Argo Group International (ARGO-PA) 10-Q 9 May 24 2024 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2024	May 08, 2024
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	1-15259
Entity Registrant Name	ARGO GROUP INTERNATIONAL HOLDINGS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-0214719
Entity Address, Address Line One	501 7th Avenue 7th Floor
Entity Address, City or Town	New York
Entity Address, Postal Zip Code	10018
Entity Address, State or Province	NY
City Area Code	210
Local Phone Number	321-8400
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		1,156,638,730
Entity Central Index Key	0001091748
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Amendment Flag	false
Guarantee of Argo Group U.S., Inc. 6.500% Senior Notes due 2042
Document Information [Line Items]
Title of 12(b) Security	6.500% Senior Notes due 2042 issued by Argo Group US, Inc. and The Guarantee With Respects Thereto
Trading Symbol	ARGD
Security Exchange Name	NYSE
Depositary Shares
Document Information [Line Items]
Title of 12(b) Security	Depositary Shares, Each Representing a 1/1000th Interest in 7.00% Resettable Fixed Rate Preferred Stock, Series A, Par Value $1.00 Per Share
Trading Symbol	ARGOPrA
Security Exchange Name	NYSE

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Investments:
Fixed maturities available-for-sale, at fair value (cost: 2024 - $2,370.0, 2023 - $2,521.5; allowance for expected credit losses: 2024 - $0.2, 2023 - $0.2)	$ 2,413.4	$ 2,585.4
Mortgage loans (cost: 2024 - $171.6, 2023 - $144.8; allowance for expected credit losses: 2024 - $0.5, 2023 - $0.2)	171.1	144.6
Equity securities, at fair value (cost: 2024 - $9.5; 2023 - $11.7)	8.6	10.7
Other investments (cost: 2024 - $344.4; 2023 - $311.0)	344.4	311
Short-term investments, at fair value (cost: 2024 - $1,073.7; 2023 - $429.0)	1,073.6	429.5
Total investments	4,011.1	3,481.2
Cash, restricted cash and cash equivalents	462.4	791.6
Accrued investment income	18	20.4
Premiums receivable	209.8	230.7
Reinsurance recoverables	2,933.1	2,959.3
Other intangible assets, net of accumulated amortization	170.3	180.6
Current income taxes receivable, net	54.2	53.1
Deferred tax asset, net	41.7	39.1
Deferred acquisition costs, net	32.2	7.2
Ceded unearned premiums	353.7	356
Operating lease right-of-use assets	52.8	51.2
Other assets	196.9	189.1
Value of business acquired, net of accumulated amortization	110.9	143.6
Total assets	8,647.1	8,503.1
Liabilities and Stockholders' Equity
Reserves for losses and loss adjustment expenses	5,543.1	5,544.5
Unearned premiums	842.1	916.6
Accrued underwriting expenses and other liabilities	56.3	73.9
Ceded reinsurance payable, net	229.4	192.7
Funds held	48.6	57.3
Borrowing under revolving credit facility	100	0
Senior unsecured fixed rate notes	128.1	128
Junior subordinated debentures	241.6	241.2
Operating lease liabilities	53.4	51.4
Total liabilities	7,242.6	7,205.6
Commitments and contingencies (Note 12)
Stockholders' equity:
Series A Preferred stock and additional paid-in capital - $1.00 par, 30,000,000 shares authorized; 6,000 and 6,000 shares issued at March 31, 2024 and December 31, 2023, respectively; liquidation preference $25,000	137.1	137.1
Common stock - $1.00 par, 2,000,000,000 shares authorized; 1,156,638,730 and 1,056,638,730 shares issued at March 31, 2024 and December 31, 2023, respectively	1,156.6	1,056.6
Additional paid-in capital	51.1	51.1
Retained earnings	23.9	0.9
Accumulated other comprehensive income, net of taxes	35.8	51.8
Total stockholders' equity	1,404.5	1,297.5
Total liabilities and stockholders' equity	$ 8,647.1	$ 8,503.1

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, at cost	$ 2,370	$ 2,521.5
Allowance for expected credit losses	0.2	0.2
Mortgage loans	171.6	144.8
Allowance for credit loss	0.5	0.2
Equity securities, cost	9.5	11.7
Other investments, cost	344.4	311
Short-term investments, cost	$ 1,073.7	$ 429
Preferred shares, par value (in dollars per share)	$ 1	$ 1
Preferred shares, shares authorized (in shares)	30,000,000	30,000,000
Preferred shares, shares issued (in shares)	6,000	6,000
Liquidation preference (in dollars per share)	$ 25,000	$ 25,000
Common shares, par value (in dollars per share)	$ 1	$ 1
Common shares, shares authorized (in shares)	2,000,000,000	2,000,000,000
Common shares, shares issued (in shares)	1,156,638,730	1,056,638,730

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Premiums and other revenue:
Net earned premiums	$ 313.7	$ 389.9
Net investment income	58.8	29.7
Net investment and other gains (losses):
Net realized investment and other gains (losses)	6.2	(21.1)
Change in fair value recognized	0	3.3
Change in allowance for credit losses on fixed maturity securities	0	(0.1)
Total net investment and other gains (losses)	6.2	(17.9)
Total revenue	378.7	401.7
Expenses:
Losses and loss adjustment expenses	220	284.6
Underwriting, acquisition and general expenses	117.1	137
Non-operating expenses	7.7	11.6
Interest expense	8.7	8.5
Fee and other (income) expense, net	0	(0.4)
Foreign currency exchange (gains) losses	(2)	2.7
Total expenses	351.5	444
Income (loss) before income taxes	27.2	(42.3)
Income tax provision (benefit)	1.6	(8.5)
Net income (loss)	25.6	(33.8)
Dividends on Series A Preferred stock	2.6	2.6
Net income (loss) attributable to common stockholders	23	(36.4)
Net income (loss) attributable to common stockholders	$ 23	$ (36.4)
Net income (loss) attributable to common stockholders per share of common stock:
Basic (in dollars per share)		$ (1.04)
Diluted (in dollars per share)		(1.04)
Dividend declared per common share (in dollars per share)		$ 0
Weighted average common stock:
Basic (in shares)		35,099,968
Diluted (in shares)		35,099,968

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 25.6	$ (33.8)
Foreign currency translation:
Foreign currency translation adjustments	(0.1)	0.4
Reclassification adjustment for foreign currency translation included in net income	0	0
Defined benefit pension plans:
Net gain arising during the period	0	1
Fixed maturity securities:
Unrealized gains (losses) arising during the period	(13.8)	33.2
Reclassification adjustment for (gains) losses included in net income	(6.5)	22.2
Other comprehensive income (loss) before tax	(20.4)	56.8
Defined benefit pension plans:
Net gain arising during the period	0	0.2
Fixed maturity securities:
Unrealized gains (losses) arising during the period	(3.1)	5.2
Reclassification adjustment for (gains) losses included in net income	(1.3)	4.7
Income tax provision (benefit) related to other comprehensive income (loss)	(4.4)	10.1
Other comprehensive income (loss), net of tax	(16)	46.7
Comprehensive income (loss)	$ 9.6	$ 12.9

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock and Additional Paid-in Capital	Common Stock	Additional Paid-In Capital	Treasury Shares	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2022	$ 1,232.9	$ 144	$ 46.4	$ 1,395.4	$ (455.1)	$ 407.3	$ (305.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(33.8)					(33.8)
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	45.5						45.5
Other comprehensive income (loss), net of tax	1.2						1.2
Activity under stock incentive plans	1.7		0.1	1.6
Retirement of common stock (tax payments on equity compensation)	(0.8)			(0.8)
Employee stock purchase plan	0.4			0.4
Dividends on Series A Preferred stock	(2.6)					(2.6)
Ending Balance at Mar. 31, 2023	1,244.5	144	46.5	1,396.6	(455.1)	370.9	(258.4)
Beginning Balance at Dec. 31, 2023	1,297.5	137.1	1,056.6	51.1	0	0.9	51.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	25.6					25.6
Other comprehensive income (loss) - change in fair value of fixed maturities, net of taxes	(15.9)						(15.9)
Other comprehensive income (loss), net of tax	(0.1)						(0.1)
Dividends on Series A Preferred stock	(2.6)					(2.6)
Issuance of common stock	100		100
Ending Balance at Mar. 31, 2024	$ 1,404.5	$ 137.1	$ 1,156.6	$ 51.1	$ 0	$ 23.9	$ 35.8

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows provided by (used in) operating activities:
Net income (loss)	$ 25.6	$ (33.8)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Amortization and depreciation	46.1	4.3
Share-based payments expense	0	1.5
Deferred income tax expense (benefit), net	2.6	(5.9)
Net investment and other (gains) losses	(6.2)	17.9
Undistributed earnings from alternative investment portfolio	(5.9)	0.2
Foreign currency exchange (gains) losses	(2)	2.7
Change in:
Accrued investment income	2.4	(0.3)
Receivables	47.1	613.8
Deferred acquisition costs	(25)	(6.5)
Ceded unearned premiums	2.3	(50)
Reserves for losses and loss adjustment expenses	0.6	(367.2)
Unearned premiums	(74.5)	(3.9)
Ceded reinsurance payable and funds held	28	(60.8)
Income taxes	(1.1)	(3)
Accrued underwriting expenses and other liabilities	(18.6)	(25.1)
Other, net	(35.1)	(44.8)
Cash (used in) provided by operating activities	(13.7)	39.1
Cash flows provided by (used in) investing activities:
Sales of fixed maturity investments	102.7	0.6
Maturities and mandatory calls of fixed maturity investments	63.7	32.5
Sales of equity securities	2.3	6
Sales of other investments	31.9	1.9
Purchases of fixed maturity investments	(1)	(1.7)
Purchases of equity securities	(0.1)	0
Purchases of other investments	(48.5)	(3.9)
Purchase of mortgage loans	(26.9)	0
Change in short-term investments	(637.8)	(215)
Settlements of foreign currency exchange forward contracts	0.8	5.1
Proceeds from business divestitures, net of cash transferred	0	54.3
Purchases of fixed assets, net	0	(1.4)
Cash used in investing activities	(512.9)	(121.6)
Cash flows provided by (used in) financing activities:
Additional debt borrowings	100	0
Issuance of common stock	100	0
Activity under stock incentive plans	0	0.5
Payment of cash dividends to preferred stockholders	(2.6)	(2.6)
Cash provided by (used in) financing activities	197.4	(2.1)
Net change in cash and restricted cash including balances classified as held-for-sale	(329.2)	(84.6)
Net change in cash balances classified as held-for-sale	0	70.8
Cash, restricted cash, and cash equivalents, beginning of period	791.6	50.2
Cash, restricted cash, and cash equivalents, end of period	$ 462.4	$ 36.4

Business and Significant Accoun

Business and Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Significant Accounting Policies	Business and Significant Accounting Policies The accompanying Condensed Consolidated Financial Statements of Argo Group International Holdings, Inc. and its subsidiaries (“Argo Group,” “we,” “us,” “our” or the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Argo Group is an underwriter of specialty insurance products in the property and casualty market. On November 16, 2023, we merged with Brookfield Reinsurance Ltd., which resulted in a change to the Company’s ownership, (the “Merger”). Brookfield Reinsurance Ltd. elected to push-down its purchase accounting, which resulted in the Company reflecting the fair market value of our assets and liabilities as of November 16, 2023, in accordance with Accounting Standards Codification (“ASC”) 805, Business Combinations. The application of push-down accounting created a new basis of accounting for all of our assets and liabilities. As such, the Company’s financial position, results of operations, and cash flows subsequent to the acquisition are not comparable with those prior to November 16, 2023, and therefore have been separated to indicate pre-acquisition and post-acquisition periods. The pre-acquisition period through November 15, 2023 is referred to as the Predecessor. The post-acquisition period, November 16, 2023 and forward, includes the impact of push-down accounting and is referred to as the Successor. The preparation of interim financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our Condensed Consolidated Financial Statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for expected credit losses; fair value of investments and assessment of potential impairment, including the allowance for credit losses on fixed maturity securities; valuation of intangibles, including those identified as part of purchase accounting related to the Merger, and our deferred tax asset valuation allowance. Actual results could materially differ from those estimates. Certain financial information that is normally included in annual Condensed Consolidated Financial Statements, including certain financial statement footnotes, prepared in accordance with GAAP, is not required for interim reporting purposes and has been condensed or omitted. These statements should be read in conjunction with the Condensed Consolidated Financial Statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2023 filed with the Securities and Exchange Commission ("SEC") (the “2023 Form 10-K”). The interim financial information as of, and for the three months ended, March 31, 2024 and 2023 is unaudited. However, in the opinion of management, the interim information includes all adjustments, consisting of normal recurring accruals, necessary for a fair presentation of the results presented for the interim periods. The operating results for the interim periods are not necessarily indicative of the results to be expected for the full year. All material intercompany amounts have been eliminated in consolidation. Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation. Sale of Argo Underwriting Agency Limited On September 8, 2022, Argo International Holdings Limited (the “Seller”), a wholly-owned subsidiary of the Company, and Ohio Farmers Insurance Company (the “Buyer”), part of the Westfield group of insurance companies, entered into a sale and purchase agreement (the “Transaction”) under which the Seller agreed to sell, and the Buyer agreed to purchase, the entire issued share capital of AUA, for which the financial results are reported in our International segment. This transaction simplifies our reporting structure and is intended to drive greater efficiencies. The base cash consideration for the purchase was $125.0 million, which was adjusted to reflect the extent by which AUA’s net assets as at completion are greater or lesser than AUA net assets as of March 31, 2022. In the third quarter of 2022, as a result of the sale, an impairment was recorded in the amount of $28.5 million, consisting of $17.3 million of indefinite lived intangible assets and $11.2 million of goodwill, representing the difference between the carrying value and implied fair value as determined by the consideration to be received. In addition, the Buyer replaced certain funds provided by the Company to support the activities of AUA and certain of its subsidiaries at Lloyd’s of London, which were subsequently released to the Company. As of December 31, 2022, the Company reported the assets and liabilities of this block of business as held-for-sale on Consolidated Balance Sheets with results continuing to be reported within the Consolidated Statements of Comprehensive Income (Loss) and the International Operations segment. The Company determined that the Transaction did not represent a strategic shift, and therefore, did not meet the requirements for discontinued operations. On February 2, 2023, the Seller completed the sale of the entire issued share capital of AUA. At the closing, the Company received total consideration of $155.7 million, which included cash proceeds of $125.1 million as base consideration and an additional $30.6 million which was placed in escrow by the Buyer related to certain reinsurance-related recoverables. The funds in escrow may be released to the Seller over a period of two years following the closing. At the end of the two-year escrow period, any remaining balance of the escrow will be returned to the Buyer. As a result of the sale, we realized a loss of $20.3 million in the first quarter of 2023, which is included as a component of Net realized investment and other gains (losses) in our Consolidated Statements of Comprehensive Income (Loss). This loss is due to the realization of unrealized investment losses, which was previously a component of accumulated other comprehensive income. The total consideration was adjusted to $161.3 million based on a mutually agreed final closing balance sheet, which resulted in an additional $5.6 million of cash proceeds received by the Company in July 2023. Since the sale of AUA, $12.9 million of the consideration placed in escrow was released to the Company.

