ASPEN INSURANCE HOLDINGS LTD, 20-F filed on 3/19/2025
Annual and Transition Report (foreign private issuer)
v3.25.1
Cover Page - shares
 12 Months Ended
Dec. 31, 2024
Jan. 02, 2025
Document Information [Line Items]    
Document Type 20-F  
Document Registration Statement false  
Document Annual Report true  
Document Period End Date Dec. 31, 2024  
Current Fiscal Year End Date --12-31  
Document Transition Report false  
Document Shell Company Report false  
Entity File Number 001-31909  
Entity Registrant Name ASPEN INSURANCE HOLDINGS LIMITED  
Entity Incorporation, State or Country Code D0  
Entity Address, Address Line One 141 Front Street  
Entity Address, City or Town Hamilton  
Entity Address, Postal Zip Code HM19  
Entity Address, Country BM  
Entity Common Stock, Shares Outstanding (in shares)   60,395,839
Entity Well-known Seasoned Issuer No  
Entity Voluntary Filers No  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Emerging Growth Company false  
Entity Shell Company false  
Amendment Flag false  
Document Fiscal Year Focus 2024  
Document Fiscal Period Focus FY  
Entity Central Index Key 0001267395  
ICFR Auditor Attestation Flag false  
Document Accounting Standard U.S. GAAP  
Document Financial Statement Error Correction [Flag] false  
Business Contact    
Document Information [Line Items]    
Entity Address, Address Line One 141 Front Street  
Entity Address, City or Town Hamilton  
Contact Personnel Name Mark Cloutier  
Entity Address, Postal Zip Code HM19  
Entity Address, Country BM  
City Area Code 441  
Local Phone Number 295-8201  
5.625% Perpetual Non-Cumulative Preference Shares    
Document Information [Line Items]    
Title of 12(b) Security 5.625% Perpetual Non-Cumulative Preference Shares  
Trading Symbol AHL PRD  
Security Exchange Name NYSE  
Depositary Shares, each representing a 1/1000th interest in a share of 5.625% Perpetual Non-Cumulative Preference Shares    
Document Information [Line Items]    
Title of 12(b) Security Depositary Shares, each representing a 1/1000th interest in a share of 5.625% Perpetual Non-Cumulative Preference Shares  
Trading Symbol AHL PRE  
Security Exchange Name NYSE  
Depositary Shares, each representing a 1/1000th interest in a share of 7.00% Perpetual Non-Cumulative Preference Shares    
Document Information [Line Items]    
Title of 12(b) Security Depositary Shares, each representing a 1/1000th interest in a share of 7.00% Perpetual Non-Cumulative Preference Shares  
Trading Symbol AHL PRF  
Security Exchange Name NYSE  
v3.25.1
Audit Information
 12 Months Ended
Dec. 31, 2024
Auditor infomation [Abstract]  
Auditor Name Ernst & Young Ltd.
Auditor Firm ID 1127
Auditor Location Hamilton
v3.25.1
CONSOLIDATED BALANCE SHEETS - USD ($)
$ in Thousands
Dec. 31, 2024
Dec. 31, 2023
Investments:    
Fixed income securities, available-for-sale [1] $ 4,692,200 $ 4,122,600
Fixed income securities, trading [1] 1,199,900 1,485,700
Short-term investments, available for sale 261,900 93,600
Short-term investments, trading at fair value 1,000 2,100
Catastrophe bonds, trading at fair value (amortized cost — 2024: $1.0 and 2023: $1.6) 1,000 1,600
Privately-held Investments, available for sale, at fair value [2] 24,200 14,900
Privately-held Investments [2] 286,800 475,000
Investments, equity method 7,300 7,600
Other Investments [3] 267,200 209,300
Investments, Excluding Derivative Assets 6,741,500 6,412,400
Reinsurance recoverables:    
Cash and Cash Equivalents, at Carrying Value [4] 914,200 1,028,100
Unpaid losses recoverable from reinsurers (net of allowance for expected credit losses of 2024: $27.5 and 2023: $3.7) 4,172,000 4,577,800
Ceded unearned premiums 901,700 733,500
Receivables:    
Underwriting premiums receivables (net of allowance for expected credit losses of 2024: $24.6 and 2023: $21.0) 1,617,000 1,435,300
Deferred acquisition costs 322,100 296,200
Derivative assets 17,000 31,700
Right-of-use operating lease assets 53,500 61,600
Income taxes refundable 900 4,300
Deferred tax assets 397,900 312,600
Other assets 590,800 309,600
Intangible assets and goodwill 19,900 21,700
Total assets 15,748,500 15,224,800
Insurance Reserve [Abstract]    
Reserve for losses and loss adjustment expenses 8,122,600 7,810,600
Unearned premiums 2,645,800 2,426,300
Total insurance reserves 10,768,400 10,236,900
Reinsurance premiums 901,100 1,416,600
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]    
Income taxes payable 6,800 12,600
Deferred tax liabilities 1,100 1,600
Accrued expenses and other payables [5] 237,200 214,400
Payables for securities purchased 36,900 22,300
Operating lease liabilities 75,600 86,100
Derivative liabilities 49,500 25,800
Short-Term Debt 300,000 300,000
Total liabilities 12,376,600 12,316,300
Commitments and contingent liabilities 0 0
Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract]    
Ordinary shares, value 604 604
Preference shares, value 970,500 753,500
Additional paid-in capital 761,200 761,200
Retained earnings 2,029,700 1,793,500
Accumulated other comprehensive (loss) (390,100) (400,300)
Total shareholders' equity 3,371,900 2,908,500
Total liabilities and shareholders’ equity $ 15,748,500 $ 15,224,800
[1] Fixed income securities, available for sale includes related party investments totaling $14.0 million (2023 — $Nil). Fixed income securities, trading at fair value includes related party investments totaling $74.9 million (2023 — $129.8 million).
[2] Privately-held investments, trading at fair value include related party investments totaling $73.6 million (2023 — $112.4 million). Privately-held investments, available for sale include related party investments totaling $Nil (2023 — $14.9 million).
[3] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
[4] Cash and cash equivalents includes restricted cash of $181.9 million (2023 — $323.2 million) which are held in trusts.
[5] Includes amounts due to related parties of $4.0 million for investment management fees (2023 — $2.1 million), and $1.3 million for management consulting fees (2023 — $1.2 million).
v3.25.1
CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Net allowance, available for sale maturities, for expected credit losses $ 1.0 $ 2.9
Fixed income securities, available for sale amortized cost 4,861.1 4,330.0
Fixed income securities, trading, amortized cost 1,207.7 1,527.0
Short term investments available for sale, amortized cost 261.9 93.6
Short-term investments, trading, amortized cost 1.0 2.1
Catastrophe Bonds, Fair Value Disclosure 1.0 1.6
Privately-held investments, available for sale, amortized cost 24.0 14.7
Privately-held investments, cost, trading at fair value 288.0 494.9
Unpaid losses recoverable from reinsurers (net of allowance for expected credit losses of 2024: $27.5 and 2023: $3.7) 27.5 3.7
Premium Receivable, Allowance for Credit Loss 24.6 21.0
Fixed income securities, trading [1] 1,199.9 1,485.7
Privately-held Investments [2] 286.8 475.0
Privately-held Investments, available for sale, at fair value [2] 24.2 14.9
Other Investments [3] 267.2 209.3
Restricted cash 181.9 323.2
Accrued expenses and other payables [4] 237.2 214.4
Asset Management Arrangement    
Accrued expenses and other payables 4.0 2.1
Management Consulting Agreement    
Accrued expenses and other payables 1.3 1.2
Fair Value, Recurring [Member] | CLOs    
Fixed income securities, AFS , RP 14.0 0.0
Fixed income securities, trading 74.9 129.8
Fair Value, Recurring [Member] | Apollo originating partnership    
Privately-held Investments 73.6 112.4
Privately-held Investments, available for sale, at fair value 0.0 14.9
Fair Value, Recurring [Member] | Funds managed by Apollo    
Other Investments $ 78.6 $ 39.8
[1] Fixed income securities, available for sale includes related party investments totaling $14.0 million (2023 — $Nil). Fixed income securities, trading at fair value includes related party investments totaling $74.9 million (2023 — $129.8 million).
[2] Privately-held investments, trading at fair value include related party investments totaling $73.6 million (2023 — $112.4 million). Privately-held investments, available for sale include related party investments totaling $Nil (2023 — $14.9 million).
[3] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
[4] Includes amounts due to related parties of $4.0 million for investment management fees (2023 — $2.1 million), and $1.3 million for management consulting fees (2023 — $1.2 million).
v3.25.1
CONSOLIDATED STATEMENTS OF OPERATIONS AND OTHER COMPREHENSIVE INCOME - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Revenues      
Net earned premiums $ 2,889.7 $ 2,614.5 $ 2,688.7
Net investment income (1) 318.0 [1] 275.7 188.1
Gain (loss) on investments 52.6 75.9 5.0
Other income 0.0 0.0 8.2
Total revenues 3,260.3 2,966.1 2,890.0
Expenses      
Losses and loss adjustment expenses 1,717.8 1,553.0 1,680.0
Acquisition costs 420.2 380.2 431.8
General, administrative and corporate expenses (3) [2] 533.1 503.6 494.2
Interest expense 62.1 55.2 43.7
Change in fair value of derivatives 21.1 (26.1) 80.5
Realized and unrealized investment losses [3] 102.1 61.4 182.6
Net realized and unrealized foreign exchange (gains)/losses 60.2 (36.2) 15.9
Other expenses 0.0 0.0 20.1
Total expenses 2,796.2 2,563.5 2,917.0
Income (loss) from operations before income taxes 464.1 402.6 (27.0)
Income tax benefit 22.0 132.1 78.1
Net Income (Loss) Attributable to Parent, Total 486.1 534.7 51.1
Debt Securities, Available-for-Sale [Abstract]      
Reclassification adjustment for net realized losses on investments included in net income 59.4 40.2 55.5
Change in net unrealized (losses)/gains on available for sale securities held (25.3) 86.0 (447.2)
Net change from current period hedged transactions (6.5) (14.0) 15.4
Change in foreign currency translation adjustment (14.1) 14.4 (30.9)
Other comprehensive (loss)/income, before income taxes 13.5 126.6 (407.2)
Income tax (expense)/benefit thereon:      
Reclassification adjustment for net realized losses on investments included in net income (11.5) (6.6) 0.0
Change in net unrealized losses/(gains) on available for sale securities held 6.8 (14.0) 23.9
Total income tax (expense)/benefit allocated to other comprehensive income/(loss) (3.3) (20.6) 23.9
Other comprehensive income/(loss), net of tax 10.2 106.0 (383.3)
Net change from current period hedged transactions 1.4 0.0 0.0
Total comprehensive (loss)/income attributable to Aspen Insurance Holdings Limited's ordinary shareholders 496.3 640.7 (332.2)
Net income      
Net income 486.1 534.7 51.1
Dividends on preference shares 54.9 49.9 44.6
Net income (loss) available to ordinary shareholders, basic $ 431.2 $ 484.8 $ 6.5
[1] Net investment income includes related party net investment income of $15.2 million (2023 — $19.6 million, 2022 — $3.1 million) and related party investment management fees of $9.2 million (2023 — $9.4 million, 2022 — $4.9 million).
[2] General, administrative and corporate expenses includes related party management consulting fees of $5.0 million (2023 — $5.0 million; 2022 — $5.0 million).
[3] Realized and unrealized investments gains includes gains of $2.5 million on related party investments (2023 — gains of $8.7 million, 2022 — loss of $0.4 million).
v3.25.1
CONSOLIDATED STATEMENTS OF OPERATIONS AND OTHER COMPREHENSIVE INCOME (Parenthetical) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Net investment income (1) $ 318.0 [1] $ 275.7 $ 188.1
Realized and unrealized investment losses [2] (102.1) (61.4) (182.6)
General and administrative expenses 405.9 354.5 386.5
Management Consulting Agreement      
General and administrative expenses 5.0 5.0 5.0
Asset Management Arrangement      
Net investment income (1) 9.2 9.4 4.9
Apollo, Class A & B Notes      
Realized and unrealized investment losses 2.5 8.7 (0.4)
Management Consulting Agreement      
Net investment income (1) $ 15.2 $ 19.6 $ 3.1
[1] Net investment income includes related party net investment income of $15.2 million (2023 — $19.6 million, 2022 — $3.1 million) and related party investment management fees of $9.2 million (2023 — $9.4 million, 2022 — $4.9 million).
[2] Realized and unrealized investments gains includes gains of $2.5 million on related party investments (2023 — gains of $8.7 million, 2022 — loss of $0.4 million).
v3.25.1
CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($)
Total
Ordinary shares
Preference shares
Additional paid-in capital
Retained earnings
Retained earnings
Ordinary shares
Cumulative foreign currency translation adjustments:
Unrealized (depreciation)/appreciation on available for sale investments:
Gain on derivatives, net of taxes
Increase (Decrease) in Stockholders' Equity [Roll Forward]                  
Equity, Including Portion Attributable to Noncontrolling Interest   $ 600,000 $ 753,500,000 [1] $ 761,200,000 $ 1,382,500,000   $ (156,000,000.0) $ 34,600,000 $ (1,600,000)
Net income/(loss) for the year $ 51,100,000                
Dividends           $ (40,000,000.0)      
Dividends on preference shares 44,600,000                
Change for the year, net of income taxes (367,800,000)           (30,900,000) (367,800,000)  
Shares issued     0            
Equity, Including Portion Attributable to Noncontrolling Interest 2,358,000,000 600,000 753,500,000 [1],[2] 761,200,000 1,349,000,000   (186,900,000) (333,200,000) 13,800,000
Net change from current period hedged transactions                 15,400,000
Total accumulated other comprehensive (loss)/income (506,300,000)                
Net income/(loss) for the year 534,700,000                
Dividends           (40,300,000)      
Dividends on preference shares 49,900,000                
Change for the year, net of income taxes 105,600,000           14,400,000 105,600,000  
Shares issued     0            
Equity, Including Portion Attributable to Noncontrolling Interest 2,908,500,000 600,000 753,500,000 [1],[2] 761,200,000 1,793,500,000   (172,500,000) (227,600,000) (200,000)
Net change from current period hedged transactions                 (14,000,000.0)
Total accumulated other comprehensive (loss)/income (400,300,000)                
Net income/(loss) for the year 486,100,000                
Dividends (54,948,800)         $ (195,000,000.0)      
Dividends on preference shares 54,900,000                
Change for the year, net of income taxes 29,400,000           (14,100,000) 29,400,000  
Shares issued     217,000,000.0            
Equity, Including Portion Attributable to Noncontrolling Interest 3,371,900,000 $ 600,000 $ 970,500,000 [2] $ 761,200,000 $ 2,029,700,000   $ (186,600,000) $ (198,200,000) (5,300,000)
Net change from current period hedged transactions                 $ (5,100,000)
Total accumulated other comprehensive (loss)/income $ (390,100,000)                
[1] Preference shares of $1,000.0 million, less issuance costs of $29.5 million (December 31, 2023 and 2022 — $775.0 million and $21.5 million).
[2] reference shares of $1,000.0 million, less issuance costs of $29.5 million (December 31, 2023 and 2022 — $775.0 million and $21.5 million).
v3.25.1
CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Aggregate Liquidation Preference Shares $ 1,000.0 $ 775.0 $ 775.0
Preferred Stock Issuance Cost $ 29.5 $ 21.5 $ 21.5
v3.25.1
CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Cash flows from operating activities:      
Net income/(loss) $ 486,100,000 $ 534,700,000 $ 51,100,000
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization (1,000,000.0) 11,000,000.0 43,300,000
Impairment of lease assets 0 0 (6,700,000)
Amortization of right-of-use operating lease assets 9,900,000 10,700,000 10,100,000
Interest on operating lease liabilities 4,100,000 4,500,000 5,400,000
Realized and unrealized investment gains (52,600,000) (75,900,000) (5,000,000.0)
Realized and unrealized investment losses [1] 102,100,000 61,400,000 182,600,000
Deferred tax expense/(benefit) (88,600,000) (197,700,000) (104,600,000)
Net realized and unrealized investment foreign exchange losses/(gains) 11,200,000 (5,300,000) 15,900,000
Net change from current period hedged transactions (6,500,000) (14,000,000.0) 15,400,000
Unrealized (gain)/loss on real estate fund in net investment income 6,100,000 17,900,000 (14,500,000)
Increase (Decrease) in Operating Capital [Abstract]      
Reserve for losses and loss adjustment expenses 312,000,000.0 99,700,000 99,100,000
Unearned premiums 219,500,000 (31,200,000) 345,200,000
Unpaid losses recoverable from reinsurers 405,800,000 319,900,000 (1,599,600,000)
Ceded unearned premiums (168,200,000) 3,800,000 (141,200,000)
Deferred acquisition costs (25,900,000) 22,800,000 (28,200,000)
Reinsurance premiums payable (515,500,000) (563,500,000) 1,404,400,000
Underwriting premiums receivable (181,700,000) 47,100,000 (177,800,000)
Income tax payable and refundable (3,000,000.0) 3,500,000 (1,300,000)
Accrued expenses and other payables 22,400,000 13,200,000 (87,000,000.0)
Derivative assets and derivative liabilities 38,400,000 15,400,000 (21,700,000)
Operating lease liabilities (15,900,000) (15,500,000) (15,500,000)
Other (1) (3,800,000) 62,200,000 (24,400,000)
Net cash provided by/(used in) operating activities 554,900,000 324,700,000 (55,000,000.0)
Cash flows from investing activities:      
(Purchases) of fixed income securities — Available for sale (2,468,500,000) (1,554,800,000) (1,613,900,000)
(Purchases) of fixed income securities — Trading (544,600,000) (418,500,000) (724,600,000)
Proceeds from sales and maturities of fixed income securities — Available for sale 1,872,700,000 1,326,700,000 2,212,500,000
Proceeds from sales and maturities of fixed income securities — Trading 850,100,000 474,000,000.0 293,600,000
Net proceeds from catastrophe bonds — Trading 500,000 1,500,000 500,000
(Purchases) of short-term investments — Available for sale (334,700,000) (265,900,000) (55,900,000)
Proceeds from sale of short-term investments — Available for sale 167,000,000.0 231,000,000.0 13,600,000
(Purchases) of short-term investments — Trading (5,700,000) (15,100,000) (7,000,000.0)
Proceeds from sale of short-term investments — Trading 6,700,000 19,500,000 2,600,000
(Purchases) of privately-held investments - Available for sale (10,000,000.0) (14,700,000) 0
(Purchases) of privately-held investments — Trading (57,000,000.0) (99,000,000.0) (377,900,000)
Proceeds from sale of privately-held investments — Trading 195,400,000 136,900,000 147,400,000
Net change in receivable/(payable) for securities sold/(purchased) 16,800,000 19,900,000 (31,800,000)
(Purchases) of other investments (32,500,000) (9,300,000) (62,500,000)
Net proceeds from sales of other investments 8,500,000 4,900,000 5,900,000
Net (purchases)/sales of fixed assets 17,500,000 8,900,000 (3,000,000.0)
Net (purchases) of investments, equity method 0 (400,000) (2,000,000.0)
Net cash (used in) investing activities (352,800,000) (172,200,000) (196,500,000)
Cash flows from financing activities:      
Repayments of Short-Term Debt 0 (300,000,000.0) 0
Proceeds from term loan facility 0 300,000,000.0 0
Redemption of preference shares (1) (275,000,000.0) [2] 0 0
Preference share issuance 217,000,000.0 0 0
Payments of Ordinary Dividends, Common Stock 195,000,000.0 40,300,000 40,000,000.0
Dividends paid on preference shares (54,900,000) (49,900,000) (44,600,000)
Net cash (used in) financing activities (307,900,000) (90,200,000) (84,600,000)
Effect of exchange rate movements on cash and cash equivalents (8,100,000) 6,600,000 (18,800,000)
(Decrease)/Increase in cash and cash equivalents (113,900,000) 68,900,000 (354,900,000)
Cash and cash equivalents at beginning of period 1,028,100,000 959,200,000 1,314,100,000
Cash and cash equivalents at end of period (2) 914,200,000 1,028,100,000 959,200,000
Supplemental disclosure of cash flow information:      
Income taxes paid 69,000,000.0 60,900,000 29,100,000
Interest paid on long-term debt $ 20,500,000 $ 15,600,000 $ 14,300,000
[1] Realized and unrealized investments gains includes gains of $2.5 million on related party investments (2023 — gains of $8.7 million, 2022 — loss of $0.4 million).
[2] On January 1, 2025, the Company redeemed all 11,000,000 shares of its issued and outstanding 5.950% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares. The redemption price was paid on January 2, 2025. To facilitate this redemption, the funds of $275.0 million were transferred to a third party transfer agent on December 30, 2024 and are included in other assets in the consolidated balance sheet. The cash flow has been included under financing activities above. For further details, refer to Note 26, “Subsequent Events”.
v3.25.1
CONSOLIDATED STATEMENTS OF CASH FLOWS (Parentheticals) - USD ($)
$ in Millions
 12 Months Ended
Jan. 01, 2025
Nov. 29, 2024
May 02, 2013
Dec. 31, 2024
Dec. 31, 2023
Jan. 02, 2025
Nov. 26, 2024
Dec. 31, 2022
Aug. 13, 2019
Restricted cash       $ 181.9 $ 323.2     $ 232.1  
Preference shares liquidation preference, value             $ 225.0   $ 250.0
5.950% Preference Shares (AHL PRC)                  
Preferred Stock, Shares Issued     11,000,000,000,000 11,000,000 11,000,000        
Preferred Stock, Dividend Rate, Percentage   5.95% 5.95% 5.95% 5.95%        
Preference shares liquidation preference, value     $ 275.0            
5.950% Preference Shares (AHL PRC) | Subsequent Event                  
Preferred Stock, Dividend Rate, Percentage 5.95%                
Preference shares liquidation preference, value           $ 275.0      
v3.25.1
History and Organization
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
History and Organization History and Organization
History and Organization. Aspen Insurance Holdings Limited (“Aspen Holdings”) was incorporated as a Bermuda exempted company on May 23, 2002 as a holding company headquartered in Bermuda. We underwrite specialty insurance and reinsurance on a global basis through our Operating Subsidiaries (as defined below) based in Bermuda, the United States and the United Kingdom: Aspen Bermuda Limited (“Aspen Bermuda”), Aspen Specialty Insurance Company (“Aspen Specialty”), Aspen American Insurance Company (“AAIC”), Aspen Insurance UK Limited (“Aspen UK”) and Aspen Underwriting Limited (“AUL”) (as the sole corporate member of our Lloyd’s operations, Syndicate 4711, which is managed by Aspen Managing Agency Limited (“AMAL”) (together, “Aspen Lloyd’s”)), each referred to herein as an “Operating Subsidiary” and collectively referred to as the “Operating Subsidiaries”, as well as through branch operations in Canada, Singapore and Switzerland. We established Aspen Capital Management, Ltd. (“ACML”) and other related entities (collectively, “ACM”) to leverage our existing underwriting franchise, increase our operational flexibility and provide third-party investors direct access to our capital markets and underwriting expertise. References to the “Company,” the “Group,” “we,” “us” or “our” refer to Aspen Holdings or Aspen Holdings and its consolidated subsidiaries.
Since February 2019, the Company has been a wholly-owned subsidiary of Highlands Bermuda Holdco, Ltd. (“Parent”), which holds all of the Company’s ordinary shares. Parent, a Bermuda exempted company, is an affiliate of certain investment funds managed by affiliates of Apollo Global Management, Inc., a leading global investment manager (collectively with its subsidiaries, “Apollo”). The Company’s preference shares and depositary shares, as at the date of issuing this report, are listed on the New York Stock Exchange (“NYSE”) under the following symbols: AHL PRD, AHL PRE and AHL PRF.
v3.25.1
Basis of Preparation and Significant Accounting Policies
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Basis of Preparation and Significant Accounting Policies Basis of Presentation and Significant Accounting Policies
The consolidated financial statements of Aspen Holdings are prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”) and are presented on a consolidated basis including the transactions of all operating subsidiaries in which the Company has a controlling financial interest and variable interest entities (“VIE”) in which the Company is considered to be the primary beneficiary. Transactions between Aspen Holdings and its subsidiaries are eliminated within the consolidated financial statements.
The consolidated financial statements have been prepared on a going concern basis.
  (a)    Use of Estimates
Assumptions and estimates made by management have a significant effect on the amounts reported within the consolidated financial statements. The most significant of these relate to losses and loss adjustment expenses, reinsurance recoverables, gross written premiums and commissions which have not been reported to the Company such as those relating to proportional treaty reinsurance contracts, unrecognized tax benefits, recoverability of deferred tax assets, the fair value of derivatives and the fair value of other and privately-held investments. 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.
  (b)    Accounting for Insurance and Reinsurance Operations
Premiums Earned. Premiums are generally recorded as written on the inception date of a policy. For proportional reinsurance treaty contracts, written premiums are generally recorded as the reinsured policies attach to the treaty. For multi-year insurance or reinsurance contracts, written premiums are recorded based on the contract terms. Premiums are recognized as revenues proportionately over the coverage period. Premiums earned are recorded in the consolidated statements of operations, net of the cost of purchased reinsurance. Premiums written which are not yet recognized as earned premium are recorded in the consolidated balance sheet as unearned premiums. Written and earned premiums and the related costs include estimates for premiums which have not been finally determined. These relate mainly to contractual provisions for the payment of adjustment or additional premiums, premiums payable under proportional treaties and delegated underwriting authorities, and reinstatement premiums.
Adjustment and additional premiums are premiums charged which relate to experience during the policy term. The proportion of adjustable premiums included in the premium estimates varies between business lines with the largest adjustment premiums being in property and casualty reinsurance, marine, aviation and energy insurance and the smallest in property and casualty insurance.
Premiums under proportional treaty contracts and delegated underwriting authorities are generally not reported to the Company until after the reinsurance coverage is in force. As a result, an estimate of these “pipeline” premiums is recorded. The Company estimates pipeline premiums based on projections of ultimate premium taking into account reported premiums and expected development patterns.
Reinstatement premiums on assumed excess of loss reinsurance contracts are provided based on experience under such contracts. Reinstatement premiums are the premiums charged for the restoration of the reinsurance limit of an excess of loss contract to its full amount after payment by the reinsurer of losses as a result of an occurrence. The original premiums are recognized as revenue in full at the date of loss, with the reinstatement premiums recognized as revenue over the remaining cover term. Reinstatement premiums provide future insurance cover for the remainder of the initial policy term. An allowance for uncollectible premiums is established for possible non-payment of premium receivables, as deemed necessary.
Credit Losses on Underwriting Premiums Receivable. Underwriting premium receivable balances are reported net of an allowance for expected credit losses. The allowance, based on ongoing review and monitoring of amounts outstanding, historical loss data, including write-offs and other current economic factors, is charged to net income in the period the receivable is recorded and revised in subsequent periods to reflect changes in the Company’s estimate of expected credit losses. For most insurance policies, credit risk is partially mitigated by the Company’s ability to cancel the policy if the policyholder does not pay the premium whereby, upon default, policy liabilities would be written-down along with premium receivables.
Losses and Loss Adjustment Expenses. Losses represent the amount paid or expected to be paid to claimants in respect of events that have occurred on or before the balance sheet date. The costs of investigating, resolving and processing these claims are known as loss adjustment expenses (“LAE”). The consolidated statements of operations records these losses net of reinsurance, meaning that gross losses and loss adjustment expenses incurred are reduced by the amounts recovered or expected to be recovered under reinsurance contracts.
Reinsurance. Written premiums, earned premiums, incurred claims, LAE and the acquisition costs all reflect the net effect of assumed and ceded reinsurance transactions. Assumed reinsurance refers to the Company’s acceptance of certain insurance risks that other insurance companies have underwritten. Ceded reinsurance arises from contracts under which other insurance companies agree to share certain risks with the Company.
Reinsurance accounting is followed when there is risk transfer, which includes significant timing risk, underwriting risk, and where applicable, a reasonable possibility of significant loss.
Outward reinsurance premiums, which are paid when the Company purchases reinsurance or retrocessional coverage, are accounted for using the same accounting methodology as the Company uses for inwards premiums. Premiums payable under reinsurance contracts that operate on a “losses occurring during” basis are expensed over the period of coverage while those arising from “risks attaching during” policies are expensed over the earnings period of the underlying premiums written from the reinsured business. Adjustment premiums and reinstatement premiums in relation to outward reinsurance are accrued when it is determined that the ultimate losses will trigger a payment and recognized within premiums payable. Reinsurance and retrocession does not isolate the ceding company from its obligations to policyholders. In the event that a reinsurer or retrocessionaire fails to meet its obligations, the ceding company’s obligations remain.
Accounting for Retroactive Reinsurance Agreements. Retroactive reinsurance agreements are reinsurance agreements under which a reinsurer agrees to reimburse the Company as a result of past insurable events. For retroactive reinsurance purchased by the Company, the excess of the amounts ultimately collectible under the agreement over the consideration paid is recognized as a deferred gain liability which is amortized into income over the settlement period of the ceded reserves once the paid losses have exceeded the minimum retention. The amount of the deferral is recalculated each period based on actual loss payments and updated estimates of ultimate losses. If the consideration paid exceeds the ultimate losses collectible under the agreement, the net loss on the retroactive reinsurance agreement is recognized within income immediately.
Premiums payable for retroactive reinsurance coverage and meeting the conditions of reinsurance accounting are reported as reinsurance recoverables to the extent that those amounts do not exceed recorded liabilities relating to underlying reinsurance contracts. Premiums paid in excess of accounts receivable are charged to income.
Reserves. Insurance reserves are established for the total unpaid cost of claims and LAE in respect of events that have occurred by the balance sheet date, including the Company’s estimates of the total cost of claims incurred but not yet reported (“IBNR”). Claim reserves are reduced for estimated amounts of salvage and subrogation recoveries. Estimated amounts recoverable from reinsurers on unpaid losses and LAE are reflected as assets.
For reported claims, reserves are established on a case-by-case basis within the parameters of coverage provided in the insurance policy or reinsurance agreement. For IBNR claims, reserves are estimated using a number of established actuarial methods to establish a range of estimates from which a management best estimate is selected. Both case and IBNR reserve estimates consider variables such as past loss experience, changes in legislative conditions, changes in judicial interpretation of legal liability, policy coverages and inflation.
As many of the coverages underwritten involve claims that may not be ultimately settled for many years after they are incurred, subjective judgments as to the ultimate exposure to losses are an integral and necessary component of the loss reserving process. The Company regularly reviews its reserves, using a variety of statistical and actuarial techniques to analyze current claims costs, frequency and severity data, and prevailing economic, social and legal factors. Reserves established in prior periods are adjusted as claim experience develops and new information becomes available. Adjustments to previously estimated reserves are reflected in the financial results of the period in which the adjustments are made.
The process of estimating required reserves does, by its very nature, involve considerable uncertainty. The level of uncertainty can be influenced by factors such as the existence of coverage with long duration payment patterns and changes in claims handling practices, as well as the factors noted above. Ultimate actual payments for claims and LAE could turn out to be significantly different from the Company’s estimates.
Credit Losses on Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability with the reinsured business. The Company maintains credit risk if a reinsurer is unable to pay recoverables when they become due. To manage this risk, the Company evaluates the financial condition of its reinsurers and retrocessionaires, and monitors concentration of credit risk to minimize its exposure to significant losses from individual reinsurers. To further reduce credit exposure on reinsurance recoverables, the Company has received collateral, including letters of credit and trust accounts, from certain reinsurers. Following the adoption of ASC 326, an allowance is established for expected credit losses to be recognized over the life of the reinsurance recoverable. The allowance considers the current financial strength of the individual reinsurer and the amount of collateral held.
Acquisition Costs. The costs directly related to writing a (re)insurance policy are referred to as acquisition expenses and include commissions, premium taxes and profit commissions. With the exception of profit commissions, these expenses are incurred when a policy is issued, and only the costs directly related to the successful acquisition of new and renewal insurance and reinsurance contracts are deferred and amortized over the same period as the corresponding premiums are recorded as revenues. Profit commissions are estimated and accrued based on the related performance criteria evaluated at the balance sheet date, with subsequent changes to those estimates recognized when they occur. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral.
On a regular basis a premium deficiency analysis is performed of the deferred acquisition costs in relation to the expected recognition of revenues, including anticipated investment income, and adjustments, if any, are reflected as period costs. Should the analysis indicate that the acquisition costs are unrecoverable, further analyses are performed to determine if a reserve is required to provide for losses which may exceed the related unearned premium.
General and Administrative Expenses. These costs represent the expenses incurred in running the business and include, but are not limited to compensation costs for employees, rental costs, IT development and professional and consultancy fees. General and administrative costs directly attributable to the successful acquisition of business are deferred and amortized over the same period as the corresponding premiums are recorded as revenues. When reporting the results for its business segments, the Company includes expenses which are directly attributable to the segment plus an allocation of central administrative costs.
Corporate Expenses. Corporate expenses are not allocated to the Company’s business segments as they typically do not fluctuate with the levels of premium written and are related to the Company’s operations which include group executive costs, group finance costs, group legal and actuarial costs and certain strategic and other costs.
  (c)    Accounting for Investments, Cash and Cash Equivalents
Fixed Income Securities. The fixed income securities portfolio comprises securities issued by governments and government agencies, corporate bonds, mortgage and other asset-backed securities and bank loans. Investments in fixed income securities are classified as available for sale or trading and are reported at estimated fair value in the consolidated balance sheet. Investment transactions are recorded on the trade date with balances pending settlement reflected in the consolidated balance sheet under receivables for securities sold and other payables for securities purchased, respectively. Fair values are based on quoted market prices and other data provided by third-party pricing services.
Short-term Investments. Short-term investments primarily comprise highly liquid debt securities with a maturity greater than three months but less than one year from the date of purchase and are held as part of the investment portfolio of the Company. Short-term investments are classified as either trading or available for sale and reported at estimated fair value.
Catastrophe Bonds. Investments in catastrophe bonds are classified as trading and are reported on the consolidated balance sheet at estimated fair value. The fair values are based on independent broker-dealer quotes.
Privately-held Investments. The Company’s privately-held investments primarily comprise commercial mortgage loans, middle market loans and other private debt, asset-backed securities and global corporate securities. These investments are classified as trading or available for sale and are reported on the consolidated balance sheet at estimated fair value. Privately-held investments are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are primarily determined using discounted cash flow models. Interest income is accrued on the principal amount of the loan based on its contractual interest rate subject to it being probable that we will receive interest on that particular underlying loan. Interest income, amortization of premiums and discounts, and prepayment fees are reported in net investment income on the consolidated statements of income.
Investments, Equity Method. These investments represent the Company’s investments in partially owned insurance and related companies that are recorded using the equity method of accounting. The carrying value of these investments are based on the Company’s proportionate share of GAAP equity.
Other Investments. Other investments represent the Company’s investments in investment funds that are reported at net asset value. For these investments, net asset value is used as a practical expedient for fair value.
Cash and Cash Equivalents. Cash and cash equivalents are reported at fair value. Cash and cash equivalents comprise cash on hand, deposits held on call with banks and other short-term highly liquid investments due to mature within three months from the date of purchase and which are subject to insignificant risk of change in fair value.
Gains and Losses. Realized gains or losses on the sale of investments are determined on the basis of the first in first out cost method and are recorded in revenue or expenses respectively. Unrealized gains and losses represent the difference between the cost, or the cost as adjusted by amortization of any difference between its cost and its redemption value (“amortized cost”), of the security and its fair value at the reporting date and are included within other comprehensive income for securities classified as available for sale and in realized and unrealized investment gains or losses in the consolidated statement of operations for securities classified as trading.
Credit Losses on Available for Sale Debt Securities. An allowance account for credit losses is recognized for available for sale debt securities based on a review of individual securities. Write-offs are recorded when amounts are deemed uncollectible, or Aspen intends to sell (or more likely than not will be required to sell) the debt security before recovery of the amortized cost basis. The amortized cost basis will be written down to the debt securities fair value through earnings. Credit losses are limited to the difference between the debt securities amortized cost basis and fair value (‘fair-value floor’). Any decline in the debt securities fair value below the amortized cost basis that is not a result of a credit loss is recorded through other comprehensive income, net of applicable taxes. The allowance for credit losses of a security may be increased or reversed upon a change in credit position with the change reflected in net income.
The credit loss models employ a discounted cash flow approach to evaluate whether a credit loss exists at the individual security level and are reviewed at each reporting period. This analysis excludes investments in U.S. Government / Agency bonds and U.S. Government Agency mortgage-backed securities due to being of ‘high credit quality’ based on the absence of risk. For any available for sale debt securities that were initially purchased with credit deterioration (PCD), the amortized cost basis shall be considered to be the purchase price, plus any allowance for credit losses. Estimated credit losses shall be discounted at the rate that equates the present value of the purchaser’s estimate of the security’s future cash flows with the purchase price of the asset.
Net Investment Income. Investment income includes amounts received and accrued in respect of periodic interest (“coupons”) payable to the Company by the issuer of fixed income securities, equity dividends and interest credited on cash and cash equivalents. It also includes amortization of premium and accretion of discount in respect of fixed income securities. Investment income also includes changes in fair value from investments in real estate funds. Investment management and custody fees are charged against net investment income reported in the consolidated statement of operations.
  (d)    Accounting for Derivative Financial Instruments
The Company enters into derivative instruments to manage certain market risks, such as forward exchange contracts used to reduce foreign currency risk relative to the U.S. dollar. The Company records derivative instruments at fair value on the Company’s consolidated balance sheet as either assets or liabilities, depending on their rights and obligations.
The accounting for the gain or loss due to the changes in the fair value of these instruments is dependent on whether the derivative qualifies as a hedge. If the derivative does not qualify as a hedge, the gains or losses are reported in the consolidated statement of operations when they occur and classified within Change in fair value of derivatives. If the derivative qualifies as a hedge, the accounting treatment varies based on the type of risk being hedged. There are two primary types of hedging relationships that may be used for accounting purposes: fair value hedge and cash flow hedge. A fair value hedge is designed to offset changes in the fair value of an underlying asset or liability, and the gain or loss from the hedging instrument offsets the change in fair value of the underlying asset or liability. Under fair value hedge accounting, both the gain or loss from the underlying asset or liability and the gain or loss from the hedging instrument are recognized in earnings in the same period. In contrast, a cash flow hedge is designed to offset changes in cash flows of an underlying asset or liability. The gain or loss from the hedging instrument is initially recognized in other comprehensive income. As the contracts settle, the realized gain or loss is reclassified from other comprehensive income into the consolidated statement of operations.
The loss portfolio transfer contract includes a funds withheld arrangement that provides a variable interest expense based on Aspen’s investment performance. As a result, this funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative. Since the economic characteristics and risks of an embedded derivative feature are not clearly and closely related to the economic characteristics and risks of the host contract, the embedded derivative is bifurcated and accounted for separately at fair value. The Company records subsequent changes in the embedded derivative fair value in the consolidated statement of operations.
  (e)    Accounting for Intangible Assets
Intangible assets are held in the consolidated balance sheet at cost less amortization and impairment. Amortization applies on a straight-line basis in respect of assets having a finite estimated useful economic life. Finite intangibles are assessed on an annual basis for impairment, or more frequently where circumstances indicate the carrying value may not be recoverable. For intangible assets considered to have an indefinite life, the Company performs a qualitative assessment annually to determine whether it is more likely than not that an intangible asset is impaired. Goodwill is assessed annually for impairment or more frequently if circumstances indicate an impairment may have occurred.
  (f)    Accounting for Office Properties and Equipment
Office properties and equipment are reported at cost less accumulated depreciation. These assets are depreciated on a straight-line basis over the estimated useful lives of the assets. Computer equipment is depreciated between three and five years, furniture and fittings are depreciated over four years and leasehold improvements are depreciated over the lesser of 15 years or the lease term.
IT development costs that are directly associated with the development of identifiable and unique software products and that are anticipated to generate economic benefits exceeding costs beyond one year, are recognized within office properties and equipment. Costs include external consultants’ fees, certain qualifying internal staff costs and other costs incurred to develop software programs. Software is depreciated over their estimated useful life, between three and five years, on a straight-line basis and is subject to impairment testing annually. Depreciation commences when the asset becomes operational. Other non-qualifying costs are expensed as incurred.
  (g)    Accounting for Leases
In the ordinary course of the business, the Company renews and enters into new leases for office real estate and other assets. At the lease inception date, the Company determines whether a contract contains a lease and recognizes operating lease Right-of-use assets and operating lease liabilities based on the present value of future minimum lease payments. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. For all office real estate leases, rent incentives, including reduced-rent and rent-free periods and contractually agreed rent increases during the lease term, have been included when determining the present value of future cash flows.
Right-of-use operating lease assets are reported at cost less accumulated depreciation on the consolidated balance sheet and depreciated over the lease term. The Company does not record office property and equipment leases with an initial term of 12 months or less (short-term) in the Company's consolidated balance sheets. Such short-term leases are expensed through the consolidated statement of operations.
Right-of-use operating lease assets are tested for impairments whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. If the carrying value of an asset is impaired, it is reduced to the recoverable amount by an immediate charge to the income statement. The recoverable amount is the higher of an asset’s fair value less costs to sell and value in use.
   (h)    Accounting for Foreign Currencies Translation
The functional currency of the Company and its subsidiaries is the U.S. Dollar, which is also the Company’s reporting currency. Transactions in currencies other than the functional currency are measured at the exchange rate prevailing at the date of the transaction.
Monetary assets and liabilities denominated in non-functional currencies are remeasured at the exchange rate prevailing at the balance sheet date and any resulting foreign exchange gains or losses are reflected in the consolidated statement of operations. Foreign exchange gains or losses related to available for sale investments denominated in non-functional currencies are included within other comprehensive income. Non-monetary assets and liabilities are remeasured to functional currency at historic exchange rates.
  (i)    Accounting for Income Taxes
Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. When the Company does not believe that, on the basis of available information, it is more likely than not that deferred tax assets will be fully recovered, it recognizes a valuation allowance against its deferred tax assets to reduce the deferred tax assets to the amount more likely than not to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.
Furthermore, a tax benefit from a tax position may be recognized in the financial statements only if it is more-likely-than-not that the position is sustainable, based solely on its technical merits and consideration of the relevant tax authority’s widely understood administrative practices and precedents.
The Company applies a portfolio approach to release the income tax effects in accumulated other comprehensive income. Under this approach, the income tax effects upon the sale of an available for sale debt security, settlement of hedged transactions and upon foreign currency translation adjustments for each period, are determined under the intra-period tax allocation approach. Any tax effects remaining in accumulated other comprehensive income are only released when the entire portfolio is liquidated, sold or extinguished.
  (j)    Accounting for Preference Shares
The Company had at the balance sheet date in issue three classes of preference shares. The Company has no obligation to pay interest on these securities but they carry entitlements to dividends payable at the discretion of the Board of Directors. In the event of non-payment of dividends for six consecutive periods, holders of preference shares have director appointment rights. The preference shares are therefore accounted for as equity instruments and included within total shareholders’ equity.
 (k)    Accounting for Share-Based Payments and Long-Term Incentive Plans
The Company operates an employee long-term incentive plan, comprised of Performance Units and Exit Units, the terms and conditions of which are described in Note 17. The Company applies a fair-value based measurement method in calculating the compensation costs of Performance Units which are recognized on a straight-line basis over the vesting period.
Certain employees of the Company participate in a Management Equity Plan (“MEP”), comprising stock options to acquire non-voting shares in a related party affiliate of the Company, at no cost to the employee. The terms and conditions of the MEP are described in Note 17. The Company recognizes compensation costs for these awards with performance conditions if, and when, the Company concludes that it is probable that the performance condition(s) will be achieved, over the requisite service period. The Company reviews and evaluates these estimates regularly and will recognize any remaining unrecognized compensation expense as an estimate revision. The stock options vest upon a number of performance conditions; an exit or liquidity event occurring; a two-year cumulative operating income hurdle being achieved over the vesting period; and certain other contractual terms being achieved. The Company applies fair-value based measurement principles to determine grant date values for the stock options. The Company has made an entity-wide accounting election to account for award forfeitures as they occur.
  (l)    Accounting for Business Combinations    
The Company accounts for a transaction as a business combination where the assets acquired and liabilities assumed following a transaction constitute a business. An acquired entity must have inputs and processes that make it capable of generating a return or economic benefit to be considered a business. If the assets acquired are not a business, the Company accounts the transaction as an asset acquisition. The Company recognizes and measures at fair value 100 percent of the assets and liabilities of any acquired business. Goodwill is recognized and measured as the difference between the consideration paid or payable less the fair value of assets acquired.
The Company accounts for the disposal of subsidiary undertakings when it ceases to control the subsidiary’s assets and liabilities or the group of assets. A gain or loss is recognized and measured as the difference between the fair value of consideration received or receivable and the value of assets, liabilities and equity components de-recognized, related to that subsidiary or group of assets when deconsolidated.
Costs that are directly related to a business combination transaction are expensed in the periods in which the costs are incurred and the services are received.
  (m)    Accounting Pronouncements
Accounting Pronouncements Adopted
In November 2023, the FASB issued Accounting Standards Update (“ASU”) No. 2023-07, “Segment Reporting (Topic 280) - Improvements to Reportable Segment Disclosures”. This update improves the disclosures about a public entity’s reportable segments and addresses requests from investors for additional, more detailed information about a reportable segment’s expenses. The amendments in this ASU are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. The Company adopted ASU 2023-07 for the annual reporting period beginning January 1, 2024. The adoption of ASU 2023-07 did not have a material impact on the Company’s reportable segment disclosures.
Accounting Pronouncements Not Yet Adopted
In November 2024, the FASB issued ASU No. 2024-03, “Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses”. This ASU requires disclosure, in the notes to the financial statements, of specified information about certain costs and expenses. The amendments in this ASU are effective for annual reporting periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027. As this guidance relates solely to financial statement disclosures, the adoption of ASU 2024-03 will have no impact upon the Company’s results of operations, financial condition, or liquidity.
Other accounting pronouncements were issued during the year ended December 31, 2024 which were either not applicable to the Company or did not impact the Company’s consolidated financial statements.
v3.25.1
Segment Reporting
 12 Months Ended
Dec. 31, 2024
Segment Reporting [Abstract]  
Segment Reporting Segment Reporting
The Company manages its underwriting operations as two business segments: Aspen Re and Aspen Insurance. The Company has determined its reportable segments by taking into account the manner in which the Company’s chief operating decision maker (“CODM”) makes operating decisions and assesses operating performance. The Company’s CODM is the Group Executive Committee, which comprises global heads of key functions and other key business leads.
Profit or loss for each of the Company’s business segments is measured by underwriting income or loss. Underwriting profit is the excess of net earned premiums over the sum of losses and loss expenses, acquisition costs and general and administrative expenses. Underwriting income or loss provides a basis for the CODM to evaluate the segment’s underwriting performance.
Reinsurance Segment. The Reinsurance segment consists of property catastrophe reinsurance, other property reinsurance, casualty reinsurance and specialty reinsurance.
Insurance Segment.  The Insurance segment consists of first party insurance, specialty insurance, casualty and liability insurance, financial and professional lines insurance and other insurance. The other insurance business line includes Aspen Underwriting Limited’s participation as a corporate member in Carbon Syndicate 4747, and the Company’s digital follow capacity offered through Ki’s Lloyd’s platform.
Non-underwriting Disclosures. The Company provides additional disclosures for corporate and other (non-operating) income and expenses. Corporate and other income and expenses include: corporate expenses, non-operating expenses, net investment income, net realized and unrealized investment gains or losses, changes in fair value of derivatives, interest expenses, net realized and unrealized foreign exchange gains or losses, and income taxes. These income and expense items are not allocated to the Company’s business segments as they are not directly related to the Company’s business segment operations and is consistent with how the CODM measures the performance of the business segments. The Company does not allocate its assets by business segment as we evaluate underwriting results of each segment separately from the results of our investment portfolio.
The Company uses underwriting ratios as measures of performance. The loss ratio is the ratio of losses and loss adjustment expenses to net earned premiums. The acquisition cost ratio is the ratio of acquisition costs to net earned premiums. The general and administrative expense ratio is the ratio of general and administrative expenses to net earned premiums. The combined ratio is the sum of the loss ratio, the acquisition cost ratio and the general and administrative expense ratio.
The following tables provide a summary of gross and net written and earned premiums, underwriting income or loss, ratios and reserves for each of the Company’s business segments for the twelve months ended December 31, 2024, 2023 and 2022:
 Twelve Months Ended December 31, 2024
 ReinsuranceInsuranceTotal
 ($ in millions)
Underwriting Revenues
Gross written premiums$1,885.8 $2,723.5 $4,609.3 
Net written premiums1,275.7 1,666.9 2,942.6 
Gross earned premiums1,822.1 2,565.7 4,387.8 
Net earned premiums1,305.7 1,584.0 2,889.7 
Underwriting Expenses
Losses and loss adjustment expenses741.3 976.5 1,717.8 
Acquisition costs227.0 193.2 420.2 
General and administrative expenses141.7 264.2 405.9 
Underwriting income195.7 150.1 345.8 
Corporate and other expenses (1)
(97.3)
Non-operating expenses (2)
(29.9)
Net investment income318.0 
Realized and unrealized investment gains52.6 
Realized and unrealized investment losses(102.1)
Change in fair value of derivatives(21.1)
Interest expense(62.1)
Net realized and unrealized foreign exchange gains
60.2 
Income before income taxes
464.1 
Income tax benefit
22.0 
Net income$486.1 
Net reserve for losses and loss adjustment expenses
$1,691.5 $2,259.1 $3,950.6 
Ratios
Loss ratio56.8 %61.6 %59.4 %
Acquisition cost ratio17.4 12.2 14.5 
General and administrative expense ratio10.9 16.7 14.0 
Expense ratio28.3 28.9 28.5 
Combined ratio85.1 %90.5 %87.9 %
 _______________
(1)    Corporate and other expenses includes other income/(expenses), which were previously presented separately.
(2)    Non-operating expenses in the twelve months ended December 31, 2024 includes expenses in relation to consulting fees, non-recurring transformation program costs, and other non-recurring costs.
 Twelve Months Ended December 31, 2023
 ReinsuranceInsuranceTotal
 
