Basis of Preparation and Consolidation	9 Months Ended
Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Preparation and Consolidation	Basis of Preparation and Consolidation On July 25, 2016, XL Group plc, an Irish public limited company ("XL-Ireland"), and XL Group Ltd, a Bermuda exempted company ("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 10, "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) at the end of 2016 or the beginning of 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. These unaudited consolidated financial statements include the accounts of the Company and have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. In addition, the year-end balance sheet data was derived from audited financial statements but do not include all disclosures required by GAAP. In the opinion of management, these unaudited financial statements reflect all adjustments considered necessary for a fair statement of financial position and results of operations at the end of and for the periods presented. The results of operations for any interim period are not necessarily indicative of the results for a full year. All inter-company accounts and transactions have been eliminated. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure about contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from these estimates. For further information, see Item 8, Note 2(a), "Significant Accounting Policies - Basis of Preparation and Consolidation," to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2015. On May 1, 2015, the Company completed its 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. For further information, see Item 8, Note 3(c), "Acquisitions and Disposals - Catlin Acquisition," to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2015. In May 2014, the Company ceded the majority of its life reinsurance business to GreyCastle Life Reinsurance ("GCLR") via 100% quota share reinsurance (the "GreyCastle Life Retro Arrangements"). 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 (the "Life Funds Withheld Assets"). The Life Funds Withheld Assets are managed pursuant to agreed 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 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. For further information, see Item 8, Note 3(e), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary," to the Consolidated Financial Statements included the Company's Annual Report on Form 10-K for the year ended December 31, 2015. To facilitate period-to-period comparisons, certain reclassifications have been made to prior period consolidated financial statement amounts to conform to current period presentation.

On July 25, 2016, XL Group plc, an Irish public limited company ("XL-Ireland"), and XL Group Ltd, a Bermuda exempted company ("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 10, "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) at the end of 2016 or the beginning of 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.

These unaudited consolidated financial statements include the accounts of the Company and have been prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP") for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and disclosures required by GAAP for complete financial statements. In addition, the year-end balance sheet data was derived from audited financial statements but do not include all disclosures required by GAAP. In the opinion of management, these unaudited financial statements reflect all adjustments considered necessary for a fair statement of financial position and results of operations at the end of and for the periods presented. The results of operations for any interim period are not necessarily indicative of the results for a full year. All inter-company accounts and transactions have been eliminated. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure about contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from these estimates. For further information, see Item 8, Note 2(a), "Significant Accounting Policies - Basis of Preparation and Consolidation," to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2015.

On May 1, 2015, the Company completed its 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. For further information, see Item 8, Note 3(c), "Acquisitions and Disposals - Catlin Acquisition," to the Consolidated Financial Statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2015.

In May 2014, the Company ceded the majority of its life reinsurance business to GreyCastle Life Reinsurance ("GCLR") via 100% quota share reinsurance (the "GreyCastle Life Retro Arrangements"). 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 (the "Life Funds Withheld Assets"). The Life Funds Withheld Assets are managed pursuant to agreed 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 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. For further information, see Item 8, Note 3(e), "Acquisitions and Disposals - Sale of Life Reinsurance Subsidiary," to the Consolidated Financial Statements included the Company's Annual Report on Form 10-K for the year ended December 31, 2015.

To facilitate period-to-period comparisons, certain reclassifications have been made to prior period consolidated financial statement amounts to conform to current period presentation.