Recently Issued Accounting Pron

Recently Issued Accounting Pronouncements	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The Company evaluated recently issued accounting pronouncements and determined none are material to our results of operations or financial position reported herein.

Investments

Investments	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Investments	Investments As a result of the push-down accounting due to the Merger, the amortized cost of our investments is based on the fair value as of November 16, 2023. Fixed Maturities The amortized cost, gross unrealized gains, gross unrealized losses, allowance for credit losses, and fair value of fixed maturity investments were as follows: March 31, 2024 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 354.4 $ 1.6 $ — $ — $ 356.0 Foreign Governments 5.6 0.6 — — 6.2 Obligations of states and political subdivisions 87.2 1.5 — — 88.7 Corporate bonds 1,097.4 19.2 0.9 0.2 1,115.5 Commercial mortgage-backed securities 264.5 11.4 0.5 — 275.4 Residential mortgage-backed securities 230.7 6.1 — — 236.8 Asset-backed securities 131.9 1.9 0.1 — 133.7 Collateralized loan obligations 198.3 3.0 0.2 — 201.1 Total fixed maturities $ 2,370.0 $ 45.3 $ 1.7 $ 0.2 $ 2,413.4 December 31, 2023 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 357.7 $ 4.5 $ — $ — $ 362.2 Foreign Governments 27.9 2.6 — 0.2 30.3 Obligations of states and political subdivisions 92.4 2.0 — — 94.4 Corporate bonds 1,185.0 28.9 0.8 — 1,213.1 Commercial mortgage-backed securities 270.9 10.1 0.5 — 280.5 Residential mortgage-backed securities 235.2 13.6 — — 248.8 Asset-backed securities 140.4 1.7 0.1 — 142.0 Collateralized loan obligations 212.0 2.1 — — 214.1 Total fixed maturities $ 2,521.5 $ 65.5 $ 1.4 $ 0.2 $ 2,585.4 Contractual Maturity The amortized cost and fair values of fixed maturity investments as of March 31, 2024, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 347.3 $ 347.6 Due after one year through five years 950.2 961.3 Due after five years through ten years 231.5 240.5 Due after ten years 15.6 17.0 Structured securities 825.4 847.0 Total $ 2,370.0 $ 2,413.4 The actual maturities may differ from the contractual maturities because debtors may have the right to call or prepay obligations. Other Invested Assets Details regarding the carrying value and unfunded investment commitments of other investments as of March 31, 2024 and December 31, 2023 were as follows: March 31, 2024 (in millions) Carrying Unfunded Investment type Hedge funds $ 31.5 $ — Private equity 257.9 82.4 Other 55.0 11.3 Total other investments $ 344.4 $ 93.7 December 31, 2023 (in millions) Carrying Unfunded Investment type Hedge funds $ 56.2 $ — Private equity 250.3 93.4 Other 4.5 — Total other investments $ 311.0 $ 93.4 The following describes each investment type: • Hedge funds: Hedge funds, carried at net asset value (“NAV”) as a practical expedient of fair value, include funds that primarily buy and sell stocks, including short sales, multi-strategy credit, relative value credit and distressed credit. • Private equity: Private equity includes buyout funds, real asset/infrastructure funds, credit special situations funds, mezzanine lending funds and direct investments and strategic non-controlling minority investments in private companies that are principally accounted for using the equity method of accounting. • Other: Other includes participation in investment pools and private loans. Unrealized Losses and Other-than-temporary Impairments An aging of unrealized losses on our investments in fixed maturities is presented below: March 31, 2024 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 103.4 $ — $ — $ — $ 103.4 $ — Obligations of states and political subdivisions 14.6 — — — 14.6 — Corporate bonds 49.9 0.9 — — 49.9 0.9 Commercial mortgage-backed securities 21.6 0.5 — — 21.6 0.5 Residential mortgage-backed securities 3.9 — — — 3.9 — Asset-backed securities 13.2 0.1 — — 13.2 0.1 Collateralized loan obligations 5.6 0.2 — — 5.6 0.2 Total fixed maturities $ 212.2 $ 1.7 $ — $ — $ 212.2 $ 1.7 December 31, 2023 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities Foreign Governments $ 0.1 $ — $ — $ — $ 0.1 $ — Obligations of states and political subdivisions 0.5 — — — 0.5 — Corporate bonds 38.7 0.8 — — 38.7 0.8 Commercial mortgage-backed securities 32.2 0.5 — — 32.2 0.5 Residential mortgage-backed securities 2.9 — — — 2.9 — Asset-backed securities 11.4 0.1 — — 11.4 0.1 Collateralized loan obligations 21.4 — — — 21.4 — Total fixed maturities $ 107.2 $ 1.4 $ — $ — $ 107.2 $ 1.4 We hold a total of 1,169 fixed maturity securities, of which 117 were in an unrealized loss position for less than one year and none were in an unrealized loss position for a period one year or greater as of March 31, 2024. The unrealized losses as of March 31, 2024 are primarily driven from interest rate movements. Allowance for Credit Losses For fixed maturities with a decline in fair value below the amortized cost due to credit-related factors, an allowance is established for the difference between the estimated recoverable value and amortized cost with a corresponding charge to Net investment and other gains (losses) in the Condensed Consolidated Statements of Income (Loss). The allowance is limited to the difference between amortized cost and fair value. The estimated recoverable value is the present value of cash flows expected to be collected, as determined by management. The difference between fair value and amortized cost that is not associated with credit-related factors is recognized in the Condensed Consolidated Statements of Comprehensive Income (Loss). Accrued interest is excluded from the measurement of the allowance for credit losses. When determining if a credit loss has been incurred, we may consider the historical performance of the security, available market information and security specific considerations such as the priority payment of the security. In addition, inputs used in our analysis include, but are not limited to, credit ratings and downgrades, delinquency rates, missed scheduled interest or principal payments, purchase yields, underlying asset performance, collateral types, modeled default rates, modeled severity rates, call/prepayment rates, expected cash flows, industry concentrations, and potential or filed bankruptcies or restructurings. In cooperation with our investment managers, we evaluate for credit losses each quarter utilizing a bottom up review approach. At the security level, a determination is made as to whether a decline in fair value below the amortized cost basis is due to credit-related or noncredit-related factors. If we determine that all or a portion of a fixed maturity is uncollectible, the uncollectible amortized cost is written off with a corresponding reduction to the allowance for credit losses. If we collect cash flows that were previously written off, the recovery is recognized in Net investment and other gains (losses) . We also consider whether we intend to sell an available-for-sale security or if it is more likely than not that we will be required to sell the security before recovery of its amortized cost. In these instances, a decline in fair value is recognized in Net investment and other gains (losses) in the Condensed Consolidated Statements of Income (Loss) based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. The following table presents a roll-forward of the changes in allowance for credit losses on available-for-sale fixed maturities by industry category for the three months ending March 31, 2024 and 2023, respectively: Successor (in millions) Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2024 $ 0.2 $ — $ — $ — $ 0.2 Securities for which allowance was not previously recorded — — 0.1 — 0.1 Additional net increases (decreases) in existing allowance (0.2) — 0.1 — (0.1) Ending balance, March 31, 2024 $ — $ — $ 0.2 $ — $ 0.2 Predecessor (in millions) Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2023 $ 0.7 $ 0.4 $ 1.6 $ 0.1 $ 2.8 Securities for which allowance was not previously recorded — — 0.2 — 0.2 Securities sold during the period — — (0.3) — (0.3) Additional net increases (decreases) in existing allowance 0.1 — (0.1) — — Ending balance, March 31, 2023 $ 0.8 $ 0.4 $ 1.4 $ 0.1 $ 2.7 The change in allowance for credit losses on fixed maturity securities, included in Net investment and other gains (losses) in the Condensed Consolidated Statements of Income (Loss) was nil and $0.1 million for the three months ended March 31, 2024, and 2023, respectively. For mortgage loans an allowance for credit losses is established at the time of origination or purchase, as necessary, and is updated each reporting period. Changes in the allowance for credit losses are recorded in Net investment and other gains (losses) . This allowance reflects the risk of loss, even when that risk is remote, that is expected over the remaining contractual life of the loan. The allowance for credit losses considers available relevant information about the collectability of cash flows, including information about past events, current conditions, and reasonable and supportable forecasts of future economic conditions. Mortgage Loans Mortgage loan investments are composed of participation interests in a portfolio of commercial and residential mortgage loans. Loan collateral is diversified with regard to property type and geography. The following table presents loans by property type: March 31, 2024 (in millions) Cost Composition Loan Count Residential $ 1.7 1.0 % 1 Apartments 76.1 44.3 % 16 Hotel 22.3 13.0 % 4 Industrial 26.0 15.2 % 4 Office 25.9 15.1 % 1 Retail 19.6 11.4 % 4 Total $ 171.6 100.0 % 30 December 31, 2023 (in millions) Cost Composition Loan Count Apartments $ 76.1 52.6 % 16 Hotel 22.4 15.4 % 4 Industrial 26.0 18.0 % 4 Retail 20.3 14.0 % 4 Total $ 144.8 100.0 % 28 The following table presents our loans by Debt Service Coverage Ratio (“DSCR”): March 31, 2024 (in millions) Cost Loan Count Less than 1.00 $ 36.2 8 1.00 to 1.50 54.5 7 Greater than 1.5 to 2.0 30.9 6 Greater than 2.0 to 3.0 36.0 6 Greater than 3.0 to 4.0 12.3 2 Total $ 169.9 29 DSCR does not include residential mortgage loans. December 31, 2023 (in millions) Cost Loan Count Less than 1.00 $ 36.2 8 1.00 to 1.50 29.4 6 Greater than 1.5 to 2.0 30.9 6 Greater than 2.0 to 3.0 36.0 6 Greater than 3.0 to 4.0 12.3 2 Total $ 144.8 28 The following table presents loans by Loan To Value (“LTV”): March 31, 2024 (in millions) Cost Loan Count Equal to or less than 50.0% $ 12.3 2 Greater than 50.0% to 55.0% 9.0 2 Greater than 55.0% to 60.0% 20.7 5 Greater than 60.0% to 70.0% 63.2 7 Greater than 70.0% 66.4 14 Total $ 171.6 30 December 31, 2023 (in millions) Cost Loan Count Equal to or less than 50.0% $ 12.3 2 Greater than 50.0% to 55.0% 9.1 2 Greater than 55.0% to 60.0% 18.9 4 Greater than 60.0% to 70.0% 37.3 6 Greater than 70.0% 67.2 14 Total $ 144.8 28 The following table presents loans by maturity: March 31, 2024 (in millions) Cost Loan Count One Year or Less $ 44.8 8 Greater than One Year and Less than Three 34.9 3 Greater than Three Years and Less than Five Years 32.4 6 Greater than Five Years and Less than Seven Years 17.2 4 Greater than Seven Years and Less than Ten Years 42.3 9 Total $ 171.6 30 December 31, 2023 (in millions) Cost Loan Count One Year or Less $ 19.7 4 Greater than One Year and Less than Three 34.9 6 Greater than Three Years and Less than Five Years 32.4 6 Greater than Five Years and Less than Seven Years 17.2 4 Greater than Seven Years and Less than Ten Years 40.6 8 Total $ 144.8 28 Investment Gains and Losses The following table presents our gross realized investment gains and losses: Successor Predecessor (in millions) Three Months Ended Three Months Ended Realized gains on fixed maturities and other: Fixed maturities $ 6.8 $ 0.2 Other investments, including short-term investments 2.6 7.8 Total realized gains on fixed maturities and other 9.4 8.0 Realized losses on fixed maturities and other: Fixed maturities (0.3) (22.4) Other investments, including short-term investments (2.8) (5.8) Total realized losses on fixed maturities and other (3.1) (28.2) Other net losses recognized on fixed maturities and other: Credit losses on fixed maturities (0.5) (0.6) Impairment related to change in intent — — Other — (3.6) Total other net losses recognized on fixed maturities and other (0.5) (4.2) Equity securities: Net realized gains (losses) on equity securities 0.4 0.3 Change in unrealized gains (losses) on equity securities held at the end of the period — 6.2 Net gains (losses) on equity securities 0.4 6.5 Net investment and other gains (losses) before income taxes 6.2 (17.9) Income tax (benefit) provision 1.6 (5.1) Net investment and other gains (losses), net of income taxes $ 4.6 $ (12.8) The cost of securities sold is based on the specific identification method. Changes in unrealized gains (losses) related to fixed maturity investments are summarized as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Change in unrealized gains (losses) Fixed maturities $ (19.9) $ 55.5 Other and short-term investments (0.4) (0.1) Net unrealized investment gains (losses) before income taxes (20.3) 55.4 Income tax provision (benefit) (4.4) 9.9 Net unrealized investment gains (losses), net of income taxes $ (15.9) $ 45.5 Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts primarily to manage currency exposure from our non-USD insurance operations. The currency forward contracts are carried at fair value in our Condensed Consolidated Balance Sheets in Other liabilities and Other assets at March 31, 2024 and December 31, 2023, respectively. The net realized gains and (losses) are included in Net realized investment and other gains (losses) in our Condensed Consolidated Statements of Income (Loss). The fair value of our foreign currency exchange forward contracts as of March 31, 2024 and December 31, 2023 was as follows: As of March 31, 2024 December 31, 2023 (in millions) Notional Amount Fair Value Notional Amount Fair Value Operational currency Open contracts in a gain position $ — $ — $ 75.4 $ 1.8 Open contracts in a loss position 100.4 (0.7) 43.3 (0.3) Net open contracts for operational currency $ (0.7) $ 1.5 Asset manager investment exposure Open contracts in a gain position $ 45.8 $ 1.0 $ — $ — Open contracts in a loss position — — 45.8 (0.2) Net open contracts for asset manager investment exposure 1.0 (0.2) Total $ 0.3 $ 1.3 The following table presents our gross realized investment gains and losses on our foreign currency exchange forward contracts: Successor Predecessor (in millions) Three Months Ended Three Months Ended Realized gains Operational currency exposure $ 1.4 $ 4.1 Asset manager investment exposure 1.2 — Gross realized investment gains 2.6 4.1 Realized losses Operational currency exposure (2.7) (3.1) Asset manager investment exposure — (0.3) Gross realized investment losses (2.7) (3.4) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (0.1) $ 0.7 Regulatory Deposits, Pledged Securities and Letters of Credit We are required to maintain assets on deposit with various regulatory authorities to support our insurance and reinsurance operations. We maintain assets pledged as collateral in support of irrevocable letters of credit issued under the terms of certain reinsurance agreements for loss and loss expense reserves. The following table presents our components of restricted investments: As of (in millions) March 31, 2024 December 31, 2023 Securities on deposit for regulatory and other purposes $ 152.7 $ 153.4 Securities pledged as collateral for letters of credit 39.7 109.2 Total restricted investments $ 192.4 $ 262.6 Fair Value Measurements Fair value is the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability, or in the absence of a principal market, the most advantageous market. Market participants are buyers and sellers in the principal (or most advantageous) market that are independent, knowledgeable, able to transact for the asset or liability and willing to transfer the asset or liability. Valuation techniques consistent with the market approach, income approach and/or cost approach are used to measure fair value. The inputs of these valuation techniques are categorized into three levels. • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that can be accessed at the reporting date. We define actively traded as a security that has traded in the past seven days. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. We receive one quote per instrument for Level 2 inputs. • Level 3 inputs are unobservable inputs. Unobservable inputs reflect our own judgments about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances. To validate the fair value of investments in the Company’s Condensed Consolidated Financial Statements, we receive prices from multiple sources including third-party pricing services and our outside investment managers. Through a comparative analysis, the Company validates the reasonableness of its valuations. These prices are determined using observable market information such as dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. We have reviewed the processes used by the third-party providers for pricing the securities and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of March 31, 2024 and December 31, 2023. A description of the valuation techniques we use to measure assets at fair value is as follows: Fixed Maturities (Available-for-Sale) Levels 1 and 2: • United States Treasury securities are typically valued using Level 1 inputs. For these securities, we obtain fair value measurements from third-party pricing services using quoted prices (unadjusted) in active markets at the reporting date. • United States Government agencies, non-U.S. Government securities, obligations of states and political subdivisions, credit securities and foreign denominated government and credit securities are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, yield curves, live trading levels, trade execution data, credit information and the security’s terms and conditions, among other things. • Asset and mortgage-backed securities and collateralized loan obligations are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Fixed Maturities (Available-for-Sale) Levels 3: We own term loans and asset-back securities that are valued using unobservable inputs. Equity Securities Level 1: Equity securities are principally reported at fair value using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Equity Securities Level 3: We own certain equity securities that are reported at fair value using Level 3 inputs. The valuation techniques for these securities include the following: • Fair value measurements for an investment in an equity fund obtained by applying final prices provided by the administrator of the fund, which is based upon certain estimates and assumptions. • Fair value measurements from brokers and independent valuation services, both based upon estimates, assumptions and other unobservable inputs. Short-term Investments: Short-term investments are principally reported at fair value using Level 1 inputs, with the exception of short-term corporate and governmental bonds reported at fair value using Level 2 inputs as described in the fixed maturities section above. Values for the investments categorized as Level 1 are obtained from various financial institutions as of the reporting date. Based on an analysis of the inputs, our financial assets and liabilities measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) March 31, Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 356.0 $ 93.8 $ 262.2 $ — Foreign Governments 6.2 — 6.2 — Obligations of states and political subdivisions 88.7 — 88.7 — Corporate bonds 1,115.5 — 1,093.2 22.3 Commercial mortgage-backed securities 275.4 — 275.4 — Residential mortgage-backed securities 236.8 — 236.8 — Asset-backed securities 133.7 — 121.0 12.7 Collateralized loan obligations 201.1 — 201.1 — Total fixed maturities 2,413.4 93.8 2,284.6 35.0 Equity securities 8.6 2.0 — 6.6 Other investments 1.3 — 0.2 1.1 Short-term investments 1,073.6 1,073.2 0.4 — Derivatives 0.3 — 0.3 — Total assets $ 3,497.2 $ 1,169.0 $ 2,285.5 $ 42.7 (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 362.2 $ 360.1 $ 2.1 $ — Foreign Governments 30.3 — 30.3 — Obligations of states and political subdivisions 94.4 — 94.4 — Corporate bonds 1,213.1 — 1,180.5 32.6 Commercial mortgage-backed securities 280.5 — 280.5 — Residential mortgage-backed securities 248.8 — 248.8 — Asset-backed securities 142.0 — 124.2 17.8 Collateralized loan obligations 214.1 — 214.1 — Total fixed maturities 2,585.4 360.1 2,174.9 50.4 Equity securities 10.7 4.3 — 6.4 Other investments 0.2 — 0.2 — Short-term investments 429.5 429.0 0.5 — Derivatives 1.3 — 1.3 — Total assets $ 3,027.1 $ 793.4 $ 2,176.9 $ 56.8 (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs The fair value measurements in the tables above do not equal Total investments on our Condensed Consolidated Balance Sheets as they primarily exclude mortgage loans and other investments. Our mortgage loans are accounted for using the amortized cost basis and other investments are accounted for under the equity-method of accounting, amortized cost basis, and hedge funds which are carried at NAV as a practical expedient. A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Unobservable Inputs (Level 3) (in millions) Credit Financial Equity Other Invested Assets Total Beginning balance, January 1, 2024 $ 50.4 $ 6.4 $ — $ 56.8 Transfers out of Level 3 (10.0) — — (10.0) Total gains or losses (realized/unrealized): Included in net income 0.8 0.1 — 0.9 Included in other comprehensive income (0.4) — — (0.4) Purchases, issuances, sales, and settlements: Purchases 0.4 0.1 1.1 1.6 Settlements (6.2) — — (6.2) Ending balance, March 31, 2024 $ 35.0 $ 6.6 $ 1.1 $ 42.7 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2024 $ — $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2023 $ 40.7 $ 15.5 $ 56.2 Transfers into Level 3 5.6 — 5.6 Transfers out of Level 3 (5.6) (7.6) (13.2) Total gains or losses (realized/unrealized): Included in net income (0.1) (0.4) (0.5) Included in other comprehensive loss 0.8 — 0.8 Purchases, issuances, sales, and settlements: Purchases 10.6 — 10.6 Sales (0.5) (1.1) (1.6) Settlements (1.1) — (1.1) Ending balance, December 31, 2023 $ 50.4 $ 6.4 $ 56.8 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2023 $ — $ (0.8) $ (0.8) At March 31, 2024 and December 31, 2023, we did not have any financial assets or financial liabilities measured at fair value on a nonrecurring basis or any financial liabilities on a recurring basis. The Company holds certain investments at cost, less an allowance for expected credit losses, on the Condensed Consolidated Balance Sheets. The fair value of the Company’s investments is estimated using a discounted cash flow analysis. Due to the level of unobservable inputs factored into the estimation of fair value, the valuation would be categorized as Level 3. The cost and estimated fair value of these investments were: As of March 31, 2024 December 31, 2023 (in millions) Cost Fair Value Cost Fair Value Mortgage loans $ 171.6 $ 176.0 $ 144.8 $ 148.8 Private loans 49.4 49.3 — — Total $ 221.0 $ 225.3 $ 144.8 $ 148.8

