31, 2016	$ 7,107

Acquisitions and Disposals - Fi

Acquisitions and Disposals - Financial Results and Supplemental Pro Forma Financial Information - Catlin (Details) - Catlin Group Limited [Member] - USD ($) $ / shares in Units, $ in Thousands	8 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	$ 2,791,789
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	$ 103,637
Business Acquisition, Pro Forma Revenue		$ 10,628,915	$ 10,938,216
Business Acquisition, Pro Forma Net Income (Loss)		$ 1,221,497	$ 475,914
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ 4.03	$ 1.50
Business Acquisition, Pro Forma Earnings Per Share, Diluted		$ 3.97	$ 1.48

Acquisitions and Disposals - 70

Acquisitions and Disposals - Sale of operating other affiliate (Details) - USD ($) $ in Millions	Apr. 02, 2015	May 30, 2014	Dec. 31, 2014	Apr. 01, 2015
ARX Holding Corporation [Member]
Business Acquisition [Line Items]
Ownership percentage remaining				40.60%
Investments in affiliates				$ 220.2
Disposal Group, Including Discontinued Operation, Consideration				$ 560.6
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal	$ 340.4
XL Re Life (SAC) Ltd [Member]
Business Acquisition [Line Items]
Disposal Group, Including Discontinued Operation, Consideration		$ 570
Sale of Subsidiary Stock, Percentage		100.00%
Quota Share Reinsurance Percentage		100.00%
Pro Forma Effect of Sale, After Tax Net Loss			$ 621.3

Segment Information - Statement

Segment Information - Statement of earnings by segment (Details) - USD ($) $ in Thousands		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]
Gross premiums written										$ 13,890,924		$ 10,978,925		$ 8,094,926
Net premiums written										10,242,683		7,951,063		5,944,841
Net premiums earned										9,777,934		8,226,425		5,895,070
Net losses and loss expenses										6,101,079	[1]	4,882,197	[1]	3,501,356
Acquisition costs										1,620,671		1,317,448		738,118
Operating expenses	[2]									1,508,859		1,439,371		1,069,689
Underwriting profit (loss)										547,325		587,409		585,907
Net investment income	[3]													721,016
Net results from structured products										14,280	[4]	17,991	[5]	54,209	[6]
Net fee income and other	[7]									(13,315)		(13,356)		(6,891)
Loss (gain) sale of subsidiaries										(7,088)		0		666,423
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments														122,991
Net realized and unrealized (gains) losses on derivative instruments										2,521		53,123		29,886
Net income (loss) from investment fund affiliates and operating affiliates										115,155		118,060		203,034
Gain on sale of operating affiliate										0		340,407		0
Extinguishment of debt										0		5,592		0
Exchange (gains) losses										(9,578)		22,504		(37,568)
Corporate operating expenses										505,483		480,755		220,165
Contribution from P&C and Corporate and Other										782,332		1,457,199		486,956
Interest expense										170,058		163,021	[8]	121,221	[8]
Non-controlling interests										129,177		106,187		80,498
Provision (benefit) for income tax										42,129		(19,161)		96,897
Net income (loss) attributable to common shareholders										440,968		1,207,152		188,340
Exclude Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[3]									618,384		624,440
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										112,689		19,997
Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income										154,751		187,489		129,575
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										259,449		182,181		(15,529)
Net realized and unrealized (gains) losses on derivative instruments										(540,090)		(151,691)		(488,222)
Corporate and other
Segment Reporting Information [Line Items]
Gross premiums written	[9]									265,315		309,916		333,436
Net premiums written	[9]									12,047		62,239		177,632
Net premiums earned	[9]									12,047		62,241		177,632
Net losses and loss expenses	[9]									28,244	[1]	115,997	[1]	242,963
Acquisition costs	[9]									5,775	[1]	10,794	[1]	14,115
Operating expenses	[2],[9]									1,356		1,232		10,693
Underwriting profit (loss)	[9]									(23,328)		(65,782)		(90,139)
Net investment income	[3],[9]													146,558
Net results from structured products	[9]									0	[4]	0	[5]	0	[6]
Net fee income and other	[7],[9]									1,911		622		360
Loss (gain) sale of subsidiaries										(7,088)	[9]			666,423
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments	[9]													3,625
Net realized and unrealized (gains) losses on derivative instruments	[9]									2,521		53,123		29,886
Net income (loss) from investment fund affiliates and operating affiliates	[9]									115,155		118,060		203,034
Gain on sale of operating affiliate												340,407
Extinguishment of debt												5,592
Exchange (gains) losses	[9]									(9,578)		22,504		(37,568)
Corporate operating expenses	[9]									505,483		480,755		220,165
Contribution from P&C and Corporate and Other	[9]									(501,563)		201,538		(929,872)
Interest expense	[8],[9]									170,058		163,021		121,221
Non-controlling interests	[9]									129,177		106,187		80,498
Provision (benefit) for income tax	[9]									42,129		(19,161)		96,897
Corporate and other | Exclude Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[3],[9]									31,726		40,569
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments	[9]									(14,844)		5,411
Corporate and other | Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income										154,751	[9]	187,489		129,575
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										259,452	[9]	182,181	[9]	(15,529)
Net realized and unrealized (gains) losses on derivative instruments										(540,090)	[9]	(151,691)	[9]	(488,222)
Operating Segments [Member] | Property and casualty operations
Segment Reporting Information [Line Items]
Gross premiums written										13,625,609		10,669,009		7,761,490
Net premiums written										10,230,636		7,888,824		5,767,209
Net premiums earned		$ 2,454,060	$ 2,431,677	$ 2,528,704	$ 2,351,446	$ 2,375,155	$ 2,405,740	$ 2,063,795	$ 1,319,494	9,765,887		8,164,184		5,717,438
Net losses and loss expenses										6,072,835	[1]	4,766,200	[1]	3,258,393
Acquisition costs										1,614,896	[1]	1,306,654	[1]	724,003
Operating expenses	[2]									1,507,503		1,438,139		1,058,996
Underwriting profit (loss)		126,420	166,851	101,893	175,489	183,458	114,118	208,779	146,836	570,653		653,191		676,046
Net investment income	[3]													574,458
Net results from structured products										14,280	[4]	17,991	[5]	54,209	[6]
Net fee income and other	[7]									(15,226)		(13,978)		(7,251)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments														119,366
Net realized and unrealized (gains) losses on derivative instruments										0				0
Contribution from P&C and Corporate and Other										$ 1,283,895		$ 1,255,661		$ 1,416,828
Ratios - P&C operations:
Loss and loss expense ratio	[10]									62.20%		58.40%		57.00%
Underwriting expense ratio	[10]									32.00%		33.60%		31.20%
Combined ratio	[10]									94.20%		92.00%		88.20%
Operating Segments [Member] | Property and casualty operations | Exclude Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Net investment income	[3]									$ 586,658		$ 583,871
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										127,533		14,586
Operating Segments [Member] | Property and casualty operations | Life Funds Withheld Assets
Segment Reporting Information [Line Items]
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments										(3)
Operating Segments [Member] | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written										9,650,503		8,395,846		$ 5,976,011
Net premiums written										6,715,969		5,859,934		4,134,151
Net premiums earned										6,651,495		5,648,482		4,026,713
Net losses and loss expenses										4,320,737	[1]	3,614,048	[1]	2,543,108
Acquisition costs										897,308	[1]	704,364	[1]	393,319
Operating expenses	[2]									1,224,233		1,154,760		865,592
Underwriting profit (loss)										209,217		175,310		224,694
Net results from structured products										8,495	[4]	12,185	[5]	43,710	[6]
Net fee income and other	[7]									$ (18,506)		$ (16,936)		$ (10,051)
Ratios - P&C operations:
Loss and loss expense ratio	[10]									65.00%		64.00%		63.20%
Underwriting expense ratio	[10]									31.90%		32.90%		31.20%
Combined ratio	[10]									96.90%		96.90%		94.40%
Operating Segments [Member] | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written										$ 3,975,106		$ 2,273,163		$ 1,785,479
Net premiums written										3,514,667		2,028,890		1,633,058
Net premiums earned										3,114,392		2,515,702		1,690,725
Net losses and loss expenses										1,752,098	[1]	1,152,152	[1]	715,285
Acquisition costs										717,588	[1]	602,290	[1]	330,684
Operating expenses	[2]									283,270		283,379		193,404
Underwriting profit (loss)										361,436		477,881		451,352
Net results from structured products										5,785	[4]	5,806	[5]	10,499	[6]
Net fee income and other	[7]									$ 3,280		$ 2,958		$ 2,800
Ratios - P&C operations:
Loss and loss expense ratio	[10]									56.30%		45.80%		42.30%
Underwriting expense ratio	[10]									32.10%		35.20%		31.00%
Combined ratio	[10]									88.40%		81.00%		73.30%
Operating Segments [Member] | Corporate and other
Segment Reporting Information [Line Items]
Net premiums earned		$ 3,015	$ 2,360	$ 3,508	$ 3,164	$ 11,665	$ 17,812	$ 18,258	$ 14,506
[1]	The Company has reflected the amortization of certain fair value adjustments recorded in conjunction with the Catlin Acquisition within the respective segments.
[2]	Operating expenses of the segments exclude Corporate operating expenses, shown separately.
[3]	Net investment income - excluding Life Funds Withheld Assets does not include net investment income related to the net results from structured products.
[4]	The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million, respectively.
[5]	The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.
[6]	The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.
[7]	Net fee income and other includes operating expenses from the Company's loss prevention consulting services business.
[8]	Interest expense excludes interest expense related to deposit liabilities recorded in the Insurance and Reinsurance segments.
[9]	Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations.
[10]	Ratios are based on net premiums earned from P&C operations.

Segment Information - Net premi

Segment Information - Net premiums earned by line of business (Details) - USD ($) $ in Thousands		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
P&C Operations:
P&C Operations										$ 9,765,887	$ 8,164,184	$ 5,717,438
Corporate and Other:
Life Operations										12,047	62,241	177,632
Net amount, premiums earned										9,777,934	8,226,425	5,895,070
Annuity
Corporate and Other:
Life Operations										1	1	53,363
Life operations
Corporate and Other:
Life Operations										12,046	62,240	124,269
Property and casualty operations | Professional
P&C Operations:
P&C Operations										1,494,066	1,332,813	1,256,643
Property and casualty operations | Casualty
P&C Operations:
P&C Operations										2,631,262	2,273,849	1,969,320
Property and casualty operations | Property catastrophe
P&C Operations:
P&C Operations										792,445	663,958	433,602
Property and casualty operations | Property Other Than Property Catastrophe [Member]
P&C Operations:
P&C Operations										2,646,759	2,126,669	1,100,439
Property and casualty operations | Specialty
P&C Operations:
P&C Operations										1,885,821	1,548,921	833,026
Property and casualty operations | Other
P&C Operations:
P&C Operations	[1]									315,534	217,974	124,408
Corporate and other
Corporate and Other:
Life Operations										12,047	62,241	177,632
Net amount, premiums earned	[2]									12,047	62,241	177,632
Corporate and other | Annuity
Corporate and Other:
Life Operations										1	1	53,363
Corporate and other | Life operations
Corporate and Other:
Life Operations										12,046	62,240	124,269
Operating Segments [Member] | Property and casualty operations
Corporate and Other:
Net amount, premiums earned		$ 2,454,060	$ 2,431,677	$ 2,528,704	$ 2,351,446	$ 2,375,155	$ 2,405,740	$ 2,063,795	$ 1,319,494	9,765,887	8,164,184	5,717,438
Operating Segments [Member] | Corporate and other
Corporate and Other:
Net amount, premiums earned		$ 3,015	$ 2,360	$ 3,508	$ 3,164	$ 11,665	$ 17,812	$ 18,258	$ 14,506
Operating Segments [Member] | Insurance Segment
P&C Operations:
P&C Operations										6,651,495	5,648,482	4,026,713
Corporate and Other:
Net amount, premiums earned										6,651,495	5,648,482	4,026,713
Operating Segments [Member] | Insurance Segment | Professional
P&C Operations:
P&C Operations	[3]									1,330,909	1,164,446	1,075,420
Operating Segments [Member] | Insurance Segment | Casualty
P&C Operations:
P&C Operations	[3]									1,973,672	1,805,563	1,669,097
Operating Segments [Member] | Insurance Segment | Property catastrophe
P&C Operations:
P&C Operations	[3]									0	0	0
Operating Segments [Member] | Insurance Segment | Property Other Than Property Catastrophe [Member]
P&C Operations:
P&C Operations	[3]									1,625,133	1,257,383	544,856
Operating Segments [Member] | Insurance Segment | Specialty
P&C Operations:
P&C Operations	[3]									1,711,344	1,421,124	737,281
Operating Segments [Member] | Insurance Segment | Other
P&C Operations:
P&C Operations	[1],[3]									10,437	(34)	59
Operating Segments [Member] | Reinsurance Segment
P&C Operations:
P&C Operations										3,114,392	2,515,702	1,690,725
Corporate and Other:
Net amount, premiums earned										3,114,392	2,515,702	1,690,725
Operating Segments [Member] | Reinsurance Segment | Professional
P&C Operations:
P&C Operations										163,157	168,367	181,223
Operating Segments [Member] | Reinsurance Segment | Casualty
P&C Operations:
P&C Operations										657,590	468,286	300,223
Operating Segments [Member] | Reinsurance Segment | Property catastrophe
P&C Operations:
P&C Operations										792,445	663,958	433,602
Operating Segments [Member] | Reinsurance Segment | Property Other Than Property Catastrophe [Member]
P&C Operations:
P&C Operations										1,021,626	869,286	555,583
Operating Segments [Member] | Reinsurance Segment | Specialty
P&C Operations:
P&C Operations										174,477	127,797	95,745
Operating Segments [Member] | Reinsurance Segment | Other
P&C Operations:
P&C Operations	[1]									$ 305,097	$ 218,008	$ 124,349
[1]	. Other within the Reinsurance segment includes: whole account contracts, accident and health and other lines.
[2]	Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations.
[3]	Amounts from the prior year have been represented to reflect current mapping of underlying lines of business to be consistent with the manner in which they are reflected in the current period. The most significant movements include the following: Energy business previously shown under Specialty is now reflected in Property; Programs business formerly in Other is now reflected in Property or Casualty, depending upon the predominant line for each program; and Excess and Surplus is now reflected primarily in Casualty.

Segment Information - Net pre73

Segment Information - Net premiums written by geographical location (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	$ 10,242,683	$ 7,951,063	$ 5,944,841
Life operations
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	12,047	62,239	177,632
Life operations | Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	12,194	62,276	91,979
Life operations | Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	(147)	(37)	85,653
Operating Segments [Member] | Property and casualty operations
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	10,230,636	7,888,824	5,767,209
Operating Segments [Member] | Property and casualty operations | Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	1,267,613	781,618	636,109
Operating Segments [Member] | Property and casualty operations | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	3,575,969	3,045,031	2,528,196
Operating Segments [Member] | Property and casualty operations | Europe
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	4,778,299	3,628,258	2,124,117
Operating Segments [Member] | Property and casualty operations | Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Net premiums written	$ 608,755	$ 433,917	$ 478,787

Segment Information - Narrative

Segment Information - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)segments		Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | segments	2
Net results from structured products	$ 14,280	[1]	$ 17,991	[2]	$ 54,209	[3]
Property and casualty operations | Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products	54,000		60,400		68,000
Property and casualty operations | Interest expense
Segment Reporting Information [Line Items]
Net results from structured products	$ (39,700)		$ (42,200)		$ (12,900)
[1]	The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million, respectively.
[2]	The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.
[3]	The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.

Investments - Cost (amortized c

Investments - Cost (amortized cost for fixed maturities and short-term investments), fair value, gross unrealized gains, gross unrealized (losses), and OTTI recorded in AOCI (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		$ 29,587,656	$ 31,517,654
Fixed maturities, AFS, at fair value		30,256,602	32,257,589
Amortized cost of short-term investments, available for sale		626,142	618,851
Short-term investments, at fair value		625,193	617,390
Cost of equity securities, available for sale		996,610	834,079
Equity securities, AFS, at fair value		1,037,331	878,919
Amortized cost		31,210,408	32,970,584
Gross unrealized gains		1,078,735	1,153,289
Gross unrealized losses		(370,017)	(369,975)
Total investments available for sale		31,919,126	33,753,898
Non credit-related OTTI	[1]	(51,135)	(57,734)
Exclude Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		27,768,929	28,839,622
Gross unrealized gains, fixed maturities		540,262	587,258
Gross unrealized losses, fixed maturities		(360,631)	(322,394)
Fixed maturities, AFS, at fair value		27,948,560	29,104,486
Amortized cost of short-term investments, available for sale		626,142	618,851
Gross unrealized gains, short term investments		227	967
Gross unrealized losses, short term investments		(1,176)	(2,428)
Short-term investments, at fair value		625,193	617,390
Cost of equity securities, available for sale		996,610	834,079
Gross unrealized gains, equities		48,931	89,993
Gross unrealized losses, equities		(8,210)	(45,153)
Equity securities, AFS, at fair value		1,037,331	878,919
Amortized cost		29,391,681	30,292,552
Gross unrealized gains		589,420	678,218
Gross unrealized losses		(370,017)	(369,975)
Total investments available for sale		29,611,084	30,600,795
Non credit-related OTTI	[1]	(51,135)	(57,734)
Exclude Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		3,874,038	5,047,621
Gross unrealized gains, fixed maturities		53,172	52,355
Gross unrealized losses, fixed maturities		(32,822)	(34,339)
Fixed maturities, AFS, at fair value		3,894,388	5,065,637
Non credit-related OTTI	[1]	0	0
Exclude Life Funds Withheld Assets | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		4,213,845	3,697,756
Gross unrealized gains, fixed maturities		49,913	77,776
Gross unrealized losses, fixed maturities		(45,391)	(17,561)
Fixed maturities, AFS, at fair value		4,218,367	3,757,971
Non credit-related OTTI	[1]	0	0
Exclude Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		265,877	319,876
Gross unrealized gains, fixed maturities		21,132	25,644
Gross unrealized losses, fixed maturities		(12,751)	(16,980)
Fixed maturities, AFS, at fair value		274,258	328,540
Non credit-related OTTI	[1]	(47,879)	(54,200)
Exclude Life Funds Withheld Assets | CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		670,005	401,713
Gross unrealized gains, fixed maturities		5,955	7,933
Gross unrealized losses, fixed maturities		(10,774)	(4,330)
Fixed maturities, AFS, at fair value		665,186	405,316
Non credit-related OTTI	[1]	(1,191)	(1,182)
Exclude Life Funds Withheld Assets | Collateralized debt obligations ('CDO')
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		379,532	41,679
Gross unrealized gains, fixed maturities		498	4
Gross unrealized losses, fixed maturities		(2,539)	(9,273)
Fixed maturities, AFS, at fair value		377,491	32,410
Non credit-related OTTI	[1]	(1,208)	(1,208)
Exclude Life Funds Withheld Assets | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		872,903	1,164,426
Gross unrealized gains, fixed maturities		12,697	17,665
Gross unrealized losses, fixed maturities		(9,703)	(13,519)
Fixed maturities, AFS, at fair value		875,897	1,168,572
Non credit-related OTTI	[1]	(821)	(1,144)
Exclude Life Funds Withheld Assets | U.S. States and political subdivisions of the States
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		2,399,490	2,514,048
Gross unrealized gains, fixed maturities		86,041	125,395
Gross unrealized losses, fixed maturities		(7,419)	(7,373)
Fixed maturities, AFS, at fair value		2,478,112	2,632,070
Non credit-related OTTI	[1]	0	0
Exclude Life Funds Withheld Assets | Non-U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		5,037,482	5,249,148
Gross unrealized gains, fixed maturities		112,772	100,383
Gross unrealized losses, fixed maturities		(120,122)	(97,917)
Fixed maturities, AFS, at fair value		5,030,132	5,251,614
Non credit-related OTTI	[1]	0	0
Exclude Life Funds Withheld Assets | Financial Services Sector | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		3,587,557	3,535,830
Gross unrealized gains, fixed maturities		59,968	49,535
Gross unrealized losses, fixed maturities		(25,235)	(23,456)
Fixed maturities, AFS, at fair value		3,622,290	3,561,909
Non credit-related OTTI	[1]	0	0
Exclude Life Funds Withheld Assets | Non-Financial Services Sector | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		6,468,200	6,867,525
Gross unrealized gains, fixed maturities		138,114	130,568
Gross unrealized losses, fixed maturities		(93,875)	(97,646)
Fixed maturities, AFS, at fair value		6,512,439	6,900,447
Non credit-related OTTI	[1]	(36)	0
Life Funds Withheld Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		1,818,727	2,678,032
Gross unrealized gains, fixed maturities		489,315	475,071
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		2,308,042	3,153,103
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		8,468	10,721
Gross unrealized gains, fixed maturities		2,109	2,021
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		10,577	12,742
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		470	591
Gross unrealized gains, fixed maturities		143	161
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		613	752
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		19,121	24,401
Gross unrealized gains, fixed maturities		2,646	2,552
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		21,767	26,953
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | CMBS
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		77,762	107,968
Gross unrealized gains, fixed maturities		16,478	14,513
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		94,240	122,481
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		84,541	132,674
Gross unrealized gains, fixed maturities		17,019	17,121
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		101,560	149,795
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | Non-U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		454,695	737,735
Gross unrealized gains, fixed maturities		169,982	195,781
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		624,677	933,516
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | Financial Services Sector | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		376,018	531,016
Gross unrealized gains, fixed maturities		63,249	67,220
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		439,267	598,236
Non credit-related OTTI	[1]	0	0
Life Funds Withheld Assets | Non-Financial Services Sector | Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost of fixed maturities, available for sale		797,652	1,132,926
Gross unrealized gains, fixed maturities		217,689	175,702
Gross unrealized losses, fixed maturities		0	0
Fixed maturities, AFS, at fair value		1,015,341	1,308,628
Non credit-related OTTI	[1]	$ 0	$ 0
[1]	Represents the non-credit component of OTTI losses, adjusted for subsequent sales of securities. It does not include the change in fair value subsequent to the impairment measurement date.

Investments - Amortized cost an

Investments - Amortized cost and fair value of trading securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	$ 1,548,178	$ 1,263,609
Amortized cost of short term investments, trading	9,536	60,176
Fixed maturities, trading, at fair value	1,617,014	1,235,699
Short-term investments, at fair value	9,563	60,330
Total investments trading	1,626,577	1,296,029
Life Funds Withheld Assets
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	1,548,178	1,263,609
Amortized cost of short term investments, trading	9,536	60,176
Trading Securities, Cost	1,557,714	1,323,785
Fixed maturities, trading, at fair value	1,617,014	1,235,699
Short-term investments, at fair value	9,563	60,330
Total investments trading	1,626,577	1,296,029
Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	14,361	4,957
Fixed maturities, trading, at fair value	14,708	4,990
Life Funds Withheld Assets | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	835	370
Fixed maturities, trading, at fair value	852	368
Life Funds Withheld Assets | RMBS - Non-Agency
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	101
Fixed maturities, trading, at fair value	109
Life Funds Withheld Assets | CMBS
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	5,242	4,874
Fixed maturities, trading, at fair value	5,526	4,803
Life Funds Withheld Assets | Other asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	38,342	26,405
Fixed maturities, trading, at fair value	39,446	25,700
Life Funds Withheld Assets | U.S. States and political subdivisions of the States
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	219
Fixed maturities, trading, at fair value	224
Life Funds Withheld Assets | Non-U.S. Government
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	426,225	373,492
Fixed maturities, trading, at fair value	444,944	370,261
Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	450,990	344,070
Fixed maturities, trading, at fair value	468,175	335,956
Non-Financial Services Sector | Life Funds Withheld Assets | Corporate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost of fixed maturities, trading	611,863	509,441
Fixed maturities, trading, at fair value	$ 643,030	$ 493,621

Investments - Contractual matur

Investments - Contractual maturities of income securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	$ 1,548,178	$ 1,263,609
Fixed maturities, trading, at fair value	1,617,014	1,235,699
AFS securities
Amortized cost of Fixed maturities	29,587,656	31,517,654
Fixed maturities, at fair value	30,256,602	32,257,589
Exclude Life Funds Withheld Assets
AFS securities
Due less than one year, amortized cost	2,121,088	2,106,851
Due less than one year, fair value	2,135,262	2,104,106
Due after 1 through 5 years, amortized cost	12,400,798	14,051,494
Due after 1 through 5 years, fair value	12,463,844	14,143,461
Due after 5 through 10 years, amortized cost	5,509,194	5,680,830
Due after 5 through 10 years, fair value	5,531,402	5,740,954
Due after 10 years, amortized cost	1,335,687	1,374,997
Due after 10 years, fair value	1,406,853	1,423,156
Subtotal - amortized cost	21,366,767	23,214,172
Subtotal - fair value	21,537,361	23,411,677
Mortgage and asset-backed securities - amortized cost	6,402,162	5,625,450
Mortgage and asset-backed securities - fair value	6,411,199	5,692,809
Amortized cost of Fixed maturities	27,768,929	28,839,622
Fixed maturities, at fair value	27,948,560	29,104,486
Exclude Life Funds Withheld Assets | RMBS - Agency
AFS securities
Mortgage and asset-backed securities - amortized cost	4,213,845	3,697,756
Mortgage and asset-backed securities - fair value	4,218,367	3,757,971
Amortized cost of Fixed maturities	4,213,845	3,697,756
Fixed maturities, at fair value	4,218,367	3,757,971
Exclude Life Funds Withheld Assets | RMBS - Non-Agency
AFS securities
Mortgage and asset-backed securities - amortized cost	265,877	319,876
Mortgage and asset-backed securities - fair value	274,258	328,540
Amortized cost of Fixed maturities	265,877	319,876
Fixed maturities, at fair value	274,258	328,540
Exclude Life Funds Withheld Assets | CMBS
AFS securities
Mortgage and asset-backed securities - amortized cost	670,005	401,713
Mortgage and asset-backed securities - fair value	665,186	405,316
Amortized cost of Fixed maturities	670,005	401,713
Fixed maturities, at fair value	665,186	405,316
Exclude Life Funds Withheld Assets | Collateralized debt obligations ('CDO')
AFS securities
Mortgage and asset-backed securities - amortized cost	379,532	41,679
Mortgage and asset-backed securities - fair value	377,491	32,410
Amortized cost of Fixed maturities	379,532	41,679
Fixed maturities, at fair value	377,491	32,410
Exclude Life Funds Withheld Assets | Other asset-backed securities
AFS securities
Mortgage and asset-backed securities - amortized cost	872,903	1,164,426
Mortgage and asset-backed securities - fair value	875,897	1,168,572
Amortized cost of Fixed maturities	872,903	1,164,426
Fixed maturities, at fair value	875,897	1,168,572
Life Funds Withheld Assets
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	1,548,178	1,263,609
Fixed maturities, trading, at fair value	1,617,014	1,235,699
AFS securities
Due less than one year, amortized cost	71,207	81,700
Due less than one year, fair value	80,749	92,921
Due after 1 through 5 years, amortized cost	289,710	386,810
Due after 1 through 5 years, fair value	318,605	416,743
Due after 5 through 10 years, amortized cost	274,727	491,621
Due after 5 through 10 years, fair value	324,759	558,805
Due after 10 years, amortized cost	1,001,189	1,452,267
Due after 10 years, fair value	1,365,749	1,784,653
Subtotal - amortized cost	1,636,833	2,412,398
Subtotal - fair value	2,089,862	2,853,122
Mortgage and asset-backed securities - amortized cost	181,894	265,634
Mortgage and asset-backed securities - fair value	218,180	299,981
Amortized cost of Fixed maturities	1,818,727	2,678,032
Fixed maturities, at fair value	2,308,042	3,153,103
Life Funds Withheld Assets | RMBS - Agency
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	835	370
Fixed maturities, trading, at fair value	852	368
AFS securities
Mortgage and asset-backed securities - amortized cost	470	591
Mortgage and asset-backed securities - fair value	613	752
Amortized cost of Fixed maturities	470	591
Fixed maturities, at fair value	613	752
Life Funds Withheld Assets | RMBS - Non-Agency
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	101
Fixed maturities, trading, at fair value	109
AFS securities
Mortgage and asset-backed securities - amortized cost	19,121	24,401
Mortgage and asset-backed securities - fair value	21,767	26,953
Amortized cost of Fixed maturities	19,121	24,401
Fixed maturities, at fair value	21,767	26,953
Life Funds Withheld Assets | CMBS
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	5,242	4,874
Fixed maturities, trading, at fair value	5,526	4,803
AFS securities
Mortgage and asset-backed securities - amortized cost	77,762	107,968
Mortgage and asset-backed securities - fair value	94,240	122,481
Amortized cost of Fixed maturities	77,762	107,968
Fixed maturities, at fair value	94,240	122,481
Life Funds Withheld Assets | Other asset-backed securities
Trading Securities [Abstract]
Amortized cost of fixed maturities, trading	38,342	26,405
Fixed maturities, trading, at fair value	39,446	25,700
AFS securities
Mortgage and asset-backed securities - amortized cost	84,541	132,674
Mortgage and asset-backed securities - fair value	101,560	149,795
Amortized cost of Fixed maturities	84,541	132,674
Fixed maturities, at fair value	101,560	149,795
Cost [Member] | Life Funds Withheld Assets
Trading Securities [Abstract]
Trading securities due less than one year	59,138	4,573
Trading securities due after 1 through 5 years	322,574	278,163
Trading securities due after 5 through 10 years	507,631	280,487
Trading securities due after 10 years	614,315	668,737
Trading Securities Debt Maturities And Short Term Investments Fixed Maturities	1,503,658	1,231,960
Trading Securities Debt Maturities Without Single Maturity Date	44,520	31,649
Amortized cost of fixed maturities, trading	1,548,178	1,263,609
Cost [Member] | Life Funds Withheld Assets | RMBS - Agency
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	835	370
Cost [Member] | Life Funds Withheld Assets | RMBS - Non-Agency
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	101	0
Cost [Member] | Life Funds Withheld Assets | CMBS
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	5,242	4,874
Cost [Member] | Life Funds Withheld Assets | Other asset-backed securities
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	38,342	26,405
Fair value [Member] | Life Funds Withheld Assets
Trading Securities [Abstract]
Trading securities due less than one year	59,553	5,096
Trading securities due after 1 through 5 years	328,997	272,220
Trading securities due after 5 through 10 years	521,505	277,920
Trading securities due after 10 years	661,026	649,592
Trading Securities Debt Maturities And Short Term Investments Fixed Maturities	1,571,081	1,204,828
Trading Securities Debt Maturities Without Single Maturity Date	45,933	30,871
Fixed maturities, trading, at fair value	1,617,014	1,235,699
Fair value [Member] | Life Funds Withheld Assets | RMBS - Agency
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	852	368
Fair value [Member] | Life Funds Withheld Assets | RMBS - Non-Agency
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	109	0
Fair value [Member] | Life Funds Withheld Assets | CMBS
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	5,526	4,803
Fair value [Member] | Life Funds Withheld Assets | Other asset-backed securities
Trading Securities [Abstract]
Trading Securities Debt Maturities Without Single Maturity Date	$ 39,446	$ 25,700

