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Credit Facilities and Short-Term Debt - Additional Information (Details) - USD ($) |  |  | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |
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Dec. 01, 2021 | Nov. 13, 2013 | Dec. 31, 2022 | Dec. 31, 2021 | Feb. 07, 2023 | Oct. 27, 2022 | Jun. 30, 2022 | Jun. 17, 2022 | Dec. 29, 2021 | Nov. 30, 2021 | Nov. 05, 2021 | Apr. 01, 2021 | Nov. 30, 2020 | Nov. 03, 2020 | Feb. 11, 2019
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit | $ 300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of credit facility Increasable capacity | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum consolidated tangible net worth under credit facility |  |  | $ 2,019,600,000 |  |  |  |  |  |  |  |  |  |  |  |
Percentage of consolidated net income |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |
Percentage of aggregate net cash proceeds from the issuance of capital stock |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |
Percentage of consolidated leverage ratio permitted |  |  | 35.00% |  |  |  |  |  |  |  |  |  |  |  |
Securities lending transaction |  |  | $ 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Securities lending transaction |  |  |  |  |  |  |  | $ 50,000,000 |  |  |  |  |  |  |
Aspen U.K. | Deutsche |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Commitment Fee Amount |  |  | 22,800,000 |  |  |  |  |  |  |  |  |  |  |  |
Aspen U.K. | Citibank Europe |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Commitment Fee Amount |  |  | 75,100,000 |  |  |  |  |  |  |  |  |  |  |  |
AUL | Lloyd's |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit to Support Funds at Lloyd's |  |  |  |  |  | $ 285,000,000 |  |  |  |  |  |  |  |  |
Funds at Lloyd's Facility Agreement |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |  | $ 150,000,000 |  |
AUL | Lloyd's | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit to Support Funds at Lloyd's |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 235,000,000 |
Bermuda | Natixis |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |
Bermuda | HSBC Bank USA, National Association |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  | $ 75,000,000 |  |  |  |  |  |
Aspen Specialty | Federal Home Loan Bank of Boston |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  |  |  |  | $ 223,000,000 |  |  |
Percentage limit of pledged assets permitted to secure debt obligations |  |  |  |  |  |  |  |  |  |  |  | 15.00% |  |  |
AAIC | Federal Home Loan Bank of Boston |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  |  |  |  | $ 141,000,000 |  |  |
Percentage limit of pledged assets permitted to secure debt obligations |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |
Citibank Europe |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding collateralized letters of credit facility |  |  | 416,800,000 | $ 452,400,000 |  |  |  |  |  |  |  |  |  |  |
Letters of credit / guarantees | Aspen U.K. | Aspen European |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000
Letters of credit / guarantees | Aspen U.K. | Aspen European | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |
Standby Letters of Credit | Bermuda |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Commitment Fee Amount |  |  | 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Standby Letters of Credit | Bermuda | Deutsche |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Commitment Fee Amount |  |  | 120,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Citibank Europe plc | Letters of credit / guarantees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  | $ 400,000,000 |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loans issued |  | $ 300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Debt stated interest rate |  | 4.65% |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from senior notes |  | $ 299,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of indebtedness subject to default in payment |  |  | 50,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Annual interest payable |  |  | $ 14,300,000 |  |  |  |  |  |  |  |  |  |  |  |

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