Basis of Preparation	3 Months Ended
Mar. 31, 2017
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 months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year ended December 31, 2017. 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, 2016 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, 2016 contained in the Company’s Annual Report on Form 10-K filed with the United States Securities and Exchange Commission (the “SEC”) on February 22, 2017 (File No. 001-31909). Except for the changes associated with ASU 2016-09, “Compensation — Stock Compensation” listed below, there have been no changes to significant accounting policies from those disclosed in the Company’s Annual Report on Form 10-K. 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 relate to losses and loss adjustment expenses, the value of investments, reinsurance recoverables and the fair value of derivatives. All material assumptions and estimates are regularly reviewed and adjustments made as necessary, but actual results could be significantly different from those expected when the assumptions or estimates were made. Accounting Pronouncements Adopted in 2017 On March 30, 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-09, “Compensation — Stock Compensation” which provides guidance on several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This ASU is effective for fiscal years beginning after December 15, 2016 and interim periods beginning after December 15, 2016. Following the adoption of this ASU, all excess tax benefits or expense related to stock-based compensation transactions are recognized prospectively as income tax benefits or expense in the Consolidated Income Statement and the excess tax benefits or expense from stock-based compensation transactions previously included in “Financing activities” on the Consolidated Statements of Cash Flows are prospectively included on that statement as “Operating activities.” The cash paid to the tax authority for tax withholding purposes has also been reclassified from operating to financing activity in the Consolidated Statement of Cash Flows and the comparative period has been restated. This ASU also allows share withholding up to the maximum statutory withholding requirement while still avoiding liability accounting. As a result, the Company has applied the equity accounting method for its restricted share units retrospectively and has recorded a cumulative effect adjustment of $2.8 million through opening retained earnings and $7.9 million through additional paid-in capital. Accounting Pronouncements Not Yet Adopted On March 10, 2017, FASB issued ASU 2017-7, “Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost” which changes how employers report defined benefit pension and/or other post-retirement benefit costs in their financial statements. This ASU is effective for fiscal years beginning after December 15, 2017 and interim periods beginning after December 15, 2017. The Company is currently assessing the impact the adoption of this ASU will have on future financial statements and disclosures. Other accounting pronouncements were issued during the three months ended March 31, 2017 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 months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year ended December 31, 2017. 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, 2016 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, 2016 contained in the Company’s Annual Report on Form 10-K filed with the United States Securities and Exchange Commission (the “SEC”) on February 22, 2017 (File No. 001-31909). Except for the changes associated with ASU 2016-09, “Compensation — Stock Compensation” listed below, there have been no changes to significant accounting policies from those disclosed in the Company’s Annual Report on Form 10-K.

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 relate to losses and loss adjustment expenses, the value of investments, reinsurance recoverables and the fair value of derivatives. All material assumptions and estimates are regularly reviewed and adjustments made as necessary, but actual results could be significantly different from those expected when the assumptions or estimates were made.

Accounting Pronouncements Adopted in 2017

On March 30, 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-09, “Compensation — Stock Compensation” which provides guidance on several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This ASU is effective for fiscal years beginning after December 15, 2016 and interim periods beginning after December 15, 2016. Following the adoption of this ASU, all excess tax benefits or expense related to stock-based compensation transactions are recognized prospectively as income tax benefits or expense in the Consolidated Income Statement and the excess tax benefits or expense from stock-based compensation transactions previously included in “Financing activities” on the Consolidated Statements of Cash Flows are prospectively included on that statement as “Operating activities.” The cash paid to the tax authority for tax withholding purposes has also been reclassified from operating to financing activity in the Consolidated Statement of Cash Flows and the comparative period has been restated. This ASU also allows share withholding up to the maximum statutory withholding requirement while still avoiding liability accounting. As a result, the Company has applied the equity accounting method for its restricted share units retrospectively and has recorded a cumulative effect adjustment of $2.8 million through opening retained earnings and $7.9 million through additional paid-in capital.

Accounting Pronouncements Not Yet Adopted

On March 10, 2017, FASB issued ASU 2017-7, “Improving the Presentation of Net Periodic Pension Cost and Net Periodic Post Retirement Benefit Cost” which changes how employers report defined benefit pension and/or other post-retirement benefit costs in their financial statements. This ASU is effective for fiscal years beginning after December 15, 2017 and interim periods beginning after December 15, 2017. The Company is currently assessing the impact the adoption of this ASU will have on future financial statements and disclosures.

Other accounting pronouncements were issued during the three months ended March 31, 2017 which were either not relevant to the Company or did not impact the Company’s consolidated financial statements.