Equity [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] 5.950% Preference Shares (AHL PRC) Series D Preferred Stock [Member] 5.625% Preference Shares (AHL PRD) Series E Preferred Stock [Member] 5.625% Preference Shares, rep by Dep Shares (AHL PRE) Series F Preferred Stock [Member] Class of Stock [Line Items] Class of Stock [Line Items] Authorized share capital: Authorized Share Capital [Abstract] Authorized share capital. Number of ordinary shares Common Stock, Shares Authorized Number of non-voting shares Non Voting Stock Shares Authorized Non voting stock shares authorized. Number of preference shares Preferred Stock, Shares Authorized Ordinary Shares, authorized Common Stock Value Authorized Common stock value authorized. Non-Voting Shares, authorized Non Voting Stock Value Authorized Non voting stock value authorized. Preference Shares, authorized Preferred Stock Value Authorized Preferred stock shares authorized. Total authorized share capital Authorized Share Capital Authorized Share Capital Issued share capital: Issued Share Capital [Abstract] Issued share capital. Ordinary shares, issued Common Stock, Shares, Issued Preference shares, issued Preferred Stock, Shares Issued Ordinary shares, value Common Stock, Value, Issued Previous Common Stock Shares Issued Previous Common Stock Shares Issued Previous Common Stock Shares Issued Preference shares, value Preferred Stock, Value, Subscriptions Total issued share capital Issued Share Capital Issued share capital. Preference shares, rate Preferred Stock Dividends Rate Percentage Preferred Stock Dividends Rate Percentage Segment Reporting [Abstract] Summary of gross and net written and earned premiums, underwriting results, ratios and reserves for each of Company's business segments Schedule of Segment Reporting Information, by Segment [Table Text Block] Schedule of gross written premiums based on geographical areas Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification out of Accumulated Other Comprehensive Income [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Foreign exchange contracts Foreign Exchange Contract [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Available for sale securities AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Including Noncontrolling Interest [Member] Foreign currency translation adjustments Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Available for sale securities — gross realized gains Available-for-sale Securities, Gross Realized Gains Realized gains/(losses) on sale of securities Available-for-sale Securities, Gross Realized Losses (Loss) from operations before income tax Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax (expense)/benefit Income Tax Expense (Benefit) General, administrative and corporate expenses Selling, General and Administrative Expense Net (loss) Income (Loss), Including Portion Attributable to Noncontrolling Interest, before Tax Net (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Leases [Abstract] Right-of-use operating lease assets Operating Lease, Right-of-Use Asset Operating lease liabilities Operating Lease, Liability Non-operating expenses related to impairment charges on lease assets Non-operating expenses related to impairment charges on lease assets Non-operating expenses related to impairment charges on lease assets Summary of Authorized and Issued Share Capital Schedule of Stock by Class [Table Text Block] Summary of Ordinary Shares Schedule Of Common Stock [Table Text Block] Schedule of common stock. Derivative Instruments and Hedging Activities Disclosure [Abstract] Fair Value of Derivative Instruments Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Gain/(Loss) Recognized in Income on Derivative Derivative Instruments, Gain (Loss) [Table Text Block] Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Debt Disclosure [Abstract] Summary of Contractual Obligations Under Long-term Debts Schedule of Maturities of Long-term Debt [Table Text Block] SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract] Schedule IV - Reinsurance SEC Schedule, 12-17, Insurance Companies, Reinsurance [Text Block] Fair Value Disclosures [Abstract] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Discounted cash flow Valuation Technique, Discounted Cash Flow [Member] Transaction value Valuation Technique, Option Pricing Model [Member] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Commercial mortgage loans Commercial Mortgage Backed Securities [Member] Middle market loans Middle market loans [Member] Middle market loans [Member] Asset-backed Asset-backed Securities [Member] Equity securities Equity Securities [Member] Held for trading financial assets, at fair value Trading Assets, Excluding Debt and Equity Securities [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Third party Third Party [Member] Third Party [Member] Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Measurement Input, Expected Term Measurement Input, Expected Term [Member] Lender Name [Axis] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Line of Credit Facility, Lender [Domain] Silverton 2016 Silverton 2016 [Member] Silverton 2016 Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Recurring Fair Value, Recurring [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Weighted Average Weighted Average [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Loan Notes, fair value Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Gross written premiums Premiums Written, Gross Reserve for losses Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings Contract period Derivative, Term of Contract Initial value of issuance Debt Instrument, Face Amount, Issued By Third Parties Debt Instrument, Face Amount, Issued By Third Parties Loan notes issued by variable interest entities, at fair value (included within accrued expenses and other payables) Debt Instrument, Accrued Interest and Payables, Fair Value Disclosure Debt Instrument, Accrued Interest and Payables, Fair Value Disclosure Privately-held Investments, at fair value Privately-held Investments, at fair value Privately-held Investments, at fair value Measurement inputs Debt Securities, Trading, Measurement Input Investments, Debt and Equity Securities [Abstract] Schedule of Investment Income, Reported Amounts, by Category [Table] Investment Income [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Fixed Income Securities Fixed Income Securities [Member] Fixed income securities Debt Securities [Member] Short-term investments Short-term Investments [Member] Short-term investment, Trading Short-term Investment, Trading [Member] Short-term Investment, Trading [Member] Fixed term deposits (included in cash and cash equivalents) Cash and Cash Equivalents [Member] Equity securities — Trading Catastrophe bonds — Trading Catastrophe Bonds [Member] Catastrophe Bonds [Member] Privately-held investments — Trading Privately-held investments [Member] Privately-held investments [Member] Other investments, at fair value Other Security Investments [Member] Schedule of Investment Income, Reported Amounts, by Category [Line Items] Net Investment Income [Line Items] Investment income Interest and Dividend Income, Operating Investment expenses Investment Income, Investment