Allowance for Credit Losses

Allowance for Credit Losses	3 Months Ended
	Mar. 31, 2024
Credit Loss [Abstract]
Allowance for Credit Losses	Allowance for Credit Losses Premiums receivable The following table presents the balances of premiums receivable, net of allowance for estimated uncollectible premiums, including expected lifetime credit losses and the changes in the allowance for the respective periods: (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Predecessor Balance, December 31, 2022 $ 292.0 $ 4.7 Current period change for estimated uncollectible premiums 0.4 Balance, March, 2023 $ 271.1 $ 5.1 Successor Balance, December 31, 2023 $ 230.7 3.0 Current period change for estimated uncollectible premiums 1.4 Write-offs of uncollectible premiums receivable (0.3) Balance, March 31, 2024 $ 209.8 $ 4.1 Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, including expected credit losses and changes in the allowance for the respective periods: (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Predecessor Balance, December 31, 2022 $ 3,029.1 $ 4.7 Balance, March 31, 2023 $ 3,016.9 $ 4.7 Successor Balance, December 31, 2023 $ 2,959.3 $ — Balance, March 31, 2024 $ 2,933.1 $ — We primarily utilize A.M. Best credit ratings when determining the allowance and adjust as needed based on our historical experience with the reinsurers. A portion of our reinsurance recoverables are collateralized by letters of credit, funds held or trust agreements.

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2024
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”): Successor Predecessor (in millions) Three Months Ended Three Months Ended Net reserves - beginning of the year $ 2,747.1 $ 2,213.1 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 195.2 236.0 Prior accident years 24.8 48.6 Losses and LAE incurred during calendar year, net of reinsurance 220.0 284.6 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 6.7 36.8 Prior accident years 174.8 149.1 Losses and LAE payments made during current calendar year, net of reinsurance: 181.5 185.9 Add/(Deduct): Divestitures (1) — 24.4 Retroactive reinsurance (2) — 21.7 Total net reserve adjustments — 46.1 Foreign exchange adjustments (1.3) 2.1 Net reserves - end of period 2,784.3 2,360.0 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,758.8 2,824.1 Gross reserves - end of period $ 5,543.1 $ 5,184.1 (1) For the three months ended March 31, 2023, the adjustment relates to the quarterly activity of Syndicate 1200 and on reinsurance contracts with AUA subsidiaries. Refer to the sale of Argo Underwriting Agency Limited in Note 1, “Business and Significant Accounting Policies” for additional information. (2) In connection with the sale of AUA, the Company entered into two retroactive reinsurance agreements with AUA subsidiaries. Reserves for losses and LAE represent the estimated indemnity cost and related adjustment expenses necessary to investigate and settle claims. Such estimates are based upon individual case estimates for reported claims, estimates from ceding companies for reinsurance assumed and actuarial estimates for losses that have been incurred but not yet reported to the insurer. Any change in probable ultimate liabilities is reflected in current operating results. The impact from the unfavorable (favorable) development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: Successor Predecessor (in millions) Three Months Ended Three Months Ended U.S. Operations $ 13.6 $ 39.7 International Operations 10.9 7.8 Run-off Lines 0.3 1.1 Total unfavorable (favorable) prior-year development $ 24.8 $ 48.6 The following describes the primary factors behind each segment’s net prior accident year loss reserve development for the three months ended March 31, 2024 and 2023: Three months ended March 31, 2024: • U.S. Operations: Net unfavorable development primarily related to movements on large individual surety claims in specialty lines. • International Operations : Net unfavorable development primarily related to our assumed business from our former Malta operations, ArgoGlobal Holdings (Malta) Ltd., which was sold in 2022. • Run-off Lines: Net unfavorable development primarily related to involuntary pools. Three months ended March 31, 2023: • U.S. Operations : Net unfavorable development primarily related to liability and professional lines. The liability lines development was driven by businesses we have exited. The professional lines development was driven by accident years 2019 and prior. • International Operations : Net unfavorable development primarily related to movements on claims in professional lines in Argo Insurance Bermuda. • Run-off Lines: Net unfavorable loss reserve development on prior accident years in other run-off lines. Our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, current technology and reasonable assumptions where facts are not known. Due to the significant uncertainties and related management judgments, there can be no assurance that future favorable or unfavorable loss development, which may be material, will not occur.

Disclosures About Fair Value of

Disclosures About Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Disclosures About Fair Value of Financial Instruments	Disclosures About Fair Value of Financial Instruments Cash. The carrying amount approximates fair value. Investment securities, mortgage loan investments, and short-term investments. See Note 3, “Investments,” for additional information. Premiums receivable and reinsurance recoverables on paid losses. The carrying value of current receivables and reinsurance recoverables on paid losses approximates fair value due to short-term nature. Debt. At March 31, 2024 and December 31, 2023, the fair value of our debt instruments is determined using both Level 1 and Level 2 inputs, as previously defined in Note 3, “Investments.” Borrowing under revolving credit facility approximates fair value due to short-term nature. We receive fair value prices for similar financial instruments being traded in active markets. These prices are determined using observable market information such as publicly traded quoted prices, and trading prices for similar financial instruments actively being traded in the current market. We have reviewed the processes used by third-party providers for pricing these instruments and have determined that they result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of March 31, 2024 and December 31, 2023. A description of the valuation techniques we use to measure these liabilities at fair value is as follows: Senior Unsecured Fixed Rate Notes Level 1: • Our senior unsecured fixed rate notes are valued using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Junior Subordinated Debentures Level 2: • Our trust preferred debentures and subordinated debentures are typically valued using Level 2 inputs. For these securities, we obtain fair value measurements using quoted prices for similar securities being traded in active markets at the reporting date, as our specific debt instruments are less frequently traded. A summary of our financial instruments whose carrying value did not equal fair value is shown below: March 31, 2024 December 31, 2023 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 161.0 $ 168.1 $ 160.8 $ 165.9 Subordinated debentures 80.6 84.7 80.4 83.3 Total junior subordinated debentures 241.6 252.8 241.2 249.2 Senior unsecured fixed rate notes 128.1 130.5 128.0 132.7 $ 369.7 $ 383.3 $ 369.2 $ 381.9 Based on an analysis of the inputs, our financial instruments measured at fair value for disclosure purposes have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) March 31, 2024 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 168.1 $ — $ 168.1 $ — Subordinated debentures 84.7 — 84.7 — Total junior subordinated debentures 252.8 — 252.8 — Senior unsecured fixed rate notes 130.5 130.5 — — $ 383.3 $ 130.5 $ 252.8 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2023 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 165.9 $ — $ 165.9 $ — Subordinated debentures 83.3 — 83.3 — Total junior subordinated debentures 249.2 — 249.2 — Senior unsecured fixed rate notes 132.7 132.7 — — $ 381.9 $ 132.7 $ 249.2 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock As a result of the Merger, the Company’s authorized and outstanding share capital is owned by BNRE Triangle Acquisition Inc. On February 20, 2024, BNRE Triangle Acquisition Inc. purchased an additional 100.0 million shares of the Company’s common stock with a par value of $1.00 per share for $100.0 million. Preferred Stock Dividend On February 8, 2024, our Board of Directors declared a quarterly cash dividend in the amount of $437.50 per share on our 7.00% Resettable Fixed Rate Preferred Stock, Series A, par value of $1.00 per share, with a liquidation preference of $25,000 per share (the “Series A Preferred Stock”). Holders of depositary shares, each representing a 1/1,000th interest in a share of Series A Preferred Stock (the “Depositary Shares”), received $0.43750 per Depositary Share. On March 15, 2024, we paid $2.6 million to our stockholders of record, as of February 29, 2024, of the Series A Preferred Stock.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component for the three months ended March 31, 2024 and 2023 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2024 $ 0.1 $ 51.1 $ 0.6 $ 51.8 Other comprehensive income before reclassifications (0.1) (10.7) — (10.8) Amounts reclassified from accumulated other comprehensive loss — (5.2) — (5.2) Net current-period other comprehensive income (loss) (0.1) (15.9) — (16.0) Balance, March 31, 2024 $ — $ 35.2 $ 0.6 $ 35.8 (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2023 $ (4.2) $ (293.1) $ (7.8) $ (305.1) Other comprehensive income before reclassifications 0.4 28.0 0.8 29.2 Amounts reclassified from accumulated other comprehensive loss — 17.5 — 17.5 Net current-period other comprehensive income 0.4 45.5 0.8 46.7 Balance, March 31, 2023 $ (3.8) $ (247.6) $ (7.0) $ (258.4) The amounts reclassified from accumulated other comprehensive income (loss) shown in the above table have been included in the following captions in our Condensed Consolidated Statements of Income (Loss): Successor Predecessor (in millions) Three Months Ended Three Months Ended Unrealized gains and losses on securities: Net realized investment and other gains (losses) $ 6.5 $ (22.2) Income tax provision (benefit) (1.3) 4.7 Total, net of taxes $ 5.2 $ (17.5) Income tax effects are released from accumulated other comprehensive income (loss) for unrealized gains or losses when the gains or losses are realized, and are taxed at the statutory rate based on jurisdiction of the underlying transaction.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2024
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information Interest paid and income taxes paid (recovered) were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Senior unsecured fixed rate notes $ 2.3 $ 2.3 Junior subordinated debentures 6.1 5.5 Other indebtedness 0.6 0.8 Total interest paid $ 9.0 $ 8.6 Income taxes paid $ — $ 0.4 Income taxes recovered — (0.1) Income taxes paid, net $ — $ 0.3

