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Credit Facilities and Long-Term Debt - Additional Information (Details) - USD ($) |  | 12 Months Ended |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 01, 2021 | Dec. 31, 2024 | Dec. 31, 2023 | Oct. 31, 2024 | Oct. 24, 2023 | Jul. 26, 2023 | Feb. 07, 2023 | Dec. 29, 2021 | Nov. 05, 2021 | Apr. 01, 2021 | Nov. 03, 2020 | Feb. 11, 2019
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Credit facilities, unutilized capacity |  | $ 774,000,000 |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit | $ 300,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Line of credit facility Increasable capacity | $ 100,000,000.0 |  |  |  |  |  |  |  |  |  |  |
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% |  |  |  |  |  |  |  |  |  |
AUL | Lloyd's |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit to Support Funds at Lloyd's |  |  |  |  | $ 430,000,000.0 |  |  |  |  |  |  |
Funds at Lloyd's Facility Agreement |  |  |  | $ 25,000,000.0 |  |  |  |  |  |  |  |
Funds at Lloyd's Amended Facility Agreement |  |  |  | $ 60,000,000.0 |  |  |  |  |  |  |  |
AUL | Lloyd's | Maximum |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Letter of Credit to Support Funds at Lloyd's |  |  |  |  |  |  |  |  |  |  | $ 235,000,000.0 |
Bermuda | Natixis |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  | $ 100,000,000.0 |  |  |
Bermuda | HSBC Bank USA, National Association |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  | $ 75,000,000.0 |  |  |  |
Aspen Specialty | Federal Home Loan Bank of Boston |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  |  |  |  | $ 262,000,000 |  |
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 |  |  |  |  |  |  |  |  |  | $ 212,000,000 |  |
Percentage limit of pledged assets permitted to secure debt obligations |  |  |  |  |  |  |  |  |  | 10.00% |  |
Letters of credit / guarantees | Aspen UK | Aspen European |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revolving credit facility, credit agreement maximum limit |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  | $ 100,000,000
Secured and unsecured financing facilities |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-term line of credit |  | $ 1,700,000,000 |  |  |  |  |  |  |  |  |  |
2026 Term Loan |  |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Loans issued |  |  |  |  |  | $ 300,000,000.0 |  |  |  |  |  |
Interest Expense |  | $ 20,500,000 | $ 3,000,000.0 |  |  |  |  |  |  |  |  |

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- Definition Credit Facility, Unutilized Capacity from the Credit Agreement and our FHLBB + References No definition available. + Details
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- Definition Funds at Lloyd's Amended Facility Agreement + References No definition available. + Details
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Balance Type: | credit
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- Definition Funds at Lloyd's Facility Agreement + References No definition available. + Details
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- Definition Letter of Credit to Support Funds at Lloyd's + References No definition available. + Details
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- Definition Line of credit facility Increasable capacity. + References No definition available. + Details
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- Definition Line of credit facility tangible net worth cash proceeds from the issuance of capital stock restriction. + References No definition available. + Details
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- Definition Line of credit facility tangible net worth net income restriction. + References No definition available. + Details
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- Definition Line of credit facility tangible net worth restrictions minimum. + References No definition available. + Details
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- Definition Percentage limit of reserve assets permitted to secure debt obligations + References No definition available. + Details
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- Definition Percentage of consolidated leverage ratio permitted. + References No definition available. + Details
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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482949/835-30-55-8 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481139/470-20-50-1B Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69B -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69B Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69C -Publisher FASB -URI https://asc.fasb.org/1943274/2147481568/470-20-55-69C Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482900/835-30-50-1 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 835 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482925/835-30-45-2 + Details
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- Definition Amount of interest expense classified as operating and nonoperating. Includes, but is not limited to, cost of borrowing accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-22 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 48 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-48 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 49 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-49 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 270 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482964/270-10-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 32 -Subparagraph (ee) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-32 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 24 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-24 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-22 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 835 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483013/835-20-50-1 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481544/470-10-50-6 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 470 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481544/470-10-50-6 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(f)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480678/235-10-S99-1 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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