($ in millions)
Underwriting Revenues
Gross written premiums$1,521.0 $2,446.6 $3,967.6 
Net written premiums1,098.0 1,483.9 2,581.9 
Gross earned premiums1,562.0 2,444.8 4,006.8 
Net earned premiums1,154.5 1,460.0 2,614.5 
Underwriting Expenses
Losses and loss adjustment expenses611.1 941.9 1,553.0 
Acquisition costs208.6 171.6 380.2 
General and administrative expenses120.6 233.9 354.5 
Underwriting income
214.2 112.6 326.8 
Corporate and other expenses (1)
(114.0)
Non-operating expenses (2)
(35.1)
Net investment income275.7 
Realized and unrealized investment gains75.9 
Realized and unrealized investment losses(61.4)
Change in fair value of derivatives26.1 
Interest expense(55.2)
Net realized and unrealized foreign exchange (losses)(36.2)
Income before income taxes402.6 
Income tax benefit
132.1 
Net income$534.7 
Net reserve for losses and loss adjustment expenses
$1,373.1 $1,859.7 $3,232.8 
Ratios
Loss ratio52.9 %64.5 %59.4 %
Acquisition cost ratio18.1 11.8 14.5 
General and administrative expense ratio 10.4 16.0 13.6 
Expense ratio28.5 27.8 28.1 
Combined ratio81.4 %92.3 %87.5 %
 ________________
(1)    Corporate and other expenses includes other income/(expenses), which were previously presented separately.
(2)    Non-operating expenses in the twelve months ended December 31, 2023 includes expenses in relation to consulting fees, non-recurring transformation program costs, and other non-recurring costs.
 Twelve Months Ended December 31, 2022
 ReinsuranceInsuranceTotal
 ($ in millions)
Underwriting Revenues
Gross written premiums$1,807.0 $2,531.7 $4,338.7 
Net written premiums1,426.4 1,469.6 2,896.0 
Gross earned premiums1,617.2 2,370.8 3,988.0 
Net earned premiums1,251.8 1,436.9 2,688.7 
Underwriting Expenses
Losses and loss adjustment expenses770.3 909.7 1,680.0 
Acquisition costs252.4 179.4 431.8 
General and administrative expenses142.5 244.0 386.5 
Underwriting income86.6 103.8 190.4 
Corporate expenses(71.7)
Non-operating expenses (1)
(36.0)
Net investment income188.1 
Realized and unrealized investment gains5.0 
Realized and unrealized investment losses(182.6)
Change in fair value of derivatives(80.5)
Interest expense(43.7)
Net realized and unrealized foreign exchange gains
15.9 
Other income8.2 
Other expenses(20.1)
(Loss) before income taxes (27.0)
Income tax benefit78.1 
Net income
$51.1 
Net reserve for losses and loss adjustment expenses
$1,360.7 $1,452.5 $2,813.2 
Ratios
Loss ratio61.5 %63.3 %62.5 %
Acquisition cost ratio20.2 12.5 16.1 
General and administrative expense ratio 11.4 17.0 14.4 
Expense ratio31.6 29.5 30.5 
Combined ratio93.1 %92.8 %93.0 %
_______________
(1)    Non-operating expenses in the twelve months ended December 31, 2022 includes expenses in relation to consulting fees, non-recurring transformation activities, and other non-recurring costs.
Geographical Areas. The following summary presents the Company’s gross written premiums based on the location of the insured risk for the twelve months ended December 31, 2024, 2023 and 2022.
Twelve Months Ended
 December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Australia/Asia$177.8 $177.8 $257.5 
Europe208.1 179.4 194.5 
United Kingdom & Ireland
614.8 532.5 485.8 
United States & Canada (1)
2,947.0 2,472.0 2,715.7 
Worldwide excluding the United States (2)
33.4 28.8 24.2 
Worldwide including the United States (3)
435.0 417.2 541.7 
Other (4)
193.2 159.9 119.3 
Total
$4,609.3 $3,967.6 $4,338.7 
 ______________
(1)    “United States & Canada” comprises individual policies that insure risks specifically in the United States and/or Canada, but not elsewhere.
(2)    “Worldwide excluding the United States” consists of individual policies that insure global risks with the specific exclusion of the United States.
(3)    “Worldwide including the United States” consists of individual policies that insure global risks with the specific inclusion of the United States.
(4)    “Other” comprises individual policies that insure risks in other countries including, but not limited to, countries in the Caribbean, South America and the Middle East.
v3.25.1
Investments
 12 Months Ended
Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]  
Investments Investments
Income Statement
Net Investment Income.  The following table summarizes net investment income for the twelve months ended December 31, 2024, 2023 and 2022:
Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Fixed income securities — Available for sale$161.5 $115.7 $95.6 
Fixed income securities — Trading88.2 98.9 57.0 
Short-term investments — Available for sale4.5 5.3 0.6 
Short-term investments — Trading0.1 0.3 0.1 
Fixed term deposits (included in cash and cash equivalents)45.3 39.9 6.6 
Catastrophe bonds — Trading— 0.2 0.3 
Privately-held investments — Available for sale
1.2 0.1 — 
Privately-held investments — Trading34.9 44.7 24.3 
Other investments, at fair value (1)
(6.2)(17.8)13.9 
Total329.5 287.3 198.4 
Investment expenses(11.5)(11.6)(10.3)
Net investment income$318.0 $275.7 $188.1 
_____________
(1)    Other investments primarily represent the Company’s investments in investment funds. The amount reported represents the change in fair value of the investments in the period.
The following table summarizes the net realized and unrealized investment gains and losses recorded in the consolidated statement of operations and the change in unrealized gains and losses on investments recorded in other comprehensive income for the twelve months ended December 31, 2024, 2023 and 2022:
Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
($ in millions)
Available for sale:
Fixed income securities — gross realized gains$2.4 $1.6 $2.9 
Fixed income securities — gross realized (losses)(60.6)(41.5)(58.4)
Short-term investments — gross realized gains0.8 0.6 1.0 
Short-term investments — gross realized (losses)(2.0)(0.9)(0.5)
Net change in expected credit gains/(losses)
1.9 4.8 (5.0)
Trading:
Fixed income securities — gross realized gains1.2 1.0 0.2 
Fixed income securities — gross realized (losses)(10.0)(3.5)(1.8)
Fixed income securities — net unrealized gains/(losses)
26.8 65.9 (113.9)
Short-term investments — gross realized gains— 0.1 — 
Short-term investments — gross realized (losses)(0.3)(0.3)— 
Privately-held investments — gross realized gains0.8 0.8 0.7 
Privately-held investments — gross realized (losses)(28.8)— (0.1)
Privately-held investments — net unrealized gains/(losses)
18.6 (15.2)(2.5)
Catastrophe bonds — net unrealized gains
— 0.1 0.2 
Investments, equity method:
Gross unrealized (losses)/gains in MVI
(0.2)0.2 — 
Gross unrealized gains/(losses) in Multi-Line Reinsurer
0.1 0.8 (0.4)
Gross realized (losses) in Digital Re
(0.2)— — 
Total net realized and unrealized investment (losses)/gains recorded in the consolidated statement of operations
$(49.5)$14.5 $(177.6)
Change in available for sale net unrealized gains/(losses):
Available for sale investments
$34.1 $126.2 $(391.7)
Income tax (expense)/benefit
(4.7)(20.6)23.9 
Total change in net unrealized gains/(losses), net of taxes recorded in other comprehensive income
$29.4 $105.6 $(367.8)
Balance Sheet
Fixed Income Securities, Short-term Investments and Privately-held Investments — Available for Sale.  The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of available for sale investments in fixed income securities, short-term investments and privately-held investments as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Allowance for Credit Losses
Fair Market Value
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,504.8 $1.5 $(25.7)$— $1,480.6 
U.S. agency7.5 — (0.3)— 7.2 
Municipal84.2 — (1.9)— 82.3 
Corporate2,045.3 8.5 (66.4)(1.0)1,986.4 
Non-U.S. government-backed corporate132.9 0.8 (2.4)— 131.3 
Non-U.S. government248.2 1.0 (2.4)— 246.8 
Asset-backed232.4 2.2 (0.1)— 234.5 
Agency commercial mortgage-backed
5.0 — (0.6)— 4.4 
Agency residential mortgage-backed
600.8 — (82.1)— 518.7 
Total fixed income securities, available for sale
4,861.1 14.0 (181.9)(1.0)4,692.2 
Short-term investments, available for sale
261.9 — — — 261.9 
Privately-held investments, available for sale
Asset-backed securities24.0 0.2 — — 24.2 
Total investments, available for sale
$5,147.0 $14.2 $(181.9)$(1.0)$4,978.3 
 As at December 31, 2023
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Allowance for Credit Losses
Fair Market Value
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,224.9 $4.4 $(26.7)$— $1,202.6 
U.S. agency7.5 — (0.3)— 7.2 
Municipal133.6 — (5.0)(0.5)128.1 
Corporate2,051.1 12.1 (101.5)(2.4)1,959.3 
Non-U.S. government-backed corporate106.5 0.1 (5.9)— 100.7 
Non-U.S. government279.9 0.6 (6.7)— 273.8 
Agency commercial mortgage-backed6.6 — (0.8)— 5.8 
Agency residential mortgage-backed519.9 0.1 (74.9)— 445.1 
Total fixed income securities, available for sale
4,330.0 17.3 (221.8)(2.9)4,122.6 
Short-term investments, available for sale
93.6 — — — 93.6 
Privately-held investments, available for sale
Asset-backed securities14.7 0.2 — — 14.9 
Total investments, available for sale
$4,438.3 $17.5 $(221.8)$(2.9)$4,231.1 
Fixed Income Securities, Short-term Investments, Catastrophe Bonds and Privately-held Investments — Trading.  The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of trading investments in fixed income securities, short-term investments, catastrophe bonds and privately-held investments as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Fair Market Value
 ($ in millions)
Fixed income securities, trading
U.S. government$262.9 $0.6 $(2.2)$261.3 
Municipal1.6 — — 1.6 
Corporate155.5 0.5 (4.9)151.1 
High yield loans101.7 0.9 (0.2)102.4 
Non-U.S. government-backed corporate2.8 — — 2.8 
Non-U.S. government24.4 0.1 (0.1)24.4 
Asset-backed624.6 4.1 (3.5)625.2 
Agency mortgage-backed34.2 — (3.1)31.1 
Total fixed income securities, trading
1,207.7 6.2 (14.0)1,199.9 
Short-term investments, trading
1.0 — — 1.0 
Catastrophe bonds, trading
1.0 — — 1.0 
Privately-held investments, trading
Commercial mortgage loans80.9 0.5 (1.7)79.7 
Middle market loans and other private debt61.6 0.1 (0.7)61.0 
Asset-backed securities126.7 0.9 — 127.6 
Global corporate securities18.8 — (0.3)18.5 
Total privately-held investments, trading
288.0 1.5 (2.7)286.8 
Total investments, trading
$1,497.7 $7.7 $(16.7)$1,488.7 
 As at December 31, 2023
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Fair Market Value
 ($ in millions)
Fixed income securities, trading
U.S. government$248.7 $0.5 $(3.7)$245.5 
Municipal3.3 — (0.2)3.1 
Corporate178.8 0.7 (8.0)171.5 
High yield loans90.8 1.3 — 92.1 
Non-U.S. government-backed corporate8.6 — (0.3)8.3 
Non-U.S. government35.8 0.1 (1.1)34.8 
Asset-backed936.0 2.1 (29.9)908.2 
Agency mortgage-backed 25.0 — (2.8)22.2 
Total fixed income securities, trading
1,527.0 4.7 (46.0)1,485.7 
Short-term investments, trading
2.1 — — 2.1 
Catastrophe bonds, trading
1.6 — — 1.6 
Privately-held investments, trading
Commercial mortgage loans293.2 1.0 (19.3)274.9 
Middle market loans and other private debt85.9 — (1.1)84.8 
Asset-backed securities83.1 0.4 (0.6)82.9 
Global corporate securities14.7 — (0.3)14.4 
Short-term investments18.0 — — 18.0 
Total privately-held investments, trading
494.9 1.4 (21.3)475.0 
Total investments, trading
$2,025.6 $6.1 $(67.3)$1,964.4 
Catastrophe Bonds. The Company has invested in catastrophe bonds with a total value of $1.0 million as at December 31, 2024 (December 31, 2023 — $1.6 million). The bonds are either zero-coupon notes or receive quarterly interest payments based on variable interest rates with scheduled maturities in 2025. The redemption value of the bonds will adjust based on the occurrence or aggregate occurrence of a covered event, such as windstorms and earthquakes in the United States, Canada, the North Atlantic, South America, Europe, Japan or Australia.
Privately-held Investments. The Company has invested in privately-held investments, which primarily include commercial mortgage loans of $79.7 million and middle market loans and other private debt of $61.0 million as at December 31, 2024 (December 31, 2023 — commercial mortgage loans of $274.9 million; middle market loans and other private debt of $84.8 million). Privately-held investments also includes investments in asset-backed securities, global corporate securities, and other short term investments.
Commercial Mortgage Loans. The commercial mortgage loans are related to investments in properties including apartments, hotels, office and retail buildings, other commercial properties and industrial properties. The commercial mortgage loan portfolio is diversified by property type, geographic region and issuer to reduce risks. As part of our investment process, we evaluate factors such as size, property type, and security to determine that properties are performing at a consistent and acceptable level to secure the related debt. 
Middle Market Loans and Other Private Debt. The middle market loans are investments in senior secured loan positions with full covenants, focused on the middle market in the U.S., Europe and the Caribbean. The other private debt consists of debt securities issued to private investment funds. The middle market loan and other private debt portfolio is diversified by industry type, geographic region and issuer to reduce risks. As part of our investment process, we evaluate factors such as size, industry and security to determine that loans are performing at a consistent and acceptable level to secure the related debt.
Asset-backed Securities. Asset-backed securities represent interests in underlying pools of diversified referenced assets that are collateralized and backed by future cash flows and these securities are performing.
Global Corporate Securities. The privately-held global corporate securities portfolio consists of debt securities issued by U.S. and foreign corporations.
Investments, Equity Method. In January 2015, the Company, along with seven other insurance companies, established a micro-insurance venture consortium and micro-insurance incubator (“MVI”) domiciled in Bermuda. The MVI is a social impact organization that provides micro-insurance products to assist global emerging consumers. In March 2021, the Company committed an additional $0.8 million equity contribution to MVI over a 2 year period and paid $0.4 million in the period ending December 31, 2022.
On January 1, 2017, the Company purchased through its wholly-owned subsidiary, Aspen U.S. Holdings, Inc. (“Aspen U.S. Holdings”), a 49% share of Digital Risk Resources, LLC (“Digital Re”), a U.S.-based enterprise engaged in the business of developing, marketing and servicing turnkey information security and privacy liability insurance products for a total consideration of $2.3 million. The investment is accounted for under the equity method and adjustments to the carrying value of this investment are made based on the Company’s share of capital, including share of income and expenses. During the year ended December 31, 2024, the Company sold its investment in Digital Re for no consideration.
On December 23, 2019, the Company committed $5.0 million as an equity investment in the holding company of a multi-line reinsurer. The strategy for the multi-line reinsurer is to combine a diversified reinsurance business, focused primarily on long-tailed lines of property and casualty business and, potentially to a lesser extent, life business, with a diversified investment strategy. During the period ending December 31, 2024, no capital was invested in the multi-line reinsurer (December 31, 2023 — $0.4 million) and the commitment has been fully funded.
The table below shows the Company’s investments in MVI, Multi-Line Reinsurer and Digital Re for the twelve months ended December 31, 2024 and 2023:
MVIMulti-Line ReinsurerDigital ReTotal
 ($ in millions)
Opening undistributed value of investment as at January 1, 2024
$1.0 $6.4 $0.2 $7.6 
Unrealized (loss)/gain for the twelve months to December 31, 2024
(0.2)0.1 — (0.1)
Realized (loss) for the twelve months to December 31, 2024
— — (0.2)(0.2)
Closing value of investment as at December 31, 2024
$0.8 $6.5 $— $7.3 
Opening undistributed value of investment as at January 1, 2023
$0.8 $5.2 $0.2 $6.2 
Investment in the period— 0.4 — 0.4 
Unrealized gain for the twelve months to December 31, 2023
0.2 0.8 — 1.0 
Closing value of investments at December 31, 2023
$1.0 $6.4 $0.2 $7.6 
Other Investments. On December 20, 2017, the Company committed, and during 2018 invested, $100.0 million as a limited partner to a real estate fund. As at December 31, 2024, the current fair value of the fund is $111.7 million (2023 — $117.1 million).
During 2020, the Company committed $10.5 million as a limited partner to a related party managed lending fund. The partnership was established to provide direct lending to large corporate borrowers. On April 1, 2021, the Company committed an additional $2.8 million to the fund. As at December 31, 2024, the current fair value of the fund is $19.3 million (2023 — $15.9 million) and the unfunded commitment is $0.2 million (2023 — $1.1 million).
On April 1, 2021, the Company established pledge accounts with its custodian bank for the ability to obtain liquidity and funding services provided by a U.S. co-operative bank, which provides liquidity and funding to its insurance member institutions. As at December 31, 2024, the fair value of the Company’s member shares in the bank is $2.0 million (2023 — $1.7 million).
On September 30, 2021, the Company committed $20.0 million as a limited partner to a third-party managed real estate fund. The Partnership was established to make equity and equity related investments in multifamily and other commercial real estate properties located in the United States and its territories, with the goal of generating superior risk-adjusted returns. The partnership seeks to acquire commercial real estate assets including real estate assets (or interests therein) that may have management or operational problems and require improvements or lack sufficient capital, including mortgage loans and development or redevelopment properties. On April 1, 2022, the Company committed an additional $10.0 million to the fund. As at December 31, 2024, the current fair value of the fund is $36.2 million (2023 — $39.8 million) and the unfunded commitment is $0.9 million (2023 — $2.2 million).
On April 1, 2022, the Company committed $30.0 million as a limited partner to a related party managed real estate fund. The partnership was established to pursue investment opportunities to acquire, recapitalize, restructure and reposition real estate assets, portfolios and companies primarily in the United States. As at December 31, 2024, the current fair value of the fund is $19.3 million (2023 — $23.9 million) and the unfunded commitment is $3.7 million (2023 — $4.1 million).
On May 5, 2022, the Company committed $15.0 million as a limited partner to a third-party managed infrastructure fund. The partnership was established to make value added infrastructure investments in environmental services, transportation, communications and digital, energy/energy transition and other infrastructure sectors primarily in North America. As at December 31, 2024, the current fair value of the fund is $12.9 million (2023 — $10.8 million) and the unfunded commitment is $2.3 million (2023 — $4.0 million).
On August 31, 2023, the Company committed £7.0 million as a limited partner to a third-party managed debt fund. The fund focuses on three core sectors: health and social care, affordable housing, and social infrastructure. The fund invests across the U.K., focusing on areas of poverty and deprivation. The fund provides fixed-rate loans typically backed by property assets. Borrowers are established, socially impactful organizations, with a history of profitable revenue generation. As at December 31, 2024, the current fair value of the fund is $0.1 million (2023 — $0.1 million) and the unfunded commitment is £6.8 million (2023 — £6.9 million).
On September 30, 2023, the Company committed $55.0 million as a limited partner to a third-party managed energy fund. The fund invests in energy transition and climate solutions, accelerating growth and business transformation through flexible capital, enabling leading energy companies to build enterprises at scale that can deliver clean, reliable and affordable energy to help meet global needs. As at December 31, 2024 the Company has not funded the investment and the unfunded commitment is $55.0 million (2023 — $55.0 million).
On August 1, 2024, the Company committed and invested $25.0 million as a limited partner to a third-party managed liquidity fund. The fund seeks to maximize total return, by investing in a portfolio of investment grade debt securities, both fixed and floating rate. As at December 31, 2024, the current fair value of the fund is $25.7 million and the unfunded commitment is $Nil.
On October 31, 2024, the Company converted one of its commercial mortgage loan investments to an equity interest in a joint venture. As at December 31, 2024, the current carrying value of the investment is $40.0 million. As at December 31, 2023, the previous commercial mortgage loan investment was classified as privately-held investments, trading. This investment has no unfunded commitments.
As at December 31, 2024, the aggregate current fair value of the investment funds described above is $267.2 million (2023 — $209.3 million).
For further information on the investment funds, refer to Note 21(a) in these consolidated financial statements, “Commitments and Contingent Liabilities.”
Fixed Income Securities, Short-term Investments and Privately-held Investments — Available for Sale.  The scheduled maturity distribution of the Company’s available for sale securities as at December 31, 2024 and December 31, 2023 is set forth below. Actual maturities may differ from contractual maturities because issuers of securities may have the right to call or prepay obligations with or without call or prepayment penalties.
 As at December 31, 2024
 
Amortized Cost or Cost
Fair Market Value
 ($ in millions)
Due one year or less$834.1 $831.2 
Due after one year through five years2,386.5 2,353.2 
Due after five years through ten years1,060.7 1,008.7 
Due after ten years3.5 3.4 
4,284.8 4,196.5 
Agency commercial mortgage-backed
5.0 4.4 
Agency residential mortgage-backed
600.8 518.7 
Asset-backed256.4 258.7 
Total investments, available for sale
$5,147.0 $4,978.3 
 At December 31, 2023
 
Amortized Cost or Cost
Fair Market Value
 ($ in millions)
Due one year or less$512.0 $505.8 
Due after one year through five years2,889.0 2,818.9 
Due after five years through ten years495.1 440.3 
Due after ten years15.7 15.2 
3,911.8 3,780.2 
Agency commercial mortgage-backed6.6 5.8 
Agency residential mortgage-backed519.9 445.1 
Total investments, available for sale
$4,438.3 $4,231.1 
Guaranteed Investments. As at December 31, 2024 and December 31, 2023, the Company held no investments which are guaranteed by mono-line insurers, excluding those with explicit government guarantees. The Company’s exposure to other third-party guaranteed debt is primarily to investments backed by non-U.S. government guaranteed issuers.
Gross Unrealized Losses, Available for Sale. The following tables summarize, by type of security, the aggregate fair value and gross unrealized loss by length of time the security has been in an unrealized loss position for the Company’s available for sale portfolio as at December 31, 2024 and December 31, 2023:
 December 31, 2024
 0-12 monthsOver 12 monthsTotal
 
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Number of Securities
 
($ in millions, except number of securities)
Fixed income securities, available for sale
U.S. government$718.1 $(11.6)$397.8 $(14.1)$1,115.9 $(25.7)137
U.S. agency— — 7.2 (0.3)7.2 (0.3)1
Municipal33.6 (0.7)45.4 (1.2)79.0 (1.9)47
Corporate570.3 (6.8)663.9 (59.6)1,234.2 (66.4)692
Non-U.S. government-backed corporate5.8 — 91.1 (2.4)96.9 (2.4)12
Non-U.S. government118.8 (0.9)43.7 (1.5)162.5 (2.4)41
Asset-backed17.2 (0.1)— — 17.2 (0.1)14
Agency commercial mortgage-backed — — 4.5 (0.6)4.5 (0.6)1
Agency residential mortgage-backed161.2 (2.2)351.3 (79.9)512.5 (82.1)225
Total fixed income securities, available for sale$1,625.0 $(22.3)$1,604.9 $(159.6)$3,229.9 $(181.9)1,170
 December 31, 2023
 0-12 monthsOver 12 monthsTotal
 
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Number of Securities
 
($ in millions, except number of securities)
Fixed income securities, available for sale
U.S. government$105.5 $(0.5)$673.3 $(26.2)$778.8 $(26.7)74
U.S. agency— — 7.2 (0.3)7.2 (0.3)1
Municipal11.1 (1.0)117.0 (4.0)128.1 (5.0)54
Corporate46.7 (0.4)1,287.2 (101.1)1,333.9 (101.5)558
Non-U.S. government-backed corporate0.2 — 95.5 (5.9)95.7 (5.9)12
Non-U.S. government32.9 (0.2)180.1 (6.5)213.0 (6.7)53
Agency commercial mortgage-backed— — 5.8 (0.8)5.8 (0.8)1
Agency residential mortgage-backed0.1 — 435.9 (74.9)436.0 (74.9)197
Total fixed income securities, available for sale$196.5 $(2.1)$2,802.0 $(219.7)$2,998.5 $(221.8)950
At December 31, 2024, 1,170 available for sale securities were in an unrealized loss position of $181.9 million, of which $0.3 million was related to securities below investment grade or not rated. At December 31, 2023, 950 available for sale securities were in an unrealized loss position of $221.8 million, of which $1.2 million was related to securities below investment grade or not rated.
The unrealized losses of $181.9 million at December 31, 2024 were due to non-credit factors and are expected to be recovered as the related securities approach maturity. The Company does not intend to sell the securities in an unrealized loss position and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases.
v3.25.1
Variable Interest Entities
 12 Months Ended
Dec. 31, 2024
Payables and Accruals [Abstract]  
Variable Interest Entities Variable Interest Entities
As at December 31, 2024, the Company held an investment in one (December 31, 2023 — one) variable interest entity (“VIE”), namely Peregrine Reinsurance Ltd (“Peregrine”).
In November 2016, Peregrine, a subsidiary of the Company, was registered as a segregated accounts company under the Segregated Accounts Companies Act 2000, as amended. As at December 31, 2024, Peregrine had six segregated accounts which were funded by third-party investors, which are not consolidated, and two segregated accounts which are funded by Aspen and are consolidated within the financial statements.
The Company has determined that Peregrine has the characteristics of a VIE as addressed by the guidance in ASC 810, Consolidation. The six segregated accounts have not been consolidated as part of the Company’s consolidated financial statements because the Company is not the primary beneficiary of those accounts. The Company has, however, concluded that it is the primary beneficiary of the Peregrine general fund and, similar to prior reporting periods, the results of the Peregrine general fund are included in the Company’s consolidated financial statements.
v3.25.1
Fair Value Measurements
 12 Months Ended
Dec. 31, 2024
Fair Value Disclosures [Abstract]  
Fair Value Measurements Fair Value Measurements
The Company’s estimates of fair value for financial assets and liabilities are based on the framework established in the fair value accounting guidance included in ASC Topic 820, “Fair Value Measurements and Disclosures.” The framework prioritizes the inputs, which refer broadly to assumptions market participants would use in pricing an asset or liability, into three levels.
The Company considers prices for actively traded securities to be derived based on quoted prices in an active market for identical assets, which are Level 1 inputs in the fair value hierarchy. The majority of these securities are valued using prices supplied by pricing services.
The Company considers prices for other securities that may not be as actively traded which are priced via pricing services, vendors and broker-dealers, or with reference to interest rates and yield curves, to be derived based on inputs that are observable for the asset, either directly or indirectly, which are Level 2 inputs in the fair value hierarchy. The majority of these securities are also valued using prices supplied by pricing services.
The Company considers securities, other financial instruments, privately-held investments and derivative insurance contracts subject to fair value measurement whose valuation is derived by internal valuation models to be based largely on unobservable inputs, which are Level 3 inputs in the fair value hierarchy.
The following tables present the level within the fair value hierarchy at which the Company’s financial assets and liabilities are measured on a recurring basis as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 Level 1Level 2Level 3Total
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,480.6 $— $— $1,480.6 
U.S. agency— 7.2 — 7.2 
Municipal— 82.3 — 82.3 
Corporate— 1,986.4 — 1,986.4 
Non-U.S. government-backed corporate— 131.3 — 131.3 
Non-U.S. government195.1 51.7 — 246.8 
Asset-backed— 234.5 — 234.5 
Agency commercial mortgage-backed
— 4.4 — 4.4 
Agency residential mortgage-backed
— 518.7 — 518.7 
Total fixed income securities, available for sale1,675.7 3,016.5 — 4,692.2 
Short-term investments, available for sale260.2 1.7 — 261.9 
Privately-held investments, available for sale— — 24.2 24.2 
Fixed income securities, trading
U.S. government261.3 — — 261.3 
Municipal— 1.6 — 1.6 
Corporate— 151.1 — 151.1 
Non-U.S. government-backed corporate— 2.8 — 2.8 
High yield loans— 102.4 — 102.4 
Non-U.S. government9.6 14.8 — 24.4 
Asset-backed— 625.2 — 625.2 
Agency mortgage-backed— 31.1 — 31.1 
Total fixed income securities, trading270.9 929.0 — 1,199.9 
Short-term investments, trading1.0 — — 1.0 
Catastrophe bonds, trading— 1.0 — 1.0 
Privately-held investments, trading— — 286.8 286.8 
Other investments (1)
— — — 267.2 
Other financial assets and liabilities
Derivative assets — foreign exchange contracts— 17.0 — 17.0 
Derivative liabilities — foreign exchange contracts— (45.9)— (45.9)
Derivative liabilities — loss portfolio transfer (2)
— — (3.6)(3.6)
Total$2,207.8 $3,919.3 $307.4 $6,701.7 
______________
(1)    Other investments represent our investments in investment funds operating strategies in real estate, infrastructure and lending and are measured at fair value using the net asset value per share practical expedient. As a result, the investments are not classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. The investment in the funds is subject to restrictions as detailed in Note 21(a), “Commitments and Contingent Liabilities.”
(2)    The loss portfolio transfer contract includes a funds withheld arrangement that provides variable interest expense based on Aspen’s investment performance. As a result, the funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative.
 At December 31, 2023
 Level 1Level 2Level 3Total
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,202.6 $— $— $1,202.6 
U.S. agency— 7.2 — 7.2 
Municipal— 128.1 — 128.1 
Corporate— 1,959.3 — 1,959.3 
Non-U.S. government-backed corporate— 100.7 — 100.7 
Non-U.S. government200.4 73.4 — 273.8 
Agency commercial mortgage-backed— 5.8 — 5.8 
Agency residential mortgage-backed— 445.1 — 445.1 
Total fixed income securities, available for sale1,403.0 2,719.6 — 4,122.6 
Short-term investments, available for sale86.7 6.9 — 93.6 
Privately-held investments, available for sale— — 14.9 14.9 
Fixed income securities, trading
U.S. government245.5 — — 245.5 
Municipal— 3.1 — 3.1 
Corporate— 171.5 — 171.5 
Non-U.S. government-backed corporate— 8.3 — 8.3 
High yield loans— 92.1 — 92.1 
Non-U.S. government13.0 21.8 — 34.8 
Asset-backed— 908.2 — 908.2 
Agency mortgage-backed— 22.2 — 22.2 
Total fixed income securities, trading258.5 1,227.2 — 1,485.7 
Short-term investments, trading0.2 1.9 — 2.1 
Catastrophe bonds, trading— 1.6 — 1.6 
Privately-held investments, trading— — 475.0 475.0 
Other investments (1)
— — — 209.3 
Other financial assets and liabilities
Derivative assets — foreign exchange contracts— 31.7 — 31.7 
Derivative liabilities — foreign exchange contracts— (9.3)— (9.3)
Derivative liabilities — loss portfolio transfer (2)
— — (16.5)(16.5)
Total$1,748.4 $3,979.6 $473.4 $6,410.7 
______________
(1)    Other investments represent our investments in investment funds operating strategies in real estate, infrastructure and lending and are measured at fair value using the net asset value per share practical expedient. As a result, the investments are not classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. The investment in the funds is subject to restrictions as detailed in Note 21(a), “Commitments and Contingent Liabilities.”
(2)    The loss portfolio transfer contract includes a funds withheld arrangement that provides variable interest expense based on Aspen’s investment performance. As a result, the funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative.
Transfers of assets into or out of a particular level are recorded at their fair values as of the end of each reporting period consistent with the date of the determination of fair value. During the twelve months ended December 31, 2024, $Nil was transferred in or out of Level 3 (December 31, 2023 — $12.1 million was transferred out of Level 3 and $5.3 million transferred into Level 3).
The following table presents a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs for the twelve months ended December 31, 2024 and December 31, 2023:
Twelve Months Ended December 31, 2024Balance at beginning of yearPurchases and issuancesTransfers inTransfers (out)
Reclassifications
Settlements and sales
(Decrease)/increase in fair value included in net income (1) / OCI (2)
Balance at end of year
Change in unrealized gains (losses) relating to assets held at end of year (1) (2)
Assets
Privately-held investments, available for sale
Asset-backed securities
$14.9 $10.0 $— $— $— $— $(0.7)$24.2 $0.2 
Privately-held investments, trading
Commercial mortgage loans$274.9 $0.5 $— $— $— $(184.4)$(11.3)$79.7 $— 
Middle market loans and other private debt
84.8 0.4 — — 10.9 (35.5)0.4 61.0 — 
Asset-backed securities82.9 56.1 — — — (12.4)1.0 127.6 1.1 
Global corporate securities14.4 4.4 — — — (0.3)— 18.5 — 
Short-term investments18.0 — — — (10.9)(7.1)— — — 
Total Level 3 assets$489.9 $71.4 $— $— $— $(239.7)$(10.6)$311.0 $1.3 
Liabilities
Derivative liabilities — loss portfolio transfer
$(16.5)$— $— $— $— $— $12.9 $(3.6)$12.9 
Total Level 3 liabilities$(16.5)$— $— $— $— $— $12.9 $(3.6)$12.9 
Twelve Months Ended December 31, 2023
Assets
Privately-held investments, available for sale
Asset-backed securities
$— $14.7 $— $— $— $— $0.2 $14.9 $0.2 
Privately-held investments, trading
Commercial mortgage loans$312.1 $40.6 $— $— $— $(61.5)$(16.3)$274.9 $(17.9)
Middle market loans and other private debt
106.9 18.3 — — — (41.9)1.5 84.8 0.5 
Asset-backed securities66.8 21.9 5.3 (5.5)— (7.6)2.0 82.9 1.7 
Global corporate securities15.0 — — — — (0.4)(0.2)14.4 (0.2)
Equity securities6.6 — — (6.6)— — — — — 
Short-term investments25.6 18.2 — — — (25.8)— 18.0 — 
Total Level 3 assets$533.0 $113.7 $5.3 $(12.1)$— $(137.2)$(12.8)$489.9 $(15.7)
Liabilities
Derivative liabilities — loss portfolio transfer
$(31.7)$— $— $— $— $— $15.2 $(16.5)$15.2 
Total Level 3 liabilities$(31.7)$— $— $— $— $— $15.2 $(16.5)$15.2 
______________
(1)    (Decreases)/increases in the fair value of privately-held investments, trading are included in realized and unrealized investment losses in the consolidated statements of operations and other comprehensive (loss). Increases/(decreases) in the fair value of derivative liabilities - loss portfolio transfer are included within change in fair value of derivatives in the consolidated statements of operations and other comprehensive income/(loss).
(2)    (Decreases)/increases in the fair value of privately-held investments, available for sale are included in other comprehensive income/(loss) (“OCI”).
Valuation of Fixed Income Securities.  The Company’s fixed income securities are classified as either available for sale or trading and are reported at fair value. As at December 31, 2024 and December 31, 2023, the Company’s fixed income securities were valued by pricing services or broker-dealers using standard market conventions. The market conventions utilize market quotations, market transactions in comparable instruments and various relationships between instruments including, but not limited to, yield to maturity, dollar prices and spread prices in determining value.
Independent Pricing Services. The underlying methodology used to determine the fair value of securities in the Company’s available for sale and trading portfolios is by the pricing services. Pricing services will gather observable pricing inputs from multiple external sources, including buy and sell-side contacts and broker-dealers, in order to develop their internal prices.
Pricing services provide pricing for less complex, liquid securities based on market quotations in active markets. Pricing services supply prices for a broad range of securities including those for actively traded securities, such as Treasury and other Government securities, in addition to those that trade less frequently or where valuation includes reference to credit spreads, pay down and pre-pay features and other observable inputs. These securities include Government agency, municipals, corporate and asset-backed securities.
For securities that may trade less frequently or do not trade on a listed exchange, these pricing services may use matrix pricing consisting of observable market inputs to estimate the fair value of a security. These observable market inputs include reported trades, benchmark yields, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, reference data, and industry and economic factors. Additionally, pricing services may use a valuation model such as an option adjusted spread model commonly used for estimating fair values of mortgage-backed and asset-backed securities. The Company does not derive dollar prices using an index as a pricing input for any individual security.
Broker-Dealers. The Company obtains quotes from broker-dealers who are active in the corresponding markets when prices are unavailable from independent pricing services or index providers. Generally, broker-dealers value securities through their trading desks based on observable market inputs. Their pricing methodologies include mapping securities based on trade data, bids or offers, observed spreads and performance of newly issued securities. They may also establish pricing through observing secondary trading of similar securities. Quotes from broker-dealers are non-binding.
The Company obtains prices for all of its fixed income investment securities via its third-party accounting service provider, and in the majority of cases receiving a number of quotes so as to obtain the most comprehensive information available to determine a security’s fair value. A single valuation is applied to each security based on the vendor hierarchy maintained by the Company’s third-party accounting service provider.
As at December 31, 2024, the Company obtained an average of 3.0 quotes per fixed income investment compared to 2.9 quotes at December 31, 2023.
The Company, in conjunction with its third-party accounting service provider, obtains an understanding of the methods, models and inputs used by the third-party pricing service and index providers to assess the ongoing appropriateness of vendors’ prices. The Company and its third-party accounting service provider also have controls in place to validate that amounts provided represent fair values. Processes to validate and review pricing include, but are not limited to:
•quantitative analysis (e.g., comparing the quarterly return for each managed portfolio to its target benchmark, with significant differences identified and investigated);
•comparison of market values obtained from pricing services and broker-dealers against alternative price sources for each security where further investigation is completed when significant differences exist for pricing of individual securities between pricing sources;
•initial and ongoing evaluation of methodologies used by outside parties to calculate fair value; and
•comparison of the fair value estimates to the Company’s knowledge of the current market.
Prices obtained from pricing services and broker-dealers are not adjusted by us; however, prices provided by a pricing service, or broker-dealer in certain instances may be challenged based on market or information available from internal sources, including those available to the Company’s third-party investment accounting service provider. Subsequent to any challenge, revisions made by the pricing service or broker-dealer to the quotes are supplied to the Company’s investment accounting service provider.
Management reviews the vendor hierarchy maintained by the Company’s third-party accounting service provider in order to determine which price source provides the most appropriate fair value (i.e., a price obtained from a pricing service with more seniority in the hierarchy will be used over a less senior one in all cases). The hierarchy level assigned to each security in the Company’s available for sale and trading portfolios is based upon its assessment of the transparency and reliability of the inputs used in the valuation as of the measurement date. The hierarchy of pricing services is determined using various qualitative and quantitative points arising from reviews of the vendors conducted by the Company’s third-party accounting service provider. Vendor reviews include annual due diligence meetings with index providers and pricing services vendors covering valuation methodology, operational walkthroughs and legal and compliance updates.
Fixed Income Securities. Fixed income securities are traded on the over-the-counter (“OTC”) market based on prices provided by one or more market makers in each security. Securities such as U.S. Government, U.S. Agency, Non-U.S. Government and investment grade corporate bonds have multiple market makers in addition to readily observable market value indicators such as expected credit spread, except for Treasury securities, over the yield curve. The Company uses a variety of pricing sources to value fixed income securities including those securities that have pay down/prepay features such as mortgage-backed securities and asset-backed securities in order to ensure fair and accurate pricing. The fair value estimates for the investment grade securities in the Company’s portfolio do not use significant unobservable inputs or modeling techniques.
U.S. Government and Agency Securities. U.S. government and agency securities consist primarily of bonds issued by the U.S. Treasury and corporate debt issued by agencies such as the Federal National Mortgage Association (“FNMA”), the Federal Home Loan Mortgage Corporation (“FHLMC”) and the Federal Home Loan Bank. As the fair values of U.S. Treasury securities are based on unadjusted market prices in active markets, they are classified within Level 1. The fair values of U.S. government agency securities are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of U.S. government agency securities are classified within Level 2.
Municipal Securities. The Company’s municipal portfolio consists of bonds issued by U.S. domiciled state and municipality entities. The fair value of these securities is determined using spreads obtained from broker-dealers, trade prices and the new issue market which are Level 2 inputs in the fair value hierarchy. Consequently, these securities are classified within Level 2.
Non-U.S. Government. The issuers for securities in this category are non-U.S. governments and their agents including, but not limited to, the U.K., Australia, Canada, France and Germany. The fair values of certain non-U.S. government bonds, primarily sourced from international indices, are based on unadjusted market prices in active markets and are therefore classified within Level 1. The remaining non-U.S. government bonds are classified within Level 2 as they are not actively traded. The fair values of the non-U.S. agency securities, again primarily sourced from international indices, are priced using the spread above the risk-free yield curve. As the yields for the risk-free yield curve and the spreads for these securities are observable market inputs, the fair values of non-U.S. agency securities are classified within Level 2. In addition, foreign government securities include a portion of the Emerging Market Debt (“EMD”) portfolio which is also classified within Level 2.
Corporate. Corporate securities consist primarily of short-term, medium-term and long-term debt issued by U.S. and foreign corporations covering a variety of industries and are generally priced by index providers and pricing vendors. Some issuers may participate in government programs which guarantee timely payment of principal and interest in the event of a default. The fair values of these securities are generally determined using the spread above the risk-free yield curve. Inputs used in the evaluation of these securities include credit data, interest rate data, market observations and sector news, broker-dealer quotes and trade volumes. In addition, corporate securities include a portion of the EMD portfolio. The Company classifies these securities within Level 2.
Mortgage-backed Securities. Residential and commercial mortgage-backed securities consist of bonds issued by the Government National Mortgage Association, the FNMA and the FHLMC. The fair values of these securities are determined through the use of a pricing model (including Option Adjusted Spread) which uses prepayment speeds and spreads to determine the appropriate average life of the mortgage-backed security. These spreads are generally obtained from broker-dealers, trade prices and the new issue market. As the significant inputs used to price mortgage-backed securities are observable market inputs, these securities are classified within Level 2.
Asset-backed Securities. Asset-backed securities are securities backed by notes or receivables against assets other than real estate. The underlying collateral for the Company’s asset-backed securities consists mainly of student loans, automobile loans and credit card receivables. These securities are primarily priced by index providers and pricing vendors. Inputs to the valuation process include broker-dealer quotes and other available trade information, prepayment speeds, interest rate data and credit spreads. The Company classifies these securities within Level 2.
Short-term Investments.  Short-term investments consist of highly liquid debt securities with a maturity greater than three months but less than one year from the date of purchase. Short-term investments are classified as either trading or available for sale according to the facts and circumstances of the investment held. Short-term investments are valued in a manner similar to the Company’s fixed maturity investments and are classified within Levels 1 and 2.
Privately-held Investments. Privately-held investments are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models. These models include inputs that are specific to each investment. The inputs used in the fair value measurements include dividend or interest rates and appropriate discount rates. The selection of an appropriate discount rate is judgmental and is the most significant unobservable input used in the valuation of these securities. A significant increase (decrease) in this input in isolation could result in significantly lower (higher) fair value measurement for privately-held investments. In order to assess the reasonableness of the inputs the Company uses in the discounted cash flow models, the Company maintains an understanding of current market conditions, issuer specific information that may impact future cash flows as well as collaboration with independent vendors for most securities to assess the reasonableness of the discount rate being used.
Commercial Mortgage Loans. Commercial mortgage loans consist of investments in properties including apartments, hotels, office and retail buildings, other commercial properties and industrial properties. The commercial mortgage loan portfolio is diversified by property type, geographic region and issuer to reduce risks. Commercial Mortgage Loans are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models and are classified as Level 3.
Middle Market Loans and Other Private Debt. The middle market loans consist of investments in senior secured loan positions with full covenants, focused on the middle market in both U.S., Europe and the Caribbean. The other private debt consists of debt securities issued to private investment funds. The middle market loan and other private debt portfolio is diversified by industry type, geographic region and issuer to reduce risks. Middle market loans and other private debt are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models and are classified as Level 3.
Asset-backed Securities. Asset-backed securities represent interests in underlying pools of diversified referenced assets that are collateralized and backed by future cash flows and these securities are performing. Asset-backed securities are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models and are classified as Level 3.
Global Corporate Securities. The global corporate securities portfolio consists of debt securities issued by U.S. and foreign corporations. The global corporate securities are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models and are classified as Level 3.
Short-term Investments — Privately-held. Short-term investments which are classified as privately-held consist of debt securities with a maturity greater than three months but less than one year from the debt of purchase. Short-term investments are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are determined using discounted cash flow models and are classified as Level 3.
The following table summarizes the quantitative inputs and assumptions used for financial assets categorized as Level 3 under the fair value hierarchy as at December 31, 2024:
At December 31, 2024Fair Value
Level 3		Valuation Techniques

 Unobservable Inputs
RangesWeighted Average
($ in millions)
Privately-held investments, available for sale
Asset-backed securities$24.2 Discounted cash flowDiscount rate5.5%—9.5%7.1%
Privately-held investments, trading
Commercial mortgage loans79.7 Discounted cash flowDiscount rate3.8%—11.9%5.7%
Middle market loans and other private debt
61.0 Discounted cash flowDiscount rate7.2%—18.0%9.8%
Asset-backed securities127.6 Discounted cash flowDiscount rate5.4%—8.3%6.6%
Global corporate securities14.1 Discounted cash flowDiscount rate6.7%—6.7%6.7%
Global corporate securities4.4 Transaction valuen/an/an/an/a
Total$311.0 
Catastrophe Bonds. Catastrophe bonds are variable rate fixed income instruments with redemption values adjusted based on the occurrence of a covered event, usually windstorms and earthquakes. Catastrophe bonds are classified as trading and reported at fair value. Catastrophe bonds are priced using an average of multiple broker-dealer quotes and as such, are classified as Level 2. 
Foreign Exchange Contracts.  The foreign exchange contracts which the Company uses to mitigate currency risk are characterized as OTC due to their customized nature and the fact that they do not trade on a major exchange. These instruments trade in a very deep liquid market, providing substantial price transparency and accordingly are classified as Level 2.
Derivative Liabilities - Loss Portfolio Transfer. The LPT embedded derivative is valued using the Black-Scholes model. The two primary inputs of this model are expected claim settlement patterns and expected return of the investment portfolio above a fixed minimum rate over the specified time horizon. The expected claim settlement pattern is determined on an actuarial basis for the cohort of business within scope of the LPT and is consistent with the patterns used in the valuation of technical provisions. The expected return of the investment portfolio, above a fixed minimum rate, directly impacts on the LPT derivative valuation and is subject to changes in the market conditions. In order to assess the reasonableness of the inputs, the Company updates the expected claim settlement patterns on a regular basis while maintaining an understanding of the current market conditions. The LPT embedded derivative is classified as Level 3.
Other Investments. The Company’s other investments represent primarily our investments in investment funds operating strategies across real estate, infrastructure and direct lending. Adjustments to the fair values are made based on the net asset value of the investments. The net valuation criteria established by the manager of such investments are established in accordance with the governing documents and the asset manager’s valuation guidelines, which include: the discounted cash flows method and the performance multiple approach, which uses a multiple derived from market data of comparable companies or assets to produce operating performance metrics. Alternative valuation methodologies may be employed for investments with unusual characteristics.
v3.25.1
Reinsurance
 12 Months Ended
Dec. 31, 2024
Reinsurance Disclosures [Abstract]  
Reinsurance Reinsurance
The Company purchases retrocession and reinsurance to limit and diversify the Company’s risk exposure and to increase its own insurance and reinsurance underwriting capacity. These agreements provide for recovery of losses and loss adjustment expenses from reinsurers. The Company remains liable to the extent that reinsurers do not meet their obligations under these agreements. In line with its risk management objectives, the Company evaluates the financial condition of its reinsurers and monitors concentrations of credit risk.
Balances pertaining to reinsurance transactions are reported “gross” on the consolidated balance sheet, meaning that reinsurance recoverable on unpaid losses and ceded unearned premiums are not deducted from insurance reserves but are recorded as assets. For more information on reinsurance recoverables, refer to Note 22, “Concentrations of Credit Risk — Reinsurance recoverables” and Note 10, “Reserve for Losses and Loss Adjustment Expenses” of these consolidated financial statements.
The effect of assumed and ceded reinsurance on premiums written, premiums earned and losses and loss adjustment expenses for the twelve months ended December 31, 2024, 2023 and 2022 was as follows:
 
Twelve Months Ended December 31,
 202420232022
 ($ in millions)
Premiums written:
   
Insurance$2,723.5 $2,446.6 $2,531.7 
Reinsurance1,885.8 1,521.0 1,807.0 
Ceded(1,666.7)(1,385.7)(1,442.7)
Net written premiums
$2,942.6 $2,581.9 $2,896.0 
    
Premiums earned:   
Insurance$2,565.7 $2,444.8 $2,370.8 
Reinsurance1,822.1 1,562.0 1,617.2 
Ceded(1,498.1)(1,392.3)(1,299.3)
Net earned premiums
$2,889.7 $2,614.5 $2,688.7 
    
Losses and loss adjustment expenses:   
Insurance$1,759.1 $1,644.5 $1,574.2 
Reinsurance915.8 707.2 939.5 
Ceded(957.1)(798.7)(833.7)
Losses and loss adjustment expenses$1,717.8 $1,553.0 $1,680.0 
Current expected credit loss model (“CECL”). As at December 31, 2024, the Company’s allowance for expected credit losses was $27.5 million (2023 — $3.7 million). For the twelve months ended December 31, 2024 there was a $23.8 million increase in the CECL allowance on reinsurance recoverables (2023 — no change, 2022 — $0.4 million increase).
The Company is potentially exposed to concentrations of credit risk in respect of amounts recoverable from reinsurers, refer to Note 22, “Concentrations of Credit Risk — Reinsurance recoverables” of these consolidated financial statements for more detail.
v3.25.1
Derivative Contracts
 12 Months Ended
Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Derivative Contracts Derivative Contracts
The following table summarizes information on the location and amounts of derivative fair values on the consolidated balance sheet as at December 31, 2024 and 2023:
  As at December 31, 2024 As at December 31, 2023
Derivatives Not Designated as Hedging Instruments
Under ASC 815		Balance Sheet Location
Notional Amount
Fair Value
 
Notional Amount
Fair Value
  ($ in millions) ($ in millions)
Foreign Exchange Contracts
Derivative assets
$550.0 $17.0 $1,262.1 $31.4 
Foreign Exchange Contracts (1)
Derivative liabilities$1,036.9 $(41.7)$540.8 $(9.3)
Loss Portfolio Transfer Liability - Embedded Derivative (2)
Derivative liabilities$— $(3.6)$— $(16.5)
 ______________ 
(1)    Fair value is net of $0.8 million of cash collateral (December 31, 2023 — $3.4 million).
(2)    The LPT contains an embedded derivative within the contract in relation to the variable interest crediting rate.
  As at December 31, 2024 As at December 31, 2023
Derivatives Designated as Cash Flow Hedges Under ASC 815
Balance Sheet LocationNotional
Amount		Fair
Value		 Notional
Amount		Fair
Value
  ($ in millions) ($ in millions)
Foreign Exchange ContractsDerivative assets$— $— $76.9 $0.3 
Foreign Exchange Contracts (1)
Derivative liabilities
$158.0 $(4.2)$— $— 
 ______________ 
(1)    Fair value is net of $2.0 million of cash collateral (December 31, 2023 — $Nil ).
The following table provides the unrealized and realized (losses)/gains recorded in the consolidated statements of operations and other comprehensive income for derivatives that are not designated or designated as hedging instruments under ASC 815 — “Derivatives and Hedging” for the twelve months ended December 31, 2024 and 2023:
Amount of (Loss)/Gain Recognized on Derivatives
For the Twelve Months Ended
Location of (Loss)/Gain
Recognized on Derivatives
December 31, 2024December 31, 2023
Derivatives not designated as hedges($ in millions)
Foreign Exchange ContractsChange in Fair Value of Derivatives$(34.0)$10.9 
Loss Portfolio Transfer Liability - Embedded DerivativeChange in Fair Value of Derivatives$12.9 $15.2 
Derivatives designated as cash flow hedges
Foreign Exchange ContractsGeneral, administrative and corporate expenses in consolidated statement of operations$(0.9)$(8.1)
Foreign Exchange Contracts
Net change gross of tax from current period hedged transactions in other comprehensive income
$(6.5)$(14.0)
Foreign Exchange Contracts. The Company uses foreign exchange contracts to manage foreign currency risk associated with our operating expenses but also foreign exchange risk associated with net assets or liabilities in currencies other than the U.S. dollar. A foreign exchange contract involves an obligation to purchase or sell a specified currency at a future date at a price set at the time of the contract. Foreign exchange contracts will not eliminate fluctuations in the value of the Company’s assets and liabilities denominated in foreign currencies but rather allow it to establish a rate of exchange for a future point in time.
As at December 31, 2024, the Company held foreign exchange contracts that were not designated as hedges under ASC 815 with an aggregate nominal amount of $1,586.9 million (2023 — $1,802.9 million). The foreign exchange contracts are recorded as derivative assets or derivative liabilities in the consolidated balance sheet with changes recorded as a change in fair value of derivatives in the consolidated statement of operations. For the twelve months ended December 31, 2024, the impact of foreign exchange contracts on net income was a loss of $34.0 million (December 31, 2023 — gain of $10.9 million).
As at December 31, 2024, the Company held foreign exchange contracts that were designated as cash flow hedges under ASC 815 with an aggregate notional amount of $158.0 million (2023 — $76.9 million). The foreign exchange contracts are recorded as derivative assets or derivative liabilities in the consolidated balance sheet with the changes in fair value recorded in other comprehensive income. For the twelve months ended December 31, 2024 the company recognized a loss of $6.5 million (December 31, 2023 — loss of $14.0 million) in other comprehensive income.
As the foreign exchange contracts settle, the realized gain or loss is reclassified from other comprehensive income into general, administrative and corporate expenses in the consolidated statement of operations. For the twelve months ended December 31, 2024, the amount recognized within general, administrative and corporate expenses for settled foreign exchange contracts was a realized loss of $0.9 million (December 31, 2023 — loss of $8.1 million). The Company estimates that $6.2 million of the existing losses as at December 31, 2024 is expected to be reclassified into earnings within the next 12 months.
Embedded derivative on loss portfolio contract. The loss portfolio transfer contract includes a funds withheld arrangement that provides returns to the reinsurer based on Aspen’s investment performance, guaranteeing a minimum of 1.75% return. Such funds withheld arrangements are examples of embedded derivatives and therefore this instrument is accounted for as an option-based derivative. For the twelve months ended December 31, 2024, the amount recognized as a change in fair value of derivatives in the consolidated statement of operations is a gain of $12.9 million (December 31, 2023 — gain of $15.2 million).
v3.25.1
Deferred Policy Acquisition Costs
 12 Months Ended
Dec. 31, 2024
Insurance [Abstract]  
Deferred Policy Acquisition Costs Deferred Acquisition Costs
The following table represents a reconciliation of beginning and ending deferred acquisition costs for the twelve months ended December 31, 2024 and 2023:
Twelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023
($ in millions)
Balance at the beginning of the period$296.2 $319.0 
Acquisition costs deferred446.1 357.4 
Amortization of deferred acquisition costs(420.2)(380.2)
Balance at the end of the period$322.1 $296.2 
v3.25.1
Reserves for Losses and Adjustment Expenses
 12 Months Ended
Dec. 31, 2024
Insurance [Abstract]  
Reserves for Losses and Adjustment Expenses Reserve for Losses and Loss Adjustment Expenses
The following table represents a reconciliation of beginning and ending consolidated reserve for losses and loss adjustment expenses for the twelve months ended December 31, 2024, 2023 and 2022:
As at December 31,
202420232022
 ($ in millions)
Reserve for losses and LAE at the start of the year$7,810.6 $7,710.9 $7,611.8 
Less reinsurance recoverable(4,577.8)(4,897.7)(3,298.1)
Net reserve for losses and LAE at the start of the year3,232.8 2,813.2 4,313.7 
Net loss and LAE expenses disposed (1)
— — (1,840.1)
Movement in net reserve for losses and LAE for claims incurred:
Current year1,682.2 1,492.2 1,651.9 
Prior years 35.6 60.8 28.1 
Total incurred1,717.8 1,553.0 1,680.0 
Net Losses and LAE payments for claims incurred:
Current year(200.2)(161.1)(192.7)
Prior years(741.3)(1,011.9)(1,098.4)
Total paid(941.5)(1,173.0)(1,291.1)
Foreign exchange (gains)/losses(58.5)39.6 (49.3)
Net reserve for losses and LAE at the end of the year3,950.6 3,232.8 2,813.2 
Plus reinsurance recoverable on unpaid losses at the end of the year4,172.0 4,577.8 4,897.7 
Reserve for losses and LAE at the end of the year$8,122.6 $7,810.6 $7,710.9 
 ______________ 
(1)    Net loss and LAE expenses disposed of $1,840.1 million represent the net loss reserves as at May 20, 2022 (“Closing Date”) for losses in relation to 2019 and prior accident years, in addition to the $770.0 million of ceded reserves under the previous ADC agreement, recognizing a total recoverable of $2,610.1 million. These reserves were rolled forward from the initial effective date of September 30, 2021, at which time the net losses reserves were $3,120.0 million.
As at December 31, 2024, the total amount recoverable from Enstar under the LPT was $1,190.9 million (December 31, 2023 — $1,627.4 million) which includes claims paid and reserve development since the Closing Date.
For the twelve months ended December 31, 2024, there was an increase of $35.6 million in the Company’s estimate of the ultimate claims to be paid in respect of prior accident years compared to an increase of $60.8 million for the twelve months ended December 31, 2023.
The following tables show an analysis of incurred claims and allocated loss adjustment expenses, net of reinsurance and cumulative paid claims and allocated claim adjustment expenses, net of reinsurance for each of the years ended December 31, 2015 through 2024. Under the LPT agreement, the Company has reinsured net losses incurred on all accident years 2019 and prior. This has resulted in IBNR in the loss development triangles for 2019 and prior to be Nil. The loss development triangles are derived from all business written by the Company as although a limited number of contracts are written which have durations of greater than one year the contracts do not meet the definition of a long duration contract. All amounts included in the following tables related to transactions denominated in a foreign currency have been translated into U.S. Dollars using the exchange rates in effect at December 31, 2024.
The Company has chosen to disaggregate the business in its Insurance segment, for the purposes of these loss development triangles as: Property; Casualty; Marine, Aviation and Energy; and Financial and Professional insurance lines. The Company considers that this presentation of its Insurance lines loss development triangles more precisely reflects meaningful trending information. The Company presents its loss development triangles for the Reinsurance segment in line with the reportable reinsurance lines: Property Catastrophe and Other Property; Casualty; and Specialty.
Property Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
 