Investments - Analysis of conti

Investments - Analysis of continual unrealized loss position (Details) - Exclude Life Funds Withheld Assets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
U.S. Government
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	$ 2,456,685	$ 3,762,869
Less than 12 months - gross unrealized losses	(30,640)	(29,339)
Equal to or greater than 12 months - fair value	43,873	89,113
Equal to or greater than 12 months - gross unrealized losses	(2,237)	(5,044)
Corporate | Financial Services Sector
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	1,111,700	1,641,021
Less than 12 months - gross unrealized losses	(19,010)	(13,280)
Equal to or greater than 12 months - fair value	59,091	102,022
Equal to or greater than 12 months - gross unrealized losses	(6,227)	(10,192)
Corporate | Non-Financial Services Sector
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	2,302,552	3,275,270
Less than 12 months - gross unrealized losses	(62,584)	(73,069)
Equal to or greater than 12 months - fair value	205,829	227,527
Equal to or greater than 12 months - gross unrealized losses	(31,368)	(24,706)
RMBS - Agency
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	2,456,028	1,065,055
Less than 12 months - gross unrealized losses	(40,989)	(10,046)
Equal to or greater than 12 months - fair value	136,014	221,211
Equal to or greater than 12 months - gross unrealized losses	(4,402)	(7,515)
RMBS - Non-Agency
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	3,517	19,614
Less than 12 months - gross unrealized losses	(205)	(1,104)
Equal to or greater than 12 months - fair value	166,796	180,146
Equal to or greater than 12 months - gross unrealized losses	(12,546)	(15,876)
CMBS
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	467,757	118,605
Less than 12 months - gross unrealized losses	(9,470)	(1,561)
Equal to or greater than 12 months - fair value	9,665	78,651
Equal to or greater than 12 months - gross unrealized losses	(1,304)	(2,769)
Collateralized debt obligations ('CDO')
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	105,653	12,311
Less than 12 months - gross unrealized losses	(58)	(516)
Equal to or greater than 12 months - fair value	2,752	20,096
Equal to or greater than 12 months - gross unrealized losses	(2,481)	(8,757)
Other asset-backed securities
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	671,782	572,671
Less than 12 months - gross unrealized losses	(3,830)	(5,252)
Equal to or greater than 12 months - fair value	34,783	57,563
Equal to or greater than 12 months - gross unrealized losses	(5,960)	(8,268)
U.S. States and political subdivisions of the States
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	457,288	565,055
Less than 12 months - gross unrealized losses	(6,983)	(6,609)
Equal to or greater than 12 months - fair value	4,287	12,259
Equal to or greater than 12 months - gross unrealized losses	(437)	(765)
Non-U.S. Government
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	1,797,405	1,921,286
Less than 12 months - gross unrealized losses	(75,596)	(53,440)
Equal to or greater than 12 months - fair value	288,490	474,929
Equal to or greater than 12 months - gross unrealized losses	(45,480)	(46,714)
Fixed maturities and short term investments
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	11,830,367	12,953,757
Less than 12 months - gross unrealized losses	(249,365)	(194,216)
Equal to or greater than 12 months - fair value	951,580	1,463,517
Equal to or greater than 12 months - gross unrealized losses	(112,442)	(130,606)
Equity securities
Fixed maturities and short-term investments - AFS: [Abstract]
Less than 12 months - fair value	130,487	356,742
Less than 12 months - gross unrealized losses	(8,210)	(45,153)
Equal to or greater than 12 months - fair value	0	0
Equal to or greater than 12 months - gross unrealized losses	$ 0	$ 0

Investments - Analysis of net i

Investments - Analysis of net investment income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income [Line Items]
Equity securities and other investments	$ 34,620	$ 28,200	$ 42,252
Interest on funds withheld	10,276	10,835	14,583
Total gross investment income	912,884	952,685	996,374
Investment expenses	(85,751)	(80,315)	(77,749)
Net investment income	827,133	872,370	918,625
Exclude Life Funds Withheld Assets
Net Investment Income [Line Items]
Fixed maturities, short term investments and cash equivalents	713,237	726,161	809,964
Net investment income	672,382	684,881	789,050
Life Funds Withheld Assets
Net Investment Income [Line Items]
Fixed maturities, short term investments and cash equivalents	154,751	187,489	129,575
Net investment income	$ 154,751	$ 187,489	$ 129,575

Investments - Analysis of net r

Investments - Analysis of net realized gains (losses) and the change in unrealized (losses) gains on investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Realized investment gains (losses):
OTTI on investments, net of amounts transferred to other comprehensive income	$ (78,600)	$ (83,000)	$ (35,700)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	372,138	202,178	107,462
Net realized and unrealized (losses) on investment related derivative instruments	2,521	(8,616)	20,121
Net realized (losses) on investments and net realized and unrealized (losses) on investment related derivative instruments	374,659	193,562	127,583
Net change in unrealized gains (losses) on investments	(137,692)	(956,986)	970,715
Total net realized (losses) on investments, net realized and unrealized (losses) on investment related derivative instruments, and net change in unrealized gains (losses) on investments	236,967	(763,424)	1,098,298
Fixed maturities | HTM
Realized investment gains (losses):
Net change in unrealized gains (losses) on investments	0	0	(272,540)
Equity securities
Realized investment gains (losses):
Net change in unrealized gains (losses) on investments	(4,119)	(59,619)	(32,577)
Affiliates and other investments
Realized investment gains (losses):
Net change in unrealized gains (losses) on investments	(63,096)	(6,072)	35,143
Exclude Life Funds Withheld Assets
Realized investment gains (losses):
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	112,689	19,997	122,991
Exclude Life Funds Withheld Assets | Fixed maturities, short term investments and cash equivalents
Realized investment gains (losses):
Gross realized gains	192,119	187,523	119,817
Gross realized losses on investments sold	(151,013)	(134,441)	(66,892)
OTTI on investments, net of amounts transferred to other comprehensive income	(48,432)	(54,346)	(12,341)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	(7,326)	(1,264)	40,584
Exclude Life Funds Withheld Assets | Fixed maturities | AFS
Realized investment gains (losses):
Net change in unrealized gains (losses) on investments	(84,721)	(486,140)	360,463
Exclude Life Funds Withheld Assets | Equity securities
Realized investment gains (losses):
Gross realized gains	140,864	79,556	96,260
Gross realized losses on investments sold	(11,882)	(49,223)	(12,270)
OTTI on investments, net of amounts transferred to other comprehensive income	(30,126)	(15,954)	(10,944)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	98,856	14,379	73,046
Exclude Life Funds Withheld Assets | Other investments
Realized investment gains (losses):
Gross realized gains	37,596	39,198	31,830
Gross realized losses on investments sold	(16,437)	(19,656)	(10,011)
OTTI on investments, net of amounts transferred to other comprehensive income	0	(12,660)	(12,458)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	21,159	6,882	9,361
Life Funds Withheld Assets
Realized investment gains (losses):
Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets	109,458	(27,734)	(9)
Life Funds Withheld Assets | Fixed maturities, short term investments and cash equivalents
Realized investment gains (losses):
Gross realized gains	185,487	259,798	7,926
Gross realized losses on investments sold	(32,898)	(36,526)	(2,859)
Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets	109,458	(27,734)	(9)
OTTI on investments, net of amounts transferred to other comprehensive income	(2,598)	(13,357)	(20,587)
Total net realized gains (losses) on investments, and net unrealized gains (losses) on investments, Trading	259,449	182,181	(15,529)
Life Funds Withheld Assets | Fixed maturities | AFS
Realized investment gains (losses):
Net change in unrealized gains (losses) on investments	$ 14,244	$ (405,155)	$ 880,226

Investments - Credit loss impai

Investments - Credit loss impairments on fixed income securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
OTTI related to credit losses recognized in earnings
Balance, beginning of period	$ 73,469	$ 131,942
Credit loss impairment recognized in the current period on securities not previously impaired	12,867	9,698
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period	(18,178)	(54,648)
Credit loss impairments previously recognized on securities impaired to fair value during the period	0	(2,629)
Additional credit loss impairments recognized in the current period on securities previously impaired	2,233	2,230
Accretion of credit loss impairments previously recognized due to an increase in cash flows expected to be collected	(8,796)	(13,124)
Balance, end of period	$ 61,595	$ 73,469

Investments - Narrative (Detail

Investments - Narrative (Details) $ in Thousands	May 01, 2014USD ($)	Dec. 31, 2016USD ($)positions	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount		$ (62,295)	$ (170,688)	$ 400,456
Fixed maturities, AFS, at fair value		$ 30,256,602	$ 32,257,589
Percentage of fixed income portfolio invested in securities below investment grade		2.40%	2.00%
Amortized cost of fixed maturities, available for sale		$ 29,587,656	$ 31,517,654
Percentage of gross unrealized losses relating to securities below investment grade		4.10%	14.70%
Pledged assets, amount		$ 17,100,000	$ 18,300,000
Gross unrealized losses		$ 370,017	369,975
Total number of positions - AFS | positions		8,495
AFS securities in unrealized loss position (number of positions) | positions		3,037
OTTI on investments, net of amounts transferred to other comprehensive income		$ 78,600	83,000	35,700
Credit loss impairments previously recognized on securities which matured, paid down, prepaid or were sold during the period		18,178	54,648
Equity securities, AFS, at fair value		1,037,331	878,919
Cost of equity securities, available for sale		996,610	834,079
Fixed Income Funds Member
Marketable Securities [Line Items]
Cost of equity securities, available for sale		100,000
XL Re Life (SAC) Ltd [Member]
Marketable Securities [Line Items]
Held To Maturity Securities Transferred Security Carrying Value	$ 2,800,000
Fixed maturities, held to maturity, gross unrealized gains	424,900
Fixed maturities, held to maturity, gross unrealized losses	0
Unrealized Gains (Losses) on Investments
Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount		(62,300)
Unrealized Gains (Losses) on Investments | XL Re Life (SAC) Ltd [Member]
Marketable Securities [Line Items]
Cumulative adjustments recorded to value of future policy benefit reserves, amount	$ 440,500
Exclude Life Funds Withheld Assets
Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		27,948,560	29,104,486
Amortized cost of fixed maturities, available for sale		27,768,929	28,839,622
Gross unrealized losses		370,017	369,975
Equity securities, AFS, at fair value		1,037,331	878,919
Cost of equity securities, available for sale		996,610	834,079
Exclude Life Funds Withheld Assets | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		4,218,367	3,757,971
Amortized cost of fixed maturities, available for sale		4,213,845	3,697,756
Exclude Life Funds Withheld Assets | Equity securities
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		30,126	15,954	10,944
Exclude Life Funds Withheld Assets | Structured Credit Securities [Member]
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		3,000	1,300	4,300
Exclude Life Funds Withheld Assets | Foreign Exchange [Member]
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		29,900	23,600	4,300
Exclude Life Funds Withheld Assets | Other Investments [Member]
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		0	8,700	12,500
Exclude Life Funds Withheld Assets | RMBS - Non-Agency
Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		274,258	328,540
Amortized cost of fixed maturities, available for sale		265,877	319,876
Exclude Life Funds Withheld Assets | CMBS
Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		665,186	405,316
Amortized cost of fixed maturities, available for sale		670,005	401,713
Exclude Life Funds Withheld Assets | Collateralized debt obligations ('CDO')
Marketable Securities [Line Items]
Fixed maturities, AFS, at fair value		377,491	32,410
Amortized cost of fixed maturities, available for sale		379,532	41,679
No Longer Intend To Hold For A Period Sufficient To Recover Fair Value To Cost [Member] | Exclude Life Funds Withheld Assets
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		29,300	29,400	3,700
In A Loss Position For More Than 11 Months Or Greater Than Fifty Percent Of Amortized Cost [Member] | Exclude Life Funds Withheld Assets
Marketable Securities [Line Items]
OTTI on investments, net of amounts transferred to other comprehensive income		$ 16,400	$ 20,000	$ 10,900

Investments in Affiliates - Cat

Investments in Affiliates - Categories of affiliates (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	$ 2,177,645	$ 1,708,899
Investment fund affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	1,674,925	1,386,837
Operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	$ 502,720	$ 322,062

Investments in Affiliates - Inv

Investments in Affiliates - Investment Fund Affiliates (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 2,177,645	$ 1,708,899
Equity in net income (loss) in operating affiliates		115,155	118,060	$ 203,034
Investment fund affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		1,674,925	1,386,837
Equity in net income (loss) in operating affiliates		$ 70,758	$ 73,320
Ownership percentage remaining		5.50%	5.80%
Combined funds/ estimated total net assets	[1]	$ 30,600,053	$ 24,101,796
Investment fund affiliates | Hedge funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		1,317,375	1,084,198
Equity in net income (loss) in operating affiliates		$ 41,670	$ 42,668
Ownership percentage remaining		4.80%	5.20%
Combined funds/ estimated total net assets	[1]	$ 27,281,980	$ 20,906,592
Investment fund affiliates | Arbitrage
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		165,633	190,016
Equity in net income (loss) in operating affiliates		$ 965	$ 612
Ownership percentage remaining		12.30%	8.60%
Combined funds/ estimated total net assets	[1]	$ 1,343,655	$ 2,202,112
Investment fund affiliates | Directional
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		672,934	551,262
Equity in net income (loss) in operating affiliates		$ 1,480	$ 31,012
Ownership percentage remaining		7.40%	7.20%
Combined funds/ estimated total net assets	[1]	$ 9,039,159	$ 7,643,134
Investment fund affiliates | Event driven
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	[2]	297,836	285,823
Equity in net income (loss) in operating affiliates	[2]	$ 9,676	$ 5,592
Ownership percentage remaining	[2]	2.60%	3.00%
Combined funds/ estimated total net assets	[1],[2]	$ 11,341,870	$ 9,460,387
Investment fund affiliates | Multi-style
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		180,972	57,097
Equity in net income (loss) in operating affiliates		$ 29,549	$ 5,452
Ownership percentage remaining		3.30%	3.60%
Combined funds/ estimated total net assets	[1]	$ 5,557,296	$ 1,600,959
Investment fund affiliates | Private investment funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		357,550	302,639
Equity in net income (loss) in operating affiliates		$ 29,088	$ 30,652
Ownership percentage remaining		10.80%	9.50%
Combined funds/ estimated total net assets	[1]	$ 3,318,073	$ 3,195,204
[1]	Total estimated net assets are generally as at November 30 for hedge fund affiliates and September 30 for private investment fund affiliates.
[2]	The Company accounts for its investment in certain funds using the equity method where the Company has significant influence over the related investment management company even though the ownership percentage is less than three percent.

Investments in Affiliates - Ope

Investments in Affiliates - Operating Affiliates (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 2,177,645	$ 1,708,899
Equity in net income (loss) in operating affiliates		115,155	118,060	$ 203,034
Operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		502,720	322,062
Equity in net income (loss) in operating affiliates		44,397	44,740
Investee summarized data - total assets		6,106,241	4,989,581
Investee summarized data - total liabilities		3,863,414	3,389,699
Investee summarized data - total revenue (loss)		1,368,641	1,053,803
Investee summarized data - net income (loss)		287,428	182,192
Operating affiliates | Other strategic operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		446,695	251,348
Equity in net income (loss) in operating affiliates		12,622	33,608
Investee summarized data - total assets		5,353,905	4,280,976
Investee summarized data - total liabilities		3,791,300	3,293,873
Investee summarized data - total revenue (loss)		1,030,859	847,131
Investee summarized data - net income (loss)		30,424	91,701
Operating affiliates | Investment manager affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	[1]	56,025	70,714
Equity in net income (loss) in operating affiliates	[1]	31,775	11,132
Investee summarized data - total assets	[1]	752,336	708,605
Investee summarized data - total liabilities	[1]	72,114	95,826
Investee summarized data - total revenue (loss)	[1]	337,782	206,672
Investee summarized data - net income (loss)	[1]	$ 257,004	$ 90,491
[1]	During the years ended December 31, 2016 and 2015, the Company received distributions from its Investment Manager Affiliates of approximately $35.9 million and $25.3 million, respectively.

Investments in Affiliates - Nar

Investments in Affiliates - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 2,177,645	$ 1,708,899
Additional investment commitment - other investments		59,300
Investment manager affiliates
Schedule of Equity Method Investments [Line Items]
Distributions received from investment manager affiliates		$ 35,900	25,300
Investment fund affiliates
Schedule of Equity Method Investments [Line Items]
Required notice period for redemption		30 days
Investments in affiliates		$ 1,674,925	$ 1,386,837
Ownership percentage remaining		5.50%	5.80%
Investment fund affiliates | Subject To Redemption Restrictions [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 553,200	$ 382,000
Investment fund affiliates | Funds held in side pockets
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		23,500	18,200
Investment fund affiliates | Hedge funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 1,317,375	$ 1,084,198
Ownership percentage remaining		4.80%	5.20%
Investment fund affiliates | Private investment funds
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 357,550	$ 302,639
Ownership percentage remaining		10.80%	9.50%
Operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 502,720	$ 322,062
Operating affiliates | CATGS I, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 17,500
Ownership percentage remaining		50.00%
Operating affiliates | Other strategic operating affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 446,695	251,348
Operating affiliates | Investment manager affiliates
Schedule of Equity Method Investments [Line Items]
Investments in affiliates	[1]	56,025	$ 70,714
Operating affiliates | Privilege Underwriters, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 129,700
Operating affiliates | Privilege Underwriters' Reciprocal Exchange [Member]
Schedule of Equity Method Investments [Line Items]
Surplus Note Term		10 years
Additional investment commitment - other investments		$ 25,000
Operating affiliates | HighVista III, Ltd. [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 106,600
Ownership percentage remaining		29.50%
Operating affiliates | Westaim HIIG LP [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 33,100
Ownership percentage remaining		13.10%
Operating affiliates | Five Oaks Investment Corp [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 25,500
Ownership percentage remaining		23.10%
Cost of operating affiliate interests acquired		$ 49,200
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		3,753
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 13.11
Operating affiliates | Common And Preferred Units [Member] | Privilege Underwriters, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 77,500
Ownership percentage remaining		9.90%
Operating affiliates | Common And Preferred Units [Member] | Privilege Group Holdings GP, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage remaining		9.90%
Operating affiliates | Surplus Notes [Member] | Privilege Underwriters' Reciprocal Exchange [Member]
Schedule of Equity Method Investments [Line Items]
Investments in affiliates		$ 50,000
Surplus Note Term		10 years
[1]	During the years ended December 31, 2016 and 2015, the Company received distributions from its Investment Manager Affiliates of approximately $35.9 million and $25.3 million, respectively.

Other Investments - Components

Other Investments - Components of other investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Other Investments [Line Items]
Other investments	$ 1,164,564	$ 1,433,057
Hedge funds
Other Investments [Line Items]
Other investments	331,972	544,070
Arbitrage
Other Investments [Line Items]
Other investments	165,053	205,117
Directional
Other Investments [Line Items]
Other investments	159,701	276,277
Event driven
Other Investments [Line Items]
Other investments	2,877	5,427
Multi-style
Other Investments [Line Items]
Other investments	4,341	57,249
Private investment funds
Other Investments [Line Items]
Other investments	175,579	244,576
Overseas deposits
Other Investments [Line Items]
Other investments	493,594	479,187
Structured transactions
Other Investments [Line Items]
Other investments	142,698	138,608
Other
Other Investments [Line Items]
Other investments	$ 20,721	$ 26,616

Other Investments - Analysis of

Other Investments - Analysis of net realized and unrealized gains on other investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Investments [Line Items]
Net unrealized gains (losses)	$ 170,889	$ 227,038
Net realized gains (losses)	20,848	22,111	$ 19,960
Hedge funds
Other Investments [Line Items]
Net unrealized gains (losses)	134,114	188,698
Net realized gains (losses)	12,212	12,769	6,685
Private investment funds
Other Investments [Line Items]
Net unrealized gains (losses)	36,775	38,340
Net realized gains (losses)	$ 8,636	$ 9,342	$ 13,275

Other Investments - Narrative (

Other Investments - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)strategy	Dec. 31, 2015USD ($)strategy
Other Investments [Line Items]
Number of strategies employed | strategy	4	4
Other investments	$ 1,164,564	$ 1,433,057
Aggregate principal amount of payment obligation purchased	150,000
Estimated fair value of payment obligation at date of purchase	$ 140,600
Coupon rate on outstanding payment obligation	3.50%
Term of payment obligation	11 years 6 months
Fair value of difference between estimated fair value and cost of payment obligation	$ 21,900
Payment obligation, fees	2,500
Other Asset Impairment Charges		8,600
Cost-method Investments, Realized Losses		6,700
Alternative funds | Funds which are subject to lockups and/or gate provisions
Other Investments [Line Items]
Other investments	223,300	399,600
Alternative funds | Funds held in side pockets
Other Investments [Line Items]
Other investments	$ 11,300	$ 26,000
Alternative funds | Funds held in side pockets | Minimum
Other Investments [Line Items]
Side pockets - liquidation period of underlying investments	2 years
Alternative funds | Funds held in side pockets | Maximum
Other Investments [Line Items]
Side pockets - liquidation period of underlying investments	4 years
Cypress Point 1 [Member]
Other Investments [Line Items]
Aggregate face amount of structured transactions purchased	$ 155,000
Cypress Point 2 [Member]
Other Investments [Line Items]
Aggregate face amount of structured transactions purchased	$ 81,900

Derivative Instruments - Gross

Derivative Instruments - Gross amounts of derivative fair values contained in the consolidated balance sheet (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Derivatives Fair Value [Line Items]
Asset derivative fair value		$ 107,496	$ 89,314
Liability derivative fair value		64,704	45,495
Derivative assets - gross amounts offset in the balance sheet	[1]	(17,947)	(3,087)
Derivative liabilities - gross amounts offset in the balance sheet	[1]	(17,947)	(3,087)
Derivative assets - net amounts in the balance sheet	[2]	89,549	86,227
Derivative liabilities - net amounts in the balance sheet	[2]	46,757	42,408
Derivative assets - cash collateral not offset in the balance sheet	[3]	(36,980)	(30,958)
Derivative liabilities - cash collateral not offset in the balance sheet	[3]	(5,810)	0
Derivative assets - net amount		52,569	55,269
Derivative liabilities - net amount		40,947	42,408
Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Asset derivative notional amount		1,396,801	1,667,585
Asset derivative fair value	[2]	85,175	64,289
Liability derivative notional amount		583,722	674,976
Liability derivative fair value	[2]	25,750	11,941
Designated as Hedging Instrument | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		1,396,801	1,667,585
Asset derivative fair value	[2]	85,175	64,289
Liability derivative notional amount		583,722	674,976
Liability derivative fair value	[2]	25,750	11,941
Not Designated as Hedging Instrument
Derivatives Fair Value [Line Items]
Asset derivative notional amount		342,182	441,843
Asset derivative fair value	[2]	22,321	25,025
Liability derivative notional amount		4,472,756	4,909,732
Liability derivative fair value	[2]	38,954	33,554
Not Designated as Hedging Instrument | Investment Related Derivatives | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		10,049	102,234
Asset derivative fair value	[2]	190	2,888
Liability derivative notional amount		273,767	144,707
Liability derivative fair value	[2]	12,137	1,702
Not Designated as Hedging Instrument | Investment Related Derivatives | Credit Exposure
Derivatives Fair Value [Line Items]
Asset derivative notional amount		32,500	8,433
Asset derivative fair value	[2]	1,077	652
Liability derivative notional amount		82,500	71,614
Liability derivative fair value	[2]	6,978	12,067
Not Designated as Hedging Instrument | Investment Related Derivatives | Financial Market Exposure
Derivatives Fair Value [Line Items]
Asset derivative notional amount		5	37
Asset derivative fair value	[2]	5	77
Liability derivative notional amount		0	26,500
Liability derivative fair value	[2]	0	417
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Foreign Exchange Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount		181,300	194,566
Asset derivative fair value	[2]	1,208	2,009
Liability derivative notional amount		0	0
Liability derivative fair value	[2]	0	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Other Credit Derivatives [Member]
Derivatives Fair Value [Line Items]
Asset derivative notional amount		0	29,874
Asset derivative fair value	[2]	0	31
Liability derivative notional amount		24,490	0
Liability derivative fair value	[2]	340	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Guaranteed Minimum Income Benefit
Derivatives Fair Value [Line Items]
Asset derivative notional amount		43,553	46,032
Asset derivative fair value	[2]	19,499	19,368
Liability derivative notional amount		43,553	46,032
Liability derivative fair value	[2]	19,499	19,368
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Modified Coinsurance Funds Withheld Contract
Derivatives Fair Value [Line Items]
Asset derivative notional amount	[4]	59,775	60,667
Asset derivative fair value	[2],[4]	0	0
Liability derivative notional amount	[4]	4,048,446	4,620,879
Liability derivative fair value	[2],[4]	0	0
Not Designated as Hedging Instrument | Other Non Investment Derivatives | Other Derivative Instruments [Member]
Derivatives Fair Value [Line Items]
Asset derivative notional amount		15,000	0
Asset derivative fair value	[2]	342	0
Liability derivative notional amount		0	0
Liability derivative fair value	[2]	$ 0	$ 0
[1]	Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy.
[2]	Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements.
[3]	As of December 31, 2016, the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015, the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.
[4]	The fair value movements in derivative assets and liabilities relating to modified coinsurance funds withheld contracts are included within the associated asset or liability at each period end on the face of the balance sheets. Notional amounts associated with reinsurance agreements under which the Company assumes reinsurance risk are recorded as asset derivative notional amounts. Included in the liability derivative notional amount as of December 31, 2016 is the cumulative net realized and unrealized loss on the life retrocession embedded derivative of $937.7 million.

