Business Overview and Basis of Presentation (Policies)	3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]
Basis of Preparation	These unaudited condensed consolidated financial statements and related notes have been prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP") for interim financial information and in conformity with the instructions to Form 10-Q and Article 10 of Regulation S-X of the Rules and Regulations of the Securities and Exchange Commission ("SEC"). Accordingly, they do not include all of the financial information and note disclosures required by U.S. GAAP for complete consolidated financial statements.
Basis of Consolidation	In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments, that are normal and recurring in nature, necessary for a fair statement of the financial results for the interim periods. All intercompany accounts and transactions have been eliminated and certain comparative information has been reclassified to conform to the current presentation.
Recently Issued Accounting Pronouncements Not Yet Adopted	ASU 2023-09 - Improvements to Income Tax Disclosures In December 2023, the FASB issued ASU 2023-09, which includes the following amendments to Topic 740 Income Taxes: •Disclose, on an annual basis, specific categories in the rate reconciliation; •Disclose, on an annual basis, additional information for reconciling items that meet a quantitative threshold (if the effect of those reconciling items is equal to or greater than 5% of the amount computed by multiplying pretax income (or loss) by the applicable statutory income tax rate); •Disclose, on an annual basis, the amount of income taxes paid (net of refunds received) disaggregated by federal (national), state, and foreign taxes; •Disclose, on an annual basis, the amount of income taxes paid (net of refunds received) disaggregated by individual jurisdictions in which income taxes paid (net of refunds received) is equal to or greater than 5% of total income taxes paid (net of refunds received); •Disclose income (or loss) from continuing operations before income tax expense (or benefit) disaggregated between domestic and foreign; •Disclose income tax expense (or benefit) from continuing operations disaggregated by federal (national), state, and foreign; •Eliminates the requirement to disclose the nature and estimate of the range of the reasonably possible change in the unrecognized tax benefits balance in the next 12 months or make a statement that an estimate of the range cannot be made; and •Eliminates the requirement to disclose the cumulative amount of each type of temporary difference when a deferred tax liability is not recognized because of the exceptions to comprehensive recognition of deferred taxes related to subsidiaries and corporate joint ventures. These amendments are effective for annual reporting periods beginning after December 15, 2024, and should be applied prospectively, however retrospective application is permitted. Early adoption is permitted. Adopting ASU 2023-09 will require us to expand our income tax disclosures. We will prospectively adopt this ASU within our annual financial statements for the year ended December 31, 2025. ASU 2024-03 - Disaggregation of Income Statement Expenses In November 2024, the FASB issued ASU 2024-03, which resulted in the addition of Subtopic 220-40 Reporting Comprehensive Income - Expense Disaggregation Disclosures and includes the following amendments: •Disclose the amounts of employee compensation, depreciation, intangible asset amortization, and certain other costs and expenses included in each relevant expense caption and include certain amounts that are already required to be disclosed under existing generally accepted accounting principles in the same disclosure; •Disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively; and •Disclose the total amount of selling expenses and, on an annual basis, an entity’s definition of selling expenses. These amendments are effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027, and must be applied prospectively with an option for retrospective application. Early adoption is permitted. Adopting ASU 2024-03 will require us to expand our disclosures related to costs and expenses. We are currently determining the period in which the new guidance will be adopted.
Investments	Funds Held Under funds held arrangements, the reinsured company has retained funds that would otherwise have been remitted to us. The funds held balance is credited with investment income and losses paid are deducted. We present funds held as a single category within the consolidated balance sheets.
Derivative Instruments	Freestanding Derivatives Freestanding derivatives are recorded on trade-dates and carried on the consolidated balance sheet either as assets within other assets or as liabilities within other liabilities at estimated fair value. We do not offset the estimated fair value amounts recognized for derivatives executed with the same counterparty under the same master netting agreement. If a derivative is not designated as an accounting hedge or its use in managing risk does not qualify for hedge accounting, changes in the estimated fair value of the derivative are reported in fair value changes in trading securities, funds held and other investments included in our consolidated statements of operations. Hedge Accounting To qualify for hedge accounting, at the inception of the hedging relationship, we formally document the risk management objective and strategy for undertaking the hedging transaction, as well as the designation of the hedge. We have qualifying net investment in foreign operation (“NIFO”) hedges. We recognize changes in the estimated fair value of the hedging derivatives within OCI, consistent with the translation adjustment for the hedged net investment in the foreign operation. Our documentation sets forth how the hedging instrument is expected to hedge the designated risks related to the hedged item and also sets forth the method that will be used to retrospectively and prospectively assess the hedging instrument’s effectiveness. A derivative designated as a hedging instrument must be assessed as being highly effective in offsetting the designated risk of the hedged item. Hedge effectiveness is formally assessed at inception and at least quarterly throughout the life of the designated hedging relationship. Assessments of hedge effectiveness are also subject to interpretation and estimation and different interpretations or estimates may have a material effect