For the Years Ended December 31, 
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$236.0 $201.7 $196.5 $198.8 $199.4 $196.3 $192.3 $192.3 $192.3 $192.3 $— 11,558 
2016235.8 246.8 241.8 243.1 244.4 233.4 232.6 232.6 232.6 — 10,752 
2017292.5 255.6 248.8 250.1 272.1 180.4 180.4 180.4 — 9,711 
2018198.7 200.8 184.8 194.7 184.4 184.4 184.4 — 8,202 
2019124.3 128.3 102.2 189.0 189.0 189.0 — 6,863 
2020202.0 197.5 207.0 212.5 213.0 23.0 7,648 
2021206.3 201.0 194.6 191.1 9.2 6,770 
2022166.0 173.2 170.9 13.5 5,801 
2023150.8 130.1 44.3 4,056 
2024132.6 84.2 1,879 
   Total$1,816.4 
Property Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$56.7 $140.2 $167.4 $176.4 $192.6 $191.3 $192.3 $192.3 $192.3 $192.3 
201666.3 167.3 199.5 221.0 230.3 233.4 232.6 232.6 232.6 
201795.5 186.4 219.0 239.7 233.6 180.4 180.4 180.4 
201860.9 156.1 178.4 172.1 184.4 184.4 184.4 
201948.5 89.9 97.7 189.0 189.0 189.0 
202060.7 123.7 151.2 169.0 178.2 
202158.4 119.2 150.6 162.9 
202241.0 113.2 143.4 
202329.8 65.2 
202419.1 
Total$1,547.5 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$268.9 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$268.9 
 Casualty Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$199.8 $219.8 $182.3 $199.4 $232.0 $230.3 $255.6 $178.9 $178.9 $178.9 $— 4,843 
2016213.3 184.3 179.4 185.8 196.9 241.3 122.9 122.9 122.9 — 4,850 
2017177.9 171.4 175.1 192.5 213.3 60.2 60.2 60.2 — 5,536 
2018120.4 123.3 133.3 162.6 42.6 42.6 42.6 — 5,500 
2019122.9 145.2 152.0 48.1 48.1 48.1 — 5,217 
2020131.8 140.4 139.4 145.5 151.8 38.1 3,888 
2021171.9 186.9 196.1 194.6 81.7 3,679 
2022202.4 212.9 208.7 119.4 3,594 
2023223.1 233.8 156.0 3,105 
2024235.6 203.2 1,782 
Total$1,477.2 
  Casualty Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
($ in millions)
2015$3.1 $16.6 $55.7 $91.0 $136.2 $165.0 $178.9 $178.9 $178.9 $178.9 
20164.1 22.3 39.1 80.6 107.2 122.0 122.9 122.9 122.9 
20173.5 22.5 51.8 94.8 88.1 60.2 60.2 60.2 
20183.1 27.5 42.1 57.3 42.6 42.6 42.6 
20196.2 17.2 63.7 48.1 48.1 48.1 
2020— 9.3 36.0 61.1 91.5 
20213.1 23.3 53.5 91.3 
20228.9 26.6 46.4 
20235.5 3.3 
202436.0 
Total$721.2 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance
$756.0 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$756.0 
Marine, Aviation and Energy Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$294.2 $296.0 $278.7 $283.6 $307.2 $309.9 $317.2 $266.0 $266.0 $266.0 $— 4,079 
2016257.8 228.1 226.4 227.0 216.8 218.6 196.2 196.2 196.2 — 4,437 
2017208.5 199.5 206.0 213.6 224.9 135.3 135.3 135.3 — 6,080 
2018169.3 206.4 207.5 234.5 149.9 149.9 149.9 — 5,201 
2019144.6 152.2 122.7 107.0 107.0 107.0 — 3,699 
2020109.6 110.7 125.0 126.1 150.9 33.5 3,866 
202192.2 95.1 94.7 96.5 11.9 4,787 
2022   107.2 105.3 112.7 25.7 5,410 
2023116.6 110.3 20.8 3,997 
2024109.6 62.3 2,358 
Total$1,434.4 
Marine, Aviation and Energy Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$44.5 $122.2 $172.6 $192.2 $220.1 $255.8 $267.5 $266.0 $266.0 $266.0 
201630.9 81.7 140.6 162.3 188.7 191.7 196.2 196.2 196.2 
201740.0 97.1 139.7 167.7 149.3 135.3 135.3 135.3 
201826.6 104.2 132.5 150.5 149.9 149.9 149.9 
201933.3 72.1 89.3 107.0 107.0 107.0 
202028.5 66.4 88.5 100.9 109.2 
202123.5 52.2 64.4 70.4 
202224.9 57.5 73.5 
202327.8 73.2 
202432.4 
   Total$1,213.1 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$221.3 
All outstanding liabilities before 2015, net of reinsurance— 
Liabilities for claims and claim adjustment expenses, net of reinsurance$221.3 
 Financial and Professional Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$171.7 $173.0 $183.1 $187.0 $188.0 $183.0 $195.8 $144.4 $144.4 $144.4 $— 1,082 
2016188.1 209.1 213.5 199.6 182.8 184.3 133.0 133.0 133.0 — 1,244 
2017203.7 179.7 184.6 185.2 206.8 134.4 134.4 134.4 — 1,758 
2018153.6 169.3 150.7 159.7 109.7 109.7 109.7 — 4,645 
2019245.9 258.1 236.3 130.8 130.8 130.8 — 23,819 
2020345.2 345.5 336.2 349.8 352.2 73.7 106,042 
2021283.9 301.6 293.5 294.8 86.2 34,963 
2022314.1 299.8 268.6 121.3 3,356 
2023338.5 347.6 169.1 3,385 
2024423.2 292.3 3,756 
   Total$2,338.7 
Financial and Professional Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$13.6 $43.2 $69.7 $88.7 $108.8 $137.7 $150.1 $144.4 $144.4 $144.4 
201614.8 70.6 100.7 128.7 124.6 129.2 133.0 133.0 133.0 
201727.0 50.9 82.7 115.8 133.5 134.4 134.4 134.4 
201818.3 72.3 97.6 109.8 109.7 109.7 109.7 
201926.8 86.2 120.4 130.8 130.8 130.8 
202047.3 120.8 173.7 225.0 240.0 
202143.1 90.0 131.1 161.9 
202217.7 75.1 113.4 
202321.3 100.6 
202489.2 
   Total$1,357.4 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$981.3 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$981.3 
Property Catastrophe and Other Property Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$206.7 $181.1 $171.5 $151.4 $166.8 $166.9 $173.0 $151.9 $151.9 $151.9 $— 1,045 
2016257.2 257.2 256.8 236.3 231.8 224.3 221.7 221.7 221.7 — 1,281 
2017544.8 524.9 508.1 496.9 568.9 431.8 431.8 431.8 — 1,940 
2018303.7 329.7 320.5 511.7 283.0 283.0 283.0 — 1,804 
2019209.9 225.0 316.3 157.5 157.5 157.5 — 1,399 
2020312.2 394.2 340.7 352.9 365.2 5.2 1,436 
2021637.7 461.2 479.8 472.5 4.9 1,518 
2022380.5 378.9 372.1 43.6 1,475 
2023223.6 215.0 40.4 1,104 
2024254.5 135.5 737 
   Total$2,925.2 
Property Catastrophe and Other Property Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$35.6 $92.4 $122.0 $135.0 $151.9 $154.2 $155.6 $151.9 $151.9 $151.9 
201654.7 157.1 196.8 207.0 219.5 224.3 221.7 221.7 221.7 
2017122.6 353.3 410.7 434.1 407.3 431.8 431.8 431.8 
2018121.4 266.8 265.6 258.0 283.0 283.0 283.0 
201928.0 134.1 158.8 157.5 157.5 157.5 
202041.1 162.2 232.7 306.0 306.0 
202174.6 229.2 351.5 414.8 
202263.3 193.6 261.3 
202343.9 103.8 
202432.8 
   Total$2,364.6 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$560.6 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$560.6 
Casualty Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$188.9 $195.2 $204.9 $207.6 $205.5 $201.9 $192.2 $115.2 $115.2 $115.2 $— 2,090 
2016226.6 238.7 238.3 248.4 255.8 246.6 135.2 135.2 135.2 — 2,268 
2017238.4 236.4 246.9 246.3 257.7 109.6 109.6 109.6 — 2,346 
2018223.7 252.6 260.6 251.2 91.7 91.7 91.7 — 2,262 
2019230.1 250.8 241.5 52.2 52.2 52.2 — 1,939 
2020250.2 231.2 195.8 178.2 187.2 42.4 1,563 
2021203.5 213.8 203.6 199.4 63.2 1,594 
2022246.6 247.8 246.0 138.5 1,650 
2023268.3 267.7 187.6 1,565 
2024286.9 260.0 848 
Total$1,691.1 
Casualty Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
($ in millions)
2015$3.3 $17.4 $37.5 $64.4 $88.0 $106.8 $115.2 $115.2 $115.2 $115.2 
20168.7 32.6 62.4 94.2 123.8 135.4 135.2 135.2 135.2 
20178.7 29.9 58.1 96.0 109.5 109.6 109.6 109.6 
20187.0 33.0 72.6 91.8 91.7 91.7 91.7 
20199.1 36.0 52.0 52.2 52.2 52.2 
20208.9 27.3 43.5 70.7 100.9 
20217.7 36.8 63.3 96.4 
20229.1 30.7 59.6 
20238.2 35.0 
20249.4 
Total$805.2 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$885.9 
All outstanding liabilities before 2015, net of reinsurance— 
Liabilities for claims and claim adjustment expenses, net of reinsurance$885.9 
Specialty Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$161.6 $164.5 $159.3 $154.0 $152.5 $148.1 $147.9 $129.2 $129.2 $129.2 $— 775 
2016233.9 234.7 232.7 225.9 221.0 208.8 185.8 185.8 185.8 — 943 
2017372.6 385.9 370.0 359.1 352.6 303.3 303.3 303.3 — 1,337 
2018389.3 388.9 387.4 412.0 322.3 322.3 322.3 — 1,428 
2019468.6 491.7 396.9 398.6 398.6 398.6 — 1,557 
2020411.2 598.7 372.9 377.1 369.5 15.1 1,519 
2021155.2 150.3 140.0 136.4 24.3 1,385 
2022192.6 191.6 196.2 98.9 1,458 
2023140.7 144.3 73.0 1,188 
2024153.5 125.6 803 
Total$2,339.1 
Specialty Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$17.2 $54.6 $101.6 $118.6 $127.1 $130.1 $129.9 $129.2 $129.2 $129.2 
201657.9 148.8 162.7 180.5 190.6 192.0 185.8 185.8 185.8 
201793.8 236.6 267.8 302.4 303.3 303.3 303.3 303.3 
201826.5 277.9 310.6 322.1 322.3 322.3 322.3 
2019272.2 379.0 396.9 398.6 398.6 398.6 
2020212.5 269.2 289.6 310.1 333.0 
202128.0 52.8 75.2 87.9 
202225.3 52.6 74.3 
202322.3 48.1 
202414.0 
Total$1,896.5 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$442.6 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$442.6 
Reconciliation of Incurred and Paid Claims Development to total Reserve for Losses and LAE
As at December 31, 2024As at December 31, 2023
 ($ in millions)($ in millions)
Net outstanding liabilities:
Insurance lines
 - Property insurance lines$268.9 $270.8 
 - Casualty insurance lines756.0 636.5 
 - Marine, aviation and energy insurance lines221.3 194.5 
 - Financial and professional insurance lines981.3 837.6 
Total insurance lines$2,227.5 $1,939.4 
Reinsurance lines
 - Property catastrophe and other property reinsurance$560.6 $562.3 
 - Casualty reinsurance885.9 733.6 
 - Specialty reinsurance442.6 394.3 
Total reinsurance lines$1,889.1 $1,690.2 
Net loss and LAE$4,116.6 $3,629.6 
Reinsurance recoverable on unpaid losses:
Insurance lines $2,698.0 $2,821.6 
Reinsurance lines 1,474.0 1,756.2 
Total reinsurance recoverable on unpaid losses$4,172.0 $4,577.8 
Deferred gain on retroactive contracts
$61.2 $27.3 
Unallocated claims incurred58.0 47.9 
Other reinsurance balances recoverable (1)
(311.7)(489.1)
Carbon syndicate reserves26.5 16.7 
Other — 0.4 
$(166.0)$(396.8)
Reserve for losses and LAE at the end of the year$8,122.6 $7,810.6 
____________________
(1)    Other reinsurance balances recoverable primarily include short term recoverables to be collected.
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (unaudited)
Years12345678910
Property insurance lines29.0 %38.0 %13.7 %12.2 %3.3 %(5.8)%— %— %— %— %
Casualty insurance lines4.1 %19.1 %32.2 %23.4 %3.5 %(3.6)%2.1 %— %— %— %
Marine, aviation and energy insurance lines23.1 %34.5 %19.6 %11.7 %2.6 %0.9 %1.7 %(0.2)%— %— %
Financial and professional insurance lines14.0 %28.4 %19.6 %14.7 %4.7 %4.8 %2.9 %(1.3)%— %— %
Property catastrophe and other property reinsurance21.5 %42.7 %16.2 %6.9 %3.2 %1.9 %(0.1)%(0.8)%— %— %
Casualty reinsurance6.1 %19.2 %21.6 %19.1 %11.8 %5.0 %1.8 %— %— %— %
Specialty reinsurance26.7 %32.8 %12.7 %7.6 %3.1 %0.6 %(0.9)%(0.2)%— %— %
v3.25.1
Income Taxes
 12 Months Ended
Dec. 31, 2024
Income Tax Disclosure [Abstract]  
Income Taxes Income Taxes
Aspen Holdings and Aspen Bermuda are incorporated under the laws of Bermuda. Under Bermuda law, the corporate tax rate is currently zero and, as a result, Aspen Holdings and Aspen Bermuda are not taxed on any Bermudian income or capital gains. On December 27, 2023, the Corporate Income Tax Act 2023 received Royal Assent in Bermuda, introducing a 15% corporate tax that applies to Bermuda businesses that are part of multinational enterprise groups. This new corporate tax takes effect for accounting periods beginning on or after January 1, 2025. We have adjusted our deferred tax to account for provisions within the Corporate Income Tax Act that allow for an equitable transition to the new regime including the Economic Transition Adjustments (“ETA”) and opening tax loss carryforward (“OTLC”).
The Company’s U.S. operating companies were subject to a U.S. federal income tax rate of 21%.
The Company’s U.K. operating companies were taxed at the effective U.K. corporate tax rate of 25.0%. The U.K. tax rate changed on April 1, 2023 from 19% to 25%.
Total income tax (benefit)/expense for the twelve months ended December 31, 2024, 2023 and 2022 was allocated as follows:
 Twelve Months Ended December 31,
 202420232022
 ($ in millions)
Income tax (benefit) allocated to net income
$(22.0)$(132.1)$(78.1)
Income tax expense/(benefit) allocated to other comprehensive income
3.3 20.6 (23.9)
Total income tax (benefit)
$(18.7)$(111.5)$(102.0)
Income/(loss) from operations before income taxes and income tax expense/(benefit) attributable to that income/(loss) for the twelve months ended December 31, 2024, 2023 and 2022 is provided in the tables below:
 Twelve Months Ended December 31, 2024
 
Income before tax
Current tax expense
Deferred tax expense/(benefit)
Total income tax expense/(benefit)
 ($ in millions)
Bermuda (1)
$85.3 $— $1.3 $1.3 
U.S. (2)
269.0 62.7 (4.4)58.3 
U.K. (3)
106.9 3.9 (85.3)(81.4)
Other (4)
2.9 — (0.2)(0.2)
Total$464.1 $66.6 $(88.6)$(22.0)
 Twelve Months Ended December 31, 2023
 
Income before tax
Current tax expense
Deferred tax (benefit)/expense
Total income tax (benefit)/expense
 ($ in millions)
Bermuda$148.8 $— $(201.1)$(201.1)
U.S. 236.3 52.4 3.0 55.4 
U.K. 0.7 5.3 0.1 5.4 
Other16.8 7.9 0.3 8.2 
Total$402.6 $65.6 $(197.7)$(132.1)
Twelve Months Ended December 31, 2022
(Loss)/Income before tax
Current tax expense
Deferred tax (benefit)
Total income tax (benefit)/expense
($ in millions)
Bermuda$(103.3)$— $— $— 
U.S34.8 14.8 (102.9)(88.1)
U.K.62.4 7.0 — 7.0 
Other
(20.9)4.7 (1.7)3.0 
Total$(27.0)$26.5 $(104.6)$(78.1)
________________
(1)    We have recorded a deferred tax asset in Bermuda consisting of $158.9 million (2023 — $156.6 million) in respect of the ETA and $40.0 million (2023 — $44.5 million) in respect of an OTLC as a result of the newly enacted Corporate Income Tax Act 2023 in Bermuda. The ETA election allows for an adjustment equal to the difference between the fair market value and carrying value of assets and liabilities. The OTLC allows losses from year 2020 to 2024 to be carried forward. We expect this deferred tax asset to be utilized predominantly over a 10-year period. We expect to incur and pay increased taxes in Bermuda beginning in 2025.
(2)    The U.S. current tax expense of $62.7 million (2023 — $52.4 million) includes $0.2 million (2023 — $0.9 million) of Base Erosion and Anti-abuse Tax.
(3)    The U.K. deferred tax benefit of $85.3 million includes a change in the judgment of the brought-forward valuation allowance of $107.7 million.
(4)    Current tax expense and deferred tax (benefit) in “Other” relates to the branches of Aspen UK and Aspen Bermuda Limited.
As noted above, the tax rate in Bermuda, the Company’s country of domicile, is currently zero. Application of the statutory income tax rate for operations in other jurisdictions produces a differential to the expected income tax (benefit)/expense as shown in the table below. The reconciliation between the income tax (benefit) and the amount that would result from applying the statutory rate for the Company for the twelve months ended December 31, 2024, 2023 and 2022 is provided in the table below:
 Twelve Months Ended December 31,
 202420232022
Income Tax Reconciliation($ in millions)
Income tax benefit at statutory tax rate of zero percent$— $— $— 
Overseas statutory tax rates differential88.1 56.3 16.8 
Base erosion and anti-abuse tax (BEAT) expense0.2 0.9 2.3 
Prior year adjustments (1)
(5.9)6.9 (2.9)
Introduction of Bermuda corporate income tax
2.2 (201.1)— 
Change in valuation allowance (2)
(106.6)4.0 (98.9)
Impact of unrecognized tax benefits (3)
— — — 
Australian non-resident withholding tax— — 1.5 
Foreign exchange0.6 (1.3)(0.3)
Non-deductible expenses0.3 2.5 2.4 
Tax effect of OCI in income statement— — 6.7 
Impact of changes in statutory tax rates
(0.9)(0.3)(5.7)
Total income tax (benefit)
$(22.0)$(132.1)$(78.1)
________________
(1)    The submission dates for filing income tax returns for the Company’s U.S. and U.K. operating subsidiaries are after the submission date of these consolidated financial statements. Accordingly, the final tax liabilities may differ from the estimated income tax expense included in these consolidated financial statements and may result in prior year adjustments being reported. The prior period adjustments for the twelve months ended December 31, 2024 predominantly relate to the determination of the results of the U.K. operating subsidiaries and its branches. The prior period adjustments for the twelve months ended December 31, 2023 and 2022 predominantly relate to the determination of results in the U.K.
(2)    The decrease in valuation allowance in 2024 related to a change in judgment about the recoverability of deferred tax assets in Aspen UK.
    The decrease in valuation allowance in 2022 related to a change in judgment about the recoverability of deferred tax assets in the U.S. operating subsidiaries.
(3)    In 2024, the Company did not have any unrecognized tax benefits.
Income tax returns that have been filed by the Company’s U.S. Operating Subsidiaries are subject to examination for 2021 and later tax years. The Company’s U.K. operating subsidiaries’ income tax returns are potentially subject to examination for 2023 and later tax years as these periods are considered “open” by the U.K. Tax Authority. The Company accrues interest and penalties related to an underpayment of income taxes, if applicable, as income tax expenses. The Company does not believe it will be subject to any penalties in any open tax years.
The tax effects of temporary differences and carryforwards that give rise to deferred tax assets and deferred tax liabilities are presented in the following table as at December 31, 2024 and 2023:
 As at December 31,
 20242023
 ($ in millions)
Deferred tax assets:
Operating loss carryforwards$181.1 $217.2 
Capital loss carryforwards17.8 9.7 
Insurance reserves: Losses and loss adjustment expenses111.2 104.1 
Unrealized losses on investments7.4 8.9 
Accrued expenses11.3 13.4 
Foreign tax credit carryforwards22.0 19.0 
Insurance reserves: Unearned premiums34.5 35.0 
Intangible assets82.7 82.9 
Office properties and equipment14.7 16.5 
Operating lease liabilities15.0 15.6 
Other temporary differences8.1 7.6 
Total deferred tax assets$505.8 $529.9 
Less valuation allowance(64.0)(172.7)
Deferred tax assets, net of valuation allowance$441.8 $357.2 
Deferred tax liabilities:  
Intangible assets$(0.2)$— 
Deferred acquisition costs(31.0)(32.4)
Right-of-use operating lease assets(10.4)(10.4)
Insurance reserves: Losses and loss adjustment expenses— (0.1)
Other temporary differences(3.4)(3.3)
Total deferred tax (liabilities)$(45.0)$(46.2)
Net deferred tax assets
$396.8 $311.0 
Deferred tax liabilities and assets represent the tax effect of carryforwards and temporary differences between the value of assets and liabilities for financial statement purposes and such values as measured by U.K., U.S., Bermuda and other tax laws and regulations.
In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences and carry forwards become deductible or creditable. Management considers the scheduled reversal of existing taxable temporary differences, carryback availability, projected future taxable income, and tax-planning strategies in making this assessment.
As at December 31, 2024, the Company has net operating losses carryforwards for U.S. federal income tax purposes of $324.8 million (2023 — $354.9 million), of which $247.2 million relates to the U.S. operating subsidiaries and $77.6 million to Aspen UK’s U.S. branch. The Company also has net operating losses carryforwards for U.K. corporate tax purposes of $249.5 million (2023 — $248.1 million), deferred syndicate losses of $29.3 million (2023 — $64.5 million profits), and losses in other jurisdictions of $86.1 million (2023 — $97.8 million losses).
The $324.8 million that are available to offset future U.S. federal taxable income will expire between 2032 and 2041. The amount of pre-merger net operating losses carryforwards that can be used each year is limited by section 382 to $6.5 million per year for Aspen UK’s U.S. branch, and $20.8 million per year for the next 15 years for the U.S. operating subsidiaries.
The net operating losses in the U.K. and other jurisdictions are available to offset future corporate income in those jurisdictions over an indefinite period.
For U.S. federal income tax purposes, the Company has capital loss carryforwards of $84.7 million, of which $51.6 million relates to the U.S. operating subsidiaries and $33.1 million to Aspen UK’s branch, expiring between 2026 and 2028.
For U.K. corporate tax purposes, the Company has foreign tax credit carryforwards of $22.0 million (2023 — $19.0 million) which are available to offset future U.K. corporate tax arising on the same foreign source of income over an indefinite period.
A valuation allowance of $22.9 million (2023 — $24.5 million) on U.S. deferred tax assets (which includes these loss carryforwards) has been recognized at December 31, 2024 relating to Aspen UK’s U.S. branch.
A valuation allowance of $26.1 million (2023 — $131.0 million) has been established against U.K. deferred tax assets.
The U.K., U.S. and other jurisdictions valuation allowance combined total is $64.0 million (2023 — $172.7 million).
v3.25.1
Capital Structure
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Capital Structure Capital Structure
The following table provides a summary of the Company’s authorized and issued share capital as at December 31, 2024 and 2023:
 As at December 31, 2024As at December 31, 2023
 Number$ in
Thousands		Number$ in
Thousands
Authorized share capital:
Ordinary Shares $0.01 per share (2023 — $0.01 per share)
750,000,000 $7,500 70,000,000 $700 
Preference Shares $0.0015144558 per share
150,000,000 227 30,000,000 45 
Total authorized share capital$7,727 $745 
Issued share capital:
Issued ordinary shares $0.01 par value per share (2023 — $0.01 par value per share)
60,395,839 $604 60,395,839 $604 
Issued 5.950% preference shares of $0.0015144558 par value per share each with a liquidation preference of $25 per preference share
11,000,000 17 11,000,000 17 
Issued 5.625% preference shares of $0.0015144558 par value per share each with a liquidation preference of $25 per preference share
10,000,000 15 10,000,000 15 
Issued 5.625% preference shares of $0.0015144558 par value per share represented by depositary shares, each with a liquidation preference of $25,000 per preference share (1)
10,000 — 10,000 — 
Issued 7.000% preference shares of $0.0015144558 par value per share represented by depositary shares, each with a liquidation preference of $25,000 per preference share (2)
9,000 — — — 
Total issued share capital$636 $636 
 ______________
(1)    Each depositary share represents a 1/1000th interest in a share of the 5.625% preference shares.
(2)    Each depositary share represents a 1/1000th interest in a share of the 7.000% preference shares.
(a)    Ordinary Shares 
Issued Ordinary Shares. The Company’s issued ordinary shares of par value $0.01 at both December 31, 2024 and 2023 was 60,395,839. The Company did not issue any ordinary shares for the twelve months ended December 31, 2024.
(b)    Preference Shares 
Preference Shares Issuance. On May 2, 2013, the Company issued 11,000,000 5.950% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares, with a liquidation preference of $25 per share (the “AHL PRC Shares”). Net proceeds were $270.6 million, consisting of $275.0 million of total liquidation preference less $4.4 million of issuance expenses. See further information below under “AHL PRC Shares Redemption.”
On September 20, 2016, the Company issued 10,000,000 shares of 5.625% Perpetual Non-Cumulative Preference Shares (the “AHL PRD Shares”). The 2016 Preference Shares have a liquidation preference of $25 per share. Net proceeds were $241.3 million, consisting of $250.0 million of total liquidation preference less $8.7 million of issuance expenses. The AHL PRD Shares are listed on the NYSE under the symbol “AHL PRD.”
On August 13, 2019, the Company issued 10,000,000 depositary shares, each of which represents 1/1000th interest in a share of the newly designated 5.625% Perpetual Non-Cumulative Preference Shares. The depositary shares have a liquidation preference of $25 per share. Net proceeds were $241.6 million, comprising $250.0 million of total liquidation preference less $8.4 million of issuance expenses. The depositary shares are listed on the NYSE under the symbol “AHL PRE.”
On November 26, 2024, the Company issued 9,000,000 depositary shares, each of which represents 1/1000th interest in a share of the newly designated 7.000% Perpetual Non-Cumulative Preference Shares. The depositary shares have a liquidation preference of $25 per share. Net proceeds were $217.0 million, comprising $225.0 million of total liquidation preference less $8.0 million of issuance expenses. The depositary shares are listed on the NYSE under the symbol “AHL PRF.”
AHL PRC Shares Redemption. On November 29, 2024, the Company issued a notice of redemption in connection with all of its issued and outstanding AHL PRC Shares. The redemption took place on January 1, 2025, to be paid on January 2, 2025, and was conducted pursuant to the terms of the certificate of designation, dated May 2, 2013, governing the AHL PRC Shares. Each holder of an AHL PRC Share received $25 per preference share, representing an aggregate amount of $275.0 million. Since the redemption date is also a dividend payment date, the redemption price does not include any declared and unpaid dividends.
v3.25.1
Earnings Per Share
 12 Months Ended
Dec. 31, 2024
Earnings Per Share [Abstract]  
Earnings Per Ordinary Share Earnings Per Ordinary Share
In December 2023, the Company filed a registration statement with the SEC relating to a proposed Initial Public Offering of our ordinary shares. As a result of that filing, and in accordance with the accounting guidance of ASC Topic 260, “Earnings Per Share”, the Company has presented the following disclosure on earnings per ordinary share. This disclosure was new for the fiscal year ended December 31, 2023.
Basic and diluted earnings per ordinary share are calculated by dividing net income available to holders of Aspen Insurance Holdings Limited’s ordinary shares by the weighted average number of ordinary shares outstanding. The following table presents the computation of basic and diluted earnings per ordinary share for the twelve months ended December 31, 2024, 2023 and 2022.
Twelve Months Ended December 31,
202420232022
($ in millions, except share and per share amounts)
Net income
$486.1 $534.7 $51.1 
Less: Preference share dividends
(54.9)(49.9)(44.6)
Net income available to Aspen Insurance Holdings Limited’s ordinary shareholders
$431.2 $484.8 $6.5 
Basic and diluted weighted average ordinary shares outstanding
60,395,83960,395,83960,395,839
Basic and diluted earnings per ordinary share$7.14 $8.03 $0.11 
v3.25.1
Statutory Requirements and Dividends Restrictions
 12 Months Ended
Dec. 31, 2024
Disclosure Statutory Requirements And Dividends Restrictions Summary Of Statutory Requirements And Dividends Restrictions [Abstract]  
Dividend Payment Restrictions [Text Block] Statutory Requirements and Dividends Restrictions
As a holding company, the Company relies on dividends and other distributions from its Operating Subsidiaries to provide cash flow to meet ongoing cash requirements, including any future debt service payments and other expenses, and to pay dividends, if any, to our preference and ordinary shareholders. The Company must comply with the provisions of the Bermuda Companies Act 1981, as amended, (the “Companies Act”) regulating the payment of dividends and distributions.
The ability of the Company’s Operating Subsidiaries to pay the Company dividends or other distributions is subject to the laws and regulations applicable to each jurisdiction, as well as the Operating Subsidiaries’ need to maintain capital requirements adequate to maintain their insurance and reinsurance operations and their financial strength ratings issued by independent rating agencies.
The company law of England and Wales prohibits Aspen UK, AMAL or AUL from declaring a dividend to its shareholders unless it has “profits available for distribution”. The determination of whether a company has profits available for distribution is based on its accumulated realized profits and other distributable reserves less its accumulated realized losses. While the U.K. insurance regulatory laws impose no statutory restrictions on a general insurer’s ability to declare a dividend, the rules of the Prudential Regulation Authority (the “PRA”) require each insurance company within its jurisdiction to maintain its solvency margin at all times. Accordingly, Aspen UK, AMAL and AUL may not pay a dividend if the payment of such dividend would result in their SCR coverage ratio falling below certain levels. In addition, any future changes regarding regulatory requirements, including those described above, may restrict the ability of Aspen UK, AMAL and AUL to pay dividends in the future. As at December 31, 2024, Aspen UK had an accumulated balance of retained losses of approximately $690 million and AUL had an accumulated balance of retained losses of approximately $31 million. Aspen UK held a capital contribution reserve of $879.9 million as at December 31, 2024 which, under certain circumstances, could be distributable.
Aspen Bermuda must comply with the provisions of the Companies Act and the Insurance Act regulating the payment of dividends and distributions. Aspen Bermuda may not in any financial year pay dividends which would exceed 25% of its total statutory capital and surplus, as shown on its statutory balance sheet in relation to the previous financial year, unless it files with the BMA a solvency affidavit at least seven days in advance of payment. As at December 31, 2024, 25% of Aspen Bermuda’s statutory capital and surplus amounted to $322.9 million. Aspen Bermuda must also obtain the prior approval of the BMA before reducing its total statutory capital as set out in its previous year’s financial statements by 15% or more.
Aspen Specialty and AAIC are subject to North Dakota and Texas law, respectively. Under such law, the maximum ordinary dividend which can be paid by insurance companies without prior regulatory approval is subject to statutory restrictions. Ordinary dividends may only be paid out of earned surplus as distinguished from contributed surplus. The maximum amount of ordinary dividend that can be paid without prior regulatory approval is the greater of 10% of a company’s surplus as of December 31 of the preceding year, or the amount of net income from the preceding fiscal year.
Actual and required statutory capital and surplus for the principal Operating Subsidiaries of the Company, excluding its Lloyd’s syndicate, as at December 31, 2024 and December 31, 2023 were estimated as follows:
 As at December 31, 2024
 
U.S.
Bermuda
U.K. 
 ($ in millions)
Required statutory capital and surplus$565.7 $579.3 $277.3 
Actual statutory capital and surplus$1,164.9 $1,761.3 $651.0 
 As at December 31, 2023
 
U.S.
Bermuda
U.K. 
 ($ in millions)
Required statutory capital and surplus$488.9 $601.1 $257.2 
Actual statutory capital and surplus$1,063.1 $1,685.2 $734.7 
As the sole corporate member of our Lloyd’s Syndicate, AUL was required to hold capital at Lloyd’s of $964.6 million as at December 31, 2024, adjusting funding to meet this level on an annual basis in the following Q2 and not holding less than 90% of this amount at any time. As at December 31, 2024, AUL had capital at Lloyd’s of $1,016.7 million of which $465.2 million was provided as Funds at Lloyd’s by Aspen Bermuda.
The Bermuda Monetary Authority is the group supervisor of the Company. The laws and regulations of Bermuda require that the Company maintain a minimum amount of group statutory capital and surplus based on the enhanced capital requirement using the group standardized risk-based capital model of the Bermuda Monetary Authority. The Company is also subject to an early-warning level based on 120% of the enhanced capital requirement which may trigger additional reporting requirements or other enhanced oversight. The statutory capital requirements of the Company’s Operating Subsidiaries are set out above. To the extent that these requirements are met, the Company do not anticipate any dividend restrictions arising as a result of the Company’s enhanced capital requirement.
v3.25.1
Dividends
 12 Months Ended
Dec. 31, 2024
Dividends [Abstract]  
Dividends Dividends
In the twelve months ended December 31, 2024, the Company’s Board of Directors paid the following preference share dividends:
Calendar Quarter
Preference Share Category (1)
Quarterly Total
Declared
Paid
5.950% PS
5.625% PS
5.625% DS
Q1 2024$6,595,600 $3,516,000 $3,515,600 $13,627,200 03/01/2404/01/24
Q2 2024$6,669,300 $3,516,000 $3,515,600 $13,700,900 05/30/2407/01/24
Q3 2024$6,741,900 $3,516,000 $3,515,600 $13,773,500 08/30/2410/01/24
Q4 2024$6,815,600 $3,516,000 $3,515,600 $13,847,200 11/29/2412/30/24
Total Paid
$26,822,400 $14,064,000 $14,062,400 $54,948,800 
Per Share
$2.44 $1.41 $1,406.24 
 ______________
(1)    5.950% Preference Shares (AHL PRC) — Fixed to Floating Rate Perpetual Non-Cumulative Preference Shares.
5.625% Preference Shares (AHL PRD) — Perpetual Non-Cumulative Preference Shares.
5.625% Preference Shares (AHL PRE) are represented by depositary shares, each representing a 1/1000th interest in a share of the 5.625% Preference Shares. The dividend paid per depositary share is likewise 1/1000th of the declared dividend, equivalent to $1.40624 per depositary share.
In the twelve months ended December 31, 2024, the Company paid an ordinary shares dividend of $3.23 per share totalling $195.0 million to Highlands Bermuda Holdco, Ltd., the holder of all the Company’s ordinary shares
v3.25.1
Retirement Plans
 12 Months Ended
Dec. 31, 2024
Retirement Benefits [Abstract]  
Retirement Plans Retirement Plans
The Company operates defined contribution retirement plans for the majority of its employees at varying rates of their salaries. Total contributions by the Company to the retirement plans were $16.9 million in the twelve months ended December 31, 2024 (2023 — $14.5 million, 2022 — $12.5 million).
v3.25.1
Share-Based Payments and Long-Term Incentive Plan
 12 Months Ended
Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Share Based Payments and Long-term Incentive Plan Share-Based Payments and Long-Term Incentive Plan
In 2019, the Company implemented a new long-term incentive scheme, under which annual awards are split equally between Performance Units and Exit Units. Performance units vest after two years subject to the Company achieving certain thresholds of operating income over a two year period. Exit Units vest upon change of control (sale or IPO) and achieving predetermined multiplies of invested capital return targets. Both Performance Units and Exit Units are cash-based awards.
During 2024, the Company amended the long-term incentive scheme, whereby the Exit Units were replaced by annual cash-based Retention Awards on a prospective basis. The Retention Awards vest over a twelve-month period subject to the recipient continuing to remain an employee of Aspen.
The Company’s total share-based compensation/long-term incentive plan expense for the twelve months ended December 31, 2024 was $14.6 million (December 31, 2023 — $5.5 million), which is related to a charge of $9.8 million (December 31, 2023 — $5.5 million) in relation to Performance Units and $4.8 million in relation to Retention Units. The income tax effect of this is not considered to be material. As at December 31, 2024, the Company had recorded a payable of $20.0 million (December 31, 2023 — $7.6 million) related to the long-term incentive plan, which is included within accrued expenses and other payables in the consolidated balance sheet.
Management Equity Plan
During 2023, selected senior employees were granted Management Equity Plan (“MEP”) stock options to acquire non-voting shares at a management equity vehicle affiliated with the Company at no cost to the employee. The stock options vest at the later of (a) certification of the attainment of the underlying operating income goal and (b) the exit or liquidity event, with vesting subject to an exit or liquidity event occurring, a two-year cumulative operating income hurdle being achieved over the cumulative two years ending December 31, 2024, and certain other contractual terms being achieved. The weighted average exercise price of the options is $0.001 and the total number of options granted was 10,000. All of the options were granted in 2023, none vested in 2023 or 2024. During 2024, 900 options were forfeited, leaving an outstanding balance as of December 31, 2024 totalling 9,100.
As of December 31, 2024, no cost has been recognized in relation to the MEP awards as management has determined that it is improbable that the exit or liquidity event will occur. The fair value of the stock options was based on an estimate of the cumulative operating income for the two year period ended December 31, 2024, which included actual results for the year ended December 31, 2024, and an estimate of the exit value using market multiples. The total cost of MEP has been determined based on the estimated fair value as of the original grant date. In the event of an exit or liquidity event, and based upon the aforementioned performance conditions being met at a future date, the cost will be recognized. If management had determined that the performance conditions were probable of achievement as of December 31, 2024, the Company would have recognized an estimated $35.0 million of cumulative stock-based compensation expense as of that date and would have $Nil of unrecognized compensation expense. The fair value of these options as of December 31, 2024 totalled $41.3 million.
v3.25.1
Intangible Assets and Goodwill
 12 Months Ended
Dec. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]  
Intangible Assets and Goodwill Intangible Assets and Goodwill
Aspen’s intangible assets relate to trademarks and licenses to trade in the U.S. and U.K. For the twelve months ended December 31, 2024 and December 31, 2023, the Company had intangible assets and goodwill totaling $19.9 million and $21.7 million, respectively.
The “Aspen” trademark, valued at $1.1 million, $16.7 million of insurance licenses and $2.1 million of goodwill are considered to have an indefinite life and are tested annually for impairment or when events or changes in circumstances indicate that these assets might be impaired.
During the year ended December 31, 2024, the Company sold its investment in Digital Re for no consideration. As a result, the associated goodwill of $1.8 million was fully written off.
For the year ended December 31, 2024, the Company performed its annual qualitative assessment and determined that it was more likely than not that the remaining intangible assets and goodwill are not impaired.
v3.25.1
Operating Leases (Notes)
 12 Months Ended
Dec. 31, 2024
Leases [Abstract]  
Lessee, Operating Leases Operating Leases
As at December 31, 2024, the Company has recognized right-of-use operating lease assets of $53.5 million, net of impairment and operating lease liabilities of $75.6 million. Right-of-use operating lease assets comprise primarily of leased office real estate globally and other assets. For all office real estate leases, rent incentives, including reduced-rent and rent-free periods and contractually agreed rent increases during the lease term, have been included when determining the present value of future cash flows.
As part of the Company’s operating effectiveness and efficiency program, the Company has consolidated its office space. Where negotiations are either in advanced stages of discussion and it is probable that the sub-lease transactions will be completed, or the Company has agreed terms to sub-lease our office space, the Company has assessed the right-of-use lease assets for impairment. During the twelve months ended December 31, 2024, no impairment has been recognized on the right-of-use lease asset (2023 — $Nil).
The Company has no lease transactions between related parties.
Operating lease charge. The following table summarizes the operating lease charge for the twelve months ended December 31, 2024, 2023 and 2022:
For the Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Amortization charge on right-of-use operating leased assets$9.9 $10.7 $10.1 
Interest on operating lease liabilities4.1 4.5 5.4 
Operating lease charge$14.0 $15.2 $15.5 
Lease Liabilities. The following table summarizes the maturity of lease liabilities under non-cancellable leases as of December 31, 2024 and 2023:
December 31, 2024December 31, 2023
 ($ in millions)
Operating leases — maturities
2024
$— $15.4 
2025
15.4 15.1 
2026
14.6 14.3 
2027
13.2 12.8 
2028
13.0 12.7 
2029
10.9 11.2 
Later years21.5 21.2 
Total minimum lease payments$88.6 $102.7 
Less imputed interest(13.0)(16.6)
Total lease liabilities$75.6 $86.1 
Other lease information. The following table summarizes the cash flows on operating leases for the twelve months ended December 31, 2024, 2023 and 2022 and other supplemental information:
For the Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Cash paid for amounts included in the measurement of lease liabilities
 - Operating cash outflow from operating leases$(15.9)$(15.5)$(15.5)
Right-of-use assets obtained in exchange for lease obligations
 - Operating leases$2.1 $0.2 $1.9 
Reduction to Right-of-use assets resulting from reductions to lease obligations
 - Operating leases$0.3 $0.1 $7.0 
Weighted Averages
 - Operating leases, remaining lease terms (years)6.47.38.1
 - Operating leases, average discount rate5.1 %5.0 %5.0 %
v3.25.1
Related Party Transactions
 12 Months Ended
Dec. 31, 2024
Related Party Transactions [Abstract]  
Related Party Transactions Related Party Transactions
Apollo’s indirect subsidiary, Apollo Asset Management Europe PC LLP (“AAME”), serves as the investment manager for the Company and certain of the Company’s subsidiaries, and Apollo’s indirect subsidiary, Apollo Management Holdings, L.P. (“AMH”), provides the Company with management consulting services and advisory services. With effect from January 1, 2025, the rights and obligations of AAME were novated to an affiliate of AAME, Apollo Asset Management Europe LLP.
Additionally, certain employees of Apollo and its affiliates serve on the Board.
A description of relationships and transactions that have existed or that the Company and certain of the Company’s subsidiaries has entered into with Apollo and its affiliates are described below.
Investment Management Relationships
AAME provides centralized asset management investment advisory and risk services for the portfolio of the Company’s investments and investments of such subsidiaries pursuant to the investment management agreements (“IMAs”) that have been entered into with AAME.
In addition, pursuant to the IMAs, AAME may engage sub-advisors or delegates to provide certain of the investment advisory and management services to the Company’s subsidiaries. Such sub-advisors may include affiliates of AAME.
Under each of the IMAs, AAME will be paid an annual investment management fee (the “Management Fee”) which will be based on a cost-plus structure. The “cost” is comprised of the direct and indirect fees, costs, expenses and other liabilities arising in or otherwise connected with the services provided under the IMAs. The “plus” component will be a mark-up in an amount of up to 25% determined based on an applicable transfer pricing study. The Management Fee will be subject to certain maximum threshold levels, including an annual fee cap of 15 bps of the total amount of investable assets. Affiliated sub-advisors, including Apollo Management International LLP, will also earn additional fees for sub-advisory services rendered.
During the year ended December 31, 2024, the Company recognized IMA fees of $9.2 million (2023 — $9.4 million; 2022 — $4.9 million), of which $4.0 million (2023 — $2.1 million) remains payable to AAME at year end.
Management Consulting Agreement
As previously disclosed, the Company entered into a Management Consulting Agreement, dated March 28, 2019 (the “Management Consulting Agreement”), with AMH. Pursuant to the Management Consulting Agreement, AMH will provide the Company management consulting and advisory services related to the business and affairs of the Company and its subsidiaries. The Company will pay AMH in consideration for its services under the Management Consulting Agreement, an annual management consulting fee equal to the greater of (i) 1% of the consolidated net income of the Company and its subsidiaries for the applicable fiscal year, or (ii) $5 million.
During the year ended December 31, 2024, the Company recognized Management Consulting fees of $5.0 million (2023 — $5.0 million; 2022 — $5.0 million), of which $1.3 million remains payable to AMH at year end (2023 — $1.2 million).
Related Party Investments
During the year, the Company bought or held the following securities or investments in Apollo:
As at December 31, 2024, the Company’s investment in Funds managed by Apollo had a fair value of $78.6 million (2023 — $39.8 million). During the twelve months ended December 31, 2024, the Company incurred income of $0.4 million (2023 — losses of $0.4 million; 2022 — income of $3.1 million) which is included in net investment income on the consolidated statement of operations and other comprehensive income. These investments are included in other investments on the consolidated balance sheet.
As at December 31, 2024, the Company’s investment in Notes issued by special purpose vehicles established and managed by subsidiaries of Apollo had a fair value of $66.6 million (2023 — $82.2 million). During the twelve months ended December 31, 2024, the Company recognized income of $5.5 million (2023 — income of $5.5 million; 2022 — losses of $0.4 million) which is included in the consolidated statement of operations and other comprehensive income. These investments are included in privately-held investments on the consolidated balance sheet.
As at December 31, 2024, the Company’s investments in Collateralized Loan Obligations issued by special purpose vehicles established and managed by subsidiaries of Apollo had a fair value of $88.9 million (2023 — $129.8 million). During the twelve months ended December 31, 2024, the Company recognized income on these investments of $11.3 million (2023 — income of $17.4 million; 2022 —$Nil) which is included in the consolidated statement of operations and other comprehensive income. Of these investments, $74.9 million are included in fixed income securities, trading, and $14.0 million are included in fixed income securities, available for sale on the consolidated balance sheet.
As at December 31, 2024, the Company’s investments in Middle Market Loans originated and managed by a subsidiary of Apollo had a fair value of $7.0 million (2023 — $45.1 million). During the twelve months ended December 31, 2024, the Company recognized income of $0.5 million (2023 — income of $5.8 million; 2022 — $Nil) which is included in the consolidated statement of operations and other comprehensive income. The Middle Market Loans are included in privately-held investments on the consolidated balance sheet.
Other Payables to Related Parties
As at year end December 31, 2024, the Company had an intercompany payable balance of $1.2 million (2023 — $1.2 million), due to its parent, Highlands Bermuda Holdco, Ltd.
v3.25.1
Commitments and Contingencies
 12 Months Ended
Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
Commitments and Contingencies Commitments and Contingent Liabilities
(a)Restricted assets
The Company’s subsidiaries are obliged by the terms of its contractual obligations to U.S. policyholders and by obligations to certain regulatory authorities to facilitate issue of letters of credit or maintain certain balances in trust funds for the benefit of policyholders.
The following table details the forms and values of the Company’s material restricted assets as at December 31, 2024 and 2023:
As at December 31, 2024As at December 31, 2023
 