Derivative Instruments - Schedu

Derivative Instruments - Schedule of derivative instruments designated as hedges of the net investment in a foreign operation (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets		$ 2,316,538	$ 1,769,106
Derivative gains (losses)	[1]	$ 130,365	$ 106,876
[1]	Derivative gains (losses) from derivative instruments designated as hedges of the net investment in a foreign operation are recorded in the cumulative translation adjustment account within AOCI for each period.

Derivative Instruments - Earnin

Derivative Instruments - Earnings relating to derivative instruments not formally designated as hedging instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments Gain Loss [Line Items]
Total derivatives not designated as hedging instruments	$ 2,521	$ 53,123	$ 30,142
Amount of gain (loss) recognized in income from ineffective portion of fair value hedges	0	0	(256)
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	2,521	53,123	29,886
Not Designated as Hedging Instrument | Investment Related Derivatives
Derivative Instruments Gain Loss [Line Items]
Interest rate exposure	781	(2,347)	15,959
Foreign exchange exposure	(592)	(1,542)	3,351
Credit exposure	(1,539)	(2,537)	400
Financial market exposure	(2,494)	(2,190)	411
Not Designated as Hedging Instrument | Financial Operations Derivatives
Derivative Instruments Gain Loss [Line Items]
Credit exposure	0	0	5,023
Not Designated as Hedging Instrument | Other Non Investment Derivatives
Derivative Instruments Gain Loss [Line Items]
Foreign exchange exposure	(1,701)	60,319	0
Credit exposure	4,424	1,375	0
Guaranteed minimum income benefit contract	0	0	2,257
Modified coinsurance funds withheld contract	3,300	45	2,741
Gain Loss On Other Not Designated As Hedging Instruments	342	0	0
Life Funds Withheld Assets
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	$ (540,090)	$ (151,691)	$ (488,222)

Derivative Instruments - Impact

Derivative Instruments - Impact of Life Retro Arrangements (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Underwriting profit (loss)		$ 547,325	$ 587,409	$ 585,907
Net investment income		827,133	872,370	918,625
Exchange (gains) losses		(9,578)	22,504	(37,568)
Other Operating Income (Expense), Net	[1]	(13,315)	(13,356)	(6,891)
Net realized and unrealized gains (losses) on derivative instruments		2,521	53,123	29,886
Net income (loss)		570,145	1,313,339	268,838
Cumulative adjustments recorded to value of future policy benefit reserves, amount		62,295	170,688	(400,456)
Foreign currency translation adjustments		95,473	(25,315)	(25,729)
Other Comprehensive Income (Loss), Net of Tax		28,930	(797,842)	747,801
Life Funds Withheld Assets
Derivative [Line Items]
Net investment income		154,751	187,489	129,575
Net realized gains (losses) on investments sold		152,589	223,272	5,067
Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets		109,458	(27,734)	(9)
Other-than-temporary impairments (OTTI) on investments		(2,598)	(13,357)	(20,587)
Net realized and unrealized gains (losses) on derivative instruments		(540,090)	(151,691)	(488,222)
Change in net unrealized gains (losses) on investments, net of tax		(4,502)	(421,604)	274,083
XL Re Life (SAC) Ltd [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Net of Tax		0	0
XL Re Life (SAC) Ltd [Member] | Life Funds Withheld Assets
Derivative [Line Items]
Underwriting profit (loss)		0	605	11,649
Net investment income		154,751	187,489	129,575
Net realized gains (losses) on investments sold		152,589	223,272	5,067
Net unrealized gains (losses) on investments, Trading - Life Funds Withheld Assets		109,458	(27,734)	(9)
Other-than-temporary impairments (OTTI) on investments		(2,598)	(13,357)	(20,587)
Exchange (gains) losses		(8,988)	4,788	10,099
Other Operating Income (Expense), Net		(154)	2,280	(1,610)
Net realized and unrealized gains (losses) on derivative instruments		(540,090)	(151,691)	(488,222)
Net income (loss)		(135,032)	225,652	(354,038)
Change in net unrealized gains (losses) on investments, net of tax		(4,502)	(421,604)	274,083
Cumulative adjustments recorded to value of future policy benefit reserves, amount		62,295	170,688	74,009
Foreign currency translation adjustments		77,239	25,869	17,595
Change In Other Comprehensive Income Life Retro Arrangements		135,032	(225,047)	365,687
Other Comprehensive Income (Loss), Net of Tax		$ 0	$ 605	$ 11,649
[1]	Net fee income and other includes operating expenses from the Company's loss prevention consulting services business.

Derivative Instruments - Compon

Derivative Instruments - Components of life retrocession embedded derivative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	$ 2,521	$ 53,123	$ 29,886
Life Funds Withheld Assets
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(473,806)	(13,084)
Net adjustments related to future policy benefit reserves, net of tax	(51,100)	(125,747)
Net realized and unrealized gains (losses) on derivative instruments - Life Funds Withheld Assets	(15,184)	(12,860)
Net realized and unrealized gains (losses) on life retrocession embedded derivative and derivative instruments - Life Funds Withheld Assets	(540,090)	(151,691)	$ (488,222)
Life Funds Withheld Assets | Interest income
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(161,887)	(193,569)
Life Funds Withheld Assets | Net realized and unrealized gains (losses
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	(312,074)	180,134
Life Funds Withheld Assets | Other
Derivative [Line Items]
Net realized and unrealized gains (losses) on life retrocession embedded derivative	$ 155	$ 351

Derivative Instruments - Hedged

Derivative Instruments - Hedged items - amount of gain/(loss) recognized in income attributable to risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments Gain Loss [Line Items]
Ineffective portion of hedging relationship - gain/(loss)	$ 0	$ 0	$ (256)
Designated as Hedging Instrument | Fair Value Hedging Member | Net realized and unrealized gains (losses) on derivative instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0	(15,663)
Ineffective portion of hedging relationship - gain/(loss)	0	0	(256)
Designated as Hedging Instrument | Fair Value Hedging Member | Net realized and unrealized gains (losses) on derivative instruments [Member] | Fixed maturities
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0	15,407
Designated as Hedging Instrument | Fair Value Hedging Member | Net realized and unrealized gains (losses) on derivative instruments [Member] | Interest Rate Contract [Member]
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	0	0	0
Designated as Hedging Instrument | Fair Value Hedging Member | Net realized and unrealized gains (losses) on derivative instruments [Member] | Foreign Exchange Exposure
Derivative Instruments Gain Loss [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ 0	$ 0	$ (15,663)

Derivative Instruments - Sche96

Derivative Instruments - Schedule of settlement of fair value hedges (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivative liabilities - cash collateral not offset in the balance sheet	[1]	$ 5,810	$ 0
Deposit Liabilities | Fair Value Hedging Member
Derivative [Line Items]
Fair Value Hedge Cumulative Reduction To Expense		113,292	103,742
Fair Value Hedge Remaining Balance		$ 119,903	$ 129,454
Derivative, Average Remaining Maturity		20 years 1 month 6 days	21 years 7 months 6 days
[1]	As of December 31, 2016, the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015, the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.

Derivative Instruments - Summar

Derivative Instruments - Summary of contingent credit features (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Collateral posted to counterparty	[1]	$ 5,810	$ 0
Contracts with downgrade provisions [Member]
Derivative [Line Items]
Aggregate fair value of derivative agreements with downgrade provisions in a net liability position		14,130	5,827
Collateral posted to counterparty		$ 4,630	$ 0
[1]	As of December 31, 2016, the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015, the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.

Derivative Instruments - Narrat

Derivative Instruments - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Jun. 30, 2014
Derivative [Line Items]
Underwriting profit (loss)		$ 547,325		$ 587,409		$ 585,907
Other Comprehensive Income (Loss), Net of Tax		28,930		(797,842)		747,801
Derivative assets - cash collateral not offset in the balance sheet	[1]	36,980		30,958
Collateral posted to counterparty	[1]	5,810		0
Net results from structured products		14,280	[2]	17,991	[3]	54,209	[4]
Asset derivative fair value		107,496		89,314
Net realized and unrealized gains (losses) on derivative instruments		2,521		53,123		29,886
Fair Value Hedging Member | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance		119,903		129,454
Fair Value Hedging Member | Structured Indemnity | Deposit Liabilities
Derivative [Line Items]
Fair Value Hedge Remaining Balance						0		$ 47,000
Life Funds Withheld Assets
Derivative [Line Items]
Cumulative net realized and unrealized gains (losses) on life retrocession embedded derivative		(937,700)
Net realized and unrealized gains (losses) on derivative instruments		(540,090)		(151,691)		(488,222)
Not Designated as Hedging Instrument
Derivative [Line Items]
Asset derivative notional amount		342,182		441,843
Asset derivative fair value	[5]	22,321		25,025
Other Non Investment Derivatives | Not Designated as Hedging Instrument | Other Credit Derivatives [Member]
Derivative [Line Items]
Asset derivative notional amount		0		29,874
Asset derivative fair value	[5]	0		31
Interest expense | Structured Indemnity
Derivative [Line Items]
Net results from structured products						28,700
Interest expense | Property and casualty operations
Derivative [Line Items]
Net results from structured products		(39,700)		(42,200)		(12,900)
XL Re Life (SAC) Ltd [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Net of Tax		0		0
XL Re Life (SAC) Ltd [Member] | Life Funds Withheld Assets
Derivative [Line Items]
Underwriting profit (loss)		0		605		11,649
Other Comprehensive Income (Loss), Net of Tax		0		605		11,649
Net realized and unrealized gains (losses) on derivative instruments		$ (540,090)		$ (151,691)		$ (488,222)
[1]	As of December 31, 2016, the Company held cash collateral related to foreign currency derivative positions and certain other derivative positions of $37.0 million for derivatives in an asset position and paid cash collateral of $5.8 million for derivatives in a liability position. As of December 31, 2015, the Company held cash collateral related to a foreign currency derivative position and certain other derivative positions of $31.0 million for derivatives in an asset position and paid cash collateral of nil for derivatives in a liability position. The assets and liabilities related to the net collateral paid or held were recorded as Other assets and Other liabilities within the Consolidated Balance Sheets as the collateral and derivative positions are not intended to be settled on a net basis.
[2]	The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million, respectively.
[3]	The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.
[4]	The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.
[5]	Derivative instruments in an asset or liability position are included within Other assets or Other liabilities, respectively, in the balance sheets on a net basis where the Company has both a legal right of offset and the intention to settle the contracts on a net basis. The Company often enters into different types of derivative contracts with a single counterparty and these contracts are covered under netting agreements.

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of assets and liabilities that were accounted for at fair value (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
ASSETS
Fixed maturities, AFS, at fair value		$ 30,256,602		$ 32,257,589
Equity securities, AFS, at fair value		1,037,331		878,919
Short-term investments, at fair value		625,193		617,390
Total investments available for sale		31,919,126		33,753,898
Fixed maturities, trading, at fair value		1,617,014		1,235,699
Short-term investments, at fair value		9,563		60,330
Total investments trading		1,626,577		1,296,029
Collateral and counterparty netting, asset	[1]	(17,947)		(3,087)
Liabilities:
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)		998,968		914,629
Collateral and counterparty netting, liability	[1]	(17,947)		(3,087)
Recurring
ASSETS
Total investments available for sale		31,919,126		33,753,898
Cash equivalents	[2]	1,669,652		1,268,666
Other investments		699,402	[3]	773,608
Other assets	[1]	89,549		86,227
Total assets accounted for at fair value		36,077,104		37,279,702
Liabilities:
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	[4]	937,721		463,915
Financial instruments sold, but not yet purchased	[5]			347
Other liabilities	[1]	46,757		42,408
Total liabilities accounted for at fair value		984,478		506,670
Recurring | Quoted prices in active markets for identical assets (Level 1)
ASSETS
Total investments available for sale		898,664		528,581
Cash equivalents	[2]	573,398		437,742
Other investments			[3]	0
Other assets	[1]	0		0
Total assets accounted for at fair value		1,472,062		966,840
Liabilities:
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	[4]	0		0
Financial instruments sold, but not yet purchased	[5]			347
Other liabilities	[1]	0		0
Total liabilities accounted for at fair value		0		347
Recurring | Significant other observable inputs (Level 2)
ASSETS
Total investments available for sale		30,974,396		33,073,039
Cash equivalents	[2]	1,096,254		830,924
Other investments		493,874	[3]	490,058
Other assets	[1]	87,655		69,914
Total assets accounted for at fair value		34,351,554		35,860,721
Liabilities:
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	[4]	937,721		463,915
Financial instruments sold, but not yet purchased	[5]			0
Other liabilities	[1]	44,865		16,304
Total liabilities accounted for at fair value		982,586		480,219
Recurring | Significant other unobservable inputs (Level 3)
ASSETS
Total investments available for sale		46,066		152,278
Cash equivalents	[2]	0		0
Other investments		205,528	[3]	283,550
Other assets	[1]	19,841		19,400
Total assets accounted for at fair value		271,435		455,228
Liabilities:
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	[4]	0		0
Financial instruments sold, but not yet purchased	[5]			0
Other liabilities	[1]	19,839		29,191
Total liabilities accounted for at fair value		19,839		29,191
Exclude Life Funds Withheld Assets
ASSETS
Fixed maturities, AFS, at fair value		27,948,560		29,104,486
Equity securities, AFS, at fair value		1,037,331		878,919
Short-term investments, at fair value		625,193		617,390
Total investments available for sale		29,611,084		30,600,795
Exclude Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		3,894,388		5,065,637
Exclude Life Funds Withheld Assets | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		4,218,367		3,757,971
Exclude Life Funds Withheld Assets | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		274,258		328,540
Exclude Life Funds Withheld Assets | CMBS
ASSETS
Fixed maturities, AFS, at fair value		665,186		405,316
Exclude Life Funds Withheld Assets | Collateralized debt obligations ('CDO')
ASSETS
Fixed maturities, AFS, at fair value		377,491		32,410
Exclude Life Funds Withheld Assets | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		875,897		1,168,572
Exclude Life Funds Withheld Assets | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, AFS, at fair value		2,478,112		2,632,070
Exclude Life Funds Withheld Assets | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		5,030,132		5,251,614
Exclude Life Funds Withheld Assets | Recurring
ASSETS
Fixed maturities, AFS, at fair value		27,948,560		29,104,486
Equity securities, AFS, at fair value		1,037,331		878,919
Short-term investments, at fair value	[6]	625,193		617,390
Total investments available for sale		29,611,084		30,600,795
Exclude Life Funds Withheld Assets | Recurring | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		3,894,388		5,065,637
Exclude Life Funds Withheld Assets | Recurring | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		4,218,367		3,757,971
Exclude Life Funds Withheld Assets | Recurring | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		274,258		328,540
Exclude Life Funds Withheld Assets | Recurring | CMBS
ASSETS
Fixed maturities, AFS, at fair value		665,186		405,316
Exclude Life Funds Withheld Assets | Recurring | Collateralized debt obligations ('CDO')
ASSETS
Fixed maturities, AFS, at fair value		377,491		32,410
Exclude Life Funds Withheld Assets | Recurring | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		875,897		1,168,572
Exclude Life Funds Withheld Assets | Recurring | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, AFS, at fair value		2,478,112		2,632,070
Exclude Life Funds Withheld Assets | Recurring | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		5,030,132		5,251,614
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1)
ASSETS
Fixed maturities, AFS, at fair value		0		0
Equity securities, AFS, at fair value		898,664		528,581
Short-term investments, at fair value		0		0	[6]
Total investments available for sale		898,664		528,581
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Collateralized debt obligations ('CDO')
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2)
ASSETS
Fixed maturities, AFS, at fair value		27,902,494		28,952,208
Equity securities, AFS, at fair value		138,667		350,338
Short-term investments, at fair value	[6]	625,193		617,390
Total investments available for sale		28,666,354		29,919,936
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		3,869,637		5,020,574
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		4,218,367		3,754,894
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		274,258		328,540
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		665,087		405,316
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Collateralized debt obligations ('CDO')
ASSETS
Fixed maturities, AFS, at fair value		377,490		2
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		874,767		1,150,715
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, AFS, at fair value		2,478,112		2,632,070
Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		5,030,132		5,251,614
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3)
ASSETS
Fixed maturities, AFS, at fair value		46,066		152,278
Equity securities, AFS, at fair value		0		0
Short-term investments, at fair value		0		0	[6]
Total investments available for sale		46,066		152,278
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		24,751		45,063
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		0		3,077
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		99		0
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Collateralized debt obligations ('CDO')
ASSETS
Fixed maturities, AFS, at fair value		1		32,408
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		1,130		17,857
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, AFS, at fair value		0		0
Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		0		0
Life Funds Withheld Assets
ASSETS
Fixed maturities, AFS, at fair value		2,308,042		3,153,103
Fixed maturities, trading, at fair value		1,617,014		1,235,699
Short-term investments, at fair value		9,563		60,330
Total investments trading		1,626,577		1,296,029
Life Funds Withheld Assets | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		10,577		12,742
Fixed maturities, trading, at fair value		14,708		4,990
Life Funds Withheld Assets | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		613		752
Fixed maturities, trading, at fair value		852		368
Life Funds Withheld Assets | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		21,767		26,953
Fixed maturities, trading, at fair value		109
Life Funds Withheld Assets | CMBS
ASSETS
Fixed maturities, AFS, at fair value		94,240		122,481
Fixed maturities, trading, at fair value		5,526		4,803
Life Funds Withheld Assets | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		101,560		149,795
Fixed maturities, trading, at fair value		39,446		25,700
Life Funds Withheld Assets | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, trading, at fair value		224
Life Funds Withheld Assets | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		624,677		933,516
Fixed maturities, trading, at fair value		444,944		370,261
Life Funds Withheld Assets | Recurring
ASSETS
Fixed maturities, AFS, at fair value		2,308,042		3,153,103
Fixed maturities, trading, at fair value		1,617,014		1,235,699
Short-term investments, at fair value		9,563		60,330
Total investments trading		1,626,577		1,296,029
Cash equivalents		72,798		101,274	[2]
Life Funds Withheld Assets | Recurring | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		10,577		12,742
Fixed maturities, trading, at fair value		14,708		4,990
Life Funds Withheld Assets | Recurring | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		613		752
Fixed maturities, trading, at fair value		852		368
Life Funds Withheld Assets | Recurring | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		21,767		26,953
Fixed maturities, trading, at fair value		109
Life Funds Withheld Assets | Recurring | CMBS
ASSETS
Fixed maturities, AFS, at fair value		94,240		122,481
Fixed maturities, trading, at fair value		5,526		4,803
Life Funds Withheld Assets | Recurring | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		101,560		149,795
Fixed maturities, trading, at fair value		39,446		25,700
Life Funds Withheld Assets | Recurring | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, trading, at fair value		224
Life Funds Withheld Assets | Recurring | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		624,677		933,516
Fixed maturities, trading, at fair value		444,944		370,261
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1)
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Short-term investments, at fair value		0		0
Total investments trading		0		0
Cash equivalents		0		517	[2]
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, trading, at fair value		0
Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2)
ASSETS
Fixed maturities, AFS, at fair value		2,308,042		3,153,103
Fixed maturities, trading, at fair value		1,617,014		1,235,699
Short-term investments, at fair value		9,563		60,330
Total investments trading		1,626,577		1,296,029
Cash equivalents		72,798		100,757	[2]
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		10,577		12,742
Fixed maturities, trading, at fair value		14,708		4,990
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		613		752
Fixed maturities, trading, at fair value		852		368
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		21,767		26,953
Fixed maturities, trading, at fair value		109
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		94,240		122,481
Fixed maturities, trading, at fair value		5,526		4,803
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		101,560		149,795
Fixed maturities, trading, at fair value		39,446		25,700
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, trading, at fair value		224
Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		624,677		933,516
Fixed maturities, trading, at fair value		444,944		370,261
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3)
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Short-term investments, at fair value		0		0
Total investments trading		0		0
Cash equivalents		0		0	[2]
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | U.S. Government and Government - Related/Supported
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | RMBS - Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | RMBS - Non-Agency
ASSETS
Fixed maturities, AFS, at fair value		0		0	[5]
Fixed maturities, trading, at fair value		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | CMBS
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Other asset-backed securities
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | U.S. States and political subdivisions of the States
ASSETS
Fixed maturities, trading, at fair value		0
Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Non-U.S. Government
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Financial Services Sector | Exclude Life Funds Withheld Assets | Corporate
ASSETS
Fixed maturities, AFS, at fair value		3,622,290		3,561,909
Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Corporate
ASSETS
Fixed maturities, AFS, at fair value		3,622,290		3,561,909
Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		3,612,006		3,508,224
Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		10,284		53,685
Financial Services Sector | Life Funds Withheld Assets | Corporate
ASSETS
Fixed maturities, AFS, at fair value		439,267		598,236
Fixed maturities, trading, at fair value		468,175		335,956
Financial Services Sector | Life Funds Withheld Assets | Recurring | Corporate
ASSETS
Fixed maturities, AFS, at fair value		439,267		598,236
Fixed maturities, trading, at fair value		468,175		335,956
Financial Services Sector | Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Financial Services Sector | Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		439,267		598,236
Fixed maturities, trading, at fair value		468,175		335,956
Financial Services Sector | Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Non-Financial Services Sector | Exclude Life Funds Withheld Assets | Corporate
ASSETS
Fixed maturities, AFS, at fair value		6,512,439		6,900,447
Non-Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Corporate
ASSETS
Fixed maturities, AFS, at fair value		6,512,439		6,900,447
Non-Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Non-Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		6,502,638		6,900,259
Non-Financial Services Sector | Exclude Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		9,801		188
Non-Financial Services Sector | Life Funds Withheld Assets | Corporate
ASSETS
Fixed maturities, AFS, at fair value		1,015,341		1,308,628
Fixed maturities, trading, at fair value		643,030		493,621
Non-Financial Services Sector | Life Funds Withheld Assets | Recurring | Corporate
ASSETS
Fixed maturities, AFS, at fair value		1,015,341		1,308,628
Fixed maturities, trading, at fair value		643,030		493,621
Non-Financial Services Sector | Life Funds Withheld Assets | Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		0		0
Non-Financial Services Sector | Life Funds Withheld Assets | Recurring | Significant other observable inputs (Level 2) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		1,015,341		1,308,628
Fixed maturities, trading, at fair value		643,030		493,621
Non-Financial Services Sector | Life Funds Withheld Assets | Recurring | Significant other unobservable inputs (Level 3) | Corporate
ASSETS
Fixed maturities, AFS, at fair value		0		0
Fixed maturities, trading, at fair value		$ 0		$ 0
[1]	Other assets and other liabilities include derivative instruments. The derivative balances included in each category are reported on a gross basis by level with a netting adjustment presented separately in the Collateral and Counterparty Netting column. The fair values of the individual derivative contracts are reported gross in their respective levels based on the fair value hierarchy.
[2]	Cash equivalents balances subject to fair value measurement include certificates of deposit and money market funds. Operating cash balances are not subject to recurring fair value measurement guidance.
[3]	Other Investments balance excludes $322.9 million and $518.1 million as of December 31, 2016 and December 31, 2015, respectively, measured using Net Asset Value, based on new accounting guidance. In addition, the Other investments balance excludes a certain payment obligation. These investments, which totaled $142.3 million at December 31, 2016 and $141.3 million at December 31, 2015, are carried at amortized cost.
[4]	Funds withheld on life retrocession arrangements (net of future policy benefit reserves recoverable) include balances related to the life retrocession embedded derivative, under which all investment results associated with the Life Funds Withheld Assets related to the GreyCastle Life Retro Arrangements described in Note 2(g), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary", accrue to the benefit of GCLR.
[5]	Financial instruments sold, but not yet purchased, represent "short sales" and are included within "Payable for investments purchased" on the balance sheets.
[6]	Short-term investments consist primarily of Corporate securities and U.S. and Non-U.S. Government and Government-Related/ Supported securities.

Fair Value Measurements - Addit

Fair Value Measurements - Additional information about assets and liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015
Level 3 assets
Balance, beginning of period		$ 426,037		$ 876,369
Realized gains (losses)		16,035		7,063
Movement in unrealized gains (losses)		4,642		3,488
Purchases and issuances		51,102		279,869	[1]
Sales		(77,197)		(375,319)
Settlements		(83,224)		(349,808)
Net transfers into (out of) Level 3		(85,799)	[2]	(15,625)
Balance, end of period		251,596		426,037
Movement in total gains (losses) above relating to instruments still held at the reporting date		7,871		8,377
Level 3 liabilities
Balance, beginning of period		(9,791)		(9,764)
Realized gains (losses)		0		0
Movement in unrealized gains (losses)		9,793		(27)
Purchases and Issuances		0		0	[1]
Sales		0		0
Settlements		0		0
Net transfers into (out of) Level 3		0		0
Balance, end of period		2		(9,791)
Movement in total gains (losses) relating to investments still held		10		80
U.S. Government and Government - Related/Supported
Level 3 assets
Balance, beginning of period		45,063		0
Realized gains (losses)		264		0
Movement in unrealized gains (losses)		687		0
Purchases and issuances		0		35,044	[1]
Sales		(19,101)		0
Settlements		(2,162)		0
Net transfers into (out of) Level 3		0		10,019
Balance, end of period		24,751		45,063
Movement in total gains (losses) above relating to instruments still held at the reporting date		886		0
Corporate | Financial Services Sector
Level 3 assets
Balance, beginning of period		53,685		0
Realized gains (losses)		(2,991)		9
Movement in unrealized gains (losses)		10		(10)
Purchases and issuances		285		53,686	[1]
Sales		(30,420)		0
Settlements		0		0
Net transfers into (out of) Level 3		(10,285)		0
Balance, end of period		10,284		53,685
Movement in total gains (losses) above relating to instruments still held at the reporting date		31		(2)
Corporate | Non-Financial Services Sector
Level 3 assets
Balance, beginning of period		188		5,894
Realized gains (losses)		0		(186)
Movement in unrealized gains (losses)		13		(13)
Purchases and issuances		1,747		(123)	[1]
Sales		0		0
Settlements		(6)		(316)
Net transfers into (out of) Level 3		7,859		(5,068)
Balance, end of period		9,801		188
Movement in total gains (losses) above relating to instruments still held at the reporting date		14		(153)
RMBS - Agency
Level 3 assets
Balance, beginning of period		3,077		1,910
Realized gains (losses)		(3)		0
Movement in unrealized gains (losses)		7		(3)
Purchases and issuances		0		1,297	[1]
Sales		0		0
Settlements		(229)		(323)
Net transfers into (out of) Level 3		(2,852)		196	[2]
Balance, end of period		0		3,077
Movement in total gains (losses) above relating to instruments still held at the reporting date		0		(2)
CMBS
Level 3 assets
Balance, beginning of period		0
Realized gains (losses)		0
Movement in unrealized gains (losses)		(3)
Purchases and issuances		0
Sales		0
Settlements		0
Net transfers into (out of) Level 3		102
Balance, end of period		99		0
Movement in total gains (losses) above relating to instruments still held at the reporting date		(3)
Collateralized debt obligations ('CDO')
Level 3 assets
Balance, beginning of period		32,408		687,958
Realized gains (losses)		189		(8,658)
Movement in unrealized gains (losses)		6,870		16,688
Purchases and issuances		0		25,882	[1]
Sales		0		(366,633)
Settlements		(23,030)		(322,829)
Net transfers into (out of) Level 3		(16,436)		0
Balance, end of period		1		32,408
Movement in total gains (losses) above relating to instruments still held at the reporting date		6,152		5,279
Other asset-backed securities
Level 3 assets
Balance, beginning of period		17,857		5,288
Realized gains (losses)		479		628
Movement in unrealized gains (losses)		(2,113)		(599)
Purchases and issuances		1,072		46,940	[1]
Sales		0		(7,269)
Settlements		(14,190)		(6,359)
Net transfers into (out of) Level 3	[2]	(1,975)		(20,772)
Balance, end of period		1,130		17,857
Movement in total gains (losses) above relating to instruments still held at the reporting date		(1,673)		451
Other investments
Level 3 assets
Balance, beginning of period		283,550		185,083
Realized gains (losses)		18,097		15,270
Movement in unrealized gains (losses)		(10,622)		(12,548)
Purchases and issuances		47,998		117,143	[1]
Sales		(27,676)		(1,417)
Settlements		(43,607)		(19,981)
Net transfers into (out of) Level 3		(62,212)	[2]	0
Balance, end of period		205,528		283,550
Movement in total gains (losses) above relating to instruments still held at the reporting date		$ 2,454		$ 2,724
[1]	Includes assets acquired as result of the transaction described in Note 2(e), "Acquisitions and Disposals - Catlin Acquisition"
[2]	Net transfers include both movement in and movement out of Level 3. Corporate - Non-Financials securities for 2016 includes $9.7 million of incoming transfers partially offset by $1.9 million outgoing transfers. Other asset-backed securities for 2016 includes $5.0 million of outgoing transfers partially offset by $3.0 million of incoming transfers, and 2015 includes $34.1 million of outgoing transfers partially offset by $13.3 million of incoming transfers. Other investments for 2016 includes $77.7 million of outgoing transfers partially offset by $15.5 million of incoming transfers. RMBS-Agency for 2015 includes $3.1 million of incoming transfers partially offset by $2.9 million of outgoing transfers.