Expense Net investment income Net Investment Income Schedule of Available-for-sale Securities [Table] Schedule of Available-for-sale Securities [Table] U.S. government US Treasury Securities [Member] U.S. agency US Government Agencies Debt Securities [Member] Municipal Municipal Bonds [Member] Corporate Corporate Debt Securities [Member] Non-U.S. government-backed corporate Debt Security, Corporate, Non-US [Member] Non-U.S government Debt Security, Government, Non-US [Member] Non-agency commercial mortgage-backed securities Non-agency commercial mortgage-backed securities [Member] Non-agency commercial mortgage-backed securities [Member] Agency mortgage-backed Collateralized Mortgage Backed Securities [Member] Fixed income securities — Available for sale Available-for-sale Securities [Member] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] 0-12 months, Fair Market Value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 0-12 months, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Over 12 months, Fair Market Value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Over 12 months, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Total, Fair Market Value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Total, Gross Unrealized Losses Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Number of Securities Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions Reinsurance Disclosures [Abstract] Summary of Assumed and Ceded Reinsurance on Premiums Written, Premiums Earned and Insurance Losses and Loss Adjustment Expenses Effects of Reinsurance [Table Text Block] Risks and Uncertainties [Abstract] Concentrations of Credit Risk Concentration Risk Disclosure [Text Block] Insurance [Abstract] Schedule of Liability for Unpaid Claims and Claims Adjustment Expense Schedule of Liability for Unpaid Claims and Claims Adjustment Expense [Table Text Block] Short-duration Insurance Contracts, Claims Development Short-duration Insurance Contracts, Claims Development [Table Text Block] Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block] Short-duration Insurance Contracts, Schedule of Historical Claims Duration Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block] Derivative Instruments, Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk [Table] Derivative Instruments, Gain (Loss) [Table] Derivative, by Nature [Axis] Interest rate swap Interest Rate Swap [Member] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Net change from current period hedged transactions Net change from current period hedged transactions [Member] Net change from current period hedged transactions General, administrative and corporate expenses General and Administrative Expense [Member] Gain (loss) on derivative instruments Gain (Loss) on Derivative Instruments [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Derivative At Fair Value Derivative At Fair Value [Member] Derivative at fair value. Liabilities Under Derivative Contracts Liabilities Under Derivative Contracts [Member] Liabilities under derivative contracts. Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Purchase of US and foreign exchange Derivative, Notional Amount Gain (loss) on foreign currency fair value hedge derivatives Gain (Loss) on Foreign Currency Fair Value Hedge Derivatives Gain (loss) to net income from derivative instruments Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net Collateral provided to counterparties as security for the Company's net liability position Collateral Already Posted, Aggregate Fair Value Initial and variation margin, posted Margin Already Posted, Aggregate Fair Value Margin Already Posted, Aggregate Fair Value Commitments and Contingencies Disclosure [Abstract] Restricted Cash And Collateral [Table] Restricted Cash And Collateral [Table] Restricted Cash And Collateral Table Partner Type [Axis] Partner Type [Axis] Partner Type of Partners' Capital Account, Name [Domain] Partner Type of Partners' Capital Account, Name [Domain] Limited Partner Limited Partner [Member] Real estate fund Real Estate Funds [Member] Equity investment Equity Funds [Member] Bermuda Aspen Bermuda [Member] Aspen Bermuda [Member] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Us Multi Beneficiary Trust Fund Us Multi Beneficiary Trust Fund [Member] U.S. Multi-beneficiary Trust Fund. Us Surplus Lines Trust Fund Us Surplus Lines Trust Fund [Member] US surplus lines trust fund. Canadian Trust Fund Canadian Trust Fund [Member] Canadian Trust Fund [Member] Australian Trust Fund Australian Trust Fund [Member] Australian Trust Fund [Member] Swiss Trust Fund Swiss Trust Fund [Member] Swiss Trust Fund [Member] Singapore Trust Fund Singapore Trust Fund [Member] Singapore trust fund Restricted Cash And Collateral [Line Items] Restricted Cash And Collateral [Line Items] Restricted Cash And Collateral [Line Items] Restricted assets Restricted Assets Restricted assets. Other investments (equity method) Other Investments Total as percent of investable assets Collateral Funds Held As Percentage Of Cash And Short Term Investments Collateral funds held as percentage of cash and short term investments. Investable assets held by the Company Cash, Cash Equivalents, and Short-term Investments Investable assets held by insurance regulators Assets Held by Insurance Regulators Minimum capital required Broker-Dealer, Minimum Net Capital Required, Aggregate Indebtedness Standard Minimum trust fund Minimum Trust Fund Minimum trust fund. Percentage of reinsurance liabilities Percentage Of Reinsurance Liabilities Percentage of reinsurance liabilities. Reinsurance liabilities Reinsurance Liabilities Reinsurance Liabilities Assets held-in-trust Assets Held-in-trust Regulatory deposits Regulatory Deposits Regulatory deposits. Deposit with states Deposit With States Deposit with states. Number of investments Number Of Investments In Variable Interest Entities Number Of Investments In Variable Interest Entities Business acquisition, share price Business Acquisition, Share Price Payables and Accruals [Abstract] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Aspen Holdings Parent Company [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Movement in Silverton Loan Notes [Roll Forward] Movement in Silverton Loan Notes [Roll Forward] Movement in Silverton Loan Notes [Roll Forward] Opening balance Notes Payable, Related Parties Total change in fair value for the period Gain (Loss) on Fair Value of Loan Notes, Issued by Variable Interest Entity Gain (Loss) on Fair Value of Loan Notes, Issued by Variable Interest Entity Total distributed in the period Repayment of Notes Receivable from Related Parties Closing balance as at December 31, 2019 Loan notes (long-term liabilities) Other Accrued Liabilities, Noncurrent Accrued expenses (current liabilities) Other Accrued Liabilities, Current SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] Schedule V - Valuation and Qualifying Accounts SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Variable Interest Entities Business Combination Disclosure [Text Block] Condensed Financial Information Disclosure [Abstract] Schedule II - Condensed Financial Information of Registrant Condensed Financial Information of Parent Company Only Disclosure [Text