($ in millions, except for percentages)
Regulatory trusts and deposits:
Affiliated transactions$433.4 $660.8 
Third party2,713.5 2,714.4 
Letters of credit / guarantees (1)
153.2 172.0 
Total restricted assets (excluding illiquid assets)$3,300.1 $3,547.2 
Other investments — illiquid assets267.2 209.3 
Total restricted assets and illiquid assets$3,567.3 $3,756.5 
Total as percentage of cash and invested assets (2)
46.4 %50.2 %
_____________
(1)    As at December 31, 2024, the Company had pledged funds of $153.2 million (December 31, 2023 — $172.0 million) as collateral for the secured letters of credit.
(2)    Investable assets comprise total investments, cash and cash equivalents, accrued interest, receivables for securities sold and payables for securities purchased.
Investment Funds. We invest in investment funds which, as is typical for this type of investment, have lock-up periods. A lock-up period is the initial amount of time an investor is contractually required to remain invested before having the ability to redeem. As at December 31, 2024, the lock-up periods across these funds range from one quarter to several years. Thereafter these funds could also be redeemed on a pro-rata basis depending on the liquidity position of the fund. There are no assurances as to when the Company may be able to withdraw, in whole or in part, its redemption request from the fund.
Letters of Credit. The Company’s current arrangements with our bankers for the issue of letters of credit require us to provide collateral in the form of cash and investments for the full amount of all secured and undrawn letters of credit that are outstanding. We monitor the proportion of our otherwise liquid assets that are committed to trust funds or to the collateralization of letters of credit. As at December 31, 2024 and 2023, these funds amounted to approximately 46.4% of the $7.7 billion and approximately 50.2% of the $7.5 billion of investable assets held by the Company, respectively. We do not consider that this unduly restricts our liquidity at this time. For more information on our credit facilities and long-term debt arrangements, refer to Note 24, “Credit Facilities and Long-term Debt” of these consolidated financial statements.
Funds at Lloyd’s. AUL operates at Lloyd’s as the corporate member for Syndicate 4711. AUL also participates in underwriting activities of Carbon Syndicate 4747. Lloyd’s determines required regulatory capital by considering the underwriting activities that AUL participates in. Such capital, called Funds at Lloyd’s, consists of investable assets as at December 31, 2024 in the amount of $471.9 million (2023 — $517.4 million).
The amounts provided as Funds at Lloyd’s will be drawn upon and become a liability of the Company in the event of Syndicate 4711 declaring a loss at a level that cannot be funded from other resources, or if Syndicate 4711 requires funds to cover a short-term liquidity gap. The amount which the Company provides as Funds at Lloyd’s is not available for distribution to the Company for the payment of dividends. Aspen Managing Agency Limited, the managing agent to Syndicate 4711, is also required by Lloyd’s to maintain a minimum level of capital which as at December 31, 2024 was £0.4 million (December 31, 2023 — £0.5 million). This is not available for distribution by the Company for the payment of dividends.
U.S. Reinsurance Trust Fund. For its U.S. reinsurance activities, Aspen UK has established and must retain a multi-beneficiary U.S. trust fund for the benefit of its U.S. cedants so that they may take financial statement credit without the need to post cedant-specific security. The minimum trust fund amount is $20.0 million plus an amount equal to 100% of Aspen UK’s U.S. reinsurance liabilities, which were $648.8 million as at December 31, 2024 and $823.5 million as at December 31, 2023. As at December 31, 2024, the balance (including applicable letter of credit facilities) held in the trust was $1,001.5 million (2023 — $1,016.9 million).
Aspen Bermuda has also established and must retain a multi-beneficiary U.S. trust fund for the benefit of its U.S. cedants so that they may take financial statement credit without the need to post cedant-specific security. The minimum trust fund amount is $20.0 million plus an amount equal to 100% of Aspen Bermuda’s liabilities to its U.S. cedants which was $182.3 million and $320.6 million as at December 31, 2024 and 2023, respectively. As at December 31, 2024, the balance held in the U.S. trust fund and other Aspen Bermuda trusts was $334.0 million (2023 — $394.7 million).
U.S. Surplus Lines Trust Fund. Aspen UK and Syndicate 4711 have also established a U.S. surplus lines trust fund with a U.S. bank to secure liabilities under U.S. surplus lines policies. The balance held in trust as at December 31, 2024 was $150.2 million (2023 — $126.6 million).
U.S. Regulatory Deposits. As at December 31, 2024, Aspen Specialty had a total of $6.9 million (2023 — $6.8 million) on deposit with six U.S. states in order to satisfy state regulations for writing business in those states. AAIC had a further $6.5 million (2023 — $6.4 million) on deposit with twelve U.S. states.
Canadian Trust Fund. Aspen UK has established a Canadian trust fund with a Canadian bank to secure a Canadian insurance license. As at December 31, 2024, the balance held in trust was CAD$219.8 million ($162.7 million) (2023 — CAD$228.4 million).
Australian Trust Fund. Aspen UK has established an Australian trust fund with an Australian bank to secure policyholder liabilities and as a condition for maintaining an Australian insurance license. As at December 31, 2024, the balance held in trust was AUD$78.1 million ($54.1 million) (2023 — AUD$131.0 million).
Swiss Trust Fund. Aspen UK has established a Swiss trust fund with a Swiss bank to secure policyholder liabilities and as a condition for maintaining a Swiss insurance license. As at December 31, 2024, the balance held in trust was CHF4.8 million ($5.7 million) (2023 — CHF9.9 million).
Singapore Fund. Aspen UK and Aspen Bermuda have established segregated Singaporean bank accounts to secure policyholder liabilities and as a condition for maintaining a Singaporean insurance license and meet local solvency requirements. As at December 31, 2024, the total balance in the accounts was SGD$201.7 million ($157.3 million) (2023 — SGD$192.1 million).
(b)Contingent liabilities    
In common with the rest of the insurance and reinsurance industry, the Company is also subject to litigation and arbitration in the ordinary course of business. The Company’s Operating Subsidiaries are regularly engaged in the investigation, conduct and defense of disputes, or potential disputes, resulting from questions of insurance or reinsurance coverage or claims activities. Pursuant to insurance and reinsurance arrangements, many of these disputes are resolved by arbitration or other forms of alternative dispute resolution. Such legal proceedings are considered in connection with estimating the Company’s Reserve for Losses and Loss Adjustment Expenses, as provided on the Company’s consolidated balance sheet.
In some jurisdictions, noticeably the U.S., a failure to deal with such disputes or potential disputes in an appropriate manner could result in an award of “bad faith” punitive damages against the Company’s Operating Subsidiaries. In accordance with ASC 450-20-50-3, for (a) reasonably possible losses for which no accrual is made because any of the conditions for accrual in ASC 450-20-25-2 are not met and (b) reasonably possible losses in excess of the amounts accrued pursuant to ASC 450-20-30-1, the Company will provide an estimate of the possible loss or range of possible loss or state that such an estimate cannot be made.
As at December 31, 2024, based on available information the probability of the ultimate resolution of pending or threatened litigation or arbitrations having a material effect on the Company’s financial condition, results of operations or liquidity is remote.
v3.25.1
Concentration of Credit Risk
 12 Months Ended
Dec. 31, 2024
Risks and Uncertainties [Abstract]  
Concentrations of Credit Risk Concentrations of Credit Risk
The Company is potentially exposed to concentrations of credit risk in respect of amounts recoverable from reinsurers, investments and cash and cash equivalents, and insurance and reinsurance balances owed by the brokers with whom the Company transacts business.
The Company defines credit risk tolerances in line with the risk appetite set by our Board and they, together with the Group’s risk management function, monitor exposures to individual counterparties. Any exceptions are reported to senior management and the Risk Committee of the Board of Directors.
Reinsurance recoverables
At December 31, 2024, the total amount recoverable by the Company from reinsurers was $4,172.0 million (December 31, 2023 — $4,577.8 million). Of the Company’s reinsurance recoverable balance at December 31, 2024, 55.9% is collateralized by our reinsurers, 44.0% is recoverable from reinsurers rated A- or higher by major rating agencies and 0.1% is recoverable from reinsurers rated lower than A- by major rating agencies (December 31, 2023 — 56.8%, 42.9% and 0.3%, respectively). As at December 31, 2024, the Company’s largest uncollateralized exposures to individual reinsurers represent 15.4% (December 31, 2023 —15.9%), 11.5% (December 31, 2023 — 11.1%), and 8.8% (December 31, 2023 — 9.2%) of the uncollateralized reinsurance recoverables.
Under the current expected credit loss model (“CECL”), the Company recognized a provision against reinsurance recoverables of $27.5 million as at December 31, 2024 (December 31, 2023 — $3.7 million). For the twelve months ended December 31, 2024, there was a $23.8 million increase in the CECL allowance on reinsurance recoverables.
Underwriting premium receivables
The total underwriting premium receivable by the Company as at December 31, 2024 was $1,617.0 million (2023 — $1,435.3 million). As at December 31, 2024, $111.1 million of the total underwriting premium receivable balance has been due for settlement for more than one year. The Company assesses the recoverability of premium receivables through a review of policies and the concentration of receivables by broker. The Company has recognized an allowance for credit losses of $24.6 million as at December 31, 2024 (December 31, 2023 — $21.0 million) on underwriting premium receivables.
Investments and cash and cash equivalents
The Company’s investment policies include specific provisions that limit the allowable holdings of a single issue and issuer. As at December 31, 2024, there were no investments in any single issuer, other than the U.S. government and the Canadian government in excess of 2% of the aggregate investment portfolio.
v3.25.1
Reclassifications from Accumulated Other Comprehensive Income
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Reclassifications from Accumulated Other Comprehensive Income Reclassifications from Accumulated Other Comprehensive Income
The following table sets out the components of the Company’s Accumulated Other Comprehensive Income (“AOCI”) that are reclassified into the consolidated statement of operations for the twelve months ended December 31, 2024, 2023 and 2022:
Amount Reclassified from AOCI
Details about the AOCI ComponentsTwelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023Twelve Months Ended December 31, 2022
Affected Line Item in the Consolidated Statement of Operations
 ($ in millions) 
Available for sale:
Realized (gains) on sale of securities$(3.2)$(2.2)$(3.9)Realized and unrealized investment gains
Realized losses on sale of securities62.6 42.4 58.9 Realized and unrealized investment losses
59.4 40.2 55.0 
Income from operations before income tax
Tax on net realized losses of securities
(11.5)(6.6)— Income tax (expense)/benefit
$47.9 $33.6 $55.0 
Net income
Realized derivatives:
Net realized losses/(gains) on settled derivatives
$0.9 $(8.1)$15.4 General, administrative and corporate expenses
Tax on settled derivatives(0.2)— — Income tax (expense)/benefit
$0.7 $(8.1)$15.4 
Net income
Total reclassifications from AOCI to the statement of operations, net of income tax$48.6 $25.5 $70.4 
Net income
v3.25.1
Credit Facilities and Long-term Debt
 12 Months Ended
Dec. 31, 2024
Debt Disclosure [Abstract]  
Credit Facilities and Long-term Debt Credit Facilities and Long-term Debt
In the normal course of its operations, the Company enters into agreements with financial institutions to obtain financing through secured and unsecured credit facilities. As at December 31, 2024, the Company had utilized or drawn on approximately $1.7 billion of capital under these facilities, with additional unutilized capacity available, notably approximately $774 million from the Credit Agreement (defined below) and our FHLBB (defined below) line of credit, with the significant facilities as follows:
Credit Facilities
On December 1, 2021, Aspen Holdings and certain of its direct or indirect subsidiaries (collectively, the “Borrowers”) entered into a Third Amended and Restated Credit Agreement, as further amended from time to time (the “Credit Agreement”) with various lenders and Barclays Bank plc, as administrative agent, which amends and restates the Amended and Restated Credit Agreement, dated as of June 12, 2013 and the Second Amended and Restated Credit Agreement, dated as of March 27, 2017, among Aspen Holdings, certain subsidiaries thereof, various lenders and Barclays Bank plc, as administrative agent. The Credit Agreement will be used by the Borrowers to finance the working capital needs of the Aspen Holdings and its subsidiaries, for letters of credit in connection with the insurance and reinsurance businesses of the Company and its subsidiaries and borrowings for other general corporate purposes. Initial availability under the Credit Agreement was $300.0 million and the Company has the right to request (subject to the terms and conditions of the Credit Agreement) an increase to the credit facility by up to $100.0 million. The Credit Agreement will expire on December 1, 2026.
As at December 31, 2024, there were no borrowings outstanding under the Credit Agreement. The fees and interest rates on the loans and the fees on the letters of credit payable by the Borrowers under the Credit Agreement are based upon the credit ratings for the Company’s long-term unsecured senior, non-credit enhanced debt rating of the Company, as determined by S&P and Moody’s. In addition, the fees for a letter of credit vary based upon whether the applicable Borrower has provided collateral (in the form of cash or qualifying debt securities) to secure its reimbursement obligations with respect to such letter of credit.
Under the Credit Agreement, the Company must not permit (a) consolidated tangible net worth as at the last day of each fiscal quarter of the Company to be less than the sum of (i) $2,019.6 million, (ii) 25% of consolidated net income during the period from January 1, 2021 to and including such last day of such fiscal quarter (if positive) and (iii) 25% of the aggregate net cash proceeds of all issuances by the Company of shares of its capital stock during the period from January 1, 2021 to and including such last day of such fiscal quarter, but excluding (x) any amount included in the Company’s accumulated other comprehensive income or loss related to unrealized gains or losses on available for sale securities and (y) during the period from January 1, 2022, any amount included in net unrealized investment gains or losses, related to unrealized gains or losses on trading securities, (b) the ratio of its total consolidated debt to the sum of such debt plus our consolidated tangible net worth to exceed 35% as at the last day of any fiscal quarter of the Company or (c) any material insurance subsidiary to have a financial strength rating of less than “B++” from A.M. Best. The Credit Agreement contains other customary affirmative and negative covenants, including (subject to various exceptions) restrictions on the ability of the Company and its subsidiaries to incur indebtedness, create or permit liens on their assets, engage in mergers or consolidations, dispose of assets, pay dividends or other distributions, purchase or redeem the Company’s equity securities, make investments and enter into transactions with affiliates. In addition, the Credit Agreement has customary events of default, including (subject to certain materiality thresholds and grace periods) payment default, failure to comply with covenants, material inaccuracy of representation or warranty, bankruptcy or insolvency proceedings, change of control and cross-default to other debt agreements.
Other Credit Facilities.
(i)    On February 7, 2019, Aspen European Holdings Limited (“Aspen European”) and Aspen Holdings (acting as guarantor of Aspen European) entered into a letter of credit facility for the purpose of obtaining a letter of credit in favor of Aspen UK for a sum not to exceed $100.0 million to provide approved regulatory capital for Aspen UK. A letter of credit was issued in favor of Aspen UK for a sum of $100.0 million. This facility was amended and restated with effect from February 7, 2023, pursuant to which the $100.0 million letter of credit was extended to February 11, 2027.
(ii)    On October 31, 2024 AUL and Aspen Holdings (acting as guarantor of AUL), effected an amendment to a letter of credit facility agreement for the account of AUL, pursuant to which a syndicate of lenders issued several letters of credit in an aggregate amount of $430.0 million, for the benefit of Lloyd’s, to support AUL’s Funds at Lloyd’s requirements in connection with the 2025 year of account at Lloyd’s. This further amended the letter of credit facility agreement, dated November 3, 2020, entered into between AUL, Aspen Holdings (acting as guarantor of AUL) and various lenders, for the account of AUL, pursuant to which a lender provided a maximum aggregate amount of $235.0 million, to support AUL’s Funds at Lloyd’s requirements in connection with the 2021 year of account at Lloyd’s, as amended on May 7, 2021, November 1, 2021, May 6, 2022, October 27, 2022, October 24, 2023 and April 29, 2024 in connection with the 2021, 2022 and 2023 underwriting years of account at Lloyd’s, as applicable.
(iii)    On October 31, 2024, AUL and Aspen Holdings (acting as guarantor of AUL) amended a Funds at Lloyd’s Facility Agreement dated November 25, 2020, as amended on December 2, 2021, December 1, 2022, and as further amended on November 29, 2023, for the account of AUL. This facility provides that a maximum aggregate amount of up to £60.0 million of acceptable securities may be deposited with, and for the benefit of, Lloyd’s on behalf of AUL to support AUL’s Funds at Lloyd’s requirements in connection with the 2025 year of account at Lloyd’s.
(iv)    On October 31, 2024, AUL and Aspen Holdings (acting as guarantor of AUL) entered into a Funds at Lloyd’s Facility, for the account of AUL. This facility provides that a maximum aggregate amount of up to £25.0 million of acceptable securities may be deposited with, and for the benefit of, Lloyd’s on behalf of AUL to support AUL’s Funds at Lloyd’s requirements in connection with the 2025 year of account at Lloyd’s.
(v)    On April 1, 2021, the Company’s subsidiaries, AAIC and Aspen Specialty, each established a secured line of credit at Federal Home Loan Bank of Boston (“FHLBB”). Advances may be used to support general corporate purposes. The maximum amount available under these facilities will vary based on the borrower’s net admitted assets or reserve assets (total invested assets) and the lender’s underwriting criteria. Aspen Specialty’s maximum borrowing capacity available from FHLBB upon initial application is 15% of net admitted assets or approximately $262 million, and is subject to North Dakota approval. Under Texas state insurance law, without the prior consent of the Texas Department of Insurance, the amount of assets AAIC may pledge to secure debt obligations is limited to 10% of its reserve assets, resulting in a maximum borrowing capacity for AAIC under its FHLBB facility of approximately $212 million. Neither AAIC nor Aspen Specialty expects to draw on these facilities in the near future.
(vi)    On November 5, 2024, Aspen Holdings effected an amendment to a letter of credit facility dated November 5, 2021 to extend the term for another 3 years. The letter of credit issued under this facility is the for the benefit of Aspen Bermuda, as beneficiary, and has been applied towards the eligible capital of Aspen Bermuda, and classified as ancillary Tier 3 capital of such entity, in accordance with applicable Bermuda laws and regulations. The total commitment under the facility is $100.0 million. A letter of credit in the full amount of the available commitment has been issued to Aspen Holdings under this facility.
(vii)    On December 29, 2021, Aspen Holdings entered into a committed letter of credit facility agreement. The letter of credit issued under this facility is for the benefit of Aspen Bermuda, as beneficiary, and has been applied towards the eligible capital of Aspen Bermuda, and classified as ancillary Tier 3 capital of such entity, in accordance with applicable Bermuda laws and regulations. The total commitment under the facility is $75.0 million. A letter of credit in the full amount of the available commitment has been issued to Aspen Holdings under this facility. In December 2024, the term of the letter of credit was extended for another 3 years.
(viii)    On November 15, and 20, 2023, Aspen Bermuda and Aspen UK each signed a Global Master Repurchase Agreement with two selected banks to enable bilateral repurchase agreement to be entered, with cash and US Government Bonds as eligible collateral for the margin transfer. Advances may be used to support general corporate purposes. As of December 31, 2024, no active repurchase agreement has been entered with either of the banks.
The above credit facilities include certain restrictive covenants customary for facilities of this type, including restrictions on indebtedness, consolidated tangible net worth, and minimum financial strength ratings, with such financial covenants largely consistent with these set forth in the Credit Agreement. In addition, the agreements include default covenants, which could require the Company to fully secure the outstanding amounts thereunder and/or result in the Company not being allowed to issue any new letters of credit.
At December 31, 2024, no conditions of default existed under these facilities.
Debt Facilities
On July 26, 2023, the Company entered into a $300.0 million term loan facility, as amended from time to time, at a borrowing rate of Term Secured Overnight Financing Rate (“SOFR”) plus an applicable margin, which will adjust depending on the form of the loan and long-term debt rating of Aspen Holdings, as determined by specified rating issuers from time to time. The Company drew down on the term loan on November 9, 2023 due November 9, 2026 (the “2026 Term Loan”) and the proceeds were used to settle the 2023 Senior Notes. Subject to applicable law, the 2026 Term Loan will be the senior unsecured obligations of Aspen Holdings and will rank equally in right of payment with all of our other senior unsecured indebtedness from time to time outstanding. The Company has recorded the long-term debt at amortized cost in the consolidated balance sheet. Interest incurred on the long-term debt is included within interest expense in the consolidated statement of operations. The interest expense for the twelve months ended December 31, 2024 was $20.5 million (December 31, 2023 — $3.0 million).
The following table summarizes our contractual obligations under long-term debt as at December 31, 2024.
 
Payments Due By Period
Contractual Basis
Less than 1 year
1-3 years
3-5 years 
More than 5 years
Total
 ($ in millions)
Long-term Debt Obligations$— $300.0 $— $— $300.0 
v3.25.1
Credit Losses
 12 Months Ended
Dec. 31, 2024
Credit Loss [Abstract]  
Allowance for Expected Credit Losses Allowance for Expected Credit Losses
The following tables summarize the Company’s allowance for expected credit losses for the twelve months ended December 31, 2024 and December 31, 2023 in available for sale investments, reinsurance recoverables and receivables:
Available for Sale InvestmentsDecember 31,
20242023
($ in millions)
Balance at the beginning of the period$2.9 $7.7 
Additions to the allowance for credit losses on securities for which credit losses were not previously recognized0.3 0.3 
Decreases to the allowance for credit losses on securities that had an allowance in the prior period
(0.9)(3.6)
Reductions to the allowance for securities sold(1.3)(1.5)
Balance at the end of the period$1.0 $2.9 
December 31, 2024December 31, 2023
Reinsurance RecoverablesReceivablesReinsurance RecoverablesReceivables
($ in millions)($ in millions)
Balance at the beginning of the year$3.7 $21.0 $3.7 $25.0 
Movement in the year23.8 3.6 — (4.0)
Balance at the end of the year$27.5 $24.6 $3.7 $21.0 
v3.25.1
Subsequent Events
 12 Months Ended
Dec. 31, 2024
Subsequent Events [Abstract]  
Subsequent Events Subsequent Events
On February 28, 2025, the Company’s Board of Directors declared the following dividends:
DividendPayable on:Record Date:
5.625% Preference Shares (AHL PRD)
$0.3516 April 1, 2025March 15, 2025
5.625% Preference Shares, represented by depositary shares (AHL PRE)(1)
$351.56 April 1, 2025March 15, 2025
7.000% Preference Shares, represented by depositary shares (AHL PRF) (2)
$612.50 April 1, 2025March 31, 2025
 ______________
(1)    The 5.625% Preference Shares are represented by depositary shares, each representing a 1/1000th interest in a share of the 5.625% Preference Shares. The dividend paid per depositary share is likewise 1/1000th of the declared dividend, equivalent to $0.3516 per depositary share.
(2)    The 7.000% Preference Shares are represented by depositary shares, each representing a 1/1000th interest in a share of the 7.000% Preference Shares. The dividend paid per depositary share is likewise 1/1000th of the declared dividend, equivalent to $0.6125 per depositary share.
Preference Shares Redemption. On November 29, 2024, the Company issued a notice of redemption in connection with all of its issued and outstanding 5.950% Fixed-to-Floating Perpetual Non-Cumulative Preference Shares (the “AHL PRC Shares”) (NYSE: AHLPRC). The redemption took place on January 1, 2025, to be paid on January 2, 2025, and was conducted pursuant to the terms of the certificate of designation, dated May 2, 2013, governing the AHL PRC Shares. Each holder of an AHL PRC Share received $25 per preference share, representing an aggregate amount of $275.0 million. Since the redemption date is also a dividend payment date, the redemption price does not include any declared and unpaid dividend.
California Wildfires. The California Wildfires, commencing in January 2025, have led to a range of publicly available industry insured loss estimates in the range of $35 to $45 billion. Based solely on the Company’s modeled loss projections, industry loss estimates and exposure analysis as of the date of this report, the Company’s preliminary assessment of pre-tax losses associated with the California Wildfires is expected to be between $50 and $75 million, net of outwards reinsurance and reinstatement premiums. The Company’s actual losses from the California Wildfires may differ materially from this preliminary estimate due to limitations in one or more of the models and because, as a recent large catastrophe event, this preliminary estimate is not based on actual terms and conditions of individual treaties and policies expected to be impacted, future loss information expected to follow from clients and brokers, further market intelligence, or any loss reports. The final settlement of claims associated with the California Wildfires is likely to take place over a considerable period of time.
v3.25.1
Schedule I - Investments
 12 Months Ended
Dec. 31, 2024
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]  
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Text Block]
SCHEDULE I - CONSOLIDATED SUMMARY OF INVESTMENTS
OTHER THAN INVESTMENTS IN RELATED PARTIES
For the Twelve Months Ended December 31, 2024
($ in millions)
Type of investment
Amortized Cost or Cost
Fair Value
Amount at which shown in the Balance Sheet
Fixed income securities
U.S. government$1,767.7 $1,741.9 $1,741.9 
U.S. agency7.5 7.2 7.2 
Municipal85.8 83.9 83.9 
Corporate2,200.8 2,137.5 2,137.5 
High Yield Loans101.7 102.4 102.4 
Non-U.S. government-backed corporate135.7 134.1 134.1 
Non-U.S. government272.6 271.2 271.2 
Asset-backed (1)
767.7 770.8 859.7 
Agency commercial mortgage-backed5.0 4.4 4.4 
Agency residential mortgage-backed635.0 549.8 549.8 
Total fixed income securities$5,979.5 $5,803.2 $5,892.1 
Short term investments$262.9 $262.9 $262.9 
Catastrophe bonds$1.0 $1.0 $1.0 
Privately held investments (2)
$312.0 $237.4 $311.0 
Investments, equity method$7.3 $7.3 
Other investments at fair value (3)
$188.6 $267.2 
Total investments$6,589.3 $6,741.5 
_________________
(1)     Fixed income securities, asset-backed excludes related party investments totaling fair value of $88.9 million.
(2)    Privately-held investments excludes related party investments totaling $73.6 million.
(3)    Other investments excludes related party investments of $78.6 million in Funds managed by Apoll
v3.25.1
Schedule II - Condensed Financial Information of Registrant
 12 Months Ended
Dec. 31, 2024
Condensed Financial Information Disclosure [Abstract]  
Schedule II - Condensed Financial Information of Registrant
SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT
BALANCE SHEETS
As at December 31, 2024 and 2023
 As at December 31, 2024As at December 31, 2023
 
($ in millions)
ASSETS 
Fixed income securities (trading)
$44.3 $43.2 
Cash and cash equivalents43.5 43.5 
Investments in subsidiaries (1)
3,361.3 3,284.2 
Intercompany funds due from affiliates20.6 4.3 
Right-of-use operating lease assets1.0 1.5 
Other receivables
275.0 — 
Other assets44.7 5.6 
Total assets$3,790.4 $3,382.3 
LIABILITIES  
Accrued expenses and other payables$20.7 $27.8 
Intercompany funds due to affiliates96.9 144.7 
Long-term debt300.0 300.0 
Operating lease liabilities0.9 1.3 
Total liabilities$418.5 $473.8 
  
SHAREHOLDERS’ EQUITY
Ordinary shares$0.6 $0.6 
Preference shares970.5 753.5 
Additional paid in capital761.2 761.2 
Retained earnings 2,029.7 1,793.5 
Accumulated other comprehensive income, net of taxes:
Unrealized (loss) on investments(198.2)(227.6)
(Loss) on derivatives
(5.3)(0.2)
Cumulative (losses) on foreign currency translation adjustments(186.6)(172.5)
Total accumulated other comprehensive (loss)(390.1)(400.3)
Total shareholders’ equity3,371.9 2,908.5 
Total liabilities and shareholders’ equity$3,790.4 $3,382.3 
____________________
(1)    The Company’s investment in subsidiaries is accounted for under the equity method and adjustments to the carrying value of these investments are made based on the Company’s share of capital, including share of income and expenses. Changes in the value were recognized in “equity in net earnings of subsidiaries and other investments, equity method” in the statement of operations.
ASPEN INSURANCE HOLDINGS LIMITED
SCHEDULE II  - CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONTINUED)
STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME
For the Twelve Months Ended December 31, 2024, 2023 and 2022
 Twelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023Twelve Months Ended December 31, 2022
 ($ in millions)
Operating Activities:
 
Equity in net earnings of subsidiaries and other investments, equity method
$108.9 $304.7 $14.2 
Dividend income511.4 364.4 121.7 
Net realized and unrealized investment gains/(losses)0.5 1.1 (4.0)
Other income4.3 3.2 1.0 
Total revenues$625.1 $673.4 $132.9 
Expenses:   
General, administrative and corporate expenses$(109.5)$(121.3)$(62.7)
Interest expense(21.1)(15.6)(14.3)
Other expense(3.9)(1.8)(4.8)
Income from operations before income taxes
490.6 534.7 51.1 
Income tax expense(4.5)— — 
Net income $486.1 $534.7 $51.1 
Other comprehensive income/(loss), net of taxes:
   
Change in unrealized gains/(losses) on investments$29.4 $105.6 $(367.8)
Net change from current period hedged transactions(5.1)(14.0)15.4 
Change in foreign currency translation adjustment (14.1)14.4 (30.9)
Other comprehensive income/(loss), net of tax10.2 106.0 (383.3)
Comprehensive Income /(loss)
$496.3 $640.7 $(332.2)
ASPEN INSURANCE HOLDINGS LIMITED
SCHEDULE II  - CONDENSED FINANCIAL INFORMATION OF REGISTRANT (CONTINUED)
STATEMENTS OF CASH FLOWS
For the Twelve Months Ended December 31, 2024, 2023 and 2022
 Twelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023Twelve Months Ended December 31, 2022
 ($ in millions)
Cash flows from operating activities:
   
Net income (excluding equity in net earnings of subsidiaries)$377.2 $230.0 $36.9 
Adjustments:   
Realized and unrealized investment (gains)/losses
(0.4)(14.8)19.7 
Loss/(gain) on derivative contracts— 14.0 (15.4)
Depreciation and amortization
0.7 0.5 0.5 
Interest on operating lease liabilities0.1 0.1 0.1 
Change in other assets(39.0)0.3 2.1 
Change in accrued expenses and other payables(7.1)5.5 (3.2)
Change in intercompany activities(64.1)(38.4)41.1 
Change in operating lease liabilities(0.5)(0.5)(0.6)
Net cash provided by operating activities$266.9 $196.7 $81.2 
Cash flows from investing activities:
   
(Purchases) of fixed income securities, trading
$(11.3)$(8.1)$(10.0)
Proceeds from sales and maturities of fixed securities, trading
10.3 6.4 7.8 
Investment in subsidiaries42.0 (105.7)5.0 
Net cash provided by/(used in) investing activities
$41.0 $(107.4)$2.8 
Cash flows from financing activities:
   
Repayment of short-term debt$— $(300.0)$— 
Proceeds from term loan facility— 300.0 — 
Redemption of preference shares
(275.0)— — 
Preference share issuance
217.0 — — 
Dividends paid on ordinary shares(195.0)(40.3)(40.0)
Dividends paid on preference shares(54.9)(49.9)(44.6)
Net cash (used in) financing activities$(307.9)$(90.2)$(84.6)
(Decrease) in cash and cash equivalents— (0.9)(0.6)
Cash and cash equivalents — beginning of period43.5 44.4 45.0 
Cash and cash equivalents — end of period$43.5 $43.5 $44.4 
v3.25.1
Schedule III - Supplementary Insurance Information
 12 Months Ended
Dec. 31, 2024
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]  
Schedule III - Supplementary Insurance Information
SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION
For the Twelve Months Ended December 31, 2024, 2023 and 2022
Supplementary Information     
($ in millions)
Year Ended December 31, 2024
Deferred
Policy
Acquisition
Costs 
Net
Reserves
for Losses
and LAE 
Net
Reserves
for
Unearned
Premiums
Net
Earned
Premiums
Net
Investment
Income 
Losses and
LAE
Expenses 
Policy
Acquisition
Expenses 
Net
Written
Premiums 
General
and
Administrative
Expenses 
Reinsurance$248.2 $1,691.5 $580.0 $1,305.7  $741.3 $227.0 $1,275.7 $141.7 
Insurance73.9 2,259.1 1,164.1 1,584.0  976.5 193.2 1,666.9 264.2 
Total$322.1 $3,950.6 $1,744.1 $2,889.7 $318.0 $1,717.8 $420.2 $2,942.6 $405.9 
Year Ended December 31, 2023
Deferred
Policy
Acquisition
Costs 
Net
Reserves
for Losses
and LAE 
Net
Reserves
for
Unearned
Premiums
Net
Earned
Premiums
Net
Investment
Income 
Losses and
LAE
Expenses 
Policy
Acquisition
Expenses 
Net
Written
Premiums 
General
and
Administrative
Expenses 
Reinsurance$201.5 $1,373.1 $644.5 $1,154.5 $611.1 $208.6 $1,098.0 $120.6 
Insurance94.7 1,859.7 1,048.3 1,460.0 941.9 171.6 1,483.9 233.9 
Total$296.2 $3,232.8 $1,692.8 $2,614.5 $275.7 $1,553.0 $380.2 $2,581.9 $354.5 
Year Ended December 31, 2022
Deferred
Policy
Acquisition
Costs 
Net
Reserves
for Losses
and LAE 
Net
Reserves
for
Unearned
Premiums
Net
Earned
Premiums
Net
Investment
Income 
Losses and
LAE
Expenses 
Policy
Acquisition
Expenses 
Net
Written
Premiums 
General
and
Administrative
Expenses 
Reinsurance$227.2 $1,360.7 $862.4 $1,251.8  $770.3 $252.4 $1,426.4 $142.5 
Insurance91.8 1,452.5 857.8 1,436.9  909.7 179.4 1,469.6 244.0 
Total$319.0 $2,813.2 $1,720.2 $2,688.7 $188.1 $1,680.0 $431.8 $2,896.0 $386.5 
v3.25.1
Schedule IV - Reinsurance
 12 Months Ended
Dec. 31, 2024
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]  
Schedule IV - Reinsurance
SCHEDULE IV - REINSURANCE
For the Twelve Months Ended December 31, 2024, 2023 and 2022
Premiums Written
 
Direct 
Assumed
Ceded 
Net Amount
 ($ in millions)
2024$2,723.5 $1,885.8 $(1,666.7)$2,942.6 
2023$2,446.6 $1,521.0 $(1,385.7)$2,581.9 
2022$2,531.7 $1,807.0 $(1,442.7)$2,896.0 

Premiums Earned
 Gross Amount
Assumed From Other Companies
Ceded to Other Companies
Net Amount
Percentage of Amount Assumed to Net Amount
 ($ in millions, except for percentages)
2024$2,565.7 $1,822.1 $(1,498.1)$2,889.7 63.1 %
2023$2,444.8 $1,562.0 $(1,392.3)$2,614.5 59.7 %
2022$2,370.8 $1,617.2 $(1,299.3)$2,688.7 60.1 %
v3.25.1
Schedule V - Valuation and Qualifying Accounts
 12 Months Ended
Dec. 31, 2024
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
Schedule V - Valuation and Qualifying Accounts
SCHEDULE V - VALUATION AND QUALIFYING ACCOUNTS
For the Twelve Months Ended December 31, 2024, 2023 and 2022
The following table shows the movement in the Company’s valuation and qualifying accounts during the twelve months ended December 31, 2024, 2023 and 2022:
 
Balance at Beginning of Year
Charged to Costs and Expenses
Charged to Other Accounts
Deductions
Balance at End of  Year

($ in millions)
2024
     
Premiums receivable from underwriting activities$21.0 $3.6 $— $— $24.6 
Reinsurance$— $27.5 $— $— $27.5 
2023     
Premiums receivable from underwriting activities$25.0 $(4.0)$— $— $21.0 
Reinsurance$— $— $— $— $— 
2022     
Premiums receivable from underwriting activities$30.2 $(5.2)$— $— $25.0 
Reinsurance$— $— $— $— $— 
v3.25.1
Pay vs Performance Disclosure - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pay vs Performance Disclosure      
Net income $ 486.1 $ 534.7 $ 51.1
v3.25.1
Insider Trading Policies and Procedures
 12 Months Ended
Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]  
Insider Trading Policies and Procedures Adopted true
v3.25.1
Cybersecurity Risk Management and Strategy Disclosure
 12 Months Ended
Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]  
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]
We maintain an enterprise-wide information security and cyber risk management framework (“Framework”) that is designed to protect our information, assets and systems and comply with applicable data security and privacy laws and regulations, in all jurisdictions in which we operate. Our Information Security and Cyber Risk Management Policy is aligned with the National Institute of Standards and Technology (“NIST”) cybersecurity framework and sets out our internal framework to enable a consistent and coordinated approach to ensure that information security risks are adequately addressed in a manner proportionate to the nature, scale and complexity of our operations. Our framework is designed to protect information from the time it is created, through its useful life, to its ultimate authorized disposal.
Our cybersecurity program is designed to provide reasonable assurance that we will have efficient and effective operations; safeguard our assets; produce reliable reporting; comply with applicable laws and regulations; and to identify, protect, detect and respond to, and manage, reasonably foreseeable cybersecurity risks and threats. Our Framework is a key part of our internal control system and uses risk management processes to enable informed and prioritized decisions regarding information and cyber security.
Effective identification of information security and cyber risk enable us to focus and prioritize risk management efforts and determine resources required to manage the risks. We regularly assess risks from cybersecurity and technology threats and monitor our information systems for potential vulnerabilities and incidents. Risk identification processes span the entity, segment, function, and operational levels, to capture key risks within business processes, group-wide risks that are not directly associated with an individual function or process, and changes that could impact the internal control environment. Risk assessment involves a dynamic and iterative process for analyzing information security and cyber risks in order to form the basis for classifying information assets according to their value, sensitivity, and criticality; and for determining how risks should be managed, in accordance with our risk tolerance. Our risk assessment considers threats, vulnerabilities, exploitability, likelihood, and magnitude of impact to our operations, assets, individuals and facilities. Risk assessments also consider risk from external parties, including contractors who operate systems on our behalf, individuals who access our systems or data, service providers, and outsourcing entities. Risk assessments play an important role in the control selection processes. As internal and external circumstances change over time, risk identification also captures emerging information security and cyber risks. These and other emerging risks are reported to the Risk Committee of the Board.
Identified risks are recorded in the Group risk register and categorized, using the NIST security control family taxonomy to categorize and aggregate risk information. Once identified, all key information security and cyber risks are assessed to form the basis for determining how risks should be managed. After information security and cyber controls are implemented, they are regularly monitored and evaluated to determine whether the controls are implemented correctly, operate as intended, produce the desired outcome, and continue to comply with laws, regulations and contractual requirements. Monitoring helps to maintain a dynamic understanding of the Group’s risk profile and identify control deficiencies which require remediation actions.
As part of our risk management process, we conduct application security assessments, vulnerability management, penetration testing, employee phishing testing, security audits, and ongoing risk assessments. We also maintain a variety of incident response plans that are utilized when incidents are detected. We require employees with access to information systems, including all employees, to undertake data protection and cybersecurity training and compliance programs annually.
Where possible, with respect to our cyber risk management processes, controls are implemented with a corresponding performance scale which is used as the basis for establishing monitoring via Key Risk Indicators (“KRIs”). KRIs are measured against the acceptable level of variance in performance relative to the achievement of control objectives and indicate whether controls are adequately addressing risk and whether risks are changing over time. KRIs that fall outside of pre-established thresholds trigger a more thorough management review and assessment, and where appropriate, any necessary adjustments to controls. Control deficiencies that result in exposures that exceed tolerance will be subject to a monitored mitigation plan with an agreed timeline to reduce residual risk to within the tolerance; and included in risk reporting. In such a case, the risk is implicitly temporarily accepted while mitigation actions progress. The development and ownership of an appropriate response is determined by relevant first line stakeholders in consultation with the Group Chief Information Security Officer (“CISO”). The action plan should be proportionate to the level of exposure and include defined actions aligned to the underlying causes.
In some cases, it might be determined that the exposure exceeds risk tolerance and cannot be brought within acceptable levels through any combination of mitigation or risk transfer. In this case, the applicable business function owner will consult with the CISO to determine the best course of action (e.g., through risk avoidance, an exception process, or increased security requirements for the relevant system/process). Exceptions and risk avoidance circumstances should be rare and will be recorded and reported to the Group Executive Committee. Notably, risk avoidance is not the same as ignoring a risk. See "Risk Factors - A failure in our data security and/or technology systems or infrastructure or those of third parties, including those caused by security breaches or cyber-attacks could disrupt our business, damage our reputation and cause losses."
In the normal course, we engage assessors, consultants and other third parties to assist in various cyber-related matters. These engagements cover a range of risk mitigation activities such as threat detection, penetration testing and red/purple team cyber-attack simulations.
We have implemented processes to identify and manage risks from cybersecurity threats associated with our use of such third-party service providers, including in relation to information security, particularly for personal information. These controls include contractual requirements to meet certain information security and testing requirements, alongside ongoing oversight procedures.
Cybersecurity Risk Management Processes Integrated [Flag] true
Cybersecurity Risk Management Processes Integrated [Text Block] Our cybersecurity program is designed to provide reasonable assurance that we will have efficient and effective operations; safeguard our assets; produce reliable reporting; comply with applicable laws and regulations; and to identify, protect, detect and respond to, and manage, reasonably foreseeable cybersecurity risks and threats. Our Framework is a key part of our internal control system and uses risk management processes to enable informed and prioritized decisions regarding information and cyber security.
Cybersecurity Risk Management Third Party Engaged [Flag] true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag] true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag] false
Cybersecurity Risk Board of Directors Oversight [Text Block]
Management has responsibility to manage risk and bring to the Board’s attention the most material near-term and long-term risks to the Company. The Company’s CISO leads management’s assessment and management of cybersecurity risk and is responsible for defining the Framework, and for establishing and maintaining security policies, standards and guidelines for group-wide applicability. Our Company CISO has extensive experience in IT and cybersecurity in particular, spanning over 25 years within multiple industries, including financial services and insurance, including CISO roles at PE owned companies. The CISO reports to the Chief Information Officer, who reports to the Group Chief Operating Officer, who in turn reports directly to the Company’s Group Chief Executive Officer.
The Board is actively engaged in overseeing and reviewing the Company’s strategic direction and objectives, taking into account, among other considerations, the Company’s risk profile and related exposures, as part of this oversight the Board has delegated certain of these responsibilities to committees of the Board. The Risk Committee reviews, on behalf of the Board, at least once annually, the Group’s cybersecurity program, its effectiveness, related exposures and risks, including actions underway or planned to reduce these risks. This review and oversight may generally encompass data breach risk; cyber prevention and detection controls; privacy matters; incident response plan; third-party cyber risk; cyber trends and events; and other cyber topics determined jointly by management and the Risk Committee. In carrying out this role, the Risk Committee takes into account the relevant work of the CISO. The CISO presents to the Risk Committee at least once annually, and the Board receives updates on operational risks, including cybersecurity matters, at its regular quarterly meetings from the Group Chief Operating Officer, alongside second-line oversight updates from the Group Chief Risk Officer. The Internal Audit function also provides third-line oversight of cyber risk elements through periodic testing of our cyber procedures, the results of which are reported to the Risk Committee and subsidiary boards of directors as appropriate.
On the recommendation of the Risk Committee, the Board reviews and approves the Group Information Security and Risk Management Policy on an annual basis and oversees our annual enterprise risk assessment on at least an annual basis to assess key risks within the business, including security and technology risks and cybersecurity threats.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block] The Risk Committee reviews, on behalf of the Board, at least once annually, the Group’s cybersecurity program, its effectiveness, related exposures and risks, including actions underway or planned to reduce these risks.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block] The CISO presents to the Risk Committee at least once annually, and the Board receives updates on operational risks, including cybersecurity matters, at its regular quarterly meetings from the Group Chief Operating Officer, alongside second-line oversight updates from the Group Chief Risk Officer. The Internal Audit function also provides third-line oversight of cyber risk elements through periodic testing of our cyber procedures, the results of which are reported to the Risk Committee and subsidiary boards of directors as appropriate.
Cybersecurity Risk Role of Management [Text Block]
Management has responsibility to manage risk and bring to the Board’s attention the most material near-term and long-term risks to the Company. The Company’s CISO leads management’s assessment and management of cybersecurity risk and is responsible for defining the Framework, and for establishing and maintaining security policies, standards and guidelines for group-wide applicability. Our Company CISO has extensive experience in IT and cybersecurity in particular, spanning over 25 years within multiple industries, including financial services and insurance, including CISO roles at PE owned companies. The CISO reports to the Chief Information Officer, who reports to the Group Chief Operating Officer, who in turn reports directly to the Company’s Group Chief Executive Officer.
Cybersecurity Risk Management Positions or Committees Responsible [Flag] true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block] The Risk Committee reviews, on behalf of the Board, at least once annually, the Group’s cybersecurity program, its effectiveness, related exposures and risks, including actions underway or planned to reduce these risks. This review and oversight may generally encompass data breach risk; cyber prevention and detection controls; privacy matters; incident response plan; third-party cyber risk; cyber trends and events; and other cyber topics determined jointly by management and the Risk Committee. In carrying out this role, the Risk Committee takes into account the relevant work of the CISO. The CISO presents to the Risk Committee at least once annually, and the Board receives updates on operational risks, including cybersecurity matters, at its regular quarterly meetings from the Group Chief Operating Officer, alongside second-line oversight updates from the Group Chief Risk Officer. The Internal Audit function also provides third-line oversight of cyber risk elements through periodic testing of our cyber procedures, the results of which are reported to the Risk Committee and subsidiary boards of directors as appropriate.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block] Our Company CISO has extensive experience in IT and cybersecurity in particular, spanning over 25 years within multiple industries, including financial services and insurance, including CISO roles at PE owned companies.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block] The CISO presents to the Risk Committee at least once annually, and the Board receives updates on operational risks, including cybersecurity matters, at its regular quarterly meetings from the Group Chief Operating Officer, alongside second-line oversight updates from the Group Chief Risk Officer. The Internal Audit function also provides third-line oversight of cyber risk elements through periodic testing of our cyber procedures, the results of which are reported to the Risk Committee and subsidiary boards of directors as appropriate.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag] true
v3.25.1
Basis of Preparation and Significant Accounting Policies Basis of Preparation and Significant Accounting Policies (Policies)
 12 Months Ended
Dec. 31, 2024
Accounting Policies [Abstract]  
Use of Estimates Use of Estimates Assumptions and estimates made by management have a significant effect on the amounts reported within the consolidated financial statements. The most significant of these relate to losses and loss adjustment expenses, reinsurance recoverables, gross written premiums and commissions which have not been reported to the Company such as those relating to proportional treaty reinsurance contracts, unrecognized tax benefits, recoverability of deferred tax assets, the fair value of derivatives and the fair value of other and privately-held investments. 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 for Insurance and Reinsurance Operations Accounting for Insurance and Reinsurance Operations
Premiums Earned. Premiums are generally recorded as written on the inception date of a policy. For proportional reinsurance treaty contracts, written premiums are generally recorded as the reinsured policies attach to the treaty. For multi-year insurance or reinsurance contracts, written premiums are recorded based on the contract terms. Premiums are recognized as revenues proportionately over the coverage period. Premiums earned are recorded in the consolidated statements of operations, net of the cost of purchased reinsurance. Premiums written which are not yet recognized as earned premium are recorded in the consolidated balance sheet as unearned premiums. Written and earned premiums and the related costs include estimates for premiums which have not been finally determined. These relate mainly to contractual provisions for the payment of adjustment or additional premiums, premiums payable under proportional treaties and delegated underwriting authorities, and reinstatement premiums.
Adjustment and additional premiums are premiums charged which relate to experience during the policy term. The proportion of adjustable premiums included in the premium estimates varies between business lines with the largest adjustment premiums being in property and casualty reinsurance, marine, aviation and energy insurance and the smallest in property and casualty insurance.
Premiums under proportional treaty contracts and delegated underwriting authorities are generally not reported to the Company until after the reinsurance coverage is in force. As a result, an estimate of these “pipeline” premiums is recorded. The Company estimates pipeline premiums based on projections of ultimate premium taking into account reported premiums and expected development patterns.
Reinstatement premiums on assumed excess of loss reinsurance contracts are provided based on experience under such contracts. Reinstatement premiums are the premiums charged for the restoration of the reinsurance limit of an excess of loss contract to its full amount after payment by the reinsurer of losses as a result of an occurrence. The original premiums are recognized as revenue in full at the date of loss, with the reinstatement premiums recognized as revenue over the remaining cover term. Reinstatement premiums provide future insurance cover for the remainder of the initial policy term. An allowance for uncollectible premiums is established for possible non-payment of premium receivables, as deemed necessary.
Credit Losses on Underwriting Premiums Receivable. Underwriting premium receivable balances are reported net of an allowance for expected credit losses. The allowance, based on ongoing review and monitoring of amounts outstanding, historical loss data, including write-offs and other current economic factors, is charged to net income in the period the receivable is recorded and revised in subsequent periods to reflect changes in the Company’s estimate of expected credit losses. For most insurance policies, credit risk is partially mitigated by the Company’s ability to cancel the policy if the policyholder does not pay the premium whereby, upon default, policy liabilities would be written-down along with premium receivables.
Losses and Loss Adjustment Expenses. Losses represent the amount paid or expected to be paid to claimants in respect of events that have occurred on or before the balance sheet date. The costs of investigating, resolving and processing these claims are known as loss adjustment expenses (“LAE”). The consolidated statements of operations records these losses net of reinsurance, meaning that gross losses and loss adjustment expenses incurred are reduced by the amounts recovered or expected to be recovered under reinsurance contracts.
Reinsurance. Written premiums, earned premiums, incurred claims, LAE and the acquisition costs all reflect the net effect of assumed and ceded reinsurance transactions. Assumed reinsurance refers to the Company’s acceptance of certain insurance risks that other insurance companies have underwritten. Ceded reinsurance arises from contracts under which other insurance companies agree to share certain risks with the Company.
Reinsurance accounting is followed when there is risk transfer, which includes significant timing risk, underwriting risk, and where applicable, a reasonable possibility of significant loss.
Outward reinsurance premiums, which are paid when the Company purchases reinsurance or retrocessional coverage, are accounted for using the same accounting methodology as the Company uses for inwards premiums. Premiums payable under reinsurance contracts that operate on a “losses occurring during” basis are expensed over the period of coverage while those arising from “risks attaching during” policies are expensed over the earnings period of the underlying premiums written from the reinsured business. Adjustment premiums and reinstatement premiums in relation to outward reinsurance are accrued when it is determined that the ultimate losses will trigger a payment and recognized within premiums payable. Reinsurance and retrocession does not isolate the ceding company from its obligations to policyholders. In the event that a reinsurer or retrocessionaire fails to meet its obligations, the ceding company’s obligations remain.
Accounting for Retroactive Reinsurance Agreements. Retroactive reinsurance agreements are reinsurance agreements under which a reinsurer agrees to reimburse the Company as a result of past insurable events. For retroactive reinsurance purchased by the Company, the excess of the amounts ultimately collectible under the agreement over the consideration paid is recognized as a deferred gain liability which is amortized into income over the settlement period of the ceded reserves once the paid losses have exceeded the minimum retention. The amount of the deferral is recalculated each period based on actual loss payments and updated estimates of ultimate losses. If the consideration paid exceeds the ultimate losses collectible under the agreement, the net loss on the retroactive reinsurance agreement is recognized within income immediately.
Premiums payable for retroactive reinsurance coverage and meeting the conditions of reinsurance accounting are reported as reinsurance recoverables to the extent that those amounts do not exceed recorded liabilities relating to underlying reinsurance contracts. Premiums paid in excess of accounts receivable are charged to income.
Reserves. Insurance reserves are established for the total unpaid cost of claims and LAE in respect of events that have occurred by the balance sheet date, including the Company’s estimates of the total cost of claims incurred but not yet reported (“IBNR”). Claim reserves are reduced for estimated amounts of salvage and subrogation recoveries. Estimated amounts recoverable from reinsurers on unpaid losses and LAE are reflected as assets.
For reported claims, reserves are established on a case-by-case basis within the parameters of coverage provided in the insurance policy or reinsurance agreement. For IBNR claims, reserves are estimated using a number of established actuarial methods to establish a range of estimates from which a management best estimate is selected. Both case and IBNR reserve estimates consider variables such as past loss experience, changes in legislative conditions, changes in judicial interpretation of legal liability, policy coverages and inflation.
As many of the coverages underwritten involve claims that may not be ultimately settled for many years after they are incurred, subjective judgments as to the ultimate exposure to losses are an integral and necessary component of the loss reserving process. The Company regularly reviews its reserves, using a variety of statistical and actuarial techniques to analyze current claims costs, frequency and severity data, and prevailing economic, social and legal factors. Reserves established in prior periods are adjusted as claim experience develops and new information becomes available. Adjustments to previously estimated reserves are reflected in the financial results of the period in which the adjustments are made.
The process of estimating required reserves does, by its very nature, involve considerable uncertainty. The level of uncertainty can be influenced by factors such as the existence of coverage with long duration payment patterns and changes in claims handling practices, as well as the factors noted above. Ultimate actual payments for claims and LAE could turn out to be significantly different from the Company’s estimates.
Credit Losses on Reinsurance Recoverables. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability with the reinsured business. The Company maintains credit risk if a reinsurer is unable to pay recoverables when they become due. To manage this risk, the Company evaluates the financial condition of its reinsurers and retrocessionaires, and monitors concentration of credit risk to minimize its exposure to significant losses from individual reinsurers. To further reduce credit exposure on reinsurance recoverables, the Company has received collateral, including letters of credit and trust accounts, from certain reinsurers. Following the adoption of ASC 326, an allowance is established for expected credit losses to be recognized over the life of the reinsurance recoverable. The allowance considers the current financial strength of the individual reinsurer and the amount of collateral held.
Acquisition Costs. The costs directly related to writing a (re)insurance policy are referred to as acquisition expenses and include commissions, premium taxes and profit commissions. With the exception of profit commissions, these expenses are incurred when a policy is issued, and only the costs directly related to the successful acquisition of new and renewal insurance and reinsurance contracts are deferred and amortized over the same period as the corresponding premiums are recorded as revenues. Profit commissions are estimated and accrued based on the related performance criteria evaluated at the balance sheet date, with subsequent changes to those estimates recognized when they occur. Commissions received related to reinsurance premiums ceded are netted against broker commissions in determining acquisition costs eligible for deferral.
On a regular basis a premium deficiency analysis is performed of the deferred acquisition costs in relation to the expected recognition of revenues, including anticipated investment income, and adjustments, if any, are reflected as period costs. Should the analysis indicate that the acquisition costs are unrecoverable, further analyses are performed to determine if a reserve is required to provide for losses which may exceed the related unearned premium.
General and Administrative Expenses. These costs represent the expenses incurred in running the business and include, but are not limited to compensation costs for employees, rental costs, IT development and professional and consultancy fees. General and administrative costs directly attributable to the successful acquisition of business are deferred and amortized over the same period as the corresponding premiums are recorded as revenues. When reporting the results for its business segments, the Company includes expenses which are directly attributable to the segment plus an allocation of central administrative costs.
Corporate Expenses. Corporate expenses are not allocated to the Company’s business segments as they typically do not fluctuate with the levels of premium written and are related to the Company’s operations which include group executive costs, group finance costs, group legal and actuarial costs and certain strategic and other costs.
Accounting for Investments, Cash and Cash Equivalents Accounting for Investments, Cash and Cash Equivalents
Fixed Income Securities. The fixed income securities portfolio comprises securities issued by governments and government agencies, corporate bonds, mortgage and other asset-backed securities and bank loans. Investments in fixed income securities are classified as available for sale or trading and are reported at estimated fair value in the consolidated balance sheet. Investment transactions are recorded on the trade date with balances pending settlement reflected in the consolidated balance sheet under receivables for securities sold and other payables for securities purchased, respectively. Fair values are based on quoted market prices and other data provided by third-party pricing services.
Short-term Investments. Short-term investments primarily comprise highly liquid debt securities with a maturity greater than three months but less than one year from the date of purchase and are held as part of the investment portfolio of the Company. Short-term investments are classified as either trading or available for sale and reported at estimated fair value.
Catastrophe Bonds. Investments in catastrophe bonds are classified as trading and are reported on the consolidated balance sheet at estimated fair value. The fair values are based on independent broker-dealer quotes.
Privately-held Investments. The Company’s privately-held investments primarily comprise commercial mortgage loans, middle market loans and other private debt, asset-backed securities and global corporate securities. These investments are classified as trading or available for sale and are reported on the consolidated balance sheet at estimated fair value. Privately-held investments are initially valued at cost or transaction value which approximates fair value. In subsequent measurement periods, the fair values of these securities are primarily determined using discounted cash flow models. Interest income is accrued on the principal amount of the loan based on its contractual interest rate subject to it being probable that we will receive interest on that particular underlying loan. Interest income, amortization of premiums and discounts, and prepayment fees are reported in net investment income on the consolidated statements of income.
Investments, Equity Method. These investments represent the Company’s investments in partially owned insurance and related companies that are recorded using the equity method of accounting. The carrying value of these investments are based on the Company’s proportionate share of GAAP equity.
Other Investments. Other investments represent the Company’s investments in investment funds that are reported at net asset value. For these investments, net asset value is used as a practical expedient for fair value.
Cash and Cash Equivalents. Cash and cash equivalents are reported at fair value. Cash and cash equivalents comprise cash on hand, deposits held on call with banks and other short-term highly liquid investments due to mature within three months from the date of purchase and which are subject to insignificant risk of change in fair value.
Gains and Losses. Realized gains or losses on the sale of investments are determined on the basis of the first in first out cost method and are recorded in revenue or expenses respectively. Unrealized gains and losses represent the difference between the cost, or the cost as adjusted by amortization of any difference between its cost and its redemption value (“amortized cost”), of the security and its fair value at the reporting date and are included within other comprehensive income for securities classified as available for sale and in realized and unrealized investment gains or losses in the consolidated statement of operations for securities classified as trading.
Credit Losses on Available for Sale Debt Securities. An allowance account for credit losses is recognized for available for sale debt securities based on a review of individual securities. Write-offs are recorded when amounts are deemed uncollectible, or Aspen intends to sell (or more likely than not will be required to sell) the debt security before recovery of the amortized cost basis. The amortized cost basis will be written down to the debt securities fair value through earnings. Credit losses are limited to the difference between the debt securities amortized cost basis and fair value (‘fair-value floor’). Any decline in the debt securities fair value below the amortized cost basis that is not a result of a credit loss is recorded through other comprehensive income, net of applicable taxes. The allowance for credit losses of a security may be increased or reversed upon a change in credit position with the change reflected in net income.
The credit loss models employ a discounted cash flow approach to evaluate whether a credit loss exists at the individual security level and are reviewed at each reporting period. This analysis excludes investments in U.S. Government / Agency bonds and U.S. Government Agency mortgage-backed securities due to being of ‘high credit quality’ based on the absence of risk. For any available for sale debt securities that were initially purchased with credit deterioration (PCD), the amortized cost basis shall be considered to be the purchase price, plus any allowance for credit losses. Estimated credit losses shall be discounted at the rate that equates the present value of the purchaser’s estimate of the security’s future cash flows with the purchase price of the asset.
Net Investment Income. Investment income includes amounts received and accrued in respect of periodic interest (“coupons”) payable to the Company by the issuer of fixed income securities, equity dividends and interest credited on cash and cash equivalents. It also includes amortization of premium and accretion of discount in respect of fixed income securities. Investment income also includes changes in fair value from investments in real estate funds. Investment management and custody fees are charged against net investment income reported in the consolidated statement of operations.
Accounting for Derivative Financial Instruments Accounting for Derivative Financial Instruments
The Company enters into derivative instruments to manage certain market risks, such as forward exchange contracts used to reduce foreign currency risk relative to the U.S. dollar. The Company records derivative instruments at fair value on the Company’s consolidated balance sheet as either assets or liabilities, depending on their rights and obligations.
The accounting for the gain or loss due to the changes in the fair value of these instruments is dependent on whether the derivative qualifies as a hedge. If the derivative does not qualify as a hedge, the gains or losses are reported in the consolidated statement of operations when they occur and classified within Change in fair value of derivatives. If the derivative qualifies as a hedge, the accounting treatment varies based on the type of risk being hedged. There are two primary types of hedging relationships that may be used for accounting purposes: fair value hedge and cash flow hedge. A fair value hedge is designed to offset changes in the fair value of an underlying asset or liability, and the gain or loss from the hedging instrument offsets the change in fair value of the underlying asset or liability. Under fair value hedge accounting, both the gain or loss from the underlying asset or liability and the gain or loss from the hedging instrument are recognized in earnings in the same period. In contrast, a cash flow hedge is designed to offset changes in cash flows of an underlying asset or liability. The gain or loss from the hedging instrument is initially recognized in other comprehensive income. As the contracts settle, the realized gain or loss is reclassified from other comprehensive income into the consolidated statement of operations.
The loss portfolio transfer contract includes a funds withheld arrangement that provides a variable interest expense based on Aspen’s investment performance. As a result, this funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative. Since the economic characteristics and risks of an embedded derivative feature are not clearly and closely related to the economic characteristics and risks of the host contract, the embedded derivative is bifurcated and accounted for separately at fair value. The Company records subsequent changes in the embedded derivative fair value in the consolidated statement of operations.
Accounting for Intangible Assets Accounting for Intangible Assets
Intangible assets are held in the consolidated balance sheet at cost less amortization and impairment. Amortization applies on a straight-line basis in respect of assets having a finite estimated useful economic life. Finite intangibles are assessed on an annual basis for impairment, or more frequently where circumstances indicate the carrying value may not be recoverable. For intangible assets considered to have an indefinite life, the Company performs a qualitative assessment annually to determine whether it is more likely than not that an intangible asset is impaired. Goodwill is assessed annually for impairment or more frequently if circumstances indicate an impairment may have occurred.
Accounting for Office Properties and Equipment Accounting for Office Properties and Equipment
Office properties and equipment are reported at cost less accumulated depreciation. These assets are depreciated on a straight-line basis over the estimated useful lives of the assets. Computer equipment is depreciated between three and five years, furniture and fittings are depreciated over four years and leasehold improvements are depreciated over the lesser of 15 years or the lease term.
IT development costs that are directly associated with the development of identifiable and unique software products and that are anticipated to generate economic benefits exceeding costs beyond one year, are recognized within office properties and equipment. Costs include external consultants’ fees, certain qualifying internal staff costs and other costs incurred to develop software programs. Software is depreciated over their estimated useful life, between three and five years, on a straight-line basis and is subject to impairment testing annually. Depreciation commences when the asset becomes operational. Other non-qualifying costs are expensed as incurred.
Accounting for Right-of-Use Operating Lease Assets Accounting for Leases
In the ordinary course of the business, the Company renews and enters into new leases for office real estate and other assets. At the lease inception date, the Company determines whether a contract contains a lease and recognizes operating lease Right-of-use assets and operating lease liabilities based on the present value of future minimum lease payments. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. For all office real estate leases, rent incentives, including reduced-rent and rent-free periods and contractually agreed rent increases during the lease term, have been included when determining the present value of future cash flows.
Right-of-use operating lease assets are reported at cost less accumulated depreciation on the consolidated balance sheet and depreciated over the lease term. The Company does not record office property and equipment leases with an initial term of 12 months or less (short-term) in the Company's consolidated balance sheets. Such short-term leases are expensed through the consolidated statement of operations.
Right-of-use operating lease assets are tested for impairments whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. If the carrying value of an asset is impaired, it is reduced to the recoverable amount by an immediate charge to the income statement. The recoverable amount is the higher of an asset’s fair value less costs to sell and value in use.
Accounting for Foreign Currencies Translation Accounting for Foreign Currencies Translation
The functional currency of the Company and its subsidiaries is the U.S. Dollar, which is also the Company’s reporting currency. Transactions in currencies other than the functional currency are measured at the exchange rate prevailing at the date of the transaction.
Monetary assets and liabilities denominated in non-functional currencies are remeasured at the exchange rate prevailing at the balance sheet date and any resulting foreign exchange gains or losses are reflected in the consolidated statement of operations. Foreign exchange gains or losses related to available for sale investments denominated in non-functional currencies are included within other comprehensive income. Non-monetary assets and liabilities are remeasured to functional currency at historic exchange rates.
Accounting for Income Tax Accounting for Income Taxes
Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and for operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. When the Company does not believe that, on the basis of available information, it is more likely than not that deferred tax assets will be fully recovered, it recognizes a valuation allowance against its deferred tax assets to reduce the deferred tax assets to the amount more likely than not to be realized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.
Furthermore, a tax benefit from a tax position may be recognized in the financial statements only if it is more-likely-than-not that the position is sustainable, based solely on its technical merits and consideration of the relevant tax authority’s widely understood administrative practices and precedents.
The Company applies a portfolio approach to release the income tax effects in accumulated other comprehensive income. Under this approach, the income tax effects upon the sale of an available for sale debt security, settlement of hedged transactions and upon foreign currency translation adjustments for each period, are determined under the intra-period tax allocation approach. Any tax effects remaining in accumulated other comprehensive income are only released when the entire portfolio is liquidated, sold or extinguished.
Accounting for Preference Shares Accounting for Preference Shares The Company had at the balance sheet date in issue three classes of preference shares. The Company has no obligation to pay interest on these securities but they carry entitlements to dividends payable at the discretion of the Board of Directors. In the event of non-payment of dividends for six consecutive periods, holders of preference shares have director appointment rights. The preference shares are therefore accounted for as equity instruments and included within total shareholders’ equity.
Accounting for Share-Based Payments and Long-Term Incentive Plans Accounting for Share-Based Payments and Long-Term Incentive Plans
The Company operates an employee long-term incentive plan, comprised of Performance Units and Exit Units, the terms and conditions of which are described in Note 17. The Company applies a fair-value based measurement method in calculating the compensation costs of Performance Units which are recognized on a straight-line basis over the vesting period.
Certain employees of the Company participate in a Management Equity Plan (“MEP”), comprising stock options to acquire non-voting shares in a related party affiliate of the Company, at no cost to the employee. The terms and conditions of the MEP are described in Note 17. The Company recognizes compensation costs for these awards with performance conditions if, and when, the Company concludes that it is probable that the performance condition(s) will be achieved, over the requisite service period. The Company reviews and evaluates these estimates regularly and will recognize any remaining unrecognized compensation expense as an estimate revision. The stock options vest upon a number of performance conditions; an exit or liquidity event occurring; a two-year cumulative operating income hurdle being achieved over the vesting period; and certain other contractual terms being achieved. The Company applies fair-value based measurement principles to determine grant date values for the stock options. The Company has made an entity-wide accounting election to account for award forfeitures as they occur.
Accounting for Business Combinations Accounting for Business Combinations    
The Company accounts for a transaction as a business combination where the assets acquired and liabilities assumed following a transaction constitute a business. An acquired entity must have inputs and processes that make it capable of generating a return or economic benefit to be considered a business. If the assets acquired are not a business, the Company accounts the transaction as an asset acquisition. The Company recognizes and measures at fair value 100 percent of the assets and liabilities of any acquired business. Goodwill is recognized and measured as the difference between the consideration paid or payable less the fair value of assets acquired.
The Company accounts for the disposal of subsidiary undertakings when it ceases to control the subsidiary’s assets and liabilities or the group of assets. A gain or loss is recognized and measured as the difference between the fair value of consideration received or receivable and the value of assets, liabilities and equity components de-recognized, related to that subsidiary or group of assets when deconsolidated.
Costs that are directly related to a business combination transaction are expensed in the periods in which the costs are incurred and the services are received.
Accounting Pronouncements Accounting Pronouncements
Accounting Pronouncements Adopted
In November 2023, the FASB issued Accounting Standards Update (“ASU”) No. 2023-07, “Segment Reporting (Topic 280) - Improvements to Reportable Segment Disclosures”. This update improves the disclosures about a public entity’s reportable segments and addresses requests from investors for additional, more detailed information about a reportable segment’s expenses. The amendments in this ASU are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. The Company adopted ASU 2023-07 for the annual reporting period beginning January 1, 2024. The adoption of ASU 2023-07 did not have a material impact on the Company’s reportable segment disclosures.
Accounting Pronouncements Not Yet Adopted
In November 2024, the FASB issued ASU No. 2024-03, “Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses”. This ASU requires disclosure, in the notes to the financial statements, of specified information about certain costs and expenses. The amendments in this ASU are effective for annual reporting periods beginning after December 15, 2026, and interim periods within annual reporting periods beginning after December 15, 2027. As this guidance relates solely to financial statement disclosures, the adoption of ASU 2024-03 will have no impact upon the Company’s results of operations, financial condition, or liquidity.
Other accounting pronouncements were issued during the year ended December 31, 2024 which were either not applicable to the Company or did not impact the Company’s consolidated financial statements.
v3.25.1
Segment Reporting (Tables)
 12 Months Ended
Dec. 31, 2024
Segment Reporting [Abstract]  
Summary of gross and net written and earned premiums, underwriting results, ratios and reserves for each of Company's business segments
The following tables provide a summary of gross and net written and earned premiums, underwriting income or loss, ratios and reserves for each of the Company’s business segments for the twelve months ended December 31, 2024, 2023 and 2022:
 Twelve Months Ended December 31, 2024
 ReinsuranceInsuranceTotal
 ($ in millions)
Underwriting Revenues
Gross written premiums$1,885.8 $2,723.5 $4,609.3 
Net written premiums1,275.7 1,666.9 2,942.6 
Gross earned premiums1,822.1 2,565.7 4,387.8 
Net earned premiums1,305.7 1,584.0 2,889.7 
Underwriting Expenses
Losses and loss adjustment expenses741.3 976.5 1,717.8 
Acquisition costs227.0 193.2 420.2 
General and administrative expenses141.7 264.2 405.9 
Underwriting income195.7 150.1 345.8 
Corporate and other expenses (1)
(97.3)
Non-operating expenses (2)
(29.9)
Net investment income318.0 
Realized and unrealized investment gains52.6 
Realized and unrealized investment losses(102.1)
Change in fair value of derivatives(21.1)
Interest expense(62.1)
Net realized and unrealized foreign exchange gains
60.2 
Income before income taxes
464.1 
Income tax benefit
22.0 
Net income$486.1 
Net reserve for losses and loss adjustment expenses
$1,691.5 $2,259.1 $3,950.6 
Ratios
Loss ratio56.8 %61.6 %59.4 %
Acquisition cost ratio17.4 12.2 14.5 
General and administrative expense ratio10.9 16.7 14.0 
Expense ratio28.3 28.9 28.5 
Combined ratio85.1 %90.5 %87.9 %
 _______________
(1)    Corporate and other expenses includes other income/(expenses), which were previously presented separately.
(2)    Non-operating expenses in the twelve months ended December 31, 2024 includes expenses in relation to consulting fees, non-recurring transformation program costs, and other non-recurring costs.
 Twelve Months Ended December 31, 2023
 ReinsuranceInsuranceTotal
 