Underwriting, Acquisition and G

Underwriting, Acquisition and General Expenses	3 Months Ended
	Mar. 31, 2024
Underwriting, Acquisition and Insurance Expenses [Abstract]
Underwriting, Acquisition and General Expenses	Underwriting, Acquisition and General Expenses Underwriting, acquisition and general expenses were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Commissions $ 31.1 $ 57.5 Other underwriting and insurance expenses 68.1 86.0 Amortization of value of business acquired and other intangible assets 42.9 — Total 142.1 143.5 Net deferral of policy acquisition costs (25.0) (6.5) Total underwriting, acquisition and general expenses $ 117.1 $ 137.0

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company was incorporated under the laws of Bermuda until November 30, 2023. Under Bermuda law, the Company was not obligated to pay any tax in Bermuda based upon income or capital gains. We previously received an undertaking from the Supervisor of Insurance in Bermuda pursuant to the provisions of the Exempted Undertakings Tax Protection Act, 2011 which exempted us from any Bermuda taxes computed on profits, income or any capital asset, gain or appreciation or any tax in the nature of estate, duty or inheritance tax, at least until the year 2035. As of November 30, 2023, the Company redomiciled from Bermuda to the United States. In connection with redomiciling from Bermuda to the United States, the Company’s predecessor pre-tax loss and tax benefit is reported in Bermuda. Subsequent to redomiciling, the Company’s successor pre-tax income and tax provision is reported in the United States. Separately, Argo Re is in the process of completing an Internal Revenue Code Section 953(d) election to treat the entity as a U.S. taxpayer. The election is deemed retroactive to the period beginning January 1, 2023. Argo Re pre-tax loss for the predecessor period is reported in Bermuda. The retroactive United States tax benefit incurred for the predecessor period is reflected in purchase accounting. Argo Re pre-tax income and tax provision is reported in the United States for the successor period. On February 2, 2023, Argo International Holdings Limited, a wholly-owned U.K. subsidiary of the Company, sold AUA. See Note 1, “Business and Significant Accounting Policies” for additional information related to this transaction. The predecessor period includes activity of AUA until it was sold. Subsequent to the AUA sale, the Company retained one U.K. subsidiary that is subject to the tax laws of that country. Under current law, the subsidiary is taxed at the applicable corporate tax rates and files a separate U.K. income tax return. We have subsidiaries based in the U.S. that are subject to U.S. tax laws. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Beginning January 1, 2024, our U.S. subsidiaries file a consolidated U.S. federal income tax return with BAMR US Holdings LLC, a subsidiary of Brookfield Reinsurance Ltd. We also have operations in Ireland and Italy which are subject to income taxes imposed by the jurisdiction in which they operate. Furthermore, we have an operation in Barbados which is not subject to income tax under the laws of that country. On August 16, 2022, U.S. legislation referred to as the Inflation Reduction Act of 2022 was enacted. This legislation enacted a new Corporate Alternative Minimum Tax (“CAMT”) and Excise Tax on Repurchases of Corporate Stock. The Company has determined as of the period ending March 31, 2024, that it is not a CAMT taxpayer or subject to Excise Tax on Repurchases of Corporate Stock. Our expected income tax provision computed on pre-tax income (loss) at the weighted average tax rate has been calculated as the sum of the pre-tax income (loss) in each jurisdiction multiplied by that jurisdiction’s applicable statutory tax rate. For the three months ended March 31, 2024 and 2023, pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: Successor Predecessor Three Months Ended Three Months Ended (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ — (1) — % $ (15.2) — % United States 28.0 5.5 % (7.3) 19.7 % United Kingdom — — % (20.1) 35.4 % United Arab Emirates — — % 0.3 — % Italy (0.8) (4.7) % — (1) — % Pre-tax income (loss) $ 27.2 5.8 % $ (42.3) 20.1 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million. A reconciliation of the difference between the provision (benefit) for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Income tax provision (benefit) at expected rate $ 5.7 $ (5.4) Tax effect of: Foreign exchange adjustments — (2.6) Impact of change in tax rate related to Finance Act 2021 — (0.5) Prior period adjustment (4.4) — Other 0.3 — Income tax provision (benefit) $ 1.6 $ (8.5) Our gross deferred tax assets are supported by taxes paid in previous periods, reversal of taxable temporary differences and recognition of future taxable income. Management regularly evaluates the recoverability of the deferred tax assets and makes any necessary adjustments to them based upon any changes in management’s expectations of future taxable income. Realization of deferred tax assets is dependent upon our generation of future taxable income sufficient to recover tax benefits that cannot be recovered from taxes paid in the carryback period, generally for our U.S. property and casualty insurers two years for net operating losses and for all our U.S. subsidiaries three years for capital losses. If a company determines that any of its deferred tax assets will not result in future tax benefits, a valuation allowance must be established for the portion of these assets that are not expected to be realized. No change to the valuation allowance was recorded for the three months ended March 31, 2024. Existing valuation allowances pertain to the following: Internal Revenue Code Section 382 limited net operating loss carryforwards within the United States, cumulative losses incurred since inception, and valuation allowances acquired through or related to acquisitions or disposals. Based upon a review of our available evidence, both positive and negative discussed above, our management concluded that it is more-likely-than-not that $36.2 million of our deferred tax assets will be realized. For any uncertain tax positions not meeting the “more-likely-than-not” recognition threshold, accounting standards require recognition, measurement and disclosure in the Company’s Condensed Consolidated Financial Statements. No change to the uncertain tax positions were recorded for federal or state income tax liability for the three months ended March 31, 2024. A net decrease of interest in the amount of $1.1 million has been recorded in the line item Interest expense in our Condensed Consolidated Statements of Income (Loss) for the three months ended March 31, 2024. A net decrease of penalty in the amount of $0.2 million has been recorded in the line item Underwriting, acquisition, and insurance in our Consolidated Statements of Income (Loss) for the three months ended March 31, 2024.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Actions Argo Group’s subsidiaries are parties to legal actions incidental to their business. As of March 31, 2024, management believes that the resolution of these matters would not materially affect our financial condition or results of operations. Federal Securities Class Action The Police & Fire Retirement System City of Detroit v. Argo Group International Holdings, Inc., et al., No. 22-cv-8971 (S.D.N.Y.) On October 20, 2022, a securities class action lawsuit was filed in the United States District Court for the Southern District of New York against the Company and certain of its current and former officers, alleging securities fraud violations under sections 10(b) and 20(a) of the Securities Exchange Act of 1934. Plaintiff alleges that from February 13, 2018 through August 9, 2022, the defendants made false and misleading statements concerning the Company’s reserves and underwriting standards. On January 18, 2023, U.S. District Judge Lewis A. Kaplan granted the Police and Fire Retirement System City of Detroit and the Oklahoma Law Enforcement Retirement System’s joint motion for appointment as lead plaintiff. On March 27, 2023, lead plaintiffs filed an amended class action complaint. On May 26, 2023, the defendants moved to dismiss the amended class action complaint. On July 13, 2023, lead plaintiffs filed an opposition to such motion, after which defendants filed a reply on August 14, 2023. Bermuda Appraisal Petitions In April 2023, appraisal petitions were filed in the Supreme Court of Bermuda (the “Court”) relating to the acquisition of the Company by Brookfield Reinsurance Ltd. for $30.00 per share (the “Transaction Price”) that closed on November 16, 2023. The petitions were filed by certain stockholders pursuant to Section 106(6) of the Bermuda Companies Act 1981 and are captioned Corbin Erisa Opportunity Fund, Ltd. v. Argo Group International Holdings, Ltd., Corbin Opportunity Fund, L.P. v. Argo Group International Holdings, Ltd., Fourworld Event Opportunities, LP v. Argo Group International Holdings, Ltd., Fourworld Global Opportunities Fund, Ltd. v. Argo Group International Holdings, Ltd., Fourworld Special Opportunities Fund, LLC v. Argo Group International Holdings, Ltd., and FW Deep Value Opportunities Fund I, LLC v. Argo Group International Holdings, Ltd. Section 106(6) permits a stockholder of a Bermuda corporation, such as the Company, to petition the Court for a determination of the fair value of the Company’s shares if they are not satisfied with the Transaction Price. On January 3, 2024, the Company filed a summons to stay the appraisal action pending judgment of the Judicial Committee of the Privy Council in the matter captioned “In re matter of Jardine Strategy Holdings Limited Case No: Civ/2022/14-31.” A hearing has been set for July 9, 2024 and the Company intends to defend this matter vigorously. Contractual Commitments We have contractual commitments to invest up to $93.7 million related to our limited partnership investments at March 31, 2024, as further disclosed in Note 3, “Investments.” These commitments will be funded as required by the partnership agreements which can be called to be fulfilled at any time, not to exceed twelve years. Additionally, the Company has commitments to fund up to $29.4 million related to its investments in term loan and mortgage loan investments.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Segment Information	Segment Information We are primarily engaged in underwriting property and casualty insurance. We have two ongoing reporting segments: U.S. Operations and International Operations. Additionally, we have Run-off Lines for certain products that we no longer underwrite. We consider many factors, including the nature of each segment’s insurance and reinsurance products, production sources, distribution strategies and the regulatory environment, in determining how to aggregate reporting segments. In evaluating the operating performance of our segments, we focus on core underwriting and investing results before the consideration of realized gains or losses from investments. Net investment and other gains (losses) are reported as a component of the Corporate and Other segment, as decisions regarding the acquisition and disposal of securities reside with the corporate investment function and are not under the control of the individual business segments. Identifiable assets by segment are those assets used in the operation of each segment. Revenue and income (loss) before income taxes for each segment were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Revenue: Net earned premiums U.S. Operations $ 286.7 $ 325.6 International Operations 26.9 64.3 Run-off Lines 0.1 — Total net earned premiums 313.7 389.9 Net investment income U.S. Operations 50.0 24.4 International Operations 7.2 4.6 Run-off Lines 1.6 0.7 Total net investment income 58.8 29.7 Net investment and other gains (losses) 6.2 (17.9) Total revenue $ 378.7 $ 401.7 Successor Predecessor (in millions) Three Months Ended Three Months Ended Income (loss) before income taxes U.S. Operations $ 32.2 $ (4.6) International Operations (7.8) 2.4 Run-off Lines (0.2) (0.7) Total segment income (loss) before income taxes 24.2 (2.9) Corporate and Other (5.2) (18.8) Net investment and other gains (losses) 6.2 (17.9) Foreign currency exchange gains (losses) 2.0 (2.7) Total income (loss) before income taxes $ 27.2 $ (42.3) The table below presents net earned premiums by geographic location for the three months ended March 31, 2024 and 2023. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. Successor Predecessor (in millions) Three Months Ended Three Months Ended United States $ 286.8 $ 325.6 United Kingdom — 48.3 Bermuda 26.9 13.2 All other jurisdictions — 2.8 Total earned premiums $ 313.7 $ 389.9 The following table represents identifiable assets: As of (in millions) March 31, 2024 December 31, 2023 U.S. Operations $ 6,678.5 $ 6,279.0 International Operations 1,635.2 1,888.9 Run-off Lines 231.6 221.4 Corporate and Other 101.8 113.8 Total assets $ 8,647.1 $ 8,503.1

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions As part of the Merger, the Company has entered into recurring transactions and agreements with certain related parties. Through March 31, 2024, the Company had purchased related party investments totaling $48.4 million, of which $27.3 million were mortgage loans and $21.1 million in other invested asset classes. Additionally, the Company has unfunded commitments totaling $40.7 million across the related party investments. Investment transactions with related parties are accounted for in the same manner as those with unrelated parties in the financial statements. For the three months ended March 31, 2024, the Company incurred investment management fees due to related party arrangements of $2.3 million, which is recognized in Net investment income on our Condensed Consolidated Statements of Income (Loss). Additionally, the Company issued common stock to BNRE Triangle Acquisition Inc. See Note 7, “Stockholders’ Equity,” for additional information.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events There are no subsequent events identified as of the date of this report.