Block] Goodwill and Intangible Assets Disclosure [Abstract] Intangible Assets and Goodwill Intangible Assets Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Authorized share capital Ordinary shares, par value Common Stock, Par or Stated Value Per Share Preference shares, par value Preferred Stock, Par or Stated Value Per Share Ordinary shares, issued Preference shares, rate Preferred Stock, Dividend Rate, Percentage Retirement Benefits [Abstract] Retirement Plans Compensation and Employee Benefit Plans [Text Block] Document Document And Entity Information [Abstract] Document Document and Entity Information [Abstract] Document Type Document Type Document Annual Report Document Annual Report Document Transition Report Document Transition Report Document Shell Company Report Document Shell Company Report Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Voluntary Filers Entity Voluntary Filers Entity Filer Category Entity Filer Category Entity Emerging Growth Company Entity Emerging Growth Company Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, by Property [Table] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, by Property [Table] Geographic Distribution [Axis] Geographic Distribution [Axis] Geographic Distribution [Domain] Geographic Distribution [Domain] U.S. Geographic Distribution, Domestic [Member] International Geographic Distribution, Foreign [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Investment, Net Carrying Value Investment, Net Carrying Value [Member] Investment, Net Carrying Value [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Product Concentration Risk Product Concentration Risk [Member] Geographic Concentration Risk Geographic Concentration Risk [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Materials Product [Member] Financials Financial Service [Member] Industrials Industrial Service [Member] Industrial Service [Member] Consumer discretionary Consumer Discretionary Service [Member] Consumer Discretionary Service [Member] Health care Health Care [Member] Energy Energy Commodities and Service [Member] Consumer staples Consumer Staples Service [Member] Consumer Staples Service [Member] Information technology Technology Service [Member] Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Office building Office Building [Member] Apartment Apartment Building [Member] Hotel Hotel [Member] Other commercial Other Property [Member] Retail Retail [Member] Industrial Industrial Property [Member] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items] Fair market value, trading Debt Securities, Trading, and Equity Securities, FV-NI Concentration risk percentage Concentration Risk, Percentage Schedule of Trading Securities and Other Trading Assets [Table] Debt Securities, Trading, and Equity Securities, FV-NI [Table] Total short-term investments — Available for sale Total fixed income securities — Available for sale Fixed Maturities [Member] Schedule of Trading Securities and Other Trading Items [Line Items] Debt and Equity Securities, FV-NI [Line Items] Gross unrealized gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Gross unrealized losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Fair market value Debt Securities, Available-for-sale Total, Available for sale investments in fixed income maturities, Cost or Amortized Cost Debt Securities, Available-for-sale, Amortized Cost Reinsurance Reinsurance [Text Block] Income Tax Disclosure [Abstract] Summary of Total Income Tax Schedule Of Income Tax Expense Benefit Intraperiod Tax Allocation [Table Text Block] Schedule of income tax expense benefit intraperiod tax allocation. Schedule of Income Tax by Taxing Authority Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block] Income Tax Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Schedule of Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Tax Effects of Deferred Tax Assets and Deferred Tax Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward] Balance at the beginning of the period Deferred Policy Acquisition Cost Acquisition costs deferred Deferred Policy Acquisition Cost, Capitalization Amortization of deferred policy acquisition costs Deferred Policy Acquisition Costs, Amortization Expense Balance at the end of the period Share-based Payment Arrangement [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Performance Shares Performance Shares [Member] Deferred cash awards Deferred cash awards [Member] Deferred cash awards [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based payment and LTIP expense Share-based payment and LTIP expense Share-based payment and LTIP expense Allocated share-based compensation expense Share-based Payment Arrangement, Expense Allocated share-based compensation expense offset Allocated Share-Based Compensation Expense Offset Allocated Share-Based Compensation Expense Offset Other share-based arrangements, expense Other share-based arrangements, expense Other share-based arrangements, expense Income tax benefit Share-based Payment Arrangement, Expense, Tax Benefit Rate of contribution on retirement plans of its employees salaries, Maximum Defined Contribution Plan Percentage Of Maximum Contribution Defined contribution plan percentage of maximum contribution. Total contributions by the Company to the retirement plan Defined Contribution Plan, Cost Additional paid-in capital Additional Paid-in Capital [Member] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Preference Shares Preferred Stock [Member] 7.401% Preference Shares Series B Preferred Stock [Member] 7.250% Preference Shares Series C Preferred Stock [Member] Additional paid in capital Additional Paid in Capital Aggregate liquidation preferences Aggregate Liquidation Preferences Aggregate liquidation preferences. Preferred stock issuance cost Preferred Stock Issuance Cost Preferred stock issuance cost. Preferred Stock, Redemption Amount Preferred Stock, Redemption Amount Redemption price per share Preferred Stock, Liquidation Preference Per Share Proceeds or share issuance Stock Issued During Period, Value, New Issues Preference shares redeemed and cancelled Stock Redeemed or Called During Period, Value Preference shares liquidation preference, value Preferred Stock, Liquidation Preference, Value Schedule Of Finite And Indefinite Lived Intangible Assets By Major Class [Table] Schedule Of Finite And Indefinite Lived Intangible Assets By Major Class [Table] Schedule Of Finite And Indefinite Lived Intangible Assets By Major Class [Table] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Digital Re Digital Risk [Member] Digital Risk Resources LLP[Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Trademarks Trademarks [Member] Aspen trademark Aspen Trademark [Member] Aspen Trademark [Member] Blue Waters Blue Waters [Member] Blue Waters [Member] Insurance Licenses Licensing Agreements [Member] Renewal Rights Contractual Rights [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Finite-Lived Intangible Assets [Line Items] Finite And Indefinite Lived Intangible Assets By Major Class [Line Items] Finite And Indefinite Lived Intangible Assets By Major Class [Line Items] Goodwill, acquired Goodwill, Acquired During Period Equity method investment, ownership percentage Equity Method Investment, Ownership Percentage Value of the asset Intangible Assets, Net (Excluding Goodwill) Economic useful life Intangible Assets Amortization Period Intangible assets amortization period. Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Business Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Reinsurance Reinsurance [Member] Reinsurance. Insurance Insurance [Member] Insurance. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Net written premiums Premiums Written, Net Gross earned premiums Premiums Earned, Gross Premiums Earned, Gross Net earned premium Premiums Earned, Net Losses and loss adjustment expenses Policyholder Benefits and Claims Incurred, Net Amortization of deferred policy acquisition costs General and administrative expenses General and Administrative Expense Underwriting income (loss) Underwriting Income (Loss) Corporate expenses Corporate Expenses Corporate expenses. Non-operating expenses Nonoperating Income (Expense) Net investment income Realized and unrealized investment gains Gain (Loss) on Investments Realized and unrealized investment losses Debt Securities, Gain (Loss) Realized loss on debt extinguishment Gain (Loss) on Extinguishment of Debt Change in fair value of loan notes issued by variable interest entities Change in fair value of derivatives Derivative, Gain (Loss) on Derivative, Net Interest expense on long term debt Interest Expense, Debt Net realized and unrealized foreign exchange (losses) Foreign Currency Transaction Gain (Loss), before Tax Other income Other Income Other expenses Other Expenses Income tax (expense)/benefit Net (loss) Losses and loss adjustment expenses Liability for Claims and Claims Adjustment Expense Net Reserves for Losses and LAE Liability for Unpaid Claims and Claims Adjustment Expense, Net Ratios Insurance Ratios [Abstract] Loss ratio Loss Ratio Policy acquisition expense ratio Acquisition Cost Ratio General and administrative expense ratio General and Administrative Expense Ratio Expense ratio Underwriting Expense Ratio Combined ratio Combined Ratio Non-operating expenses related to Merger Agreement Non-operating expenses related to Merger Agreement Non-operating expenses related to Merger Agreement Non-operating expenses related to Effectiveness And Efficiency Program Nonoperating Expenses Related To Effectiveness And Efficiency Program Nonoperating Expenses Related To Effectiveness And Efficiency Program Non-operating expenses related to retention costs Non-operating expenses related to retention costs Non-operating expenses related to retention costs Write back of buy out provision Loss Contingency Accrual, Provision Liability, Payments, Next twelve months (2020) Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months Liability, Payments, Due year two (2021) Lessee, Operating Lease, Liability, Payments, Due Year Two Liability, Payments, Due year three (2022) Lessee, Operating Lease, Liability, Payments, Due Year Three Liability, Payments, Due year four (2023) Lessee, Operating Lease, Liability, Payments, Due Year Four Liability, Payments, Due year five (2024) Lessee, Operating Lease, Liability, Payments, Due Year Five Liability, Payments, Due after year five Lessee, Operating Lease, Liability, Payments, Due after Year Five Total minimum lease payments Lessee, Operating Lease, Liability, Payments, Due Less imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract] Schedule III - Supplementary Insurance Information SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Disclosure [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Restatement [Axis] Restatement [Axis] Restatement [Domain] Restatement [Domain] Restatement Adjustment Restatement Adjustment [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-09 Accounting Standards Update 2016-09 [Member] Non-controlling interest Noncontrolling Interest [Member] Minority interest buy-out Minority interest buy-out [Member] Minority Interest Buy-out [Member] Retained earnings Retained Earnings [Member] Gain/(loss) on derivatives, net of taxes: Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Cumulative foreign currency translation adjustments, net of taxes: Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Unrealized appreciation on available for sale investments, net of taxes: AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] Ordinary Shares Common Stock [Member] Statement [Line Items] Statement [Line Items] Preference share redemption costs Changes In Redemption Value Of Preference Shares Changes In Redemption Value Of Preference Shares of the 7.401% preference shares Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Shareholder's equity beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net change attributable to non-controlling interest for the year Net Income (Loss) Attributable to Noncontrolling Interest Shares issued Ordinary shares repurchased and canceled Stock Repurchased and Retired During Period, Value Preference shares redemption Changes In Redemption Cost Of Preference Shares Changes In Redemption Cost Of Preference Shares Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Consideration of minority interest Consideration of minority interest Consideration of minority interest Buy-out of minority interest Buy-out of minority interest Buy-out of Minority Interest Dividends Dividends Dividends due to non-controlling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Share-based payment Cumulative Effect of New Accounting Principle in Period of Adoption Change for the year, net of income tax Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax Net change from current period hedged transactions Derivative Assets (Liabilities), at Fair Value, Net Total accumulated other comprehensive income/(loss), net of taxes Accumulated Other Comprehensive Income (Loss), Net of Tax Shareholder's equity ending balance Retained earnings restatement Cumulative Effect on Retained Earnings, before Tax Preferred Stock, Dividend Rate, Percentage Segment Reporting Segment Reporting Disclosure [Text Block] Text Block [Abstract] Statutory Requirements and Dividends Restrictions Statutory Requirements And Dividends Restriction [Text Block] Statutory requirements and dividends restriction. Income Statement [Abstract] Revenues Revenues [Abstract] Total revenues Revenues Expenses Operating Expenses [Abstract] Amortization of deferred policy acquisition costs General, administrative and corporate expenses Interest on long-term debt Change in fair value of derivatives Change in fair value of loan notes issued by variable interest entities Realized and unrealized investment losses Realized loss on debt extinguishment Net realized and unrealized foreign exchange losses Other expenses Total expenses Expense Expense. Amount attributable to non-controlling interest Net (loss) attributable to Aspen Insurance Holdings Limited’s ordinary shareholders Net Income (Loss) Attributable to Parent Other Comprehensive Income/(Loss): Other Comprehensive Income (Loss), before Tax [Abstract] Available for sale investments: Debt Securities, Available-for-sale [Abstract] Reclassification adjustment for net realized (losses)/gains on investments included in net income Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax Change in net unrealized gains/(losses) on available for sale securities held Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax Net change from current period hedged transactions Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax Change in foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax Other comprehensive income/(loss), gross of tax Other Comprehensive Income (Loss), before Tax Income tax thereon: Other Comprehensive Income (Loss), Tax [Abstract] Reclassification adjustment for net realized losses on investments included in net income Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Change in net unrealized gains on available for sale securities held Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax Net change from current period hedged transactions Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Change in foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax Total income tax on other comprehensive income/(loss) Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Other comprehensive (loss)/income, net of tax Other Comprehensive Income (Loss), Net of Tax Total comprehensive (loss) attributable to Aspen Insurance Holdings Limited’s ordinary shareholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Australia/Asia Asia Pacific [Member] Caribbean Caribbean [Member] Caribbean [Member] Europe Europe [Member] United Kingdom UNITED KINGDOM United States & Canada United States And Canada [Member] United States & Canada. Worldwide excluding United States Non-US [Member] Worldwide including United States Worldwide Including United States [Member] Worldwide including United States. Others Other Countries [Member] Other Countries. Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table] Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table] Property Insurance Property Insurance [Member] Casualty Insurance Casualty, Commercial Insurance Product Line [Member] Casualty, Commercial Insurance Product Line [Member] Marine, Aviation and Energy Insurance Marine, Aviation and Energy, Commercial Insurance Product Line [Member] Marine, Aviation and Energy, Commercial Insurance Product Line [Member] Financial and Professional Insurance Financial and Professional, Commercial Insurance Product Line [Member] Financial and Professional, Commercial Insurance Product Line [Member] Insurance lines Property and Casualty, Commercial Insurance [Member] Property Catastrophe and Other Property Reinsurance Assumed Property Catastrophe and Other Property, Commercial Insurance Product Line [Member] Assumed Property Catastrophe and Other Property, Commercial Insurance Product Line [Member] Casualty Reinsurance Assumed Casualty, Commercial Insurance Product Line [Member] Assumed Casualty, Commercial Insurance Product Line Specialty Reinsurance Assumed Specialty, Commercial Insurance Product Line [Member] Assumed Specialty, Commercial Insurance Product Line Reinsurance lines Short-Duration Insurance, Other [Member] Insurance lines other than short-duration Long-Duration Insurance, Other [Member] Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] Liability for claims and claim adjustment expenses, net of reinsurance Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net Reinsurance recoverable on unpaid losses Reinsurance Recoverable for Unpaid Claims and Claims Adjustments Unallocated claims incurred Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense Other reinsurance balances recoverable Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Other Reconciling Item, Other Reinsurance Balances Recoverable Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Other Reconciling Item, Other Reinsurance Balances Recoverable Other Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item Liability for unpaid claims and claim adjustment expense, aggregate reconciling items Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Aggregate Reconciling Items Capital Structure Stockholders' Equity Note Disclosure [Text Block] Total fixed income securities — Available for sale Fixed maturities Due one year or less, Cost or Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost Due after one year through five years, Cost or Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost Due after five years through ten years, Cost or Amortized Cost Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost Due after ten years, Cost or Amortized Cost Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost Cost or Amortized Cost Available-for-sale Securities, Amortized Cost Basis Due one year or less, Fair Market Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Available For Sale Securities Debt Maturities Within One Year Average Ratings By Maturity Available For Sale Securities Debt Maturities Within One Year Average Ratings By Maturity Available for sale securities debt maturities within one year average ratings by maturity. Due after one year through five years, Fair Market Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value Available For Sale Securities Debt Maturities After One Through Five Years Average Ratings By Maturity Available For Sale Securities Debt Maturities After One Through Five Years Average Ratings By Maturity Available for sale securities debt maturities after one through five years average ratings by maturity. Due after five years through ten years, Fair Market Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value Available For Sale Securities Debt Maturities After Five Through Ten Years Average Ratings By Maturity Available For Sale Securities Debt Maturities After Five Through Ten Years Average Ratings By Maturity Available for sale securities debt maturities after five through ten years average ratings by maturity. Due after ten years, Fair Market Value Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value Available For Sale Securities Debt Maturities After Ten Years Average Ratings By Maturity Available For Sale Securities Debt Maturities After Ten Years Average Ratings By Maturity Available for sale securities debt maturities after ten years average ratings by maturity. Available for sale investments in fixed income maturities, Fair Market Value Available For Sale Securities Average Ratings By Maturity Available For Sale Securities Average Ratings By Maturity Available for sale securities average ratings by maturity. Condensed Financial Statements [Table] Condensed Financial Statements [Table] Parent Company Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] Equity in net earnings of subsidiaries and other investments, equity method Equity In Net Earnings Of Subsidiaries Equity in net earnings of subsidiaries. Dividend income Interest income on Eurobond Interest Income, Operating Net realized and unrealized investment gains/(losses) Realized Investment Gains (Losses) General, administrative and corporate expenses Interest expense Interest Expense Proportion due to non-controlling interest Net (loss)/income attributable to Aspen Insurance Holdings Limited’s ordinary shareholders Other Comprehensive Income: Other Comprehensive Income Loss [Abstract] Other Comprehensive Income Loss [Abstract] Change in unrealized gains on investments Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Net change from current period