($ in millions)
Underwriting Revenues
Gross written premiums$1,521.0 $2,446.6 $3,967.6 
Net written premiums1,098.0 1,483.9 2,581.9 
Gross earned premiums1,562.0 2,444.8 4,006.8 
Net earned premiums1,154.5 1,460.0 2,614.5 
Underwriting Expenses
Losses and loss adjustment expenses611.1 941.9 1,553.0 
Acquisition costs208.6 171.6 380.2 
General and administrative expenses120.6 233.9 354.5 
Underwriting income
214.2 112.6 326.8 
Corporate and other expenses (1)
(114.0)
Non-operating expenses (2)
(35.1)
Net investment income275.7 
Realized and unrealized investment gains75.9 
Realized and unrealized investment losses(61.4)
Change in fair value of derivatives26.1 
Interest expense(55.2)
Net realized and unrealized foreign exchange (losses)(36.2)
Income before income taxes402.6 
Income tax benefit
132.1 
Net income$534.7 
Net reserve for losses and loss adjustment expenses
$1,373.1 $1,859.7 $3,232.8 
Ratios
Loss ratio52.9 %64.5 %59.4 %
Acquisition cost ratio18.1 11.8 14.5 
General and administrative expense ratio 10.4 16.0 13.6 
Expense ratio28.5 27.8 28.1 
Combined ratio81.4 %92.3 %87.5 %
 ________________
(1)    Corporate and other expenses includes other income/(expenses), which were previously presented separately.
(2)    Non-operating expenses in the twelve months ended December 31, 2023 includes expenses in relation to consulting fees, non-recurring transformation program costs, and other non-recurring costs.
 Twelve Months Ended December 31, 2022
 ReinsuranceInsuranceTotal
 ($ in millions)
Underwriting Revenues
Gross written premiums$1,807.0 $2,531.7 $4,338.7 
Net written premiums1,426.4 1,469.6 2,896.0 
Gross earned premiums1,617.2 2,370.8 3,988.0 
Net earned premiums1,251.8 1,436.9 2,688.7 
Underwriting Expenses
Losses and loss adjustment expenses770.3 909.7 1,680.0 
Acquisition costs252.4 179.4 431.8 
General and administrative expenses142.5 244.0 386.5 
Underwriting income86.6 103.8 190.4 
Corporate expenses(71.7)
Non-operating expenses (1)
(36.0)
Net investment income188.1 
Realized and unrealized investment gains5.0 
Realized and unrealized investment losses(182.6)
Change in fair value of derivatives(80.5)
Interest expense(43.7)
Net realized and unrealized foreign exchange gains
15.9 
Other income8.2 
Other expenses(20.1)
(Loss) before income taxes (27.0)
Income tax benefit78.1 
Net income
$51.1 
Net reserve for losses and loss adjustment expenses
$1,360.7 $1,452.5 $2,813.2 
Ratios
Loss ratio61.5 %63.3 %62.5 %
Acquisition cost ratio20.2 12.5 16.1 
General and administrative expense ratio 11.4 17.0 14.4 
Expense ratio31.6 29.5 30.5 
Combined ratio93.1 %92.8 %93.0 %
_______________
(1)    Non-operating expenses in the twelve months ended December 31, 2022 includes expenses in relation to consulting fees, non-recurring transformation activities, and other non-recurring costs.
Schedule of gross written premiums based on geographical areas
Geographical Areas. The following summary presents the Company’s gross written premiums based on the location of the insured risk for the twelve months ended December 31, 2024, 2023 and 2022.
Twelve Months Ended
 December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Australia/Asia$177.8 $177.8 $257.5 
Europe208.1 179.4 194.5 
United Kingdom & Ireland
614.8 532.5 485.8 
United States & Canada (1)
2,947.0 2,472.0 2,715.7 
Worldwide excluding the United States (2)
33.4 28.8 24.2 
Worldwide including the United States (3)
435.0 417.2 541.7 
Other (4)
193.2 159.9 119.3 
Total
$4,609.3 $3,967.6 $4,338.7 
 ______________
(1)    “United States & Canada” comprises individual policies that insure risks specifically in the United States and/or Canada, but not elsewhere.
(2)    “Worldwide excluding the United States” consists of individual policies that insure global risks with the specific exclusion of the United States.
(3)    “Worldwide including the United States” consists of individual policies that insure global risks with the specific inclusion of the United States.
(4)    “Other” comprises individual policies that insure risks in other countries including, but not limited to, countries in the Caribbean, South America and the Middle East.
v3.25.1
Investments (Tables)
 12 Months Ended
Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]  
Summary of Investment Income The following table summarizes net investment income for the twelve months ended December 31, 2024, 2023 and 2022:
Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Fixed income securities — Available for sale$161.5 $115.7 $95.6 
Fixed income securities — Trading88.2 98.9 57.0 
Short-term investments — Available for sale4.5 5.3 0.6 
Short-term investments — Trading0.1 0.3 0.1 
Fixed term deposits (included in cash and cash equivalents)45.3 39.9 6.6 
Catastrophe bonds — Trading— 0.2 0.3 
Privately-held investments — Available for sale
1.2 0.1 — 
Privately-held investments — Trading34.9 44.7 24.3 
Other investments, at fair value (1)
(6.2)(17.8)13.9 
Total329.5 287.3 198.4 
Investment expenses(11.5)(11.6)(10.3)
Net investment income$318.0 $275.7 $188.1 
_____________
(1)    Other investments primarily represent the Company’s investments in investment funds. The amount reported represents the change in fair value of the investments in the period.
Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments
The following table summarizes the net realized and unrealized investment gains and losses recorded in the consolidated statement of operations and the change in unrealized gains and losses on investments recorded in other comprehensive income for the twelve months ended December 31, 2024, 2023 and 2022:
Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
($ in millions)
Available for sale:
Fixed income securities — gross realized gains$2.4 $1.6 $2.9 
Fixed income securities — gross realized (losses)(60.6)(41.5)(58.4)
Short-term investments — gross realized gains0.8 0.6 1.0 
Short-term investments — gross realized (losses)(2.0)(0.9)(0.5)
Net change in expected credit gains/(losses)
1.9 4.8 (5.0)
Trading:
Fixed income securities — gross realized gains1.2 1.0 0.2 
Fixed income securities — gross realized (losses)(10.0)(3.5)(1.8)
Fixed income securities — net unrealized gains/(losses)
26.8 65.9 (113.9)
Short-term investments — gross realized gains— 0.1 — 
Short-term investments — gross realized (losses)(0.3)(0.3)— 
Privately-held investments — gross realized gains0.8 0.8 0.7 
Privately-held investments — gross realized (losses)(28.8)— (0.1)
Privately-held investments — net unrealized gains/(losses)
18.6 (15.2)(2.5)
Catastrophe bonds — net unrealized gains
— 0.1 0.2 
Investments, equity method:
Gross unrealized (losses)/gains in MVI
(0.2)0.2 — 
Gross unrealized gains/(losses) in Multi-Line Reinsurer
0.1 0.8 (0.4)
Gross realized (losses) in Digital Re
(0.2)— — 
Total net realized and unrealized investment (losses)/gains recorded in the consolidated statement of operations
$(49.5)$14.5 $(177.6)
Change in available for sale net unrealized gains/(losses):
Available for sale investments
$34.1 $126.2 $(391.7)
Income tax (expense)/benefit
(4.7)(20.6)23.9 
Total change in net unrealized gains/(losses), net of taxes recorded in other comprehensive income
$29.4 $105.6 $(367.8)
Cost or Amortized Cost, Unrealized and Realized Gains and Losses and Estimated Fair Value of Available for Sale Investments The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of available for sale investments in fixed income securities, short-term investments and privately-held investments as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Allowance for Credit Losses
Fair Market Value
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,504.8 $1.5 $(25.7)$— $1,480.6 
U.S. agency7.5 — (0.3)— 7.2 
Municipal84.2 — (1.9)— 82.3 
Corporate2,045.3 8.5 (66.4)(1.0)1,986.4 
Non-U.S. government-backed corporate132.9 0.8 (2.4)— 131.3 
Non-U.S. government248.2 1.0 (2.4)— 246.8 
Asset-backed232.4 2.2 (0.1)— 234.5 
Agency commercial mortgage-backed
5.0 — (0.6)— 4.4 
Agency residential mortgage-backed
600.8 — (82.1)— 518.7 
Total fixed income securities, available for sale
4,861.1 14.0 (181.9)(1.0)4,692.2 
Short-term investments, available for sale
261.9 — — — 261.9 
Privately-held investments, available for sale
Asset-backed securities24.0 0.2 — — 24.2 
Total investments, available for sale
$5,147.0 $14.2 $(181.9)$(1.0)$4,978.3 
 As at December 31, 2023
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Allowance for Credit Losses
Fair Market Value
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,224.9 $4.4 $(26.7)$— $1,202.6 
U.S. agency7.5 — (0.3)— 7.2 
Municipal133.6 — (5.0)(0.5)128.1 
Corporate2,051.1 12.1 (101.5)(2.4)1,959.3 
Non-U.S. government-backed corporate106.5 0.1 (5.9)— 100.7 
Non-U.S. government279.9 0.6 (6.7)— 273.8 
Agency commercial mortgage-backed6.6 — (0.8)— 5.8 
Agency residential mortgage-backed519.9 0.1 (74.9)— 445.1 
Total fixed income securities, available for sale
4,330.0 17.3 (221.8)(2.9)4,122.6 
Short-term investments, available for sale
93.6 — — — 93.6 
Privately-held investments, available for sale
Asset-backed securities14.7 0.2 — — 14.9 
Total investments, available for sale
$4,438.3 $17.5 $(221.8)$(2.9)$4,231.1 
Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities The following tables present the cost or amortized cost, gross unrealized gains and losses, and estimated fair market value of trading investments in fixed income securities, short-term investments, catastrophe bonds and privately-held investments as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Fair Market Value
 ($ in millions)
Fixed income securities, trading
U.S. government$262.9 $0.6 $(2.2)$261.3 
Municipal1.6 — — 1.6 
Corporate155.5 0.5 (4.9)151.1 
High yield loans101.7 0.9 (0.2)102.4 
Non-U.S. government-backed corporate2.8 — — 2.8 
Non-U.S. government24.4 0.1 (0.1)24.4 
Asset-backed624.6 4.1 (3.5)625.2 
Agency mortgage-backed34.2 — (3.1)31.1 
Total fixed income securities, trading
1,207.7 6.2 (14.0)1,199.9 
Short-term investments, trading
1.0 — — 1.0 
Catastrophe bonds, trading
1.0 — — 1.0 
Privately-held investments, trading
Commercial mortgage loans80.9 0.5 (1.7)79.7 
Middle market loans and other private debt61.6 0.1 (0.7)61.0 
Asset-backed securities126.7 0.9 — 127.6 
Global corporate securities18.8 — (0.3)18.5 
Total privately-held investments, trading
288.0 1.5 (2.7)286.8 
Total investments, trading
$1,497.7 $7.7 $(16.7)$1,488.7 
 As at December 31, 2023
 
Cost or Amortized Cost
Gross Unrealized Gains
Gross Unrealized Losses
Fair Market Value
 ($ in millions)
Fixed income securities, trading
U.S. government$248.7 $0.5 $(3.7)$245.5 
Municipal3.3 — (0.2)3.1 
Corporate178.8 0.7 (8.0)171.5 
High yield loans90.8 1.3 — 92.1 
Non-U.S. government-backed corporate8.6 — (0.3)8.3 
Non-U.S. government35.8 0.1 (1.1)34.8 
Asset-backed936.0 2.1 (29.9)908.2 
Agency mortgage-backed 25.0 — (2.8)22.2 
Total fixed income securities, trading
1,527.0 4.7 (46.0)1,485.7 
Short-term investments, trading
2.1 — — 2.1 
Catastrophe bonds, trading
1.6 — — 1.6 
Privately-held investments, trading
Commercial mortgage loans293.2 1.0 (19.3)274.9 
Middle market loans and other private debt85.9 — (1.1)84.8 
Asset-backed securities83.1 0.4 (0.6)82.9 
Global corporate securities14.7 — (0.3)14.4 
Short-term investments18.0 — — 18.0 
Total privately-held investments, trading
494.9 1.4 (21.3)475.0 
Total investments, trading
$2,025.6 $6.1 $(67.3)$1,964.4 
Equity Method Investments
The table below shows the Company’s investments in MVI, Multi-Line Reinsurer and Digital Re for the twelve months ended December 31, 2024 and 2023:
MVIMulti-Line ReinsurerDigital ReTotal
 ($ in millions)
Opening undistributed value of investment as at January 1, 2024
$1.0 $6.4 $0.2 $7.6 
Unrealized (loss)/gain for the twelve months to December 31, 2024
(0.2)0.1 — (0.1)
Realized (loss) for the twelve months to December 31, 2024
— — (0.2)(0.2)
Closing value of investment as at December 31, 2024
$0.8 $6.5 $— $7.3 
Opening undistributed value of investment as at January 1, 2023
$0.8 $5.2 $0.2 $6.2 
Investment in the period— 0.4 — 0.4 
Unrealized gain for the twelve months to December 31, 2023
0.2 0.8 — 1.0 
Closing value of investments at December 31, 2023
$1.0 $6.4 $0.2 $7.6 
Summary of Fixed Maturities The scheduled maturity distribution of the Company’s available for sale securities as at December 31, 2024 and December 31, 2023 is set forth below. Actual maturities may differ from contractual maturities because issuers of securities may have the right to call or prepay obligations with or without call or prepayment penalties.
 As at December 31, 2024
 
Amortized Cost or Cost
Fair Market Value
 ($ in millions)
Due one year or less$834.1 $831.2 
Due after one year through five years2,386.5 2,353.2 
Due after five years through ten years1,060.7 1,008.7 
Due after ten years3.5 3.4 
4,284.8 4,196.5 
Agency commercial mortgage-backed
5.0 4.4 
Agency residential mortgage-backed
600.8 518.7 
Asset-backed256.4 258.7 
Total investments, available for sale
$5,147.0 $4,978.3 
 At December 31, 2023
 
Amortized Cost or Cost
Fair Market Value
 ($ in millions)
Due one year or less$512.0 $505.8 
Due after one year through five years2,889.0 2,818.9 
Due after five years through ten years495.1 440.3 
Due after ten years15.7 15.2 
3,911.8 3,780.2 
Agency commercial mortgage-backed6.6 5.8 
Agency residential mortgage-backed519.9 445.1 
Total investments, available for sale
$4,438.3 $4,231.1 
Aggregate Fair Value and Gross Unrealized Loss by Type of Security The following tables summarize, by type of security, the aggregate fair value and gross unrealized loss by length of time the security has been in an unrealized loss position for the Company’s available for sale portfolio as at December 31, 2024 and December 31, 2023:
 December 31, 2024
 0-12 monthsOver 12 monthsTotal
 
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Number of Securities
 
($ in millions, except number of securities)
Fixed income securities, available for sale
U.S. government$718.1 $(11.6)$397.8 $(14.1)$1,115.9 $(25.7)137
U.S. agency— — 7.2 (0.3)7.2 (0.3)1
Municipal33.6 (0.7)45.4 (1.2)79.0 (1.9)47
Corporate570.3 (6.8)663.9 (59.6)1,234.2 (66.4)692
Non-U.S. government-backed corporate5.8 — 91.1 (2.4)96.9 (2.4)12
Non-U.S. government118.8 (0.9)43.7 (1.5)162.5 (2.4)41
Asset-backed17.2 (0.1)— — 17.2 (0.1)14
Agency commercial mortgage-backed — — 4.5 (0.6)4.5 (0.6)1
Agency residential mortgage-backed161.2 (2.2)351.3 (79.9)512.5 (82.1)225
Total fixed income securities, available for sale$1,625.0 $(22.3)$1,604.9 $(159.6)$3,229.9 $(181.9)1,170
 December 31, 2023
 0-12 monthsOver 12 monthsTotal
 
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Fair Market Value
Gross Unrealized Losses
Number of Securities
 
($ in millions, except number of securities)
Fixed income securities, available for sale
U.S. government$105.5 $(0.5)$673.3 $(26.2)$778.8 $(26.7)74
U.S. agency— — 7.2 (0.3)7.2 (0.3)1
Municipal11.1 (1.0)117.0 (4.0)128.1 (5.0)54
Corporate46.7 (0.4)1,287.2 (101.1)1,333.9 (101.5)558
Non-U.S. government-backed corporate0.2 — 95.5 (5.9)95.7 (5.9)12
Non-U.S. government32.9 (0.2)180.1 (6.5)213.0 (6.7)53
Agency commercial mortgage-backed— — 5.8 (0.8)5.8 (0.8)1
Agency residential mortgage-backed0.1 — 435.9 (74.9)436.0 (74.9)197
Total fixed income securities, available for sale$196.5 $(2.1)$2,802.0 $(219.7)$2,998.5 $(221.8)950
v3.25.1
Fair Value Measurements (Tables)
 12 Months Ended
Dec. 31, 2024
Fair Value Disclosures [Abstract]  
Financial Assets Measured on Recurring Basis
The following tables present the level within the fair value hierarchy at which the Company’s financial assets and liabilities are measured on a recurring basis as at December 31, 2024 and December 31, 2023:
 As at December 31, 2024
 Level 1Level 2Level 3Total
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,480.6 $— $— $1,480.6 
U.S. agency— 7.2 — 7.2 
Municipal— 82.3 — 82.3 
Corporate— 1,986.4 — 1,986.4 
Non-U.S. government-backed corporate— 131.3 — 131.3 
Non-U.S. government195.1 51.7 — 246.8 
Asset-backed— 234.5 — 234.5 
Agency commercial mortgage-backed
— 4.4 — 4.4 
Agency residential mortgage-backed
— 518.7 — 518.7 
Total fixed income securities, available for sale1,675.7 3,016.5 — 4,692.2 
Short-term investments, available for sale260.2 1.7 — 261.9 
Privately-held investments, available for sale— — 24.2 24.2 
Fixed income securities, trading
U.S. government261.3 — — 261.3 
Municipal— 1.6 — 1.6 
Corporate— 151.1 — 151.1 
Non-U.S. government-backed corporate— 2.8 — 2.8 
High yield loans— 102.4 — 102.4 
Non-U.S. government9.6 14.8 — 24.4 
Asset-backed— 625.2 — 625.2 
Agency mortgage-backed— 31.1 — 31.1 
Total fixed income securities, trading270.9 929.0 — 1,199.9 
Short-term investments, trading1.0 — — 1.0 
Catastrophe bonds, trading— 1.0 — 1.0 
Privately-held investments, trading— — 286.8 286.8 
Other investments (1)
— — — 267.2 
Other financial assets and liabilities
Derivative assets — foreign exchange contracts— 17.0 — 17.0 
Derivative liabilities — foreign exchange contracts— (45.9)— (45.9)
Derivative liabilities — loss portfolio transfer (2)
— — (3.6)(3.6)
Total$2,207.8 $3,919.3 $307.4 $6,701.7 
______________
(1)    Other investments represent our investments in investment funds operating strategies in real estate, infrastructure and lending and are measured at fair value using the net asset value per share practical expedient. As a result, the investments are not classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. The investment in the funds is subject to restrictions as detailed in Note 21(a), “Commitments and Contingent Liabilities.”
(2)    The loss portfolio transfer contract includes a funds withheld arrangement that provides variable interest expense based on Aspen’s investment performance. As a result, the funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative.
 At December 31, 2023
 Level 1Level 2Level 3Total
 ($ in millions)
Fixed income securities, available for sale
U.S. government$1,202.6 $— $— $1,202.6 
U.S. agency— 7.2 — 7.2 
Municipal— 128.1 — 128.1 
Corporate— 1,959.3 — 1,959.3 
Non-U.S. government-backed corporate— 100.7 — 100.7 
Non-U.S. government200.4 73.4 — 273.8 
Agency commercial mortgage-backed— 5.8 — 5.8 
Agency residential mortgage-backed— 445.1 — 445.1 
Total fixed income securities, available for sale1,403.0 2,719.6 — 4,122.6 
Short-term investments, available for sale86.7 6.9 — 93.6 
Privately-held investments, available for sale— — 14.9 14.9 
Fixed income securities, trading
U.S. government245.5 — — 245.5 
Municipal— 3.1 — 3.1 
Corporate— 171.5 — 171.5 
Non-U.S. government-backed corporate— 8.3 — 8.3 
High yield loans— 92.1 — 92.1 
Non-U.S. government13.0 21.8 — 34.8 
Asset-backed— 908.2 — 908.2 
Agency mortgage-backed— 22.2 — 22.2 
Total fixed income securities, trading258.5 1,227.2 — 1,485.7 
Short-term investments, trading0.2 1.9 — 2.1 
Catastrophe bonds, trading— 1.6 — 1.6 
Privately-held investments, trading— — 475.0 475.0 
Other investments (1)
— — — 209.3 
Other financial assets and liabilities
Derivative assets — foreign exchange contracts— 31.7 — 31.7 
Derivative liabilities — foreign exchange contracts— (9.3)— (9.3)
Derivative liabilities — loss portfolio transfer (2)
— — (16.5)(16.5)
Total$1,748.4 $3,979.6 $473.4 $6,410.7 
______________
(1)    Other investments represent our investments in investment funds operating strategies in real estate, infrastructure and lending and are measured at fair value using the net asset value per share practical expedient. As a result, the investments are not classified in the fair value hierarchy. The fair value amounts presented in the table above are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. The investment in the funds is subject to restrictions as detailed in Note 21(a), “Commitments and Contingent Liabilities.”
(2)    The loss portfolio transfer contract includes a funds withheld arrangement that provides variable interest expense based on Aspen’s investment performance. As a result, the funds withheld arrangement is considered an embedded derivative and accounted for as an option-based derivative.
Fair Value, Measured on a Recurring Basis, Gain (Loss) Included in Earnings
The following table presents a reconciliation of the beginning and ending balances for all assets and liabilities measured at fair value on a recurring basis using Level 3 inputs for the twelve months ended December 31, 2024 and December 31, 2023:
Twelve Months Ended December 31, 2024Balance at beginning of yearPurchases and issuancesTransfers inTransfers (out)
Reclassifications
Settlements and sales
(Decrease)/increase in fair value included in net income (1) / OCI (2)
Balance at end of year
Change in unrealized gains (losses) relating to assets held at end of year (1) (2)
Assets
Privately-held investments, available for sale
Asset-backed securities
$14.9 $10.0 $— $— $— $— $(0.7)$24.2 $0.2 
Privately-held investments, trading
Commercial mortgage loans$274.9 $0.5 $— $— $— $(184.4)$(11.3)$79.7 $— 
Middle market loans and other private debt
84.8 0.4 — — 10.9 (35.5)0.4 61.0 — 
Asset-backed securities82.9 56.1 — — — (12.4)1.0 127.6 1.1 
Global corporate securities14.4 4.4 — — — (0.3)— 18.5 — 
Short-term investments18.0 — — — (10.9)(7.1)— — — 
Total Level 3 assets$489.9 $71.4 $— $— $— $(239.7)$(10.6)$311.0 $1.3 
Liabilities
Derivative liabilities — loss portfolio transfer
$(16.5)$— $— $— $— $— $12.9 $(3.6)$12.9 
Total Level 3 liabilities$(16.5)$— $— $— $— $— $12.9 $(3.6)$12.9 
Twelve Months Ended December 31, 2023
Assets
Privately-held investments, available for sale
Asset-backed securities
$— $14.7 $— $— $— $— $0.2 $14.9 $0.2 
Privately-held investments, trading
Commercial mortgage loans$312.1 $40.6 $— $— $— $(61.5)$(16.3)$274.9 $(17.9)
Middle market loans and other private debt
106.9 18.3 — — — (41.9)1.5 84.8 0.5 
Asset-backed securities66.8 21.9 5.3 (5.5)— (7.6)2.0 82.9 1.7 
Global corporate securities15.0 — — — — (0.4)(0.2)14.4 (0.2)
Equity securities6.6 — — (6.6)— — — — — 
Short-term investments25.6 18.2 — — — (25.8)— 18.0 — 
Total Level 3 assets$533.0 $113.7 $5.3 $(12.1)$— $(137.2)$(12.8)$489.9 $(15.7)
Liabilities
Derivative liabilities — loss portfolio transfer
$(31.7)$— $— $— $— $— $15.2 $(16.5)$15.2 
Total Level 3 liabilities$(31.7)$— $— $— $— $— $15.2 $(16.5)$15.2 
______________
(1)    (Decreases)/increases in the fair value of privately-held investments, trading are included in realized and unrealized investment losses in the consolidated statements of operations and other comprehensive (loss). Increases/(decreases) in the fair value of derivative liabilities - loss portfolio transfer are included within change in fair value of derivatives in the consolidated statements of operations and other comprehensive income/(loss).
(2)    (Decreases)/increases in the fair value of privately-held investments, available for sale are included in other comprehensive income/(loss) (“OCI”).
Fair Value Inputs, and Valuation Techniques
The following table summarizes the quantitative inputs and assumptions used for financial assets categorized as Level 3 under the fair value hierarchy as at December 31, 2024:
At December 31, 2024Fair Value
Level 3		Valuation Techniques

 Unobservable Inputs
RangesWeighted Average
($ in millions)
Privately-held investments, available for sale
Asset-backed securities$24.2 Discounted cash flowDiscount rate5.5%—9.5%7.1%
Privately-held investments, trading
Commercial mortgage loans79.7 Discounted cash flowDiscount rate3.8%—11.9%5.7%
Middle market loans and other private debt
61.0 Discounted cash flowDiscount rate7.2%—18.0%9.8%
Asset-backed securities127.6 Discounted cash flowDiscount rate5.4%—8.3%6.6%
Global corporate securities14.1 Discounted cash flowDiscount rate6.7%—6.7%6.7%
Global corporate securities4.4 Transaction valuen/an/an/an/a
Total$311.0 
v3.25.1
Reinsurance (Tables)
 12 Months Ended
Dec. 31, 2024
Reinsurance Disclosures [Abstract]  
Summary of Assumed and Ceded Reinsurance on Premiums Written, Premiums Earned and Insurance Losses and Loss Adjustment Expenses
The effect of assumed and ceded reinsurance on premiums written, premiums earned and losses and loss adjustment expenses for the twelve months ended December 31, 2024, 2023 and 2022 was as follows:
 
Twelve Months Ended December 31,
 202420232022
 ($ in millions)
Premiums written:
   
Insurance$2,723.5 $2,446.6 $2,531.7 
Reinsurance1,885.8 1,521.0 1,807.0 
Ceded(1,666.7)(1,385.7)(1,442.7)
Net written premiums
$2,942.6 $2,581.9 $2,896.0 
    
Premiums earned:   
Insurance$2,565.7 $2,444.8 $2,370.8 
Reinsurance1,822.1 1,562.0 1,617.2 
Ceded(1,498.1)(1,392.3)(1,299.3)
Net earned premiums
$2,889.7 $2,614.5 $2,688.7 
    
Losses and loss adjustment expenses:   
Insurance$1,759.1 $1,644.5 $1,574.2 
Reinsurance915.8 707.2 939.5 
Ceded(957.1)(798.7)(833.7)
Losses and loss adjustment expenses$1,717.8 $1,553.0 $1,680.0 
v3.25.1
Derivative Contracts (Tables)
 12 Months Ended
Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Fair Value of Derivative Instruments
The following table summarizes information on the location and amounts of derivative fair values on the consolidated balance sheet as at December 31, 2024 and 2023:
  As at December 31, 2024 As at December 31, 2023
Derivatives Not Designated as Hedging Instruments
Under ASC 815		Balance Sheet Location
Notional Amount
Fair Value
 
Notional Amount
Fair Value
  ($ in millions) ($ in millions)
Foreign Exchange Contracts
Derivative assets
$550.0 $17.0 $1,262.1 $31.4 
Foreign Exchange Contracts (1)
Derivative liabilities$1,036.9 $(41.7)$540.8 $(9.3)
Loss Portfolio Transfer Liability - Embedded Derivative (2)
Derivative liabilities$— $(3.6)$— $(16.5)
 ______________ 
(1)    Fair value is net of $0.8 million of cash collateral (December 31, 2023 — $3.4 million).
(2)    The LPT contains an embedded derivative within the contract in relation to the variable interest crediting rate.
  As at December 31, 2024 As at December 31, 2023
Derivatives Designated as Cash Flow Hedges Under ASC 815
Balance Sheet LocationNotional
Amount		Fair
Value		 Notional
Amount		Fair
Value
  ($ in millions) ($ in millions)
Foreign Exchange ContractsDerivative assets$— $— $76.9 $0.3 
Foreign Exchange Contracts (1)
Derivative liabilities
$158.0 $(4.2)$— $— 
 ______________ 
(1)    Fair value is net of $2.0 million of cash collateral (December 31, 2023 — $Nil ).
Gain/(Loss) Recognized in Income on Derivative
The following table provides the unrealized and realized (losses)/gains recorded in the consolidated statements of operations and other comprehensive income for derivatives that are not designated or designated as hedging instruments under ASC 815 — “Derivatives and Hedging” for the twelve months ended December 31, 2024 and 2023:
Amount of (Loss)/Gain Recognized on Derivatives
For the Twelve Months Ended
Location of (Loss)/Gain
Recognized on Derivatives
December 31, 2024December 31, 2023
Derivatives not designated as hedges($ in millions)
Foreign Exchange ContractsChange in Fair Value of Derivatives$(34.0)$10.9 
Loss Portfolio Transfer Liability - Embedded DerivativeChange in Fair Value of Derivatives$12.9 $15.2 
Derivatives designated as cash flow hedges
Foreign Exchange ContractsGeneral, administrative and corporate expenses in consolidated statement of operations$(0.9)$(8.1)
Foreign Exchange Contracts
Net change gross of tax from current period hedged transactions in other comprehensive income
$(6.5)$(14.0)
v3.25.1
Deferred Policy Acquisition Costs (Tables)
 12 Months Ended
Dec. 31, 2024
Insurance [Abstract]  
Reconciliation of beginning and ending deferred policy acquisition costs
The following table represents a reconciliation of beginning and ending deferred acquisition costs for the twelve months ended December 31, 2024 and 2023:
Twelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023
($ in millions)
Balance at the beginning of the period$296.2 $319.0 
Acquisition costs deferred446.1 357.4 
Amortization of deferred acquisition costs(420.2)(380.2)
Balance at the end of the period$322.1 $296.2 
v3.25.1
Reserves for Losses and Adjustment Expenses (Tables)
 12 Months Ended
Dec. 31, 2024
Insurance [Abstract]  
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense
The following table represents a reconciliation of beginning and ending consolidated reserve for losses and loss adjustment expenses for the twelve months ended December 31, 2024, 2023 and 2022:
As at December 31,
202420232022
 ($ in millions)
Reserve for losses and LAE at the start of the year$7,810.6 $7,710.9 $7,611.8 
Less reinsurance recoverable(4,577.8)(4,897.7)(3,298.1)
Net reserve for losses and LAE at the start of the year3,232.8 2,813.2 4,313.7 
Net loss and LAE expenses disposed (1)
— — (1,840.1)
Movement in net reserve for losses and LAE for claims incurred:
Current year1,682.2 1,492.2 1,651.9 
Prior years 35.6 60.8 28.1 
Total incurred1,717.8 1,553.0 1,680.0 
Net Losses and LAE payments for claims incurred:
Current year(200.2)(161.1)(192.7)
Prior years(741.3)(1,011.9)(1,098.4)
Total paid(941.5)(1,173.0)(1,291.1)
Foreign exchange (gains)/losses(58.5)39.6 (49.3)
Net reserve for losses and LAE at the end of the year3,950.6 3,232.8 2,813.2 
Plus reinsurance recoverable on unpaid losses at the end of the year4,172.0 4,577.8 4,897.7 
Reserve for losses and LAE at the end of the year$8,122.6 $7,810.6 $7,710.9 
 ______________ 
(1)    Net loss and LAE expenses disposed of $1,840.1 million represent the net loss reserves as at May 20, 2022 (“Closing Date”) for losses in relation to 2019 and prior accident years, in addition to the $770.0 million of ceded reserves under the previous ADC agreement, recognizing a total recoverable of $2,610.1 million. These reserves were rolled forward from the initial effective date of September 30, 2021, at which time the net losses reserves were $3,120.0 million.
As at December 31, 2024, the total amount recoverable from Enstar under the LPT was $1,190.9 million (December 31, 2023 — $1,627.4 million) which includes claims paid and reserve development since the Closing Date.
Short-duration Insurance Contracts, Claims Development
The following tables show an analysis of incurred claims and allocated loss adjustment expenses, net of reinsurance and cumulative paid claims and allocated claim adjustment expenses, net of reinsurance for each of the years ended December 31, 2015 through 2024. Under the LPT agreement, the Company has reinsured net losses incurred on all accident years 2019 and prior. This has resulted in IBNR in the loss development triangles for 2019 and prior to be Nil. The loss development triangles are derived from all business written by the Company as although a limited number of contracts are written which have durations of greater than one year the contracts do not meet the definition of a long duration contract. All amounts included in the following tables related to transactions denominated in a foreign currency have been translated into U.S. Dollars using the exchange rates in effect at December 31, 2024.
The Company has chosen to disaggregate the business in its Insurance segment, for the purposes of these loss development triangles as: Property; Casualty; Marine, Aviation and Energy; and Financial and Professional insurance lines. The Company considers that this presentation of its Insurance lines loss development triangles more precisely reflects meaningful trending information. The Company presents its loss development triangles for the Reinsurance segment in line with the reportable reinsurance lines: Property Catastrophe and Other Property; Casualty; and Specialty.
Property Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
 