Business and Significant Acco_2

Business and Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying Condensed Consolidated Financial Statements of Argo Group International Holdings, Inc. and its subsidiaries (“Argo Group,” “we,” “us,” “our” or the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and with the instructions for Form 10-Q and Article 10 of Regulation S-X. Argo Group is an underwriter of specialty insurance products in the property and casualty market. On November 16, 2023, we merged with Brookfield Reinsurance Ltd., which resulted in a change to the Company’s ownership, (the “Merger”). Brookfield Reinsurance Ltd. elected to push-down its purchase accounting, which resulted in the Company reflecting the fair market value of our assets and liabilities as of November 16, 2023, in accordance with Accounting Standards Codification (“ASC”) 805, Business Combinations. The application of push-down accounting created a new basis of accounting for all of our assets and liabilities. As such, the Company’s financial position, results of operations, and cash flows subsequent to the acquisition are not comparable with those prior to November 16, 2023, and therefore have been separated to indicate pre-acquisition and post-acquisition periods. The pre-acquisition period through November 15, 2023 is referred to as the Predecessor. The post-acquisition period, November 16, 2023 and forward, includes the impact of push-down accounting and is referred to as the Successor. The preparation of interim financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and reported amounts of revenues and expenses during the reporting period. The major estimates reflected in our Condensed Consolidated Financial Statements include, but are not limited to, reserves for losses and loss adjustment expenses; reinsurance recoverables, including the reinsurance recoverables allowance for expected credit losses; fair value of investments and assessment of potential impairment, including the allowance for credit losses on fixed maturity securities; valuation of intangibles, including those identified as part of purchase accounting related to the Merger, and our deferred tax asset valuation allowance. Actual results could materially differ from those estimates. Certain financial information that is normally included in annual Condensed Consolidated Financial Statements, including certain financial statement footnotes, prepared in accordance with GAAP, is not required for interim reporting purposes and has been condensed or omitted. These statements should be read in conjunction with the Condensed Consolidated Financial Statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2023 filed with the Securities and Exchange Commission ("SEC") (the “2023 Form 10-K”).
Reclassification	Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation.
Allowance for Credit Losses	Allowance for Credit Losses For fixed maturities with a decline in fair value below the amortized cost due to credit-related factors, an allowance is established for the difference between the estimated recoverable value and amortized cost with a corresponding charge to Net investment and other gains (losses) in the Condensed Consolidated Statements of Income (Loss). The allowance is limited to the difference between amortized cost and fair value. The estimated recoverable value is the present value of cash flows expected to be collected, as determined by management. The difference between fair value and amortized cost that is not associated with credit-related factors is recognized in the Condensed Consolidated Statements of Comprehensive Income (Loss). Accrued interest is excluded from the measurement of the allowance for credit losses. When determining if a credit loss has been incurred, we may consider the historical performance of the security, available market information and security specific considerations such as the priority payment of the security. In addition, inputs used in our analysis include, but are not limited to, credit ratings and downgrades, delinquency rates, missed scheduled interest or principal payments, purchase yields, underlying asset performance, collateral types, modeled default rates, modeled severity rates, call/prepayment rates, expected cash flows, industry concentrations, and potential or filed bankruptcies or restructurings. In cooperation with our investment managers, we evaluate for credit losses each quarter utilizing a bottom up review approach. At the security level, a determination is made as to whether a decline in fair value below the amortized cost basis is due to credit-related or noncredit-related factors. If we determine that all or a portion of a fixed maturity is uncollectible, the uncollectible amortized cost is written off with a corresponding reduction to the allowance for credit losses. If we collect cash flows that were previously written off, the recovery is recognized in Net investment and other gains (losses) . We also consider whether we intend to sell an available-for-sale security or if it is more likely than not that we will be required to sell the security before recovery of its amortized cost. In these instances, a decline in fair value is recognized in Net investment and other gains (losses) in the Condensed Consolidated Statements of Income (Loss) based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security.
Disclosures about Fair Value of Financial Instruments	Disclosures About Fair Value of Financial Instruments Cash. The carrying amount approximates fair value. Investment securities, mortgage loan investments, and short-term investments. See Note 3, “Investments,” for additional information. Premiums receivable and reinsurance recoverables on paid losses. The carrying value of current receivables and reinsurance recoverables on paid losses approximates fair value due to short-term nature. Debt. At March 31, 2024 and December 31, 2023, the fair value of our debt instruments is determined using both Level 1 and Level 2 inputs, as previously defined in Note 3, “Investments.” Borrowing under revolving credit facility approximates fair value due to short-term nature. We receive fair value prices for similar financial instruments being traded in active markets. These prices are determined using observable market information such as publicly traded quoted prices, and trading prices for similar financial instruments actively being traded in the current market. We have reviewed the processes used by third-party providers for pricing these instruments and have determined that they result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of March 31, 2024 and December 31, 2023. A description of the valuation techniques we use to measure these liabilities at fair value is as follows: Senior Unsecured Fixed Rate Notes Level 1: • Our senior unsecured fixed rate notes are valued using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Junior Subordinated Debentures Level 2: • Our trust preferred debentures and subordinated debentures are typically valued using Level 2 inputs. For these securities, we obtain fair value measurements using quoted prices for similar securities being traded in active markets at the reporting date, as our specific debt instruments are less frequently traded.
Fair Value Measurement	Fair Value Measurements Fair value is the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability, or in the absence of a principal market, the most advantageous market. Market participants are buyers and sellers in the principal (or most advantageous) market that are independent, knowledgeable, able to transact for the asset or liability and willing to transfer the asset or liability. Valuation techniques consistent with the market approach, income approach and/or cost approach are used to measure fair value. The inputs of these valuation techniques are categorized into three levels. • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that can be accessed at the reporting date. We define actively traded as a security that has traded in the past seven days. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. We receive one quote per instrument for Level 2 inputs. • Level 3 inputs are unobservable inputs. Unobservable inputs reflect our own judgments about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances. To validate the fair value of investments in the Company’s Condensed Consolidated Financial Statements, we receive prices from multiple sources including third-party pricing services and our outside investment managers. Through a comparative analysis, the Company validates the reasonableness of its valuations. These prices are determined using observable market information such as dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. We have reviewed the processes used by the third-party providers for pricing the securities and have determined that these processes result in fair values consistent with GAAP requirements. In addition, we review these prices for reasonableness, and have not adjusted any prices received from the third-party providers as of March 31, 2024 and December 31, 2023. A description of the valuation techniques we use to measure assets at fair value is as follows: Fixed Maturities (Available-for-Sale) Levels 1 and 2: • United States Treasury securities are typically valued using Level 1 inputs. For these securities, we obtain fair value measurements from third-party pricing services using quoted prices (unadjusted) in active markets at the reporting date. • United States Government agencies, non-U.S. Government securities, obligations of states and political subdivisions, credit securities and foreign denominated government and credit securities are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, yield curves, live trading levels, trade execution data, credit information and the security’s terms and conditions, among other things. • Asset and mortgage-backed securities and collateralized loan obligations are reported at fair value using Level 2 inputs. For these securities, we obtain fair value measurements from third-party pricing services. Observable data may include dealer quotes, market spreads, cash flows, yield curves, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the security’s terms and conditions, among other things. Fixed Maturities (Available-for-Sale) Levels 3: We own term loans and asset-back securities that are valued using unobservable inputs. Equity Securities Level 1: Equity securities are principally reported at fair value using Level 1 inputs. For these securities, we obtain fair value measurements from a third-party pricing service using quoted prices (unadjusted) in active markets at the reporting date. Equity Securities Level 3: We own certain equity securities that are reported at fair value using Level 3 inputs. The valuation techniques for these securities include the following: • Fair value measurements for an investment in an equity fund obtained by applying final prices provided by the administrator of the fund, which is based upon certain estimates and assumptions. • Fair value measurements from brokers and independent valuation services, both based upon estimates, assumptions and other unobservable inputs. Short-term Investments: Short-term investments are principally reported at fair value using Level 1 inputs, with the exception of short-term corporate and governmental bonds reported at fair value using Level 2 inputs as described in the fixed maturities section above. Values for the investments categorized as Level 1 are obtained from various financial institutions as of the reporting date.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments	The amortized cost, gross unrealized gains, gross unrealized losses, allowance for credit losses, and fair value of fixed maturity investments were as follows: March 31, 2024 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 354.4 $ 1.6 $ — $ — $ 356.0 Foreign Governments 5.6 0.6 — — 6.2 Obligations of states and political subdivisions 87.2 1.5 — — 88.7 Corporate bonds 1,097.4 19.2 0.9 0.2 1,115.5 Commercial mortgage-backed securities 264.5 11.4 0.5 — 275.4 Residential mortgage-backed securities 230.7 6.1 — — 236.8 Asset-backed securities 131.9 1.9 0.1 — 133.7 Collateralized loan obligations 198.3 3.0 0.2 — 201.1 Total fixed maturities $ 2,370.0 $ 45.3 $ 1.7 $ 0.2 $ 2,413.4 December 31, 2023 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 357.7 $ 4.5 $ — $ — $ 362.2 Foreign Governments 27.9 2.6 — 0.2 30.3 Obligations of states and political subdivisions 92.4 2.0 — — 94.4 Corporate bonds 1,185.0 28.9 0.8 — 1,213.1 Commercial mortgage-backed securities 270.9 10.1 0.5 — 280.5 Residential mortgage-backed securities 235.2 13.6 — — 248.8 Asset-backed securities 140.4 1.7 0.1 — 142.0 Collateralized loan obligations 212.0 2.1 — — 214.1 Total fixed maturities $ 2,521.5 $ 65.5 $ 1.4 $ 0.2 $ 2,585.4
Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity	The amortized cost and fair values of fixed maturity investments as of March 31, 2024, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 347.3 $ 347.6 Due after one year through five years 950.2 961.3 Due after five years through ten years 231.5 240.5 Due after ten years 15.6 17.0 Structured securities 825.4 847.0 Total $ 2,370.0 $ 2,413.4
Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio	Details regarding the carrying value and unfunded investment commitments of other investments as of March 31, 2024 and December 31, 2023 were as follows: March 31, 2024 (in millions) Carrying Unfunded Investment type Hedge funds $ 31.5 $ — Private equity 257.9 82.4 Other 55.0 11.3 Total other investments $ 344.4 $ 93.7 December 31, 2023 (in millions) Carrying Unfunded Investment type Hedge funds $ 56.2 $ — Private equity 250.3 93.4 Other 4.5 — Total other investments $ 311.0 $ 93.4
Unrealized Gain (Loss) on Investments	An aging of unrealized losses on our investments in fixed maturities is presented below: March 31, 2024 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 103.4 $ — $ — $ — $ 103.4 $ — Obligations of states and political subdivisions 14.6 — — — 14.6 — Corporate bonds 49.9 0.9 — — 49.9 0.9 Commercial mortgage-backed securities 21.6 0.5 — — 21.6 0.5 Residential mortgage-backed securities 3.9 — — — 3.9 — Asset-backed securities 13.2 0.1 — — 13.2 0.1 Collateralized loan obligations 5.6 0.2 — — 5.6 0.2 Total fixed maturities $ 212.2 $ 1.7 $ — $ — $ 212.2 $ 1.7 December 31, 2023 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities Foreign Governments $ 0.1 $ — $ — $ — $ 0.1 $ — Obligations of states and political subdivisions 0.5 — — — 0.5 — Corporate bonds 38.7 0.8 — — 38.7 0.8 Commercial mortgage-backed securities 32.2 0.5 — — 32.2 0.5 Residential mortgage-backed securities 2.9 — — — 2.9 — Asset-backed securities 11.4 0.1 — — 11.4 0.1 Collateralized loan obligations 21.4 — — — 21.4 — Total fixed maturities $ 107.2 $ 1.4 $ — $ — $ 107.2 $ 1.4
Debt Securities, Available-for-sale, Allowance for Credit Loss	The following table presents a roll-forward of the changes in allowance for credit losses on available-for-sale fixed maturities by industry category for the three months ending March 31, 2024 and 2023, respectively: Successor (in millions) Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2024 $ 0.2 $ — $ — $ — $ 0.2 Securities for which allowance was not previously recorded — — 0.1 — 0.1 Additional net increases (decreases) in existing allowance (0.2) — 0.1 — (0.1) Ending balance, March 31, 2024 $ — $ — $ 0.2 $ — $ 0.2 Predecessor (in millions) Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Beginning balance, January 1, 2023 $ 0.7 $ 0.4 $ 1.6 $ 0.1 $ 2.8 Securities for which allowance was not previously recorded — — 0.2 — 0.2 Securities sold during the period — — (0.3) — (0.3) Additional net increases (decreases) in existing allowance 0.1 — (0.1) — — Ending balance, March 31, 2023 $ 0.8 $ 0.4 $ 1.4 $ 0.1 $ 2.7
Schedule of Accounts, Notes, Loans and Financing Receivable	The following table presents loans by property type: March 31, 2024 (in millions) Cost Composition Loan Count Residential $ 1.7 1.0 % 1 Apartments 76.1 44.3 % 16 Hotel 22.3 13.0 % 4 Industrial 26.0 15.2 % 4 Office 25.9 15.1 % 1 Retail 19.6 11.4 % 4 Total $ 171.6 100.0 % 30 December 31, 2023 (in millions) Cost Composition Loan Count Apartments $ 76.1 52.6 % 16 Hotel 22.4 15.4 % 4 Industrial 26.0 18.0 % 4 Retail 20.3 14.0 % 4 Total $ 144.8 100.0 % 28
Financing Receivable Credit Quality Indicators	The following table presents our loans by Debt Service Coverage Ratio (“DSCR”): March 31, 2024 (in millions) Cost Loan Count Less than 1.00 $ 36.2 8 1.00 to 1.50 54.5 7 Greater than 1.5 to 2.0 30.9 6 Greater than 2.0 to 3.0 36.0 6 Greater than 3.0 to 4.0 12.3 2 Total $ 169.9 29 DSCR does not include residential mortgage loans. December 31, 2023 (in millions) Cost Loan Count Less than 1.00 $ 36.2 8 1.00 to 1.50 29.4 6 Greater than 1.5 to 2.0 30.9 6 Greater than 2.0 to 3.0 36.0 6 Greater than 3.0 to 4.0 12.3 2 Total $ 144.8 28 The following table presents loans by Loan To Value (“LTV”): March 31, 2024 (in millions) Cost Loan Count Equal to or less than 50.0% $ 12.3 2 Greater than 50.0% to 55.0% 9.0 2 Greater than 55.0% to 60.0% 20.7 5 Greater than 60.0% to 70.0% 63.2 7 Greater than 70.0% 66.4 14 Total $ 171.6 30 December 31, 2023 (in millions) Cost Loan Count Equal to or less than 50.0% $ 12.3 2 Greater than 50.0% to 55.0% 9.1 2 Greater than 55.0% to 60.0% 18.9 4 Greater than 60.0% to 70.0% 37.3 6 Greater than 70.0% 67.2 14 Total $ 144.8 28
Financing Receivable, before Allowance for Credit Loss, Maturity	The following table presents loans by maturity: March 31, 2024 (in millions) Cost Loan Count One Year or Less $ 44.8 8 Greater than One Year and Less than Three 34.9 3 Greater than Three Years and Less than Five Years 32.4 6 Greater than Five Years and Less than Seven Years 17.2 4 Greater than Seven Years and Less than Ten Years 42.3 9 Total $ 171.6 30 December 31, 2023 (in millions) Cost Loan Count One Year or Less $ 19.7 4 Greater than One Year and Less than Three 34.9 6 Greater than Three Years and Less than Five Years 32.4 6 Greater than Five Years and Less than Seven Years 17.2 4 Greater than Seven Years and Less than Ten Years 40.6 8 Total $ 144.8 28
Schedule of Company's Gross Realized Investment Gains (Losses)	The following table presents our gross realized investment gains and losses: Successor Predecessor (in millions) Three Months Ended Three Months Ended Realized gains on fixed maturities and other: Fixed maturities $ 6.8 $ 0.2 Other investments, including short-term investments 2.6 7.8 Total realized gains on fixed maturities and other 9.4 8.0 Realized losses on fixed maturities and other: Fixed maturities (0.3) (22.4) Other investments, including short-term investments (2.8) (5.8) Total realized losses on fixed maturities and other (3.1) (28.2) Other net losses recognized on fixed maturities and other: Credit losses on fixed maturities (0.5) (0.6) Impairment related to change in intent — — Other — (3.6) Total other net losses recognized on fixed maturities and other (0.5) (4.2) Equity securities: Net realized gains (losses) on equity securities 0.4 0.3 Change in unrealized gains (losses) on equity securities held at the end of the period — 6.2 Net gains (losses) on equity securities 0.4 6.5 Net investment and other gains (losses) before income taxes 6.2 (17.9) Income tax (benefit) provision 1.6 (5.1) Net investment and other gains (losses), net of income taxes $ 4.6 $ (12.8)
Schedule of Changes in Unrealized Appreciation (Depreciation)	Changes in unrealized gains (losses) related to fixed maturity investments are summarized as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Change in unrealized gains (losses) Fixed maturities $ (19.9) $ 55.5 Other and short-term investments (0.4) (0.1) Net unrealized investment gains (losses) before income taxes (20.3) 55.4 Income tax provision (benefit) (4.4) 9.9 Net unrealized investment gains (losses), net of income taxes $ (15.9) $ 45.5
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of March 31, 2024 and December 31, 2023 was as follows: As of March 31, 2024 December 31, 2023 (in millions) Notional Amount Fair Value Notional Amount Fair Value Operational currency Open contracts in a gain position $ — $ — $ 75.4 $ 1.8 Open contracts in a loss position 100.4 (0.7) 43.3 (0.3) Net open contracts for operational currency $ (0.7) $ 1.5 Asset manager investment exposure Open contracts in a gain position $ 45.8 $ 1.0 $ — $ — Open contracts in a loss position — — 45.8 (0.2) Net open contracts for asset manager investment exposure 1.0 (0.2) Total $ 0.3 $ 1.3
Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts	The following table presents our gross realized investment gains and losses on our foreign currency exchange forward contracts: Successor Predecessor (in millions) Three Months Ended Three Months Ended Realized gains Operational currency exposure $ 1.4 $ 4.1 Asset manager investment exposure 1.2 — Gross realized investment gains 2.6 4.1 Realized losses Operational currency exposure (2.7) (3.1) Asset manager investment exposure — (0.3) Gross realized investment losses (2.7) (3.4) Net realized investment (losses) gains on foreign currency exchange forward contracts $ (0.1) $ 0.7
Schedule of Restricted Assets	The following table presents our components of restricted investments: As of (in millions) March 31, 2024 December 31, 2023 Securities on deposit for regulatory and other purposes $ 152.7 $ 153.4 Securities pledged as collateral for letters of credit 39.7 109.2 Total restricted investments $ 192.4 $ 262.6
Financial Assets Measured at Fair Value on Recurring Basis	Based on an analysis of the inputs, our financial assets and liabilities measured at fair value on a recurring basis have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) March 31, Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 356.0 $ 93.8 $ 262.2 $ — Foreign Governments 6.2 — 6.2 — Obligations of states and political subdivisions 88.7 — 88.7 — Corporate bonds 1,115.5 — 1,093.2 22.3 Commercial mortgage-backed securities 275.4 — 275.4 — Residential mortgage-backed securities 236.8 — 236.8 — Asset-backed securities 133.7 — 121.0 12.7 Collateralized loan obligations 201.1 — 201.1 — Total fixed maturities 2,413.4 93.8 2,284.6 35.0 Equity securities 8.6 2.0 — 6.6 Other investments 1.3 — 0.2 1.1 Short-term investments 1,073.6 1,073.2 0.4 — Derivatives 0.3 — 0.3 — Total assets $ 3,497.2 $ 1,169.0 $ 2,285.5 $ 42.7 (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 362.2 $ 360.1 $ 2.1 $ — Foreign Governments 30.3 — 30.3 — Obligations of states and political subdivisions 94.4 — 94.4 — Corporate bonds 1,213.1 — 1,180.5 32.6 Commercial mortgage-backed securities 280.5 — 280.5 — Residential mortgage-backed securities 248.8 — 248.8 — Asset-backed securities 142.0 — 124.2 17.8 Collateralized loan obligations 214.1 — 214.1 — Total fixed maturities 2,585.4 360.1 2,174.9 50.4 Equity securities 10.7 4.3 — 6.4 Other investments 0.2 — 0.2 — Short-term investments 429.5 429.0 0.5 — Derivatives 1.3 — 1.3 — Total assets $ 3,027.1 $ 793.4 $ 2,176.9 $ 56.8 (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs
Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3	A reconciliation of the beginning and ending balances for the investments categorized as Level 3 are as follows: Fair Value Measurements Using Unobservable Inputs (Level 3) (in millions) Credit Financial Equity Other Invested Assets Total Beginning balance, January 1, 2024 $ 50.4 $ 6.4 $ — $ 56.8 Transfers out of Level 3 (10.0) — — (10.0) Total gains or losses (realized/unrealized): Included in net income 0.8 0.1 — 0.9 Included in other comprehensive income (0.4) — — (0.4) Purchases, issuances, sales, and settlements: Purchases 0.4 0.1 1.1 1.6 Settlements (6.2) — — (6.2) Ending balance, March 31, 2024 $ 35.0 $ 6.6 $ 1.1 $ 42.7 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at March 31, 2024 $ — $ — $ — $ — (in millions) Credit Financial Equity Total Beginning balance, January 1, 2023 $ 40.7 $ 15.5 $ 56.2 Transfers into Level 3 5.6 — 5.6 Transfers out of Level 3 (5.6) (7.6) (13.2) Total gains or losses (realized/unrealized): Included in net income (0.1) (0.4) (0.5) Included in other comprehensive loss 0.8 — 0.8 Purchases, issuances, sales, and settlements: Purchases 10.6 — 10.6 Sales (0.5) (1.1) (1.6) Settlements (1.1) — (1.1) Ending balance, December 31, 2023 $ 50.4 $ 6.4 $ 56.8 Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at December 31, 2023 $ — $ (0.8) $ (0.8)
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	The Company holds certain investments at cost, less an allowance for expected credit losses, on the Condensed Consolidated Balance Sheets. The fair value of the Company’s investments is estimated using a discounted cash flow analysis. Due to the level of unobservable inputs factored into the estimation of fair value, the valuation would be categorized as Level 3. The cost and estimated fair value of these investments were: As of March 31, 2024 December 31, 2023 (in millions) Cost Fair Value Cost Fair Value Mortgage loans $ 171.6 $ 176.0 $ 144.8 $ 148.8 Private loans 49.4 49.3 — — Total $ 221.0 $ 225.3 $ 144.8 $ 148.8 A summary of our financial instruments whose carrying value did not equal fair value is shown below: March 31, 2024 December 31, 2023 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 161.0 $ 168.1 $ 160.8 $ 165.9 Subordinated debentures 80.6 84.7 80.4 83.3 Total junior subordinated debentures 241.6 252.8 241.2 249.2 Senior unsecured fixed rate notes 128.1 130.5 128.0 132.7 $ 369.7 $ 383.3 $ 369.2 $ 381.9