hedged transactions Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Change in foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Premiums written: Premiums Written, Net [Abstract] Direct Direct Premiums Written Assumed Assumed Premiums Written Ceded Ceded Premiums Written Net premiums written Premiums earned: Premiums Earned, Net [Abstract] Direct Direct Premiums Earned Assumed Assumed Premiums Earned Ceded Ceded Premiums Earned Net premiums earned Insurance losses and loss adjustment expenses: Policyholder Benefits and Claims Incurred, Net [Abstract] Direct Policyholder Benefits and Claims Incurred, Direct Assumed Policyholder Benefits and Claims Incurred, Assumed Ceded Policyholder Benefits and Claims Incurred, Ceded Net insurance losses and loss adjustment expenses Summary of Changes in Intangible Assets Schedule of Indefinite-Lived Intangible Assets [Table Text Block] Schedule of Accumulated Other Comprehensive Income Reclassification Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Summary of Statutory Requirements and Dividends Restrictions Dividend Payment Restrictions [Text Block] Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated transactions Affiliated Entity [Member] Beneficial owner Beneficial Owner [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Asset Management Arrangement Asset Management Arrangement [Member] Management Consulting Agreement Management Consulting Agreement [Member] Management Consulting Agreement [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Related party contracts, aggregate and individual, maximum Related Party Transaction, Amounts of Transaction Plus component of annual investment management fee Related Party Transaction, Rate of Interest Related Party Transaction, Rate of Interest Annual fee cap Related Party Transaction, Maximum Rate Increase Related Party Transaction, Maximum Rate Increase Notice of termination of agreement Related Party Transactions, Notice of Termination of Agreement Related Party Transactions, Notice of Termination of Agreement Percentage of consolidated group's net income due to Apollo Management Related Party Transaction, Rate Fees due to Apollo Management Due from Officers or Stockholders, Current Initial term Related party transactions, initial term Related party transactions, initial term Automatic twelve month extension Related party transactions, automatic twelve month extension Related party transactions, automatic twelve month extension Automatic twelve month extension, eight years Related party transactions, automatic twelve month extension, one Related party transactions, automatic twelve month extension, one Automatic twelve month extension, nine years Related party transactions, automatic twelve month extension, two Related party transactions, automatic twelve month extension, two Term extension period Related party transactions, term extension period Related party transactions, term extension period Ownership percentage Related party transactions, ownership percentage Related party transactions, ownership percentage Related party fees Due to Affiliate, Current Related party fees still due Due to Affiliate Intercompany balance payable Accounts Payable, Related Parties, Current Short-duration Insurance Contracts, Claims Development [Table] Short-duration Insurance Contracts, Claims Development [Table] Short-duration Insurance Contracts, Accident Year [Axis] Short-duration Insurance Contracts, Accident Year [Axis] Short-duration Insurance Contracts, Accident Year [Domain] Short-duration Insurance Contracts, Accident Year [Domain] Accident Year 2012 Short-duration Insurance Contracts, Accident Year 2012 [Member] Accident Year 2013 Short-duration Insurance Contracts, Accident Year 2013 [Member] Accident Year 2014 Short-duration Insurance Contracts, Accident Year 2014 [Member] Accident Year 2015 Short-duration Insurance Contracts, Accident Year 2015 [Member] Accident Year 2016 Short-duration Insurance Contracts, Accident Year 2016 [Member] Accident Year 2017 Short-duration Insurance Contracts, Accident Year 2017 [Member] Accident Year 2018 Short-duration Insurance Contracts, Accident Year 2018 [Member] Accident Year 2019 Short-Duration Insurance Contract, Accident Year 2019 [Member] Claims Development [Line Items] Claims Development [Line Items] Incurred Claims and Allocated Claim Adjustment Expense, Net Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net Incurred but Not Reported (IBNR) Claims Liability, Net Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net Number of Reported Claims Short-duration Insurance Contract, Cumulative Number of Reported Claims Cumulative paid claims and allocated claim adjustment expense, Net Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net All outstanding liabilities for 2012 and subsequent years, net of reinsurance Short Duration Insurance Contracts, Liability for Unpaid Claim Adjustment Expense, Net, Not Separately Presented, Subtotal Undiscounted subtotal amount, after reinsurance, of the liability for unpaid claim adjustment expense for short durations insurance contracts not separately presented in claim development information. All outstanding liabilities before 2012, net of reinsurance Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented Liability for claims and claim adjustment expenses, net of reinsurance Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivatives at Fair Value Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Fair Value Derivative, Notional Amount Cash collateral Disclosure Statutory Requirements And Dividends Restrictions Summary Of Statutory Requirements And Dividends Restrictions [Abstract] Disclosure - Statutory Requirements and Dividends Restrictions - Summary of Statutory Requirements and Dividends Restrictions [Abstract] Jurisdiction [Axis] Jurisdiction [Axis] Statutory Accounting Practices, Jurisdiction [Domain] Statutory Accounting Practices, Jurisdiction [Domain] U.S. UNITED STATES Bermuda BERMUDA U.K. Required statutory capital and surplus Dividend Payments Restrictions Schedule Required Statutory Capital And Surplus Dividend payments restrictions schedule required statutory capital and surplus. Actual statutory capital and surplus Dividend Payments Restrictions Schedule, Statutory Capital and Surplus Deferred Policy Acquisition Costs Deferred Policy Acquisition Costs [Text Block] Earnings Per Share [Abstract] Dividends Payable [Table] Dividends Payable [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Dividends Payable [Line Items] Dividends Payable [Line Items] Dividend, in usd per share Dividends Payable, Amount Per Share Payable Date Dividends Payable, Date to be Paid Record Date Dividends Payable, Date of Record Depositary share interest of 1/1000th in each 5.625% DepositaryShareDividendRateFractionalInterest Preferred Stock, Dividend Rate, Depositary Share Fractional Interest (1/1000th of 5.625% Preference Share) Depositary share dividend, equivalent to 1/1000th pref share dividend Depositary Share Dividend Depositary Share Dividend Income Taxes Income Tax Disclosure [Text Block] Number of business segments Number of Reportable Segments Fair Value, Separate Account Investment [Table] Fair Value, Separate Account Investment [Table] Third party