on the amount reported in net income. When hedge accounting is discontinued pursuant to a NIFO hedge (due to a revaluation, payment of a dividend or the disposal of our investment in a foreign operation), the derivative continues to be carried on the balance sheet at its estimated fair value. Deferred gains and losses recorded in OCI pursuant to a discontinued NIFO hedge are recognized immediately in net foreign exchange losses (gains) in our consolidated statements of operations. Embedded Derivatives We are party to certain reinsurance agreements that have embedded derivatives. We also have embedded derivatives on our convertible bond portfolio, recorded within fixed maturities, trading on the consolidated balance sheets. We assess each identified embedded derivative to determine whether it is required to be bifurcated. The embedded derivative is bifurcated from the host contract and accounted for as a freestanding derivative if: •the combined instrument is not accounted for in its entirety at estimated fair value with changes in estimated fair value recorded in net income; •the terms of the embedded derivative are not clearly and closely related to the economic characteristics of the host contract; and •a separate instrument with the same terms as the embedded derivative would qualify as a derivative instrument. Such embedded derivatives are carried on the consolidated balance sheet at estimated fair value with the host contract and changes in their estimated fair value are generally reported within fair value changes in trading securities, funds held and other investments. Derivative Strategies We are exposed to various risks relating to our ongoing business operations, including interest rate, foreign currency exchange rate, credit and equity price risks. We use a variety of strategies to manage these risks, including the use of derivatives. Derivatives are financial instruments with values derived from interest rates, foreign currency exchange rates, credit spreads and/or other financial indices. The types of derivatives we use include swaps and forwards. Foreign Currency Derivatives We use foreign currency exchange rate derivatives, including foreign currency forwards, to reduce the risk from fluctuations in foreign currency exchange rates associated with our assets and liabilities denominated in foreign currencies. We also use foreign currency derivatives to hedge the foreign currency exchange rate risk associated with certain of our net investments in foreign operations. In a foreign currency forward transaction, we agree with another party to deliver a specified amount of an identified currency at a specified future date. The price is agreed upon at the time of the contract and payment for such a contract is made at the specified future date. We utilize foreign currency forwards in fair value, NIFO hedges and nonqualifying hedging relationships. Interest Rate Derivatives We use interest rate derivatives, specifically interest rate swaps, to reduce our exposure to changes in interest rates. Interest rate swaps are used by us primarily to reduce market risks from changes in interest rates and to alter interest rate exposure arising from mismatches between assets and liabilities (duration mismatches). In an interest rate swap, we agree with another party to exchange, at specified intervals, the difference between fixed rate and floating rate interest amounts as calculated by reference to an agreed notional amount. We utilize interest rate swaps in nonqualifying hedging relationships.
Deferred Charges	If, at the inception of a retroactive reinsurance contract, the estimated liabilities for losses and LAE exceed the consideration received, a deferred charge asset (“DCA”) is recorded for this difference. We amortize the DCA balances over the estimated claim payment period of the related contracts with the amortization prospectively adjusted at each reporting period to reflect new estimates of the pattern and timing of remaining losses and LAE payments.
Losses and LAE	The liability for losses and LAE, also referred to as loss reserves, represents both gross estimates before reinsurance for unpaid reported losses (Outstanding Loss Reserves, or "OLR") and losses that have been incurred but not yet reported ("IBNR") estimated using actuarial methods. We recognize an asset for the portion of the liability that we expect to recover from reinsurers. LAE reserves include allocated LAE ("ALAE") and unallocated LAE ("ULAE"). ALAE are linked to the settlement of an individual claim or loss, whereas ULAE are based on our estimates of future costs to administer the claims. IBNR includes amounts for unreported claims, development on known claims and reopened claims. Our loss reserves cover multiple lines of business, including asbestos, environmental, general casualty, workers' compensation, marine, aviation and transit, construction defect, professional indemnity/directors and officers, motor, property and other non-life lines of business. We complete most of our annual loss reserve studies in the fourth quarter of each year and, as a result, tend to record the largest movements, both favorable and adverse, to net incurred losses and LAE in this period. We have elected to apply the fair value option for certain reinsurance contracts including loss portfolio transfers ("LPTs") and reinsurance to close ("RITC") transactions. This is an irrevocable election that applies to all balances under the reinsurance contract, including reinsurance balances recoverable on paid and unpaid losses and the liability for losses and LAE. The primary reason for electing the fair value option was to reduce the earnings volatility created by carrying the liabilities for losses and LAE at cost and the assets supporting those liabilities at fair value. During 2017 and 2018, we elected the fair value option on select new business and classified the supporting portfolio investments as trading securities, whereby all changes in fair value were recorded in the statements of operations. Commencing in 2019, we discontinued electing the fair value option on new business in order to better align with our evolving investment objectives.
Variable Interest Entities	We have investments in certain limited partnership funds which are deemed to be variable interest entities ("VIEs"). The activities of these VIEs are generally limited to holding investments and our involvement in these entities is passive in nature. We consolidate all VIEs in which we are considered to be the primary beneficiary.

