Basis of Preparation	9 Months Ended
Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Preparation The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of generally accepted accounting principles in the United States (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation have been included. Results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ended December 31, 2018. The unaudited condensed consolidated financial statements include the accounts of Aspen Holdings and its subsidiaries. All intercompany transactions and balances have been eliminated on consolidation. The balance sheet as at December 31, 2017 has been derived from the audited consolidated financial statements at that date, but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements and notes thereto should be read in conjunction with the consolidated financial statements and notes thereto for the year ended December 31, 2017 contained in the Company’s Annual Report on Form 10-K filed with the SEC on February 22, 2018 (File No. 001-31909). Assumptions and estimates made by management have a significant effect on the amounts reported within the unaudited condensed consolidated financial statements. The most significant of these assumptions and estimates relate to losses and loss adjustment expenses, reinsurance recoverables, gross written premiums and commissions which have not been reported to the Company such as those relating to proportional treaty reinsurance contracts, unrecognized tax benefits, the fair value of derivatives and the fair value of other investments. All material assumptions and estimates are regularly reviewed and adjustments made as necessary, but actual results could differ significantly from those expected when the assumptions or estimates were made. Accounting Pronouncements Adopted in 2018 On August 12, 2015, the Financial Standards Accounting Board (“FASB”) issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606)” which delayed the effective date of ASU 2014-09 by one year. This ASU is effective for annual periods beginning after December 15, 2017. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements because insurance contracts accounted for within the scope of Topic 944, Financial Services are exempt from this ASU and the Company has immaterial other revenue. On January 5, 2016, the FASB issued ASU 2016-1, “Financial Instruments - Overall (Subtopic 825-10)” which enhances the reporting model for financial instruments. Included within the requirements of this ASU are the following: a) equity investments to be measured at fair value with changes in fair value recognized in net income; b) a simplification of the impairment assessment of equity investments without readily determinable fair values; c) public business entities to use the exit price concept when measuring the fair value of financial instruments for disclosure purposes; and d) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity’s other deferred tax assets. The amendments required as a result of this ASU are effective for fiscal years beginning after December 15, 2017. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements because the Company’s equity portfolio, prior to being sold, was classified as held for trading with changes in fair value recognized through net income and no valuation allowance was required in relation to deferred tax asset related to available-for-sale securities. On February 28, 2018, the FASB issued ASU 2018-03, “Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10)” which amends multiple areas in Subtopic 825-10 via improvements to clarify the Codification or to correct unintended application of guidance. This ASU is effective for fiscal years beginning after December 15, 2017 and for interim periods within those fiscal years beginning after June 15, 2018. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements. 2018 Accounting Pronouncements Not Yet Adopted On February 14, 2018, the FASB issued ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220)” which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU will be effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the provisions of ASU 2018-02 to determine how it will be affected but no material impact is expected on the consolidated financial statements. On June 20, 2018, the FASB issued ASU 2018-07, “Compensation - Stock Compensation (Topic 718)” which amends the scope of Topic 718 via improvements to non-employee share-based payment accounting. Amendments include allowing companies to account for share-based payment transactions with non-employees in the same way as share-based payment transactions with employees and includes elections that offer relief to non-public companies when measuring non-employee equity share options. This ASU will be effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the provisions of ASU 2018-07 to determine how it will be affected but no material impact is expected on the consolidated financial statements. On July 30, 2018, the FASB issued ASU 2018-11, “Targeted Improvements (Topic 984)” which amends the transitional guidance of ASU 2016-2, “Leases (Topic 842)” providing an alternative transition method to the existing modified retrospective method, allowing entities to initially apply the new leases standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The amendments of this ASU are effective for fiscal years beginning after December 15, 2018, aligned to the effective date and transition requirements of ASU 2016-2. ASU 2016-2 is expected to have a material impact on the Company’s consolidated financial statements, by increasing the Company’s assets and liabilities as all leases greater than twelve months will be recognized on the balance sheet as a right of use asset and lease liability. On August 28, 2018, the FASB issued ASU 2018-13, “Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurements (Topic 820)” which amends the disclosure requirements on fair value measurements. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. This ASU will not have a material impact on the Company’s consolidated financial results but it will have an impact on the disclosures in the Company’s Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q for periods beginning after December 15, 2019. Other accounting pronouncements were issued during the three and nine months ended September 30, 2018 which were either not relevant to the Company or did not impact the Company’s consolidated financial statements.