For the Years Ended December 31, 
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$236.0 $201.7 $196.5 $198.8 $199.4 $196.3 $192.3 $192.3 $192.3 $192.3 $— 11,558 
2016235.8 246.8 241.8 243.1 244.4 233.4 232.6 232.6 232.6 — 10,752 
2017292.5 255.6 248.8 250.1 272.1 180.4 180.4 180.4 — 9,711 
2018198.7 200.8 184.8 194.7 184.4 184.4 184.4 — 8,202 
2019124.3 128.3 102.2 189.0 189.0 189.0 — 6,863 
2020202.0 197.5 207.0 212.5 213.0 23.0 7,648 
2021206.3 201.0 194.6 191.1 9.2 6,770 
2022166.0 173.2 170.9 13.5 5,801 
2023150.8 130.1 44.3 4,056 
2024132.6 84.2 1,879 
   Total$1,816.4 
Property Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$56.7 $140.2 $167.4 $176.4 $192.6 $191.3 $192.3 $192.3 $192.3 $192.3 
201666.3 167.3 199.5 221.0 230.3 233.4 232.6 232.6 232.6 
201795.5 186.4 219.0 239.7 233.6 180.4 180.4 180.4 
201860.9 156.1 178.4 172.1 184.4 184.4 184.4 
201948.5 89.9 97.7 189.0 189.0 189.0 
202060.7 123.7 151.2 169.0 178.2 
202158.4 119.2 150.6 162.9 
202241.0 113.2 143.4 
202329.8 65.2 
202419.1 
Total$1,547.5 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$268.9 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$268.9 
 Casualty Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$199.8 $219.8 $182.3 $199.4 $232.0 $230.3 $255.6 $178.9 $178.9 $178.9 $— 4,843 
2016213.3 184.3 179.4 185.8 196.9 241.3 122.9 122.9 122.9 — 4,850 
2017177.9 171.4 175.1 192.5 213.3 60.2 60.2 60.2 — 5,536 
2018120.4 123.3 133.3 162.6 42.6 42.6 42.6 — 5,500 
2019122.9 145.2 152.0 48.1 48.1 48.1 — 5,217 
2020131.8 140.4 139.4 145.5 151.8 38.1 3,888 
2021171.9 186.9 196.1 194.6 81.7 3,679 
2022202.4 212.9 208.7 119.4 3,594 
2023223.1 233.8 156.0 3,105 
2024235.6 203.2 1,782 
Total$1,477.2 
  Casualty Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
($ in millions)
2015$3.1 $16.6 $55.7 $91.0 $136.2 $165.0 $178.9 $178.9 $178.9 $178.9 
20164.1 22.3 39.1 80.6 107.2 122.0 122.9 122.9 122.9 
20173.5 22.5 51.8 94.8 88.1 60.2 60.2 60.2 
20183.1 27.5 42.1 57.3 42.6 42.6 42.6 
20196.2 17.2 63.7 48.1 48.1 48.1 
2020— 9.3 36.0 61.1 91.5 
20213.1 23.3 53.5 91.3 
20228.9 26.6 46.4 
20235.5 3.3 
202436.0 
Total$721.2 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance
$756.0 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$756.0 
Marine, Aviation and Energy Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$294.2 $296.0 $278.7 $283.6 $307.2 $309.9 $317.2 $266.0 $266.0 $266.0 $— 4,079 
2016257.8 228.1 226.4 227.0 216.8 218.6 196.2 196.2 196.2 — 4,437 
2017208.5 199.5 206.0 213.6 224.9 135.3 135.3 135.3 — 6,080 
2018169.3 206.4 207.5 234.5 149.9 149.9 149.9 — 5,201 
2019144.6 152.2 122.7 107.0 107.0 107.0 — 3,699 
2020109.6 110.7 125.0 126.1 150.9 33.5 3,866 
202192.2 95.1 94.7 96.5 11.9 4,787 
2022   107.2 105.3 112.7 25.7 5,410 
2023116.6 110.3 20.8 3,997 
2024109.6 62.3 2,358 
Total$1,434.4 
Marine, Aviation and Energy Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$44.5 $122.2 $172.6 $192.2 $220.1 $255.8 $267.5 $266.0 $266.0 $266.0 
201630.9 81.7 140.6 162.3 188.7 191.7 196.2 196.2 196.2 
201740.0 97.1 139.7 167.7 149.3 135.3 135.3 135.3 
201826.6 104.2 132.5 150.5 149.9 149.9 149.9 
201933.3 72.1 89.3 107.0 107.0 107.0 
202028.5 66.4 88.5 100.9 109.2 
202123.5 52.2 64.4 70.4 
202224.9 57.5 73.5 
202327.8 73.2 
202432.4 
   Total$1,213.1 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$221.3 
All outstanding liabilities before 2015, net of reinsurance— 
Liabilities for claims and claim adjustment expenses, net of reinsurance$221.3 
 Financial and Professional Insurance Lines
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$171.7 $173.0 $183.1 $187.0 $188.0 $183.0 $195.8 $144.4 $144.4 $144.4 $— 1,082 
2016188.1 209.1 213.5 199.6 182.8 184.3 133.0 133.0 133.0 — 1,244 
2017203.7 179.7 184.6 185.2 206.8 134.4 134.4 134.4 — 1,758 
2018153.6 169.3 150.7 159.7 109.7 109.7 109.7 — 4,645 
2019245.9 258.1 236.3 130.8 130.8 130.8 — 23,819 
2020345.2 345.5 336.2 349.8 352.2 73.7 106,042 
2021283.9 301.6 293.5 294.8 86.2 34,963 
2022314.1 299.8 268.6 121.3 3,356 
2023338.5 347.6 169.1 3,385 
2024423.2 292.3 3,756 
   Total$2,338.7 
Financial and Professional Insurance Lines
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$13.6 $43.2 $69.7 $88.7 $108.8 $137.7 $150.1 $144.4 $144.4 $144.4 
201614.8 70.6 100.7 128.7 124.6 129.2 133.0 133.0 133.0 
201727.0 50.9 82.7 115.8 133.5 134.4 134.4 134.4 
201818.3 72.3 97.6 109.8 109.7 109.7 109.7 
201926.8 86.2 120.4 130.8 130.8 130.8 
202047.3 120.8 173.7 225.0 240.0 
202143.1 90.0 131.1 161.9 
202217.7 75.1 113.4 
202321.3 100.6 
202489.2 
   Total$1,357.4 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$981.3 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$981.3 
Property Catastrophe and Other Property Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$206.7 $181.1 $171.5 $151.4 $166.8 $166.9 $173.0 $151.9 $151.9 $151.9 $— 1,045 
2016257.2 257.2 256.8 236.3 231.8 224.3 221.7 221.7 221.7 — 1,281 
2017544.8 524.9 508.1 496.9 568.9 431.8 431.8 431.8 — 1,940 
2018303.7 329.7 320.5 511.7 283.0 283.0 283.0 — 1,804 
2019209.9 225.0 316.3 157.5 157.5 157.5 — 1,399 
2020312.2 394.2 340.7 352.9 365.2 5.2 1,436 
2021637.7 461.2 479.8 472.5 4.9 1,518 
2022380.5 378.9 372.1 43.6 1,475 
2023223.6 215.0 40.4 1,104 
2024254.5 135.5 737 
   Total$2,925.2 
Property Catastrophe and Other Property Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$35.6 $92.4 $122.0 $135.0 $151.9 $154.2 $155.6 $151.9 $151.9 $151.9 
201654.7 157.1 196.8 207.0 219.5 224.3 221.7 221.7 221.7 
2017122.6 353.3 410.7 434.1 407.3 431.8 431.8 431.8 
2018121.4 266.8 265.6 258.0 283.0 283.0 283.0 
201928.0 134.1 158.8 157.5 157.5 157.5 
202041.1 162.2 232.7 306.0 306.0 
202174.6 229.2 351.5 414.8 
202263.3 193.6 261.3 
202343.9 103.8 
202432.8 
   Total$2,364.6 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$560.6 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$560.6 
Casualty Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$188.9 $195.2 $204.9 $207.6 $205.5 $201.9 $192.2 $115.2 $115.2 $115.2 $— 2,090 
2016226.6 238.7 238.3 248.4 255.8 246.6 135.2 135.2 135.2 — 2,268 
2017238.4 236.4 246.9 246.3 257.7 109.6 109.6 109.6 — 2,346 
2018223.7 252.6 260.6 251.2 91.7 91.7 91.7 — 2,262 
2019230.1 250.8 241.5 52.2 52.2 52.2 — 1,939 
2020250.2 231.2 195.8 178.2 187.2 42.4 1,563 
2021203.5 213.8 203.6 199.4 63.2 1,594 
2022246.6 247.8 246.0 138.5 1,650 
2023268.3 267.7 187.6 1,565 
2024286.9 260.0 848 
Total$1,691.1 
Casualty Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
($ in millions)
2015$3.3 $17.4 $37.5 $64.4 $88.0 $106.8 $115.2 $115.2 $115.2 $115.2 
20168.7 32.6 62.4 94.2 123.8 135.4 135.2 135.2 135.2 
20178.7 29.9 58.1 96.0 109.5 109.6 109.6 109.6 
20187.0 33.0 72.6 91.8 91.7 91.7 91.7 
20199.1 36.0 52.0 52.2 52.2 52.2 
20208.9 27.3 43.5 70.7 100.9 
20217.7 36.8 63.3 96.4 
20229.1 30.7 59.6 
20238.2 35.0 
20249.4 
Total$805.2 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$885.9 
All outstanding liabilities before 2015, net of reinsurance— 
Liabilities for claims and claim adjustment expenses, net of reinsurance$885.9 
Specialty Reinsurance
Incurred Claims, IBNR and Loss Adjustment Expenses, Net of ReinsuranceAs at December 31, 2024
Total of IBNR Plus Expected Development on Reported ClaimsCumulative Number of Reported Claims
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 
($ in millions)
2015$161.6 $164.5 $159.3 $154.0 $152.5 $148.1 $147.9 $129.2 $129.2 $129.2 $— 775 
2016233.9 234.7 232.7 225.9 221.0 208.8 185.8 185.8 185.8 — 943 
2017372.6 385.9 370.0 359.1 352.6 303.3 303.3 303.3 — 1,337 
2018389.3 388.9 387.4 412.0 322.3 322.3 322.3 — 1,428 
2019468.6 491.7 396.9 398.6 398.6 398.6 — 1,557 
2020411.2 598.7 372.9 377.1 369.5 15.1 1,519 
2021155.2 150.3 140.0 136.4 24.3 1,385 
2022192.6 191.6 196.2 98.9 1,458 
2023140.7 144.3 73.0 1,188 
2024153.5 125.6 803 
Total$2,339.1 
Specialty Reinsurance
Cumulative Paid Claims and Allocated Loss Adjustment Expenses, Net of Reinsurance
 
For the Years Ended December 31, 
Accident Year
Unaudited Prior Years
2015201620172018201920202021202220232024
 ($ in millions)
2015$17.2 $54.6 $101.6 $118.6 $127.1 $130.1 $129.9 $129.2 $129.2 $129.2 
201657.9 148.8 162.7 180.5 190.6 192.0 185.8 185.8 185.8 
201793.8 236.6 267.8 302.4 303.3 303.3 303.3 303.3 
201826.5 277.9 310.6 322.1 322.3 322.3 322.3 
2019272.2 379.0 396.9 398.6 398.6 398.6 
2020212.5 269.2 289.6 310.1 333.0 
202128.0 52.8 75.2 87.9 
202225.3 52.6 74.3 
202322.3 48.1 
202414.0 
Total$1,896.5 
All outstanding liabilities for 2015 and subsequent years, net of reinsurance$442.6 
All outstanding liabilities before 2015, net of reinsurance — 
Liabilities for claims and claim adjustment expenses, net of reinsurance$442.6 
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability
Reconciliation of Incurred and Paid Claims Development to total Reserve for Losses and LAE
As at December 31, 2024As at December 31, 2023
 ($ in millions)($ in millions)
Net outstanding liabilities:
Insurance lines
 - Property insurance lines$268.9 $270.8 
 - Casualty insurance lines756.0 636.5 
 - Marine, aviation and energy insurance lines221.3 194.5 
 - Financial and professional insurance lines981.3 837.6 
Total insurance lines$2,227.5 $1,939.4 
Reinsurance lines
 - Property catastrophe and other property reinsurance$560.6 $562.3 
 - Casualty reinsurance885.9 733.6 
 - Specialty reinsurance442.6 394.3 
Total reinsurance lines$1,889.1 $1,690.2 
Net loss and LAE$4,116.6 $3,629.6 
Reinsurance recoverable on unpaid losses:
Insurance lines $2,698.0 $2,821.6 
Reinsurance lines 1,474.0 1,756.2 
Total reinsurance recoverable on unpaid losses$4,172.0 $4,577.8 
Deferred gain on retroactive contracts
$61.2 $27.3 
Unallocated claims incurred58.0 47.9 
Other reinsurance balances recoverable (1)
(311.7)(489.1)
Carbon syndicate reserves26.5 16.7 
Other — 0.4 
$(166.0)$(396.8)
Reserve for losses and LAE at the end of the year$8,122.6 $7,810.6 
____________________
(1)    Other reinsurance balances recoverable primarily include short term recoverables to be collected.
Short-duration Insurance Contracts, Schedule of Historical Claims Duration
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (unaudited)
Years12345678910
Property insurance lines29.0 %38.0 %13.7 %12.2 %3.3 %(5.8)%— %— %— %— %
Casualty insurance lines4.1 %19.1 %32.2 %23.4 %3.5 %(3.6)%2.1 %— %— %— %
Marine, aviation and energy insurance lines23.1 %34.5 %19.6 %11.7 %2.6 %0.9 %1.7 %(0.2)%— %— %
Financial and professional insurance lines14.0 %28.4 %19.6 %14.7 %4.7 %4.8 %2.9 %(1.3)%— %— %
Property catastrophe and other property reinsurance21.5 %42.7 %16.2 %6.9 %3.2 %1.9 %(0.1)%(0.8)%— %— %
Casualty reinsurance6.1 %19.2 %21.6 %19.1 %11.8 %5.0 %1.8 %— %— %— %
Specialty reinsurance26.7 %32.8 %12.7 %7.6 %3.1 %0.6 %(0.9)%(0.2)%— %— %
v3.25.1
Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2024
Income Tax Disclosure [Abstract]  
Summary of Total Income Tax
Total income tax (benefit)/expense for the twelve months ended December 31, 2024, 2023 and 2022 was allocated as follows:
 Twelve Months Ended December 31,
 202420232022
 ($ in millions)
Income tax (benefit) allocated to net income
$(22.0)$(132.1)$(78.1)
Income tax expense/(benefit) allocated to other comprehensive income
3.3 20.6 (23.9)
Total income tax (benefit)
$(18.7)$(111.5)$(102.0)
Schedule of Income Tax by Taxing Authority
Income/(loss) from operations before income taxes and income tax expense/(benefit) attributable to that income/(loss) for the twelve months ended December 31, 2024, 2023 and 2022 is provided in the tables below:
 Twelve Months Ended December 31, 2024
 
Income before tax
Current tax expense
Deferred tax expense/(benefit)
Total income tax expense/(benefit)
 ($ in millions)
Bermuda (1)
$85.3 $— $1.3 $1.3 
U.S. (2)
269.0 62.7 (4.4)58.3 
U.K. (3)
106.9 3.9 (85.3)(81.4)
Other (4)
2.9 — (0.2)(0.2)
Total$464.1 $66.6 $(88.6)$(22.0)
 Twelve Months Ended December 31, 2023
 
Income before tax
Current tax expense
Deferred tax (benefit)/expense
Total income tax (benefit)/expense
 ($ in millions)
Bermuda$148.8 $— $(201.1)$(201.1)
U.S. 236.3 52.4 3.0 55.4 
U.K. 0.7 5.3 0.1 5.4 
Other16.8 7.9 0.3 8.2 
Total$402.6 $65.6 $(197.7)$(132.1)
Twelve Months Ended December 31, 2022
(Loss)/Income before tax
Current tax expense
Deferred tax (benefit)
Total income tax (benefit)/expense
($ in millions)
Bermuda$(103.3)$— $— $— 
U.S34.8 14.8 (102.9)(88.1)
U.K.62.4 7.0 — 7.0 
Other
(20.9)4.7 (1.7)3.0 
Total$(27.0)$26.5 $(104.6)$(78.1)
________________
(1)    We have recorded a deferred tax asset in Bermuda consisting of $158.9 million (2023 — $156.6 million) in respect of the ETA and $40.0 million (2023 — $44.5 million) in respect of an OTLC as a result of the newly enacted Corporate Income Tax Act 2023 in Bermuda. The ETA election allows for an adjustment equal to the difference between the fair market value and carrying value of assets and liabilities. The OTLC allows losses from year 2020 to 2024 to be carried forward. We expect this deferred tax asset to be utilized predominantly over a 10-year period. We expect to incur and pay increased taxes in Bermuda beginning in 2025.
(2)    The U.S. current tax expense of $62.7 million (2023 — $52.4 million) includes $0.2 million (2023 — $0.9 million) of Base Erosion and Anti-abuse Tax.
(3)    The U.K. deferred tax benefit of $85.3 million includes a change in the judgment of the brought-forward valuation allowance of $107.7 million.
(4)    Current tax expense and deferred tax (benefit) in “Other” relates to the branches of Aspen UK and Aspen Bermuda Limited.
Income Tax Reconciliation The reconciliation between the income tax (benefit) and the amount that would result from applying the statutory rate for the Company for the twelve months ended December 31, 2024, 2023 and 2022 is provided in the table below:
 Twelve Months Ended December 31,
 202420232022
Income Tax Reconciliation($ in millions)
Income tax benefit at statutory tax rate of zero percent$— $— $— 
Overseas statutory tax rates differential88.1 56.3 16.8 
Base erosion and anti-abuse tax (BEAT) expense0.2 0.9 2.3 
Prior year adjustments (1)
(5.9)6.9 (2.9)
Introduction of Bermuda corporate income tax
2.2 (201.1)— 
Change in valuation allowance (2)
(106.6)4.0 (98.9)
Impact of unrecognized tax benefits (3)
— — — 
Australian non-resident withholding tax— — 1.5 
Foreign exchange0.6 (1.3)(0.3)
Non-deductible expenses0.3 2.5 2.4 
Tax effect of OCI in income statement— — 6.7 
Impact of changes in statutory tax rates
(0.9)(0.3)(5.7)
Total income tax (benefit)
$(22.0)$(132.1)$(78.1)
________________
(1)    The submission dates for filing income tax returns for the Company’s U.S. and U.K. operating subsidiaries are after the submission date of these consolidated financial statements. Accordingly, the final tax liabilities may differ from the estimated income tax expense included in these consolidated financial statements and may result in prior year adjustments being reported. The prior period adjustments for the twelve months ended December 31, 2024 predominantly relate to the determination of the results of the U.K. operating subsidiaries and its branches. The prior period adjustments for the twelve months ended December 31, 2023 and 2022 predominantly relate to the determination of results in the U.K.
(2)    The decrease in valuation allowance in 2024 related to a change in judgment about the recoverability of deferred tax assets in Aspen UK.
    The decrease in valuation allowance in 2022 related to a change in judgment about the recoverability of deferred tax assets in the U.S. operating subsidiaries.
(3)    In 2024, the Company did not have any unrecognized tax benefits.
Tax Effects of Deferred Tax Assets and Deferred Tax Liabilities
The tax effects of temporary differences and carryforwards that give rise to deferred tax assets and deferred tax liabilities are presented in the following table as at December 31, 2024 and 2023:
 As at December 31,
 20242023
 ($ in millions)
Deferred tax assets:
Operating loss carryforwards$181.1 $217.2 
Capital loss carryforwards17.8 9.7 
Insurance reserves: Losses and loss adjustment expenses111.2 104.1 
Unrealized losses on investments7.4 8.9 
Accrued expenses11.3 13.4 
Foreign tax credit carryforwards22.0 19.0 
Insurance reserves: Unearned premiums34.5 35.0 
Intangible assets82.7 82.9 
Office properties and equipment14.7 16.5 
Operating lease liabilities15.0 15.6 
Other temporary differences8.1 7.6 
Total deferred tax assets$505.8 $529.9 
Less valuation allowance(64.0)(172.7)
Deferred tax assets, net of valuation allowance$441.8 $357.2 
Deferred tax liabilities:  
Intangible assets$(0.2)$— 
Deferred acquisition costs(31.0)(32.4)
Right-of-use operating lease assets(10.4)(10.4)
Insurance reserves: Losses and loss adjustment expenses— (0.1)
Other temporary differences(3.4)(3.3)
Total deferred tax (liabilities)$(45.0)$(46.2)
Net deferred tax assets
$396.8 $311.0 
v3.25.1
Capital Structure (Tables)
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Summary of Authorized and Issued Share Capital
The following table provides a summary of the Company’s authorized and issued share capital as at December 31, 2024 and 2023:
 As at December 31, 2024As at December 31, 2023
 Number$ in
Thousands		Number$ in
Thousands
Authorized share capital:
Ordinary Shares $0.01 per share (2023 — $0.01 per share)
750,000,000 $7,500 70,000,000 $700 
Preference Shares $0.0015144558 per share
150,000,000 227 30,000,000 45 
Total authorized share capital$7,727 $745 
Issued share capital:
Issued ordinary shares $0.01 par value per share (2023 — $0.01 par value per share)
60,395,839 $604 60,395,839 $604 
Issued 5.950% preference shares of $0.0015144558 par value per share each with a liquidation preference of $25 per preference share
11,000,000 17 11,000,000 17 
Issued 5.625% preference shares of $0.0015144558 par value per share each with a liquidation preference of $25 per preference share
10,000,000 15 10,000,000 15 
Issued 5.625% preference shares of $0.0015144558 par value per share represented by depositary shares, each with a liquidation preference of $25,000 per preference share (1)
10,000 — 10,000 — 
Issued 7.000% preference shares of $0.0015144558 par value per share represented by depositary shares, each with a liquidation preference of $25,000 per preference share (2)
9,000 — — — 
Total issued share capital$636 $636 
 ______________
(1)    Each depositary share represents a 1/1000th interest in a share of the 5.625% preference shares.
(2)    Each depositary share represents a 1/1000th interest in a share of the 7.000% preference shares.
v3.25.1
Earnings Per Share (Tables)
 12 Months Ended
Dec. 31, 2024
Earnings Per Share [Abstract]  
Schedule of Earnings Per Share, Basic and Diluted
In December 2023, the Company filed a registration statement with the SEC relating to a proposed Initial Public Offering of our ordinary shares. As a result of that filing, and in accordance with the accounting guidance of ASC Topic 260, “Earnings Per Share”, the Company has presented the following disclosure on earnings per ordinary share. This disclosure was new for the fiscal year ended December 31, 2023.
Basic and diluted earnings per ordinary share are calculated by dividing net income available to holders of Aspen Insurance Holdings Limited’s ordinary shares by the weighted average number of ordinary shares outstanding. The following table presents the computation of basic and diluted earnings per ordinary share for the twelve months ended December 31, 2024, 2023 and 2022.
Twelve Months Ended December 31,
202420232022
($ in millions, except share and per share amounts)
Net income
$486.1 $534.7 $51.1 
Less: Preference share dividends
(54.9)(49.9)(44.6)
Net income available to Aspen Insurance Holdings Limited’s ordinary shareholders
$431.2 $484.8 $6.5 
Basic and diluted weighted average ordinary shares outstanding
60,395,83960,395,83960,395,839
Basic and diluted earnings per ordinary share$7.14 $8.03 $0.11 
v3.25.1
Statutory Requirements and Dividends Restrictions (Tables)
 12 Months Ended
Dec. 31, 2024
Disclosure Statutory Requirements And Dividends Restrictions Summary Of Statutory Requirements And Dividends Restrictions [Abstract]  
Summary of Statutory Capital and Surplus Requirements
Actual and required statutory capital and surplus for the principal Operating Subsidiaries of the Company, excluding its Lloyd’s syndicate, as at December 31, 2024 and December 31, 2023 were estimated as follows:
 As at December 31, 2024
 
U.S.
Bermuda
U.K. 
 ($ in millions)
Required statutory capital and surplus$565.7 $579.3 $277.3 
Actual statutory capital and surplus$1,164.9 $1,761.3 $651.0 
 As at December 31, 2023
 
U.S.
Bermuda
U.K. 
 ($ in millions)
Required statutory capital and surplus$488.9 $601.1 $257.2 
Actual statutory capital and surplus$1,063.1 $1,685.2 $734.7 
v3.25.1
Dividends (Tables)
 12 Months Ended
Dec. 31, 2024
Dividends [Abstract]  
Schedule of Dividends Payable [Table Text Block] n the twelve months ended December 31, 2024, the Company’s Board of Directors paid the following preference share dividends:
Calendar Quarter
Preference Share Category (1)
Quarterly Total
Declared
Paid
5.950% PS
5.625% PS
5.625% DS
Q1 2024$6,595,600 $3,516,000 $3,515,600 $13,627,200 03/01/2404/01/24
Q2 2024$6,669,300 $3,516,000 $3,515,600 $13,700,900 05/30/2407/01/24
Q3 2024$6,741,900 $3,516,000 $3,515,600 $13,773,500 08/30/2410/01/24
Q4 2024$6,815,600 $3,516,000 $3,515,600 $13,847,200 11/29/2412/30/24
Total Paid
$26,822,400 $14,064,000 $14,062,400 $54,948,800 
Per Share
$2.44 $1.41 $1,406.24 
 ______________
(1)    5.950% Preference Shares (AHL PRC) — Fixed to Floating Rate Perpetual Non-Cumulative Preference Shares.
5.625% Preference Shares (AHL PRD) — Perpetual Non-Cumulative Preference Shares.
5.625% Preference Shares (AHL PRE) are represented by depositary shares, each representing a 1/1000th interest in a share of the 5.625% Preference Shares. The dividend paid per depositary share is likewise 1/1000th of the declared dividend, equivalent to $1.40624 per depositary share.
v3.25.1
Operating Leases (Tables)
 12 Months Ended
Dec. 31, 2024
Leases [Abstract]  
Lease, Cost
Operating lease charge. The following table summarizes the operating lease charge for the twelve months ended December 31, 2024, 2023 and 2022:
For the Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Amortization charge on right-of-use operating leased assets$9.9 $10.7 $10.1 
Interest on operating lease liabilities4.1 4.5 5.4 
Operating lease charge$14.0 $15.2 $15.5 
Lessee, Operating Lease, Liability
Lease Liabilities. The following table summarizes the maturity of lease liabilities under non-cancellable leases as of December 31, 2024 and 2023:
December 31, 2024December 31, 2023
 ($ in millions)
Operating leases — maturities
2024
$— $15.4 
2025
15.4 15.1 
2026
14.6 14.3 
2027
13.2 12.8 
2028
13.0 12.7 
2029
10.9 11.2 
Later years21.5 21.2 
Total minimum lease payments$88.6 $102.7 
Less imputed interest(13.0)(16.6)
Total lease liabilities$75.6 $86.1 
Summary of Other Lease Information
Other lease information. The following table summarizes the cash flows on operating leases for the twelve months ended December 31, 2024, 2023 and 2022 and other supplemental information:
For the Twelve Months Ended
December 31, 2024December 31, 2023December 31, 2022
 ($ in millions)
Cash paid for amounts included in the measurement of lease liabilities
 - Operating cash outflow from operating leases$(15.9)$(15.5)$(15.5)
Right-of-use assets obtained in exchange for lease obligations
 - Operating leases$2.1 $0.2 $1.9 
Reduction to Right-of-use assets resulting from reductions to lease obligations
 - Operating leases$0.3 $0.1 $7.0 
Weighted Averages
 - Operating leases, remaining lease terms (years)6.47.38.1
 - Operating leases, average discount rate5.1 %5.0 %5.0 %
v3.25.1
Commitments and Contingencies (Tables)
 12 Months Ended
Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]  
Schedule of Company's Restricted Assets
The following table details the forms and values of the Company’s material restricted assets as at December 31, 2024 and 2023:
As at December 31, 2024As at December 31, 2023
 
($ in millions, except for percentages)
Regulatory trusts and deposits:
Affiliated transactions$433.4 $660.8 
Third party2,713.5 2,714.4 
Letters of credit / guarantees (1)
153.2 172.0 
Total restricted assets (excluding illiquid assets)$3,300.1 $3,547.2 
Other investments — illiquid assets267.2 209.3 
Total restricted assets and illiquid assets$3,567.3 $3,756.5 
Total as percentage of cash and invested assets (2)
46.4 %50.2 %
_____________
(1)    As at December 31, 2024, the Company had pledged funds of $153.2 million (December 31, 2023 — $172.0 million) as collateral for the secured letters of credit.
(2)    Investable assets comprise total investments, cash and cash equivalents, accrued interest, receivables for securities sold and payables for securities purchased.
v3.25.1
Reclassifications from Accumulated Other Comprehensive Income (Tables)
 12 Months Ended
Dec. 31, 2024
Equity [Abstract]  
Schedule of Accumulated Other Comprehensive Income Reclassification
The following table sets out the components of the Company’s Accumulated Other Comprehensive Income (“AOCI”) that are reclassified into the consolidated statement of operations for the twelve months ended December 31, 2024, 2023 and 2022:
Amount Reclassified from AOCI
Details about the AOCI ComponentsTwelve Months Ended December 31, 2024Twelve Months Ended December 31, 2023Twelve Months Ended December 31, 2022
Affected Line Item in the Consolidated Statement of Operations
 ($ in millions) 
Available for sale:
Realized (gains) on sale of securities$(3.2)$(2.2)$(3.9)Realized and unrealized investment gains
Realized losses on sale of securities62.6 42.4 58.9 Realized and unrealized investment losses
59.4 40.2 55.0 
Income from operations before income tax
Tax on net realized losses of securities
(11.5)(6.6)— Income tax (expense)/benefit
$47.9 $33.6 $55.0 
Net income
Realized derivatives:
Net realized losses/(gains) on settled derivatives
$0.9 $(8.1)$15.4 General, administrative and corporate expenses
Tax on settled derivatives(0.2)— — Income tax (expense)/benefit
$0.7 $(8.1)$15.4 
Net income
Total reclassifications from AOCI to the statement of operations, net of income tax$48.6 $25.5 $70.4 
Net income
v3.25.1
Credit Facility and Long-term Debt (Tables)
 12 Months Ended
Dec. 31, 2024
Debt Disclosure [Abstract]  
Summary of Contractual Obligations Under Long-term Debts
The following table summarizes our contractual obligations under long-term debt as at December 31, 2024.
 