Fair Value Measurements - Finan

Fair Value Measurements - Financial instruments not carried at fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deposit liabilities	$ 1,116,233	$ 1,168,376
Notes payable and debt	2,647,677	2,644,970
Carrying Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Financial Assets - Other investments, structured transactions	142,271	141,329
Deposit liabilities	1,116,233	1,168,376
Notes payable and debt	2,647,677	2,644,970
Financial Liabilities	3,763,910	3,813,346
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Financial Assets - Other investments, structured transactions	153,173	154,065
Deposit liabilities	1,337,406	1,436,210
Notes payable and debt	2,813,257	2,805,152
Financial Liabilities	$ 4,150,663	$ 4,241,362

Fair Value Measurements - Narra

Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments Net Asset Value		$ 322,900	$ 518,100
Spread on US Treasury rate for determining discount rate for fair value of deposit liabilities		0.50%	0.265%
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments - structured transactions		$ 142,271	$ 141,329
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	[1]	(77,700)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[1]	15,500
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	[1]		(2,900)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[1]		3,100
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	[1]	(5,000)	(34,100)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	[1]	3,000	$ 13,300
Non-Financial Services Sector | Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3		(1,900)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3		$ 9,700
[1]	Net transfers include both movement in and movement out of Level 3. Corporate - Non-Financials securities for 2016 includes $9.7 million of incoming transfers partially offset by $1.9 million outgoing transfers. Other asset-backed securities for 2016 includes $5.0 million of outgoing transfers partially offset by $3.0 million of incoming transfers, and 2015 includes $34.1 million of outgoing transfers partially offset by $13.3 million of incoming transfers. Other investments for 2016 includes $77.7 million of outgoing transfers partially offset by $15.5 million of incoming transfers. RMBS-Agency for 2015 includes $3.1 million of incoming transfers partially offset by $2.9 million of outgoing transfers.

Goodwill and Other Intangibl103

Goodwill and Other Intangible Assets - Analysis of Goodwill and intangible assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, beginning of year	$ 1,213,630	$ 415,936	$ 396,245
Goodwill, acquired during period	14,084	807,381	25,159
Foreign currency translation, goodwill	(14,190)	(9,687)	(5,468)
Goodwill, end of year	1,213,524	1,213,630	415,936
Intangible assets with an indefinite life, beginning of year	682,859	15,366	15,366
Indefinite-lived Intangible Assets Acquired	8,000	673,000	0
Foreign currency translation, indefinite-lived intangible assets	(8,080)	(5,507)
Intangible assets with an indefinite life, end of year	682,779	682,859	15,366
Intangible assets with a definite life, beginning of year	313,777	16,650	0
Finite-lived Intangible Assets Acquired	28,948	315,000	18,500
Amortization	(22,422)	(15,517)	(1,850)
Foreign currency translation, intangible assets with an definite life	(12,953)	(2,356)
Intangible assets with a definite life, end of year	307,350	313,777	16,650
Goodwill and other intangible assets, beginning of year	2,210,266	447,952	411,611
Additions	51,032	1,795,381	43,659
Foreign currency translation, intangible assets including goodwill	(35,223)	(17,550)	(5,468)
Goodwill and other intangible assets, end of year	$ 2,203,653	$ 2,210,266	$ 447,952

Goodwill and Other Intangibl104

Goodwill and Other Intangible Assets - Estimated future amortization (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2,017	$ 21,957
2,018	20,291
2,019	20,041
2,020	19,957
2,021	19,957
2022-2037	205,147
Total expected amortization expense	$ 307,350	$ 313,777	$ 16,650	$ 0

Goodwill and Other Intangibl105

Goodwill and Other Intangible Assets - Intangible Assets Acquired - Catlin (Details) - USD ($) $ in Thousands	May 01, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 8,000	$ 673,000	$ 0
Finite-lived Intangible Assets Acquired		$ 28,948	$ 315,000	$ 18,500
Catlin Group Limited [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 673,000
Finite-lived Intangible Assets Acquired	315,000
Intangible Assets Acquired	988,000
Catlin Group Limited [Member] | Trademarks and Trade Names [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Finite-lived Intangible Assets Acquired	10,000
Finite-Lived Intangible Asset, Useful Life		2 years
Catlin Group Limited [Member] | Distribution Rights [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Finite-lived Intangible Assets Acquired	290,000
Finite-Lived Intangible Asset, Useful Life		20 years
Catlin Group Limited [Member] | Managing Agent Contracts [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Finite-lived Intangible Assets Acquired	15,000
Finite-Lived Intangible Asset, Useful Life		15 years
Insurance Licenses [Member] | Catlin Group Limited [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Indefinite-lived Intangible Assets Acquired	13,000
Syndicate Capacity [Member] | Catlin Group Limited [Member]
Schedule Of Acquired Intangible Assets By Major Class [Line Items]
Indefinite-lived Intangible Assets Acquired	$ 660,000

Goodwill and Other Intangibl106

Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Feb. 01, 2016	Jul. 24, 2015	May 01, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross						$ 347,200	$ 333,500
Finite-Lived Intangible Assets, Accumulated Amortization						39,800	17,400
Finite-lived Intangible Assets Acquired						28,948	315,000	$ 18,500
Indefinite-lived Intangible Assets Acquired						8,000	673,000	0
Goodwill						1,213,524	1,213,630	415,936	$ 396,245
Goodwill, acquired during period						14,084	807,381	25,159
Gross goodwill						2,600,000	2,600,000
Accumulated impairment loss on goodwill						1,400,000	1,400,000
Indefinite-Lived Intangible Assets (Excluding Goodwill)						682,779	682,859	$ 15,366	$ 15,366
Insurance Segment
Goodwill [Line Items]
Goodwill						483,600	479,500
Reinsurance Segment
Goodwill [Line Items]
Goodwill						$ 730,000	$ 734,200
Allied International Holdings, Inc.
Goodwill [Line Items]
Finite-lived Intangible Assets Acquired			$ 6,000
Indefinite-lived Intangible Assets Acquired			8,000
Goodwill, acquired during period			14,100
Allied International Holdings, Inc. | Insurance Segment
Goodwill [Line Items]
Goodwill, acquired during period			$ 14,100
Catlin Group Limited [Member]
Goodwill [Line Items]
Finite-lived Intangible Assets Acquired					$ 315,000
Indefinite-lived Intangible Assets Acquired					673,000
Goodwill, acquired during period	[1]				793,990
Catlin Group Limited [Member] | Insurance Segment
Goodwill [Line Items]
Goodwill, acquired during period	[1]				466,100
Catlin Group Limited [Member] | Reinsurance Segment
Goodwill [Line Items]
Goodwill, acquired during period	[1]				$ 327,900
New Energy Risk Inc. [Member]
Goodwill [Line Items]
Goodwill, acquired during period				$ 13,400
Brooklyn Underwriting Pty Limited and Brooklyn IT Pty Limited [Member]
Goodwill [Line Items]
Finite-lived Intangible Assets Acquired		$ 22,900
[1]	ncludes an increase of $15.9 million to goodwill from the amount initially recorded at June 30, 2015, as a result of several tax-related adjustments, including a decrease in other assets of $7.5 million, a decrease in deferred tax liability of $11.3 million, and an increase in other liabilities of $19.8 million.

Losses and Loss Expenses - Loss

Losses and Loss Expenses - Loss Reserve Rollforward and Components of Net Losses and Loss Expenses (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid losses and loss expenses at beginning of year		$ 25,439,744	$ 19,353,243	$ 20,481,065
Unpaid losses and loss expenses recoverable, beginning of year		5,262,706
Net unpaid losses and loss expenses at beginning of year		20,190,839	15,941,715	17,066,330
Increase (decrease) in net losses and loss expenses incurred in respect of losses occurring in:
Current year		6,374,377	5,072,830	3,513,465
Prior year development		(301,542)	(306,630)	(255,072)
Total net incurred losses and loss expenses		6,072,835	4,766,200	3,258,393
Loss and loss expense reserves acquired in business combination		101,315	5,439,876	0
Exchange rate effects		(571,198)	(582,300)	(561,673)
Less net losses and loss expenses paid in respect of losses occurring in:
Current year		1,444,251	1,047,277	381,008
Prior years		3,890,269	4,327,375	3,440,327
Total net paid losses		5,334,520	5,374,652	3,821,335
Net unpaid losses and loss expenses at end of year		20,459,271	20,190,839	15,941,715
Unpaid losses and loss expenses recoverable, end of year		5,491,297	5,262,706
Unpaid losses and loss expenses at end of year		25,939,571	25,439,744	19,353,243
Reserve for reported losses and loss expenses		10,343,481	10,293,448
Reserve for losses incurred but not reported		15,596,090	15,146,296
Property and casualty operations
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Unpaid losses and loss expenses recoverable, beginning of year	[1]	5,248,905	3,411,528	3,414,735
Less net losses and loss expenses paid in respect of losses occurring in:
Unpaid losses and loss expenses recoverable, end of year	[1]	$ 5,480,300	$ 5,248,905	$ 3,411,528
[1]	Property and Casualty business only.

Losses and Loss Expenses - Rese

Losses and Loss Expenses - Reserving Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)classes	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Claims Development [Line Items]
Loss exposure classes | classes	250
Loss and loss expense reserves acquired in business combination | $	$ 101,315	$ 5,439,876	$ 0
Minimum
Claims Development [Line Items]
High layer excess casualty settlement period	5 years
Minimum | Property and other short-tail lines
Claims Development [Line Items]
Claims Reported Period	2 years
Minimum | Casualty and Other Long-Tail Lines
Claims Development [Line Items]
Claims Reported Period	3 years
Maximum
Claims Development [Line Items]
High layer excess casualty settlement period	15 years
Maximum | Property and other short-tail lines
Claims Development [Line Items]
Claims Reported Period	3 years
Maximum | Casualty and Other Long-Tail Lines
Claims Development [Line Items]
Claims Reported Period	20 years

Losses and Loss Expenses - Info

Losses and Loss Expenses - Information about incurred and paid claims development (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	$ 521,083
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	$ 788,760
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	$ 638,179
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	$ 840,030
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	$ 1,246,596
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	$ 952,158
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	$ 976,023
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	$ 957,525
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	$ 970,277
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,192,137
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I110

Losses and Loss Expenses - Information about incurred and paid claims development - Insurance (Details) $ in Thousands		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	$ 367,171
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	$ 461,606
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	$ 462,090
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	$ 607,658
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	$ 649,690
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	$ 634,043
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	$ 657,753
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	$ 669,745
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	$ 691,253
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I111

Losses and Loss Expenses - Information about incurred and paid claims development - Insurance - Professional (Details) $ in Thousands		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		9,795,663
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,984,309
All outstanding liabilities prior to 2007, net of reinsurance		140,029
Liabilities for unpaid losses and loss expenses, net of reinsurance		3,951,383
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	367,171
Accident Year 2007 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		928,677	944,024	1,000,256	993,007	995,364	1,070,028	1,061,995	1,106,630	1,130,926	911,695
IBNR (1)	[1]	$ 68,144
Number of Claims | Claim		4,371
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 801,141	776,445	738,301	692,492	612,498	540,255	421,654	240,287	111,289	$ 25,207
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	461,606
Accident Year 2008 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,114,924	1,136,720	1,167,289	1,174,486	1,195,931	1,221,906	1,131,685	1,087,436	1,033,982
IBNR (1)	[1]	$ 60,568
Number of Claims | Claim		5,187
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 969,698	911,634	853,405	782,381	697,071	516,426	346,923	185,149	$ 17,987
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	462,090
Accident Year 2009 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,164,825	1,169,232	1,202,994	1,196,078	1,158,091	1,094,824	1,036,140	968,336
IBNR (1)	[1]	$ 77,399
Number of Claims | Claim		5,589
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 948,015	922,453	838,990	745,836	507,629	337,568	161,125	$ 22,350
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	607,658
Accident Year 2010 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,061,340	1,016,013	996,024	1,035,571	957,486	984,780	989,432
IBNR (1)	[1]	$ 113,635
Number of Claims | Claim		5,418
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 803,916	735,626	623,975	480,475	324,580	155,845	$ 21,803
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	649,690
Accident Year 2011 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,111,524	1,104,107	1,027,504	1,012,458	960,895	967,386
IBNR (1)	[1]	$ 162,147
Number of Claims | Claim		5,253
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 815,129	683,043	480,248	315,130	144,365	$ 28,625
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	634,043
Accident Year 2012 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,117,970	1,124,437	1,011,363	976,593	976,450
IBNR (1)	[1]	$ 212,997
Number of Claims | Claim		5,320
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 713,165	591,820	378,059	195,088	$ 44,486
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	657,753
Accident Year 2013 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		922,634	942,022	963,634	965,875
IBNR (1)	[1]	$ 339,380
Number of Claims | Claim		5,595
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 457,890	304,503	152,052	$ 36,582
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	669,745
Accident Year 2014 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		843,003	799,952	747,671
IBNR (1)	[1]	$ 371,270
Number of Claims | Claim		5,969
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 312,548	138,832	$ 17,042
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	691,253
Accident Year 2015 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		800,568	755,087
IBNR (1)	[1]	$ 493,667
Number of Claims | Claim		6,391
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 139,345	$ 22,521
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
Accident Year 2016 | Professional lines | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		730,198
IBNR (1)	[1]	$ 654,395
Number of Claims | Claim		3,704
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 23,462
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I112

Losses and Loss Expenses - Information about incurred and paid claims development - Insurance - Casualty (Details) $ in Thousands		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		12,501,951
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		6,913,174
All outstanding liabilities prior to 2007, net of reinsurance		765,300
Liabilities for unpaid losses and loss expenses, net of reinsurance		6,354,077
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	367,171
Accident Year 2007 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,162,152	1,171,058	1,179,115	1,163,024	1,159,030	1,175,846	1,166,693	1,087,608	1,112,540	1,082,033
IBNR (1)	[1]	$ 85,633
Number of Claims | Claim		17,237
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,011,066	993,114	961,739	917,798	855,446	751,437	470,594	315,942	142,855	$ 22,680
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	461,606
Accident Year 2008 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,078,619	1,085,898	1,102,780	1,105,909	1,093,984	1,106,258	1,112,589	1,112,464	1,140,247
IBNR (1)	[1]	$ 111,716
Number of Claims | Claim		18,669
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 898,297	886,979	843,167	771,029	673,130	557,222	384,593	175,724	$ 46,589
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	462,090
Accident Year 2009 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,041,605	1,048,630	1,089,350	1,064,751	1,083,830	1,089,006	1,101,930	1,116,831
IBNR (1)	[1]	$ 104,475
Number of Claims | Claim		20,836
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 818,732	771,855	727,782	638,617	535,197	414,586	237,264	$ 43,912
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	607,658
Accident Year 2010 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,230,374	1,233,729	1,276,555	1,253,471	1,258,380	1,250,384	1,112,521
IBNR (1)	[1]	$ 193,273
Number of Claims | Claim		23,029
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 937,451	862,584	759,673	649,167	516,383	292,403	$ 101,673
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	649,690
Accident Year 2011 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,138,849	1,160,467	1,134,783	1,160,676	1,139,829	1,092,125
IBNR (1)	[1]	$ 175,768
Number of Claims | Claim		24,942
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 818,838	748,537	594,047	418,204	258,861	$ 115,807
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	634,043
Accident Year 2012 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,217,096	1,258,868	1,235,541	1,212,625	1,195,390
IBNR (1)	[1]	$ 229,162
Number of Claims | Claim		26,613
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 775,521	644,936	471,949	297,186	$ 117,735
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	657,753
Accident Year 2013 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,375,254	1,403,279	1,344,357	1,295,006
IBNR (1)	[1]	$ 407,549
Number of Claims | Claim		29,179
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 710,905	533,465	307,950	$ 124,226
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	669,745
Accident Year 2014 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,463,809	1,417,460	1,351,268
IBNR (1)	[1]	$ 607,888
Number of Claims | Claim		30,254
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 555,967	335,216	$ 133,592
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	691,253
Accident Year 2015 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,399,039	1,335,856
IBNR (1)	[1]	$ 722,174
Number of Claims | Claim		31,862
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 282,670	$ 109,217
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
Accident Year 2016 | Casualty and other | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,395,154
IBNR (1)	[1]	$ 1,088,868
Number of Claims | Claim		18,283
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 103,727
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I113

Losses and Loss Expenses - Information about incurred and paid claims development - Insurance - EPC (Details) $ in Thousands		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,691,915
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,480,891
All outstanding liabilities prior to 2007, net of reinsurance		24,692
Liabilities for unpaid losses and loss expenses, net of reinsurance		1,235,716
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	367,171
Accident Year 2007 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		355,709	356,106	357,009	358,820	361,632	364,454	365,395	385,373	394,730	439,938
IBNR (1)		$ (213)
Number of Claims | Claim		5,380
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 351,151	350,602	348,059	347,421	341,442	329,883	316,321	298,622	208,210	$ 69,288
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	461,606
Accident Year 2008 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		767,031	768,610	774,108	769,906	777,476	782,005	806,976	834,562	841,913
IBNR (1)		$ 10,701
Number of Claims | Claim		9,013
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 750,022	747,374	752,294	748,607	730,513	653,749	604,163	467,537	$ 152,946
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	462,090
Accident Year 2009 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		342,072	344,108	345,668	349,819	356,069	364,526	382,644	400,045
IBNR (1)		$ 6,549
Number of Claims | Claim		7,596
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 331,246	328,222	313,434	311,335	287,809	254,420	190,194	$ 84,638
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	607,658
Accident Year 2010 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		568,574	574,091	565,494	571,375	589,119	611,917	596,340
IBNR (1)		$ (5,681)
Number of Claims | Claim		8,532
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 547,486	542,011	543,985	526,375	476,832	380,649	$ 166,353
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	649,690
Accident Year 2011 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		842,481	846,315	857,510	890,820	911,684	979,353
IBNR (1)		$ 7,165
Number of Claims | Claim		10,172
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 815,694	813,298	784,418	744,330	610,086	$ 211,176
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	634,043
Accident Year 2012 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		626,132	636,896	635,712	660,128	689,032
IBNR (1)		$ 6,086
Number of Claims | Claim		11,131
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 593,981	574,467	531,299	389,827	$ 161,117
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	657,753
Accident Year 2013 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		684,578	690,102	715,909	740,573
IBNR (1)		$ 9,763
Number of Claims | Claim		12,141
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 636,623	586,539	452,805	$ 165,460
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	669,745
Accident Year 2014 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		723,382	735,789	703,860
IBNR (1)	[1]	$ 6,921
Number of Claims | Claim		14,609
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 645,682	504,925	$ 180,735
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	691,253
Accident Year 2015 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		812,247	791,724
IBNR (1)		$ 64,949
Number of Claims | Claim		16,424
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 484,431	$ 224,497
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
Accident Year 2016 | EPC | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		969,709
IBNR (1)		$ 228,630
Number of Claims | Claim		15,279
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 324,575
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I114

Losses and Loss Expenses - Information about incurred and paid claims development - Insurance - Specialty (Details) $ in Thousands		Dec. 31, 2016USD ($)Claim	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)	Dec. 31, 2010USD ($)	Dec. 31, 2009USD ($)	Dec. 31, 2008USD ($)	Dec. 31, 2007USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		38,032,090
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		25,758,860
All outstanding liabilities prior to 2007, net of reinsurance		1,069,908
Liabilities for unpaid losses and loss expenses, net of reinsurance		13,343,138
Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		9,042,561
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		7,380,486
All outstanding liabilities prior to 2007, net of reinsurance		139,887
Liabilities for unpaid losses and loss expenses, net of reinsurance		1,801,962
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,246,355	3,274,775	3,318,423	3,317,676	3,329,848	3,442,331	3,431,600	3,426,696	3,490,955	3,258,668
IBNR (1)	[1]	$ 158,351
Number of Claims | Claim		45,542
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,943,144	2,896,977	2,822,610	2,715,861	2,549,256	2,333,047	1,884,318	1,462,857	930,428	367,171
Accident Year 2007 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		799,817	803,587	782,043	802,825	813,822	832,003	837,517	847,085	852,759	825,002
IBNR (1)		$ 4,787
Number of Claims | Claim		18,554
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 779,786	776,816	774,511	758,150	739,870	711,472	675,749	608,006	468,074	$ 249,996
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,786,671	3,822,133	3,857,758	3,889,538	3,918,450	3,974,071	3,935,499	3,969,259	3,891,682
IBNR (1)	[1]	$ 186,723
Number of Claims | Claim		54,952
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,415,212	3,337,607	3,234,869	3,069,812	2,843,188	2,427,033	1,973,577	1,339,577	461,606
Accident Year 2008 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		826,097	830,905	813,581	839,237	851,059	863,902	884,249	934,797	875,540
IBNR (1)	[1]	$ 3,738
Number of Claims | Claim		22,083
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 797,195	791,620	786,003	767,795	742,474	699,636	637,898	511,167	$ 244,084
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,346,817	3,369,614	3,500,575	3,483,027	3,480,715	3,458,320	3,499,124	3,472,222
IBNR (1)	[1]	$ 190,193
Number of Claims | Claim		54,896
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,865,558	2,787,167	2,634,783	2,432,021	2,043,196	1,666,673	1,140,796	462,090
Accident Year 2009 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		798,315	807,644	862,563	872,379	882,725	909,964	978,410	987,010
IBNR (1)		$ 1,770
Number of Claims | Claim		20,875
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 767,565	764,637	754,577	736,233	712,561	660,099	552,213	$ 311,190
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,697,761	3,661,919	3,688,045	3,735,809	3,699,234	3,809,102	3,702,458
IBNR (1)	[1]	$ 313,815
Number of Claims | Claim		61,416
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,072,546	2,914,856	2,685,015	2,370,062	1,978,027	1,377,513	607,658
Accident Year 2010 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		837,473	838,086	849,972	875,392	894,249	962,021	1,004,165
IBNR (1)		$ 12,588
Number of Claims | Claim		24,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 783,693	774,635	757,382	714,045	660,232	548,616	$ 317,829
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,001,271	4,026,511	3,921,559	4,009,166	3,986,420	4,014,389
IBNR (1)	[1]	$ 379,349
Number of Claims | Claim		65,437
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 3,290,213	3,062,399	2,653,619	2,216,640	1,617,155	649,690
Accident Year 2011 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		908,417	915,622	901,762	945,212	974,012	975,525
IBNR (1)		$ 34,269
Number of Claims | Claim		25,070
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 840,552	817,521	794,906	738,976	603,843	$ 294,082
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,851,259	3,921,415	3,800,046	3,799,876	3,870,871
IBNR (1)	[1]	$ 468,002
Number of Claims | Claim		70,919
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,886,674	2,578,639	2,079,400	1,471,761	634,043
Accident Year 2012 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		890,061	901,214	917,430	950,530	1,009,999
IBNR (1)	[1]	$ 19,757
Number of Claims | Claim		27,855
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 804,007	767,416	698,093	589,660	$ 310,705
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,924,048	3,978,956	4,003,359	3,942,360
IBNR (1)	[1]	$ 802,611
Number of Claims | Claim		78,018
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,597,422	2,141,332	1,509,232	657,753
Accident Year 2013 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		941,582	943,553	979,459	940,906
IBNR (1)		$ 45,919
Number of Claims | Claim		31,103
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 792,004	716,825	596,425	$ 331,485
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		3,978,436	3,917,364	3,748,154
IBNR (1)	[1]	$ 1,052,314
Number of Claims | Claim		87,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 2,263,643	1,597,123	669,745
Accident Year 2014 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		948,242	964,163	945,355
IBNR (1)		$ 66,235
Number of Claims | Claim		36,659
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 749,446	618,150	$ 338,376
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,039,203	3,849,731
IBNR (1)	[1]	$ 1,418,476
Number of Claims | Claim		94,229
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 1,563,019	691,253
Accident Year 2015 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,027,349	967,064
IBNR (1)		$ 137,686
Number of Claims | Claim		39,552
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 656,573	$ 335,018
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,160,269
IBNR (1)	[1]	$ 2,358,172
Number of Claims | Claim		65,684
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 861,429
Accident Year 2016 | Specialty | Insurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,065,208
IBNR (1)		$ 386,279
Number of Claims | Claim		28,418
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 409,665
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I115

Losses and Loss Expenses - Information about incurred and paid claims development - Reinsurance (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		15,130,780
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		9,853,346
All outstanding liabilities prior to 2007, net of reinsurance		1,431,871
Liabilities for unpaid losses and loss expenses, net of reinsurance		6,709,305
Accident Year 2007
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,144,626	1,157,375	1,201,176	1,224,302	1,239,171	1,246,925	1,252,940	1,292,265	1,315,895	1,373,989
IBNR (1)	[1]	88,476
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		951,136	925,230	922,262	897,073	848,114	793,787	703,600	592,431	359,533	$ 153,912
Accident Year 2008
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,535,533	1,535,515	1,559,314	1,559,826	1,561,457	1,550,254	1,567,923	1,605,756	1,613,114
IBNR (1)	[1]	121,015
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,285,355	1,244,802	1,216,006	1,170,828	1,104,015	1,019,382	883,897	654,658	$ 327,154
Accident Year 2009
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,046,087	1,052,553	1,049,967	1,067,335	1,076,187	1,084,088	1,128,445	1,150,325
IBNR (1)	[1]	127,390
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		797,666	764,307	732,134	685,901	611,967	526,118	389,499	$ 176,089
Accident Year 2010
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,284,178	1,295,555	1,286,737	1,290,292	1,302,827	1,302,532	1,280,586
IBNR (1)	[1]	150,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,011,698	936,971	836,148	774,216	667,841	477,894	$ 232,372
Accident Year 2011
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		2,082,525	2,089,535	2,059,076	2,102,613	2,201,054	2,222,386
IBNR (1)	[1]	178,659
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,730,787	1,675,428	1,588,434	1,448,330	1,255,164	$ 596,906
Accident Year 2012
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,812,667	1,832,972	1,840,530	1,860,740	1,827,087
IBNR (1)	[1]	247,825
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,313,092	1,223,403	1,070,442	785,212	$ 318,115
Accident Year 2013
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,502,096	1,544,739	1,551,432	1,615,956
IBNR (1)	[1]	279,880
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,016,654	908,575	685,680	$ 318,270
Accident Year 2014
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,418,828	1,452,029	1,434,902
IBNR (1)	[1]	344,569
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		826,700	653,323	$ 287,780
Accident Year 2015
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,459,003	1,504,763
IBNR (1)	[1]	543,530
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		589,550	$ 279,024
Accident Year 2016
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,845,237
IBNR (1)	[1]	1,067,346
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 330,708
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I116