Basis of Preparation

The accompanying unaudited condensed consolidated financial statements have been prepared on the basis of generally accepted accounting principles in the United States (“U.S. GAAP”) for interim financial information and in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. In the opinion of management, all adjustments considered necessary for a fair presentation have been included. Results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ended December 31, 2018. The unaudited condensed consolidated financial statements include the accounts of Aspen Holdings and its subsidiaries. All intercompany transactions and balances have been eliminated on consolidation.

The balance sheet as at December 31, 2017 has been derived from the audited consolidated financial statements at that date, but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These unaudited condensed consolidated financial statements and notes thereto should be read in conjunction with the consolidated financial statements and notes thereto for the year ended December 31, 2017 contained in the Company’s Annual Report on Form 10-K filed with the SEC on February 22, 2018 (File No. 001-31909).

Assumptions and estimates made by management have a significant effect on the amounts reported within the unaudited condensed consolidated financial statements. The most significant of these assumptions and estimates relate to losses and loss adjustment expenses, reinsurance recoverables, gross written premiums and commissions which have not been reported to the Company such as those relating to proportional treaty reinsurance contracts, unrecognized tax benefits, the fair value of derivatives and the fair value of other investments. All material assumptions and estimates are regularly reviewed and adjustments made as necessary, but actual results could differ significantly from those expected when the assumptions or estimates were made.

Accounting Pronouncements Adopted in 2018

On August 12, 2015, the Financial Standards Accounting Board (“FASB”) issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606)” which delayed the effective date of ASU 2014-09 by one year. This ASU is effective for annual periods beginning after December 15, 2017. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements because insurance contracts accounted for within the scope of Topic 944, Financial Services are exempt from this ASU and the Company has immaterial other revenue.

On January 5, 2016, the FASB issued ASU 2016-1, “Financial Instruments - Overall (Subtopic 825-10)” which enhances the reporting model for financial instruments. Included within the requirements of this ASU are the following: a) equity investments to be measured at fair value with changes in fair value recognized in net income; b) a simplification of the impairment assessment of equity investments without readily determinable fair values; c) public business entities to use the exit price concept when measuring the fair value of financial instruments for disclosure purposes; and d) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale securities in combination with the entity’s other deferred tax assets. The amendments required as a result of this ASU are effective for fiscal years beginning after December 15, 2017. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements because the Company’s equity portfolio, prior to being sold, was classified as held for trading with changes in fair value recognized through net income and no valuation allowance was required in relation to deferred tax asset related to available-for-sale securities.

On February 28, 2018, the FASB issued ASU 2018-03, “Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10)” which amends multiple areas in Subtopic 825-10 via improvements to clarify the Codification or to correct unintended application of guidance. This ASU is effective for fiscal years beginning after December 15, 2017 and for interim periods within those fiscal years beginning after June 15, 2018. Adoption of this ASU during the three and nine months ended September 30, 2018 did not have a material impact on the Company’s consolidated financial statements.

2018 Accounting Pronouncements Not Yet Adopted

On February 14, 2018, the FASB issued ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220)” which allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. This ASU will be effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the provisions of ASU 2018-02 to determine how it will be affected but no material impact is expected on the consolidated financial statements.

On June 20, 2018, the FASB issued ASU 2018-07, “Compensation - Stock Compensation (Topic 718)” which amends the scope of Topic 718 via improvements to non-employee share-based payment accounting. Amendments include allowing companies to account for share-based payment transactions with non-employees in the same way as share-based payment transactions with employees and includes elections that offer relief to non-public companies when measuring non-employee equity share options. This ASU will be effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the provisions of ASU 2018-07 to determine how it will be affected but no material impact is expected on the consolidated financial statements.

On July 30, 2018, the FASB issued ASU 2018-11, “Targeted Improvements (Topic 984)” which amends the transitional guidance of ASU 2016-2, “Leases (Topic 842)” providing an alternative transition method to the existing modified retrospective method, allowing entities to initially apply the new leases standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. The amendments of this ASU are effective for fiscal years beginning after December 15, 2018, aligned to the effective date and transition requirements of ASU 2016-2. ASU 2016-2 is expected to have a material impact on the Company’s consolidated financial statements, by increasing the Company’s assets and liabilities as all leases greater than twelve months will be recognized on the balance sheet as a right of use asset and lease liability.

On August 28, 2018, the FASB issued ASU 2018-13, “Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurements (Topic 820)” which amends the disclosure requirements on fair value measurements. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. This ASU will not have a material impact on the Company’s consolidated financial results but it will have an impact on the disclosures in the Company’s Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q for periods beginning after December 15, 2019.

Other accounting pronouncements were issued during the three and nine months ended September 30, 2018 which were either not relevant to the Company or did not impact the Company’s consolidated financial statements.