Significant New Business	12 Months Ended
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant New Business	4. SIGNIFICANT NEW BUSINESS 2020 AXA Group On February 24, 2020, we entered into a loss portfolio transfer reinsurance agreement with AXA XL, a division of AXA, to reinsure specified legacy construction general liability multi-year policies. We will assume reinsurance reserves of approximately $225.0 million in the transaction. Completion of the transaction is subject to, among other things, regulatory approvals and satisfaction of various closing conditions. The transaction is expected to close in the first half of 2020. Munich Re On September 10, 2019, we signed an agreement with Great Lakes Insurance SE and HSB Engineering Insurance Limited, both subsidiaries of Munich Reinsurance Company ("Munich Re"), pursuant to which we will acquire certain portfolios from their Australian branches. In the transaction, which is subject to regulatory and Federal Court of Australia approval, we will receive total assets of approximately AUD$228.2 million (approximately $160.3 million) for assuming the associated net insurance reserves, which primarily relate to long tail insurance business. We are pursuing a portfolio transfer of the insurance business under Division 3A of Part III of Australia’s Insurance Act 1973 (Cth), which would provide legal finality for Munich Re and its subsidiaries. This transaction is expected to close in 2020. 2019 Zurich On October 1, 2019, we completed a reinsurance transaction with Zurich Insurance Group ("Zurich"), pursuant to which we reinsured certain of Zurich's U.S. asbestos and environmental liability insurance portfolios. In the transaction, we assumed $622.9 million of gross reserves, relating to 1986 and prior year business, for reinsurance premium of $465.5 million and recorded a deferred charge of $115.8 million. We have ceded 10% of this transaction to Enhanzed Reinsurance Ltd. ("Enhanzed Re"), in which we have an investment, on the same terms and conditions as those received by Enstar. Maiden ADC On August 5, 2019, we and Maiden Reinsurance Ltd. (“Maiden Re Bermuda”) completed a transaction pursuant to a Master Agreement with Maiden Holdings, Ltd. and Maiden Re Bermuda to provide adverse development cover reinsurance to Maiden Re Bermuda, effective January 1, 2019. In the transaction, Maiden Re Bermuda ceded and we assumed as retrocessionaire Maiden Re Bermuda's liability under its quota share agreement with the Bermuda subsidiary ("AmTrust Bermuda") of AmTrust Financial Services, Inc. (“AmTrust”). The adverse development cover reinsurance is for losses incurred on or prior to December 31, 2018 in excess of a $2.2 billion retention up to a $600.0 million limit, in exchange for a premium of $445.0 million. We assumed total gross reserves of $530.2 million and recorded a deferred charge of $85.2 million. Enstar's reinsurance performance obligations in the transaction are collateralized in accordance with a Master Collateral Agreement among Enstar, Maiden Re Bermuda, AmTrust and certain subsidiaries of AmTrust. Amerisure On April 11, 2019, we completed a loss portfolio transfer reinsurance agreement with Amerisure Mutual Insurance Company ("Amerisure") and Allianz Risk Transfer (Bermuda) Limited (“ART Bermuda”). In the transaction, Amerisure ceded, and each of Enstar and ART Bermuda severally assumed, a 50% quota share of the construction defect losses incurred by Amerisure and certain of its subsidiaries on or before December 31, 2012. Under the agreement, which was effective as of January 1, 2019, we assumed $48.3 million of gross reserves in exchange for consideration of $45.5 million and recorded a deferred charge asset of $2.9 million. AmTrust RITC Transactions On February 14, 2019, we completed four RITC transactions with Syndicates 1206, 1861, 2526 and 5820 (collectively the "AmTrust RITC Transactions"), managed by AmTrust Syndicates Limited, under which we reinsured to close the 2016 and prior underwriting years. We assumed, among other items, gross loss reserves of £703.8 million ($897.1 million) and net loss reserves of £486.8 million ($620.4 million) relating to the portfolios in exchange for consideration of £539.9 million ($688.2 million) and recorded a deferred charge asset of $20.6 million. We have an investment in AmTrust, as described further in Note 21 - "Related Party Transactions". 2018 Allianz Effective December 31, 2018, we and Allianz SE ("Allianz") amended the January 1, 2016 reinsurance agreement between our subsidiary and Allianz, which related to our reinsurance of certain U.S. workers' compensation, construction defect, and asbestos, pollution and toxic tort business originally held by Fireman's Fund Insurance Company. The amendment increased the original sub-limit related to asbestos & environmental (“A&E”) liabilities in exchange for a premium of $70.0 million. This additional business is also covered by the consulting agreement that we entered into with San Francisco Reinsurance Company, an affiliate of Allianz, in connection with our 2016 transaction with Allianz discussed below. Maiden LPT On December 27, 2018, as part of the acquisition of Maiden Re North America as discussed in Note 3 - "Acquisitions", we also novated and assumed certain reinsurance agreements from Maiden Re Bermuda, including certain affiliate reinsurance agreements with Maiden Re North America. We assumed total gross unaffiliated reserves of $72.1 million for total assets of $70.4 million on a funds held basis and recorded a deferred charge asset of $1.7 million. Coca-Cola On August 1, 2018, we entered into a reinsurance transaction with The Coca-Cola Company and its subsidiaries ("Coca-Cola"), pursuant to which we reinsured certain of