Losses and Loss Expenses - Information about incurred and paid claims development - Reinsurance - Property and Other Short-Tail LInes (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		15,130,780
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		9,853,346
All outstanding liabilities prior to 2007, net of reinsurance		1,431,871
Liabilities for unpaid losses and loss expenses, net of reinsurance		6,709,305
Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		9,228,576
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		7,315,241
All outstanding liabilities prior to 2007, net of reinsurance		287,838
Liabilities for unpaid losses and loss expenses, net of reinsurance		2,201,173
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,144,626	1,157,375	1,201,176	1,224,302	1,239,171	1,246,925	1,252,940	1,292,265	1,315,895	1,373,989
IBNR (1)	[1]	88,476
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		951,136	925,230	922,262	897,073	848,114	793,787	703,600	592,431	359,533	153,912
Accident Year 2007 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		504,777	505,908	531,757	542,517	543,586	556,160	576,823	591,325	612,847	655,785
IBNR (1)	[1]	9,948
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		483,023	478,062	497,701	503,233	491,862	487,471	470,765	427,810	274,682	$ 128,299
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,535,533	1,535,515	1,559,314	1,559,826	1,561,457	1,550,254	1,567,923	1,605,756	1,613,114
IBNR (1)	[1]	121,015
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,285,355	1,244,802	1,216,006	1,170,828	1,104,015	1,019,382	883,897	654,658	327,154
Accident Year 2008 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		856,596	849,351	855,891	851,340	855,385	870,757	893,143	913,108	922,391
IBNR (1)	[1]	22,281
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		816,877	803,919	805,951	801,027	784,005	757,091	693,174	541,613	$ 291,995
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,046,087	1,052,553	1,049,967	1,067,335	1,076,187	1,084,088	1,128,445	1,150,325
IBNR (1)	[1]	127,390
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		797,666	764,307	732,134	685,901	611,967	526,118	389,499	176,089
Accident Year 2009 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		472,758	468,240	474,526	479,539	488,419	507,488	541,926	574,748
IBNR (1)	[1]	4,958
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		453,626	445,861	445,905	441,032	421,579	389,835	307,294	$ 145,413
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,284,178	1,295,555	1,286,737	1,290,292	1,302,827	1,302,532	1,280,586
IBNR (1)	[1]	150,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,011,698	936,971	836,148	774,216	667,841	477,894	232,372
Accident Year 2010 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		840,582	840,206	857,788	852,550	846,563	842,728	821,119
IBNR (1)	[1]	26,847
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		783,155	734,453	665,932	639,012	577,128	429,578	$ 215,463
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		2,082,525	2,089,535	2,059,076	2,102,613	2,201,054	2,222,386
IBNR (1)	[1]	178,659
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,730,787	1,675,428	1,588,434	1,448,330	1,255,164	596,906
Accident Year 2011 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,585,694	1,593,064	1,589,207	1,617,499	1,697,826	1,728,879
IBNR (1)	[1]	42,172
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,493,813	1,472,992	1,432,899	1,344,405	1,196,404	$ 581,324
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,812,667	1,832,972	1,840,530	1,860,740	1,827,087
IBNR (1)	[1]	247,825
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,313,092	1,223,403	1,070,442	785,212	318,115
Accident Year 2012 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,243,866	1,255,565	1,285,569	1,294,768	1,268,108
IBNR (1)	[1]	69,188
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,068,475	1,028,319	933,717	713,154	$ 293,705
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,502,096	1,544,739	1,551,432	1,615,956
IBNR (1)	[1]	279,880
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,016,654	908,575	685,680	318,270
Accident Year 2013 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		939,295	975,565	1,011,548	1,068,975
IBNR (1)	[1]	45,977
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		819,523	768,385	604,497	$ 291,534
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,418,828	1,452,029	1,434,902
IBNR (1)	[1]	344,569
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		826,700	653,323	287,780
Accident Year 2014 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		814,558	855,081	865,668
IBNR (1)	[1]	57,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		658,511	556,548	$ 250,708
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,459,003	1,504,763
IBNR (1)	[1]	543,530
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		589,550	279,024
Accident Year 2015 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		829,691	878,711
IBNR (1)	[1]	163,854
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		472,543	$ 236,009
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,845,237
IBNR (1)	[1]	1,067,346
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		330,708
Accident Year 2016 | Property and other short-tail lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,140,759
IBNR (1)	[1]	531,843
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 265,695
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I117

Losses and Loss Expenses - Information about incurred and paid claims development - Reinsurance - Casualty and Other Long-Tail Lines (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		$ 53,162,870
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		35,612,206
All outstanding liabilities prior to 2007, net of reinsurance		2,501,779
Liabilities for unpaid losses and loss expenses, net of reinsurance		20,052,443
Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		15,130,780
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		9,853,346
All outstanding liabilities prior to 2007, net of reinsurance		1,431,871
Liabilities for unpaid losses and loss expenses, net of reinsurance		6,709,305
Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,902,204
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,538,105
All outstanding liabilities prior to 2007, net of reinsurance		1,144,033
Liabilities for unpaid losses and loss expenses, net of reinsurance		4,508,132
Accident Year 2007
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,390,981	$ 4,432,150	$ 4,519,599	$ 4,541,978	$ 4,569,019	$ 4,689,256	$ 4,684,540	$ 4,718,961	$ 4,806,850	$ 4,632,657
IBNR (1)	[1]	246,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,894,280	3,822,207	3,744,872	3,612,934	3,397,370	3,126,834	2,587,918	2,055,288	1,289,961	521,083
Accident Year 2007 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,144,626	1,157,375	1,201,176	1,224,302	1,239,171	1,246,925	1,252,940	1,292,265	1,315,895	1,373,989
IBNR (1)	[1]	88,476
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		951,136	925,230	922,262	897,073	848,114	793,787	703,600	592,431	359,533	153,912
Accident Year 2007 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		639,849	651,467	669,419	681,785	695,585	690,765	676,117	700,940	703,048	718,204
IBNR (1)	[1]	78,528
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		468,113	447,168	424,561	393,840	356,252	306,316	232,835	164,621	84,851	$ 25,613
Accident Year 2008
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,322,204	5,357,648	5,417,072	5,449,364	5,479,907	5,524,325	5,503,422	5,575,015	5,504,796
IBNR (1)	[1]	307,738
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,700,567	4,582,409	4,450,875	4,240,640	3,947,203	3,446,415	2,857,474	1,994,235	788,760
Accident Year 2008 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,535,533	1,535,515	1,559,314	1,559,826	1,561,457	1,550,254	1,567,923	1,605,756	1,613,114
IBNR (1)	[1]	121,015
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,285,355	1,244,802	1,216,006	1,170,828	1,104,015	1,019,382	883,897	654,658	327,154
Accident Year 2008 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		678,937	686,164	703,423	708,486	706,072	679,497	674,780	692,648	690,723
IBNR (1)	[1]	98,734
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		468,478	440,883	410,055	369,801	320,010	262,291	190,723	113,045	$ 35,159
Accident Year 2009
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,392,904	4,422,167	4,550,542	4,550,362	4,556,902	4,542,408	4,627,569	4,622,547
IBNR (1)	[1]	317,583
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,663,224	3,551,474	3,366,917	3,117,922	2,655,163	2,192,791	1,530,295	638,179
Accident Year 2009 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,046,087	1,052,553	1,049,967	1,067,335	1,076,187	1,084,088	1,128,445	1,150,325
IBNR (1)	[1]	127,390
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		797,666	764,307	732,134	685,901	611,967	526,118	389,499	176,089
Accident Year 2009 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		573,329	584,313	575,441	587,796	587,768	576,600	586,519	575,577
IBNR (1)	[1]	122,432
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		344,040	318,446	286,229	244,869	190,388	136,283	82,205	$ 30,676
Accident Year 2010
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		4,981,939	4,957,474	4,974,782	5,026,101	5,002,061	5,111,634	4,983,044
IBNR (1)	[1]	464,306
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,084,244	3,851,827	3,521,163	3,144,278	2,645,868	1,855,407	840,030
Accident Year 2010 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,284,178	1,295,555	1,286,737	1,290,292	1,302,827	1,302,532	1,280,586
IBNR (1)	[1]	150,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,011,698	936,971	836,148	774,216	667,841	477,894	232,372
Accident Year 2010 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		443,596	455,349	428,949	437,742	456,264	459,804	459,467
IBNR (1)	[1]	123,644
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		228,543	202,518	170,216	135,204	90,713	48,316	$ 16,909
Accident Year 2011
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,083,796	6,116,046	5,980,635	6,111,779	6,187,474	6,236,775
IBNR (1)	[1]	558,008
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		5,021,000	4,737,827	4,242,053	3,664,970	2,872,319	1,246,596
Accident Year 2011 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		2,082,525	2,089,535	2,059,076	2,102,613	2,201,054	2,222,386
IBNR (1)	[1]	178,659
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,730,787	1,675,428	1,588,434	1,448,330	1,255,164	596,906
Accident Year 2011 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		496,831	496,471	469,869	485,114	503,228	493,507
IBNR (1)	[1]	136,487
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		236,974	202,436	155,535	103,925	58,760	$ 15,582
Accident Year 2012
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,663,926	5,754,387	5,640,576	5,660,616	5,697,958
IBNR (1)	[1]	715,827
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		4,199,766	3,802,042	3,149,842	2,256,973	952,158
Accident Year 2012 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,812,667	1,832,972	1,840,530	1,860,740	1,827,087
IBNR (1)	[1]	247,825
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,313,092	1,223,403	1,070,442	785,212	318,115
Accident Year 2012 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		568,801	577,407	554,961	565,972	558,979
IBNR (1)	[1]	178,637
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		244,617	195,084	136,725	72,058	$ 24,410
Accident Year 2013
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,426,144	5,523,695	5,554,791	5,558,316
IBNR (1)	[1]	1,082,491
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,614,076	3,049,907	2,194,912	976,023
Accident Year 2013 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,502,096	1,544,739	1,551,432	1,615,956
IBNR (1)	[1]	279,880
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,016,654	908,575	685,680	318,270
Accident Year 2013 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		562,801	569,174	539,884	546,981
IBNR (1)	[1]	233,903
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		197,131	140,190	81,183	$ 26,736
Accident Year 2014
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,397,264	5,369,393	5,183,056
IBNR (1)	[1]	1,396,883
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		3,090,343	2,250,446	957,525
Accident Year 2014 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,418,828	1,452,029	1,434,902
IBNR (1)	[1]	344,569
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		826,700	653,323	287,780
Accident Year 2014 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		604,270	596,948	569,234
IBNR (1)	[1]	287,078
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		168,189	96,775	$ 37,072
Accident Year 2015
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		5,498,206	5,354,494
IBNR (1)	[1]	1,962,006
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		2,152,569	970,277
Accident Year 2015 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,459,003	1,504,763
IBNR (1)	[1]	543,530
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		589,550	279,024
Accident Year 2015 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		629,312	626,052
IBNR (1)	[1]	379,676
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		117,007	$ 43,015
Accident Year 2016
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		6,005,506
IBNR (1)	[1]	3,425,518
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		1,192,137
Accident Year 2016 | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		1,845,237
IBNR (1)	[1]	1,067,346
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		330,708
Accident Year 2016 | Casualty and Other Long-Tail Lines | Reinsurance Segment
Claims Development [Line Items]
Incurred Losses and Allocated Loss Expenses, Net of Reinsurance		704,478
IBNR (1)	[1]	535,503
Cumulative Paid Losses and Allocated Loss Expenses, Net of Reinsurance		$ 65,013
[1]	Total IBNR Liabilities Plus Expected Development on Reported Claims

Losses and Loss Expenses - I118

Losses and Loss Expenses - Information about average percentage payout (Details)	Dec. 31, 2016
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	17.00%
Year Two	22.00%
Year Three	15.00%
Year Four	10.00%
Year Five	9.00%
Year Six	6.00%
Year Seven	3.00%
Year Eight	3.00%
Year Nine	3.00%
Year Ten	1.00%
Insurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	16.00%
Year Two	21.00%
Year Three	16.00%
Year Four	11.00%
Year Five	10.00%
Year Six	6.00%
Year Seven	4.00%
Year Eight	3.00%
Year Nine	3.00%
Year Ten	1.00%
Insurance Segment | Professional lines
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	3.00%
Year Two	13.00%
Year Three	16.00%
Year Four	16.00%
Year Five	15.00%
Year Six	9.00%
Year Seven	6.00%
Year Eight	4.00%
Year Nine	4.00%
Year Ten	1.00%
Insurance Segment | Casualty and other
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	7.00%
Year Two	14.00%
Year Three	16.00%
Year Four	13.00%
Year Five	13.00%
Year Six	8.00%
Year Seven	5.00%
Year Eight	4.00%
Year Nine	3.00%
Year Ten	3.00%
Insurance Segment | EPC
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	26.00%
Year Two	38.00%
Year Three	20.00%
Year Four	6.00%
Year Five	5.00%
Year Six	1.00%
Year Seven	1.00%
Year Eight	0.00%
Year Nine	1.00%
Year Ten	1.00%
Insurance Segment | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	35.00%
Year Two	30.00%
Year Three	14.00%
Year Four	7.00%
Year Five	4.00%
Year Six	3.00%
Year Seven	2.00%
Year Eight	1.00%
Year Nine	1.00%
Year Ten	1.00%
Reinsurance Segment
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	20.00%
Year Two	24.00%
Year Three	15.00%
Year Four	8.00%
Year Five	5.00%
Year Six	4.00%
Year Seven	1.00%
Year Eight	2.00%
Year Nine	3.00%
Year Ten	1.00%
Reinsurance Segment | Property and other short-tail lines
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	29.00%
Year Two	34.00%
Year Three	17.00%
Year Four	7.00%
Year Five	3.00%
Year Six	4.00%
Year Seven	2.00%
Year Eight	1.00%
Year Nine	(1.00%)
Year Ten	1.00%
Reinsurance Segment | Casualty and Other Long-Tail Lines
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year One	5.00%
Year Two	9.00%
Year Three	10.00%
Year Four	10.00%
Year Five	9.00%
Year Six	7.00%
Year Seven	7.00%
Year Eight	6.00%
Year Nine	6.00%
Year Ten	4.00%

Losses and Loss Expenses - Reco

Losses and Loss Expenses - Reconciliation (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		$ 20,052,443
Unallocated loss expenses		482,680
Discount	[1]	(413,522)
Total allowance recorded relating to reinsurance recoverables		42,119	$ 58,200
Other		295,551
Total net liability for unpaid losses and loss expenses		20,459,271	20,190,839	$ 15,941,715	$ 17,066,330
Unpaid losses and loss expenses recoverable		5,491,297	5,262,706
Unpaid losses and loss expenses		25,939,571	25,439,744	19,353,243	20,481,065
Other
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and loss expenses recoverable		71,605
Property and casualty operations
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid losses and loss expenses recoverable	[2]	5,480,300	$ 5,248,905	$ 3,411,528	$ 3,414,735
Insurance Segment
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		13,343,138
Insurance Segment | Professional lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		3,951,383
Unpaid losses and loss expenses recoverable		1,195,720
Insurance Segment | Casualty and other
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		6,354,077
Unpaid losses and loss expenses recoverable		2,836,800
Insurance Segment | EPC
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		1,235,716
Unpaid losses and loss expenses recoverable		486,595
Insurance Segment | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		1,801,962
Unpaid losses and loss expenses recoverable		524,545
Reinsurance Segment
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		6,709,305
Reinsurance Segment | Property and other short-tail lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		2,201,173
Unpaid losses and loss expenses recoverable		242,845
Reinsurance Segment | Casualty and Other Long-Tail Lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Net outstanding liabilities		4,508,132
Unpaid losses and loss expenses recoverable		$ 122,190
[1]	As noted in Note 10(c), "Losses and Loss Expenses - Loss Reserve Discounting," the Company discounts only certain workers’ compensation (including long term disability) liabilities and certain bodily injury liability claims, emanating from U.K. exposures, predominantly from the U.K. motor liability portfolio.
[2]	Property and Casualty business only.

Losses and Loss Expenses - Net

Losses and Loss Expenses - Net losses and loss expenses incurred (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Abstract]
Loss and loss expenses payments	$ 6,828,012	$ 6,505,075	$ 4,499,642
Change in unpaid losses and loss expenses	976,401	(168,263)	(514,406)
Change in unpaid losses and loss expenses recoverable	(238,086)	(440,189)	(48,536)
Paid loss recoveries	(1,493,492)	(1,130,423)	(678,307)
Net losses and loss expenses incurred	$ 6,072,835	$ 4,766,200	$ 3,258,393

Losses and Loss Expenses - N121

Losses and Loss Expenses - Net losses and loss expenses incurred - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (301,542)	$ (306,630)	$ (255,072)
Insurance Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(91,459)	(65,030)	(99,758)
Reinsurance Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (210,083)	$ (241,600)	$ (155,314)

Losses and Loss Expenses - N122

Losses and Loss Expenses - Net losses and loss expenses incurred - Insurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (301,542)	$ (306,630)	$ (255,072)
Insurance Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(91,459)	(65,030)	(99,758)
Insurance Segment | Casualty and other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(58,251)	28,720	23,371
Insurance Segment | Excess Casualty [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(21,700)
Insurance Segment | EPC
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(38,366)	(6,447)	(57,465)
Insurance Segment | Professional lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	10,813	5,740	17,092
Insurance Segment | Specialty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(5,655)	$ (93,043)	$ (82,756)
Insurance Segment | Marine Lines [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(19,800)
Insurance Segment | Fine Art and Specie [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(5,900)
Insurance Segment | Accident and Health Insurance Product Line [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	26,000
Insurance Segment | International [Member] | Casualty and other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (72,200)

Losses and Loss Expenses - N123

Losses and Loss Expenses - Net losses and loss expenses incurred - Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (301,542)	$ (306,630)	$ (255,072)
Reinsurance Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(210,083)	(241,600)	(155,314)
Reinsurance Segment | Property and other short-tail lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(134,440)	(173,754)	(85,324)
Reinsurance Segment | Property catastrophe lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(76,600)	(50,300)	12,400
Reinsurance Segment | Property other lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(25,600)	(88,900)
Reinsurance Segment | Marine and aviation lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(32,200)	(34,600)	(34,400)
Reinsurance Segment | Casualty and Other Long-Tail Lines
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(75,643)	(67,846)	(69,990)
Reinsurance Segment | Casualty and other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	(65,500)	(40,100)	(44,300)
Reinsurance Segment | Other
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development	$ (10,000)	$ (27,800)
Reinsurance Segment | Property Other Than Property Catastrophe [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development			(63,400)
Reinsurance Segment | Casualty
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior year development			$ (25,700)

Losses and Loss Expenses - L124

Losses and Loss Expenses - Loss Reserve Discounting (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss And Loss Expenses Disclosure [Line Items]
Unpaid losses and loss expenses	$ 25,939,571	$ 25,439,744	$ 19,353,243	$ 20,481,065
Liabilities for unpaid losses and loss expenses, net of reinsurance	20,052,443
Bodily Injury Liability Claims, Discount, Amount	125,900	130,200
Workers' Compensation Discount, Amount	$ 287,700	302,100
Workers' compensation
Loss And Loss Expenses Disclosure [Line Items]
Discount rate used on unpaid losses for workers compensation	3.75%
Liabilities for unpaid losses and loss expenses, net of reinsurance	$ 727,400	747,400
Tabular unpaid losses and loss expenses	439,700	445,300
Interest accretion related to the unwind of discounted reserves	$ 18,600	$ 7,800
UK motor liabilities
Loss And Loss Expenses Disclosure [Line Items]
Discount rate used on unpaid losses	2.00%	2.00%
Liabilities for unpaid losses and loss expenses, net of reinsurance	$ 281,600	$ 298,100
Tabular unpaid losses and loss expenses	155,700	167,900
Periodic Payment Orders Related To Bodily Injury Claims [Member]
Loss And Loss Expenses Disclosure [Line Items]
Interest accretion related to the unwind of discounted reserves	$ 2,800	$ 2,600

Losses and Loss Expenses - Asbe

Losses and Loss Expenses - Asbestos and Environmental Exposures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of opening and closing unpaid losses and loss expenses related to asbestos and environmental exposure claims:
Net unpaid losses and loss expenses at beginning of year	$ 93,704	$ 81,416	$ 80,435
Net incurred losses and loss expenses	9,042	15,663	8,903
Less net paid losses and loss expenses	9,912	9,087	7,922
Net increase (decrease) in unpaid losses and loss expenses	(870)	6,576	981
Acquired reserves	0	5,712	0
Net unpaid losses and loss expenses at end of year	92,834	93,704	81,416
Unpaid losses and loss expenses recoverable at end of year	83,430	93,688	100,537
Gross unpaid losses and loss expenses at end of year	176,264	187,392	181,953
Reserves for incurred but not reported losses, net of reinsurance	$ 60,300	$ 65,100	$ 49,300

Losses and Loss Expenses - A126

Losses and Loss Expenses - Asbestos and Environmental Exposures Claims Rollforward (Details) - claims	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asbestos claims
Reconciliation of opening and closing unpaid losses and loss expenses related to asbestos and environmental exposure claims:
Total number of claims outstanding, beginning of period	2,591	1,399	1,097
New claims reported	579	272	456
Claims resolved	(753)	(246)	(154)
Reserves acquired		1,166
Total number of claims outstanding, end of period	2,417	2,591	1,399
Environmental claims
Reconciliation of opening and closing unpaid losses and loss expenses related to asbestos and environmental exposure claims:
Total number of claims outstanding, beginning of period	430	459	338
New claims reported	69	67	190
Claims resolved	(41)	(96)	(69)
Reserves acquired		0
Total number of claims outstanding, end of period	458	430	459

Losses and Loss Expenses - A127

Losses and Loss Expenses - Asbestos and Environmental Exposures Discussion (Details) $ in Millions	12 Months Ended
	Dec. 31, 2006USD ($)	Dec. 31, 2016USD ($)claims	Dec. 31, 2015USD ($)claims	Dec. 31, 2014USD ($)claims	Dec. 31, 2013claims
Loss And Loss Expenses Disclosure [Line Items]
Losses acquired through portfolio transfer, amount	$ 40.2
Combined aggregate limit on reserves acquired	60
Reserves for incurred but not reported losses, net of reinsurance		$ 60.3	$ 65.1	$ 49.3
Net asbestos and environmental reserves to total reserves, percentage		1.00%	1.00%
Asbestos and environmental claims
Loss And Loss Expenses Disclosure [Line Items]
Losses acquired through portfolio transfer, amount	$ 18.3
Claim files due to precautionary claim notices, percentage		34.00%	32.00%	46.00%
Environmental claims
Loss And Loss Expenses Disclosure [Line Items]
Total number of claims outstanding | claims		458	430	459	338
Asbestos claims
Loss And Loss Expenses Disclosure [Line Items]
Total number of claims outstanding | claims		2,417	2,591	1,399	1,097

Future Policy Benefit Reserv128

Future Policy Benefit Reserve (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ (3,072,615)	$ (3,719,131)
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	998,968	914,629
Future policy benefit reserves are comprised of the following:
Traditional life	737,252	792,001
Annuities	2,768,795	3,371,499
Total future policy benefit reserves	$ 3,506,047	$ 4,163,500
Other information:
Average interest rate used for future policy benefits, percent	4.00%	3.30%
XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Funds Held under Reinsurance Agreements, Liability	$ 4,071,583	$ 4,633,760
Reinsurance recoverable from GCLR	(3,072,615)	(3,719,131)
U.S. Term Life Reinsurance [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	(270,238)	(284,481)
Other Life Retrocessions [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	(10,997)	(13,801)
Corporate and other | XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future Policy Benefit Reserve Retention	$ 152,197	$ 146,087

Reinsurance - Effects of Reinsu

Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net premiums written:
Net premiums written	$ 10,242,683	$ 7,951,063	$ 5,944,841
Net premiums earned:
Direct premiums earned	9,142,690	7,717,173	5,173,403
Assumed premiums earned	4,340,132	3,775,337	2,676,765
Ceded premiums earned	(3,704,888)	(3,266,085)	(1,955,098)
Net amount, premiums earned	9,777,934	8,226,425	5,895,070
Property and casualty operations
Net premiums written:
Direct premiums written	9,166,627	7,847,236	5,450,868
Assumed premiums written	4,458,981	2,821,771	2,310,621
Ceded premiums written	(3,394,972)	(2,780,183)	(1,994,280)
Net premiums written	10,230,636	7,888,824	5,767,209
Net premiums earned:
Direct premiums earned	9,142,690	7,717,173	5,173,403
Assumed premiums earned	4,074,817	3,465,421	2,343,329
Ceded premiums earned	(3,451,620)	(3,018,410)	(1,799,294)
Net amount, premiums earned	$ 9,765,887	$ 8,164,184	$ 5,717,438

Reinsurance - Components of Unp

Reinsurance - Components of Unpaid Losses and Loss Expenses Recoverable (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable		$ 5,491,297	$ 5,262,706
Property and casualty operations
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable	[1]	5,480,300	5,248,905	$ 3,411,528	$ 3,414,735
Corporate and other
Analysis of total unpaid losses and loss expenses recoverable by segment:
Unpaid losses and loss expenses recoverable		$ 10,997	$ 13,801
[1]	Property and Casualty business only.

Reinsurance - Ceded Credit Risk

Reinsurance - Ceded Credit Risk (Details) - Reinsurance Recoverable [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
A or better rating
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	95.00%	96.00%
Ceded Credit Risk, Concentrated Credit Risk [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	100.00%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AAA
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	2.80%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AA
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	44.50%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AA- | Munich Reinsurance Company
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	25.60%
Ceded Credit Risk, Concentrated Credit Risk [Member] | AA- | Swiss Reinsurance Company
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	7.20%
Ceded Credit Risk, Concentrated Credit Risk [Member] | A+ | Transatlantic Reinsurance Company [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	4.10%
Ceded Credit Risk, Concentrated Credit Risk [Member] | A+ | Arch Reinsurance Co [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	3.70%
Ceded Credit Risk, Concentrated Credit Risk [Member] | A+ | Lloyds Syndicate
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	15.90%
Ceded Credit Risk, Concentrated Credit Risk [Member] | A+ | Axis Reinsurance Co [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	3.00%
Ceded Credit Risk, Concentrated Credit Risk [Member] | A
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	48.10%
Ceded Credit Risk, Concentrated Credit Risk [Member] | BBB
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	0.60%
Ceded Credit Risk, Concentrated Credit Risk [Member] | Standard Poors BB And Below Rating [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	0.60%
Ceded Credit Risk, Concentrated Credit Risk [Member] | Captives
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	3.30%
Ceded Credit Risk, Concentrated Credit Risk [Member] | Not Rated NR [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	0.10%
Minimum | Ceded Credit Risk, Concentrated Credit Risk [Member]
Ceded Credit Risk [Line Items]
Maximum percentage of ceded written premium	3.00%

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ 3,072,615	$ 3,719,131
Reinsurance recoveries on losses and loss expenses recorded during period	1,700,000	1,600,000	$ 700,000
Total reinsurance assets	6,100,000	5,700,000
Reinsurance balances receivable	577,479	418,666
Unpaid losses and loss expenses recoverable	5,491,297	5,262,706
Total allowance for uncollectible reinsurance	62,800	82,100
Collateral held related to reinsurance recoverables	4,100,000	3,800,000
Total allowance recorded relating to reinsurance recoverables	42,119	58,200
Total allowance recorded relating to reinsurance balances receivable	20,700	23,900
U.S. Term Life Reinsurance [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	270,238	284,481
XL Re Life (SAC) Ltd [Member]
Liability for Future Policy Benefit, by Product Segment [Line Items]
Reinsurance recoverable from GCLR	$ 3,072,615	$ 3,719,131

Deposit Liabilities (Details)

Deposit Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Net results from structured products	$ 14,280	[1]	$ 17,991	[2]	$ 54,209	[3]
Deposit liabilities	1,116,233		1,168,376
Accretion expense on deposit liabilities	$ 39,700		$ 42,200		12,900
Interest expense | Structured Indemnity
Net results from structured products					$ 28,700
[1]	The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million, respectively.
[2]	The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.
[3]	The net results from P&C structured products include net investment income and interest expense of $68.0 million and $12.9 million, respectively.

