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Income Taxes - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Income Taxes [Line Items]    
United States corporate tax at a rate 21.00%  
Capital loss carryforwards $ 6.7 $ 0.3
Less valuation allowance 145.7 225.9
Deferred Tax Liabilities, Net   2.8
Deferred Tax Assets, Gross 322.2 277.5
Internal Revenue Service (IRS)    
Income Taxes [Line Items]    
Capital loss carryforwards 31.7  
Aspen U.K. | Internal Revenue Service (IRS)    
Income Taxes [Line Items]    
Capital loss carryforwards 16.7  
U.S. operating subsidiaries | Internal Revenue Service (IRS)    
Income Taxes [Line Items]    
Capital loss carryforwards 15.0  
Lloyd's | U.K.    
Income Taxes [Line Items]    
Deferred tax losses, operating loss carryforward (19.9) (66.2)
Other juridictions | U.K.    
Income Taxes [Line Items]    
Deferred tax losses, operating loss carryforward (118.8) (103.9)
Internal Revenue Service (IRS)    
Income Taxes [Line Items]    
Net operating loss carryforwards 376.5 443.1
Operating loss carryforwards, remaining 376.5  
Charitable contribution carryforwards 0.0 0.1
Less valuation allowance 18.0 119.7
Internal Revenue Service (IRS) | Aspen U.K.    
Income Taxes [Line Items]    
Net operating loss carryforwards 67.1  
Operating loss carryforwards, subject to s382 limitation 6.5  
Internal Revenue Service (IRS) | U.S. operating subsidiaries    
Income Taxes [Line Items]    
Net operating loss carryforwards 309.4  
Operating loss carryforwards, subject to s382 limitation $ 20.8  
Internal Revenue Service (IRS) | Minimum    
Income Taxes [Line Items]    
Operating loss carryforwards, date of expiration 2032  
Internal Revenue Service (IRS) | Maximum    
Income Taxes [Line Items]    
Operating loss carryforwards, date of expiration 2041  
U.K.    
Income Taxes [Line Items]    
U. K. corporate tax rate 19.00%  
Net operating loss carryforwards $ 280.5 168.9
Operating loss carryforwards, remaining 19.8 20.2
Less valuation allowance $ 106.7 $ 88.7
Bermuda    
Income Taxes [Line Items]    
Bermuda tax rate 0.00%