Business Overview and Basis of Presentation (Policies)

3 Months Ended

Mar. 31, 2025

These unaudited condensed consolidated financial statements and related notes have been prepared in accordance with accounting principles generally accepted in the United States ("U.S. GAAP") for interim financial information and in conformity with the instructions to Form 10-Q and Article 10 of Regulation S-X of the Rules and Regulations of the Securities and Exchange Commission ("SEC"). Accordingly, they do not include all of the financial information and note disclosures required by U.S. GAAP for complete consolidated financial statements.

Basis of Consolidation

In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments, that are normal and recurring in nature, necessary for a fair statement of the financial results for the interim periods. All intercompany accounts and transactions have been eliminated and certain comparative information has been reclassified to conform to the current presentation.

Recently Issued Accounting Pronouncements Not Yet Adopted

ASU 2023-09 - Improvements to Income Tax Disclosures

In December 2023, the FASB issued ASU 2023-09, which includes the following amendments to Topic 740 Income Taxes:

•Disclose, on an annual basis, specific categories in the rate reconciliation;

•Disclose, on an annual basis, additional information for reconciling items that meet a quantitative threshold (if the effect of those reconciling items is equal to or greater than 5% of the amount computed by multiplying pretax income (or loss) by the applicable statutory income tax rate);

•Disclose, on an annual basis, the amount of income taxes paid (net of refunds received) disaggregated by federal (national), state, and foreign taxes;

•Disclose, on an annual basis, the amount of income taxes paid (net of refunds received) disaggregated by individual jurisdictions in which income taxes paid (net of refunds received) is equal to or greater than 5% of total income taxes paid (net of refunds received);

•Disclose income (or loss) from continuing operations before income tax expense (or benefit) disaggregated between domestic and foreign;

•Disclose income tax expense (or benefit) from continuing operations disaggregated by federal (national), state, and foreign;

•Eliminates the requirement to disclose the nature and estimate of the range of the reasonably possible change in the unrecognized tax benefits balance in the next 12 months or make a statement that an estimate of the range cannot be made; and

•Eliminates the requirement to disclose the cumulative amount of each type of temporary difference when a deferred tax liability is not recognized because of the exceptions to comprehensive recognition of deferred taxes related to subsidiaries and corporate joint ventures.