Notes Payable and Debt and F134

Notes Payable and Debt and Financing Arrangements - Financing Structure (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt instrument, face amount		$ 2,675,000	$ 2,675,000
Notes payable and debt		2,647,677	2,644,970
Senior notes | 2.3% Senior Notes due 2018
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	300,000	300,000
Notes payable and debt	[2]	$ 298,686	298,015
Debt instrument interest rate, stated percentage		2.30%
Senior notes | 5.75% Senior Notes due 2021
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 400,000	400,000
Notes payable and debt	[2]	$ 397,953	397,523
Debt instrument interest rate, stated percentage		5.75%
Senior notes | 6.375% Senior Notes due 2024
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 350,000	350,000
Notes payable and debt	[2]	$ 349,139	349,029
Debt instrument interest rate, stated percentage		6.375%
Senior notes | 6.25% Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 325,000	325,000
Notes payable and debt	[2]	$ 323,375	323,218
Debt instrument interest rate, stated percentage		6.25%
Senior notes | 5.25% Senior Notes due 2043
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 300,000	300,000
Notes payable and debt	[2]	$ 296,427	296,294
Debt instrument interest rate, stated percentage		5.25%
Subordinated debt | 4.45% Subordinated Notes due 2025
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 500,000	500,000
Notes payable and debt	[2]	$ 493,329	492,521
Debt instrument interest rate, stated percentage		4.45%
Subordinated debt | 5.5% Subordinated Notes due 2045
Debt Instrument [Line Items]
Debt instrument, face amount	[1]	$ 500,000	500,000
Notes payable and debt	[2]	$ 488,768	488,370
Debt instrument interest rate, stated percentage		5.50%
Revolving credit facility
Debt Instrument [Line Items]
Available letter of credit facilities - commitments		$ 1,000,000	1,400,000
Available letter of credit facilities - in use		245,000	527,100
Line of credit facility, remaining borrowing capacity		$ 755,000	$ 822,900
[1]	Excluded from the table are certain credit facilities under which the Company is permitted to utilize up to $1.0 billion and $1.4 billion as of December 31, 2016 and December 31, 2015, respectively, for revolving loans to support general operating and financing needs. However, as of December 31, 2016 and December 31, 2015, $245 million and $527.1 million, respectively, were utilized under these facilities to issue letters of credit, leaving $755.0 million and $822.9 million, respectively, available to support other operating and financing need
[2]	"In Use/Outstanding" data represent December 31, 2016 and December 31, 2015 accreted values.

Notes Payable and Debt and F135

Notes Payable and Debt and Financing Arrangements - Narrative relating to debt (Details) $ in Thousands, € in Millions		Mar. 30, 2015USD ($)	Sep. 15, 2014USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2016EUR (€)
Debt Instrument [Line Items]
Percentage ownership of subsidiaries				100.00%
Debt instrument, face amount				$ 2,675,000	$ 2,675,000
Notes payable and debt				2,647,677	2,644,970
Extinguishment of debt				$ 0	5,592	$ 0
Subordinated debt | 4.45% Subordinated Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage				4.45%			4.45%
Debt instrument, face amount	[1]			$ 500,000	500,000
Notes payable and debt	[2]			$ 493,329	492,521
Subordinated debt | 5.5% Subordinated Notes due 2045
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage				5.50%			5.50%
Debt instrument, face amount	[1]			$ 500,000	500,000
Notes payable and debt	[2]			$ 488,768	$ 488,370
XL Group Ltd
Debt Instrument [Line Items]
Percentage ownership of subsidiaries				100.00%
XL Cayman
Debt Instrument [Line Items]
Percentage ownership of subsidiaries				100.00%
XL Cayman | Senior notes
Debt Instrument [Line Items]
Extinguishment of debt			$ 600,000
Debt instrument interest rate, stated percentage			5.25%
XL Cayman | Subordinated debt | 4.45% Subordinated Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage		4.45%
Debt issuance percentage of face value		99.633%
Proceeds from debt, net of issuance costs		$ 492,200
Debt issuance cost		$ 5,900
XL Cayman | Subordinated debt | 5.5% Subordinated Notes due 2045
Debt Instrument [Line Items]
Debt instrument interest rate, stated percentage		5.50%
Debt issuance percentage of face value		99.115%
Proceeds from debt, net of issuance costs		$ 488,400
Debt issuance cost		$ 7,200
Allied International Holdings, Inc. | Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trust Preferred Securities Eight Million Face Value [Member]
Debt Instrument [Line Items]
Notes payable and debt				$ 8,200
Catlin Underwriting | Subordinated debt | Variable Rate Subordinated Notes Face Amount Seven Million Euro [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				2.95%
Debt instrument, face amount | €							€ 7
Catlin Underwriting | Subordinated debt | Variable Rate Subordinated Notes Face Amount Twenty Seven Million [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				3.17%
Debt instrument, face amount				$ 27,000
Catlin Underwriting | Subordinated debt | Variable Rate Subordinated Notes Face Amount Thirty One Million [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				3.10%
Debt instrument, face amount				$ 31,000
Catlin Underwriting | Subordinated debt | Variable Rate Subordinated Notes Face Amount Ten Million [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				3.00%
Debt instrument, face amount				$ 10,000
Catlin Underwriting | Subordinated debt | Variable Rate Subordinated Notes Face Amount Eleven Million Euro [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				3.00%
Debt instrument, face amount | €							€ 11
LIBOR | Allied International Holdings, Inc. | Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trust Preferred Securities Eight Million Face Value [Member]
Debt Instrument [Line Items]
Spread on variable rate basis				3.75%
[1]	Excluded from the table are certain credit facilities under which the Company is permitted to utilize up to $1.0 billion and $1.4 billion as of December 31, 2016 and December 31, 2015, respectively, for revolving loans to support general operating and financing needs. However, as of December 31, 2016 and December 31, 2015, $245 million and $527.1 million, respectively, were utilized under these facilities to issue letters of credit, leaving $755.0 million and $822.9 million, respectively, available to support other operating and financing need
[2]	"In Use/Outstanding" data represent December 31, 2016 and December 31, 2015 accreted values.

Notes Payable and Debt and F136

Notes Payable and Debt and Financing Arrangements - Letter of credit summary (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments	[1],[2]	$ 3,991,687	$ 4,463,041
Available letter of credit facilities - in use	[2]	$ 2,345,293	$ 2,515,653
Collateralized by certain assets of the Company's investment portfolio	[2]	48.60%	50.90%
Revolving credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 1,000,000	$ 1,400,000
Available letter of credit facilities - in use		$ 245,000	$ 527,100
[1]	As of December 31, 2016 and December 31, 2015 the stated portion of allowable credit facilities permitted to be utilized for revolving loans was $1.0 billion and $1.4 billion, respectively. However, as of December 31, 2016 and December 31, 2015, $245.0 million and $527.1 million, respectively, of such facilities' limits were utilized to issue letters of credit, leaving $755.0 million and $822.9 million, respectively, available either to issue additional letters of credit or to support other operating or financing needs under these particular facilities.
[2]	As of December 31, 2016 and December 31, 2015, there were fifteen available credit facilities.

Notes Payable and Debt and F137

Notes Payable and Debt and Financing Arrangements - Narrative relating to credit facilities (Details)		Dec. 31, 2016USD ($)Credit_Facilities	Dec. 31, 2015USD ($)Credit_Facilities	Dec. 30, 2014USD ($)
Line of Credit Facility [Line Items]
Notes payable and debt		$ 2,647,677,000	$ 2,644,970,000
Number of letter of credit facilities available | Credit_Facilities		15	15
Credit Agricole Facility II [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 125,000,000
Funds at Lloyds Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Number of letter of credit facilities available | Credit_Facilities		4
Available letter of credit facilities - commitments		$ 500,000,000
Funds at Lloyds Bilateral Facility I [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		125,000,000
Funds at Lloyds Bilateral Facility II [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		125,000,000
Funds at Lloyds Bilateral Facility III [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		125,000,000
Funds at Lloyds Bilateral Facility IV [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		125,000,000
Two Thousand Thirteen Citi Agreements [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		250,000,000
Revolving credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		245,000,000	$ 527,100,000
Available letter of credit facilities - commitments		1,000,000,000	1,400,000,000
Line of credit facility, remaining borrowing capacity		755,000,000	822,900,000
Syndicated Credit Agreements [Member]
Line of Credit Facility [Line Items]
Optional increase capacity		500,000,000
Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use	[1]	2,345,293,000	2,515,653,000
Available letter of credit facilities - commitments	[1],[2]	3,991,687,000	4,463,041,000
Credit Agricole Facility I [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		125,000,000
Twenty Fifteen Goldman Sachs Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		200,000,000
Catlin Bermuda [Member] | Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		180,000,000
Catlin Re Switzerland [Member] | Bilateral Facility [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		250,000,000
Catlin Group Limited [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use			$ 4
Citibank Europe plc [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		600,000,000		$ 750,000,000
Lloyds Syndicate | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		12,000,000
Citibank N.A. [Member] | Letter of credit facility
Line of Credit Facility [Line Items]
Available letter of credit facilities - in use		250,000,000
Trust Preferred Securities Subject to Mandatory Redemption [Member] | Trust Preferred Securities Eight Million Face Value [Member] | Allied International Holdings, Inc.
Line of Credit Facility [Line Items]
Notes payable and debt		8,200,000
Two Thousand Sixteen Secured Credit Agreement [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		750,000,000
Two Thousand Sixteen Unsecured Credit Agreement [Member]
Line of Credit Facility [Line Items]
Available letter of credit facilities - commitments		$ 750,000,000
[1]	As of December 31, 2016 and December 31, 2015, there were fifteen available credit facilities.
[2]	As of December 31, 2016 and December 31, 2015 the stated portion of allowable credit facilities permitted to be utilized for revolving loans was $1.0 billion and $1.4 billion, respectively. However, as of December 31, 2016 and December 31, 2015, $245.0 million and $527.1 million, respectively, of such facilities' limits were utilized to issue letters of credit, leaving $755.0 million and $822.9 million, respectively, available either to issue additional letters of credit or to support other operating or financing needs under these particular facilities.

Related Party Transactions - Sc

Related Party Transactions - Schedule of related party transactions activity (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)management_company	Dec. 31, 2015USD ($)management_company	Dec. 31, 2014USD ($)
Related Party Transaction [Line Items]
Reported net premiums written	$ 10,242,683	$ 7,951,063	$ 5,944,841
Net losses and loss expenses incurred	6,072,835	4,766,200	3,258,393
Reported acquisition costs	$ 1,620,671	$ 1,317,448	738,118
Number of investment management companies | management_company	4	6
Other strategic affiliates or subsidiaries
Related Party Transaction [Line Items]
Reported net premiums written	$ 94,358	$ 42,042	91,261
Net losses and loss expenses incurred	44,728	13,246	38,927
Reported acquisition costs	$ 39,131	$ 14,682	$ 35,711

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) $ in Millions	Jul. 24, 2015USD ($)	Dec. 31, 2016management_company	Dec. 31, 2015management_company
Related Party Transaction [Line Items]
Number of investment management companies		4	6
Percentage ownership of subsidiaries		100.00%
Related Party Transactions Number of Investment Technology Service Firms		1	2
New Energy Risk Inc. [Member]
Related Party Transaction [Line Items]
Business acquisition, percentage of voting interests acquired	63.63%
Cash consideration | $	$ 8.8
Business combination, step acquisition, equity interest in acquiree, including subsequent acquisition, percentage	94.79%
Noncontrolling interest, ownership percentage by noncontrolling owners	5.21%
New Energy Risk Inc. [Member]
Related Party Transaction [Line Items]
Percentage ownership of subsidiaries		100.00%

Variable Interest Entities (Det

Variable Interest Entities (Details) - Equity interest attributable to third party investors in New Ocean - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Non-controlling interest in consolidated subsidiaries	$ 112.1	$ 70.5
Variable Interest Entity, Consolidated, Carrying Amount, Assets	223.4	175.8
New Ocean Capital Management Ltd
Variable Interest Entity [Line Items]
Non-controlling interest in consolidated subsidiaries	$ 1	$ 0.4

Retirement Plans - Funded statu

Retirement Plans - Funded status of plan by geographic location (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2015
Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	$ (42,786)	$ (42,763)
US Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	(14,093)	(16,306)
UK Plans
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	(2,316)	(4,650)	$ (1,000)
Europe plans
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	$ (26,377)	$ (21,807)

Retirement Plans - Projected be

Retirement Plans - Projected benefit obligation and plan assets (Details) - Defined benefit plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Change in projected benefit obligation:
Projected benefit obligation, beginning of year	$ 122,165		$ 93,124
Projected benefit obligation assumed due to Catlin Acquisition	0		28,414
Service cost	1,701	[1]	1,494	[1]	$ 1,279
Interest cost	5,126		4,382		3,747
Actuarial (gain) loss	7,948		2,821
Benefits and expenses paid	(5,977)		(3,747)
Foreign currency (gains) losses	(10,248)		(4,047)
Settlements	(677)		(276)
Projected benefit obligation, end of year	120,038		122,165		93,124
Change in plan assets:
Fair value of plan assets - beginning of year	79,402		49,281
Fair value of plan assets acquired due to Catlin Acquisition	0		33,131
Actual return on plan assets	8,499		(119)
Employer contributions	2,077		1,775
Benefits and expenses paid	(4,577)		(3,305)
Foreign currency (gains) losses	(8,149)		(1,361)
Fair value of plan assets - end of year	77,252		79,402		$ 49,281
Funded status - end of year	(42,786)		(42,763)
Accrued pension liability	$ 42,786		$ 42,763
[1]	Service costs include cost of living adjustments on curtailed plans.

Retirement Plans - Net benefit

Retirement Plans - Net benefit cost (Details) - Defined benefit plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,701	[1]	$ 1,494	[1]	$ 1,279
Interest cost	5,126		4,382		3,747
Expected return on plan assets	(4,357)		(3,903)		(2,859)
Amortization of net actuarial loss	1,705		1,617		812
Net benefit cost	$ 4,175		$ 3,590		$ 2,979
[1]	Service costs include cost of living adjustments on curtailed plans.

Retirement Plans - Assumptions

Retirement Plans - Assumptions used (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
US Plan
Net benefit cost - weighted average assumptions
Discount rate	4.25%	3.91%
Expected long-term rate of return on plan assets	6.00%	6.00%
Benefit obligation - weighted-average assumptions
Discount rate	4.04%	4.25%
UK Plans
Net benefit cost - weighted average assumptions
Discount rate	2.74%	3.70%
Expected long-term rate of return on plan assets	2.77%	3.48%
Rate of compensation increase	3.62%	3.96%
Benefit obligation - weighted-average assumptions
Discount rate	2.76%	3.70%
Rate of compensation increase	3.62%	3.96%
Europe plans
Net benefit cost - weighted average assumptions
Discount rate	1.33%	2.42%
Rate of compensation increase	2.50%	2.50%
Benefit obligation - weighted-average assumptions
Discount rate	1.33%	2.42%
Rate of compensation increase	2.50%	2.50%

Retirement Plans - UK plans (De

Retirement Plans - UK plans (Details) - UK Plans $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)employee	Dec. 31, 2015USD ($)	Jun. 30, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	2.77%	3.48%
Fair value of plan assets	$ 38,520	$ 42,716
Funding deficit based on most recent valuation	$ 2,316	4,650	$ 1,000
Period over which the deficit is being funded	4 years
Transferred to defined contribution plan
Defined Benefit Plan Disclosure [Line Items]
Number of members in the plan | employee	6
Accrued pension liability	$ 4,100	$ 4,800
Still employed by company
Defined Benefit Plan Disclosure [Line Items]
Number of members in the plan | employee	3
Equities
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	5.70%	6.20%
Fair value of plan assets	$ 9,122	$ 7,893
Gilts
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	2.40%	2.40%
Fair value of plan assets	$ 15,459	$ 17,856
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	3.30%	3.40%
Fair value of plan assets	$ 13,850	$ 16,915
Other (cash)
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	0.50%	1.80%
Fair value of plan assets	$ 89	$ 52

Retirement Plans - Expected fut

Retirement Plans - Expected future benefit payments of US plan (Details) $ in Thousands	Dec. 31, 2016USD ($)
Defined Benefit Plan Disclosure [Line Items]
2,017	$ 1,382
2,018	1,410
2,019	1,676
2,020	1,856
2,021	2,185
2022 - 2026	13,576
US Plan
Defined Benefit Plan Disclosure [Line Items]
2,017	1,029
2,018	1,057
2,019	1,226
2,020	1,389
2,021	1,683
2022 - 2026	10,753
Benefits equalization plan
Defined Benefit Plan Disclosure [Line Items]
2,017	353
2,018	353
2,019	450
2,020	467
2,021	502
2022 - 2026	$ 2,823

Retirement Plans - Narrative (D

Retirement Plans - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)funds	Dec. 31, 2015USD ($)funds	Dec. 31, 2014USD ($)	Jun. 30, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Vesting period for defined contribution plan	5 years
Expense recognized on defined contribution plans	$ 88,300	$ 87,500	$ 56,600
Number of years of compensation for calculating benefit	3 years
Number of years of employment considered at retirement	10 years
Estimated employer contributions in next fiscal year	$ 1,400
US Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	$ (14,093)	$ (16,306)
Number of mutual funds held by plan | funds	3	2
Fair value of plan assets	$ 38,700	$ 36,700
Benefits equalization plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	2,300	3,200
UK Plans
Defined Benefit Plan Disclosure [Line Items]
Funded status - end of year	(2,316)	(4,650)		$ (1,000)
Fair value of plan assets	$ 38,520	$ 42,716

Commitments and Contingencies -

Commitments and Contingencies - Broker credit risk (Details) - Gross written premium - Property and casualty operations - Credit concentration risk	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Maximum percentage of ceded written premium	10.00%
AON Corporation and subsidiaries
Concentration Risk [Line Items]
Maximum percentage of ceded written premium	18.00%	18.00%	18.00%
Marsh & McLennan Companies
Concentration Risk [Line Items]
Maximum percentage of ceded written premium	18.00%	19.00%	20.00%
Willis Group and subsidiaries
Concentration Risk [Line Items]
Maximum percentage of ceded written premium	11.00%	13.00%	11.00%

Commitments and Contingencie149

Commitments and Contingencies - Future minimum operating lease payments (Details) $ in Thousands	Dec. 31, 2016USD ($)
Future minimum payments on operating leases:
2,016	$ 70,359
2,017	62,590
2,018	57,030
2,019	51,566
2,020	47,738
2021-2031	96,602
Total minimum future rentals	$ 385,885

Commitments and Contingencie150

Commitments and Contingencies - Future minimum capital lease payments (Details) $ in Thousands	Dec. 31, 2016USD ($)
Future minimum payments on capital leases:
2,016	$ 9,998
2,017	10,248
2,018	10,504
2,019	10,767
2,020	11,036
2021 - 2028	78,736
Total minimum future lease payments	$ 131,289

Commitments and Contingencie151

Commitments and Contingencies - Financial and other guarantee exposures(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Aggregate exposure outstanding	$ 80.8
Weighted average contractual term to maturity in years	23 years 2 months 12 days	24 years 2 months 12 days

Commitments and Contingencie152

Commitments and Contingencies - Narrative (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2016USD ($)Guarantee_contracts	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Commitments And Contingencies Disclosure [Line Items]
Additional investment commitment - other investments		$ 59,300
Time period over which commitment exists - limited partnerships		4 years 9 months 18 days
Additional investment commitment - investments in affiliates		$ 237,100
Time period over which commitment exists, investments in affiliates		4 years 10 months 24 days
Maximum percentage tax on branch profits, contingent		30.00%
Total rent expense under operating leases		$ 68,000	$ 71,100	$ 36,600
Capital lease asset recognized		55,500	73,400
Capital lease liability		89,900	113,800
Deferred gain on sale/leaseback transaction		16,900	$ 22,300
Future minimum lease payments		131,289
Total gross claim liability recorded		$ 0
Weighted average contractual term to maturity in years		23 years 2 months 12 days	24 years 2 months 12 days
Shareholders' equity | Credit concentration risk
Commitments And Contingencies Disclosure [Line Items]
Maximum percentage of aggregate direct investment in any single corporate issuer		5.00%
Letter of credit facility
Commitments And Contingencies Disclosure [Line Items]
Letters of credit, amount outstanding	[1]	$ 2,345,293	$ 2,515,653
Percentage of letters of credit collateralized by investment portfolios	[1]	48.60%	50.90%
Financial Guarantee Related to Securities Including Some Issued By European Financials [Member]
Commitments And Contingencies Disclosure [Line Items]
Number Of Financial Guarantee Contracts | Guarantee_contracts		2
[1]	As of December 31, 2016 and December 31, 2015, there were fifteen available credit facilities.

Share Capital - Authorized and

Share Capital - Authorized and issued (Details) - USD ($)		May 01, 2015	Oct. 15, 2011	Mar. 15, 2007	Dec. 31, 2016	Dec. 31, 2015	May 13, 2016	Aug. 06, 2015
Shareholders Equity Disclosure [Line Items]
Authorized share capital, value					$ 9,999,900
Ordinary shares, shares authorized (in shares)					999,990,000	999,990,000
Common shares, par value (in dollars per share)					$ 0.01	$ 0.01
Rollforward of ordinary shares issued and outstanding:
Balance at beginning of year, shares					294,745,045	255,183,000
Exercise of options, shares					802,000	480,000
Issue of shares					0	49,935,000
Net issuance of restricted shares, shares					1,598,000	1,581,000
Share buybacks, shares	[1]				(30,256,000)	(12,434,000)
Balance at end of year, shares					266,889,127	294,745,045
Ordinary share buybacks:
Shares purchased and canceled during the period					30,300,000
Value of shares purchased and canceled during the period					$ 1,051,000,000
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Shares purchased and canceled during the period					30,300,000
Articles Of Association maximum voting power, percentage					10.00%
Ordinary shares
Shareholders Equity Disclosure [Line Items]
Ordinary shares, shares authorized (in shares)					500,000,000
Common shares, par value (in dollars per share)					$ 0.01
Undesignated shares
Shareholders Equity Disclosure [Line Items]
Ordinary shares, shares authorized (in shares)					499,990,000
Common shares, par value (in dollars per share)					$ 0.01
Series D preference ordinary shares
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Proceeds on issuance of preferred shares			$ 350,000,000
Series D preference ordinary shares | LIBOR
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Dividend rate, spread on LIBOR			3.12%
Series E Preferred Stock [Member]
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Dividend rate, spread on LIBOR					6.50%
Series E Preferred Stock [Member] | LIBOR
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Dividend rate, spread on LIBOR					2.4575%
Series E preference ordinary shares
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Liquidation preference per share				$ 1,000
Preferred shares, shares issued				1,000,000
Preferred shares, stated dividend per share				$ 32.5
Preferred shares, par value				$ 0.01
Two Thousand Fifteen Share Repurchase Authorization [Member]
Ordinary share buybacks:
Share repurchase authorization								$ 1,000,000,000
Shares purchased and canceled during the period					14,200,000
Value of shares purchased and canceled during the period					$ 499,300,000
Amount remaining under share repurchase plan							$ 204,100,000
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Shares purchased and canceled during the period					14,200,000
Two Thousand Sixteen Share Repurchase Authorization [Member]
Ordinary share buybacks:
Share repurchase authorization							$ 1,000,000,000
Shares purchased and canceled during the period					16,000,000
Value of shares purchased and canceled during the period					$ 550,700,000
Amount remaining under share repurchase plan					$ 449,300,000
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Shares purchased and canceled during the period					16,000,000
Settling of employee withholding taxes [Member]
Ordinary share buybacks:
Value of shares purchased and canceled during the period					$ 1,100,000
Catlin Group Limited [Member]
Shareholders Equity Disclosure [Line Items]
Common shares, par value (in dollars per share)		$ 0.01
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
XL Share issuance to Catlin shareholders		49,935,000
XL Share issuance consideration		$ 1,851,601,000
Catlin Group Limited [Member] | Noncumulative perpetual preferred shares
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Liquidation preference per share					$ 1,000
Preferred Stock, Shares Outstanding					600,000
Dividend rate, spread on LIBOR					7.249%
Preferred shares, par value					$ 0.01
Preferred Stock, Value, Outstanding					$ 562,300,000
Change In Dividend Rate If Shares Not Redeemed at Specified Date [Member] | Catlin Group Limited [Member] | Noncumulative perpetual preferred shares
Preferred shares and non-controlling interest in equity of consolidated subsidiaries:
Dividend rate, spread on LIBOR					2.975%
[1]	Includes share buybacks associated with authorized share buyback programs as well as purchases related to satisfying tax withholding obligations of employees in connection with the vesting of restricted shares granted under the Company’s equity compensation programs.

Share Capital - Options valuati

Share Capital - Options valuation assumptions (Details) - Stock options	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted average assumptions and option awards:
Dividend yield	2.00%	2.00%	2.00%
Risk free interest rate	1.37%	1.70%	1.81%
Volatility	21.70%	21.60%	34.00%
Expected lives	6 years	6 years	6 years

Share Capital - Options (Detail

Share Capital - Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of stock option plans:
Options exercised during the year		802	480
Summary of stock options and related activity:
Options exercised during the year		(802)	(480)
Stock options
Summary of stock option plans:
Options granted to purchase ordinary shares under directors and employees incentive compensation plans (shares)		2,200	1,974	1,025
Weighted average grant date fair value (per share)		$ 5.99	$ 6.51	$ 8.60
Total intrinsic value of stock options exercised		$ 19,471	$ 8,546	$ 7,499
Options exercised during the year		810	480	424
Compensation expense related to stock option plans		$ 11,065	$ 8,961	$ 9,961
Estimated tax benefit related to stock option plans		$ 355	$ 0	$ (2)
Summary of stock options and related activity:
Outstanding at beginning of year, shares		10,749
Granted, shares		2,200
Options exercised during the year		(810)	(480)	(424)
Canceled/expired, shares		(278)
Outstanding at end of year, shares		11,861	10,749
Options exercisable, shares		8,002
Options available for grant, shares	[1]	8,355
Outstanding at beginning of year, weighted average exercise price		$ 28.59
Granted, weighted average exercise price		34.64
Exercised, weighted average exercise price		12.35
Canceled/expired, weighted average exercise price		60.83
Outstanding at end of year, weighted average exercise price		30.07	$ 28.59
Options exercisable, weighted average exercise price		$ 27.75
Weighted average remaining contractual term		5 years 6 months	5 years 4 months 24 days
Weighted average remaining contractual term, options exercisable		4 years
Aggregate intrinsic value, beginning of year		$ 121,085
Aggregate intrinsic value, end of year		86,558	$ 121,085
Aggregate intrinsic value, options exercisable		77,366
Total unrecognized stock based compensation expense		$ 15,300
Number of non-vested options outstanding		3,900
Period for recognition of unrecognized expense		1 year 3 months 18 days
[1]	Available for grant includes shares that may be granted as either stock options, restricted stock, restricted stock units or performance units.