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	3 Months Ended
	Mar. 31, 2024
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table presents the balances of premiums receivable, net of allowance for estimated uncollectible premiums, including expected lifetime credit losses and the changes in the allowance for the respective periods: (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Predecessor Balance, December 31, 2022 $ 292.0 $ 4.7 Current period change for estimated uncollectible premiums 0.4 Balance, March, 2023 $ 271.1 $ 5.1 Successor Balance, December 31, 2023 $ 230.7 3.0 Current period change for estimated uncollectible premiums 1.4 Write-offs of uncollectible premiums receivable (0.3) Balance, March 31, 2024 $ 209.8 $ 4.1
Reinsurance Recoverable, Allowance for Credit Loss	Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, including expected credit losses and changes in the allowance for the respective periods: (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Predecessor Balance, December 31, 2022 $ 3,029.1 $ 4.7 Balance, March 31, 2023 $ 3,016.9 $ 4.7 Successor Balance, December 31, 2023 $ 2,959.3 $ — Balance, March 31, 2024 $ 2,933.1 $ —

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2024
Insurance [Abstract]
Reserves for Losses and Loss Adjustment Expenses	The following table provides a reconciliation of reserves for losses and loss adjustment expenses (“LAE”): Successor Predecessor (in millions) Three Months Ended Three Months Ended Net reserves - beginning of the year $ 2,747.1 $ 2,213.1 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 195.2 236.0 Prior accident years 24.8 48.6 Losses and LAE incurred during calendar year, net of reinsurance 220.0 284.6 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 6.7 36.8 Prior accident years 174.8 149.1 Losses and LAE payments made during current calendar year, net of reinsurance: 181.5 185.9 Add/(Deduct): Divestitures (1) — 24.4 Retroactive reinsurance (2) — 21.7 Total net reserve adjustments — 46.1 Foreign exchange adjustments (1.3) 2.1 Net reserves - end of period 2,784.3 2,360.0 Add: Reinsurance recoverables on unpaid losses and LAE, end of period 2,758.8 2,824.1 Gross reserves - end of period $ 5,543.1 $ 5,184.1 (1) For the three months ended March 31, 2023, the adjustment relates to the quarterly activity of Syndicate 1200 and on reinsurance contracts with AUA subsidiaries. Refer to the sale of Argo Underwriting Agency Limited in Note 1, “Business and Significant Accounting Policies” for additional information. (2)
Impact from (Favorable) Unfavorable Development of Prior Accident Years’ Loss and LAE Reserves on Each Reporting Segment	The impact from the unfavorable (favorable) development of prior accident years’ loss and LAE reserves on each reporting segment is presented below: Successor Predecessor (in millions) Three Months Ended Three Months Ended U.S. Operations $ 13.6 $ 39.7 International Operations 10.9 7.8 Run-off Lines 0.3 1.1 Total unfavorable (favorable) prior-year development $ 24.8 $ 48.6

Disclosures About Fair Value _2

Disclosures About Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	The Company holds certain investments at cost, less an allowance for expected credit losses, on the Condensed Consolidated Balance Sheets. The fair value of the Company’s investments is estimated using a discounted cash flow analysis. Due to the level of unobservable inputs factored into the estimation of fair value, the valuation would be categorized as Level 3. The cost and estimated fair value of these investments were: As of March 31, 2024 December 31, 2023 (in millions) Cost Fair Value Cost Fair Value Mortgage loans $ 171.6 $ 176.0 $ 144.8 $ 148.8 Private loans 49.4 49.3 — — Total $ 221.0 $ 225.3 $ 144.8 $ 148.8 A summary of our financial instruments whose carrying value did not equal fair value is shown below: March 31, 2024 December 31, 2023 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 161.0 $ 168.1 $ 160.8 $ 165.9 Subordinated debentures 80.6 84.7 80.4 83.3 Total junior subordinated debentures 241.6 252.8 241.2 249.2 Senior unsecured fixed rate notes 128.1 130.5 128.0 132.7 $ 369.7 $ 383.3 $ 369.2 $ 381.9
Fair Value, Assets Measured on Recurring and Nonrecurring Basis	Based on an analysis of the inputs, our financial instruments measured at fair value for disclosure purposes have been categorized as follows: Fair Value Measurements at Reporting Date Using (in millions) March 31, 2024 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 168.1 $ — $ 168.1 $ — Subordinated debentures 84.7 — 84.7 — Total junior subordinated debentures 252.8 — 252.8 — Senior unsecured fixed rate notes 130.5 130.5 — — $ 383.3 $ 130.5 $ 252.8 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2023 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 165.9 $ — $ 165.9 $ — Subordinated debentures 83.3 — 83.3 — Total junior subordinated debentures 249.2 — 249.2 — Senior unsecured fixed rate notes 132.7 132.7 — — $ 381.9 $ 132.7 $ 249.2 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Changes in Accumulated Other Comprehensive (Loss) Income	A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component for the three months ended March 31, 2024 and 2023 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2024 $ 0.1 $ 51.1 $ 0.6 $ 51.8 Other comprehensive income before reclassifications (0.1) (10.7) — (10.8) Amounts reclassified from accumulated other comprehensive loss — (5.2) — (5.2) Net current-period other comprehensive income (loss) (0.1) (15.9) — (16.0) Balance, March 31, 2024 $ — $ 35.2 $ 0.6 $ 35.8 (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Balance, January 1, 2023 $ (4.2) $ (293.1) $ (7.8) $ (305.1) Other comprehensive income before reclassifications 0.4 28.0 0.8 29.2 Amounts reclassified from accumulated other comprehensive loss — 17.5 — 17.5 Net current-period other comprehensive income 0.4 45.5 0.8 46.7 Balance, March 31, 2023 $ (3.8) $ (247.6) $ (7.0) $ (258.4)
Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income	The amounts reclassified from accumulated other comprehensive income (loss) shown in the above table have been included in the following captions in our Condensed Consolidated Statements of Income (Loss): Successor Predecessor (in millions) Three Months Ended Three Months Ended Unrealized gains and losses on securities: Net realized investment and other gains (losses) $ 6.5 $ (22.2) Income tax provision (benefit) (1.3) 4.7 Total, net of taxes $ 5.2 $ (17.5)

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2024
Supplemental Cash Flow Elements [Abstract]
Schedule of Interest Paid and Income Taxes Paid (Recovered)	Interest paid and income taxes paid (recovered) were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Senior unsecured fixed rate notes $ 2.3 $ 2.3 Junior subordinated debentures 6.1 5.5 Other indebtedness 0.6 0.8 Total interest paid $ 9.0 $ 8.6 Income taxes paid $ — $ 0.4 Income taxes recovered — (0.1) Income taxes paid, net $ — $ 0.3

Underwriting, Acquisition and_2

Underwriting, Acquisition and General Expenses (Tables)	3 Months Ended
	Mar. 31, 2024
Underwriting, Acquisition and Insurance Expenses [Abstract]
Underwriting, Acquisition and General Expenses	Underwriting, acquisition and general expenses were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Commissions $ 31.1 $ 57.5 Other underwriting and insurance expenses 68.1 86.0 Amortization of value of business acquired and other intangible assets 42.9 — Total 142.1 143.5 Net deferral of policy acquisition costs (25.0) (6.5) Total underwriting, acquisition and general expenses $ 117.1 $ 137.0

Income Taxes (Tables)

Income Taxes (Tables)	3 Months Ended
	Mar. 31, 2024
Income Tax Disclosure [Abstract]
Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates	For the three months ended March 31, 2024 and 2023, pre-tax income (loss) attributable to our operations and the corresponding operations’ effective tax rates were as follows: Successor Predecessor Three Months Ended Three Months Ended (in millions) Pre-Tax Effective Pre-Tax Effective Bermuda $ — (1) — % $ (15.2) — % United States 28.0 5.5 % (7.3) 19.7 % United Kingdom — — % (20.1) 35.4 % United Arab Emirates — — % 0.3 — % Italy (0.8) (4.7) % — (1) — % Pre-tax income (loss) $ 27.2 5.8 % $ (42.3) 20.1 % (1) Pre-tax income (loss) for the respective year was less than $0.1 million.
Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate	A reconciliation of the difference between the provision (benefit) for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Income tax provision (benefit) at expected rate $ 5.7 $ (5.4) Tax effect of: Foreign exchange adjustments — (2.6) Impact of change in tax rate related to Finance Act 2021 — (0.5) Prior period adjustment (4.4) — Other 0.3 — Income tax provision (benefit) $ 1.6 $ (8.5)

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Revenue and Income (Loss) Before Income Taxes for Each Segment	Revenue and income (loss) before income taxes for each segment were as follows: Successor Predecessor (in millions) Three Months Ended Three Months Ended Revenue: Net earned premiums U.S. Operations $ 286.7 $ 325.6 International Operations 26.9 64.3 Run-off Lines 0.1 — Total net earned premiums 313.7 389.9 Net investment income U.S. Operations 50.0 24.4 International Operations 7.2 4.6 Run-off Lines 1.6 0.7 Total net investment income 58.8 29.7 Net investment and other gains (losses) 6.2 (17.9) Total revenue $ 378.7 $ 401.7 Successor Predecessor (in millions) Three Months Ended Three Months Ended Income (loss) before income taxes U.S. Operations $ 32.2 $ (4.6) International Operations (7.8) 2.4 Run-off Lines (0.2) (0.7) Total segment income (loss) before income taxes 24.2 (2.9) Corporate and Other (5.2) (18.8) Net investment and other gains (losses) 6.2 (17.9) Foreign currency exchange gains (losses) 2.0 (2.7) Total income (loss) before income taxes $ 27.2 $ (42.3)
Schedule of Earned Premiums by Geographic Location	The table below presents net earned premiums by geographic location for the three months ended March 31, 2024 and 2023. For this disclosure, we determine geographic location by the country of domicile of our subsidiaries that underwrite the business and not by the location of insureds or reinsureds from whom the business was generated. Successor Predecessor (in millions) Three Months Ended Three Months Ended United States $ 286.8 $ 325.6 United Kingdom — 48.3 Bermuda 26.9 13.2 All other jurisdictions — 2.8 Total earned premiums $ 313.7 $ 389.9
Identifiable Assets	The following table represents identifiable assets: As of (in millions) March 31, 2024 December 31, 2023 U.S. Operations $ 6,678.5 $ 6,279.0 International Operations 1,635.2 1,888.9 Run-off Lines 231.6 221.4 Corporate and Other 101.8 113.8 Total assets $ 8,647.1 $ 8,503.1