Payments Due By Period
Contractual Basis
Less than 1 year
1-3 years
3-5 years 
More than 5 years
Total
 ($ in millions)
Long-term Debt Obligations$— $300.0 $— $— $300.0 
v3.25.1
Credit Losses (Tables)
 12 Months Ended
Dec. 31, 2024
Credit Loss [Abstract]  
Debt Securities, Available-for-Sale, Allowance for Credit Loss
The following tables summarize the Company’s allowance for expected credit losses for the twelve months ended December 31, 2024 and December 31, 2023 in available for sale investments, reinsurance recoverables and receivables:
Available for Sale InvestmentsDecember 31,
20242023
($ in millions)
Balance at the beginning of the period$2.9 $7.7 
Additions to the allowance for credit losses on securities for which credit losses were not previously recognized0.3 0.3 
Decreases to the allowance for credit losses on securities that had an allowance in the prior period
(0.9)(3.6)
Reductions to the allowance for securities sold(1.3)(1.5)
Balance at the end of the period$1.0 $2.9 
Reinsurance Recoverable, Allowance for Credit Loss
December 31, 2024December 31, 2023
Reinsurance RecoverablesReceivablesReinsurance RecoverablesReceivables
($ in millions)($ in millions)
Balance at the beginning of the year$3.7 $21.0 $3.7 $25.0 
Movement in the year23.8 3.6 — (4.0)
Balance at the end of the year$27.5 $24.6 $3.7 $21.0 
v3.25.1
Basis of Preparation and Significant Accounting Policies - Additional Information (Details)
 12 Months Ended
Dec. 31, 2024
period
Property, Plant and Equipment [Line Items]  
Non-Payment Of Dividends, Number Of Periods 6
Computer Equipment | Minimum  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 3 years
Computer Equipment | Maximum  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 5 years
Furniture and Fixtures  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 4 years
Leasehold Improvements  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 15 years
Computer Software, Intangible Asset | Minimum  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 3 years
Computer Software, Intangible Asset | Maximum  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment, Useful Life 5 years
v3.25.1
Segment Reporting - Additional Information - Narrative (Details)
 12 Months Ended
Dec. 31, 2024
segement
Segment Reporting [Abstract]  
Number of business segments 2
v3.25.1
Segment Reporting - Summary of Gross and Net Written and Earned Premiums, Underwriting Results, Ratios and Reserves for Each of Company's Business Segments (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Segment Reporting Information [Line Items]        
Gross written premiums $ 4,609.3 $ 3,967.6 $ 4,338.7  
Net written premiums 2,942.6 2,581.9 2,896.0  
Gross earned premiums 4,387.8 4,006.8 3,988.0  
Net earned premiums 2,889.7 2,614.5 2,688.7  
Losses and loss adjustment expenses 1,717.8 1,553.0 1,680.0  
Acquisition costs 420.2 380.2 431.8  
General and administrative expenses 405.9 354.5 386.5  
Underwriting income (loss) 345.8 326.8 190.4  
Corporate and other expenses (97.3) (114.0) (71.7)  
Non-operating expenses (2) (29.9) (35.1) (36.0)  
Net investment income (1) 318.0 [1] 275.7 188.1  
Gain (loss) on investments 52.6 75.9 5.0  
Realized and unrealized investment losses [2] (102.1) (61.4) (182.6)  
Change in fair value of derivatives (21.1) 26.1 (80.5)  
Interest Expense, Debt (62.1) (55.2) (43.7)  
Net realized and unrealized foreign exchange gains 60.2 (36.2) 15.9  
Other income 0.0 0.0 8.2  
Other expenses 0.0 0.0 20.1  
Income (loss) from operations before income taxes 464.1 402.6 (27.0)  
Income Tax Expense (Benefit) 22.0 132.1 78.1  
Net income/(loss) 486.1 534.7 51.1  
Reserve for losses and loss adjustment expenses 8,122.6 7,810.6 7,710.9 $ 7,611.8
Net reserve for losses and LAE at the start of the year $ 3,950.6 $ 3,232.8 $ 2,813.2 $ 4,313.7
Ratios        
Loss ratio 59.40% 59.40% 62.50%  
Acquisition cost ratio 14.50% 14.50% 16.10%  
General and administrative expense ratio 14.00% 13.60% 14.40%  
Expense ratio 28.50% 28.10% 30.50%  
Combined ratio 87.90% 87.50% 93.00%  
Reinsurance        
Segment Reporting Information [Line Items]        
Net written premiums $ 1,275.7 $ 1,098.0 $ 1,426.4  
Net earned premiums 1,305.7 1,154.5 1,251.8  
Reserve for losses and loss adjustment expenses 1,691.5 1,373.1 1,360.7  
Net reserve for losses and LAE at the start of the year $ 1,691.5 $ 1,373.1 $ 1,360.7  
Ratios        
Loss ratio 56.80% 52.90% 61.50%  
Acquisition cost ratio 17.40% 18.10% 20.20%  
General and administrative expense ratio 10.90% 10.40% 11.40%  
Expense ratio 28.30% 28.50% 31.60%  
Combined ratio 85.10% 81.40% 93.10%  
Insurance        
Segment Reporting Information [Line Items]        
Net written premiums $ 1,666.9 $ 1,483.9 $ 1,469.6  
Net earned premiums 1,584.0 1,460.0 1,436.9  
Reserve for losses and loss adjustment expenses 2,259.1 1,859.7 1,452.5  
Net reserve for losses and LAE at the start of the year $ 2,259.1 $ 1,859.7 $ 1,452.5  
Ratios        
Loss ratio 61.60% 64.50% 63.30%  
Acquisition cost ratio 12.20% 11.80% 12.50%  
General and administrative expense ratio 16.70% 16.00% 17.00%  
Expense ratio 28.90% 27.80% 29.50%  
Combined ratio 90.50% 92.30% 92.80%  
Operating Segments | Reinsurance        
Segment Reporting Information [Line Items]        
Gross written premiums $ 1,885.8 $ 1,521.0 $ 1,807.0  
Net written premiums 1,275.7 1,098.0 1,426.4  
Gross earned premiums 1,822.1 1,562.0 1,617.2  
Net earned premiums 1,305.7 1,154.5 1,251.8  
Losses and loss adjustment expenses 741.3 611.1 770.3  
Acquisition costs 227.0 208.6 252.4  
General and administrative expenses 141.7 120.6 142.5  
Underwriting income (loss) 195.7 214.2 86.6  
Operating Segments | Insurance        
Segment Reporting Information [Line Items]        
Gross written premiums 2,723.5 2,446.6 2,531.7  
Net written premiums 1,666.9 1,483.9 1,469.6  
Gross earned premiums 2,565.7 2,444.8 2,370.8  
Net earned premiums 1,584.0 1,460.0 1,436.9  
Losses and loss adjustment expenses 976.5 941.9 909.7  
Acquisition costs 193.2 171.6 179.4  
General and administrative expenses 264.2 233.9 244.0  
Underwriting income (loss) $ 150.1 $ 112.6 $ 103.8  
[1] Net investment income includes related party net investment income of $15.2 million (2023 — $19.6 million, 2022 — $3.1 million) and related party investment management fees of $9.2 million (2023 — $9.4 million, 2022 — $4.9 million).
[2] Realized and unrealized investments gains includes gains of $2.5 million on related party investments (2023 — gains of $8.7 million, 2022 — loss of $0.4 million).
v3.25.1
Segment Reporting - Summary of the Schedule of the Company's gross written premiums based on the location of the insured risk (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Segment Reporting Information [Line Items]      
Gross written premiums $ 4,609.3 $ 3,967.6 $ 4,338.7
Australia/Asia      
Segment Reporting Information [Line Items]      
Gross written premiums 177.8 177.8 257.5
Europe      
Segment Reporting Information [Line Items]      
Gross written premiums 208.1 179.4 194.5
United Kingdom & Ireland      
Segment Reporting Information [Line Items]      
Gross written premiums 614.8 532.5 485.8
United States & Canada      
Segment Reporting Information [Line Items]      
Gross written premiums 2,947.0 2,472.0 2,715.7
Worldwide excluding United States      
Segment Reporting Information [Line Items]      
Gross written premiums 33.4 28.8 24.2
Worldwide including United States      
Segment Reporting Information [Line Items]      
Gross written premiums 435.0 417.2 541.7
Other (4)      
Segment Reporting Information [Line Items]      
Gross written premiums $ 193.2 $ 159.9 $ 119.3
v3.25.1
Investments - Summary of Investment Income (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income $ 329.5 $ 287.3 $ 198.4
Gain (loss) on investments 52.6 75.9 5.0
Investment expenses (11.5) (11.6) (10.3)
Net investment income 318.0 [1] 275.7 188.1
Fixed income securities — Available for sale      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 161.5 115.7 95.6
Fixed income securities — Trading      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 88.2 98.9 57.0
Short-term investments — Available for sale      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 4.5 5.3 0.6
Short-term investments — Trading      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 0.1 0.3 0.1
Fixed term deposits (included in cash and cash equivalents)      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 45.3 39.9 6.6
Catastrophe bonds — Trading      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 0.0 0.2 0.3
Privately-held investments — Available for sale      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 1.2 0.1 0.0
Privately-held investments — Trading      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Investment income 34.9 44.7 24.3
Other investments, at fair value      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Gain (loss) on investments $ 6.2 $ 17.8 $ 13.9
[1] Net investment income includes related party net investment income of $15.2 million (2023 — $19.6 million, 2022 — $3.1 million) and related party investment management fees of $9.2 million (2023 — $9.4 million, 2022 — $4.9 million).
v3.25.1
Investments - Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Fixed income securities - gross realized gains $ 2.4 $ 1.6 $ 2.9
Realized losses on sale of securities (60.6) (41.5) (58.4)
Net change in expected credit gains (losses) 1.9 4.8 (5.0)
Fixed income securities, trading - gross realized gains 1.2 1.0 0.2
Fixed income securities, trading, gross realizes (losses) (10.0) (3.5) (1.8)
Privately-held investments net unrealized gains/(losses) 26.8 65.9 (113.9)
Catastrophe bonds 0.0 0.1 0.2
Total net realized and unrealized investment (losses)/gains recorded in the consolidated statement of operations (49.5) 14.5 (177.6)
Change in available for sale net unrealized gains/(losses):      
Available for sale investments 34.1 126.2 (391.7)
Income tax (expense)/benefit (4.7) (20.6) 23.9
Total change in net unrealized gains/(losses), net of taxes recorded in other comprehensive income 29.4 105.6 (367.8)
Privately-held investments      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Fixed income securities, trading - gross realized gains 0.8 0.8 0.7
Fixed income securities, trading, gross realizes (losses) (28.8) 0.0 (0.1)
Privately-held investments net unrealized gains/(losses) 18.6 (15.2) (2.5)
Short-term investments — Available for sale      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Fixed income securities - gross realized gains 0.8 0.6 1.0
Realized losses on sale of securities (2.0) (0.9) (0.5)
Fixed income securities, trading - gross realized gains 0.0 0.1 0.0
Fixed income securities, trading, gross realizes (losses) (0.3) (0.3) 0.0
MVI      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Income/(loss) from equity method investment (0.2) 0.2 0.0
Multi-Line Insurer      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Income/(loss) from equity method investment 0.1 0.8 (0.4)
Digital Re      
Schedule of Investment Income, Reported Amounts, by Category [Line Items]      
Income/(loss) from equity method investment $ (0.2) $ 0.0 $ 0.0
v3.25.1
Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Available for Sale Investments in Fixed Income Maturities and Short-Term Investments (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost $ 5,147.0 $ 4,438.3
Gross Unrealized Gains 14.2 17.5
Gross Unrealized Losses (181.9) (221.8)
Allowance for Credit Losses (1.0) (2.9)
Fair Market Value 4,978.3 4,231.1
Fixed income investments    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 4,861.1 4,330.0
Gross Unrealized Gains 14.0 17.3
Gross Unrealized Losses (181.9) (221.8)
Allowance for Credit Losses (1.0) (2.9)
Fair Market Value 4,692.2 4,122.6
U.S. government    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 1,504.8 1,224.9
Gross Unrealized Gains 1.5 4.4
Gross Unrealized Losses (25.7) (26.7)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 1,480.6 1,202.6
U.S. agency    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 7.5 7.5
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses (0.3) (0.3)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 7.2 7.2
Municipal    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 84.2 133.6
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses (1.9) (5.0)
Allowance for Credit Losses 0.0 (0.5)
Fair Market Value 82.3 128.1
Corporate    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 2,045.3 2,051.1
Gross Unrealized Gains 8.5 12.1
Gross Unrealized Losses (66.4) (101.5)
Allowance for Credit Losses (1.0) (2.4)
Fair Market Value 1,986.4 1,959.3
Non-U.S. government-backed corporate    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 132.9 106.5
Gross Unrealized Gains 0.8 0.1
Gross Unrealized Losses (2.4) (5.9)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 131.3 100.7
Non-U.S. government    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 248.2 279.9
Gross Unrealized Gains 1.0 0.6
Gross Unrealized Losses (2.4) (6.7)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 246.8 273.8
Asset-backed    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 232.4  
Gross Unrealized Gains 2.2  
Gross Unrealized Losses (0.1)  
Allowance for Credit Losses 0.0  
Fair Market Value 234.5  
Agency commercial mortgage-backed securities    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 5.0 6.6
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses (0.6) (0.8)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 4.4 5.8
Agency residential mortgage-backed securities    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 600.8 519.9
Gross Unrealized Gains 0.0 0.1
Gross Unrealized Losses (82.1) (74.9)
Allowance for Credit Losses 0.0 0.0
Fair Market Value 518.7 445.1
Short-term investments — Available for sale    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 261.9 93.6
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Allowance for Credit Losses 0.0 0.0
Fair Market Value 261.9 93.6
Privately-held investments    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 24.0 14.7
Gross Unrealized Gains 0.2 0.2
Gross Unrealized Losses 0.0 0.0
Allowance for Credit Losses 0.0 0.0
Fair Market Value $ 24.2 $ 14.9
v3.25.1
Investments - Cost, Gross Unrealized Gains and Losses, and Estimated Fair Value of Trading Investments in Fixed Income Maturities (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost $ 1,497.7 $ 2,025.6
Gross Unrealized Gains 7.7 6.1
Gross Unrealized Losses (16.7) (67.3)
Fair Market Value 1,488.7 1,964.4
Fixed income investments    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 1,207.7 1,527.0
Gross Unrealized Gains 6.2 4.7
Gross Unrealized Losses (14.0) (46.0)
Fair Market Value 1,199.9 1,485.7
U.S. government    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 262.9 248.7
Gross Unrealized Gains 0.6 0.5
Gross Unrealized Losses (2.2) (3.7)
Fair Market Value 261.3 245.5
Municipal    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 1.6 3.3
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 (0.2)
Fair Market Value 1.6 3.1
Corporate    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 155.5 178.8
Gross Unrealized Gains 0.5 0.7
Gross Unrealized Losses (4.9) (8.0)
Fair Market Value 151.1 171.5
High yield loans    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 101.7 90.8
Gross Unrealized Gains 0.9 1.3
Gross Unrealized Losses (0.2) 0.0
Fair Market Value 102.4 92.1
Non-U.S. government-backed corporate    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 2.8 8.6
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 (0.3)
Fair Market Value 2.8 8.3
Non-U.S. government    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 24.4 35.8
Gross Unrealized Gains 0.1 0.1
Gross Unrealized Losses (0.1) (1.1)
Fair Market Value 24.4 34.8
Asset-backed    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 624.6 936.0
Gross Unrealized Gains 4.1 2.1
Gross Unrealized Losses (3.5) (29.9)
Fair Market Value 625.2 908.2
Agency mortgage-backed    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 34.2 25.0
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses (3.1) (2.8)
Fair Market Value 31.1 22.2
Short-term investments — Available for sale    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 1.0 2.1
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Fair Market Value 1.0 2.1
Catastrophe bonds, trading    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 1.0 1.6
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses 0.0 0.0
Fair Market Value 1.0 1.6
Privately-held investments    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 288.0 494.9
Gross Unrealized Gains 1.5 1.4
Gross Unrealized Losses (2.7) (21.3)
Fair Market Value 286.8 475.0
Commercial mortgage loans    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 80.9 293.2
Gross Unrealized Gains 0.5 1.0
Gross Unrealized Losses (1.7) (19.3)
Fair Market Value 79.7 274.9
Middle market loans and other private debt    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 61.6 85.9
Gross Unrealized Gains 0.1 0.0
Gross Unrealized Losses (0.7) (1.1)
Fair Market Value 61.0 84.8
Asset-backed securities    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 126.7 83.1
Gross Unrealized Gains 0.9 0.4
Gross Unrealized Losses 0.0 (0.6)
Fair Market Value 127.6 82.9
Global corporate securities    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost 18.8 14.7
Gross Unrealized Gains 0.0 0.0
Gross Unrealized Losses (0.3) (0.3)
Fair Market Value $ 18.5 14.4
Short-term investments    
Schedule of Trading Securities and Other Trading Items [Line Items]    
Cost or Amortized Cost   18.0
Gross Unrealized Gains   0.0
Gross Unrealized Losses   0.0
Fair Market Value   $ 18.0
v3.25.1
Investments - Equity Method Investments (Details) - USD ($)
$ in Millions
 1 Months Ended 12 Months Ended
Jan. 01, 2017
Mar. 31, 2021
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Equity Method Investment, Aggregate Cost [Roll Forward]          
Equity method investments, opening balance     $ 7.6 $ 6.2  
Investment in the period     0.0 0.4 $ 2.0
Equity method investments, closing balance     7.3 7.6 6.2
Equity Method Investments          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Unrealized (loss)/gain     (0.1) 1.0  
Realized (loss) for the twelve months to December 31, 2024     (0.2)    
MVI          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Equity method investments, opening balance     1.0 0.8  
Investment in the period   $ 0.8   0.0 0.4
Equity method investments, closing balance     0.8 1.0 0.8
MVI | Equity Method Investments          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Unrealized (loss)/gain     (0.2) 0.2  
Realized (loss) for the twelve months to December 31, 2024     0.0    
Multi-Line Insurer          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Equity method investments, opening balance     6.4 5.2  
Investment in the period     0.0 0.4  
Equity method investments, closing balance     6.5 6.4 5.2
Multi-Line Insurer | Equity Method Investments          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Unrealized (loss)/gain     0.1 0.8  
Realized (loss) for the twelve months to December 31, 2024     0.0    
Digital Re          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Equity method investments, opening balance     0.2 0.2  
Investment in the period $ 2.3     0.0  
Equity method investments, closing balance     0.0 0.2 $ 0.2
Digital Re | Equity Method Investments          
Equity Method Investment, Aggregate Cost [Roll Forward]          
Unrealized (loss)/gain     0.0 $ 0.0  
Realized (loss) for the twelve months to December 31, 2024     $ (0.2)    
v3.25.1
Investments - Summary of Fixed Maturities (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]    
Cost or Amortized Cost $ 5,147.0 $ 4,438.3
Fair Market Value 4,978.3 4,231.1
Fixed income securities    
Debt Securities, Available-for-sale [Line Items]    
Due one year or less, Cost or Amortized Cost 834.1 512.0
Due one year or less, Fair Market Value 831.2 505.8
Due after one year through five years, Cost or Amortized Cost 2,386.5 2,889.0
Due after one year through five years, Fair Market Value 2,353.2 2,818.9
Due after five years through ten years, Cost or Amortized Cost 1,060.7 495.1
Due after five years through ten years, Fair Market Value 1,008.7 440.3
Due after ten years, Cost or Amortized Cost 3.5 15.7
Due after ten years, Fair Market Value 3.4 15.2
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost 4,284.8 3,911.8
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Fair Value 4,196.5 3,780.2
Non-agency commercial mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost 5.0 6.6
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value 4.4 5.8
Cost or Amortized Cost 5.0 6.6
Fair Market Value 4.4 5.8
Agency mortgage-backed    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost 600.8 519.9
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value 518.7 $ 445.1
Asset backed securities and privately held asset backed securities    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Amortized Cost 256.4  
Debt Securities, Available-for-Sale, Maturity, without Single Maturity Date, Fair Value $ 258.7  
v3.25.1
Investments - Aggregate Fair Value and Gross Unrealized Loss by Type of Security (Details)
$ in Millions
Dec. 31, 2024
USD ($)
security
Dec. 31, 2023
USD ($)
Security
security
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 1,625.0 $ 196.5
Gross unrealized losses, less than twelve months (22.3) (2.1)
Over 12 months, Fair Market Value 1,604.9 2,802.0
Over 12 months, Gross Unrealized Losses (159.6) (219.7)
Total, Fair Market Value 3,229.9 2,998.5
Total, Gross Unrealized Losses $ (181.9) $ (221.8)
Number of Securities 1,170 950
Securities Below Investment Grade or NR $ 1.2  
Fixed income securities — Available for sale    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value   $ 0.1
Gross unrealized losses, less than twelve months   0.0
Over 12 months, Fair Market Value   435.9
Over 12 months, Gross Unrealized Losses   (74.9)
Total, Fair Market Value   436.0
Total, Gross Unrealized Losses   $ (74.9)
Number of Securities | Security   197
U.S. government    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value 718.1 $ 105.5
Gross unrealized losses, less than twelve months (11.6) (0.5)
Over 12 months, Fair Market Value 397.8 673.3
Over 12 months, Gross Unrealized Losses (14.1) (26.2)
Total, Fair Market Value 1,115.9 778.8
Total, Gross Unrealized Losses $ (25.7) $ (26.7)
Number of Securities | security 137 74
U.S. agency    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 0.0  
Gross unrealized losses, less than twelve months 0.0  
Over 12 months, Fair Market Value 7.2  
Over 12 months, Gross Unrealized Losses (0.3)  
Total, Fair Market Value 7.2  
Total, Gross Unrealized Losses $ (0.3)  
Number of Securities | security 1  
Municipal    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 33.6 $ 0.0
Gross unrealized losses, less than twelve months (0.7) 0.0
Over 12 months, Fair Market Value 45.4 7.2
Over 12 months, Gross Unrealized Losses (1.2) (0.3)
Total, Fair Market Value 79.0 7.2
Total, Gross Unrealized Losses $ (1.9) $ (0.3)
Number of Securities | security 47 1
Corporate    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 570.3 $ 11.1
Gross unrealized losses, less than twelve months (6.8) (1.0)
Over 12 months, Fair Market Value 663.9 117.0
Over 12 months, Gross Unrealized Losses (59.6) (4.0)
Total, Fair Market Value 1,234.2 128.1
Total, Gross Unrealized Losses $ (66.4) $ (5.0)
Number of Securities | security 692 54
Non-U.S. government-backed corporate    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 5.8 $ 46.7
Gross unrealized losses, less than twelve months 0.0 (0.4)
Over 12 months, Fair Market Value 91.1 1,287.2
Over 12 months, Gross Unrealized Losses (2.4) (101.1)
Total, Fair Market Value 96.9 1,333.9
Total, Gross Unrealized Losses $ (2.4) $ (101.5)
Number of Securities | security 12 558
Non-U.S. government    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 118.8 $ 0.2
Gross unrealized losses, less than twelve months (0.9) 0.0
Over 12 months, Fair Market Value 43.7 95.5
Over 12 months, Gross Unrealized Losses (1.5) (5.9)
Total, Fair Market Value 162.5 95.7
Total, Gross Unrealized Losses $ (2.4) $ (5.9)
Number of Securities | security 41 12
Non-agency commercial mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 0.0  
Gross unrealized losses, less than twelve months 0.0  
Over 12 months, Fair Market Value 4.5  
Over 12 months, Gross Unrealized Losses (0.6)  
Total, Fair Market Value 4.5  
Total, Gross Unrealized Losses $ (0.6)  
Number of Securities | security 1  
Agency residential mortgage-backed securities    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 161.2  
Gross unrealized losses, less than twelve months (2.2)  
Over 12 months, Fair Market Value 351.3  
Over 12 months, Gross Unrealized Losses (79.9)  
Total, Fair Market Value 512.5  
Total, Gross Unrealized Losses $ (82.1)  
Number of Securities | security 225  
Agency mortgage-backed    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value   $ 0.0
Gross unrealized losses, less than twelve months   0.0
Over 12 months, Fair Market Value   5.8
Over 12 months, Gross Unrealized Losses   (0.8)
Total, Fair Market Value   5.8
Total, Gross Unrealized Losses   $ (0.8)
Number of Securities | security   1
Asset-backed    
Debt Securities, Available-for-sale [Line Items]    
0-12 months, Fair Market Value $ 17.2 $ 32.9
Gross unrealized losses, less than twelve months (0.1) (0.2)
Over 12 months, Fair Market Value 0.0 180.1
Over 12 months, Gross Unrealized Losses 0.0 (6.5)
Total, Fair Market Value 17.2 213.0
Total, Gross Unrealized Losses $ (0.1) $ (6.7)
Number of Securities | security 14 53
v3.25.1
Investments - Additional Information (Narrative) (Details)
 1 Months Ended 12 Months Ended
Jan. 01, 2017
USD ($)
Mar. 31, 2021
USD ($)
Dec. 31, 2024
USD ($)
security
Dec. 31, 2023
USD ($)
security
Dec. 31, 2022
USD ($)
Dec. 31, 2024
GBP (£)
security
Aug. 01, 2024
USD ($)
Dec. 31, 2023
GBP (£)
security
Sep. 30, 2023
USD ($)
Aug. 31, 2023
GBP (£)
Apr. 01, 2023
USD ($)
May 05, 2022
USD ($)
Apr. 01, 2022
USD ($)
Sep. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 23, 2019
USD ($)
Dec. 20, 2017
USD ($)
Gain (Loss) on Securities [Line Items]                                  
Catastrophe bonds, trading at fair value (amortized cost — 2024: $1.0 and 2023: $1.6)     $ 1,000,000.0 $ 1,600,000                          
Fair Market Value     1,488,700,000 1,964,400,000                          
Investment in the period     0 400,000 $ 2,000,000.0                        
Other Investments [1]     267,200,000 $ 209,300,000                          
Investment funded     $ 0                            
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions     (1,170) (950)   (1,170)   (950)                  
Total, Gross Unrealized Losses     $ (181,900,000) $ (221,800,000)                          
Securities Below Investment Grade or NR     1,200,000                            
Investment, Identifier [Axis]: Unfunded Commitment, Real Estate (2021)Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     900,000 2,200,000                          
Investment, Identifier [Axis]: Unfunded Commitment, Apollo Real Estate Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     3,700,000 4,100,000                          
Investment, Identifier [Axis]: Unfunded Commitment, Energy Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     55,000,000.0 55,000,000.0                          
Investment, Identifier [Axis]: Unfunded Commitment, Infrastructure fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     2,300,000 4,000,000.0                          
Investment, Identifier [Axis]: Unfunded Commitment, Lloyd's Enhanced Liquidity Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     0                            
Investment, Identifier [Axis]: Unfunded Commitment, Managed Debt Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment | £           £ 6,800,000   £ 6,900,000                  
Investment, Identifier [Axis]: Unfunded Commitment, Managed lending fund                                  
Gain (Loss) on Securities [Line Items]                                  
Unfunded commitment     200,000 1,100,000                          
Fair Value, Recurring [Member]                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     111,700,000 117,100,000                          
Fair Value, Recurring [Member] | Managed Lending Fund (Dec 2020)                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     19,300,000 15,900,000                          
Fair Value, Recurring [Member] | Pledge Accounts, Custodian Bank (April 2021)                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     2,000,000 1,700,000                          
Fair Value, Recurring [Member] | Real estate fund (Sept 2021)                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     36,200,000 39,800,000                 $ 10,000,000.0        
Fair Value, Recurring [Member] | Real estate fund                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     267,200,000 209,300,000                          
Fair Value, Recurring [Member] | Apollo real estate fund                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     19,300,000 23,900,000                          
Fair Value, Recurring [Member] | Infrastructure fund                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     12,900,000 10,800,000                          
Fair Value, Recurring [Member] | Managed Debt Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     100,000 100,000                          
Fair Value, Recurring [Member] | Lloyd's enhanced liquidity fund                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     25,700,000                            
Fair Value, Recurring [Member] | Five Times Square                                  
Gain (Loss) on Securities [Line Items]                                  
Investments, fair value     40,000,000.0                            
Limited Partner                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets                           $ 20,000,000.0     $ 100,000,000.0
Limited Partner | Managed lending fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets                     $ 2,800,000       $ 10,500,000    
Limited Partner | Real estate fund | Apollo real estate fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets                         $ 30,000,000.0        
Limited Partner | Infrastructure fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets                       $ 15,000,000.0          
Limited Partner | Managed Debt Fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets | £                   £ 7,000,000.0              
Limited Partner | Third party energy fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets                 $ 55,000,000.0                
Limited Partner | Lloyd's enhanced liquidity fund                                  
Gain (Loss) on Securities [Line Items]                                  
Restricted Assets             $ 25,000,000.0                    
MVI                                  
Gain (Loss) on Securities [Line Items]                                  
Investment in the period   $ 800,000   0 $ 400,000                        
Digital Re                                  
Gain (Loss) on Securities [Line Items]                                  
Investment in the period $ 2,300,000     0                          
Equity method investment, ownership percentage 49.00%                                
Multi-Line Insurer                                  
Gain (Loss) on Securities [Line Items]                                  
Investment in the period     0 400,000                          
Unfunded commitment                               $ 5,000,000.0  
Commercial mortgage loans                                  
Gain (Loss) on Securities [Line Items]                                  
Fair Market Value     79,700,000 274,900,000                          
Middle market loans and other private debt                                  
Gain (Loss) on Securities [Line Items]                                  
Fair Market Value     $ 61,000,000.0 $ 84,800,000                          
[1] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
v3.25.1
Variable Interest Entities - Narrative (Details) - Investment
Dec. 31, 2024
Dec. 31, 2023
Payables and Accruals [Abstract]    
Number of investments in VIEs 1 1
v3.25.1
Fair Value Measurements - Financial Assets Measured on Recurring Basis (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value [1] $ 24,200,000 $ 14,900,000  
Catastrophe Bonds, Fair Value Disclosure 1,000,000.0 1,600,000  
Derivative assets 17,000,000.0 31,700,000  
Fair Market Value 4,978,300,000 4,231,100,000  
Fair Market Value 1,488,700,000 1,964,400,000  
Recurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 111,700,000 117,100,000  
Privately-held Investments, at fair value 286,800,000    
Total 6,701,700,000 6,410,700,000  
Recurring | Derivatives at fair value | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Derivative assets 17,000,000.0 31,700,000  
Recurring | Liabilities under derivative contracts | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value (45,900,000) (9,300,000)  
Recurring | Liabilities under derivative contracts | Loss Portfolio Transfer      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value (3,600,000) (16,500,000)  
Recurring | Fixed income securities | Non-agency commercial mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 4,400,000    
Recurring | Fixed income securities — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 4,692,200,000 4,122,600,000  
Recurring | Short-term investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 261,900,000 93,600,000  
Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,199,900,000 1,485,700,000  
Catastrophe Bonds, Fair Value Disclosure 1,000,000.0 1,600,000  
Recurring | Short-term investments trading at fair value      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,000,000.0    
Recurring | Real estate fund      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 267,200,000 209,300,000  
Recurring | Privately-held investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value 24,200,000    
Recurring | Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, at fair value 0    
Total 2,207,800,000 1,748,400,000  
Recurring | Level 1 | Derivatives at fair value | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Derivative assets 0 0  
Recurring | Level 1 | Liabilities under derivative contracts | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value 0 0  
Recurring | Level 1 | Liabilities under derivative contracts | Loss Portfolio Transfer      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value 0 0  
Recurring | Level 1 | Fixed income securities | Non-agency commercial mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Recurring | Level 1 | Fixed income securities — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,675,700,000 1,403,000,000  
Recurring | Level 1 | Short-term investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 260,200,000 86,700,000  
Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 270,900,000 258,500,000  
Catastrophe Bonds, Fair Value Disclosure 0 0  
Recurring | Level 1 | Short-term investments trading at fair value      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,000,000.0    
Recurring | Level 1 | Real estate fund      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Recurring | Level 1 | Privately-held investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value 0    
Recurring | Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, at fair value 0    
Total 3,919,300,000 3,979,600,000  
Recurring | Level 2 | Derivatives at fair value | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Derivative assets 17,000,000.0 31,700,000  
Recurring | Level 2 | Liabilities under derivative contracts | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value (45,900,000) (9,300,000)  
Recurring | Level 2 | Liabilities under derivative contracts | Loss Portfolio Transfer      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value 0 0  
Recurring | Level 2 | Fixed income securities | Non-agency commercial mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 4,400,000    
Recurring | Level 2 | Fixed income securities — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 3,016,500,000 2,719,600,000  
Recurring | Level 2 | Short-term investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,700,000 6,900,000  
Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 929,000,000.0 1,227,200,000  
Catastrophe Bonds, Fair Value Disclosure 1,000,000.0 1,600,000  
Recurring | Level 2 | Short-term investments trading at fair value      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Recurring | Level 2 | Real estate fund      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Recurring | Level 2 | Privately-held investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value 0    
Recurring | Level 3      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, at fair value 286,800,000    
Total 307,400,000 473,400,000  
Change in unrealized investment gains (losses) 1,300,000 (15,700,000)  
Fair Market Value 311,000,000.0 489,900,000  
Recurring | Level 3 | Liability      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities at beginning of year (3,600,000) (16,500,000) $ (31,700,000)
Liability purchases 0 0  
Liability transfers 0 0  
Liability, Transfers out of Level 3 0 0  
Liability sales 0 0  
Liability, increase (decrease) in fv included in net income 12,900,000 15,200,000  
Change in unrealized gains or losses 12,900,000 15,200,000  
Recurring | Level 3 | Loss Portfolio Transfer | Liability      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities at beginning of year (3,600,000) (16,500,000) (31,700,000)
Liability purchases 0 0  
Liability transfers 0 0  
Liability, Transfers out of Level 3 0 0  
Liability sales 0 0  
Liability, increase (decrease) in fv included in net income 12,900,000 15,200,000  
Change in unrealized gains or losses 12,900,000 15,200,000  
Recurring | Level 3 | Derivatives at fair value | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Derivative assets 0 0  
Recurring | Level 3 | Liabilities under derivative contracts | Foreign exchange contracts      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value 0 0  
Recurring | Level 3 | Liabilities under derivative contracts | Loss Portfolio Transfer      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Liabilities under derivative contracts, fair value (3,600,000) (16,500,000)  
Recurring | Level 3 | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 71,400,000 113,700,000  
Transferred in or out of Level 3 0    
Transfers Into Level 3 0 5,300,000  
Transfers out of Level 3   12,100,000  
Settlements and sales (239,700,000) (137,200,000)  
Increase (decrease) in fair value included in net income (10,600,000) (12,800,000)  
Fair Market Value   489,900,000 533,000,000.0
Recurring | Level 3 | Fixed income securities | Non-agency commercial mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Recurring | Level 3 | Fixed income securities — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Recurring | Level 3 | Short-term investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Catastrophe Bonds, Fair Value Disclosure 0 0  
Recurring | Level 3 | Short-term investments trading at fair value      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Recurring | Level 3 | Real estate fund      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Recurring | Level 3 | Commercial mortgage loans      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses) 0 (17,900,000)  
Fair Market Value 79,700,000 274,900,000  
Recurring | Level 3 | Commercial mortgage loans | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 500,000 40,600,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Settlements and sales (184,400,000) (61,500,000)  
Increase (decrease) in fair value included in net income (11,300,000) (16,300,000)  
Fair Market Value   274,900,000 312,100,000
Recurring | Level 3 | Middle market loans and other private debt      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses) 0 500,000  
Fair Market Value 61,000,000.0 84,800,000  
Recurring | Level 3 | Middle market loans and other private debt | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 400,000 18,300,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Settlements and sales (35,500,000) (41,900,000)  
Increase (decrease) in fair value included in net income 400,000 1,500,000  
Fair Market Value   84,800,000 106,900,000
Recurring | Level 3 | Global corporate securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses) 0 (200,000)  
Fair Market Value 18,500,000 14,400,000  
Recurring | Level 3 | Global corporate securities | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 4,400,000 0  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Settlements and sales (300,000) (400,000)  
Increase (decrease) in fair value included in net income 0 (200,000)  
Fair Market Value   14,400,000 15,000,000.0
Recurring | Level 3 | Equity Securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses)   0  
Fair Market Value   0  
Recurring | Level 3 | Equity Securities | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances   0  
Transfers Into Level 3   0  
Transfers out of Level 3   (6,600,000)  
Settlements and sales   0  
Increase (decrease) in fair value included in net income   0  
Fair Market Value     6,600,000
Recurring | Level 3 | Short-term investments      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses) 0 0  
Fair Market Value 0 18,000,000.0  
Recurring | Level 3 | Short-term investments | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 0 18,200,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Settlements and sales (7,100,000) (25,800,000)  
Increase (decrease) in fair value included in net income 0 0  
Fair Market Value   18,000,000.0 25,600,000
Recurring | Level 3 | Asset-backed      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized investment gains (losses) 1,100,000 1,700,000  
Fair Market Value 127,600,000 82,900,000  
Recurring | Level 3 | Asset-backed | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Purchases and issuances 56,100,000 21,900,000  
Transfers Into Level 3 0 5,300,000  
Transfers out of Level 3 0 (5,500,000)  
Settlements and sales (12,400,000) (7,600,000)  
Increase (decrease) in fair value included in net income 1,000,000.0 2,000,000.0  
Fair Market Value   82,900,000 66,800,000
Recurring | Level 3 | Privately-held investments — Available for sale      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value 24,200,000    
U.S. government      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 1,480,600,000 1,202,600,000  
Fair Market Value 261,300,000 245,500,000  
U.S. government | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,480,600,000 1,202,600,000  
U.S. government | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 261,300,000 245,500,000  
U.S. government | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,480,600,000 1,202,600,000  
U.S. government | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 261,300,000 245,500,000  
U.S. government | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
U.S. government | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
U.S. government | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
U.S. government | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
U.S. agency      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 7,200,000 7,200,000  
U.S. agency | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 7,200,000 7,200,000  
U.S. agency | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
U.S. agency | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 7,200,000 7,200,000  
U.S. agency | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Municipal      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 82,300,000 128,100,000  
Fair Market Value 1,600,000 3,100,000  
Municipal | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 82,300,000 128,100,000  
Municipal | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,600,000 3,100,000  
Municipal | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Municipal | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Municipal | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 82,300,000 128,100,000  
Municipal | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,600,000 3,100,000  
Municipal | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Municipal | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Corporate      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 1,986,400,000 1,959,300,000  
Fair Market Value 151,100,000 171,500,000  
Corporate | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,986,400,000 1,959,300,000  
Corporate | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 151,100,000 171,500,000  
Corporate | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Corporate | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Corporate | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 1,986,400,000 1,959,300,000  
Corporate | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 151,100,000 171,500,000  
Corporate | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Corporate | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government-backed corporate      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 131,300,000 100,700,000  
Fair Market Value 2,800,000 8,300,000  
Non-U.S. government-backed corporate | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 131,300,000 100,700,000  
Non-U.S. government-backed corporate | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 2,800,000 8,300,000  
Non-U.S. government-backed corporate | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government-backed corporate | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government-backed corporate | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 131,300,000 100,700,000  
Non-U.S. government-backed corporate | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 2,800,000 8,300,000  
Non-U.S. government-backed corporate | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government-backed corporate | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 246,800,000 273,800,000  
Fair Market Value 24,400,000 34,800,000  
Non-U.S. government | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 246,800,000 273,800,000  
Non-U.S. government | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 24,400,000 34,800,000  
Non-U.S. government | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 195,100,000 200,400,000  
Non-U.S. government | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 9,600,000 13,000,000.0  
Non-U.S. government | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 51,700,000 73,400,000  
Non-U.S. government | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 14,800,000 21,800,000  
Non-U.S. government | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-U.S. government | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Asset-backed      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 234,500,000    
Fair Market Value 625,200,000 908,200,000  
Asset-backed | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 234,500,000    
Asset-backed | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 625,200,000 908,200,000  
Asset-backed | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Asset-backed | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Asset-backed | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 234,500,000    
Asset-backed | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 625,200,000 908,200,000  
Asset-backed | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Asset-backed | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Non-agency commercial mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 4,400,000 5,800,000  
Non-agency commercial mortgage-backed securities | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   5,800,000  
Non-agency commercial mortgage-backed securities | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   0  
Non-agency commercial mortgage-backed securities | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   5,800,000  
Non-agency commercial mortgage-backed securities | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   0  
Agency residential mortgage-backed securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 518,700,000 445,100,000  
Agency residential mortgage-backed securities | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 518,700,000    
Agency residential mortgage-backed securities | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Agency residential mortgage-backed securities | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 518,700,000    
Agency residential mortgage-backed securities | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0    
Agency mortgage-backed      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 31,100,000 22,200,000  
Agency mortgage-backed | Recurring | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   445,100,000  
Agency mortgage-backed | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 31,100,000 22,200,000  
Agency mortgage-backed | Recurring | Level 1 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   0  
Agency mortgage-backed | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Agency mortgage-backed | Recurring | Level 2 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   445,100,000  
Agency mortgage-backed | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 31,100,000 22,200,000  
Agency mortgage-backed | Recurring | Level 3 | Fixed income securities      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   0  
Agency mortgage-backed | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
High yield loans      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 102,400,000 92,100,000  
High yield loans | Recurring | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 102,400,000 92,100,000  
High yield loans | Recurring | Level 1 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
High yield loans | Recurring | Level 2 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 102,400,000 92,100,000  
High yield loans | Recurring | Level 3 | Fixed income securities, trading      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value 0 0  
Fixed income securities, trading | Recurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value   14,900,000  
Privately-held Investments, at fair value   475,000,000.0  
Fixed income securities, trading | Recurring | Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value   0  
Privately-held Investments, at fair value   0  
Fixed income securities, trading | Recurring | Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value   0  
Privately-held Investments, at fair value   0  
Fixed income securities, trading | Recurring | Level 3      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Privately-held Investments, available for sale, at fair value   14,900,000  
Privately-held Investments, at fair value   475,000,000.0  
Short-term investments trading at fair value | Recurring      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   2,100,000  
Short-term investments trading at fair value | Recurring | Level 1      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   200,000  
Short-term investments trading at fair value | Recurring | Level 2      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   1,900,000  
Short-term investments trading at fair value | Recurring | Level 3      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Investments, fair value   0  
Asset backed securities, privately-held afs | Recurring | Level 3      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value 24,200,000 14,900,000  
Change in unrealized investment gains (losses) 200,000 200,000  
Asset backed securities, privately-held afs | Recurring | Level 3 | Assets      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Fair Market Value   14,900,000 $ 0
Purchases and issuances 10,000,000.0 14,700,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Settlements and sales 0 0  
Increase (decrease) in fair value included in net income $ (700,000) $ 200,000  
[1] Privately-held investments, trading at fair value include related party investments totaling $73.6 million (2023 — $112.4 million). Privately-held investments, available for sale include related party investments totaling $Nil (2023 — $14.9 million).
v3.25.1
Fair Value Measurements Fair Value Measurements - Reconciliation of Level 3 Assets and Liabilities (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration] Accumulated other comprehensive (loss)    
Fair Market Value $ 4,978,300,000 $ 4,231,100,000  
Fair Market Value 1,488,700,000 1,964,400,000  
Level 3 | Fair Value, Recurring [Member]      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 1,300,000 (15,700,000)  
Fair Market Value 311,000,000.0 489,900,000  
Level 3 | Fair Value, Recurring [Member] | Liability      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Asset reclassification 0 0  
Liabilities at beginning of year (3,600,000) (16,500,000) $ (31,700,000)
Liability purchases 0 0  
Liability transfers 0 0  
Liability, Transfers out of Level 3 0 0  
Liability sales 0 0  
Liability, increase (decrease) in fv included in net income 12,900,000 15,200,000  
Change in unrealized gains or losses 12,900,000 15,200,000  
Level 3 | Fair Value, Recurring [Member] | Loss Portfolio Transfer | Liability      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Asset reclassification 0 0  
Liabilities at beginning of year (3,600,000) (16,500,000) (31,700,000)
Liability purchases 0 0  
Liability transfers 0 0  
Liability, Transfers out of Level 3 0 0  
Liability sales 0 0  
Liability, increase (decrease) in fv included in net income 12,900,000 15,200,000  
Change in unrealized gains or losses 12,900,000 15,200,000  
Level 3 | Fair Value, Recurring [Member] | Commercial mortgage loans      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 0 (17,900,000)  
Fair Market Value 79,700,000 274,900,000  
Level 3 | Fair Value, Recurring [Member] | Middle market loans and other private debt      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 0 500,000  
Fair Market Value 61,000,000.0 84,800,000  
Level 3 | Fair Value, Recurring [Member] | Asset-backed      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 1,100,000 1,700,000  
Fair Market Value 127,600,000 82,900,000  
Level 3 | Fair Value, Recurring [Member] | Global corporate securities      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 0 (200,000)  
Fair Market Value 18,500,000 14,400,000  
Level 3 | Fair Value, Recurring [Member] | Short-term investments      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses) 0 0  
Fair Market Value 0 18,000,000.0  
Level 3 | Fair Value, Recurring [Member] | Equity Securities      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Change in unrealized investment gains (losses)   0  
Fair Market Value   0  
Level 3 | Fair Value, Recurring [Member] | Asset backed securities, privately-held afs      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Fair Market Value 24,200,000 14,900,000  
Change in unrealized investment gains (losses) 200,000 200,000  
Assets | Level 3 | Fair Value, Recurring [Member]      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 71,400,000 113,700,000  
Transfers Into Level 3 0 5,300,000  
Transfers out of Level 3   12,100,000  
Asset reclassification 0 0  
Settlements and sales (239,700,000) (137,200,000)  
Increase (decrease) in fair value included in net income (10,600,000) (12,800,000)  
Fair Market Value   489,900,000 533,000,000.0
Assets | Level 3 | Fair Value, Recurring [Member] | Commercial mortgage loans      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 500,000 40,600,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Asset reclassification 0 0  
Settlements and sales (184,400,000) (61,500,000)  
Increase (decrease) in fair value included in net income (11,300,000) (16,300,000)  
Fair Market Value   274,900,000 312,100,000
Assets | Level 3 | Fair Value, Recurring [Member] | Middle market loans and other private debt      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 400,000 18,300,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Asset reclassification 10,900,000 0  
Settlements and sales (35,500,000) (41,900,000)  
Increase (decrease) in fair value included in net income 400,000 1,500,000  
Fair Market Value   84,800,000 106,900,000
Assets | Level 3 | Fair Value, Recurring [Member] | Asset-backed      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 56,100,000 21,900,000  
Transfers Into Level 3 0 5,300,000  
Transfers out of Level 3 0 (5,500,000)  
Asset reclassification 0 0  
Settlements and sales (12,400,000) (7,600,000)  
Increase (decrease) in fair value included in net income 1,000,000.0 2,000,000.0  
Fair Market Value   82,900,000 66,800,000
Assets | Level 3 | Fair Value, Recurring [Member] | Global corporate securities      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 4,400,000 0  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Asset reclassification 0 0  
Settlements and sales (300,000) (400,000)  
Increase (decrease) in fair value included in net income 0 (200,000)  
Fair Market Value   14,400,000 15,000,000.0
Assets | Level 3 | Fair Value, Recurring [Member] | Short-term investments      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances 0 18,200,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Asset reclassification (10,900,000) 0  
Settlements and sales (7,100,000) (25,800,000)  
Increase (decrease) in fair value included in net income 0 0  
Fair Market Value   18,000,000.0 25,600,000
Assets | Level 3 | Fair Value, Recurring [Member] | Equity Securities      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Purchases and issuances   0  
Transfers Into Level 3   0  
Transfers out of Level 3   (6,600,000)  
Asset reclassification   0  
Settlements and sales   0  
Increase (decrease) in fair value included in net income   0  
Fair Market Value     6,600,000
Assets | Level 3 | Fair Value, Recurring [Member] | Asset backed securities, privately-held afs      
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward]      
Fair Market Value   14,900,000 $ 0
Purchases and issuances 10,000,000.0 14,700,000  
Transfers Into Level 3 0 0  
Transfers out of Level 3 0 0  
Asset reclassification 0 0  
Settlements and sales 0 0  
Increase (decrease) in fair value included in net income $ (700,000) $ 200,000  
v3.25.1
Fair Value Measurements - Inputs Used (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Recurring  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 286.8
Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value 286.8
Total, Privately-held Investments $ 311.0
Discounted cash flow | Commercial mortgage loans | Minimum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.038
Discounted cash flow | Commercial mortgage loans | Maximum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.119
Discounted cash flow | Commercial mortgage loans | Weighted Average | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.057
Discounted cash flow | Commercial mortgage loans | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 79.7
Discounted cash flow | Middle market loans | Minimum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.072
Discounted cash flow | Middle market loans | Maximum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.180
Discounted cash flow | Middle market loans | Weighted Average | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.098
Discounted cash flow | Middle market loans | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 61.0
Discounted cash flow | Asset-backed | Minimum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.054
Available-for-Sale, Measurement input 0.055
Discounted cash flow | Asset-backed | Maximum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.083
Available-for-Sale, Measurement input 0.095
Discounted cash flow | Asset-backed | Weighted Average | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.066
Available-for-Sale, Measurement input 0.071
Discounted cash flow | Asset-backed | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 127.6
Discounted cash flow | Global corporate securities | Minimum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.067
Discounted cash flow | Global corporate securities | Maximum | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.067
Discounted cash flow | Global corporate securities | Weighted Average | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Trading, Measurement inputs 0.067
Discounted cash flow | Global corporate securities | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 14.1
Discounted cash flow | Short-term investments — Available for sale | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value 4.4
Valuation, Market Approach | Asset-backed | Recurring | Level 3  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Privately-held Investments, at fair value $ 24.2
v3.25.1
Fair Value Measurements - Additional Information - Narrative (Details)
 12 Months Ended
Dec. 31, 2024
USD ($)
quotesPerInvestment
Dec. 31, 2023
USD ($)
quotesPerInvestment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Quotes per fixed income investment | quotesPerInvestment 3.0 2.9
Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Privately-held Investments, at fair value $ 286,800,000  
Recurring | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Privately-held Investments, at fair value 286,800,000  
Total, Privately-held Investments 311,000,000.0  
Assets | Recurring | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Transfers out of Level 3   $ 12,100,000
Transfers Into Level 3 0 5,300,000
Settlements and sales $ (239,700,000) (137,200,000)
Equity Securities | Assets | Recurring | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Transfers out of Level 3   (6,600,000)
Transfers Into Level 3   0
Settlements and sales   $ 0
v3.25.1
Reinsurance - Summary of Assumed and Ceded Reinsurance on Premiums Written, Premiums Earned and Insurance Losses and Loss Adjustment Expenses (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Premiums written:      
Insurance $ 2,723.5 $ 2,446.6 $ 2,531.7
Reinsurance 1,885.8 1,521.0 1,807.0
Ceded (1,666.7) (1,385.7) (1,442.7)
Net written premiums 2,942.6 2,581.9 2,896.0
Premiums earned:      
Insurance 2,565.7 2,444.8 2,370.8
Reinsurance 1,822.1 1,562.0 1,617.2
Ceded (1,498.1) (1,392.3) (1,299.3)
Net earned premiums 2,889.7 2,614.5 2,688.7
Losses and loss adjustment expenses:      
Insurance 1,759.1 1,644.5 1,574.2
Reinsurance 915.8 707.2 939.5
Ceded (957.1) (798.7) (833.7)
Losses and loss adjustment expenses $ 1,717.8 $ 1,553.0 $ 1,680.0
v3.25.1
Reinsurance - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]      
Reinsurance Recoverable, Allowance for Credit Loss $ 27.5 $ 3.7 $ 3.7
Reinsurance Recoverable, Allowance for Credit Loss, Period Increase (Decrease) $ 23.8 $ 0.0 $ 0.4
v3.25.1
Derivative Contracts - Fair Value of Derivative Instruments (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Not Designated as Hedging Instrument | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Derivative, Notional Amount $ 1,586.9 $ 1,802.9
Cash collateral 0.8 3.4
Not Designated as Hedging Instrument | Derivative assets | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Fair Value 17.0 31.4
Derivative, Notional Amount 550.0 1,262.1
Not Designated as Hedging Instrument | Derivative liabilities | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Fair Value (41.7) (9.3)
Derivative, Notional Amount 1,036.9 540.8
Not Designated as Hedging Instrument | Derivative liabilities | Embedded Derivative Financial Instruments    
Derivatives, Fair Value [Line Items]    
Fair Value (3.6) (16.5)
Derivative, Notional Amount 0.0 0.0
Designated as Hedging Instrument | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Cash collateral 2.0 0.0
Designated as Hedging Instrument | Derivative assets | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Fair Value 0.0 0.3
Derivative, Notional Amount 0.0 76.9
Designated as Hedging Instrument | Derivative liabilities | Foreign exchange contracts    
Derivatives, Fair Value [Line Items]    
Fair Value (4.2) 0.0
Derivative, Notional Amount $ 158.0 $ 0.0
v3.25.1
Derivative Contracts - Gain/(Loss) Recognized in Income on Derivative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Not Designated as Hedging Instrument | Foreign exchange contracts    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) to net income from derivative instruments $ (34.0) $ 10.9
Not Designated as Hedging Instrument | Loss portfolio transfer liability, embedded derivative    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) to net income from derivative instruments 12.9 15.2
Designated as Hedging Instrument | Foreign exchange contracts | General, administrative and corporate expenses    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) on foreign currency fair value hedge derivatives (0.9) (8.1)
Designated as Hedging Instrument | Foreign exchange contracts | Net change from current period hedged transactions    
Derivative Instruments, Gain (Loss) [Line Items]    
Gain (loss) on foreign currency fair value hedge derivatives $ (6.5) $ (14.0)
v3.25.1
Derivative Contracts - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Oct. 01, 2022
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Reinsurance Contracts [Axis]: Funds withheld credited with interest for periods after October 1, 2022        
Derivative Instruments, Gain (Loss) [Line Items]        
Reinsurance Retention Policy, Retrocession Premium, Interest Rate 1.75%      
Level 3 | Liability | Fair Value, Recurring [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Liability, increase (decrease) in fv included in net income     $ 12.9 $ 15.2
Foreign exchange contracts | Not Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Purchase of US and foreign exchange     1,586.9 1,802.9
Gain (loss) to net income from derivative instruments     (34.0) 10.9
Foreign exchange contracts | Not Designated as Hedging Instrument | Derivative liabilities        
Derivative Instruments, Gain (Loss) [Line Items]        
Purchase of US and foreign exchange     1,036.9 540.8
Foreign exchange contracts | Designated as Hedging Instrument | Derivative liabilities        
Derivative Instruments, Gain (Loss) [Line Items]        
Purchase of US and foreign exchange     158.0 0.0
Foreign exchange contracts | Net change from current period hedged transactions | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (loss) on foreign currency fair value hedge derivatives     (6.5) (14.0)
Foreign exchange contracts | General, administrative and corporate expenses | Designated as Hedging Instrument        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (loss) on foreign currency fair value hedge derivatives     (0.9) (8.1)
Foreign exchange contracts | General, administrative and corporate expenses | Designated as Hedging Instrument | Forecast        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain (loss) on foreign currency fair value hedge derivatives   $ (6.2)    
Loss Portfolio Transfer | Level 3 | Liability | Fair Value, Recurring [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Liability, increase (decrease) in fv included in net income     $ 12.9 $ 15.2
v3.25.1
Deferred Policy Acquisition Costs (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]      
Deferred Policy Acquisition Cost, Beginning Balance $ 296.2 $ 319.0  
Acquisition costs deferred 446.1 357.4  
Amortization of deferred acquisition costs (420.2) (380.2) $ (431.8)
Deferred Policy Acquisition Cost, Ending Balance $ 322.1 $ 296.2 $ 319.0
v3.25.1
Reserves for Losses and Adjustment Expenses - Reconciliation of Beginning and Ending Consolidated Loss and Loss Adjustment Expenses (LAE) Reserves (Details) - USD ($)
$ in Millions
 12 Months Ended
Jan. 10, 2022
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
May 30, 2022
Dec. 31, 2021
Jan. 01, 2020
Insurance [Abstract]              
Provision for losses and LAE, beginning balance   $ 7,810.6 $ 7,710.9 $ 7,611.8      
Less reinsurance recoverable     (4,577.8) (4,897.7)   $ (3,298.1)  
Net loss and LAE expenses disposed (1)   0.0 0.0 1,840.1      
Net losses and LAE reserves, beginning balance   3,232.8 2,813.2 4,313.7      
Movement in net reserve for losses and LAE for claims incurred:              
Current year   1,682.2 1,492.2 1,651.9      
Prior Year   35.6 60.8 28.1      
Total incurred   1,717.8 1,553.0 1,680.0      
Net Losses and LAE payments for claims incurred:              
Current year   (200.2) (161.1) (192.7)      
Prior years   (741.3) (1,011.9) (1,098.4)      
Total paid   (941.5) (1,173.0) (1,291.1)      
Foreign exchange (gains)/losses   (58.5) 39.6 (49.3)      
Net reserve for losses and LAE at the start of the year   3,950.6 3,232.8 2,813.2   $ 4,313.7  
Plus reinsurance recoverable on unpaid losses at the end of the year   4,172.0 4,577.8 4,897.7      
Reserve for losses and LAE at the end of the year   8,122.6 7,810.6 7,710.9      
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]              
Reinsurance recoverable on unpaid losses   4,172.0 4,577.8        
Plus reinsurance recoverable on unpaid losses at the end of the year   4,172.0 4,577.8 4,897.7      
Prior Year   35.6 60.8 28.1      
Reinsurance Contracts [Axis]: LPT              
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]              
Reinsurance recoverable total         $ 2,610.1    
Reinsurance recoverables, premium paid and recognized         $ 1,840.1    
Reinsurance Contracts [Axis]: Retroactive Reinsurance              
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]              
Reinsurance recoverable on unpaid losses   1,190.9 1,627.4        
Insurance              
Insurance [Abstract]              
Provision for losses and LAE, beginning balance   1,859.7 1,452.5        
Net losses and LAE reserves, beginning balance   1,859.7 1,452.5        
Net Losses and LAE payments for claims incurred:              
Net reserve for losses and LAE at the start of the year   2,259.1 1,859.7 1,452.5      
Reserve for losses and LAE at the end of the year   $ 2,259.1 $ 1,859.7 $ 1,452.5      
Enstar              
Net Losses and LAE payments for claims incurred:              
Plus reinsurance recoverable on unpaid losses at the end of the year             $ 770.0
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]              
Plus reinsurance recoverable on unpaid losses at the end of the year             $ 770.0
Enstar | Reinsurance Contracts [Axis]: LPT net losses reinsured              
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]              
Reinsurance, Excess Retention, Amount Reinsured, Per Event $ 3,120.0            
v3.25.1
Reserves for Losses and Adjustment Expenses - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Insurance [Abstract]      
Provision for losses and LAE for claims incurred $ 35.6 $ 60.8 $ 28.1
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Line Items]      
Prior Year $ 35.6 $ 60.8 $ 28.1
v3.25.1
Reserves for Losses and Adjustment Expenses - Reconciliation of Reinsurance Recoverables on Unpaid Losses (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
May 30, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]        
Reinsurance recoverable for unpaid claims under retroactive reinsurance, beginning balance $ 4,577.8      
Reinsurance recoverable for unpaid claims under retroactive reinsurance, beginning balance, Ending Balance 4,172.0 $ 4,577.8    
Provision for losses and LAE for claims incurred 35.6 60.8 $ 28.1  
Reinsurance Contracts [Axis]: LPT        
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]        
Reinsurance recoverables, premium paid and recognized       $ 1,840.1
Reinsurance Contracts [Axis]: Retroactive Reinsurance        
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]        
Reinsurance recoverable for unpaid claims under retroactive reinsurance, beginning balance 1,627.4      
Reinsurance recoverable for unpaid claims under retroactive reinsurance, beginning balance, Ending Balance $ 1,190.9 $ 1,627.4    
v3.25.1
Reserves for Losses and Adjustment Expenses Short-duration Insurance Contracts, Claims by Accident Year (Details)
Dec. 31, 2024
USD ($)
Integer
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Claims Development [Line Items]                    
Liability for claims and claim adjustment expenses, net of reinsurance $ 4,116,600,000 $ 3,629,600,000                
Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 1,816,400,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 1,547,500,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 268,900,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 268,900,000 270,800,000                
Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 1,477,200,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 721,200,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 756,000,000.0                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 756,000,000.0 636,500,000                
Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 1,434,400,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 1,213,100,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 221,300,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 221,300,000 194,500,000                
Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 2,338,700,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 1,357,400,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 981,300,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 981,300,000 837,600,000                
Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 2,925,200,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 2,364,600,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 560,600,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 560,600,000 562,300,000                
Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 1,691,100,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 805,200,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 885,900,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 885,900,000 733,600,000                
Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 2,339,100,000                  
Cumulative paid claims and allocated claim adjustment expense, Net 1,896,500,000                  
All outstanding liabilities for 2015 and subsequent years, net of reinsurance 442,600,000                  
All outstanding liabilities before 2015, net of reinsurance 0                  
Liability for claims and claim adjustment expenses, net of reinsurance 442,600,000 394,300,000                
Accident Year 2015 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 192,300,000 192,300,000 $ 192,300,000 $ 192,300,000 $ 196,300,000 $ 199,400,000 $ 198,800,000 $ 196,500,000 $ 201,700,000 $ 236,000,000.0
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 11,558                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 192,300,000 192,300,000 192,300,000 192,300,000 191,300,000 192,600,000 176,400,000 167,400,000 140,200,000 56,700,000
Accident Year 2015 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 178,900,000 178,900,000 178,900,000 255,600,000 230,300,000 232,000,000.0 199,400,000 182,300,000 219,800,000 199,800,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 4,843                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 178,900,000 178,900,000 178,900,000 178,900,000 165,000,000.0 136,200,000 91,000,000.0 55,700,000 16,600,000 3,100,000
Accident Year 2015 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 266,000,000.0 266,000,000.0 266,000,000.0 317,200,000 309,900,000 307,200,000 283,600,000 278,700,000 296,000,000.0 294,200,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 4,079                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 266,000,000.0 266,000,000.0 266,000,000.0 267,500,000 255,800,000 220,100,000 192,200,000 172,600,000 122,200,000 44,500,000
Accident Year 2015 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 144,400,000 144,400,000 144,400,000 195,800,000 183,000,000.0 188,000,000.0 187,000,000.0 183,100,000 173,000,000.0 171,700,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,082                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 144,400,000 144,400,000 144,400,000 150,100,000 137,700,000 108,800,000 88,700,000 69,700,000 43,200,000 13,600,000
Accident Year 2015 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 151,900,000 151,900,000 151,900,000 173,000,000.0 166,900,000 166,800,000 151,400,000 171,500,000 181,100,000 206,700,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,045                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 151,900,000 151,900,000 151,900,000 155,600,000 154,200,000 151,900,000 135,000,000.0 122,000,000.0 92,400,000 35,600,000
Accident Year 2015 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 115,200,000 115,200,000 115,200,000 192,200,000 201,900,000 205,500,000 207,600,000 204,900,000 195,200,000 188,900,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 2,090                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 115,200,000 115,200,000 115,200,000 115,200,000 106,800,000 88,000,000.0 64,400,000 37,500,000 17,400,000 3,300,000
Accident Year 2015 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 129,200,000 129,200,000 129,200,000 147,900,000 148,100,000 152,500,000 154,000,000.0 159,300,000 164,500,000 161,600,000
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 775                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 129,200,000 129,200,000 129,200,000 129,900,000 130,100,000 127,100,000 118,600,000 101,600,000 54,600,000 $ 17,200,000
Accident Year 2016 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 232,600,000 232,600,000 232,600,000 233,400,000 244,400,000 243,100,000 241,800,000 246,800,000 235,800,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 10,752                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 232,600,000 232,600,000 232,600,000 233,400,000 230,300,000 221,000,000.0 199,500,000 167,300,000 66,300,000  
Accident Year 2016 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 122,900,000 122,900,000 122,900,000 241,300,000 196,900,000 185,800,000 179,400,000 184,300,000 213,300,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 4,850                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 122,900,000 122,900,000 122,900,000 122,000,000.0 107,200,000 80,600,000 39,100,000 22,300,000 4,100,000  
Accident Year 2016 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 196,200,000 196,200,000 196,200,000 218,600,000 216,800,000 227,000,000.0 226,400,000 228,100,000 257,800,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 4,437                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 196,200,000 196,200,000 196,200,000 191,700,000 188,700,000 162,300,000 140,600,000 81,700,000 30,900,000  
Accident Year 2016 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 133,000,000.0 133,000,000.0 133,000,000.0 184,300,000 182,800,000 199,600,000 213,500,000 209,100,000 188,100,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,244                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 133,000,000.0 133,000,000.0 133,000,000.0 129,200,000 124,600,000 128,700,000 100,700,000 70,600,000 14,800,000  