Share Capital - Restricted stoc

Share Capital - Restricted stock, restricted stock units and performance units (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Minimum
Summary of awards:
Vesting period required	3 years
Maximum
Summary of awards:
Vesting period required	4 years
Restricted stock awards
Summary of awards:
Granted, shares	48	44	46
Weighted average grant date fair value (per share)	$ 34.05	$ 37.11	$ 31.86
Aggregate grant date fair value	$ 1,650	$ 1,613	$ 1,463
Compensation expense	2,078	3,889	5,239
Estimated tax benefit (charge)	129	$ 709	$ 1,233
Total unrecognized stock based compensation expense	$ 0
Award activity:
Unvested at beginning of period, shares	275
Granted, shares	48	44	46
Vested, shares	(132)
Unvested at end of period, shares	191	275
Unvested at beginning of period, weighted average grant date fair value	$ 41.90
Granted, weighted average grant date fair value	34.05
Vested, weighted average grant date fair value	36.35
Unvested at end of period, weighted average grant date fair value	$ 43.72	$ 41.90
Restricted stock units
Summary of awards:
Granted, shares	1,117	1,534	1,867
Aggregate grant date fair value	$ 38,681	$ 55,540	$ 57,134
Compensation expense	46,209	48,937	41,879
Estimated tax benefit (charge)	12,701	$ 13,271	$ 11,607
Total unrecognized stock based compensation expense	$ 49,900
Period for recognition of unrecognized expense	1 year 4 months 24 days
Vesting period required	3 years
Award activity:
Unvested at beginning of period, shares	3,070
Granted, shares	1,117	1,534	1,867
Vested, shares	(1,559)
Forfeited, shares	(137)
Unvested at end of period, shares	2,491	3,070
Unvested at beginning of period, weighted average grant date fair value	$ 32.99
Granted, weighted average grant date fair value	34.64
Vested, weighted average grant date fair value	31.83
Forfeited, weighted average grant date fair value	36.37
Unvested at end of period, weighted average grant date fair value	$ 34.30	$ 32.99
Performance units
Summary of awards:
Granted, shares	738	781	572
Potential maximum share payout	1,477	1,563	1,144
Aggregate grant date fair value	$ 25,578	$ 28,082	$ 16,345
Compensation expense	21,647	12,942	24,089
Estimated tax benefit (charge)	3,152	$ 1,459	$ 4,250
Total unrecognized stock based compensation expense	$ 29,800
Period for recognition of unrecognized expense	1 year 9 months 18 days
Vesting period required	3 years
Award activity:
Unvested at beginning of period, shares	1,881
Granted, shares	738	781	572
Vested, shares	(746)
Forfeited, shares	(28)
Performance driven reduction, shares	(477)
Unvested at end of period, shares	1,368	1,881
Unvested at beginning of period, weighted average grant date fair value	$ 31.02
Granted, weighted average grant date fair value	34.64
Vested, weighted average grant date fair value	27
Forfeited, weighted average grant date fair value	34.12
Performance driven reduction, weighted average grant date fair value	34.60
Unvested at end of period, weighted average grant date fair value	$ 32.83	$ 31.02
Performance units | Minimum
Summary of awards:
Final payout percentage	0.00%
Performance units | Maximum
Summary of awards:
Final payout percentage	200.00%

Share Capital - Restricted cash

Share Capital - Restricted cash units (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares	1,826	2,559	0
Aggregate grant date fair value	$ 63,261	$ 94,525	$ 0
Compensation expense	39,433	19,834	0
Estimated tax benefit (charge)	8,543	$ 4,374	$ 0
Total unrecognized stock based compensation expense	$ 74,100
Period for recognition of unrecognized expense	1 year 6 months
Unvested at beginning of period, shares	2,006
Vested, shares	(892)
Forfeited, shares	(367)
Unvested at end of period, shares	2,573	2,006
Unvested at beginning of period, weighted average grant date fair value	$ 36.95
Granted, weighted average grant date fair value	34.64
Vested, weighted average grant date fair value	36.93
Forfeited, weighted average grant date fair value	36.27
Unvested at end of period, weighted average grant date fair value	$ 35.41	$ 36.95
Deferred compensation, share-based payments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, shares	1,800
Aggregate grant date fair value	$ 63,200
Deferred compensation, share-based payments | Three Year Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period required	3 years
Deferred compensation, share-based payments | Two Year Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period required	2 years

Computation of Earnings Per 158

Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent - Computation of basic and diluted earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	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 ordinary share and ordinary share equivalents:
Net income (loss) attributable to common shareholders									$ 440,968	$ 1,207,152	$ 188,340
Weighted average ordinary shares outstanding									278,957	286,194	267,103
Basic earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ 1.13	$ 0.26	$ 0.16	$ 0.07	$ 0.77	$ 0.09	$ 3.16	$ 0.14	$ 1.58	$ 4.22	$ 0.71
Diluted earnings per ordinary share and ordinary share equivalents:
Weighted average ordinary shares outstanding									278,957	286,194	267,103
Impact of share based compensation and certain conversion features									3,801	4,805	4,424
Weighted average ordinary shares outstanding - diluted									282,758	290,999	271,527
Diluted earnings per ordinary share & ordinary share equivalents outstanding (in Dollars per share)	$ 1.12	$ 0.25	$ 0.15	$ 0.07	$ 0.76	$ 0.09	$ 3.11	$ 0.14	$ 1.56	$ 4.15	$ 0.69
Dividends per share paid on ordinary shares									$ 0.80	$ 0.72	$ 0.64

Computation of Earnings Per 159

Computation of Earnings Per Ordinary Share and Ordinary Share Equivalent - Narrative (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock compensation plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	6.8	2.5	5.5

Dividends (Details)

Dividends (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, 2014

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Feb. 16, 2017

Jan. 12, 2017

Dec. 29, 2016

Oct. 28, 2016

Dividends Paid [Line Items]

Dividends per share paid on ordinary shares

$ 0.80

$ 0.72

$ 0.64

Ordinary shares

Dividends Paid [Line Items]

Dividends per share paid on ordinary shares

$ 0.20

$ 0.20

$ 0.20

$ 0.20

$ 0.20

$ 0.20

$ 0.16

$ 0.16

$ 0.16

$ 0.16

$ 0.16

$ 0.16

Series D preference ordinary shares

Dividends Paid [Line Items]

Dividends on preference ordinary shares

[1],[2]

$ 12.9

$ 11.8

$ 11.7

Dividends declared and payable per share

$ 0.3525

$ 10.2222

Series E preference ordinary shares

Dividends Paid [Line Items]

Dividends on preference ordinary shares

[3]

65

65.1

65.1

Subsequent Event [Member] | Series D preference ordinary shares

Dividends Paid [Line Items]

Dividends declared and payable per share

$ 10.473

Subsequent Event [Member] | Series E preference ordinary shares

Dividends Paid [Line Items]

Dividends declared and payable per share

$ 32.50

Catlin Group Limited [Member] | Noncumulative perpetual preferred shares

Dividends Paid [Line Items]

Dividends on preference ordinary shares

[4]

$ 43.5

$ 21.8

$ 0

Catlin Group Limited [Member] | Subsequent Event [Member] | Noncumulative perpetual preferred shares

Dividends Paid [Line Items]

Dividends declared and payable per share

$ 21,800,000

[1]

On February 17, 2017, the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $10.473 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017.

[2]

On October 28, 2016, the Company announced that the Board of Directors of XL-Cayman resolved to pay a dividend of $10.2222 per share on XL-Cayman’s Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017. On December 29, 2016, the Board of Directors of XL-Cayman also resolved to pay an additional one-time dividend of $0.3525 per share on XL-Cayman's Series D Preference Ordinary Shares. The dividend was paid on January 17, 2017 to all shareholders of record at January 13, 2017.

[3]

On February 17, 2017, the Company announced that the Board of Directors of XL-Cayman resolved on February 16, 2017 to pay a dividend of $32.50 per share on XL-Cayman’s Series E Preference Ordinary Shares. The dividend will be paid on April 18, 2017 to all shareholders of record at April 14, 2017.

[4]

On January 12, 2017, the Board of Directors of Catlin-Bermuda resolved to pay a dividend in the aggregate amount of $21.8 million on CICL Prefs. The dividend was paid on January 19, 2017 to all shareholders of record at December 31, 2016.

Accumulated Other Comprehens161

Accumulated Other Comprehensive Income - Changes in AOCI, net of tax (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period		$ 686,616	$ 1,484,458	$ 736,657
OCI before reclassifications		355,773	(514,094)	916,952
Amounts reclassified from AOCI		(344,393)	(326,979)	(128,094)
Tax benefit (expense)		17,550	43,231	(41,057)
Net current period OCI - net of tax		28,930	(797,842)	747,801
Balance, net of tax, end of period		715,546	686,616	1,484,458
Cumulative adjustments recorded to value of future policy benefit reserves, amount		(62,295)	(170,688)	400,456
Unrealized Gains (Losses) on Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period	[1]	803,094	1,590,114	822,432
OCI before reclassifications	[1]	254,333	(474,304)	954,326
Amounts reclassified from AOCI	[1]	(353,910)	(346,911)	(143,330)
Tax benefit (expense)	[1]	26,912	34,195	(43,314)
Net current period OCI - net of tax	[1]	(72,665)	(787,020)	767,682
Balance, net of tax, end of period	[1]	730,429	803,094	1,590,114
Cumulative adjustments recorded to value of future policy benefit reserves, amount		(62,300)
Cumulative impact of net unrealized gains (losses) on future policy benefit reserve		212,100	274,400
OTTI Losses Recognized in AOCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period		(57,502)	(76,047)	(89,190)
OCI before reclassifications		0	0	0
Amounts reclassified from AOCI		6,599	18,987	14,082
Tax benefit (expense)		(49)	(442)	(939)
Net current period OCI - net of tax		6,550	18,545	13,143
Balance, net of tax, end of period		(50,952)	(57,502)	(76,047)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period		(36,503)	(11,188)	14,541
OCI before reclassifications		102,772	(33,690)	(26,497)
Amounts reclassified from AOCI		0	0	87
Tax benefit (expense)		(7,299)	8,375	681
Net current period OCI - net of tax		95,473	(25,315)	(25,729)
Balance, net of tax, end of period		58,970	(36,503)	(11,188)
Underfunded Pension Liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period		(24,641)	(20,789)	(13,239)
OCI before reclassifications		(1,332)	(6,100)	(10,877)
Amounts reclassified from AOCI		3,100	1,145	812
Tax benefit (expense)		(2,014)	1,103	2,515
Net current period OCI - net of tax		(246)	(3,852)	(7,550)
Balance, net of tax, end of period		(24,887)	(24,641)	(20,789)
Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, net of tax, beginning of period		2,168	2,368	2,113
OCI before reclassifications		0	0	0
Amounts reclassified from AOCI		(182)	(200)	255
Tax benefit (expense)		0	0	0
Net current period OCI - net of tax		(182)	(200)	255
Balance, net of tax, end of period		$ 1,986	$ 2,168	$ 2,368
[1]	Included in these amounts is the impact of Shadow Adjustments on future policy benefit reserves. As of December 31, 2015, $274.4 million was recorded. During the year ended December 31, 2016, additional net impacts of $(62.3) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $212.1 million at December 31, 2016.

Accumulated Other Comprehens162

Accumulated Other Comprehensive Income - Details about AOCI components (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized and unrealized gains (losses) on derivative instruments		$ 2,521	$ 53,123	$ 29,886
Operating Expenses		(2,063,362)	(1,966,939)	(1,341,315)
Exchange gains (losses) before tax		9,578	(22,504)	37,568
Amounts reclassified from AOCI		(344,393)	(326,979)	(128,094)
Provision for income tax		(42,129)	19,161	(96,897)
Unrealized Gains (Losses) on Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	[1]	(353,910)	(346,911)	(143,330)
OTTI Losses Recognized in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		6,599	18,987	14,082
Foreign Currency Translation Adjustments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		0	0	87
Underfunded Pension Liability
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		3,100	1,145	812
Cash Flow Hedge
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		(182)	(200)	255
Life Funds Withheld Assets
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold		152,589	223,272	5,067
OTTI on investments		(2,598)	(13,357)	(20,587)
Net adjustments related to future policy benefit reserves, net of tax		(51,100)	(125,747)
Net realized and unrealized gains (losses) on derivative instruments		(540,090)	(151,691)	$ (488,222)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		(344,393)	(326,979)
Provision for income tax		8,950	7,164
Total amount reclassified from AOCI, net of tax		(335,443)	(319,815)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold		(350,875)	(316,508)
OTTI on investments		81,595	95,344
Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Investments Transferred From Available for sale To Equity Method		33,530	0
Amounts reclassified from AOCI		(353,910)	(346,911)
Provision for income tax		10,084	7,597
Total amount reclassified from AOCI, net of tax		(343,826)	(339,314)
Reclassification out of Accumulated Other Comprehensive Income [Member] | OTTI Losses Recognized in AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold		7,038	18,014
OTTI on investments		(439)	973
Amounts reclassified from AOCI		6,599	18,987
Provision for income tax		(49)	(32)
Total amount reclassified from AOCI, net of tax		6,550	18,955
Reclassification out of Accumulated Other Comprehensive Income [Member] | Underfunded Pension Liability
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Expenses		3,100	1,145
Provision for income tax		(1,085)	(401)
Total amount reclassified from AOCI, net of tax		2,015	744
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI		(182)	(200)
Provision for income tax		0	0
Total amount reclassified from AOCI, net of tax		(182)	(200)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Life Funds Withheld Assets | Unrealized Gains (Losses) on Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net adjustments related to future policy benefit reserves, net of tax		$ (51,100)	$ (125,747)
[1]	Included in these amounts is the impact of Shadow Adjustments on future policy benefit reserves. As of December 31, 2015, $274.4 million was recorded. During the year ended December 31, 2016, additional net impacts of $(62.3) million were recorded, resulting in a total cumulative net impact of Shadow Adjustments on future policy benefit reserves of $212.1 million at December 31, 2016.

Taxation - Summary of tax years

Taxation - Summary of tax years open to examination by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2016
United States | Minimum
Income Tax Examination [Line Items]
Year under Examination	2,013
Open Tax Year	2,013
United States | Maximum
Income Tax Examination [Line Items]
Year under Examination	2,015
Open Tax Year	2,016
Ireland | Minimum
Income Tax Examination [Line Items]
Year under Examination	2,008
Open Tax Year	2,008
Ireland | Maximum
Income Tax Examination [Line Items]
Year under Examination	2,009
Open Tax Year	2,016
United Kingdom
Income Tax Examination [Line Items]
Year under Examination	2,014
United Kingdom | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,014
United Kingdom | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,016
Germany | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,014
Germany | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,016
Switzerland | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,011
Switzerland | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,016
France | Minimum
Income Tax Examination [Line Items]
Year under Examination	2,013
Open Tax Year	2,013
France | Maximum
Income Tax Examination [Line Items]
Year under Examination	2,014
Open Tax Year	2,016
Spain | Minimum
Income Tax Examination [Line Items]
Year under Examination	2,011
Open Tax Year	2,011
Spain | Maximum
Income Tax Examination [Line Items]
Year under Examination	2,012
Open Tax Year	2,016
Italy | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2,012
Italy | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2,016

Taxation - Distribution of pre-

Taxation - Distribution of pre-tax income by jurisdiction and components of income tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Distribution of pre-tax income by jurisdiction:
U.S.	$ 68,970	$ (5,931)	$ 228,708
Non U.S.	543,304	1,300,109	137,027
Income (loss) before income taxes	612,274	1,294,178	365,735
Current expense:
U.S.	(12,201)	(22,698)	45,598
Non U.S.	59,031	67,784	81,371
Total current expense	46,830	45,086	126,969
Deferred expense (benefit):
U.S.	8,502	(63,491)	8,572
Non U.S.	(13,203)	(756)	(38,644)
Total deferred expense (benefit)	(4,701)	(64,247)	(30,072)
Total tax expense	$ 42,129	$ (19,161)	$ 96,897

Taxation - Tax rates by jurisdi

Taxation - Tax rates by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2016
Ireland | Active income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	12.50%	[1]
Ireland | Passive income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	25.00%
Bermuda
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	0.00%
United States
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	35.00%
United Kingdom
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	20.00%
Switzerland | Active income
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	21.15%	[2]
Germany
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	15.00%	[3]
Germany | Including surcharge and other taxes
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	33.00%
France
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	33.33%	[4]
France | Including surcharge and other taxes
Income Tax Disclosure [Line Items]
Applicable statutory tax rate, by jurisdiction	34.43%
[1]	The 12.5% statutory corporate income tax rate applies to active income from the conduct of a trade in Ireland. For passive income or income from other defined activities the rate increases to 25%.
[2]	Represents the combined federal and cantonal rate primarily applicable to XL Catlin Swiss entities.
[3]	The statutory corporate income tax rate is 15% . However, including applicable surcharges and local trade tax, which can vary by location, would increase the combined statutory rate to approximately 33%.
[4]	The statutory corporate income tax rate is 33.33%. However, with the mandatory social surcharge, the combined statutory rate would increase to 34.43%.

Taxation - Reconciliation of ef

Taxation - Reconciliation of effective tax rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected tax provision at weighted average rate	$ (31,080)	$ (50,797)	$ 132,775
Permanent differences:
Non taxable (income) loss	(19,937)	(23,036)	(19,870)
Revision to prior year estimates	(24,121)	7,402	2,016
State, local and foreign taxes	23,157	27,499	47,078
Valuation allowance	1,197	9,517	(181)
Net allocated investment income	5,990	(405)	3,399
Stock awards	543	(433)	411
Non-deductible expenses	48,206	42,839	22,556
Realized capital loss carry-forward valuation allowance reduction	(905)	2,075	(2,916)
Adjustments related to Life Retro Arrangements	21,682	(35,045)	(99,535)
Non-taxable reserve release	(6,233)	(11,877)	3,974
Uncertain tax positions	23,630	13,100	7,190
Total tax expense	$ 42,129	$ (19,161)	$ 96,897

Taxation - Components of deferr

Taxation - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net unpaid loss reserve discount	$ 96,357	$ 111,584
Net unearned premiums	95,676	80,434
Compensation liabilities	96,280	94,013
Net operating loss	323,716	181,295
Investment adjustments	14,030	14,399
Pension	6,817	10,370
Bad debt reserve	12,418	7,425
Amortizable goodwill	967	5,396
Net unrealized depreciation on investments	5,915	5,051
Stock options	7,249	16,192
Depreciation	26,525	13,299
Net realized capital losses	89,568	98,756
Deferred intercompany capital losses	18,221	26,164
Untaxed Lloyd's result	0	3,769
Deferred acquisition costs	17,820	31,133
Currency translation adjustments	0	6,280
Capital loss carryforwards, tax effected	71,651	5,047
Other	34,708	19,930
Deferred tax asset, gross of valuation allowance	917,918	730,537
Valuation allowance	367,366	276,301
Deferred Tax Assets, net of valuation allowance	550,552	454,236
Deferred tax liabilities:
Net unrealized appreciation on investments	21,500	51,010
Unremitted earnings	0	3,739
Deferred acquisition costs	10,858	8,308
Currency translation adjustments	12,813	1,210
Regulatory reserves	116,500	64,352
Deferred Tax Liabilities Unearned Revenue	4,380	0
Investment adjustment	5,269	6,373
Untaxed Lloyd's result	11,940	0
Depreciation expense	15,601	11,500
Syndicate capacity	82,106	92,756
Intangible assets	32,508	40,126
Other	3,806	13,202
Deferred tax liability	317,281	292,576
Net deferred tax assets	$ 233,271	$ 161,660

Taxation - Summary of valuation

Taxation - Summary of valuation allowance (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance [Line Items]
Valuation allowance	$ 367,366	$ 276,301
Ireland
Valuation Allowance [Line Items]
Valuation allowance	96,642	93,396
United States
Valuation Allowance [Line Items]
Valuation allowance	92,999	106,624
United Kingdom
Valuation Allowance [Line Items]
Valuation allowance	32,528	46,732
Switzerland
Valuation Allowance [Line Items]
Valuation allowance	15,025	7,818
Other
Valuation Allowance [Line Items]
Valuation allowance	$ 130,172	$ 21,731

Taxation - Reconciliation of un

Taxation - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of the year	$ 80,590	$ 37,190	$ 30,000
Increases for tax positions taken during the year	25,250	20,370	12,182
Increases for tax positions taken in prior years	11,700	38,650	15,304
Decreases for tax positions taken in prior years	(6,440)	(4,850)	(20,296)
Decreases for lapse of the applicable statute of limitations	(13,320)	(10,770)	0
Unrecognized tax benefits, end of the year	$ 97,780	$ 80,590	$ 37,190

Taxation - Narrative (Details)

Taxation - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Line Items]
Deferred tax asset, per balance sheet	$ 310,542	$ 282,311
Deferred tax liability, per balance sheet	77,271	120,651
Valuation allowance	367,366	276,301
Increase (decrease) in valuation allowance, amount	91,100
Capital loss valuation allowance, amount	89,600
Capital loss carryforwards, tax effected	71,651	5,047
Capital loss carryforwards available	293,500
Net operating loss carryforwards, amount	1,600,000
Net operating loss	323,716	181,295
Net operating loss carryforwards valuation allowance, amount	206,600
Net operating loss carryforwards, tax effected	117,100
Net realized capital losses	89,568	98,756
Excess tax benefits on share-based compensation	10,600	9,200
Unrecognized tax benefits	97,780	80,590	$ 37,190	$ 30,000
Accrued interest and penalties	900	400	$ 400
United States
Income Tax Disclosure [Line Items]
Valuation allowance	92,999	106,624
Capital loss valuation allowance, amount	57,900
Capital loss carryforwards available	165,500
Net operating loss carryforwards, amount	108,000
Net operating loss	37,800
Net operating loss carryforwards valuation allowance, amount	800
Net operating loss carryforwards, tax effected	37,000
Net realized capital losses	57,900
United States | Deferred tax asset restricted under Internal Revenue Code Section 382
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	47,000
United States | Carryforwards expiring In 2018
Income Tax Disclosure [Line Items]
Capital loss carryforwards available	59,100
United States | Expiring in future years
Income Tax Disclosure [Line Items]
Capital loss carryforwards available	106,300
United States | Alternative minimum tax
Income Tax Disclosure [Line Items]
Capital loss carryforwards, tax effected	32,300
United States | Foreign tax credit
Income Tax Disclosure [Line Items]
Capital loss carryforwards, tax effected	5,600
United States | Research and development tax credit
Income Tax Disclosure [Line Items]
Capital loss carryforwards, tax effected	3,100
Ireland
Income Tax Disclosure [Line Items]
Valuation allowance	96,642	93,396
Capital loss valuation allowance, amount	30,500
Capital loss carryforwards available	122,100
Net operating loss carryforwards, amount	484,900
Net operating loss	60,600
Net operating loss carryforwards valuation allowance, amount	60,600
Net realized capital losses	30,500
Other jurisdictions
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	629,100
Net operating loss	162,600
Net operating loss carryforwards valuation allowance, amount	104,100
Net operating loss carryforwards, tax effected	58,500
Other jurisdictions | No expiration date
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	609,100
United Kingdom
Income Tax Disclosure [Line Items]
Valuation allowance	32,528	46,732
Capital loss valuation allowance, amount	1,100
Capital loss carryforwards available	5,900
Net operating loss carryforwards, amount	203,300
Net operating loss	39,000
Net operating loss carryforwards valuation allowance, amount	26,200
Net operating loss carryforwards, tax effected	12,800
Net realized capital losses	1,100
United Kingdom | Foreign tax credit
Income Tax Disclosure [Line Items]
Capital loss carryforwards, tax effected	30,700
Switzerland
Income Tax Disclosure [Line Items]
Valuation allowance	15,025	$ 7,818
Net operating loss carryforwards, amount	200,100
Net operating loss	23,700
Net operating loss carryforwards valuation allowance, amount	14,900
Net operating loss carryforwards, tax effected	8,800
Switzerland | Carryforwards Expiring in Next Fiscal Year [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	5,300
Switzerland | Carryforwards expiring In 2018
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	4,000
Switzerland | Expiring in future years
Income Tax Disclosure [Line Items]
Net operating loss carryforwards, amount	$ 190,800

Statutory Financial Data (Detai

Statutory Financial Data (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2016USD ($)subsidiary	Dec. 31, 2015USD ($)subsidiary	Dec. 31, 2014USD ($)
XL Group Ltd
Statutory Accounting Practices [Line Items]
Cash and investments, net of liabilities associated with cash sweeping arrangements		$ 1,000	$ 11,600
XL Cayman
Statutory Accounting Practices [Line Items]
Cash and investments, net of liabilities associated with cash sweeping arrangements		700,000	900,000
Bermuda
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	[1]	6,351,874	7,722,123
Actual statutory capital and surplus	[1],[2]	12,333,870	11,112,176
Statutory net income (loss)		$ 724,711	1,513,924	$ 361,022
BSCR level for principal operating subsidiaries		100.00%
Maximum permitted dividends as a percentage of prior year statutory capital and surplus		25.00%
Maximum permitted dividends as a percentage of statutory capital		15.00%
Maximum dividend permitted without affidavit		$ 3,200,000	2,800,000
Distributable reserves, amount		8,100,000
United States
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus	[3]	822,651	747,313
Actual statutory capital and surplus	[2],[3]	2,362,827	2,234,767
Statutory net income (loss)		$ 96,481	17,574	155,751
RBC level for certain operating subsidiaries		100.00%
Maximum permitted dividends as a percentage of statutory policyholder surplus		10.00%
Maximum permitted dividends as a percentage of "Adjusted net investment income"		100.00%
United States | XL Reinsurance America, Inc. [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[2],[3]	$ 2,100,000
Maximum dividend permitted without affidavit		66,900
Statutory earned surplus, amount		$ 66,900	31,700
Number of property and casualty subsidiaries | subsidiary		7
United States | Catlin Specialty Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[2],[3]	$ 234,200
Maximum dividend permitted without affidavit		0
Statutory earned surplus, amount		$ 3,400
Number of property and casualty subsidiaries | subsidiary		3
United States | T.H.E. Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus	[2],[3]	$ 52,300
Maximum dividend permitted without affidavit		0
Europe, UK, and other
Statutory Accounting Practices [Line Items]
Required statutory capital and surplus		4,320,140	4,445,247
Actual statutory capital and surplus	[2]	5,201,602	6,054,122
Statutory net income (loss)		366,708	$ (125,758)	$ 215,787
Ireland
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus		900,000
Funds at Lloyds [Member]
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus		1,500,000
United Kingdom
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus		1,200,000
Switzerland
Statutory Accounting Practices [Line Items]
Actual statutory capital and surplus		$ 1,500,000
Statutory earned surplus deficit | United States | XL Reinsurance America, Inc. [Member]
Statutory Accounting Practices [Line Items]
Number of property and casualty subsidiaries | subsidiary		1	2
Statutory earned surplus deficit | United States | Catlin Specialty Insurance Company [Member]
Statutory Accounting Practices [Line Items]
Number of property and casualty subsidiaries | subsidiary		2
[1]	Required statutory capital and surplus at December 31, 2016 represents 100% Bermuda Solvency Capital Requirement ("BSCR") level for the top Bermuda operating subsidiary, XL Bermuda Ltd, calculated on a consolidated basis (and therefore includes a BSCR requirement for all regions).
[2]	Statutory assets in Bermuda include investments in other U.S. and international subsidiaries reported separately herein.
[3]	Required statutory capital and surplus represents 100% Risk-Based Capital level for principal U.S. operating subsidiaries.

Unaudited Quarterly Financia172

Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands		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
Interim Reporting [Line Items]
Net premiums earned										$ 9,777,934	$ 8,226,425	$ 5,895,070
Underwriting profit (loss)										$ 547,325	$ 587,409	$ 585,907
Net income (loss) attributable to ordinary shareholders		$ 304,700	$ 70,601	$ 43,782	$ 21,885	$ 228,550	$ 27,282	$ 915,039	$ 36,281
Earnings (loss) per ordinary share and ordinary share equivalent - basic (in dollars per share)		$ 1.13	$ 0.26	$ 0.16	$ 0.07	$ 0.77	$ 0.09	$ 3.16	$ 0.14	$ 1.58	$ 4.22	$ 0.71
Earnings (loss) per ordinary share and ordinary share equivalent - diluted (in dollars per share)		$ 1.12	$ 0.25	$ 0.15	$ 0.07	$ 0.76	$ 0.09	$ 3.11	$ 0.14	$ 1.56	$ 4.15	$ 0.69
Corporate and other
Interim Reporting [Line Items]
Net premiums earned	[1]									$ 12,047	$ 62,241	$ 177,632
Underwriting profit (loss)	[1]									(23,328)	(65,782)	(90,139)
Operating Segments [Member] | Property and casualty operations
Interim Reporting [Line Items]
Net premiums earned		$ 2,454,060	$ 2,431,677	$ 2,528,704	$ 2,351,446	$ 2,375,155	$ 2,405,740	$ 2,063,795	$ 1,319,494	9,765,887	8,164,184	5,717,438
Underwriting profit (loss)		126,420	166,851	101,893	175,489	183,458	114,118	208,779	146,836	$ 570,653	$ 653,191	$ 676,046
Operating Segments [Member] | Corporate and other
Interim Reporting [Line Items]
Net premiums earned		$ 3,015	$ 2,360	$ 3,508	$ 3,164	$ 11,665	$ 17,812	$ 18,258	$ 14,506
[1]	Corporate and Other includes other items of our revenue and expenditures that are not evaluated at the segment level for reporting purposes, as well as the Company's Run-Off Life Operations.