Business and Significant Acco_3

Business and Significant Accounting Policies (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - Argo Underwriting Agency Limited - USD ($) $ in Millions		1 Months Ended	3 Months Ended		14 Months Ended
	Feb. 02, 2023	Jul. 31, 2023	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2024	Sep. 08, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale	$ 155.7				$ 161.3	$ 125
Impairment of goodwill and intangibles				$ 28.5
Disposal group, intangible assets				17.3
Impairment of goodwill and intangible assets				$ 11.2
Proceeds from sale of Trident assets	125.1	$ 5.6
Consideration placed in escrow	$ 30.6
Consideration placed in escrow, term	2 years
Loss on disposal			$ 20.3
Consideration placed in escrow,					$ 12.9

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) security	Mar. 31, 2023 USD ($)
Investments, Debt and Equity Securities [Abstract]
Number of securities in an unrealized loss position, total	1,169
Number of securities in an unrealized loss position for less than one year	117
Number of securities in an unrealized loss position for a period of one year or greater	0
Credit losses on fixed maturities | $	$ 0	$ 0.1

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Fixed maturities
Amortized Cost	$ 2,370	$ 2,521.5
Gross Unrealized Gains	45.3	65.5
Gross Unrealized Losses	1.7	1.4
Allowance for Credit Losses	0.2	0.2	$ 2.7	$ 2.8
Fair value	2,413.4	2,585.4
U.S. Governments
Fixed maturities
Amortized Cost	354.4	357.7
Gross Unrealized Gains	1.6	4.5
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair value	356	362.2
Foreign Governments
Fixed maturities
Amortized Cost	5.6	27.9
Gross Unrealized Gains	0.6	2.6
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0.2
Fair value	6.2	30.3
Obligations of states and political subdivisions
Fixed maturities
Amortized Cost	87.2	92.4
Gross Unrealized Gains	1.5	2
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair value	88.7	94.4
Corporate bonds
Fixed maturities
Amortized Cost	1,097.4	1,185
Gross Unrealized Gains	19.2	28.9
Gross Unrealized Losses	0.9	0.8
Allowance for Credit Losses	0.2	0
Fair value	1,115.5	1,213.1
Commercial mortgage-backed securities
Fixed maturities
Amortized Cost	264.5	270.9
Gross Unrealized Gains	11.4	10.1
Gross Unrealized Losses	0.5	0.5
Allowance for Credit Losses	0	0
Fair value	275.4	280.5
Residential mortgage-backed securities
Fixed maturities
Amortized Cost	230.7	235.2
Gross Unrealized Gains	6.1	13.6
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0	0
Fair value	236.8	248.8
Asset-backed securities
Fixed maturities
Amortized Cost	131.9	140.4
Gross Unrealized Gains	1.9	1.7
Gross Unrealized Losses	0.1	0.1
Allowance for Credit Losses	0	0
Fair value	133.7	142
Collateralized loan obligations
Fixed maturities
Amortized Cost	198.3	212
Gross Unrealized Gains	3	2.1
Gross Unrealized Losses	0.2	0
Allowance for Credit Losses	0	0
Fair value	$ 201.1	$ 214.1

Investments - Schedule of Amo_2

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) $ in Millions	Mar. 31, 2024 USD ($)
Amortized Cost
Due in one year or less	$ 347.3
Due after one year through five years	950.2
Due after five years through ten years	231.5
Due after ten years	15.6
Structured securities	825.4
Total	2,370
Fair Value
Due in one year or less	347.6
Due after one year through five years	961.3
Due after five years through ten years	240.5
Due after ten years	17
Structured securities	847
Total	$ 2,413.4

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Carrying Value	$ 4,011.1	$ 3,481.2
Unfunded Commitments	93.7	93.4
Hedge funds
Schedule of Investments [Line Items]
Carrying Value	31.5	56.2
Unfunded Commitments	0	0
Private equity
Schedule of Investments [Line Items]
Carrying Value	257.9	250.3
Unfunded Commitments	82.4	93.4
Other
Schedule of Investments [Line Items]
Carrying Value	55	4.5
Unfunded Commitments	11.3	0
Other Invested Assets
Schedule of Investments [Line Items]
Carrying Value	$ 344.4	$ 311

Investments - Schedule of Aging

Investments - Schedule of Aging of Unrealized Losses on Company's Investments in Fixed Maturities, Equity Securities and Other Investments (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	$ 212.2	$ 107.2
Unrealized Losses, Less Than One Year	1.7	1.4
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	212.2	107.2
Unrealized Losses, Total	1.7	1.4
U.S. Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	103.4
Unrealized Losses, Less Than One Year	0
Fair Value, One Year or Greater	0
Unrealized Losses, One Year or Greater	0
Fair Value, Total	103.4
Unrealized Losses, Total	0
Foreign Governments
Schedule of Investments [Line Items]
Fair Value, Less Than One Year		0.1
Unrealized Losses, Less Than One Year		0
Fair Value, One Year or Greater		0
Unrealized Losses, One Year or Greater		0
Fair Value, Total		0.1
Unrealized Losses, Total		0
Obligations of states and political subdivisions
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	14.6	0.5
Unrealized Losses, Less Than One Year	0	0
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	14.6	0.5
Unrealized Losses, Total	0	0
Corporate bonds
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	49.9	38.7
Unrealized Losses, Less Than One Year	0.9	0.8
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	49.9	38.7
Unrealized Losses, Total	0.9	0.8
Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	21.6	32.2
Unrealized Losses, Less Than One Year	0.5	0.5
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	21.6	32.2
Unrealized Losses, Total	0.5	0.5
Residential mortgage-backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	3.9	2.9
Unrealized Losses, Less Than One Year	0	0
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	3.9	2.9
Unrealized Losses, Total	0	0
Asset-backed securities
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	13.2	11.4
Unrealized Losses, Less Than One Year	0.1	0.1
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	13.2	11.4
Unrealized Losses, Total	0.1	0.1
Collateralized loan obligations
Schedule of Investments [Line Items]
Fair Value, Less Than One Year	5.6	21.4
Unrealized Losses, Less Than One Year	0.2	0
Fair Value, One Year or Greater	0	0
Unrealized Losses, One Year or Greater	0	0
Fair Value, Total	5.6	21.4
Unrealized Losses, Total	$ 0.2	$ 0

Investments - Allowance for Cre

Investments - Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 0.2	$ 2.8
Securities for which allowance was not previously recorded	0.1	0.2
Securities sold during the period		(0.3)
Additional net increases (decreases) in existing allowance	(0.1)	0
Ending balance	0.2	2.7
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0.2	0.7
Securities for which allowance was not previously recorded	0	0
Securities sold during the period		0
Additional net increases (decreases) in existing allowance	(0.2)	0.1
Ending balance	0	0.8
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0.4
Securities for which allowance was not previously recorded	0	0
Securities sold during the period		0
Additional net increases (decreases) in existing allowance	0	0
Ending balance	0	0.4
Corporate bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	1.6
Securities for which allowance was not previously recorded	0.1	0.2
Securities sold during the period		(0.3)
Additional net increases (decreases) in existing allowance	0.1	(0.1)
Ending balance	0.2	1.4
Asset-backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0.1
Securities for which allowance was not previously recorded	0	0
Securities sold during the period		0
Additional net increases (decreases) in existing allowance	0	0
Ending balance	$ 0	$ 0.1

Investments - Schedule of Comme

Investments - Schedule of Commercial Mortgage Loans (Details) $ in Millions	Mar. 31, 2024 USD ($) loan	Dec. 31, 2023 USD ($)	Dec. 31, 2023	Dec. 31, 2023 loan	Dec. 31, 2023 security
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 171.6	$ 144.8
Composition	100%		100%
Loan Count	30			28	28
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 1.7
Composition	1%
Loan Count | loan	1
Apartments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 76.1	76.1
Composition	44.30%		52.60%
Loan Count | loan	16			16
Hotel
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 22.3	22.4
Composition	13%		15.40%
Loan Count | loan	4			4
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 26	26
Composition	15.20%		18%
Loan Count | loan	4			4
Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 25.9
Composition	15.10%
Loan Count | loan	1
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 19.6	$ 20.3
Composition	11.40%		14%
Loan Count | loan	4			4

Investments - Schedule of Loans

Investments - Schedule of Loans by Ratio (Details) $ in Millions	Mar. 31, 2024 USD ($) security loan	Dec. 31, 2023 USD ($)	Dec. 31, 2023 loan	Dec. 31, 2023 security
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 171.6	$ 144.8
Loan Count	30		28	28
Cost	$ 169.9
Loan Count | loan	29
Equal to or less than 50.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 12.3	12.3
Loan Count | security	2			2
Greater than 50.0% to 55.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 9	9.1
Loan Count | security	2			2
Greater than 55.0% to 60.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 20.7	18.9
Loan Count | security	5			4
Greater than 60.0% to 70.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 63.2	37.3
Loan Count | security	7			6
Greater than 70.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 66.4	67.2
Loan Count | security	14			14
Less than 1.00
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans		36.2
Loan Count | security				8
Cost	$ 36.2
Loan Count | security	8
1.00 to 1.50
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans		29.4
Loan Count | security				6
Cost	$ 54.5
Loan Count | security	7
Greater than 1.5 to 2.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans		30.9
Loan Count | security				6
Cost	$ 30.9
Loan Count | security	6
Greater than 2.0 to 3.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans		36
Loan Count | security				6
Cost	$ 36
Loan Count | security	6
Greater than 3.0 to 4.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans		$ 12.3
Loan Count | security				2
Cost	$ 12.3
Loan Count | security	2

Investments - Schedule of Loa_2

Investments - Schedule of Loans by Maturity (Details) $ in Millions	Mar. 31, 2024 USD ($) security loan	Dec. 31, 2023 USD ($)	Dec. 31, 2023 loan	Dec. 31, 2023 security
Cost
One Year or Less	$ 44.8	$ 19.7
Greater than One Year and Less than Three	34.9	34.9
Greater than Three Years and Less than Five Years	32.4	32.4
Greater than Five Years and Less than Seven Years	17.2	17.2
Greater than Seven Years and Less than Ten Years	42.3	40.6
Cost	$ 171.6	$ 144.8
Loan Count
One Year or Less | security	8			4
Greater than One Year and Less than Three | security	3			6
Greater than Three Years and Less than Five Years | security	6			6
Greater than Five Years and Less than Seven Years | security	4			4
Greater than Seven Years and Less than Ten Years | security	9			8
Loan Count	30		28	28

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	$ 9.4	$ 8
Realized losses on fixed maturities and other:	(3.1)	(28.2)
Credit losses on fixed maturities	0	0.1
Other	0	(3.6)
Total other net losses recognized on fixed maturities and other	(0.5)	(4.2)
Net realized gains (losses) on equity securities	0.4	0.3
Change in unrealized gains (losses) on equity securities held at the end of the period	0	6.2
Net gains (losses) on equity securities	0.4	6.5
Net investment and other gains (losses) before income taxes	6.2	(17.9)
Income tax (benefit) provision	1.6	(5.1)
Net investment and other gains (losses), net of income taxes	4.6	(12.8)
Fixed maturities
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	6.8	0.2
Realized losses on fixed maturities and other:	(0.3)	(22.4)
Other investments
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	2.6	7.8
Realized losses on fixed maturities and other:	(2.8)	(5.8)
Other than temporary impairment losses
Schedule of Investments [Line Items]
Credit losses on fixed maturities	(0.5)	(0.6)
Impairment Related to Change in Intent
Schedule of Investments [Line Items]
Impairment related to change in intent	$ 0	$ 0

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ (20.3)	$ 55.4
Income tax provision (benefit)	(4.4)	9.9
Net unrealized investment gains (losses), net of income taxes	(15.9)	45.5
Fixed maturities
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	(19.9)	55.5
Other and short-term investments
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ (0.4)	$ (0.1)

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	$ 0.3	$ 1.3
Operational currency
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	(0.7)	1.5
Open contracts in a gain position
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	0	75.4
Foreign currency exchange, fair value	0	1.8
Open contracts in a loss position
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	100.4	43.3
Foreign currency exchange, fair value	(0.7)	(0.3)
Asset manager investment exposure
Schedule of Investments [Line Items]
Foreign currency exchange, fair value	1	(0.2)
Open contracts in a gain position
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	45.8	0
Foreign currency exchange, fair value	1	0
Open contracts in a loss position
Schedule of Investments [Line Items]
Foreign currency exchange, notional amount	0	45.8
Foreign currency exchange, fair value	$ 0	$ (0.2)

Investments - Schedule of Reali

Investments - Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts (Detail) - Foreign Currency Exchange Forward Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule of Investments [Line Items]
Gross realized investment gains	$ 2.6	$ 4.1
Gross realized investment losses	(2.7)	(3.4)
Net realized investment (losses) gains on foreign currency exchange forward contracts	(0.1)	0.7
Operational currency
Schedule of Investments [Line Items]
Gross realized investment gains	1.4	4.1
Gross realized investment losses	(2.7)	(3.1)
Asset manager investment exposure
Schedule of Investments [Line Items]
Gross realized investment gains	1.2	0
Gross realized investment losses	$ 0	$ (0.3)

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - Asset Pledged as Collateral - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	$ 192.4	$ 262.6
Securities Deposits for Regulatory and Other Purposes
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	152.7	153.4
Letter of Credit
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	$ 39.7	$ 109.2