Letters of credit / guarantees Letter of Credit [Member] Fair Value, Separate Account Investment [Line Items] Fair Value, Separate Account Investment [Line Items] Total restricted assets Other investments Securities and cash as collateral secured letters of credit Deposit Securities And Cash As Collateral Secured Letters Of Credit Deposit securities and cash as collateral secured letters of credit. Previous ordinary shares in issue at the beginning of the year Ordinary shares issued to employees under the 2013 share incentive plan and/or 2008 share purchase plan Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Ordinary shares issued to non-employee directors Stock Issued During Period Shares Non Employee Options Stock issued during period shares non employee options. Ordinary shares canceled Stock Repurchased During Period, Shares Previous ordinary shares in issue at the end of the year Ordinary shares in issue at the beginning of the year New ordinary shares issued of $0.01 per share Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Valuation Allowance by Deferred Tax Asset [Axis] Valuation Allowance by Deferred Tax Asset [Axis] Deferred Tax Asset [Domain] Deferred Tax Asset [Domain] U.S branch of Aspen U.K. U.S branch of Aspen U.K. [Member] U.S branch of Aspen U.K. [Member] Lloyds syndicate Lloyds [Member] Lloyds. Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Expected tax (benefit)/expense Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Overseas statutory tax rates differential Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Amount Base erosion and anti-abuse tax (BEAT) expense Effective Income Tax Reconcilation, Base Erosion Anti-Abuse Tax expense U.S Base Erosion Anti-Abuse Tax (BEAT) on premiums ceded from U.S. subsidiaries to non-U.S. related parties. Prior year adjustments Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Amount Valuation allowance (2) Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Impact of unrecognized tax benefits Effective Income Tax Rate Reconciliation, Tax Contingency, Amount Restricted foreign tax credits Effective Income Tax Rate Reconciliation, Tax Settlement, Foreign, Amount Australian non-resident withholding tax Effective Income Tax Rate Reconciliation, Tax Settlement, Non-Resident Withholding Tax, Amount Effective Income Tax Rate Reconciliation, Tax Settlement, Non-Resident Withholding Tax, Amount Share-based payments Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Payment Arrangement, Amount Foreign exchange Effective Income Tax Rate Reconciliation, Tax Contingency, Foreign, Amount Non-deductible expenses Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount Non-taxable items Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount Impact of changes in statutory tax rates Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Total tax expense/(benefit) Valuation allowance, associated losses Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation, Allowance, Associated Losses Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation, Allowance, Associated Losses Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table] Silverton 2017 Silverton 2017 [Member] Silverton 2017 [Member] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] Debt Instrument, Accrued Interest and Payables, Fair Value Disclosure Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Balance at the beginning of the period Liability for unpaid claims and claims adjustment expense amount ceded Liability For Unpaid Claims And Claims Adjustment Expense Amount Disposed of or Ceded Liability For Unpaid Claims And Claims Adjustment Expense Amount Disposed of or Ceded Distributed to third parties Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements Balance at the end of the period Amount classified within accrued expenses and other payables Provision for losses and LAE for claims incurred Prior Year Claims and Claims Adjustment Expense Liability for unpaid claims and claims adjustment expense amount ceded Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Liability Liability [Member] Silverton Silverton [Member] Silverton [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Assets Assets [Member] Change in unrealized investment gains (losses) Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss) Change in unrealized investment gains (losses), liability Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss) Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] Balance at the beginning of the year Purchases and issuances Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances Settlements and sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements Increase (decrease) in fair value included in net income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings Balance at the end of the year Liability purchases Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases Liability sales Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Sales Liability, increase (decrease) in fv included in net income Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings Statement of Financial Position [Abstract] Fixed income securities, available for sale amortized cost Fixed income securities, trading, amortized cost Debt Securities, Trading, Amortized Cost Short term investments available for sale, amortized cost Short term investments available for sale, amortized cost Short term investments available for sale, amortized cost Short-term investments, trading, amortized cost Short Term Investments Trading Amortized Cost Short-term investments, trading, amortized cost. Cash and cash equivalents, within VIEs Cash and Cash Equivalents, within VIEs Cash and Cash Equivalents, within VIEs Catastrophe bonds trading, at fair value Catastrophe Bonds, Fair Value Disclosure Catastrophe Bonds, Fair Value Disclosure Privately-held investments, cost, trading at fair value Privately-held investments, amortized cost, trading at fair value Privately-held investments, amortized cost, trading at fair value Summary of Investment Income Investment Income [Table Text Block] Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments Realized Gain (Loss) on Investments [Table Text Block] Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available for Sale Investments in Fixed Income Maturities and Short-Term Investments Available-for-sale Securities [Table Text Block] Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities Debt Securities, Trading, and Equity Securities, FV-NI [Table Text Block] Schedule of Commercial Mortgage and Middle Market Loans Schedule of Participating Mortgage Loans [Table Text Block] Credit Quality Indicators of Commercial Mortgage and Middle Market Loans Financing Receivable Credit Quality Indicators [Table Text Block] Debt Service and Fixed Charge Coverage Ratios Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Other Investments Schedule of Variable Interest Entities [Table Text Block] Summary of Fixed Maturities Investments Classified by Contractual Maturity Date [Table Text Block] Aggregate Fair Value and Gross Unrealized Loss by Type of Security Schedule of Unrealized Loss on Investments [Table Text Block] Provision for losses and LAE, beginning balance Less reinsurance recoverable Reinsurance