Guarantor Financial Informat173

Guarantor Financial Information - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
ASSETS
Total investments available for sale	$ 31,919,126		$ 33,753,898
Total investments trading	1,626,577		1,296,029
Investments in affiliates	2,177,645		1,708,899
Other investments	1,164,564		1,433,057
Total investments	36,887,912		38,191,883
Cash and cash equivalents	3,426,988		3,256,236		$ 2,521,814	$ 1,800,832
Restricted cash	153,504		154,992
Investments in subsidiaries on an equity basis	0		0
Accrued investment income	284,366		312,667
Deferred acquisition costs and value of business acquired	946,721		890,568
Ceded unearned premiums	1,687,864		1,821,793
Premiums receivable	5,522,976		4,712,493
Reinsurance balances receivable	577,479		418,666
Unpaid losses and loss expenses recoverable	5,491,297		5,262,706
Receivable from investments sold	128,411		231,158
Goodwill and other intangible assets	2,203,653		2,210,266		447,952	411,611
Deferred tax asset	310,542		282,311
Amounts due from subsidiaries	0		0
Other assets	812,389		937,199
Total assets	58,434,102		58,682,938
LIABILITIES AND SHAREHOLDERS' EQUITY
Unpaid losses and loss expenses	25,939,571		25,439,744		19,353,243	20,481,065
Deposit liabilities	1,116,233		1,168,376
Future policy benefit reserves	3,506,047		4,163,500
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	998,968		914,629
Unearned premiums	7,293,028		7,043,358
Notes payable and debt	2,647,677		2,644,970
Reinsurance balances payable	2,451,717		2,117,727
Payable for investments purchased	226,009		130,060
Deferred tax liability	77,271		120,651
Amounts due to subsidiaries	0		0
Other liabilities	1,216,902		1,285,460
Total liabilities	45,473,423		45,028,475
Shareholders' equity attributable to XL Group Ltd	10,938,512		11,677,079
Non-controlling interest in equity of consolidated subsidiaries	2,022,167		1,977,384
Total shareholders' equity	12,960,679		13,654,463		11,435,766
Total liabilities and shareholders' equity	58,434,102		58,682,938
Consolidating Adjustments and Eliminations
ASSETS
Total investments available for sale	0		0
Total investments trading	0		0
Investments in affiliates	0		0
Other investments	0		0
Total investments	0		0
Cash and cash equivalents	0		0		0	0
Restricted cash	0		0
Investments in subsidiaries on an equity basis	(25,135,893)		(27,485,324)
Accrued investment income	(55)		0
Deferred acquisition costs and value of business acquired	0		0
Ceded unearned premiums	0		0
Premiums receivable	0		0
Reinsurance balances receivable	0		0
Unpaid losses and loss expenses recoverable	0		0
Receivable from investments sold	0		0
Goodwill and other intangible assets	0		0
Deferred tax asset	0		0
Amounts due from subsidiaries	(115,742)		(1,087,594)
Other assets	0		0
Total assets	(25,251,690)		(28,572,918)
LIABILITIES AND SHAREHOLDERS' EQUITY
Unpaid losses and loss expenses	0		0
Deposit liabilities	0		0
Future policy benefit reserves	0		0
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	0		0
Unearned premiums	0		0
Notes payable and debt	0		0
Reinsurance balances payable	0		0
Payable for investments purchased	0		0
Deferred tax liability	0		0
Amounts due to subsidiaries	(115,742)		(1,087,594)
Other liabilities	0		0
Total liabilities	(115,742)		(1,087,594)
Shareholders' equity attributable to XL Group Ltd	(25,135,893)		(27,485,324)
Non-controlling interest in equity of consolidated subsidiaries	(55)		0
Total shareholders' equity	(25,135,948)		(27,485,324)
Total liabilities and shareholders' equity	(25,251,690)		(28,572,918)
XL-Bermuda
ASSETS
Total investments available for sale	0	[1]	0
Total investments trading	0	[1]	0
Investments in affiliates	0	[1]	0
Other investments	0	[1]	0
Total investments	0	[1]	0
Cash and cash equivalents	1,022	[1]	11,557	[1]	22,443	12,709
Restricted cash	0	[1]	0
Investments in subsidiaries on an equity basis	10,897,195	[1]	11,648,673
Accrued investment income	55	[1]	0
Deferred acquisition costs and value of business acquired	0	[1]	0
Ceded unearned premiums	0	[1]	0
Premiums receivable	0	[1]	0
Reinsurance balances receivable	0	[1]	0
Unpaid losses and loss expenses recoverable	0	[1]	0
Receivable from investments sold	0	[1]	0
Goodwill and other intangible assets	0	[1]	0
Deferred tax asset	0	[1]	0
Amounts due from subsidiaries	42,780	[1]	33,417
Other assets	15,188	[1]	2,748
Total assets	10,956,240	[1]	11,696,395
LIABILITIES AND SHAREHOLDERS' EQUITY
Unpaid losses and loss expenses	0	[1]	0
Deposit liabilities	0	[1]	0
Future policy benefit reserves	0	[1]	0
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	0	[1]	0
Unearned premiums	0	[1]	0
Notes payable and debt	0	[1]	0
Reinsurance balances payable	0	[1]	0
Payable for investments purchased	0	[1]	0
Deferred tax liability	0	[1]	0
Amounts due to subsidiaries	0	[1]	0
Other liabilities	17,728	[1]	19,316
Total liabilities	17,728	[1]	19,316
Shareholders' equity attributable to XL Group Ltd	10,938,512	[1]	11,677,079
Non-controlling interest in equity of consolidated subsidiaries	0	[1]	0
Total shareholders' equity	10,938,512	[1]	11,677,079
Total liabilities and shareholders' equity	10,956,240	[1]	11,696,395
XL-Cayman
ASSETS
Total investments available for sale	638,236		516,425
Total investments trading	0		0
Investments in affiliates	0		0
Other investments	9		877
Total investments	638,245		517,302
Cash and cash equivalents	84,286		369,997		42,970	35,794
Restricted cash	0		0
Investments in subsidiaries on an equity basis	14,238,698		15,836,651
Accrued investment income	2,981		2,323
Deferred acquisition costs and value of business acquired	0		0
Ceded unearned premiums	0		0
Premiums receivable	0		0
Reinsurance balances receivable	0		0
Unpaid losses and loss expenses recoverable	0		0
Receivable from investments sold	0		0
Goodwill and other intangible assets	0		0
Deferred tax asset	0		0
Amounts due from subsidiaries	0		0
Other assets	40,108		44,570
Total assets	15,004,318		16,770,843
LIABILITIES AND SHAREHOLDERS' EQUITY
Unpaid losses and loss expenses	0		0
Deposit liabilities	0		0
Future policy benefit reserves	0		0
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	0		0
Unearned premiums	0		0
Notes payable and debt	2,647,677		2,644,970
Reinsurance balances payable	0		0
Payable for investments purchased	0		0
Deferred tax liability	0		0
Amounts due to subsidiaries	72,962		1,087,594
Other liabilities	41,984		45,106
Total liabilities	2,762,623		3,777,670
Shareholders' equity attributable to XL Group Ltd	10,897,195		11,648,673
Non-controlling interest in equity of consolidated subsidiaries	1,344,500		1,344,500
Total shareholders' equity	12,241,695		12,993,173
Total liabilities and shareholders' equity	15,004,318		16,770,843
Other XL-Bermuda Subsidiaries
ASSETS
Total investments available for sale	31,280,890		33,237,473
Total investments trading	1,626,577		1,296,029
Investments in affiliates	2,177,645		1,708,899
Other investments	1,164,555		1,432,180
Total investments	36,249,667		37,674,581
Cash and cash equivalents	3,341,680		2,874,682		$ 2,456,401	$ 1,752,329
Restricted cash	153,504		154,992
Investments in subsidiaries on an equity basis	0		0
Accrued investment income	281,385		310,344
Deferred acquisition costs and value of business acquired	946,721		890,568
Ceded unearned premiums	1,687,864		1,821,793
Premiums receivable	5,522,976		4,712,493
Reinsurance balances receivable	577,479		418,666
Unpaid losses and loss expenses recoverable	5,491,297		5,262,706
Receivable from investments sold	128,411		231,158
Goodwill and other intangible assets	2,203,653		2,210,266
Deferred tax asset	310,542		282,311
Amounts due from subsidiaries	72,962		1,054,177
Other assets	757,093		889,881
Total assets	57,725,234		58,788,618
LIABILITIES AND SHAREHOLDERS' EQUITY
Unpaid losses and loss expenses	25,939,571		25,439,744
Deposit liabilities	1,116,233		1,168,376
Future policy benefit reserves	3,506,047		4,163,500
Funds withheld on GreyCastle life retrocession arrangements (net of future policy benefit reserves recoverable: 2016 - $3,072,615; 2015 - $3,719,131)	998,968		914,629
Unearned premiums	7,293,028		7,043,358
Notes payable and debt	0		0
Reinsurance balances payable	2,451,717		2,117,727
Payable for investments purchased	226,009		130,060
Deferred tax liability	77,271		120,651
Amounts due to subsidiaries	42,780		0
Other liabilities	1,157,190		1,221,038
Total liabilities	42,808,814		42,319,083
Shareholders' equity attributable to XL Group Ltd	14,238,698		15,836,651
Non-controlling interest in equity of consolidated subsidiaries	677,722		632,884
Total shareholders' equity	14,916,420		16,469,535
Total liabilities and shareholders' equity	$ 57,725,234		$ 58,788,618
[1]	Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation.

Guarantor Financial Informat174

Guarantor Financial Information - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Condensed Statement of Income Captions [Line Items]
Net premiums earned	$ 9,777,934		$ 8,226,425	$ 5,895,070
Net investment income	827,133		872,370	918,625
Total net realized gains (losses) on investments	372,138		202,178	107,462
Net realized and unrealized gains (losses) on derivative instruments	2,521		53,123	29,886
Income (loss) from investment fund affiliates	70,758		73,320	95,816
Fee income and other	35,692		33,201	43,630
Total revenues	10,546,086		9,308,926	6,602,267
Net losses and loss expenses incurred	6,072,835		4,766,200	3,258,393
Claims and policy benefits	28,244		115,997	242,963
Acquisition costs	1,620,671		1,317,448	738,118
Operating expenses	2,063,362		1,966,939	1,341,315
Exchange (gains) losses	(9,578)		22,504	(37,568)
Loss (gain) sale of subsidiaries	(7,088)		0	666,423
Extinguishment of debt	0		5,592	0
Interest expense	209,763		205,215	134,106
Total expenses	9,978,209		8,399,895	6,343,750
Income (loss) before income tax and income (loss) from operating affiliates	567,877		909,031	258,517
Income (loss) from operating affiliates	44,397		44,740	107,218
Gain on sale of operating affiliate	0		340,407	0
Equity in net earnings (losses) of subsidiaries	0		0	0
Provision (benefit) for income tax	42,129		(19,161)	96,897
Net income (loss)	570,145		1,313,339	268,838
Non-controlling interests	129,177		106,187	80,498
Net income (loss) attributable to common shareholders	440,968		1,207,152	188,340
Comprehensive income (loss)	469,898		409,310	936,141
Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net investment income	154,751		187,489	129,575
Net realized and unrealized gains (losses) on derivative instruments	(540,090)		(151,691)	(488,222)
Consolidating Adjustments and Eliminations
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0		0	0
Net investment income	(436)		3,836	8,483
Total net realized gains (losses) on investments	0		(8,765)	(22,229)
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
Income (loss) from investment fund affiliates	0		0	0
Fee income and other	0		0	0
Total revenues	(436)		(4,929)	(13,746)
Net losses and loss expenses incurred	0		0	0
Claims and policy benefits	0		0	0
Acquisition costs	0		0	0
Operating expenses	0		0	0
Exchange (gains) losses	0		0	0
Loss (gain) sale of subsidiaries	0			0
Extinguishment of debt			0
Interest expense	0		0	0
Total expenses	0		0	0
Income (loss) before income tax and income (loss) from operating affiliates	(436)		(4,929)	(13,746)
Income (loss) from operating affiliates	0		0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	(1,276,926)		(2,703,013)	(548,445)
Provision (benefit) for income tax	0		0	0
Net income (loss)	(1,277,362)		(2,707,942)	(562,191)
Non-controlling interests	(436)		0	0
Net income (loss) attributable to common shareholders	(1,276,926)		(2,707,942)	(562,191)
Comprehensive income (loss)	(1,334,786)		(1,112,258)	(2,057,793)
Consolidating Adjustments and Eliminations | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
XL-Bermuda
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0	[1]	0	0
Net investment income	436	[1]	169	275
Total net realized gains (losses) on investments	0	[1]	0	0
Net realized and unrealized gains (losses) on derivative instruments	0	[1]	0	0
Income (loss) from investment fund affiliates	0	[1]	0	0
Fee income and other	0	[1]	0	0
Total revenues	436	[1]	169	275
Net losses and loss expenses incurred	0	[1]	0	0
Claims and policy benefits	0	[1]	0	0
Acquisition costs	0	[1]	0	0
Operating expenses	93,247	[1]	46,340	9,646
Exchange (gains) losses	(1,106)	[1]	(345)	127
Loss (gain) sale of subsidiaries	0	[1]		0
Extinguishment of debt			0
Interest expense	(4)	[1]	11	5
Total expenses	92,137	[1]	46,006	9,778
Income (loss) before income tax and income (loss) from operating affiliates	(91,701)	[1]	(45,837)	(9,503)
Income (loss) from operating affiliates	0	[1]	0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	532,049	[1]	1,253,609	197,843
Provision (benefit) for income tax	(620)	[1]	620	0
Net income (loss)	440,968	[1]	1,207,152	188,340
Non-controlling interests	0	[1]	0	0
Net income (loss) attributable to common shareholders	440,968	[1]	1,207,152	188,340
Comprehensive income (loss)	469,898	[1]	409,310	936,141
XL-Bermuda | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0	[1]	0	0
XL-Cayman
Condensed Statement of Income Captions [Line Items]
Net premiums earned	0		0	0
Net investment income	9,135		9,363	20,256
Total net realized gains (losses) on investments	1,918		13,814	27,541
Net realized and unrealized gains (losses) on derivative instruments	0		12,363	0
Income (loss) from investment fund affiliates	0		0	0
Fee income and other	0		0	0
Total revenues	11,053		35,540	47,797
Net losses and loss expenses incurred	0		0	0
Claims and policy benefits	0		0	0
Acquisition costs	0		0	0
Operating expenses	4,985		10,565	13,102
Exchange (gains) losses	(343)		20	168
Loss (gain) sale of subsidiaries	0			0
Extinguishment of debt			0
Interest expense	140,644		143,330	110,323
Total expenses	145,286		153,915	123,593
Income (loss) before income tax and income (loss) from operating affiliates	(134,233)		(118,375)	(75,796)
Income (loss) from operating affiliates	0		0	0
Gain on sale of operating affiliate			0
Equity in net earnings (losses) of subsidiaries	744,877		1,449,404	350,602
Provision (benefit) for income tax	0		245	(212)
Net income (loss)	610,644		1,330,784	275,018
Non-controlling interests	78,595		77,175	77,175
Net income (loss) attributable to common shareholders	532,049		1,253,609	197,843
Comprehensive income (loss)	560,979		455,767	945,644
XL-Cayman | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	0		0	0
Other XL-Bermuda Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net premiums earned	9,777,934		8,226,425	5,895,070
Net investment income	817,998		859,002	889,611
Total net realized gains (losses) on investments	370,220		197,129	102,150
Net realized and unrealized gains (losses) on derivative instruments	2,521		40,760	29,886
Income (loss) from investment fund affiliates	70,758		73,320	95,816
Fee income and other	35,692		33,201	43,630
Total revenues	10,535,033		9,278,146	6,567,941
Net losses and loss expenses incurred	6,072,835		4,766,200	3,258,393
Claims and policy benefits	28,244		115,997	242,963
Acquisition costs	1,620,671		1,317,448	738,118
Operating expenses	1,965,130		1,910,034	1,318,567
Exchange (gains) losses	(8,129)		22,829	(37,863)
Loss (gain) sale of subsidiaries	(7,088)			666,423
Extinguishment of debt			5,592
Interest expense	69,123		61,874	23,778
Total expenses	9,740,786		8,199,974	6,210,379
Income (loss) before income tax and income (loss) from operating affiliates	794,247		1,078,172	357,562
Income (loss) from operating affiliates	44,397		44,740	107,218
Gain on sale of operating affiliate			340,407
Equity in net earnings (losses) of subsidiaries	0		0	0
Provision (benefit) for income tax	42,749		(20,026)	97,109
Net income (loss)	795,895		1,483,345	367,671
Non-controlling interests	51,018		29,012	3,323
Net income (loss) attributable to common shareholders	744,877		1,454,333	364,348
Comprehensive income (loss)	773,807		656,491	1,112,149
Other XL-Bermuda Subsidiaries | Life Funds Withheld Assets
Condensed Statement of Income Captions [Line Items]
Net realized and unrealized gains (losses) on derivative instruments	$ (540,090)		$ (151,691)	$ (488,222)
[1]	Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation.

Guarantor Financial Informat175

Guarantor Financial Information - Cash Flow (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 915,337		$ 615,556		$ 963,184
Proceeds from sale of fixed maturities and short-term investments	12,757,580		16,868,228		4,896,112
Proceeds from redemption of fixed maturities and short-term investments	3,847,709		3,751,174		3,601,793
Proceeds from sale of equity securities	848,779		664,735		571,410
Purchases of fixed maturities and short term investments	(15,457,689)		(19,718,064)		(7,158,258)
Purchases of equity securities	(1,103,447)		(567,334)		(445,504)
Proceeds from sale of affiliates	397,091		748,575		240,785
Purchases of affiliates	(681,385)		(280,856)		(371,226)
Purchase of subsidiaries, net of acquired cash	(92,893)		(1,020,015)		0
Proceeds from sale of subsidiary	22,998		0		570,000
Returns of capital from subsidiaries	0		0		0
Change in restricted cash	1,488		(154,992)		0
Other, net	197,536		(155,019)		(193,491)
Net cash provided by (used in) investing activities	737,767		136,432		1,711,621
Proceeds from issuance of ordinary shares and exercise of stock options	9,854		9,976		6,367
Buybacks of ordinary shares	(1,051,050)		(468,971)		(801,953)
Dividends paid on ordinary shares	(222,761)		(208,516)		(169,620)
Return of capital	0		0		0
Distributions to non-controlling interests	(130,447)		(117,683)		(78,465)
Contributions from non-controlling interest	47,524		23,610		48,261
Proceeds from issuance of debt	0		980,600		0
Repayment of debt	(8,248)		(87,447)		(600,000)
Net proceeds from affiliated notional cash pooling programs			0		0
Deposit liabilities	(69,482)		(84,758)		(268,298)
Net cash provided by (used in) financing activities	(1,424,610)		46,811		(1,863,708)
Effects of exchange rate changes on foreign currency cash	(57,742)		(64,377)		(90,115)
Net change in cash and cash equivalents	170,752		734,422		720,982
Cash and cash equivalents – beginning of period	3,256,236		2,521,814		1,800,832
Cash and cash equivalents – end of period	3,426,988		3,256,236		2,521,814
Consolidating Adjustments and Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(2,955,038)		(764,277)		(858,521)
Proceeds from sale of fixed maturities and short-term investments	(583,466)		(359,894)		(472,539)
Proceeds from redemption of fixed maturities and short-term investments	0		0		0
Proceeds from sale of equity securities	0		0		0
Purchases of fixed maturities and short term investments	583,466		359,894		472,539
Purchases of equity securities	0		0		0
Proceeds from sale of affiliates	0		0		0
Purchases of affiliates	0		0		0
Purchase of subsidiaries, net of acquired cash	0		2,317,699
Proceeds from sale of subsidiary	0		(2,317,699)		0
Returns of capital from subsidiaries	(739,930)		(2,112,037)		(561,656)
Change in restricted cash	0		0
Other, net	0		0		0
Net cash provided by (used in) investing activities	(739,930)		(2,112,037)		(561,656)
Proceeds from issuance of ordinary shares and exercise of stock options	0		0		0
Buybacks of ordinary shares	0		0		0
Dividends paid on ordinary shares	2,955,038		764,277		858,521
Return of capital	739,930		2,112,037		561,656
Distributions to non-controlling interests	0		0		0
Contributions from non-controlling interest	0		0		0
Proceeds from issuance of debt			0
Repayment of debt	0		0		0
Net proceeds from affiliated notional cash pooling programs			0		0
Deposit liabilities	0		0		0
Net cash provided by (used in) financing activities	3,694,968		2,876,314		1,420,177
Effects of exchange rate changes on foreign currency cash	0		0		0
Net change 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
XL-Bermuda
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	978,695	[1]	561,468		895,854
Proceeds from sale of fixed maturities and short-term investments	0	[1]	0		0
Proceeds from redemption of fixed maturities and short-term investments	0	[1]	0		0
Proceeds from sale of equity securities	0	[1]	0		0
Purchases of fixed maturities and short term investments	0	[1]	0		0
Purchases of equity securities	0	[1]	0		0
Proceeds from sale of affiliates	0	[1]	0		0
Purchases of affiliates	0	[1]	0		0
Purchase of subsidiaries, net of acquired cash	0	[1]	(2,287,579)
Proceeds from sale of subsidiary	0	[1]	2,317,699		0
Returns of capital from subsidiaries	274,727	[1]	65,037		79,086
Change in restricted cash	0	[1]	0
Other, net	0	[1]	0		0
Net cash provided by (used in) investing activities	274,727	[1]	95,157		79,086
Proceeds from issuance of ordinary shares and exercise of stock options	9,854	[1]	9,976		6,367
Buybacks of ordinary shares	(1,051,050)	[1]	(468,971)		(801,953)
Dividends paid on ordinary shares	(222,761)	[1]	(208,516)		(169,620)
Return of capital	0	[1]	0		0
Distributions to non-controlling interests	0	[1]	0		0
Contributions from non-controlling interest	0	[1]	0		0
Proceeds from issuance of debt			0
Repayment of debt	0	[1]	0		0
Net proceeds from affiliated notional cash pooling programs			0		0
Deposit liabilities	0	[1]	0		0
Net cash provided by (used in) financing activities	(1,263,957)	[1]	(667,511)		(965,206)
Effects of exchange rate changes on foreign currency cash	0	[1]	0		0
Net change in cash and cash equivalents	(10,535)	[1]	(10,886)		9,734
Cash and cash equivalents – beginning of period	11,557	[1]	22,443		12,709
Cash and cash equivalents – end of period	1,022	[1]	11,557	[1]	22,443
XL-Cayman
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	775,100		148,850		518,715
Proceeds from sale of fixed maturities and short-term investments	303,070		1,482,875		574,673
Proceeds from redemption of fixed maturities and short-term investments	97,168		188,788		351,737
Proceeds from sale of equity securities	0		0		0
Purchases of fixed maturities and short term investments	(534,502)		(1,296,980)		(307,830)
Purchases of equity securities	0		0		0
Proceeds from sale of affiliates	324		0		0
Purchases of affiliates	0		0		0
Purchase of subsidiaries, net of acquired cash	0		(2,317,699)
Proceeds from sale of subsidiary	0		0		0
Returns of capital from subsidiaries	465,203		2,047,000		482,570
Change in restricted cash	0		0
Other, net	0		0		1,920
Net cash provided by (used in) investing activities	331,263		103,984		1,103,070
Proceeds from issuance of ordinary shares and exercise of stock options	0		0		0
Buybacks of ordinary shares	0		0		0
Dividends paid on ordinary shares	(1,039,253)		(764,277)		(858,521)
Return of capital	(274,727)		(65,037)		(79,086)
Distributions to non-controlling interests	(78,094)		(77,093)		(77,002)
Contributions from non-controlling interest	0		0		0
Proceeds from issuance of debt			980,600
Repayment of debt	0		0		(600,000)
Net proceeds from affiliated notional cash pooling programs			0		0
Deposit liabilities	0		0		0
Net cash provided by (used in) financing activities	(1,392,074)		74,193		(1,614,609)
Effects of exchange rate changes on foreign currency cash	0		0		0
Net change in cash and cash equivalents	(285,711)		327,027		7,176
Cash and cash equivalents – beginning of period	369,997		42,970		35,794
Cash and cash equivalents – end of period	84,286		369,997		42,970
Other XL-Bermuda Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	2,116,580		669,515		407,136
Proceeds from sale of fixed maturities and short-term investments	13,037,976		15,745,247		4,793,978
Proceeds from redemption of fixed maturities and short-term investments	3,750,541		3,562,386		3,250,056
Proceeds from sale of equity securities	848,779		664,735		571,410
Purchases of fixed maturities and short term investments	(15,506,653)		(18,780,978)		(7,322,967)
Purchases of equity securities	(1,103,447)		(567,334)		(445,504)
Proceeds from sale of affiliates	396,767		748,575		240,785
Purchases of affiliates	(681,385)		(280,856)		(371,226)
Purchase of subsidiaries, net of acquired cash	(92,893)		1,267,564
Proceeds from sale of subsidiary	22,998		0		570,000
Returns of capital from subsidiaries	0		0		0
Change in restricted cash	1,488		(154,992)
Other, net	197,536		(155,019)		(195,411)
Net cash provided by (used in) investing activities	871,707		2,049,328		1,091,121
Proceeds from issuance of ordinary shares and exercise of stock options	0		0		0
Buybacks of ordinary shares	0		0		0
Dividends paid on ordinary shares	(1,915,785)		0		0
Return of capital	(465,203)		(2,047,000)		(482,570)
Distributions to non-controlling interests	(52,353)		(40,590)		(1,463)
Contributions from non-controlling interest	47,524		23,610		48,261
Proceeds from issuance of debt			0
Repayment of debt	(8,248)		(87,447)		0
Net proceeds from affiliated notional cash pooling programs			0		0
Deposit liabilities	(69,482)		(84,758)		(268,298)
Net cash provided by (used in) financing activities	(2,463,547)		(2,236,185)		(704,070)
Effects of exchange rate changes on foreign currency cash	(57,742)		(64,377)		(90,115)
Net change in cash and cash equivalents	466,998		418,281		704,072
Cash and cash equivalents – beginning of period	2,874,682		2,456,401		1,752,329
Cash and cash equivalents – end of period	$ 3,341,680		$ 2,874,682		$ 2,456,401
[1]	Results for the period include XL-Ireland, which prior to the Redomestication was the ultimate parent and is now in liquidation proceedings as outlined in Note 1, "Significant Accounting Policies." The Company expects the net assets of XL-Ireland to ultimately be distributed to XL-Bermuda upon completion of the liquidation.

Guarantor Financial Informat176

Guarantor Financial Information Guarantor Financial Information (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Group Ltd
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%
XL Cayman
Condensed Financial Statements, Captions [Line Items]
Percentage ownership of subsidiaries	100.00%

Schedule IV - Reinsurance (Deta

Schedule IV - Reinsurance (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Life reinsurance in force:
Gross amount, life reinsurance in force	[1]	$ 0	$ 0	$ 0
Ceded to other companies, life reinsurance in force	[1]	51,176,725	62,290,992	46,947,677
Assumed from other companies, life reinsurance in force	[1]	51,971,475	63,158,304	68,854,340
Net amount, life reinsurance in force	[1]	794,750	867,312	21,906,663
Total premiums earned:
Gross amount, premiums earned		9,142,690	7,717,173	5,173,403
Ceded to other companies, premiums earned		3,704,888	3,266,085	1,955,098
Assumed from other companies, premiums earned		4,340,132	3,775,337	2,676,765
Net amount, premiums earned		$ 9,777,934	$ 8,226,425	$ 5,895,070
Percentage of amount assumed to net		44.40%	45.90%	45.40%
Property and casualty operations
Total premiums earned:
Gross amount, premiums earned		$ 9,142,690	$ 7,717,173	$ 5,173,403
Ceded to other companies, premiums earned		3,451,620	3,018,410	1,799,294
Assumed from other companies, premiums earned		4,074,817	3,465,421	2,343,329
Net amount, premiums earned		$ 9,765,887	$ 8,164,184	$ 5,717,438
Percentage of amount assumed to net		41.70%	42.40%	41.00%
Life operations
Total premiums earned:
Gross amount, premiums earned		$ 0	$ 0	$ 0
Ceded to other companies, premiums earned		253,268	247,675	155,804
Assumed from other companies, premiums earned		265,315	309,916	333,436
Net amount, premiums earned		$ 12,047	$ 62,241	$ 177,632
[1]	Represents the sum face value outstanding of the in force life reinsurance policies.

Schedule VI - Supplementary 178

Schedule VI - Supplementary Information Concerning Property/Casualty Insurance Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Losses and loss expenses incurred related to - current year	$ 6,374,377	$ 5,072,830	$ 3,513,465
Losses and loss expenses incurred related to - prior year	(301,542)	(306,630)	(255,072)
P&C Operations
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred acquisition costs	947,702	893,111	357,067
Reserves for losses and loss expenses	25,939,571	25,439,744	19,353,241
Reserves for unearned premiums	7,292,593	7,043,383	3,973,159
Net earned premiums	9,765,887	8,164,184	5,717,438
Net investment income	640,656	644,312	642,492
Losses and loss expenses incurred related to - current year	6,374,377	5,072,830	3,513,465
Losses and loss expenses incurred related to - prior year	(301,542)	(306,630)	(255,072)
Net paid losses and loss expenses	5,334,520	5,374,652	3,821,335
Amortization of deferred acquisition costs	1,614,896	1,306,654	724,003
Net premiums written	$ 10,230,636	$ 7,888,824	$ 5,767,209