Coca-Cola's retention and deductible risks under its subsidiaries' U.S. workers' compensation, auto liability, general liability and product liability insurance coverage. We assumed total gross reserves of $120.8 million for cash consideration of $103.6 million and recorded a deferred charge asset of $17.2 million. We transferred the cash consideration received of $103.6 million into a trust to support our obligations under the reinsurance agreement. Zurich Australia On February 23, 2018, we entered into a reinsurance agreement with Zurich Australian Insurance Limited, a subsidiary of Zurich Insurance Group ("Zurich"), to reinsure its New South Wales Vehicle Compulsory Third Party ("CTP") insurance business. Under the agreement, which was effective as of January 1, 2018, we assumed gross loss reserves of AUD$359.4 million ($280.8 million) in exchange for consideration of AUD$343.9 million ($268.7 million). We elected the fair value option for this reinsurance contract and recorded an initial fair value adjustment of AUD$15.5 million ($12.1 million) on the assumed gross loss reserves. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made. Following the initial reinsurance transaction, which transferred the economics of the CTP insurance business, we and Zurich also completed a portfolio transfer of the CTP insurance business under Division 3A Part III of Australia's Insurance Act 1973 (Cth), effective December 31, 2018, which provided legal finality for Zurich's obligations. Neon RITC Transaction On February 16, 2018, we completed a reinsurance-to-close (“RITC”) transaction with Neon Underwriting Limited ("Neon"), under which we reinsured to close the 2015 and prior underwriting years of account (comprising underwriting years 2008 to 2015) of Neon's Syndicate 2468, with effect from January 1, 2018. We assumed gross loss reserves of£403.9 million ($546.3 million) and net loss reserves of £342.1 million ($462.6 million) relating to the portfolio in exchange for consideration of £329.1 million ($445.1 million). We elected the fair value option for this reinsurance contract and recorded initial fair value adjustments of $20.6 million and $17.5 million on the gross and net loss reserves assumed, respectively. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made. Novae RITC Transaction On January 29, 2018, we completed an RITC transaction with AXIS Managing Agency Limited, under which we reinsured to close the 2015 and prior underwriting years of account of Novae Syndicate 2007 ("Novae"), with effect from January 1, 2018. We assumed gross loss reserves of £860.1 million ($1,163.2 million) and net loss reserves of £630.7 million ($853.0 million) relating to the portfolio in exchange for consideration of £594.1 million ($803.5 million) and recorded initial fair value adjustments of $67.5 million and $49.5 million on the gross and net loss reserves assumed, respectively. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made. Allianz On December 28, 2017, we entered into a reinsurance agreement with Allianz to reinsure a portfolio of Allianz’s run-off business, effective December 31, 2017. Pursuant to the reinsurance agreement, we reinsured 50% of certain U.S. workers' compensation, asbestos, and toxic tort business originally held by San Francisco Reinsurance Company, an affiliate of Allianz, and in the process assumed net reinsurance reserves of $81.4 million. Affiliates of Allianz retained $81.4 million of reinsurance premium as funds withheld collateral for the obligations under the reinsurance agreement and we transferred $8.1 million to a reinsurance trust to further support our obligations. We also provide ongoing consulting services with respect to the entire $162.8 million portfolio, including the 50% share retained by affiliates of Allianz. RSA On February 7, 2017, we entered into an agreement to reinsure the U.K. employers' liability legacy business of RSA Insurance Group PLC ("RSA"). Pursuant to the transaction, our subsidiary assumed gross insurance reserves of £1,046.4 million ($1,301.8 million), relating to 2005 and prior year business. Net insurance reserves assumed were £927.5 million ($1,153.9 million) and the reinsurance premium received was £801.6 million ($997.2 million). We elected the fair value option for this reinsurance contract. The initial fair value adjustment on the gross reserves was $174.1 million, and on the net reserves was $156.7 million. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and assumptions. In addition to the initial reinsurance transaction, which transferred the economics of the portfolio up to the policy's limits, we and RSA completed a portfolio transfer of the business under Part VII of the Financial Services and Markets Act 2000 on July 1, 2019, which provided legal finality for RSA's obligations. QBE On January 11, 2017, we closed a transaction to reinsure multi-line property and casualty business of QBE Insurance Group Limited ("QBE"). We assumed gross reinsurance reserves of approximately $1,019.0 million (net reserves of $447.0 million) relating to the portfolio, which primarily includes workers' compensation, construction defect, and general liability discontinued lines of business. The reinsurance premium received was $403.8 million, comprised of $227.6 million in restricted cash and $176.2 million in funds held. We elected the fair value option for this reinsurance contract. The initial fair value adjustment was $180.0 million on the gross reserves and $43.2 million on the net reserves. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and assumptions. In addition, we pledged a portion of the premium as collateral to a subsidiary of QBE, and we have provided additional collateral and a limited parental guarantee.

