History, Organization and Business Combination	9 Months Ended
Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
History and Organization and Business Combination	History, Organization and Business Combination History and Organization. Aspen Insurance Holdings Limited (“Aspen Holdings”) was incorporated on May 23, 2002 as a holding company headquartered in Bermuda. We underwrite specialty insurance and reinsurance on a global basis through our Operating Subsidiaries (as defined below) based in Bermuda, the United States and the United Kingdom: Aspen Insurance UK Limited (“Aspen U.K.”) and Aspen Underwriting Limited (corporate member of Lloyd’s Syndicate 4711, “AUL” and managed by Aspen Managing Agency Limited (“AMAL”)) (United Kingdom), Aspen Bermuda Limited (“Aspen Bermuda”) (Bermuda), Aspen Specialty Insurance Company (“Aspen Specialty”) and Aspen American Insurance Company (“AAIC”) (United States) (collectively, the “Operating Subsidiaries”). We also have branches in Australia, Canada, Ireland, Singapore, Switzerland and the United Arab Emirates. We established Aspen Capital Management, Ltd. and other related entities (collectively, “ACM”) to leverage our existing underwriting franchise, increase our operational flexibility in the capital markets and provide investors direct access to our underwriting expertise. References to the “Company,” the “Group,” “we,” “us” or “our” refer to Aspen Holdings or Aspen Holdings and its subsidiaries. Business Combination. On August 28, 2018, the Company entered into a definitive agreement and plan of merger (the “Merger Agreement”) with Highlands Holdings, Ltd., a Bermuda exempted company (“Highlands”), and Highlands Merger Sub, Ltd., a Bermuda exempted company and wholly owned subsidiary of Highlands (“Merger Sub”). Under the Merger Agreement, subject to the satisfaction or waiver of certain conditions set forth therein, and in the related statutory merger agreement, the Company will merge with and into Merger Sub in accordance with the Bermuda Companies Act (the “Merger”), with the Company surviving the Merger as a wholly-owned subsidiary of Highlands. Highlands and Merger Sub are affiliates of certain investment funds managed by affiliates of Apollo Global Management, LLC (“Apollo”). Pursuant to the Merger Agreement, at the effective time of the Merger, each ordinary share of the Company issued and outstanding immediately prior to such time (other than ordinary shares owned by Aspen as treasury shares, owned by any subsidiary of the Company or owned by Highlands, Merger Sub or or any subsidiary of Highlands, which will be canceled as set forth in the Merger Agreement) will be converted into the right to receive $42.75 in cash, without interest and less any required withholding taxes. Each of the Company’s issued and outstanding 5.95% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares and 5.625% Perpetual Non-Cumulative Preference Shares (collectively, the “Preference Shares”) will remain issued and outstanding following the Merger. The Merger Agreement restricts the Company from declaring or paying any dividends other than the quarterly dividend on Aspen’s ordinary shares that were previously declared and publicly announced prior to the date of the Merger Agreement and periodic cash dividends on the Preference Shares in accordance with the terms of the applicable certificate of designation. The Merger is expected to close in the first half of 2019, subject to shareholder and regulatory approvals, and other closing conditions as set forth in the Merger Agreement including, among others, the maintenance of certain financial strength ratings of certain of the Company’s insurance subsidiaries. The Merger Agreement also contains certain termination rights, including Highlands’ right to terminate if the Company suffers aggregate losses exceeding $350 million resulting from certain catastrophic events occurring between July 1, 2018 and January 31, 2019. Additional information about the Merger is set forth in the Company's Current Report on Form 8-K filed with the United States Securities and Exchange Commission (the “SEC”) on August 28, 2018 and the exhibits thereto, including the Merger Agreement, and the Company's preliminary proxy statement on Schedule 14A filed with the SEC on September 22, 2018.

History, Organization and Business Combination

History and Organization. Aspen Insurance Holdings Limited (“Aspen Holdings”) was incorporated on May 23, 2002 as a holding company headquartered in Bermuda. We underwrite specialty insurance and reinsurance on a global basis through our Operating Subsidiaries (as defined below) based in Bermuda, the United States and the United Kingdom: Aspen Insurance UK Limited (“Aspen U.K.”) and Aspen Underwriting Limited (corporate member of Lloyd’s Syndicate 4711, “AUL” and managed by Aspen Managing Agency Limited (“AMAL”)) (United Kingdom), Aspen Bermuda Limited (“Aspen Bermuda”) (Bermuda), Aspen Specialty Insurance Company (“Aspen Specialty”) and Aspen American Insurance Company (“AAIC”) (United States) (collectively, the “Operating Subsidiaries”). We also have branches in Australia, Canada, Ireland, Singapore, Switzerland and the United Arab Emirates. We established Aspen Capital Management, Ltd. and other related entities (collectively, “ACM”) to leverage our existing underwriting franchise, increase our operational flexibility in the capital markets and provide investors direct access to our underwriting expertise. References to the “Company,” the “Group,” “we,” “us” or “our” refer to Aspen Holdings or Aspen Holdings and its subsidiaries.

Business Combination. On August 28, 2018, the Company entered into a definitive agreement and plan of merger (the “Merger Agreement”) with Highlands Holdings, Ltd., a Bermuda exempted company (“Highlands”), and Highlands Merger Sub, Ltd., a Bermuda exempted company and wholly owned subsidiary of Highlands (“Merger Sub”). Under the Merger Agreement, subject to the satisfaction or waiver of certain conditions set forth therein, and in the related statutory merger agreement, the Company will merge with and into Merger Sub in accordance with the Bermuda Companies Act (the “Merger”), with the Company surviving the Merger as a wholly-owned subsidiary of Highlands. Highlands and Merger Sub are affiliates of certain investment funds managed by affiliates of Apollo Global Management, LLC (“Apollo”).

Pursuant to the Merger Agreement, at the effective time of the Merger, each ordinary share of the Company issued and outstanding immediately prior to such time (other than ordinary shares owned by Aspen as treasury shares, owned by any subsidiary of the Company or owned by Highlands, Merger Sub or or any subsidiary of Highlands, which will be canceled as set forth in the Merger Agreement) will be converted into the right to receive $42.75 in cash, without interest and less any required withholding taxes. Each of the Company’s issued and outstanding 5.95% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares and 5.625% Perpetual Non-Cumulative Preference Shares (collectively, the “Preference Shares”) will remain issued and outstanding following the Merger. The Merger Agreement restricts the Company from declaring or paying any dividends other than the quarterly dividend on Aspen’s ordinary shares that were previously declared and publicly announced prior to the date of the Merger Agreement and periodic cash dividends on the Preference Shares in accordance with the terms of the applicable certificate of designation.

The Merger is expected to close in the first half of 2019, subject to shareholder and regulatory approvals, and other closing conditions as set forth in the Merger Agreement including, among others, the maintenance of certain financial strength ratings of certain of the Company’s insurance subsidiaries. The Merger Agreement also contains certain termination rights, including Highlands’ right to terminate if the Company suffers aggregate losses exceeding $350 million resulting from certain catastrophic events occurring between July 1, 2018 and January 31, 2019.

Additional information about the Merger is set forth in the Company's Current Report on Form 8-K filed with the United States Securities and Exchange Commission (the “SEC”) on August 28, 2018 and the exhibits thereto, including the Merger Agreement, and the Company's preliminary proxy statement on Schedule 14A filed with the SEC on September 22, 2018.