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	$ 4,011.1	$ 3,481.2
Fair Value, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0.3	1.3
Total assets	3,497.2	3,027.1
Fair Value, Recurring | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	2,413.4	2,585.4
Fair Value, Recurring | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	201.1	214.1
Fair Value, Recurring | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	356	362.2
Fair Value, Recurring | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	6.2	30.3
Fair Value, Recurring | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	88.7	94.4
Fair Value, Recurring | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1,115.5	1,213.1
Fair Value, Recurring | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	275.4	280.5
Fair Value, Recurring | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	236.8	248.8
Fair Value, Recurring | Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	133.7	142
Fair Value, Recurring | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	8.6	10.7
Fair Value, Recurring | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1.3	0.2
Fair Value, Recurring | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1,073.6	429.5
Fair Value, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0	0
Total assets	1,169	793.4
Fair Value, Recurring | Level 1 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	93.8	360.1
Fair Value, Recurring | Level 1 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	93.8	360.1
Fair Value, Recurring | Level 1 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	2	4.3
Fair Value, Recurring | Level 1 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 1 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1,073.2	429
Fair Value, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0.3	1.3
Total assets	2,285.5	2,176.9
Fair Value, Recurring | Level 2 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	2,284.6	2,174.9
Fair Value, Recurring | Level 2 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	201.1	214.1
Fair Value, Recurring | Level 2 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	262.2	2.1
Fair Value, Recurring | Level 2 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	6.2	30.3
Fair Value, Recurring | Level 2 | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	88.7	94.4
Fair Value, Recurring | Level 2 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1,093.2	1,180.5
Fair Value, Recurring | Level 2 | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	275.4	280.5
Fair Value, Recurring | Level 2 | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	236.8	248.8
Fair Value, Recurring | Level 2 | Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	121	124.2
Fair Value, Recurring | Level 2 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 2 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0.2	0.2
Fair Value, Recurring | Level 2 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0.4	0.5
Fair Value, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0	0
Total assets	42.7	56.8
Fair Value, Recurring | Level 3 | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	35	50.4
Fair Value, Recurring | Level 3 | Fixed maturities | Collateralized Loan Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	22.3	32.6
Fair Value, Recurring | Level 3 | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	0	0
Fair Value, Recurring | Level 3 | Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	12.7	17.8
Fair Value, Recurring | Level 3 | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	6.6	6.4
Fair Value, Recurring | Level 3 | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	1.1	0
Fair Value, Recurring | Level 3 | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total investments	$ 0	$ 0

Investments - Schedule of Recon

Investments - Schedule of Reconciliation of Beginning and Ending Balances for Investments Categorized as Level 3 (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 56.8	$ 56.2
Transfers into Level 3		5.6
Transfers out of Level 3	(10)	(13.2)
Included in net income	0.9	(0.5)
Included in other comprehensive income	(0.4)	0.8
Purchases	1.6	10.6
Sales		(1.6)
Settlements	(6.2)	(1.1)
Ending balance	42.7	56.8
Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	(0.8)
Credit Financial
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	50.4	40.7
Transfers into Level 3		5.6
Transfers out of Level 3	(10)	(5.6)
Included in net income	0.8	(0.1)
Included in other comprehensive income	(0.4)	0.8
Purchases	0.4	10.6
Sales		(0.5)
Settlements	(6.2)	(1.1)
Ending balance	35	50.4
Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	6.4	15.5
Transfers into Level 3		0
Transfers out of Level 3	0	(7.6)
Included in net income	0.1	(0.4)
Included in other comprehensive income	0	0
Purchases	0.1	0
Sales		(1.1)
Settlements	0	0
Ending balance	6.6	6.4
Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at end of period	0	(0.8)
Other Invested Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0
Transfers out of Level 3	0
Included in net income	0
Included in other comprehensive income	0
Purchases	1.1
Settlements	0
Ending balance	1.1	$ 0
Amount of total gains or losses for the year included in net income attributable to the change in unrealized gains or losses relating to assets still held at end of period	$ 0

Investments - Commercial Mortga

Investments - Commercial Mortgage Loans (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 171.6	$ 144.8
Total Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	221	144.8
Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	171.6	144.8
Private loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	49.4	0
Fair Value | Total Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	225.3	148.8
Fair Value | Mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	176	148.8
Fair Value | Private loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage loans	$ 49.3	$ 0

Allowance for Credit Losses - P

Allowance for Credit Losses - Premiums Receivable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Credit Loss [Abstract]
Premiums receivable	$ 209.8	$ 271.1	$ 230.7	$ 292
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Balance, March, 2023	3	4.7
Current period change for estimated uncollectible premiums	1.4	0.4
Write-offs of uncollectible premiums receivable	(0.3)
Balance, March 31, 2024	$ 4.1	$ 5.1

Allowance for Credit Losses - R

Allowance for Credit Losses - Reinsurance Recoverables (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Credit Loss [Abstract]
Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance	$ 2,933.1	$ 2,959.3	$ 3,016.9	$ 3,029.1
Allowance for Estimated Uncollectible Reinsurance	$ 0	$ 0	$ 4.7	$ 4.7

Reserves for Losses and Loss _3

Reserves for Losses and Loss Adjustment Expenses - Reserves for Losses and Loss Adjustment Expenses (Detail) $ in Millions	3 Months Ended		11 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Nov. 15, 2023 USD ($) agreement	Dec. 31, 2023 USD ($)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves - beginning of the year	$ 2,747.1	$ 2,213.1	$ 2,213.1
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year	195.2	236
Prior accident years	24.8	48.6
Losses and LAE incurred during calendar year, net of reinsurance	220	284.6
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year	6.7	36.8
Prior accident years	174.8	149.1
Losses and LAE payments made during current calendar year, net of reinsurance:	181.5	185.9
Divestitures	0	24.4
Retroactive reinsurance	0	21.7
Total net reserve adjustments	0	46.1
Foreign exchange adjustments	(1.3)	2.1
Net reserves - end of period	2,784.3	2,360		$ 2,747.1
Reinsurance recoverables on unpaid losses and LAE, end of period	2,758.8	2,824.1
Gross reserves - end of period	$ 5,543.1	$ 5,184.1		$ 5,544.5
Number of retroactive reinsurance agreements entered into | agreement			2

Reserves for Losses and Loss _4

Reserves for Losses and Loss Adjustment Expenses - Impact from (Favorable) Unfavorable Development of Prior Accident Years' Loss and LAE Reserves on Each Reporting Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	$ 24.8	$ 48.6
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	13.6	39.7
International Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	10.9	7.8
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total unfavorable (favorable) prior-year development	$ 0.3	$ 1.1

Disclosures About Fair Value _3

Disclosures About Fair Value of Financial Instruments - Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 369.7	$ 369.2
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	383.3	381.9
Junior subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	241.6	241.2
Junior subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	252.8	249.2
Junior subordinated debentures | Trust preferred debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	161	160.8
Junior subordinated debentures | Trust preferred debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	168.1	165.9
Junior subordinated debentures | Subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	80.6	80.4
Junior subordinated debentures | Subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	84.7	83.3
Senior unsecured fixed rate notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	128.1	128
Senior unsecured fixed rate notes | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 130.5	$ 132.7

Disclosures About Fair Value _4

Disclosures About Fair Value of Financial Instruments - Summary of Fair Values Measured on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	$ 383.3	$ 381.9
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	130.5	132.7
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	252.8	249.2
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	252.8	249.2
Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	252.8	249.2
Junior subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Trust preferred debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	168.1	165.9
Junior subordinated debentures | Trust preferred debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Trust preferred debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	168.1	165.9
Junior subordinated debentures | Trust preferred debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	84.7	83.3
Junior subordinated debentures | Subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Junior subordinated debentures | Subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	84.7	83.3
Junior subordinated debentures | Subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Senior unsecured fixed rate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	130.5	132.7
Senior unsecured fixed rate notes | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	130.5	132.7
Senior unsecured fixed rate notes | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Senior unsecured fixed rate notes | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	$ 0	$ 0

Stockholders' Equity (Detail)

Stockholders' Equity (Detail) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended
	Mar. 15, 2024 USD ($)	Feb. 20, 2024 USD ($) $ / shares shares	Feb. 08, 2024 $ / shares	Mar. 31, 2024 USD ($) $ / shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 $ / shares	Feb. 15, 2023
Class of Stock [Line Items]
Preferred shares par value (in dollars per share)				$ 1		$ 1
Liquidation preference (in dollars per share)				$ 25,000		$ 25,000
Fractional interest per one preference share			0.001				0.001
Depositary shares, dividends per share (in dollars per share)			$ 0.43750
Dividends paid | $				$ 2.6	$ 2.6
Argo Group International Holdings, Inc. | Brookfield Reinsurance
Class of Stock [Line Items]
Number of shares purchased (in shares) | shares		100
Share price (in dollars per share)		$ 1
Consideration transferred, equity interests issued | $		$ 100
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividends declared (in dollars per share)			$ 437.50
Preferred stock, dividend rate (in percentage)			7%
Preferred shares par value (in dollars per share)			$ 1
Liquidation preference (in dollars per share)			$ 25,000
Dividends paid | $	$ 2.6

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,297.5	$ 1,232.9
Other comprehensive income before reclassifications	(10.8)	29.2
Amounts reclassified from accumulated other comprehensive loss	(5.2)	17.5
Net current-period other comprehensive income	(16)	46.7
Ending Balance	1,404.5	1,244.5
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	51.8	(305.1)
Ending Balance	35.8	(258.4)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0.1	(4.2)
Other comprehensive income before reclassifications	(0.1)	0.4
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income	(0.1)	0.4
Ending Balance	0	(3.8)
Unrealized Holding Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	51.1	(293.1)
Other comprehensive income before reclassifications	(10.7)	28
Amounts reclassified from accumulated other comprehensive loss	(5.2)	17.5
Net current-period other comprehensive income	(15.9)	45.5
Ending Balance	35.2	(247.6)
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0.6	(7.8)
Other comprehensive income before reclassifications	0	0.8
Amounts reclassified from accumulated other comprehensive loss	0	0
Net current-period other comprehensive income	0	0.8
Ending Balance	$ 0.6	$ (7)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Unrealized gains and losses on securities:
Net realized investment and other gains (losses)	$ 6.2	$ (17.9)
Income tax provision (benefit)	1.6	(8.5)
Net income (loss)	25.6	(33.8)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized gains and losses on securities:
Net income (loss)	5.2	(17.5)
Unrealized Gains and Losses on Securities | Reclassification out of Accumulated Other Comprehensive Income
Unrealized gains and losses on securities:
Net realized investment and other gains (losses)	6.5	(22.2)
Income tax provision (benefit)	$ (1.3)	$ 4.7

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Interest Paid and Income Taxes Paid (Recovered) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Supplemental Cash Flow [Line Items]
Total interest paid	$ 9	$ 8.6
Income taxes paid	0	0.4
Income taxes recovered	0	(0.1)
Income taxes paid, net	0	0.3
Senior unsecured fixed rate notes
Supplemental Cash Flow [Line Items]
Total interest paid	2.3	2.3
Junior subordinated debentures
Supplemental Cash Flow [Line Items]
Total interest paid	6.1	5.5
Other indebtedness
Supplemental Cash Flow [Line Items]
Total interest paid	$ 0.6	$ 0.8

Underwriting, Acquisition and_3

Underwriting, Acquisition and General Expenses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Underwriting, Acquisition and Insurance Expenses [Abstract]
Commissions	$ 31.1	$ 57.5
Other underwriting and insurance expenses	68.1	86
Amortization of value of business acquired and other intangible assets	42.9	0
Total	142.1	143.5
Net deferral of policy acquisition costs	(25)	(6.5)
Total underwriting, acquisition and general expenses	$ 117.1	$ 137

Income Taxes - Schedule of Pre-

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 27.2	$ (42.3)
Pre-tax income (loss) less than	$ 27.2	$ (42.3)
Effective Tax Rate	5.80%	20.10%
Bermuda
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ (15.2)
Pre-tax income (loss) less than	$ 0	$ (15.2)
Effective Tax Rate	0%	0%
United States
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 28	$ (7.3)
Pre-tax income (loss) less than	$ 28	$ (7.3)
Effective Tax Rate	5.50%	19.70%
United Kingdom
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ (20.1)
Pre-tax income (loss) less than	$ 0	$ (20.1)
Effective Tax Rate	0%	35.40%
United Arab Emirates
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0.3
Pre-tax income (loss) less than	$ 0	$ 0.3
Effective Tax Rate	0%	0%
Italy
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (0.8)	$ 0.1
Pre-tax income (loss) less than	$ (0.8)	$ 0.1
Effective Tax Rate	(4.70%)	0%

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Difference Between Provision for Income Taxes and Expected Tax Provision at Weighted Average Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate	$ 5.7	$ (5.4)
Tax effect of:
Foreign exchange adjustments	0	(2.6)
Impact of change in tax rate related to Finance Act 2021	0	(0.5)
Prior period adjustment	(4.4)	0
Other	0.3	0
Income tax provision (benefit)	$ 1.6	$ (8.5)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Income Tax Disclosure [Abstract]
Net operating losses carryback period	2 years
Capital losses carryback period	3 years
Deferred tax assets, net	$ 36.2
Decrease in tax penalty expense	1.1
Decrease in income tax penalties expense	$ 0.2

Commitments and Contingencies (

Commitments and Contingencies (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Nov. 16, 2023	Mar. 31, 2024
Other Commitments [Line Items]
Contractual commitments related to its limited partnership investments (up to)		$ 93.7
Contractual commitments period (not to exceed)		12 years
Commitment to fund loan and mortgage loans		$ 29.4
Argo Group International Holdings, Inc. | Common Stock | Brookfield Reinsurance
Other Commitments [Line Items]
Equity interests issued and issuable (in dollars per share)	$ 30

Segment Information - Additiona

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2024 segment
Segment Reporting [Abstract]
Number of reportable segments	2

Segment Information - Revenue a

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net earned premiums	$ 313.7	$ 389.9
Net investment income	58.8	29.7
Net investment and other gains (losses)	6.2	(17.9)
Total revenue	378.7	401.7
Pre-Tax Income (Loss)	27.2	(42.3)
Foreign currency exchange gains (losses)	2	(2.7)
Operating Segments
Segment Reporting Information [Line Items]
Pre-Tax Income (Loss)	24.2	(2.9)
Corporate and Other
Segment Reporting Information [Line Items]
Pre-Tax Income (Loss)	(5.2)	(18.8)
U.S. Operations | Operating Segments
Segment Reporting Information [Line Items]
Net earned premiums	286.7	325.6
Net investment income	50	24.4
Pre-Tax Income (Loss)	32.2	(4.6)
International Operations | Operating Segments
Segment Reporting Information [Line Items]
Net earned premiums	26.9	64.3
Net investment income	7.2	4.6
Pre-Tax Income (Loss)	(7.8)	2.4
Run-off Lines | Operating Segments
Segment Reporting Information [Line Items]
Net earned premiums	0.1	0
Net investment income	1.6	0.7
Pre-Tax Income (Loss)	$ (0.2)	$ (0.7)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 313.7	$ 389.9
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	286.8	325.6
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	0	48.3
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	26.9	13.2
All other jurisdictions
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 0	$ 2.8

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 8,647.1	$ 8,503.1
Operating Segments | U.S. Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	6,678.5	6,279
Operating Segments | International Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,635.2	1,888.9
Operating Segments | Run-off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	231.6	221.4
Corporate and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 101.8	$ 113.8

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Related Party Transaction [Line Items]
Total investments	$ 4,011.1	$ 3,481.2
Mortgage loans	171.6	144.8
Unfunded commitments	93.7	93.4
Other Invested Assets
Related Party Transaction [Line Items]
Total investments	344.4	$ 311
Related Party
Related Party Transaction [Line Items]
Total investments	48.4
Mortgage loans	27.3
Unfunded commitments	40.7
Investment management fees	2.3
Related Party | Other Invested Assets
Related Party Transaction [Line Items]
Total investments	$ 21.1