On February 24, 2020, we entered into a loss portfolio transfer reinsurance agreement with AXA XL, a division of AXA, to reinsure specified legacy construction general liability multi-year policies. We will assume reinsurance reserves of approximately $225.0 million in the transaction. Completion of the transaction is subject to, among other things, regulatory approvals and satisfaction of various closing conditions. The transaction is expected to close in the first half of 2020.

On September 10, 2019, we signed an agreement with Great Lakes Insurance SE and HSB Engineering Insurance Limited, both subsidiaries of Munich Reinsurance Company ("Munich Re"), pursuant to which we will acquire certain portfolios from their Australian branches. In the transaction, which is subject to regulatory and Federal Court of Australia approval, we will receive total assets of approximately AUD$228.2 million (approximately $160.3 million) for assuming the associated net insurance reserves, which primarily relate to long tail insurance business. We are pursuing a portfolio transfer of the insurance business under Division 3A of Part III of Australia’s Insurance Act 1973 (Cth), which would provide legal finality for Munich Re and its subsidiaries. This transaction is expected to close in 2020.

On February 14, 2019, we completed four RITC transactions with Syndicates 1206, 1861, 2526 and 5820 (collectively the "AmTrust RITC Transactions"), managed by AmTrust Syndicates Limited, under which we reinsured to close the 2016 and prior underwriting years. We assumed, among other items, gross loss reserves of £703.8 million ($897.1 million) and net loss reserves of £486.8 million ($620.4 million) relating to the portfolios in exchange for consideration of £539.9 million ($688.2 million) and recorded a deferred charge asset of $20.6 million. We have an investment in AmTrust, as described further in Note 21 - "Related Party Transactions".

On December 27, 2018, as part of the acquisition of Maiden Re North America as discussed in Note 3 - "Acquisitions", we also novated and assumed certain reinsurance agreements from Maiden Re Bermuda, including certain affiliate reinsurance agreements with Maiden Re North America. We assumed total gross unaffiliated reserves of $72.1 million for total assets of $70.4 million on a funds held basis and recorded a deferred charge asset of $1.7 million.

On August 1, 2018, we entered into a reinsurance transaction with The Coca-Cola Company and its subsidiaries ("Coca-Cola"), pursuant to which we reinsured certain of Coca-Cola's retention and deductible risks under its subsidiaries' U.S. workers' compensation, auto liability, general liability and product liability insurance coverage. We assumed total gross reserves of $120.8 million for cash consideration of $103.6 million and recorded a deferred charge asset of $17.2 million. We transferred the cash consideration received of $103.6 million into a trust to support our obligations under the reinsurance agreement.

On February 23, 2018, we entered into a reinsurance agreement with Zurich Australian Insurance Limited, a subsidiary of Zurich Insurance Group ("Zurich"), to reinsure its New South Wales Vehicle Compulsory Third Party ("CTP") insurance business. Under the agreement, which was effective as of January 1, 2018, we assumed gross loss reserves of AUD$359.4 million ($280.8 million) in exchange for consideration of AUD$343.9 million ($268.7 million). We elected the fair value option for this reinsurance contract and recorded an initial fair value adjustment of AUD$15.5 million ($12.1 million) on the assumed gross loss reserves. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made.

On February 16, 2018, we completed a reinsurance-to-close (“RITC”) transaction with Neon Underwriting Limited ("Neon"), under which we reinsured to close the 2015 and prior underwriting years of account (comprising underwriting years 2008 to 2015) of Neon's Syndicate 2468, with effect from January 1, 2018. We assumed gross loss reserves of£403.9 million ($546.3 million) and net loss reserves of £342.1 million ($462.6 million) relating to the portfolio in exchange for consideration of £329.1 million ($445.1 million). We elected the fair value option for this reinsurance contract and recorded initial fair value adjustments of $20.6 million and $17.5 million on the gross and net loss reserves assumed, respectively. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made.

On January 29, 2018, we completed an RITC transaction with AXIS Managing Agency Limited, under which we reinsured to close the 2015 and prior underwriting years of account of Novae Syndicate 2007 ("Novae"), with effect from January 1, 2018. We assumed gross loss reserves of £860.1 million ($1,163.2 million) and net loss reserves of £630.7 million ($853.0 million) relating to the portfolio in exchange for consideration of £594.1 million ($803.5 million) and recorded initial fair value adjustments of $67.5 million and $49.5 million on the gross and net loss reserves assumed, respectively. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and the assumptions made.

On December 28, 2017, we entered into a reinsurance agreement with Allianz to reinsure a portfolio of Allianz’s run-off business, effective December 31, 2017. Pursuant to the reinsurance agreement, we reinsured 50% of certain U.S. workers' compensation, asbestos, and toxic tort business originally held by San Francisco Reinsurance Company, an affiliate of Allianz, and in the process assumed net reinsurance reserves of $81.4 million. Affiliates of Allianz retained $81.4 million of reinsurance premium as funds withheld collateral for the obligations under the reinsurance agreement and we transferred $8.1 million to a reinsurance trust to further support our obligations. We also provide ongoing consulting services with respect to the entire $162.8 million portfolio, including the 50% share retained by affiliates of Allianz.

On February 7, 2017, we entered into an agreement to reinsure the U.K. employers' liability legacy business of RSA Insurance Group PLC ("RSA"). Pursuant to the transaction, our subsidiary assumed gross insurance reserves of £1,046.4 million ($1,301.8 million), relating to 2005 and prior year business. Net insurance reserves assumed were £927.5 million ($1,153.9 million) and the reinsurance premium received was £801.6 million ($997.2 million). We elected the fair value option for this reinsurance contract. The initial fair value adjustment on the gross reserves was $174.1 million, and on the net reserves was $156.7 million. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and assumptions.

In addition to the initial reinsurance transaction, which transferred the economics of the portfolio up to the policy's limits, we and RSA completed a portfolio transfer of the business under Part VII of the Financial Services and Markets Act 2000 on July 1, 2019, which provided legal finality for RSA's obligations.

On January 11, 2017, we closed a transaction to reinsure multi-line property and casualty business of QBE Insurance Group Limited ("QBE"). We assumed gross reinsurance reserves of approximately $1,019.0 million (net reserves of $447.0 million) relating to the portfolio, which primarily includes workers' compensation, construction defect, and general liability discontinued lines of business. The reinsurance premium received was $403.8 million, comprised of $227.6 million in restricted cash and $176.2 million in funds held. We elected the fair value option for this reinsurance contract. The initial fair value adjustment was $180.0 million on the gross reserves and $43.2 million on the net reserves. Refer to Note 12 - "Fair Value Measurements" for a description of the fair value process and assumptions. In addition, we pledged a portion of the premium as collateral to a subsidiary of QBE, and we have provided additional collateral and a limited parental guarantee.