Accident Year 2016 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 221,700,000 221,700,000 221,700,000 224,300,000 231,800,000 236,300,000 256,800,000 257,200,000 257,200,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,281                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 221,700,000 221,700,000 221,700,000 224,300,000 219,500,000 207,000,000.0 196,800,000 157,100,000 54,700,000  
Accident Year 2016 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 135,200,000 135,200,000 135,200,000 246,600,000 255,800,000 248,400,000 238,300,000 238,700,000 226,600,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 2,268                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 135,200,000 135,200,000 135,200,000 135,400,000 123,800,000 94,200,000 62,400,000 32,600,000 8,700,000  
Accident Year 2016 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 185,800,000 185,800,000 185,800,000 208,800,000 221,000,000.0 225,900,000 232,700,000 234,700,000 233,900,000  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 943                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 185,800,000 185,800,000 185,800,000 192,000,000.0 190,600,000 180,500,000 162,700,000 148,800,000 $ 57,900,000  
Accident Year 2017 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 180,400,000 180,400,000 180,400,000 272,100,000 250,100,000 248,800,000 255,600,000 292,500,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 9,711                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 180,400,000 180,400,000 180,400,000 233,600,000 239,700,000 219,000,000.0 186,400,000 95,500,000    
Accident Year 2017 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 60,200,000 60,200,000 60,200,000 213,300,000 192,500,000 175,100,000 171,400,000 177,900,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 5,536                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 60,200,000 60,200,000 60,200,000 88,100,000 94,800,000 51,800,000 22,500,000 3,500,000    
Accident Year 2017 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 135,300,000 135,300,000 135,300,000 224,900,000 213,600,000 206,000,000.0 199,500,000 208,500,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 6,080                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 135,300,000 135,300,000 135,300,000 149,300,000 167,700,000 139,700,000 97,100,000 40,000,000.0    
Accident Year 2017 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 134,400,000 134,400,000 134,400,000 206,800,000 185,200,000 184,600,000 179,700,000 203,700,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,758                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 134,400,000 134,400,000 134,400,000 133,500,000 115,800,000 82,700,000 50,900,000 27,000,000.0    
Accident Year 2017 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 431,800,000 431,800,000 431,800,000 568,900,000 496,900,000 508,100,000 524,900,000 544,800,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,940                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 431,800,000 431,800,000 431,800,000 407,300,000 434,100,000 410,700,000 353,300,000 122,600,000    
Accident Year 2017 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 109,600,000 109,600,000 109,600,000 257,700,000 246,300,000 246,900,000 236,400,000 238,400,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 2,346                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 109,600,000 109,600,000 109,600,000 109,500,000 96,000,000.0 58,100,000 29,900,000 8,700,000    
Accident Year 2017 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 303,300,000 303,300,000 303,300,000 352,600,000 359,100,000 370,000,000.0 385,900,000 372,600,000    
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,337                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 303,300,000 303,300,000 303,300,000 303,300,000 302,400,000 267,800,000 236,600,000 $ 93,800,000    
Accident Year 2018 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 184,400,000 184,400,000 184,400,000 194,700,000 184,800,000 200,800,000 198,700,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 8,202                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 184,400,000 184,400,000 184,400,000 172,100,000 178,400,000 156,100,000 60,900,000      
Accident Year 2018 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 42,600,000 42,600,000 42,600,000 162,600,000 133,300,000 123,300,000 120,400,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 5,500                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 42,600,000 42,600,000 42,600,000 57,300,000 42,100,000 27,500,000 3,100,000      
Accident Year 2018 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 149,900,000 149,900,000 149,900,000 234,500,000 207,500,000 206,400,000 169,300,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 5,201                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 149,900,000 149,900,000 149,900,000 150,500,000 132,500,000 104,200,000 26,600,000      
Accident Year 2018 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 109,700,000 109,700,000 109,700,000 159,700,000 150,700,000 169,300,000 153,600,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 4,645                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 109,700,000 109,700,000 109,700,000 109,800,000 97,600,000 72,300,000 18,300,000      
Accident Year 2018 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 283,000,000.0 283,000,000.0 283,000,000.0 511,700,000 320,500,000 329,700,000 303,700,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,804                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 283,000,000.0 283,000,000.0 283,000,000.0 258,000,000.0 265,600,000 266,800,000 121,400,000      
Accident Year 2018 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 91,700,000 91,700,000 91,700,000 251,200,000 260,600,000 252,600,000 223,700,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 2,262                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 91,700,000 91,700,000 91,700,000 91,800,000 72,600,000 33,000,000.0 7,000,000.0      
Accident Year 2018 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 322,300,000 322,300,000 322,300,000 412,000,000.0 387,400,000 388,900,000 389,300,000      
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,428                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 322,300,000 322,300,000 322,300,000 322,100,000 310,600,000 277,900,000 $ 26,500,000      
Accident Year 2019 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 189,000,000.0 189,000,000.0 189,000,000.0 102,200,000 128,300,000 124,300,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 6,863                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 189,000,000.0 189,000,000.0 189,000,000.0 97,700,000 89,900,000 48,500,000        
Accident Year 2019 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 48,100,000 48,100,000 48,100,000 152,000,000.0 145,200,000 122,900,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 5,217                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 48,100,000 48,100,000 48,100,000 63,700,000 17,200,000 6,200,000        
Accident Year 2019 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 107,000,000.0 107,000,000.0 107,000,000.0 122,700,000 152,200,000 144,600,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 3,699                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 107,000,000.0 107,000,000.0 107,000,000.0 89,300,000 72,100,000 33,300,000        
Accident Year 2019 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 130,800,000 130,800,000 130,800,000 236,300,000 258,100,000 245,900,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 23,819                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 130,800,000 130,800,000 130,800,000 120,400,000 86,200,000 26,800,000        
Accident Year 2019 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 157,500,000 157,500,000 157,500,000 316,300,000 225,000,000.0 209,900,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,399                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 157,500,000 157,500,000 157,500,000 158,800,000 134,100,000 28,000,000.0        
Accident Year 2019 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 52,200,000 52,200,000 52,200,000 241,500,000 250,800,000 230,100,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,939                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 52,200,000 52,200,000 52,200,000 52,000,000.0 36,000,000.0 9,100,000        
Accident Year 2019 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 398,600,000 398,600,000 398,600,000 396,900,000 491,700,000 468,600,000        
Incurred but Not Reported (IBNR) Claims Liability, Net $ 0                  
Number of Reported Claims | Integer 1,557                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 398,600,000 398,600,000 398,600,000 396,900,000 379,000,000.0 $ 272,200,000        
Accident Year 2020 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 213,000,000.0 212,500,000 207,000,000.0 197,500,000 202,000,000.0          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 23,000,000.0                  
Number of Reported Claims | Integer 7,648                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 178,200,000 169,000,000.0 151,200,000 123,700,000 60,700,000          
Accident Year 2020 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 151,800,000 145,500,000 139,400,000 140,400,000 131,800,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 38,100,000                  
Number of Reported Claims | Integer 3,888                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 91,500,000 61,100,000 36,000,000.0 9,300,000 0          
Accident Year 2020 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 150,900,000 126,100,000 125,000,000.0 110,700,000 109,600,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 33,500,000                  
Number of Reported Claims | Integer 3,866                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 109,200,000 100,900,000 88,500,000 66,400,000 28,500,000          
Accident Year 2020 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 352,200,000 349,800,000 336,200,000 345,500,000 345,200,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 73,700,000                  
Number of Reported Claims | Integer 106,042                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 240,000,000.0 225,000,000.0 173,700,000 120,800,000 47,300,000          
Accident Year 2020 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 365,200,000 352,900,000 340,700,000 394,200,000 312,200,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 5,200,000                  
Number of Reported Claims | Integer 1,436                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 306,000,000.0 306,000,000.0 232,700,000 162,200,000 41,100,000          
Accident Year 2020 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 187,200,000 178,200,000 195,800,000 231,200,000 250,200,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 42,400,000                  
Number of Reported Claims | Integer 1,563                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 100,900,000 70,700,000 43,500,000 27,300,000 8,900,000          
Accident Year 2020 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 369,500,000 377,100,000 372,900,000 598,700,000 411,200,000          
Incurred but Not Reported (IBNR) Claims Liability, Net $ 15,100,000                  
Number of Reported Claims | Integer 1,519                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 333,000,000.0 310,100,000 289,600,000 269,200,000 $ 212,500,000          
Accident Year 2021 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 191,100,000 194,600,000 201,000,000.0 206,300,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 9,200,000                  
Number of Reported Claims | Integer 6,770                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 162,900,000 150,600,000 119,200,000 58,400,000            
Accident Year 2021 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 194,600,000 196,100,000 186,900,000 171,900,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 81,700,000                  
Number of Reported Claims | Integer 3,679                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 91,300,000 53,500,000 23,300,000 3,100,000            
Accident Year 2021 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 96,500,000 94,700,000 95,100,000 92,200,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 11,900,000                  
Number of Reported Claims | Integer 4,787                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 70,400,000 64,400,000 52,200,000 23,500,000            
Accident Year 2021 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 294,800,000 293,500,000 301,600,000 283,900,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 86,200,000                  
Number of Reported Claims | Integer 34,963                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 161,900,000 131,100,000 90,000,000.0 43,100,000            
Accident Year 2021 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 472,500,000 479,800,000 461,200,000 637,700,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 4,900,000                  
Number of Reported Claims | Integer 1,518                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 414,800,000 351,500,000 229,200,000 74,600,000            
Accident Year 2021 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 199,400,000 203,600,000 213,800,000 203,500,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 63,200,000                  
Number of Reported Claims | Integer 1,594                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 96,400,000 63,300,000 36,800,000 7,700,000            
Accident Year 2021 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 136,400,000 140,000,000.0 150,300,000 155,200,000            
Incurred but Not Reported (IBNR) Claims Liability, Net $ 24,300,000                  
Number of Reported Claims | Integer 1,385                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 87,900,000 75,200,000 52,800,000 $ 28,000,000.0            
Accident Year 2022 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 170,900,000 173,200,000 166,000,000.0              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 13,500,000                  
Number of Reported Claims | Integer 5,801                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 143,400,000 113,200,000 41,000,000.0              
Accident Year 2022 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 208,700,000 212,900,000 202,400,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 119,400,000                  
Number of Reported Claims | Integer 3,594                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 46,400,000 26,600,000 8,900,000              
Accident Year 2022 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 112,700,000 105,300,000 107,200,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 25,700,000                  
Number of Reported Claims | Integer 5,410                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 73,500,000 57,500,000 24,900,000              
Accident Year 2022 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 268,600,000 299,800,000 314,100,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 121,300,000                  
Number of Reported Claims | Integer 3,356                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 113,400,000 75,100,000 17,700,000              
Accident Year 2022 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 372,100,000 378,900,000 380,500,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 43,600,000                  
Number of Reported Claims | Integer 1,475                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 261,300,000 193,600,000 63,300,000              
Accident Year 2022 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 246,000,000.0 247,800,000 246,600,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 138,500,000                  
Number of Reported Claims | Integer 1,650                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 59,600,000 30,700,000 9,100,000              
Accident Year 2022 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 196,200,000 191,600,000 192,600,000              
Incurred but Not Reported (IBNR) Claims Liability, Net $ 98,900,000                  
Number of Reported Claims | Integer 1,458                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 74,300,000 52,600,000 $ 25,300,000              
Accident Year 2023 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 130,100,000 150,800,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 44,300,000                  
Number of Reported Claims 4,056                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 65,200,000 29,800,000                
Accident Year 2023 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 233,800,000 223,100,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 156,000,000.0                  
Number of Reported Claims 3,105                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 3,300,000 5,500,000                
Accident Year 2023 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 110,300,000 116,600,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 20,800,000                  
Number of Reported Claims 3,997                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 73,200,000 27,800,000                
Accident Year 2023 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 347,600,000 338,500,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 169,100,000                  
Number of Reported Claims 3,385                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 100,600,000 21,300,000                
Accident Year 2023 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 215,000,000.0 223,600,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 40,400,000                  
Number of Reported Claims | Integer 1,104                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 103,800,000 43,900,000                
Accident Year 2023 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 267,700,000 268,300,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 187,600,000                  
Number of Reported Claims | Integer 1,565                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 35,000,000.0 8,200,000                
Accident Year 2023 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 144,300,000 140,700,000                
Incurred but Not Reported (IBNR) Claims Liability, Net $ 73,000,000.0                  
Number of Reported Claims | Integer 1,188                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 48,100,000 $ 22,300,000                
Accident Year 2024 | Property Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 132,600,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 84,200,000                  
Number of Reported Claims 1,879                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 19,100,000                  
Accident Year 2024 | Casualty Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 235,600,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 203,200,000                  
Number of Reported Claims 1,782                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 36,000,000.0                  
Accident Year 2024 | Marine, Aviation and Energy Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 109,600,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 62,300,000                  
Number of Reported Claims 2,358                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 32,400,000                  
Accident Year 2024 | Financial and Professional Insurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 423,200,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 292,300,000                  
Number of Reported Claims 3,756                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 89,200,000                  
Accident Year 2024 | Property Catastrophe and Other Property Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 254,500,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 135,500,000                  
Number of Reported Claims | Integer 737                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 32,800,000                  
Accident Year 2024 | Casualty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 286,900,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 260,000,000.0                  
Number of Reported Claims | Integer 848                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 9,400,000                  
Accident Year 2024 | Specialty Reinsurance                    
Claims Development [Line Items]                    
Incurred Claims and Allocated Claim Adjustment Expense, Net 153,500,000                  
Incurred but Not Reported (IBNR) Claims Liability, Net $ 125,600,000                  
Number of Reported Claims | Integer 803                  
Cumulative paid claims and allocated claim adjustment expense, Net $ 14,000,000.0                  
v3.25.1
Reserves for Losses and Adjustment Expenses Short-duration insurance contracts - Reconciliation of Claims Development (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance $ 4,116.6 $ 3,629.6    
Reinsurance recoverable on unpaid losses 4,172.0 4,577.8    
Unallocated claims incurred 58.0 47.9    
Carbon syndicate reserves 26.5 16.7    
Other 0.0 0.4    
Liability for unpaid claims and claim adjustment expense, aggregate reconciling items (166.0) (396.8)    
Reserve for losses and loss adjustment expenses 8,122.6 7,810.6 $ 7,710.9 $ 7,611.8
Property Insurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 268.9 270.8    
Casualty Insurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 756.0 636.5    
Marine, Aviation and Energy Insurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 221.3 194.5    
Financial and Professional Insurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 981.3 837.6    
Insurance lines        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 2,227.5 1,939.4    
Reinsurance recoverable on unpaid losses 2,698.0 2,821.6    
Property Catastrophe and Other Property Reinsurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 560.6 562.3    
Casualty Reinsurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 885.9 733.6    
Specialty Reinsurance        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 442.6 394.3    
Reinsurance lines        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Liability for claims and claim adjustment expenses, net of reinsurance 1,889.1 1,690.2    
Reinsurance recoverable on unpaid losses 1,474.0 1,756.2    
Insurance lines other than short-duration        
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]        
Other reinsurance balances recoverable (311.7) (489.1)    
Reserve for losses and loss adjustment expenses $ 61.2 $ 27.3    
v3.25.1
Reserves for Losses and Adjustment Expenses Short-duration Contracts - Historical Claims Duration (Details)
Dec. 31, 2024
Property Insurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 29.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 38.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 13.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 12.20%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 3.30%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (5.80%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven 0.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight 0.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Casualty Insurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 4.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 19.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 32.20%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 23.40%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 3.50%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (3.60%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (2.10%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight 0.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Marine, Aviation and Energy Insurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 23.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 34.50%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 19.60%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 11.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 2.60%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (0.90%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (1.70%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight (0.20%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Financial and Professional Insurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 14.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 28.40%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 19.60%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 14.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 4.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (4.80%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (2.90%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight (1.30%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Property Catastrophe and Other Property Reinsurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 21.50%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 42.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 16.20%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 6.90%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 3.20%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (1.90%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (0.10%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight (0.80%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Casualty Reinsurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 6.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 19.20%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 21.60%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 19.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 11.80%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (5.00%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (1.80%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight 0.00%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
Specialty Reinsurance  
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]  
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year One 26.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Two 32.80%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Three 12.70%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Four 7.60%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Five 3.10%
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Six (0.60%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Seven (0.90%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Eight (0.20%)
Average Annual Percentage Payout of Incurred Claims, Net of Reinsurance, Year Nine 0.00%
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance, Year Ten 0.00%
v3.25.1
Income Taxes - Summary of Total Income Tax (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax Disclosure [Abstract]      
Income tax (benefit) allocated to net income $ (22.0) $ (132.1) $ (78.1)
Income tax expense/(benefit) allocated to other comprehensive income 3.3 20.6 (23.9)
Total income tax (benefit) $ (18.7) $ (111.5) $ (102.0)
v3.25.1
Income Taxes - Income/(Loss) Before Tax and Income Tax Expense/(Benefit) Attributable to that Income (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax Examination [Line Items]      
(Loss) before tax, U.S. $ 269.0 $ 236.3 $ 34.8
Income (loss) from operations before income taxes 464.1 402.6 (27.0)
Current tax (benefit)/expense, U.S. 62.7 52.4 14.8
Current tax (benefit)/expense, Total 66.6 65.6 26.5
Deferred tax (benefit), U.S. (4.4) 3.0 (102.9)
Deferred tax, Total (88.6) (197.7) (104.6)
Total tax expense/(benefit), U.S. 58.3 55.4 (88.1)
Total tax expense/(benefit) (22.0) (132.1) (78.1)
Base erosion and anti-abuse (BEAT) expense 0.2 0.9 2.3
Bermuda      
Income Tax Examination [Line Items]      
(Loss) before tax, Non-U.S. 85.3 148.8 (103.3)
Current tax (benefit)/expense, Non-U.S. 0.0 0.0 0.0
Deferred tax (benefit), Non-U.S. 1.3 (201.1) 0.0
Total tax expense/(benefit), Non-U.S. 1.3 (201.1) 0.0
Net deferred tax asset, Bermuda 158.9 156.6  
Opening tax loss adjustment 40.0 44.5  
U.K.      
Income Tax Examination [Line Items]      
(Loss) before tax, Non-U.S. 106.9 0.7 62.4
Current tax (benefit)/expense, Non-U.S. 3.9 5.3 7.0
Deferred tax (benefit), Non-U.S. (85.3) 0.1 0.0
Total tax expense/(benefit), Non-U.S. (81.4) 5.4 7.0
Deferred foreign income tax, brought forward valuation allowance 107.7    
Other      
Income Tax Examination [Line Items]      
(Loss) before tax, Non-U.S. 2.9 16.8 (20.9)
Current tax (benefit)/expense, Non-U.S. 0.0 7.9 4.7
Deferred tax (benefit), Non-U.S. (0.2) 0.3 (1.7)
Total tax expense/(benefit), Non-U.S. $ (0.2) $ 8.2 $ 3.0
v3.25.1
Income Taxes - Income Tax Reconciliation (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Operating Loss Carryforwards [Line Items]      
Income tax benefit at statutory tax rate of zero percent $ 0.0 $ 0.0 $ 0.0
Overseas statutory tax rates differential 88.1 56.3 16.8
Base erosion and anti-abuse (BEAT) expense 0.2 0.9 2.3
Prior year adjustments (5.9) 6.9 (2.9)
Introduction of Bermuda corporate income tax 2.2 (201.1) 0.0
Change in valuation allowance (2) (106.6) 4.0 (98.9)
Impact of unrecognized tax benefits 0.0 0.0 0.0
Australian non-resident withholding tax 0.0 0.0 1.5
Foreign exchange 0.6 (1.3) (0.3)
Non-deductible expenses 0.3 2.5 2.4
Tax effect of OCI in income statement 0.0 0.0 6.7
Non-taxabke items (0.9) (0.3) (5.7)
Total tax expense/(benefit) $ (22.0) $ (132.1) $ (78.1)
v3.25.1
Income Taxes - Tax Effects of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Income Tax Disclosure [Abstract]    
Operating loss carryforwards $ 181.1 $ 217.2
Capital loss carryforwards 17.8 9.7
Insurance reserves: Losses and loss adjustment expenses 111.2 104.1
Unrealized losses on investments 7.4 8.9
Accrued expenses 11.3 13.4
Foreign tax credit carryforwards 22.0 19.0
Unearned premiums 34.5 35.0
Intangible assets 82.7 82.9
Office properties and equipment 14.7 16.5
Operating lease liability 15.0 15.6
Other temporary differences 8.1 7.6
Total deferred tax assets 505.8 529.9
Less valuation allowance (64.0) (172.7)
Deferred tax assets, net of valuation allowance 441.8 357.2
Deferred acquisition costs (31.0) (32.4)
Intangible assets 0.2 0.0
Operating lease assets (10.4) (10.4)
Deferred Tax Liabilities, GAAP differences 0.0 0.1
Other temporary differences (3.4) (3.3)
Total deferred tax (liabilities) (45.0) (46.2)
Deferred tax assets, net $ 396.8 $ 311.0
v3.25.1
Income Taxes - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Apr. 01, 2023
Dec. 31, 2024
Dec. 31, 2022
Dec. 31, 2026
Dec. 31, 2023
Income Taxes [Line Items]          
United States corporate tax at a rate   21.00%      
Capital loss carryforwards   $ 17.8     $ 9.7
Less valuation allowance   64.0     172.7
Deferred Tax Assets, Gross   505.8     529.9
Internal Revenue Service (IRS)          
Income Taxes [Line Items]          
Net operating loss carryforwards   324.8     354.9
Operating loss carryforwards, remaining   324.8      
Capital loss carryforwards   84.7      
Less valuation allowance   22.9     24.5
Internal Revenue Service (IRS) | Aspen UK          
Income Taxes [Line Items]          
Capital loss carryforwards   33.1      
Internal Revenue Service (IRS) | U.S. operating subsidiaries          
Income Taxes [Line Items]          
Net operating loss carryforwards   247.2      
Capital loss carryforwards   51.6      
Internal Revenue Service (IRS) | U.S. operating subsidiaries | Subsequent Event          
Income Taxes [Line Items]          
Operating loss carryforwards, subject to s382 limitation       $ 20.8  
Internal Revenue Service (IRS) | Aspen UK's U.S. branch          
Income Taxes [Line Items]          
Net operating loss carryforwards   77.6      
Operating loss carryforwards, subject to s382 limitation   $ 6.5      
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 25.00% 25.00% 19.00%    
Net operating loss carryforwards   $ 249.5     248.1
Operating loss carryforwards, remaining   22.0     19.0
Less valuation allowance   26.1     131.0
U.K. | Lloyd's          
Income Taxes [Line Items]          
Deferred tax losses, operating loss carryforward   (29.3)     64.5
U.K. | Other juridictions          
Income Taxes [Line Items]          
Deferred tax losses, operating loss carryforward   $ (86.1)     $ (97.8)
Bermuda          
Income Taxes [Line Items]          
Bermuda tax rate   0.00%      
v3.25.1
Capital Structure - Summary of Authorized and Issued Share Capital (Details) - USD ($)
 12 Months Ended
Nov. 29, 2024
Nov. 26, 2024
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Dec. 31, 2024
Dec. 31, 2023
Authorized share capital:              
Number of ordinary shares           750,000,000 70,000,000
Number of preference shares           150,000,000 30,000,000
Ordinary Shares, authorized           $ 7,500,000 $ 700,000
Preference Shares, authorized           227,000 45,000
Total authorized share capital           $ 7,727,000 $ 745,000
Issued share capital:              
Ordinary shares, issued           60,395,839 60,395,839
Ordinary shares, value           $ 604,000 $ 604,000
Total issued share capital           $ 636,000 $ 636,000
Ordinary shares, par value           $ 0.01 $ 0.01
Preference shares, par value           $ 0.0015144558  
5.950% Preference Shares (AHL PRC)              
Issued share capital:              
Preference shares, issued         11,000,000,000,000 11,000,000 11,000,000
Preference shares, value           $ 17,000 $ 17,000
Preferred Stock, Dividend Rate, Percentage 5.95%       5.95% 5.95% 5.95%
Preference shares, par value           $ 0.0015144558 $ 0.0015144558
Redemption price per share         $ 25 $ 25 $ 25
5.625% Preference Shares (AHL PRD)              
Issued share capital:              
Preference shares, issued       10,000,000   10,000,000 10,000,000
Preference shares, value           $ 15,000 $ 15,000
Preferred Stock, Dividend Rate, Percentage       5.625%   5.625% 5.625%
Preference shares, par value           $ 0.0015144558 $ 0.0015144558
Redemption price per share       $ 25   $ 25 $ 25
5.625% Preference Shares, rep by Dep Shares (AHL PRE)              
Issued share capital:              
Preference shares, issued     10,000,000     10,000,000 10,000,000
Preference shares, value           $ 0 $ 0
Preferred Stock, Dividend Rate, Percentage     5.625%     5.625% 5.625%
Preference shares, par value           $ 0.0015144558 $ 0.0015144558
Redemption price per share     $ 25     $ 25,000 $ 25,000
7.00% Preference Shares, rep by Dep Shares (AHL PRF)              
Issued share capital:              
Preference shares, issued   9,000,000       9,000,000 0
Preference shares, value           $ 0 $ 0
Preferred Stock, Dividend Rate, Percentage   7.00%       7.00% 7.00%
Preference shares, par value           $ 0.0015144558 $ 0.0015144558
Redemption price per share   $ 25       $ 25,000 $ 25,000
v3.25.1
Capital Structure - Summary of Authorized and Issued Share Capital (Details)(Phantom) - $ / shares
Dec. 31, 2024
Dec. 31, 2023
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Class of Stock [Line Items]          
Ordinary shares, par value $ 0.01 $ 0.01      
Preference shares, par value 0.0015144558        
5.950% Preference Shares (AHL PRC)          
Class of Stock [Line Items]          
Preference shares, par value 0.0015144558 0.0015144558      
Redemption price per share 25 25     $ 25
5.625% Preference Shares (AHL PRD)          
Class of Stock [Line Items]          
Preference shares, par value 0.0015144558 0.0015144558      
Redemption price per share 25 25   $ 25  
5.625% Preference Shares, rep by Dep Shares (AHL PRE)          
Class of Stock [Line Items]          
Preference shares, par value 0.0015144558 0.0015144558      
Redemption price per share $ 25,000 $ 25,000 $ 25    
Depositary share interest of 1/1000th in each 5.625%     0.001%    
v3.25.1
Capital Structure - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Nov. 29, 2024
Nov. 26, 2024
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Class of Stock [Line Items]                
Additional paid in capital           $ 761,200 $ 761,200  
Aggregate Liquidation Preference Shares           1,000,000 775,000 $ 775,000
Preferred Stock Issuance Cost           29,500 21,500 $ 21,500
Authorized share capital           $ 7,727 $ 745  
Number of ordinary shares           750,000,000 70,000,000  
Ordinary shares, par value           $ 0.01 $ 0.01  
Number of preference shares           150,000,000 30,000,000  
Preference shares, par value           $ 0.0015144558    
Ordinary shares, issued           60,395,839 60,395,839  
Preference shares liquidation preference, value   $ 225,000 $ 250,000          
5.950% Preference Shares (AHL PRC)                
Class of Stock [Line Items]                
Preferred Stock Issuance Cost         $ 4,400      
Preference shares, par value           $ 0.0015144558 $ 0.0015144558  
Preference shares, issued         11,000,000,000,000 11,000,000 11,000,000  
Preference shares, rate 5.95%       5.95% 5.95% 5.95%  
Redemption price per share         $ 25 $ 25 $ 25  
Proceeds or share issuance         $ 270,600      
Preference shares liquidation preference, value         $ 275,000      
5.625% Preference Shares (AHL PRD)                
Class of Stock [Line Items]                
Preferred Stock Issuance Cost       $ 8,700        
Preference shares, par value           $ 0.0015144558 $ 0.0015144558  
Preference shares, issued       10,000,000   10,000,000 10,000,000  
Preference shares, rate       5.625%   5.625% 5.625%  
Redemption price per share       $ 25   $ 25 $ 25  
Proceeds or share issuance       $ 241,300        
Preference shares liquidation preference, value       $ 250,000        
5.625% Preference Shares, rep by Dep Shares (AHL PRE)                
Class of Stock [Line Items]                
Preferred Stock Issuance Cost     $ 8,400          
Preference shares, par value           $ 0.0015144558 $ 0.0015144558  
Preference shares, issued     10,000,000     10,000,000 10,000,000  
Preference shares, rate     5.625%     5.625% 5.625%  
Redemption price per share     $ 25     $ 25,000 $ 25,000  
7.00% Preference Shares, rep by Dep Shares (AHL PRF)                
Class of Stock [Line Items]                
Preferred Stock Issuance Cost   $ 8,000            
Preference shares, par value           $ 0.0015144558 $ 0.0015144558  
Preference shares, issued   9,000,000       9,000,000 0  
Preference shares, rate   7.00%       7.00% 7.00%  
Redemption price per share   $ 25       $ 25,000 $ 25,000  
Proceeds or share issuance   $ 217,000            
Additional paid-in capital | Preference shares                
Class of Stock [Line Items]                
Proceeds or share issuance     $ 241,600          
v3.25.1
Earnings Per Share (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Earnings Per Share [Abstract]      
Net income $ 486.1 $ 534.7 $ 51.1
Redeemable Preferred Stock Dividends (54.9) (49.9) (44.6)
Net income (loss) available to ordinary shareholders, basic $ 431.2 $ 484.8 $ 6.5
Basic weighted average ordinary shares outstanding 60,395,839 60,395,839 60,395,839
Diluted weighted average ordinary shares outstanding 60,395,839 60,395,839 60,395,839
Earnings Per Share, Basic $ 7.14 $ 8.03 $ 0.11
Earnings Per Share, Diluted $ 7.14 $ 8.03 $ 0.11
v3.25.1
Statutory Requirements and Dividends Restrictions - Summary of Statutory Requirements and Dividends Restrictions (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
U.S.    
Required statutory capital and surplus $ 565.7 $ 488.9
Actual statutory capital and surplus 1,164.9 1,063.1
Bermuda    
Required statutory capital and surplus 579.3 601.1
Actual statutory capital and surplus 1,761.3 1,685.2
U.K.    
Required statutory capital and surplus 277.3 257.2
Actual statutory capital and surplus $ 651.0 $ 734.7
v3.25.1
Statutory Requirements and Dividends Restrictions - Additional Information (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Statutory Accounting Practices [Line Items]  
Capital contributions reserves $ 879.9
Aspen UK  
Statutory Accounting Practices [Line Items]  
Dividend payment made without regulatory approval (690.0)
AUL  
Statutory Accounting Practices [Line Items]  
Dividend payment made without regulatory approval (31.0)
Syndicate to maintain funds at Lloyd 964.6
Total funds held by AUL 1,016.7
Bermuda  
Statutory Accounting Practices [Line Items]  
Dividend payment made without regulatory approval $ (322.9)
Statutory capital and surplus, percent 25.00%
Statutory capital and surplus, percent reduction requiring approval 15.00%
Percent warning level of amount of enhanced capital required from statutory capital and surplus 120.00%
Bermuda | AUL  
Statutory Accounting Practices [Line Items]  
Total funds held by AUL $ 465.2
v3.25.1
Dividends - Summary of Declared Dividends (Details) - USD ($)
 3 Months Ended 12 Months Ended
Jan. 01, 2025
Nov. 29, 2024
Nov. 26, 2024
Oct. 01, 2024
Aug. 30, 2024
Jul. 01, 2024
May 30, 2024
Apr. 01, 2024
Mar. 01, 2024
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Dec. 31, 2024
Sep. 30, 2024
Jun. 30, 2024
Mar. 31, 2024
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dividends Payable [Line Items]                                      
Dividends                         $ 13,847,200 $ 13,773,500 $ 13,700,900 $ 13,627,200 $ 54,948,800    
Ordinary Stock, Dividends Rate, Per Dollar Amount                                 $ 3.23    
Payments of Ordinary Dividends, Common Stock                                 $ 195,000,000.0 $ 40,300,000 $ 40,000,000.0
S2024Q1 Dividends                                      
Dividends Payable [Line Items]                                      
Dividends Payable, Date Declared                 Mar. 01, 2024                    
Payable Date               Apr. 01, 2024                      
S2024Q2 Dividends                                      
Dividends Payable [Line Items]                                      
Dividends Payable, Date Declared             May 30, 2024                        
Payable Date           Jul. 01, 2024                          
S2024Q3 Dividends                                      
Dividends Payable [Line Items]                                      
Dividends Payable, Date Declared         Aug. 30, 2024                            
Payable Date       Oct. 01, 2024                              
S2024Q4 Dividends                                      
Dividends Payable [Line Items]                                      
Dividends Payable, Date Declared   Nov. 29, 2024                                  
Payable Date Dec. 30, 2024                                    
5.950% Preference Shares (AHL PRC)                                      
Dividends Payable [Line Items]                                      
Dividends                         6,815,600 6,741,900 6,669,300 6,595,600 $ 26,822,400    
Preferred Stock, Dividend Rate, Per-Dollar-Amount                                 $ 2.44    
Preferred Stock, Dividend Rate, Percentage   5.95%                   5.95%         5.95% 5.95%  
5.625% Preference Shares (AHL PRD)                                      
Dividends Payable [Line Items]                                      
Dividends                         3,516,000 3,516,000 3,516,000 3,516,000 $ 14,064,000    
Preferred Stock, Dividend Rate, Per-Dollar-Amount                                 $ 1.41    
Preferred Stock, Dividend Rate, Percentage                     5.625%           5.625% 5.625%  
5.625% Preference Shares, rep by Dep Shares (AHL PRE)                                      
Dividends Payable [Line Items]                                      
Dividends                         $ 3,515,600 $ 3,515,600 $ 3,515,600 $ 3,515,600 $ 14,062,400    
Depositary share dividend                         $ 1.40624       $ 1.40624    
Depositary share interest of 1/1000th in each 5.625%                   0.001%                  
Preferred Stock, Dividend Rate, Per-Dollar-Amount                                 $ 1,406.24    
Preferred Stock, Dividend Rate, Percentage                   5.625%             5.625% 5.625%  
7.00% Preference Shares, rep by Dep Shares (AHL PRF)                                      
Dividends Payable [Line Items]                                      
Depositary share interest of 1/1000th in each 5.625%     0.001%                                
Preferred Stock, Dividend Rate, Percentage     7.00%                           7.00% 7.00%  
v3.25.1
Retirement Plans (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Retirement Benefits [Abstract]      
Total contributions by the Company to the retirement plan $ 16.9 $ 14.5 $ 12.5
v3.25.1
Share-Based Payments and Long-term Incentive Plan - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based payment and LTIP expense $ 14.6 $ 5.5
Accrued expenses and other payables [1] $ 237.2 $ 214.4
Weighted Average Exercise Price   $ 0.001
Number of options granted   10,000
Number of options vested 0 0
Number of options forfeited 900  
Outstanding options balance 9,100  
Performance Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense $ 9.8 $ 5.5
Retention shares or units    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense 4.8  
Long-term incentive plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Accrued expenses and other payables 20.0 $ 7.6
Management equity plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Estimated compensation expense 35.0  
Unrecognized compensation expense 0.0  
Fair value if vested at period end $ 41.3  
[1] Includes amounts due to related parties of $4.0 million for investment management fees (2023 — $2.1 million), and $1.3 million for management consulting fees (2023 — $1.2 million).
v3.25.1
Intangible Assets - Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]    
Intangible assets and goodwill $ 19.9 $ 21.7
Goodwill 2.1  
Digital Re    
Finite-Lived Intangible Assets [Line Items]    
Goodwill, impairment loss 1.8  
Aspen trademark    
Finite-Lived Intangible Assets [Line Items]    
Value of the asset 1.1  
Insurance Licenses    
Finite-Lived Intangible Assets [Line Items]    
Value of the asset $ 16.7  
v3.25.1
Operating Leases - Schedule of Operating Lease Costs (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]      
Amortization of right-of-use operating lease assets $ 9.9 $ 10.7 $ 10.1
Interest on operating lease liability 4.1 4.5 5.4
Operating Lease, Expense $ 14.0 $ 15.2 $ 15.5
v3.25.1
Operating Leases - Schedule of Operating Lease Liability, Maturity (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Leases [Abstract]    
Liability, Payments, Due prior year $ 0.0 $ 15.4
Liability, Payments, Next twelve months 15.4 15.1
Liability, Payments, Due year two 14.6 14.3
Liability, Payments, Due year three 13.2 12.8
Liability, Payments, Due year four 13.0 12.7
Liability, Payments, Due year five 10.9 11.2
Liability, Payments, Due after year five 21.5 21.2
Total minimum lease payments 88.6 102.7
Less imputed interest (13.0) (16.6)
Operating lease liabilities $ 75.6 $ 86.1
v3.25.1
Operating Leases - Schedule of Operating Leases Cash Flows (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]      
Operating lease liabilities $ (15.9) $ (15.5) $ (15.5)
Asset obtained in exchange for operating lease liability 2.1 0.2 1.9
Reduction of right-of use assets resulting from reductions to lease obligations $ 0.3 $ 0.1 $ 7.0
Operating lease, weighted average remaining lease term (years( 6 years 4 months 24 days 7 years 3 months 18 days 8 years 1 month 6 days
Operating lease, weighted average discount rate (percent) 5.10% 5.00% 5.00%
v3.25.1
Operating Leases - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Leases [Abstract]      
Right-of-use operating lease assets $ 53,500,000 $ 61,600,000  
Operating lease liabilities 75,600,000 86,100,000  
Impairment of lease assets $ 0 $ 0 $ (6,700,000)
v3.25.1
Related Party Transactions - Narrative (Details)
 12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Related Party Transaction [Line Items]      
Plus component of annual investment management fee 0.25    
Annual fee cap 0.15    
Privately-held Investments [1] $ 286,800,000 $ 475,000,000.0  
Other Investments [2] 267,200,000 209,300,000  
Net investment income (1) 318,000,000.0 [3] 275,700,000 $ 188,100,000
Accrued expenses and other payables [4] 237,200,000 214,400,000  
Gain (loss) on investments 52,600,000 75,900,000 5,000,000.0
Other expenses 0 0 20,100,000
Asset Management Arrangement      
Related Party Transaction [Line Items]      
Net investment income (1) 9,200,000 9,400,000 4,900,000
Accrued expenses and other payables 4,000,000.0 2,100,000  
Apollo real estate fund      
Related Party Transaction [Line Items]      
Gain (loss) on investments 400,000 (400,000) 3,100,000
Apollo real estate fund | Fair Value, Recurring [Member]      
Related Party Transaction [Line Items]      
Other Investments 78,600,000    
Beneficial owner      
Related Party Transaction [Line Items]      
Accounts Payable, Current 1,200,000 1,200,000  
Funds managed by Apollo | Fair Value, Recurring [Member]      
Related Party Transaction [Line Items]      
Other Investments 78,600,000 39,800,000  
Apollo Notes, SPV      
Related Party Transaction [Line Items]      
Privately-held investment, losses incurred (5,500,000) (5,500,000) (400,000)
Apollo Notes, SPV | Fair Value, Recurring [Member]      
Related Party Transaction [Line Items]      
Privately-held Investments 66,600,000 82,200,000  
CLOs      
Related Party Transaction [Line Items]      
Net investment income (1) 11,300,000 17,400,000 0
CLOs | Fair Value, Recurring [Member]      
Related Party Transaction [Line Items]      
Debt Securities, Trading 88,900,000 129,800,000  
Middle Market Term Loans managed by a subsidiary of Apollo      
Related Party Transaction [Line Items]      
Net investment income (1) 500,000 5,800,000 $ 0
Middle Market Term Loans managed by a subsidiary of Apollo | Fair Value, Recurring [Member]      
Related Party Transaction [Line Items]      
Debt Securities, Trading $ 7,000,000.0 $ 45,100,000  
Maximum      
Related Party Transaction [Line Items]      
Percentage of consolidated group's net income due to Apollo Management 1.00%    
Dollar amount option to percentage fee $ 5,000,000    
[1] Privately-held investments, trading at fair value include related party investments totaling $73.6 million (2023 — $112.4 million). Privately-held investments, available for sale include related party investments totaling $Nil (2023 — $14.9 million).
[2] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
[3] Net investment income includes related party net investment income of $15.2 million (2023 — $19.6 million, 2022 — $3.1 million) and related party investment management fees of $9.2 million (2023 — $9.4 million, 2022 — $4.9 million).
[4] Includes amounts due to related parties of $4.0 million for investment management fees (2023 — $2.1 million), and $1.3 million for management consulting fees (2023 — $1.2 million).
v3.25.1
Commitments and Contingencies - Schedule of Company's Restricted Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]    
Affiliated transactions $ 433.4 $ 660.8
Third party 2,713.5 2,714.4
Letters of credit / guarantees (1) 153.2 172.0
Total restricted assets (excluding illiquid assets) 3,300.1 3,547.2
Other Investments [1] 267.2 209.3
Total restricted assets and illiquid assets $ 3,567.3 $ 3,756.5
Total as percent of invested assets 46.40% 50.20%
[1] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
v3.25.1
Commitments and Contingencies - Additional Information (Details)
£ in Millions, SFr in Millions, $ in Millions, $ in Millions, $ in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Investment
Dec. 31, 2023
USD ($)
Investment
Dec. 31, 2022
USD ($)
Dec. 31, 2024
GBP (£)
Investment
Dec. 31, 2024
CAD ($)
Investment
Dec. 31, 2024
AUD ($)
Investment
Dec. 31, 2024
CHF (SFr)
Investment
Dec. 31, 2024
SGD ($)
Investment
Dec. 31, 2023
GBP (£)
Investment
Dec. 31, 2023
CAD ($)
Investment
Dec. 31, 2023
AUD ($)
Investment
Dec. 31, 2023
CHF (SFr)
Investment
Dec. 31, 2023
SGD ($)
Investment
Sep. 30, 2021
USD ($)
Dec. 20, 2017
USD ($)
Restricted Cash And Collateral [Line Items]                              
Other investments (equity method) [1] $ 267.2 $ 209.3                          
Total as percent of invested assets 46.40% 50.20%                          
Investable assets held by the Company $ 7,700.0 $ 7,500.0                          
Commitment to invest in private assets 57.0 99.0 $ 377.9                        
Investable assets held by insurance regulators $ 471.9 517.4                          
Minimum capital required | £       £ 0.4         £ 0.5            
Percentage of reinsurance liabilities 100.00%     100.00% 100.00% 100.00% 100.00% 100.00%              
Reinsurance liabilities $ 648.8 823.5                          
Assets held-in-trust 1,001.5 1,016.9                          
Regulatory deposits 6.9 6.8                          
Deposit with states $ 6.5 $ 6.4                          
Number of investments | Investment 1 1   1 1 1 1 1 1 1 1 1 1    
Us Multi Beneficiary Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Minimum trust fund $ 20.0                            
Assets held-in-trust 334.0 $ 394.7                          
US Surplus Lines Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Assets held-in-trust 150.2 126.6                          
Canadian Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Assets held-in-trust 162.7       $ 219.8         $ 228.4          
Australian Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Assets held-in-trust 54.1         $ 78.1         $ 131.0        
Swiss Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Assets held-in-trust 5.7           SFr 4.8         SFr 9.9      
Singapore Trust Fund                              
Restricted Cash And Collateral [Line Items]                              
Assets held-in-trust $ 157.3             $ 201.7         $ 192.1    
Bermuda                              
Restricted Cash And Collateral [Line Items]                              
Percentage of reinsurance liabilities 100.00%     100.00% 100.00% 100.00% 100.00% 100.00%              
Reinsurance liabilities $ 182.3 $ 320.6                          
Limited Partner                              
Restricted Cash And Collateral [Line Items]                              
Restricted assets                           $ 20.0 $ 100.0
[1] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
v3.25.1
Concentration of Credit Risk - Additional Information (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Concentration Risk [Line Items]      
Amount recoverable from reinsurers $ 4,172.0 $ 4,577.8  
Concentration risk 0.559 0.568  
Reinsurance Recoverable, Allowance for Credit Loss $ 27.5 $ 3.7 $ 3.7
Underwriting premiums receivables (net of allowance for expected credit losses of 2024: $24.6 and 2023: $21.0) 1,617.0 1,435.3  
Due for settlement 111.1    
Premium Receivable, Allowance for Credit Loss $ 24.6 $ 21.0  
Allowable holdings of a single issue or issuer, percentage 2.00%    
Maximum      
Concentration Risk [Line Items]      
Gross written premiums, percentage 15.40% 15.90%  
Minimum      
Concentration Risk [Line Items]      
Gross written premiums, percentage 8.80% 9.20%  
Median      
Concentration Risk [Line Items]      
Gross written premiums, percentage 11.50% 11.10%  
A- rating or higher      
Concentration Risk [Line Items]      
Concentration risk 0.440 0.429  
A- rating or lower      
Concentration Risk [Line Items]      
Concentration risk 0.001 0.003  
v3.25.1
Reclassifications from Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income Reclassification (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Realized losses on sale of securities $ (60.6) $ (41.5) $ (58.4)
Income (loss) from operations before income taxes 464.1 402.6 (27.0)
Income tax (expense)/benefit 22.0 132.1 78.1
General, administrative and corporate expenses [1] (533.1) (503.6) (494.2)
Net income/(loss) 486.1 534.7 51.1
Net realized and unrealized foreign exchange gains/(losses) (14.1) 14.4 (30.9)
Income tax expense, foreign currency translation adjustments 1.4 0.0 0.0
Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Net income/(loss) 48.6 25.5 70.4
Available for sale securities | Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Available for sale securities — gross realized (losses) (3.2) (2.2) (3.9)
Realized losses on sale of securities 62.6 42.4 58.9
Income (loss) from operations before income taxes 59.4 40.2 55.0
Income tax (expense)/benefit (11.5) (6.6) 0.0
Net income/(loss) 47.9 33.6 55.0
Realized derivatives | Reclassification out of Accumulated Other Comprehensive Income      
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]      
Income tax (expense)/benefit (0.2) 0.0 0.0
General, administrative and corporate expenses 0.9 (8.1) 15.4
Net income/(loss) $ 0.7 $ (8.1) $ 15.4
[1] General, administrative and corporate expenses includes related party management consulting fees of $5.0 million (2023 — $5.0 million; 2022 — $5.0 million).
v3.25.1
Credit Facilities and Long-Term Debt - Summary of Contractual Obligations Under Long-term Debts (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Line of Credit Facility [Line Items]    
Short-Term Debt $ 300.0 $ 300.0
Long-Term Debt, Maturity, Year Two and Three 300.0  
Long-Term Debt, Maturity, Year Four and Five 0.0  
Long-Term Debt, Maturity, after Year Five 0.0  
Total 300.0  
Short-Term Debt    
Line of Credit Facility [Line Items]    
Short-Term Debt $ 0.0  
v3.25.1
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                  
v3.25.1
Credit Losses (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Credit Loss [Abstract]      
Available-for-sale Investments, Allowance for Credit Loss, Beginning Balance $ 2.9 $ 7.7  
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Not Previously Recorded 0.3 0.3  
Available-for-sale investment, allowance for credit loss, increase (decrease) (0.9) (3.6)  
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Securities Sold (1.3) (1.5)  
Available-for-sale Investments, Allowance for Credit Loss, Ending Balance 1.0 2.9 $ 7.7
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance 3.7 3.7  
Reinsurance Recoverable, Allowance for Credit Loss, Period Increase (Decrease) 23.8 0.0 0.4
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance 27.5 3.7 3.7
Accounts Receivable, Allowance for Credit Loss, Beginning Balance 21.0 25.0  
Accounts Receivable, Allowance for Credit Loss, Period Increase (Decrease) 3.6 (4.0)  
Accounts Receivable, Allowance for Credit Loss, Ending Balance $ 24.6 $ 21.0 $ 25.0
v3.25.1
Subsequent Events - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
 1 Months Ended 12 Months Ended
Feb. 28, 2025
Jan. 01, 2025
Nov. 29, 2024
Nov. 26, 2024
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Jan. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Mar. 01, 2025
Jan. 02, 2025
Subsequent Event [Line Items]                          
Payments of Ordinary Dividends, Common Stock                 $ 195.0 $ 40.3 $ 40.0    
Preference shares liquidation preference, value       $ 225.0 $ 250.0                
Forecast | California Wildfires | Minimum                          
Subsequent Event [Line Items]                          
Loss contingency, estimate of possible loss                       $ 50.0  
Forecast | California Wildfires | Maximum                          
Subsequent Event [Line Items]                          
Loss contingency, estimate of possible loss                       $ 75.0  
5.950% Preference Shares (AHL PRC)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage     5.95%       5.95%   5.95% 5.95%      
Redemption price per share             $ 25   $ 25 $ 25      
Preference shares liquidation preference, value             $ 275.0            
5.625% Preference Shares (AHL PRD)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage           5.625%     5.625% 5.625%      
Redemption price per share           $ 25     $ 25 $ 25      
Preference shares liquidation preference, value           $ 250.0              
5.625% Preference Shares (AHL PRE)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage         5.625%       5.625% 5.625%      
Depositary share interest of 1/1000th in each 5.625%         0.001%                
Depositary share dividend                 $ 1.40624        
Redemption price per share         $ 25       $ 25,000 $ 25,000      
7.00% Preference Shares, rep by Dep Shares (AHL PRF)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage       7.00%         7.00% 7.00%      
Depositary share interest of 1/1000th in each 5.625%       0.001%                  
Redemption price per share       $ 25         $ 25,000 $ 25,000      
Subsequent Event | California Wildfires | Minimum                          
Subsequent Event [Line Items]                          
Loss contingency industry amount incurred               $ 35,000.0          
Subsequent Event | California Wildfires | Maximum                          
Subsequent Event [Line Items]                          
Loss contingency industry amount incurred               $ 45,000.0          
Subsequent Event | 5.950% Preference Shares (AHL PRC)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage   5.95%                      
Redemption price per share                         $ 25
Preference shares liquidation preference, value                         $ 275.0
Subsequent Event | 5.625% Preference Shares (AHL PRD)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage 5.625%                        
Dividend, in usd per share $ 0.3516                        
Subsequent Event | 5.625% Preference Shares (AHL PRD) | S2025Q1SeriesEDividends                          
Subsequent Event [Line Items]                          
Payable Date Apr. 01, 2025                        
Dividends Payable, Date Declared Mar. 15, 2025                        
Subsequent Event | 5.625% Preference Shares (AHL PRE)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage 5.625%                        
Dividend, in usd per share $ 351.56                        
Depositary share interest of 1/1000th in each 5.625% 0.001%                        
Depositary share dividend $ 0.3516                        
Subsequent Event | 5.625% Preference Shares (AHL PRE) | S2025Q1SeriesFDividends                          
Subsequent Event [Line Items]                          
Payable Date Apr. 01, 2025                        
Dividends Payable, Date Declared Mar. 15, 2025                        
Subsequent Event | 7.00% Preference Shares, rep by Dep Shares (AHL PRF)                          
Subsequent Event [Line Items]                          
Preferred Stock, Dividend Rate, Percentage 7.00%                        
Dividend, in usd per share $ 612.50                        
Depositary share interest of 1/1000th in each 7.00% 0.001%                        
Depositary share dividend $ 0.6125                        
Subsequent Event | 7.00% Preference Shares, rep by Dep Shares (AHL PRF) | S2025Q1SeriesGDividends                          
Subsequent Event [Line Items]                          
Payable Date Apr. 01, 2025                        
Dividends Payable, Date Declared Mar. 31, 2025                        
v3.25.1
Schedule I - Investments (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value $ 6,589.3  
Amount at which shown at the balance sheet 6,741.5  
Privately-held Investments [1] 286.8 $ 475.0
Other Investments [2] 267.2 209.3
Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Privately-held Investments 73.6  
Fair Value, Recurring [Member] | Apollo real estate fund    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Other Investments 78.6  
Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Privately-held Investments 73.6 $ 112.4
U.S. government    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 1,767.7  
Fair Value 1,741.9  
Amount at which shown at the balance sheet 1,741.9  
U.S. agency    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 7.5  
Fair Value 7.2  
Amount at which shown at the balance sheet 7.2  
Municipal    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 85.8  
Fair Value 83.9  
Amount at which shown at the balance sheet 83.9  
Corporate    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 2,200.8  
Fair Value 2,137.5  
Amount at which shown at the balance sheet 2,137.5  
High yield loans    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 101.7  
Fair Value 102.4  
Amount at which shown at the balance sheet 102.4  
Non-U.S. government-backed corporate    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 135.7  
Fair Value 134.1  
Amount at which shown at the balance sheet 134.1  
Non-U.S. government    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 272.6  
Fair Value 271.2  
Amount at which shown at the balance sheet 271.2  
Asset-backed    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 767.7  
Fair Value 770.8  
Amount at which shown at the balance sheet 859.7  
Asset-backed | Fair Value, Recurring [Member] | Apollo originating partnership    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Other Investments 88.9  
Non-agency commercial mortgage-backed securities    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 5.0  
Fair Value 4.4  
Amount at which shown at the balance sheet 4.4  
Agency mortgage-backed    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 635.0  
Fair Value 549.8  
Amount at which shown at the balance sheet 549.8  
Fixed maturities    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 5,979.5  
Fair Value 5,803.2  
Amount at which shown at the balance sheet 5,892.1  
Short-term investments — Available for sale    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 262.9  
Fair Value 262.9  
Amount at which shown at the balance sheet 262.9  
Catastrophe bonds, trading    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 1.0  
Fair Value 1.0  
Amount at which shown at the balance sheet 1.0  
Privately-held investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Amortized Cost or Cost 312.0  
Fair Value 237.4  
Amount at which shown at the balance sheet 311.0  
Equity Method Investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value 7.3  
Amount at which shown at the balance sheet 7.3  
Other investments    
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]    
Fair Value 188.6  
Amount at which shown at the balance sheet $ 267.2  
[1] Privately-held investments, trading at fair value include related party investments totaling $73.6 million (2023 — $112.4 million). Privately-held investments, available for sale include related party investments totaling $Nil (2023 — $14.9 million).
[2] Other investments includes related party investments in Funds Managed by Apollo of $78.6 million (2023 — $39.8 million).
v3.25.1
Schedule II - Condensed Financial Information of Registrant Balance Sheets (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Nov. 29, 2024
Aug. 13, 2019
Sep. 20, 2016
May 02, 2013
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
ASSETS                
Fair Market Value         $ 1,488,700 $ 1,964,400    
Cash and Cash Equivalents, at Carrying Value [1]         914,200 1,028,100    
Right-of-use operating lease assets         53,500 61,600    
Other assets         590,800 309,600    
Total assets         15,748,500 15,224,800    
LIABILITIES                
Accrued expenses and other payables [2]         237,200 214,400    
Short-Term Debt         300,000 300,000    
Operating lease liabilities         75,600 86,100    
Total liabilities         12,376,600 12,316,300    
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]                
Ordinary shares         604 604    
Preference shares, value         970,500 753,500    
Additional paid in capital         761,200 761,200    
Retained earnings         2,029,700 1,793,500    
Total accumulated other comprehensive (loss)         (390,100) (400,300) $ (506,300)  
Total shareholders’ equity         3,371,900 2,908,500    
Total liabilities and shareholders’ equity         $ 15,748,500 $ 15,224,800    
Ordinary shares, issued         60,395,839 60,395,839    
Ordinary shares, par value         $ 0.01 $ 0.01    
Preference shares, par value         $ 0.0015144558      
5.950% Preference Shares (AHL PRC)                
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]                
Preference shares, issued       11,000,000,000,000 11,000,000 11,000,000    
Preference shares, rate 5.95%     5.95% 5.95% 5.95%    
Preference shares, par value         $ 0.0015144558 $ 0.0015144558    
5.625% Preference Shares (AHL PRD)                
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]                
Preference shares, issued     10,000,000   10,000,000 10,000,000    
Preference shares, rate     5.625%   5.625% 5.625%    
Preference shares, par value         $ 0.0015144558 $ 0.0015144558    
5.625% Preference Shares (AHL PRE)                
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]                
Preference shares, issued   10,000,000     10,000,000 10,000,000    
Preference shares, rate   5.625%     5.625% 5.625%    
Preference shares, par value         $ 0.0015144558 $ 0.0015144558    
Parent Company                
ASSETS                
Fair Market Value         $ 44,300 $ 43,200    
Cash and Cash Equivalents, at Carrying Value         43,500 43,500 $ 44,400 $ 45,000
Investments in subsidiaries (1)         3,361,300 3,284,200    
Other Receivables         275,000 0    
Other recievables due from affiliates         20,600 4,300    
Right-of-use operating lease assets         1,000 1,500    
Other assets         44,700 5,600    
Total assets         3,790,400 3,382,300    
LIABILITIES                
Accrued expenses and other payables         20,700 27,800    
Other Liabilities         96,900 144,700    
Long-term debt         300,000 300,000    
Operating lease liabilities         900 1,300    
Total liabilities         418,500 473,800    
Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]                
Ordinary shares         600 600    
Preference shares, value         970,500 753,500    
Additional paid in capital         761,200 761,200    
Retained earnings         2,029,700 1,793,500    
Unrealized (loss)/gains on investments         (198,200) (227,600)    
(Loss)/gain on derivatives         (5,300) (200)    
Gains on foreign currency translation (start of period)         (172,500)      
Gains on foreign currency translation (end of period)         (186,600) (172,500)    
Total accumulated other comprehensive (loss)         (390,100) (400,300)    
Total liabilities and shareholders’ equity         $ 3,790,400 $ 3,382,300    
[1] Cash and cash equivalents includes restricted cash of $181.9 million (2023 — $323.2 million) which are held in trusts.
[2] Includes amounts due to related parties of $4.0 million for investment management fees (2023 — $2.1 million), and $1.3 million for management consulting fees (2023 — $1.2 million).
v3.25.1
Schedule II - Condensed Financial Information of Registrant Statements of Operations and Comprehensive Income (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]      
Dividend income $ 329.5 $ 287.3 $ 198.4
Other income 0.0 0.0 8.2
Total revenues 3,260.3 2,966.1 2,890.0
Expenses      
General, administrative and corporate expenses [1] (533.1) (503.6) (494.2)
Other Expenses 0.0 0.0 (20.1)
Income (loss) from operations before income taxes 464.1 402.6 (27.0)
Income tax benefit 22.0 132.1 78.1
Net income/(loss) 486.1 534.7 51.1
Other Comprehensive Income:      
Other comprehensive income/(loss), net of tax 10.2 106.0 (383.3)
Total comprehensive (loss)/income attributable to Aspen Insurance Holdings Limited's ordinary shareholders 496.3 640.7 (332.2)
Parent Company      
Condensed Financial Statements, Captions [Line Items]      
Equity in net earnings of subsidiaries and other investments, equity method 108.9 304.7 14.2
Dividend income 511.4 364.4 121.7
Realized (loss) for the twelve months to December 31, 2024 0.5 1.1 (4.0)
Other income 4.3 3.2 1.0
Total revenues 625.1 673.4 132.9
Expenses      
General, administrative and corporate expenses (109.5) (121.3) (62.7)
Interest expense (21.1) (15.6) (14.3)
Other Expenses (3.9) (1.8) (4.8)
Income (loss) from operations before income taxes 490.6 534.7 51.1
Income tax benefit (4.5) 0.0 0.0
Net income/(loss) 486.1 534.7 51.1
Other Comprehensive Income:      
Change in unrealized gains/(losses) on investments 29.4 105.6 (367.8)
Net change from current period hedged transactions (5.1) (14.0) 15.4
Change in foreign currency translation adjustment (14.1) 14.4 (30.9)
Other comprehensive income/(loss), net of tax 10.2 106.0 (383.3)
Total comprehensive (loss)/income attributable to Aspen Insurance Holdings Limited's ordinary shareholders $ 496.3 $ 640.7 $ (332.2)
[1] General, administrative and corporate expenses includes related party management consulting fees of $5.0 million (2023 — $5.0 million; 2022 — $5.0 million).
v3.25.1
Schedule II - Condensed Financial Information of Registrant Statements of Cash Flows (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Cash flows from operating activities:      
Amortization of right-of-use operating lease assets $ 9,900,000 $ 10,700,000 $ 10,100,000
Change in right of lease assets 0 0 (6,700,000)
Change in operating lease liabilities (15,900,000) (15,500,000) (15,500,000)
Net cash provided by/(used in) operating activities 554,900,000 324,700,000 (55,000,000.0)
Cash flows from investing activities:      
Proceeds from sales and maturities of fixed income securities — Trading 850,100,000 474,000,000.0 293,600,000
Net cash (used in) investing activities (352,800,000) (172,200,000) (196,500,000)
Cash flows from financing activities:      
Repayments of Short-Term Debt 0 (300,000,000.0) 0
Proceeds from term loan facility 0 300,000,000.0 0
Payments of Ordinary Dividends, Common Stock (195,000,000.0) (40,300,000) (40,000,000.0)
Payments of Ordinary Dividends, Preferred Stock and Preference Stock 54,900,000 49,900,000 44,600,000
Net cash (used in) financing activities (307,900,000) (90,200,000) (84,600,000)
(Decrease) in cash and cash equivalents (113,900,000) 68,900,000 (354,900,000)
Cash and cash equivalents at beginning of period [1] 1,028,100,000    
Cash and cash equivalents at end of period (2) [1] 914,200,000 1,028,100,000  
Redemption of preference shares (1) (275,000,000.0) [2] 0 0
Preference share issuance 217,000,000.0 0 0
Parent      
Cash flows from financing activities:      
Proceeds from term loan facility 0 300,000,000.0 0
Redemption of preference shares (1) (275,000,000.0) 0 0
Preference share issuance 217,000,000.0 0  
Parent Company      
Cash flows from operating activities:      
Net income (excluding equity in net earnings of subsidiaries) 377,200,000 230,000,000.0 36,900,000
Realized and unrealized investment (gains)/losses (400,000) (14,800,000) 19,700,000
Loss/(gain) on derivative contracts 0 14,000,000.0 (15,400,000)
Amortization of right-of-use operating lease assets 700,000 500,000 500,000
Interest on operating lease liability 100,000 100,000 100,000
Change in other assets (39,000,000.0) 300,000 2,100,000
Change in accrued expenses and other payables (7,100,000) 5,500,000 (3,200,000)
Change in intercompany activities (64,100,000) (38,400,000) 41,100,000
Change in operating lease liabilities (500,000) (500,000) (600,000)
Net cash provided by/(used in) operating activities 266,900,000 196,700,000 81,200,000
Cash flows from investing activities:      
(Purchases) of fixed income securities (11,300,000) (8,100,000) (10,000,000.0)
Proceeds from sales and maturities of fixed income securities — Trading 10,300,000 6,400,000 7,800,000
Investment in subsidiaries 42,000,000.0 (105,700,000) 5,000,000.0
Net cash (used in) investing activities 41,000,000.0 (107,400,000) 2,800,000
Cash flows from financing activities:      
Repayments of Short-Term Debt 0 (300,000,000.0) 0
Net cash (used in) financing activities (307,900,000) (90,200,000) (84,600,000)
(Decrease) in cash and cash equivalents 0 (900,000) (600,000)
Cash and cash equivalents at beginning of period 43,500,000 44,400,000 45,000,000.0
Cash and cash equivalents at end of period (2) $ 43,500,000 $ 43,500,000 $ 44,400,000
[1] Cash and cash equivalents includes restricted cash of $181.9 million (2023 — $323.2 million) which are held in trusts.
[2] On January 1, 2025, the Company redeemed all 11,000,000 shares of its issued and outstanding 5.950% Fixed-to-Floating Rate Perpetual Non-Cumulative Preference Shares. The redemption price was paid on January 2, 2025. To facilitate this redemption, the funds of $275.0 million were transferred to a third party transfer agent on December 30, 2024 and are included in other assets in the consolidated balance sheet. The cash flow has been included under financing activities above. For further details, refer to Note 26, “Subsequent Events”.
v3.25.1
Schedule III - Supplementary Insurance Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Deferred Policy Acquisition Costs  $ 322.1 $ 296.2 $ 319.0  
Net Reserves for Losses and LAE  3,950.6 3,232.8 2,813.2 $ 4,313.7
Net Reserves for Unearned Premiums 1,744.1 1,692.8 1,720.2  
Net earned premiums 2,889.7 2,614.5 2,688.7  
Net Investment Income  318.0 275.7 188.1  
Losses and LAE Expenses  1,717.8 1,553.0 1,680.0  
Policy Acquisition Expenses  420.2 380.2 431.8  
Net written premiums 2,942.6 2,581.9 2,896.0  
General and Administrative Expenses  405.9 354.5 386.5  
Reinsurance        
Deferred Policy Acquisition Costs  248.2 201.5 227.2  
Net Reserves for Losses and LAE  1,691.5 1,373.1 1,360.7  
Net Reserves for Unearned Premiums 580.0 644.5 862.4  
Net earned premiums 1,305.7 1,154.5 1,251.8  
Losses and LAE Expenses  741.3 611.1 770.3  
Policy Acquisition Expenses  227.0 208.6 252.4  
Net written premiums 1,275.7 1,098.0 1,426.4  
General and Administrative Expenses  141.7 120.6 142.5  
Insurance        
Deferred Policy Acquisition Costs  73.9 94.7 91.8  
Net Reserves for Losses and LAE  2,259.1 1,859.7 1,452.5  
Net Reserves for Unearned Premiums 1,164.1 1,048.3 857.8  
Net earned premiums 1,584.0 1,460.0 1,436.9  
Losses and LAE Expenses  976.5 941.9 909.7  
Policy Acquisition Expenses  193.2 171.6 179.4  
Net written premiums 1,666.9 1,483.9 1,469.6  
General and Administrative Expenses  $ 264.2 $ 233.9 $ 244.0  
v3.25.1
Schedule IV - Reinsurance Premiums Written and Premiums Earned (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]      
Insurance $ 2,723.5 $ 2,446.6 $ 2,531.7
Reinsurance 1,885.8 1,521.0 1,807.0
Ceded (1,666.7) (1,385.7) (1,442.7)
Net written premiums 2,942.6 2,581.9 2,896.0
Gross Amount 2,565.7 2,444.8 2,370.8
Assumed From Other Companies 1,822.1 1,562.0 1,617.2
Ceded (1,498.1) (1,392.3) (1,299.3)
Net premiums earned $ 2,889.7 $ 2,614.5 $ 2,688.7
Percentage of Amount Assumed to Net Amount 63.10% 59.70% 60.10%
Gross written premiums $ 4,609.3 $ 3,967.6 $ 4,338.7
v3.25.1
Schedule V - Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Premiums receivable from underwriting activities      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year $ 21.0 $ 25.0 $ 30.2
Charged to Costs and Expenses 3.6 4.0 5.2
Charged to Other Accounts 0.0 0.0 0.0
Deductions 0.0 0.0 0.0
Balance at End of  Year 24.6 21.0 25.0
Reinsurance      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year 0.0 0.0 0.0
Charged to Costs and Expenses 27.5    
Charged to Other Accounts 0.0 0.0 0.0
Deductions 0.0 0.0 0.0
Balance at End of  Year $ 27.5 $ 0.0 $ 0.0