These amendments are effective for annual reporting periods beginning after December 15, 2024, and should be applied prospectively, however retrospective application is permitted. Early adoption is permitted.

Adopting ASU 2023-09 will require us to expand our income tax disclosures. We will prospectively adopt this ASU within our annual financial statements for the year ended December 31, 2025.

ASU 2024-03 - Disaggregation of Income Statement Expenses

In November 2024, the FASB issued ASU 2024-03, which resulted in the addition of Subtopic 220-40 Reporting Comprehensive Income - Expense Disaggregation Disclosures and includes the following amendments:

•Disclose the amounts of employee compensation, depreciation, intangible asset amortization, and certain other costs and expenses included in each relevant expense caption and include certain amounts that are already required to be disclosed under existing generally accepted accounting principles in the same disclosure;

•Disclose a qualitative description of the amounts remaining in relevant expense captions that are not separately disaggregated quantitatively; and

•Disclose the total amount of selling expenses and, on an annual basis, an entity’s definition of selling expenses.

These amendments are effective for annual reporting periods beginning after December 15, 2026 and interim reporting periods beginning after December 15, 2027, and must be applied prospectively with an option for retrospective application. Early adoption is permitted.

Adopting ASU 2024-03 will require us to expand our disclosures related to costs and expenses. We are currently determining the period in which the new guidance will be adopted.

Investments

Funds Held

Under funds held arrangements, the reinsured company has retained funds that would otherwise have been remitted to us. The funds held balance is credited with investment income and losses paid are deducted.

We present funds held as a single category within the consolidated balance sheets.

Derivative Instruments

Freestanding Derivatives

Freestanding derivatives are recorded on trade-dates and carried on the consolidated balance sheet either as assets within other assets or as liabilities within other liabilities at estimated fair value. We do not offset the estimated fair value amounts recognized for derivatives executed with the same counterparty under the same master netting agreement.

If a derivative is not designated as an accounting hedge or its use in managing risk does not qualify for hedge accounting, changes in the estimated fair value of the derivative are reported in fair value changes in trading securities, funds held and other investments included in our consolidated statements of operations.

Hedge Accounting

To qualify for hedge accounting, at the inception of the hedging relationship, we formally document the risk management objective and strategy for undertaking the hedging transaction, as well as the designation of the hedge.

We have qualifying net investment in foreign operation (“NIFO”) hedges. We recognize changes in the estimated fair value of the hedging derivatives within OCI, consistent with the translation adjustment for the hedged net investment in the foreign operation.

Our documentation sets forth how the hedging instrument is expected to hedge the designated risks related to the hedged item and also sets forth the method that will be used to retrospectively and prospectively assess the hedging instrument’s effectiveness. A derivative designated as a hedging instrument must be assessed as being highly effective in offsetting the designated risk of the hedged item. Hedge effectiveness is formally assessed at inception and at least quarterly throughout the life of the designated hedging relationship. Assessments of hedge effectiveness are also subject to interpretation and estimation and different interpretations or estimates may have a material effect on the amount reported in net income.

When hedge accounting is discontinued pursuant to a NIFO hedge (due to a revaluation, payment of a dividend or the disposal of our investment in a foreign operation), the derivative continues to be carried on the balance sheet at

its estimated fair value. Deferred gains and losses recorded in OCI pursuant to a discontinued NIFO hedge are recognized immediately in net foreign exchange losses (gains) in our consolidated statements of operations.

Embedded Derivatives

We are party to certain reinsurance agreements that have embedded derivatives. We also have embedded derivatives on our convertible bond portfolio, recorded within fixed maturities, trading on the consolidated balance sheets. We assess each identified embedded derivative to determine whether it is required to be bifurcated. The embedded derivative is bifurcated from the host contract and accounted for as a freestanding derivative if:

•the combined instrument is not accounted for in its entirety at estimated fair value with changes in estimated fair value recorded in net income;

•the terms of the embedded derivative are not clearly and closely related to the economic characteristics of the host contract; and

•a separate instrument with the same terms as the embedded derivative would qualify as a derivative instrument.

Such embedded derivatives are carried on the consolidated balance sheet at estimated fair value with the host contract and changes in their estimated fair value are generally reported within fair value changes in trading securities, funds held and other investments.

Derivative Strategies

We are exposed to various risks relating to our ongoing business operations, including interest rate, foreign currency exchange rate, credit and equity price risks. We use a variety of strategies to manage these risks, including the use of derivatives.

Derivatives are financial instruments with values derived from interest rates, foreign currency exchange rates, credit spreads and/or other financial indices. The types of derivatives we use include swaps and forwards.

Foreign Currency Derivatives

We use foreign currency exchange rate derivatives, including foreign currency forwards, to reduce the risk from fluctuations in foreign currency exchange rates associated with our assets and liabilities denominated in foreign currencies. We also use foreign currency derivatives to hedge the foreign currency exchange rate risk associated with certain of our net investments in foreign operations.

In a foreign currency forward transaction, we agree with another party to deliver a specified amount of an identified currency at a specified future date. The price is agreed upon at the time of the contract and payment for such a contract is made at the specified future date. We utilize foreign currency forwards in fair value, NIFO hedges and nonqualifying hedging relationships.

Interest Rate Derivatives

We use interest rate derivatives, specifically interest rate swaps, to reduce our exposure to changes in interest rates.

Interest rate swaps are used by us primarily to reduce market risks from changes in interest rates and to alter interest rate exposure arising from mismatches between assets and liabilities (duration mismatches). In an interest rate swap, we agree with another party to exchange, at specified intervals, the difference between fixed rate and floating rate interest amounts as calculated by reference to an agreed notional amount. We utilize interest rate swaps in nonqualifying hedging relationships.

Deferred Charges

If, at the inception of a retroactive reinsurance contract, the estimated liabilities for losses and LAE exceed the consideration received, a deferred charge asset (“DCA”) is recorded for this difference.

We amortize the DCA balances over the estimated claim payment period of the related contracts with the amortization prospectively adjusted at each reporting period to reflect new estimates of the pattern and timing of remaining losses and LAE payments.

Losses and LAE

The liability for losses and LAE, also referred to as loss reserves, represents both gross estimates before reinsurance for unpaid reported losses (Outstanding Loss Reserves, or "OLR") and losses that have been incurred but not yet reported ("IBNR") estimated using actuarial methods. We recognize an asset for the portion of the liability that we expect to recover from reinsurers. LAE reserves include allocated LAE ("ALAE") and unallocated LAE ("ULAE"). ALAE are linked to the settlement of an individual claim or loss, whereas ULAE are based on our estimates of future costs to administer the claims. IBNR includes amounts for unreported claims, development on known claims and reopened claims.

Our loss reserves cover multiple lines of business, including asbestos, environmental, general casualty, workers' compensation, marine, aviation and transit, construction defect, professional indemnity/directors and officers, motor, property and other non-life lines of business. We complete most of our annual loss reserve studies in the fourth quarter of each year and, as a result, tend to record the largest movements, both favorable and adverse, to net incurred losses and LAE in this period.

We have elected to apply the fair value option for certain reinsurance contracts including loss portfolio transfers ("LPTs") and reinsurance to close ("RITC") transactions. This is an irrevocable election that applies to all balances under the reinsurance contract, including reinsurance balances recoverable on paid and unpaid losses and the liability for losses and LAE. The primary reason for electing the fair value option was to reduce the earnings volatility created by carrying the liabilities for losses and LAE at cost and the assets supporting those liabilities at fair value. During 2017 and 2018, we elected the fair value option on select new business and classified the supporting portfolio investments as trading securities, whereby all changes in fair value were recorded in the statements of operations. Commencing in 2019, we discontinued electing the fair value option on new business in order to better align with our evolving investment objectives.

Variable Interest Entities

We have investments in certain limited partnership funds which are deemed to be variable interest entities ("VIEs"). The activities of these VIEs are generally limited to holding investments and our involvement in these entities is passive in nature. We consolidate all VIEs in which we are considered to be the primary beneficiary.