Recoverables Adjustment Reinsurance Recoverables Adjustment. Net losses and LAE reserves, beginning balance Net loss and LAE expenses (disposed) Liability For Unpaid Claims And Claims Adjustment Expense Amount Disposed Of Liability for unpaid claims and claims adjustment expense amount disposed of. Movement in net provision for losses and LAE for claims incurred: Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract] Current year Current Year Claims and Claims Adjustment Expense Prior years Total incurred Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims Losses and LAE payments for claims incurred: Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid [Abstract] Current year Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year Prior years Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years Total paid Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid Foreign exchange losses/(gains) Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss) Net losses and LAE reserves, ending balance Plus reinsurance recoverable on unpaid losses at the end of the year Reinsurance Recoverables, Including Reinsurance Premium Paid Provision for losses and LAE at the end of the year Share-based payments Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Net loss reserves and loss adjustment expenses Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves Unrealized losses on investments Deferred Tax Assets, Unrealized Losses on Available-for-Sale Securities, Gross Accrued expenses Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals Foreign tax credit carryforwards Deferred Tax Assets, Operating Loss Carryforwards, Foreign Unearned premiums Deferred Tax Assets, Unearned Premiums Deferred Tax Assets, Unearned Premiums Deferred policy acquisition costs Deferred Tax Assets (Liabilities), Tax Deferred Expense Deferred Tax Assets (Liabilities), Tax Deferred Expense [Line Items] Office properties and equipment Deferred Tax Assets, Timing Differences On Fixed Assets Deferred Tax Assets, Timing Differences On Fixed Assets Operating lease liability Deferred Tax Assets, Operating Lease Liability Deferred Tax Assets, Operating Lease Liability Other temporary differences Deferred Tax Assets, Other Total gross deferred tax assets Deferred Tax Assets, Gross Less valuation allowance Deferred Tax Assets, Valuation Allowance Net deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Equalization provision reserves Deferred Tax Liabilities Insurance Equalization Provision Deferred tax liabilities insurance equalization provision. Unrealized (gains) on investments Deferred Tax Liabilities, Unrealized Gains on Trading Securities Intangible assets Deferred Tax Liabilities, Intangible Assets Deferred policy acquisition costs Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost Quota share losses Deferred tax liabilities, quota share losses Deferred tax liabilities, quota share losses Loss portfolio transfer costs Deferred Tax Liability, Intra-entity Transfer, Asset Other than Inventory Operating lease assets Deferred Tax Liabilities, Operating Lease Assets Deferred Tax Liabilities, Operating Lease Assets Other temporary differences Deferred Tax Liabilities, Other Total gross deferred tax (liabilities) Deferred Tax Liabilities, Gross Deferred Tax Assets, Net Deferred Tax Assets, Net Fixed income securities - trading Trading Fixed Maturity Investments [Member] Trading fixed maturity investments. Catastrophe Bonds Securities, asset-backed Securities, asset-backed [Member] Securities, asset-backed [Member] Privately-held investments Total - Trading Total - Trading [Member] Total - Trading [Member] Gross Unrealized Gains Trading Securities, Accumulated Gross Unrealized Gain, before Tax Trading Securities, Accumulated Gross Unrealized Gain, before Tax Gross Unrealized Losses Trading Securities, Accumulated Gross Unrealized Loss, before Tax Trading Securities, Accumulated Gross Unrealized Loss, before Tax Debt Securities, Trading, Amortized Cost Segment [Domain] Deferred Policy Acquisition Costs SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Deferred Policy Acquisition Cost Net Reserves for Unearned Premiums SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Unearned Premium Net Investment Income SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Net Investment Income Losses and LAE Expenses Losses And Loss Adjustment Expenses Losses And Loss Adjustment Expenses Policy Acquisition Expenses Deferred Policy Acquisition Cost Other Expenses Deferred Policy Acquisition Cost Other Expenses General and Administrative Expenses SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Other Operating Expense Financing Receivable, Credit Quality Indicator [Table] Financing Receivable, Credit Quality Indicator [Table] Debt-to-Value [Axis] Debt-to-Value [Axis] Debt-to-Value [Domain] Debt-to-Value [Domain] Less than 50 Percent Debt to Value Ratio, Less than 50 Percent [Member] Debt to Value Ratio, Less than 50 Percent [Member] 50 to 60 Percent Debt to Value Ratio, 50 to 60 Percent [Member] Debt to Value Ratio, 50 to 60 Percent [Member] 61 to 70 Percent Debt to Value Ratio, 61 to 70 Percent [Member] Debt to Value Ratio, 61 to 70 Percent [Member] 71 to 80 Percent Debt to Value Ratio, 71 to 80 Percent [Member] Debt to Value Ratio, 71 to 80 Percent [Member] Financing Receivable, Credit Quality Indicator [Line Items] Financing Receivable, Credit Quality Indicator [Line Items] Summary of Declared Dividends Schedule of Dividends Payable [Table Text Block] Income Tax Examination [Table] Income Tax Examination [Table] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Bermuda Office of the Tax Commissioner, Bermuda [Member] U.K. Her Majesty's Revenue and Customs (HMRC) [Member] Income Tax Examination [Line Items] Income Tax Examination [Line Items] (Loss) before tax, Non-U.S. Income (Loss) from Continuing Operations before Income Taxes, Foreign (Loss) before tax, U.S. Income (Loss) from Continuing Operations before Income Taxes, Domestic Current tax (benefit)/expense, Non-U.S. Current Foreign Tax Expense (Benefit) Current tax (benefit)/expense, U.S. Current Federal Tax Expense (Benefit) Current tax (benefit)/expense, Total Current Income Tax Expense (Benefit) Deferred tax (benefit), Non-U.S. Deferred Foreign Income Tax Expense (Benefit) Deferred tax (benefit), U.S. Deferred State and Local Income Tax Expense (Benefit) Deferred tax, Total Deferred Income Tax Expense (Benefit) Total tax expense/(benefit), Non-U.S. Foreign Income Tax Expense (Benefit), Continuing Operations Total tax expense/(benefit), U.S. Federal Income Tax Expense (Benefit), Continuing Operations Current tax expenses (benefit) related to prior year Current Federal Tax Expenses (Benefit) Related to Prior Year Current Federal Tax Expenses (Benefit) Related to Prior Year Deferred tax benefit, unrealized gain on investments Deferred Income Tax (Expense) Benefit, Unrealized Gain on Investments Deferred Income Tax (Expense) Benefit, Unrealized Gain on Investments Income Taxes [Table] Income Taxes [Table] Income Taxes [Table] Valuation Allowance, Operating Loss Carryforwards SEC Schedule, 12-09, Valuation Allowance, Operating Loss Carryforward [Member] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain]