Argo Group International (ARGO-PA) 10-K 19 Mar 24 2023 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 18, 2024	Jun. 30, 2023
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 1,037.7
Entity Common Stock, Shares Outstanding		1,056,638,730
Entity Central Index Key	0001091748
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
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

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Auditor Information [Abstract]
Auditor Name	KPMG LLP
Auditor Location	New York, New York
Auditor Firm ID	185

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments:
Fixed maturities available-for-sale, at fair value (cost: 2023 - $2,521.5, 2022 - $3,016.4; allowance for expected credit losses: 2023 - $0.2, 2022 - $2.8)	$ 2,585.4	$ 2,675.5
Commercial mortgage loans (cost: 2023 - $144.8, 2022 - $159.9; allowance for expected credit losses: 2023 - $0.2, 2022 - $0.2)	144.6	159.7
Equity securities, at fair value (cost: 2023 - $11.7; 2022 - $54.7)	10.7	43.9
Other investments (cost: 2023 - $311.0; 2022 - $323.2)	311	323.2
Short-term investments, at fair value (cost: 2023 - $429.0; 2022 - $449.4)	429.5	449.6
Investments	3,481.2	3,651.9
Cash, restricted cash and cash equivalents	791.6	50.2
Accrued investment income	20.4	18.6
Premiums receivable	230.7	292
Reinsurance recoverables	2,959.3	3,029.1
Goodwill	0	118.6
Other intangible assets, net of accumulated amortization	180.6	0
Current income taxes receivable, net	53.1	44.9
Deferred tax assets, net	39.1	101.2
Deferred acquisition costs, net	7.2	107
Ceded unearned premiums	356	375.5
Operating lease right-of-use assets	51.2	57.7
Other assets	189.1	121.5
Value of business acquired, net of accumulated amortization	143.6	0
Assets held-for-sale	0	2,066.2
Total assets	8,503.1	10,034.4
Liabilities and Stockholders' Equity
Reserves for losses and loss adjustment expenses	5,544.5	5,051.6
Unearned premiums	916.6	1,039.9
Accrued underwriting expenses and other liabilities	73.9	121.3
Ceded reinsurance payable, net	192.7	158.7
Funds held	57.3	50
Senior unsecured fixed rate notes	128	140.5
Junior subordinated debentures	241.2	258.6
Operating lease liabilities	51.4	66.4
Liabilities held-for-sale	0	1,914.5
Total liabilities	7,205.6	8,801.5
Commitments and contingencies
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 December 31, 2023 and December 31, 2022, respectively; liquidation preference $25,000	137.1	144
Common stock - $1.00 par, 2,000,000,000 and 500,000,000 shares authorized at December 31, 2023 and December 31, 2022, respectively; 1,056,638,730 and 46,379,297 shares issued at December 31, 2023 and December 31, 2022, respectively	1,056.6	46.4
Additional paid-in capital	51.1	1,395.4
Treasury shares (0 and 11,318,339 shares at December 31, 2023 and December 31, 2022, respectively)	0	(455.1)
Retained earnings	0.9	407.3
Accumulated other comprehensive gain (loss), net of taxes	51.8	(305.1)
Total stockholders' equity	1,297.5	1,232.9
Total liabilities and stockholders' equity	$ 8,503.1	$ 10,034.4

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Fixed maturities available-for-sale, cost	$ 2,521.5	$ 3,016.4
Fixed maturities available-for-sale, allowance for expected credit losses	0.2	2.8
Commercial mortgage loans, cost	144.8	159.9
Commercial mortgage loans, allowance for expected credit losses	0.2	0.2
Equity securities, cost	11.7	54.7
Other investments, cost	311	323.2
Short-term investments, cost	$ 429	$ 449.4
Preferred shares, par value (in dollars per share)	$ 1	$ 1
Preferred shares, authorized (in shares)	30,000,000	30,000,000
Preferred shares, issued (in shares)	6,000	6,000
Preferred stock, 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	500,000,000
Common shares, shares issued (in shares)	1,056,638,730	46,379,297
Treasury shares (in shares)	0	11,318,339

Consolidated Statements of Inco

Consolidated Statements of Income (Loss) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Premiums and other revenue:
Net earned premiums	$ 162.3	$ 1,225.9	$ 1,740.4	$ 1,910.1
Net investment income	28.6	121.3	129.8	187.6
Net investment and other gains (losses):
Net realized investment and other gains (losses)	0.1	(20.4)	(115.9)	72.4
Change in fair value recognized	(0.2)	(0.2)	3.1	(40.4)
Change in allowance for credit losses on fixed maturity securities	(0.2)	(2.1)	(2.5)	0.6
Total net investment and other gains (losses)	(0.3)	(22.7)	(115.3)	32.6
Total revenue	190.6	1,324.5	1,754.9	2,130.3
Expenses:
Losses and loss adjustment expenses	94.2	1,043.2	1,166.9	1,314.6
Underwriting, acquisition and general expenses	77.2	419	670.7	702.3
Non-operating expenses	13.1	41.1	51.5	43.7
Interest expense	3.5	29.8	26.8	21.6
Fee and other (income) expense, net	(0.2)	(0.3)	(1.3)	(2)
Foreign currency exchange (gains) losses	0.6	1.8	(5)	1.6
Impairment of goodwill and intangibles	0	0	28.5	43.2
Total expenses	188.4	1,534.6	1,938.1	2,125
Income (loss) before income taxes	2.2	(210.1)	(183.2)	5.3
Income tax provision (benefit)	1.3	0.3	(8)	(1.4)
Net income (loss)	0.9	(210.4)	(175.2)	6.7
Dividends on Series A Preferred stock	0	10.5	10.5	10.5
Net income (loss) attributable to common shareholders, diluted	0.9	(220.9)	(185.7)	(3.8)
Net income (loss) attributable to common shareholders, basic	0.9	$ (220.9)	$ (185.7)	$ (3.8)
Net income (loss) attributable to common stockholders per share of common stock:
Basic (in dollars per share)		$ (6.28)	$ (5.31)	$ (0.11)
Diluted (in dollars per share)		(6.28)	(5.31)	(0.11)
Dividend declared per common share (in dollars per share)		$ 0	$ 1.24	$ 1.24
Weighted average common stock:
Basic (in shares)		35,166,679	34,980,608	34,816,160
Diluted (in shares)		35,166,679	34,980,608	34,816,160
Other-than-temporary impairment losses recognized in earnings:
Net realized investment gains (losses) before other-than-temporary impairment losses	(0.3)	$ (19.8)	$ (79.2)	$ 32.6
Other-than-temporary impairment losses on fixed maturities	0	(2.9)	(36.1)	0
Investment impairment losses recognized in earnings	$ 0	$ (2.9)	$ (36.1)	$ 0
Financial Designation, Predecessor and Successor [Fixed List]	Successor

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 0.9	$ (210.4)	$ (175.2)	$ 6.7
Foreign currency translation:
Foreign currency translation adjustments	0.1	1	(0.7)	2.6
Reclassification adjustment for foreign currency translation included in net income	0	0	31.8	0
Defined benefit pension plans:
Net gain (loss) arising during the period	0.8	1	(0.9)	1.9
Fixed maturity securities:
Unrealized gains (losses) arising during the year	64.7	15.2	(428.1)	(94.7)
Reclassification adjustment for (gains) losses included in net income	(0.1)	28	43.6	(12.2)
Other comprehensive (loss) income before tax	65.5	45.2	(354.3)	(102.4)
Defined benefit pension plans:
Net gain (loss) arising during the period	0.2	0.2	(0.2)	0.4
Fixed maturity securities:
Unrealized gains (losses) arising during the period	13.5	1.5	(80.9)	(17.3)
Reclassification adjustment for (gains) losses included in net income	0	5.9	9.2	(4.2)
Income tax provision (benefit) related to other comprehensive income (loss)	13.7	7.6	(71.9)	(21.1)
Other comprehensive income (loss), net of tax	51.8	37.6	(282.4)	(81.3)
Comprehensive income (loss)	$ 52.7	$ (172.8)	$ (457.6)	$ (74.6)

Consolidated Statements of Stoc

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, 2020	$ 1,857.8	$ 144	$ 46	$ 1,380.2	$ (455.1)	$ 684.1	$ 58.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	6.7					6.7
Other comprehensive income - change in fair value of fixed maturities, net of taxes	(85.4)						(85.4)
Other comprehensive income, net - other	4.1						4.1
Activity under stock incentive plans	7.1		0.2	6.9
Retirement of common stock (tax payments on equity compensation)	(2.8)		(0.1)	(2.7)
Employee stock purchase plan	2.1		0.1	2
Dividends on preferred stock	(10.5)					(10.5)
Cash dividend declared - common shares	(43.9)					(43.9)
Ending Balance at Dec. 31, 2021	1,735.2	144	46.2	1,386.4	(455.1)	636.4	(22.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(175.2)					(175.2)
Other comprehensive income - change in fair value of fixed maturities, net of taxes	(312.8)						(312.8)
Other comprehensive income, net - other	30.4						30.4
Activity under stock incentive plans	9.6		0.2	9.4
Retirement of common stock (tax payments on equity compensation)	(2.2)		(0.1)	(2.1)
Employee stock purchase plan	1.8		0.1	1.7
Dividends on preferred stock	(10.5)					(10.5)
Cash dividend declared - common shares	(43.4)					(43.4)
Ending 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 income (loss)	(210.4)					(210.4)
Other comprehensive income - change in fair value of fixed maturities, net of taxes	35.8						35.8
Other comprehensive income, net - other	1.8						1.8
Activity under stock incentive plans	(0.6)		0.1	(0.7)
Retirement of common stock (tax payments on equity compensation)	(0.9)			(0.9)
Employee stock purchase plan	1.5			1.5
Dividends on preferred stock	(10.5)					(10.5)
Cash dividend declared - common shares	0.3					0.3
Ending Balance at Nov. 15, 2023	1,049.9	144	46.5	1,395.3	(455.1)	186.7	(267.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	0.9
Ending Balance at Dec. 31, 2023	1,297.5	137.1	1,056.6	51.1	0	0.9	51.8
Beginning Balance at Nov. 16, 2023	1,244.8	137.1	1,056.6	51.1	0	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	0.9					0.9
Other comprehensive income - change in fair value of fixed maturities, net of taxes	51.1						51.1
Other comprehensive income, net - other	0.7						0.7
Ending Balance at Dec. 31, 2023	$ 1,297.5	$ 137.1	$ 1,056.6	$ 51.1	$ 0	$ 0.9	$ 51.8

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	11 Months Ended	12 Months Ended
	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]
Cash dividend declared - common shares (in dollars per share)	$ 0	$ 1.24	$ 1.24

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions		2 Months Ended	11 Months Ended	12 Months Ended
		Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows provided by (used in) operating activities:
Net income (loss)		$ 0.9	$ (210.4)	$ (175.2)	$ 6.7
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Amortization and depreciation		39.6	12.2	18.5	43.4
Share-based payments expense		0	1.5	9.6	8
Deferred income tax benefit, net		1.3	(14.9)	15.4	(38.6)
Net investment and other (gains) losses		0.3	22.7	115.3	(32.6)
Undistributed earnings from alternative investment portfolio		(2.2)	(11.5)	(17.7)	(95.5)
Loss on disposals of long-lived assets, net		0	1.2	0.6	23.3
Foreign currency exchange loss		0.6	1.8	0	0
Impairment of goodwill and intangibles		0	0	28.5	43.2
Change in:
Accrued investment income		(3.3)	1.4	0.2	0.8
Receivables		98.5	614.3	(193.6)	47.4
Deferred acquisition costs		(7.2)	8.8	(12.6)	0.8
Ceded unearned premiums		31.6	(69.7)	88.4	65.7
Reserves for losses and loss adjustment expenses		17.2	(27.9)	446.2	210.8
Unearned premiums		(69.6)	(12)	(74.7)	7.2
Ceded reinsurance payable and funds held		(57.3)	20.1	(162.9)	(207.3)
Income taxes		0.1	14.6	(47.5)	(4.5)
Accrued underwriting expenses and other liabilities		(19.3)	18.7	14.7	3
Other, net		(14.3)	(77.2)	0	17.9
Net cash flows from operating activities		16.9	293.7	53.2	99.7
Cash flows provided by (used in) investing activities:
Sales of fixed maturity investments		0.7	24.2	818.5	992.9
Maturities and mandatory calls of fixed maturity investments		22.3	139.3	380.1	717.7
Sales of equity securities		0	45.7	17.8	125.8
Sales of other investments		22.2	24	58.1	212.3
Purchases of fixed maturity investments		(10.1)	(11.9)	(1,093.6)	(1,932.9)
Purchases of equity securities		0	(0.3)	(1)	(5.3)
Purchases of other investments		(2.9)	(19.3)	(52.8)	(47.4)
Change in foreign regulatory deposits and voluntary pools		0	0	(6.7)	(27.1)
Purchase of mortgage loans		0	0	(159.9)	0
Change in short-term investments		24.1	(627)	26.1	(116.4)
Settlements of foreign currency exchange forward contracts		1.3	4.5	(22)	(1.2)
Proceeds from business divestitures, net of cash transferred		4.2	63.8	14.9	0
Purchases of fixed assets, net		0	(2.7)	(6.1)	18
Other, net		0	0	0	7.7
Cash provided by (used in) investing activities		61.8	(359.7)	(26.6)	(55.9)
Cash flows provided by (used in) financing activities:
Activity under stock incentive plans		0	0.7	1.8	1.3
Payment of cash dividends to preferred stockholders		0	(10.5)	(10.5)	(10.5)
Payment of cash dividends to common stockholders		0	0.3	(43.4)	(43.7)
Cash used in financing activities		0	(9.5)	(52.1)	(52.9)
Effect of exchange rate changes on cash		0	0.3	0.4	6.4
Net change in cash and restricted cash including balances classified as held-for-sale		78.7	(75.2)	(25.1)	(2.7)
Cash, restricted cash and cash equivalents	[1]	0	70.8	(70.8)	0
Cash, restricted cash, and cash equivalents, beginning of period		45.8	50.2	146.1	148.8
Cash, restricted cash, and cash equivalents, end of period		$ 791.6	$ 45.8	$ 50.2	$ 146.1
[1]See Note 2 for details of the assets and liabilities classified as “held-for-sale” as of December 31, 2022.

Business and Significant Accoun

Business and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Business and Significant Accounting Policies	Business and Significant Accounting Policies Business Argo Group International Holdings, Inc. (“Argo Group,” “we” or the “Company”) is an underwriter of specialty insurance products in the property and casualty market. Argo Group US, Inc. (“Argo Group US”) is a subsidiary of Argo Financial Holding (Ireland) UC (“Argo Ireland”). Argo Re Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. We conduct our ongoing business through two primary segments - U.S. Operations and International Operations. In addition to these main business segments, we have a Run-off Lines segment for certain products we no longer underwrite. U.S. Operations is comprised of the Excess and Surplus Lines businesses focusing on the U.S.-based risks that the standard, admitted insurance market is unwilling or unable to underwrite, and through other specialized admitted and non-admitted business distributed through retail, wholesale, and managing general brokers/agents in the specialty insurance market. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). The other U.S. specialized admitted and non-admitted businesses consist of the following operations: Argo Pro, U.S. Specialty Programs, Argo Surety, Rockwood Casualty Insurance Company (“Rockwood”), Argo Insurance and Inland Marine. International Operations is comprised of Argo Insurance Bermuda and Italy. This business provides a broad range of commercial property, casualty, professional liability and specialty coverages. Our Run-off Lines segment includes liabilities associated with other liability policies that were issued in the 1960s, 1970s and into the 1980s, as well as the former risk-management business and other business no longer underwritten. On February 2, 2023, we completed the sale of Argo Underwriting Agency Limited (“Syndicate 1200” or “AUA”) to Ohio Farmers Insurance Company (the “Buyer”), part of the Westfield group of insurance companies. AUA was a subsidiary of Argo International Holdings, Ltd. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for further information. On November 16, 2023, we merged with Brookfield Reinsurance Ltd., which resulted in a change to Company’s ownership. See Merger below and Note 2, “Recent Acquisitions, Disposals & Other Transactions” for further information. Merger On February 8, 2023, we entered into an Agreement and Plan of Merger (the “Merger Agreement”), with Brookfield Reinsurance Ltd. and BNRE Bermuda Merger Sub Ltd. (“Merger Sub”), a wholly-owned subsidiary of Brookfield Reinsurance Ltd. The Merger Agreement provides for the merger of the Merger Sub with and into us, which we refer to as the “Merger,” with us surviving the Merger as an indirect wholly-owned subsidiary of Brookfield Reinsurance Ltd. On April 19, 2023, Argo stockholders approved the Merger and the Merger Agreement. The Company also received the required regulatory approvals for this transaction. On November 16, 2023, we completed the Merger, which resulted in a change to Company’s ownership. Pursuant to the Merger Agreement, each share of common stock of the Company issued and outstanding immediately prior to the Merger was automatically canceled and converted into the right to receive an amount in cash equal to $30.00, without interest (the “Merger Consideration”). 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 summary of the total consideration paid for the Company by Brookfield Reinsurance Ltd. and Company’s fair values assigned to its assets and liabilities as of November 16, 2023 are presented in Note 2, “Recent Acquisitions, Disposals & Other Transactions.” On November 16, 2023, each issued and outstanding depositary share, each representing a 1/1,000th interest in a share of 7.00% Resettable Fixed Rate Preferred stock, Series A, par value $1.00 per share, of the Company (each, a share of “preferred stock”), remains issued and outstanding as a depositary share. Each issued and outstanding share of preferred stock remains issued and outstanding as a share of preferred stock and is entitled to the same dividend and all other preferences and privileges, voting rights, relative, participating, optional and other special rights, and qualifications, limitations and restrictions set forth in the certificate of designations applicable to the preferred stock, which certificate of designations remains in full force and effect as an obligation of the Surviving Company in accordance with Section 109(2) of the Companies Act, as described further in the Merger Agreement. Basis of Presentation and Use of Estimates The Consolidated Financial Statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of Consolidated 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 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 goodwill and intangibles, including those identified as part of purchase accounting related to the Merger, and our deferred tax asset valuation allowance. Actual results could differ from those estimates. Specifically, estimates for reserves for losses and loss adjustment expenses are based upon past claim experience modified for current trends as well as prevailing economic, legal and social conditions. Although management believes that amounts included in the accompanying Consolidated Financial Statements are reasonable, such estimates may be more or less than the amounts ultimately paid when the claims are settled. The estimates are continually reviewed and any changes are reflected in current operating results. Further, the nature of loss exposures involves significant variability due to the nature of the long-tailed payments on certain claims. As such, losses and loss adjustment expenses could vary significantly from the recorded amounts. Accounting for business combinations requires significant estimates and assumptions, especially at the acquisition date. In determining the Company’s estimated fair value of assets acquired and liabilities assumed by Brookfield Reinsurance as part of the Merger, we used various recognized valuation methods including the income, market and cost approaches. Valuations were performed by independent valuation specialists under the Company’s supervision. The value of business acquired represents the fair value of the expected future profits in unearned premiums, net of reinsurance, utilizing primarily ultimate loss and expense related assumptions, for insurance contracts acquired as a result of the Merger. The fair value adjustment for reserves for losses and loss adjustment expenses represents the difference between the fair value and book value of unpaid incurred claims net of reinsurance recoveries. Value of business acquired is classified separately on our Consolidated Balances Sheets, while the fair value adjustment for reserves for losses and loss adjustment expenses is included in our other intangible assets. These intangible assets were based primarily on an income valuation technique with assumptions for: (i) settlement patterns that reflect an actuarial estimate of the expected future net cash flows, (ii) a discount rate that reflect a market participant’s view of (a) a reduction to those cash flows for the time value of money and (b) a risk component to reflect the net present value of profit that an investor would demand in return for the assumption of the development risk. The Consolidated Financial Statements include the accounts and operations of Argo Group and its subsidiaries. All material intercompany accounts and transactions have been eliminated. Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation. Amounts related to trade capital providers, who are third-party capital participants that provided underwriting capital to the sold Syndicate 1200 are included in the balance sheet as held-for-sale at December 31, 2022. Trade capital providers participated on a quota share basis, assuming 100% of their contractual participation in the underwriting syndicate results and with such results settled on a year of account basis. We have evaluated our investment in our eleven statutory trusts (collectively, the “Trusts”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts are variable interest entities due to the fact that the Trusts do not have sufficient equity to finance their activities without additional subordinate financial support from other parties. We do not have any power to direct the activities that impact the Trusts’ economic performance. We are not entitled to receive a majority of the residual returns of the Trusts. Additionally, we are not responsible for absorbing the majority of the expected losses of the Trusts; therefore, we are not the primary beneficiary and, accordingly, the Trusts are not included in our Consolidated Financial Statements. Investments Investments in fixed maturities at December 31, 2023 and 2022 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, and voluntary pools. Short-term investments consist of money market funds, certificates of deposit, bonds, sovereign debt and interest-bearing cash accounts. Investments with original maturities of over 90 days and less than one year are classified as short-term investments in our Consolidated Financial Statements as they are part of our investing activities. Previous to the Merger and the application of push-down accounting, the Company classified interest-bearing cash accounts and short-term investments with original maturities of 90 days or less as Short-term investments in our Consolidated Balance Sheets. Post Merger, these securities are classified in Cash, restricted cash and cash equivalents in our Consolidated Balance Sheets. The amortized cost of fixed maturity securities is adjusted for amortization of premiums and accretion of discounts. This amortization or accretion is included in Net investment income in our Consolidated Statements of Income (Loss). For the structured securities portion of the fixed maturity securities portfolio, we recognize income using a constant effective yield based on anticipated prepayments and the estimated economic life of the securities. Premium or discount is amortized into income using the retrospective method. Our investments in fixed maturities are considered available-for-sale and are carried at fair value. As available-for-sale investments, changes in the fair value of fixed maturities are not recognized in income during the period, but rather are recognized as a separate component of stockholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by (1) obtaining and reviewing internal control reports for our service providers that obtain fair values from third-party pricing services, (2) obtaining and reviewing evaluated pricing methodology documentation from third-party pricing services and (3) comparing the security pricing received from a secondary third-party pricing service versus the prices used in the Consolidated Financial Statements and obtaining additional information for variances that exceeded a defined threshold. As of December 31, 2023, investments reported at fair value for which we did not receive a fair value from a pricing service or broker accounted for less than 2% of our investment portfolio. The actual value at which such securities could be sold or settled with a willing buyer or seller may differ from such estimated fair values depending on a number of factors including, but not limited to, current and future economic conditions, the quantity sold or settled, the presence of an active market and the availability of a willing buyer or seller. The cost of securities sold is based on the specific identification method. Commercial mortgage loans are carried at unpaid principal balances less allowance for credit losses, plus or minus adjustments for the accretion or amortization of discount or premium. Interest income on such loans is accrued as earned. Our investments in equity securities are reported at fair value, changes in the fair value of equity securities are included in Net realized investment and other gains (losses) in the Consolidated Statements of Income (Loss). Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized in income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s was the appointed investment manager for the funds. The underlying assets were invested in government securities, agency securities and corporate bonds whose values were obtained from Lloyd’s. Our AUA business was sold in February 2023. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency exchanges rates. We regularly review our investments to identify and evaluate those that may be credit impaired. For fixed maturity securities, the evaluation for credit losses is generally based on the present value of expected cash flows of the security as compared to the amortized book value, the financial condition, near-term and long-term prospects for the issuer, including industry conditions, implications of rating agency actions, the likelihood of principal and interest recoverability and whether it is more likely than not we will be required to sell the investment prior to the anticipated recovery in value. Effective January 1, 2020 with the adoption of ASU 2016-13 Financial Instruments-Credit Losses, we recognize credit losses on fixed maturities through an allowance account. For fixed maturities that we do not intend to sell or for which it is more likely than not we will not be required to sell prior to the anticipated recovery in value, we separate the credit component of the impairment from the component related to all other market factors and report the credit loss component to net realized investment gains (losses) in the Consolidated Statement of Income (Loss). The impairment related to all other market factors is reported as a separate component of stockholder’s equity in other comprehensive income (loss). The credit loss allowance account is adjusted for any additional credit losses or subsequent recoveries and the cost basis of the fixed maturity security is not adjusted. For fixed maturity securities that we intend to sell or for which it is more likely than not that we will be required to sell before an anticipated recovery in value, the full amount of the impairment is recognized in Net realized investment and other gains (losses) in the Consolidated Statements of Income (Loss) and the cost basis of the fixed maturity security is adjusted to reflect the recognized realized loss. The new cost basis is not adjusted for any recoveries in fair value. We report accrued investment income separately from fixed maturity securities and have elected to not measure an allowance for credit losses for accrued investment income. The write-off of investment income accrued for fixed maturities that have defaulted on interest payments is recognized as a loss in Net realized investment and other gains (losses) , in the period of the default, in the Consolidated Statements of Income (Loss). At December 31, 2022, amounts relating to Syndicate 1200 trade capital providers were reclassified to Assets held-for-sale on our Consolidated Balance Sheets. The results of operations and other comprehensive income exclude amounts relating to trade capital providers. Cash, restricted cash, and cash equivalents Cash, restricted cash, and cash equivalents consists of cash deposited in operating accounts with commercial banks and short-term investments with original maturities of 90 days or less. Previous to the Merger and the application of push-down accounting, the Company classified short-term investments with original maturities of 90 days or less as Short-term investments in our Consolidated Balance Sheets. Premiums Receivables and Reinsurance Recoverables Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected lifetime credit losses, both dispute and credit related. The allowance is based upon our ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by our ability to cancel the policy if the policyholder does not pay the premium. Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and incurred but not reported (“IBNR”) amounts ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. We report our reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon our ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors. We use the rating-based method to estimate the uncollectible reinsurance reserves due to credit losses. Under this method, reinsurance credit risk is estimated by considering the reinsurers probability of default. Reinsurance recoverables are forecasted out of the assumed billing periods and a liquidation factor is applied based on the rating of the reinsurer and adjusted as needed based on our historical experience with the reinsurers. Additionally, reinsurance recoverable balances are evaluated to identify any dispute risk and when required, an additional reserve is recorded. Amounts deemed to be uncollectible, including amounts due from known insolvent reinsurers, are written off against the allowance. Changes in the allowance, as well as any subsequent collections of amounts previously written off, are reported as part of underwriting expense. We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. As a result of push-down accounting due to the Merger, the fair value of the allowance for uncollectible premiums as well as reinsurance recoverables were nil as of November 16, 2023. The previous allowances were applied to the premium receivable or reinsurance recoverable balance, resulting in no net change in the asset. At December 31, 2022, premiums receivable and reinsurance recoverables include amounts relating to the trade capital providers’ quota share, which were reclassified to Assets held-for-sale in our Consolidated Balance Sheets. Recoveries occur when subsequent collection or litigation results in the receipt of amounts previously written off. Amounts recovered are applied against the allowance for expected credit losses. For further disclosures about the allowance for expected credit losses, see Note 4, “Allowance for Credit Losses.” Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which it arose. The amortization of deferred acquisition costs is included in Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss). The Company evaluates the recoverability of deferred acquisition costs by determining if the future-earned premiums is greater than the expected future claims and expenses. The Company considers anticipated investment income in this determination. If a loss is probable on the unexpired portion of policies in force, a premium deficiency reserve is recognized. At December 31, 2023 and 2022, the deferred acquisition costs were considered fully recoverable and no premium deficiency reserve was recorded. As a result of push-down accounting due to the Merger, the fair value of our deferred acquisition costs was nil as of November 16, 2023. Our deferred acquisition costs as of December 31, 2023 relates to policy acquisition costs incurred after November 16, 2023. The 2022 net amortization of policy acquisition costs will not equal the change in our Consolidated Balance Sheets as Syndicate 1200 deferred acquisition costs were reclassified to Assets held-for-sale on our Consolidated Balance Sheets at December 31, 2022. The 2022 net amortization of policy acquisition costs will not equal the change in our Consolidated Balance Sheets as the trade capital providers’ share is not reflected in our Consolidated Statements of Income (Loss) and differences arise from foreign currency exchange rates applied to deferred acquisition costs which are treated as a nonmonetary asset. Goodwill, Value of Business Acquired and Other Intangible Assets Goodwill and intangible assets are allocated to reporting units in which the results of operations for the acquired company are reported (see Note 19, “Segment Information” for further discussion). Intangible assets with a finite life are amortized over the estimated useful life of the asset. Goodwill and intangible assets with an indefinite useful life are not amortized. Goodwill and intangible assets are tested for impairment on an annual basis or more frequently if events or changes in circumstances indicate that the carrying amount may not be recoverable. We perform our annual goodwill and intangible asset impairment test on October 1 of each year. The intangible asset amortization expense is reflected in Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss). Successor The following table presents our intangible assets recognized on our Consolidated Balance Sheets as result of push-down accounting and the accumulated amortization: As of December 31, 2023 (in millions) Gross Carrying Accumulated Net Value Useful Life Value of business acquired $ 176.3 $ (32.7) $ 143.6 (a) Other intangible assets: Broker relations 21.5 (0.2) 21.3 13 to 16 years Trade names 12.9 (0.3) 12.6 5 years Insurance licenses 25.0 — 25.0 Indefinite Leases 7.1 (0.1) 7.0 9 years Internally developed software 16.5 (0.3) 16.2 5 to 7 years Fair value adjustment for reserves for losses and loss adjustment expenses 102.8 (4.3) 98.5 (b) Total other intangible assets 185.8 (5.2) 180.6 Total intangible assets $ 362.1 $ (37.9) $ 324.2 (a) Amortized based on unearned premium earnout pattern. (b) Amortized based on settlement pattern. Total intangible asset amortization expense was $37.9 million for the period November 16, 2023 through December 31, 2023 (Successor). The Company did not recognize any goodwill as a result of the Merger as the Company’s fair value of assets acquired and liabilities assumed exceeded the total consideration paid by $48.9 million, resulting in a bargain purchase. This amount is reflected as Additional paid-in capital on our Consolidated Balance Sheets as of the Merger Date. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional detail. The following table outlines the estimated future amortization expense related to definite lived intangible assets held as of December 31, 2023: (in millions) Years As of December 31, 2024 $ 171.7 2025 39.8 2026 25.7 2027 17.4 2028 13.3 Thereafter 31.3 Total amortization expense $ 299.2 Intangible asset amortization expense is included in Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss). Predecessor In conjunction with our annual test, the estimated fair value of each reporting unit exceeded its carrying value for the year ended December 31, 2022, except for our Syndicate 1200 reporting unit. As a result of the announced sale of Argo Underwriting Agency Limited and its Lloyd’s Syndicate 1200, an estimated fair value was established for Syndicate 1200 that was below its carrying value. For the year ended December 31, 2022, we recorded a $28.5 million impairment charge in the third quarter, consisting of $17.3 million of indefinite lived intangible assets and $11.2 million of goodwill so that carrying value equals fair value. For the year ended December 31, 2021, the carrying value of the Syndicate 1200 reporting unit exceeded the fair value by $43.2 million. Goodwill assigned to this reporting unit totaled $28.7 million (pre-tax) and indefinite-lived intangible assets totaled $60.5 million (pre-tax). In accordance with ASC Topic 350-10, “Impairment and Disposal of Long-Lived Assets”, we applied the impairment against the indefinite-lived intangible asset, resulting in a carrying value of $17.3 million. Our Syndicate 1200 reporting unit in past years has been adversely impacted by catastrophe and other losses. As a result, we have exited a number of business lines, focusing on profitability. Due to the change in our business plan, we performed a stress test on our fair value testing, focusing on low to negative growth. The result of this stress testing resulted in the indication that the carrying value of the reporting unit exceeded its fair value, resulting in the impairment. As of December 31, 2020, all of our finite-lived intangible assets had been fully amortized and we had no amortization expense for the years ended December 31, 2022 and 2021. Leases We determine if a contract contains a lease at inception and recognize operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. Lease agreements have lease and non-lease components. We account for these components separately, therefore our operating lease right-of-use asset and operating lease liabilities represent base rent only. Lease expense is recognized on a straight-line basis over the lease term. Renewal options are evaluated prior to the expiration date and recorded upon exercise. Property and Equipment Property and equipment used in operations, including certain costs incurred to develop or obtain computer software for internal use, are capitalized and carried at cost less accumulated depreciation and are reported in Other assets in our Consolidated Balance Sheets. Depreciation is calculated using a straight-line method over the estimated useful lives of the assets, generally three Derivative Instruments We enter into short-term, currency spot and forward contracts to manage operational currency exposure from our non-USD insurance operations. The forward contracts are typically thirty to ninety days and are renewed as management deems necessary to accomplish the objectives of the contracts. These foreign currency forward contracts are carried at fair value in Other assets on our Consolidated Balance Sheets at December 31, 2023 and 2022, respectively. The realized and unrealized gains and losses are included in Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). The forwards contracts are not designated as hedges for accounting purposes. Assets held-for-sale Assets held-for-sale consists of assets associated with pending business dispositions. The Company classifies a business as held-for-sale when the Company has entered into an agreement to sell the business and certain other specified criteria are met. The business classified as held-for-sale is recorded at the lower of carrying value or estimated fair value, less costs to sell. If the carrying value of the business exceeds its estimated fair value, less costs to sell, a loss is recognized when the criteria for the held-for-sale classification as described above are met. If the estimated fair value, less costs to sell, exceeds the carrying value of the business, the gain is recorded when the sale is completed. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for further discussion. Reserves for Losses and Loss Adjustment Expenses Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reserves for loss and loss adjustment expenses represents management's best estimate of the ultimate liability to settle these claims as of the balance sheet date. The effects of changes in this estimate are included in results of operations in the period in which the estimates are changed. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy. Reinsurance In the normal course of business, our insurance subsidiaries cede risks above certain retention levels to other insurance companies. Reinsurance recoverables include claims we paid and estimates of unpaid losses and loss adjustment expenses that are subject to reimbursement under reinsurance and retrocessional contracts. The method for determining reinsurance recoverables for unpaid losses and loss adjustment expenses involves reviewing actuarial estimates of gross unpaid losses and loss adjustment expenses to determine our ability to cede unpaid losses and loss adjustment expenses under our existing reinsurance contracts. This method is continually reviewed and updated and any resulting adjustments are reflected in earnings in the period identified. Reins

Recent Acquisitions, Disposals

Recent Acquisitions, Disposals & Other Transactions	12 Months Ended
	Dec. 31, 2023
Business Combination and Asset Acquisition [Abstract]
Recent Acquisitions, Disposals & Other Transactions	Recent Acquisitions, Disposals & Other Transactions Merger On November 16, 2023, the Company completed the Merger, which resulted in a change to the Company’s ownership. The Company became an indirect wholly-owned subsidiary of Brookfield Reinsurance Ltd. Pursuant to ASC 805, the total value of the consideration transferred was $1,058.9 million. This which consisted of $1,056.6 million for 35,221,291 shares of common stock issued and outstanding immediately prior to the Merger which were automatically canceled and converted into the right to receive an amount in cash equal to $30.00, without interest, and a $2.3 million settlement of unvested employee stock. There is no contingent consideration arrangement in connection with the Merger. The Merger resulted in a $48.9 million bargain purchase since the value of the net assets acquired exceeded the purchase consideration. The bargain purchase determination is consistent with the fact that the Company’s shares traded at a discount to book value, and when considering the circumstances surrounding the Company at the time of sale, including those related to the strategic review. As the Merger resulted in a bargain purchase, which is uncommon, the values of certain assets and liabilities are considered preliminary in nature that are subject to adjustment as additional information is obtained. The valuations will be finalized within the measurement period which cannot exceed 12 months from the close of the acquisition. When the valuations are finalized, any changes to the preliminary valuation of assets acquired or liabilities assumed may result in retrospective adjustments to the provisional amounts recognized at the acquisition date to reflect new information obtained about facts and circumstances that existed as of the acquisition date that, if known, would have affected the measurement of the amounts recognized as of that date. The following table is a summary of the purchase price and the fair value of assets acquired and liabilities assumed as part of the Merger as of November 16, 2023: As of (in millions) November 16, 2023 Consideration transferred settling 35,221,291 shares of outstanding common stock $ 1,056.6 Consideration transferred settling unvested employee stock 2.3 Total consideration $ 1,058.9 Assets Investments: Fixed maturities available-for-sale, at fair value $ 2,525.3 Commercial mortgage loans 144.9 Equity securities, at fair value 11.7 Other investments 327.8 Short-term investments, at fair value 450.1 Total investments 3,459.8 Cash 712.9 Accrued investment income 17.1 Premiums receivable 306.8 Reinsurance recoverables 2,981.6 Other intangible assets 186.1 Current income taxes receivable, net 53.2 Deferred tax asset, net 54.0 Ceded unearned premiums 387.6 Operating lease right-of-use assets 51.6 Other assets 190.8 Value of business acquired 176.3 Total assets (1) $ 8,577.8 Liabilities Reserves for losses and loss adjustment expenses 5,526.4 Unearned premiums 986.2 Accrued underwriting expenses and other liabilities 92.0 Ceded reinsurance payable, net 257.4 Funds held 49.9 Senior unsecured fixed rate notes 127.9 Junior subordinated debentures 241.0 Operating lease liabilities 52.1 Total liabilities assumed (2) $ 7,332.9 Fair value of net assets acquired $ 1,244.9 Other claims on net assets: Preferred stock $ 137.1 Bargain purchase recognized in Additional paid-in capital $ 48.9 (1) Reflects net fair value adjustments of $114.2 million to increase the total assets acquired, including value of business acquired and other intangible assets. (2) Reflects net fair value adjustments of $80.9 million to reduce the total liabilities assumed. Business Dispositions 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 is $125.0 million, which will be 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 will be obliged to replace certain funds provided by the Company to support the activities of AUA and certain of its subsidiaries at Lloyd’s of London, which would then be 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 has determined that the Transaction does not represent a strategic shift, and therefore, does 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. The table below reflects the carrying amounts of assets and liabilities held-for-sale related to the pending disposition described above: As of (in millions) December 31, 2022 Assets Investments: Fixed maturities available-for-sale, at fair value $ 490.6 Other investments 81.6 Short-term investments, at fair value 114.1 Total investments 686.4 Cash 70.8 Accrued investment income 2.1 Premiums receivable 331.9 Reinsurance recoverables 733.1 Current income taxes receivable, net 6.3 Deferred tax asset, net 28.1 Deferred acquisition costs, net 69.4 Ceded unearned premiums 76.1 Other assets 62.0 Total assets $ 2,066.2 Liabilities Reserves for losses and loss adjustment expenses 993.4 Unearned premiums 335.6 Accrued underwriting expenses and other liabilities 34.4 Ceded reinsurance payable, net 323.5 Funds held 172.9 Other indebtedness 54.7 Total liabilities $ 1,914.5 The pretax net income (loss) of our held-for-sale business was $15.6 million, $66.8 million, and $22.4 million for the period January 1, 2023 through November 15, 2023 (Predecessor), 2022, and 2021, respectively. These amounts include business that is assumed from Westfield post the sale of the Syndicate. Sale of ArgoGlobal SE On June 22, 2022, we completed the sale of our Malta operations, ArgoGlobal Holdings (Malta) Ltd. and its subsidiaries (“AGSE”) to RiverStone Holdings Limited (part of the RiverStone International Group) for €4.9 million (approximately $5.2 million), subject to the terms and conditions set forth in the purchase agreement. AGSE is one of the business units within our International Operations reporting segment. As a result, we realized a loss on the sale of AGSE of $21.3 million, which is included as a component of Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). This amount includes $4.5 million of losses from the realization of historical foreign currency translation, which was previously a component of accumulated other comprehensive income. Sale of Argo Seguros Brasil S.A. On February 15, 2022, we completed the sale of our Brazilian operations, Argo Seguros Brasil S.A. (“Argo Seguros”), to Spice Private Equity Ltd., an investment company focused on global private equity investments, for a final purchase price of 140 million Brazilian Reais (approximately $26.9 million), subject to the terms and conditions set forth in the purchase agreement. Argo Seguros is one of the business units within our International Operations reporting segment. As a result, we realized a loss on the sale of Argo Seguros of $33.8 million in 2022, which is included as a component of Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). This amount includes $27.3 million of losses from the realization of historical foreign currency translation, which was previously a component of accumulated other comprehensive income. We previously recognized a $6.3 million loss during 2021 as we adjusted the carrying value of Argo Seguros to its fair value. Other Transactions Loss Portfolio Transfer - U.S. On August 8, 2022, the Company entered into a loss portfolio transfer agreement with a wholly-owned subsidiary of Enstar Group Limited (“Enstar”) covering a majority of the Company’s U.S. casualty insurance reserves, including construction, for accident years 2011 to 2019. Enstar’s subsidiary will provide ground up cover of $746.0 million of reserves, and an additional $275.0 million of cover in excess of $821.0 million, up to a policy limit of $1,096.0 million effective January 1, 2022. The Company will retain a loss corridor of $75.0 million up to $821.0 million. For the year ended December 31, 2022, the Company recognized $75.0 million of losses that fall within the corridor and $188.6 million of the $275.0 million LPT limit remains available to the Company. In addition, as a result of the anticipated loss portfolio transfer in the third quarter of 2022, the Company determined that it was more likely than not it would be required to sell certain securities before recovery of its amortized cost. As such, the Company recognized $34.2 million of realized losses related to the impairment of assets that were transferred at fair value to a third party at the close of the transaction. These losses were previously a component of accumulated other comprehensive income. In addition, in the fourth quarter of 2022, the Company recognized an additional $3.4 million loss at the close of the transaction. The realized losses are included as a component of Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). On November 9, 2022, the U.S. loss portfolio transaction with Enstar covering a majority of the Company’s U.S. casualty insurance reserves, including construction, for accident years 2011 to 2019 closed. The estimated subject reserves transferred to Enstar on the closing date were $509.0 million, which represents the $746.0 million in loss reserves as of January 1, 2022, less estimated claims paid through October 31, 2022. On the closing date, the Company also transferred approximately $630.0 million of cash and investments to Enstar for which a portion was deposited into a Trust established to secure Enstar’s claim payment obligation to the Company. The financial statement impact of this transaction on the closing date, which was recorded in the fourth quarter of 2022, is a $509.0 million increase in Reinsurance recoverables, a reduction of $630.0 million in cash and investments, and an after-tax charge of approximately $100.0 million. The charge consists mainly of ceded premiums for a total of $121.0 million and is reflected in Earned premiums in our Consolidated Statements of Income (Loss). In 2023, the reserves ceded under the U.S. loss portfolio transfer exceeded the consideration paid by $82.4 million, and was reflected as a deferred gain liability included in Accrued underwriting expenses and other liabilities on the Consolidated Balance Sheets, net of amortization, prior to the Merger. The deferred gain was amortized to earnings using the recovery method over the estimated claims settlement period. At the time of the Merger, the deferred gain liability was eliminated as it has no future cash flows associated with it. In addition, any potential future adverse loss development covered under the loss portfolio transfer will not result in any deferred gains. Loss Portfolio Transfer - Syndicate 1200 In April 2022, Argo Managing Agency Limited, for and on behalf of Lloyd’s Syndicate 1200, reached an agreement to enter into a loss portfolio transfer of the 2018 and 2019 years of account to Riverstone Managing Agency Limited, for and on behalf of Lloyd's Syndicate 3500, retrospectively from January 1, 2022. These years of account are included in a reinsurance to close transaction with Riverstone Managing Agency Limited entered into on January 1, 2023. As of December 31, 2022, these balances are classified as held-for-sale on our Consolidated Balance Sheets as described in Sale of Argo Underwriting Agency Limited above.

Investments

Investments	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Investments	Investments As a result of the push-down accounting due the Merger, the amortized cost of our investments is based on the fair value as of November 16, 2023. Included in our Assets held-for-sale at December 31, 2022 in our Consolidated Balance Sheets is $55.9 million, respectively, of assets managed on behalf of the trade capital providers, who are third-party participants that provide underwriting capital to the operations of Syndicates 1200 and 1910. Fixed Maturities The amortized cost, gross unrealized gains, gross unrealized losses, allowance for credit losses, and fair value in fixed maturity investments were as follows: 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 December 31, 2022 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 410.9 $ — $ 30.2 $ — $ 380.7 Foreign Governments 35.6 0.3 6.7 0.8 28.4 Obligations of states and political subdivisions 109.9 0.4 10.1 0.4 99.8 Corporate bonds 1,394.8 0.9 160.0 1.6 1,234.1 Commercial mortgage-backed securities 337.4 — 52.0 — 285.4 Residential mortgage-backed securities 320.0 0.2 50.2 — 270.0 Asset-backed securities 153.4 — 14.2 — 139.2 Collateralized loan obligations 254.4 0.3 16.8 — 237.9 Total fixed maturities $ 3,016.4 $ 2.1 $ 340.2 $ 2.8 $ 2,675.5 Contractual Maturity The amortized cost and fair values of fixed maturity investments as of December 31, 2023, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 290.2 $ 290.8 Due after one year through five years 1,019.7 1,037.4 Due after five years through ten years 322.1 337.7 Due after ten years 30.9 34.1 Structured securities 858.6 885.4 Total $ 2,521.5 $ 2,585.4 The actual maturities may differ from the contractual maturities because debtors may have the right to call or prepay obligations. The model duration of the assets comprising our fixed maturity investment portfolio was 2.68 years and 3.29 years at December 31, 2023 and 2022, respectively. Other Invested Assets Details regarding the carrying value and unfunded investment commitments of other investments as of December 31, 2023 and 2022 were as follows: 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 December 31, 2022 (in millions) Carrying Unfunded Investment Type Hedge funds $ 54.0 $ — Private equity 264.6 108.9 Other 4.6 — Total other investments $ 323.2 $ 108.9 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. Unrealized Losses and Other-than-temporary Impairments An aging of unrealized losses on our investments in fixed maturities is presented below: December 31, 2023 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ — $ — $ — $ — $ — $ — 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 December 31, 2022 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 271.0 $ 18.1 $ 109.8 $ 12.1 $ 380.8 $ 30.2 Foreign Governments 16.7 4.9 2.6 1.8 19.3 6.7 Obligations of states and political subdivisions 67.4 4.1 24.3 6.0 91.7 10.1 Corporate bonds 695.1 68.3 519.6 91.7 1,214.7 160.0 Commercial mortgage-backed securities 144.2 18.6 141.2 33.4 285.4 52.0 Residential mortgage-backed securities 88.7 8.8 178.8 41.4 267.5 50.2 Asset-backed securities 93.3 7.5 45.9 6.7 139.2 14.2 Collateralized loan obligations 181.1 13.3 44.2 3.5 225.3 16.8 Total fixed maturities $ 1,557.5 $ 143.6 $ 1,066.4 $ 196.6 $ 2,623.9 $ 340.2 We hold a total of 1,431 fixed maturity securities, of which 104 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 December 31, 2023. 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 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 realized investment gains. 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 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 months ending December 31, 2023 and 2022, respectively: Predecessor Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Balance, January 1, 2022 $ 0.2 $ — $ 2.2 $ 0.1 $ 2.5 Securities for which allowance was not previously recorded 0.4 — 1.8 — 2.2 Securities sold during the period (0.1) — (0.7) — (0.8) Reductions for credit impairments — — (1.4) — (1.4) Additional net increases (decreases) in existing allowance 0.2 0.4 (0.3) — 0.3 Balance, December 31, 2022 $ 0.7 $ 0.4 $ 1.6 $ 0.1 $ 2.8 Additions-initial adoption of accounting standard — — — — — Securities for which allowance was not previously recorded 0.1 0.5 2.1 — 2.7 Securities sold during the period — — (0.7) — (0.7) Reductions for credit impairments — — — — — Additional net increases (decreases) in existing allowance 0.3 (0.4) (0.4) — (0.5) Balance, November 15, 2023 $ 1.1 $ 0.5 $ 2.6 $ 0.1 $ 4.3 Successor Balance, November 16, 2023 $ — $ — $ — $ — $ — Additional net increases (decreases) in existing allowance — — 0.2 — 0.2 Balance, December 31, 2023 $ — $ — $ 0.2 $ — $ 0.2 Total credit impairment (gains) losses, net of allowance for credit losses, included in Net investment and other gains (losses) in the Consolidated Statements of Income (Loss) was $0.2 million for the period November 16, 2023 through December 31, 2023 (Successor), $2.2 million for the period January 1, 2023 through November 15, 2023 and $2.5 million for the year ended December 31, 2022, respectively. For commercial 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. Commercial Mortgage Loans Commercial mortgage loan investments are composed of participation interests in a portfolio of commercial mortgage loans. Loan collateral is diversified with regard to property type and geography. The following table presents loans by property type: 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 December 31, 2022 (in millions) Cost Composition Loan Count Apartments $ 87.4 54.5 % 16 Hotel 25.0 15.6 % 4 Industrial 26.0 16.3 % 4 Retail 21.5 13.6 % 4 Total $ 159.9 100.0 % 28 The following table presents our loans by Debt Service Coverage Ratio (“DSCR”): 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 December 31, 2022 (in millions) Cost Loan Count 1.00 to 1.50 $ 10.4 2 Greater than 1.5 to 2.0 60.4 10 Greater than 2.0 to 3.0 52.0 10 Greater than 3.0 to 4.0 25.8 4 Greater than 4.0 11.3 2 Total $ 159.9 28 The following table presents loans by Loan To Value (“LTV”): 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 December 31, 2022 (in millions) Cost Loan Count Equal to or less than 50.0% $ 36.7 6 Greater than 50.0% to 55.0% 9.1 2 Greater than 55.0% to 60.0% 42.6 8 Greater than 60.0% to 70.0% 71.5 12 Total $ 159.9 28 The following table presents loans by maturity: 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 December 31, 2022 (in millions) Cost Loan Count Greater than One Year and Less than Three $ 54.8 $ 10 Greater than Three Years and Less than Five Years 33.8 6 Greater than Five Years and Less than Seven Years 20.4 4 Greater than Seven Years and Less than Ten Years 50.9 8 Total $ 159.9 28 Investment Gains and Losses The following table presents our gross realized investment gains and losses: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Realized gains on fixed maturities and other: Fixed maturities $ 0.1 $ 0.6 $ 20.5 $ 30.6 Other investments, including short-terms 5.4 14.9 34.8 9.8 Other assets — — — 3.3 5.5 15.5 55.3 43.7 Realized losses on fixed maturities and other: Fixed maturities — (25.7) (29.9) (11.8) Other investments, including short-terms (5.4) (11.3) (51.1) (18.5) Other assets — — — (12.5) (5.4) (37.0) (81.0) (42.8) Other net losses recognized on fixed maturities and other: Credit gains (losses) on fixed maturities (0.2) (2.2) (4.6) 0.6 Impairment related to change in intent (1) — (2.9) (34.2) — Other (2) — (8.4) (55.1) (6.3) (0.2) (13.5) (93.9) (5.7) Equity securities Net realized gains (losses) on equity securities — 6.8 1.2 71.5 Change in unrealized gains (losses) on equity securities held at the end of the period (0.2) 5.5 3.1 (34.1) Net gains (losses) on equity securities (0.2) 12.3 4.3 37.4 Net investment and other gains (losses) before income taxes (0.3) (22.7) (115.3) 32.6 Income tax (benefit) provision (0.1) (6.8) (10.0) 6.2 Net investment and other gains (losses), net of income taxes $ (0.2) $ (15.9) $ (105.3) $ 26.4 (1) Refer to the Loss Portfolio Transfer - U.S. in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for the year ended December 31, 2022. (2) Refer to the sale of AGSE and Argo Seguros in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for the year ended December 31, 2022. The cost of securities sold is based on the specific identification method. Changes in unrealized gains (losses) related to investments are summarized as follows: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Change in unrealized gains (losses) Fixed maturities $ 64.2 $ 41.2 $ (383.7) $ (105.9) Other and short-term investments 0.4 2.0 (0.8) (1.0) Net unrealized investment gains (losses) before income taxes 64.6 43.2 (384.5) (106.9) Income tax provision (benefit) 13.5 7.4 (71.7) (21.5) Net unrealized investment gains (losses), net of income taxes $ 51.1 $ 35.8 $ (312.8) $ (85.4) Foreign Currency Exchange Forward Contracts We entered into foreign currency exchange forward contracts primarily to manage operation currency exposure from our non-USD insurance operations. We also invested in a total return strategy which invested in multiple currencies, and that investment was terminated in mid-2021. The currency forward contracts are carried at fair value in our Consolidated Balance Sheets in Other liabilities and Other assets at December 31, 2023 and 2022. The net realized gains and (losses) are included in Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). The fair value of our foreign currency exchange forward contracts as of December 31, 2023 and 2022 was as follows: As of (in millions) December 31, 2023 December 31, 2022 Operational currency exposure $ 1.8 $ 5.8 Asset manager investment exposure (0.5) (0.6) Total $ 1.3 $ 5.2 The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Realized gains Operational currency exposure $ 4.5 $ 12.0 $ 30.0 $ 16.5 Asset manager investment exposure — 1.5 3.9 3.7 Total return strategy — — — 13.0 Gross realized investment gains 4.5 13.5 33.9 33.2 Realized losses Operational currency exposure (2.9) (11.4) (46.3) (28.9) Asset manager investment exposure (0.7) (1.0) (0.9) (1.0) Total return strategy — — — (12.0) Gross realized investment losses (3.6) (12.4) (47.2) (41.9) Net realized investment gains (losses) on foreign $ 0.9 $ 1.1 $ (13.3) $ (8.7) 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 reported loss and loss expense reserves. The following table presents our components of restricted assets: As of (in millions) December 31, 2023 December 31, 2022 Securities and cash on deposit for regulatory and other purposes $ 153.4 $ 149.3 Securities pledged as collateral for letters of credit and other 109.2 169.8 Securities on deposit supporting Lloyd’s business (1) — 171.4 Total restricted investments $ 262.6 $ 490.5 (1) Argo Group was required to maintain Funds at Lloyd’s (“FAL”) to support its business for Syndicate 1200 and Syndicate 1910. At December 31, 2022 the amount of securities pledged for FAL was $171.4 million, which was provided by Argo Re, Ltd. FAL of $123.7 million held by Syndicate 1200 and 1910 was reclassified to Assets held-for-sale . During the second quarter 2023, the funds at Lloyd’s (FAL) previously used to support the activities of AUA and its subsidiaries, were released to the Company. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. Fair Value Measurements Fair value is the price that would be received to sell 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 and income 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. We receive one quote per instrument for Level 1 inputs. • 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 assumptions about the assumptions market participants would use in pricing the asset or liability based on the best information available in the circumstances. We receive fair value prices from third-party pricing services and our outside investment managers. 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 December 31, 2023 and 2022. 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: • U.S. 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. • U.S. 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 Level 3: We own term loans and asset-backed 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 a broker and an independent valuation service, both based upon estimates and assumptions. 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) December 31, 2023 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 asset (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2022 Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 380.7 $ 378.7 $ 2.0 $ — Foreign Governments 28.4 — 28.4 — Obligations of states and political subdivisions 99.8 — 99.8 — Corporate bonds 1,234.1 — 1,212.1 22.0 Commercial mortgage-backed securities 285.4 — 285.4 — Residential mortgage-backed securities 270.0 — 270.0 — Asset-backed securities 139.2 — 120.5 18.7 Collateralized loan obligations 237.9 — 237.9 — Total fixed maturities 2,675.5 378.7 2,256.1 40.7 Equity securities 43.9 28.4 — 15.5 Other investments 0.3 — 0.3 — Short-term investments 449.6 449.3 0.3 — Derivatives 5.2 — 5.2 — Total assets $ 3,174.5 $ 856.4 $ 2,261.9 $ 56.2 (1) Quoted prices in active markets for identical asset (2) Significant other observable inputs (3) Significant unobservable inputs The fair value measurements in the tables above do not equal Total investments on our Consolidated Balance Sheets as they primarily exclude private equity 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 Observable Inputs (Level 3) (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 income 0.8 — 0.8 Purchases, issuances, sales, and settlements: Purchases 10.6 — 10.6 Issuances — — — 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) (in millions) Credit Financial Equity Total Beginning balance, January 1, 2022 $ 2.8 $ 14.7 $ 17.5 Transfers into Level 3 36.1 1.5 37.6 Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income (0.4) (0.7) (1.1) Included in other comprehensive loss (4.8) — (4.8) Purchases, issuances, sales, and settlements: Purchases 9.0 1.0 10.0 Issuances — — — Sales (2.0) (1.0) (3.0) Settlements — — — Ending balance, December 31, 2022 $ 40.7 $ 15.5 $ 56.2 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, 2022 $ — $ (4.4) $ (4.4) At December 31, 2023 and 2022, 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 investments in commercial mortgage loans reported at cost, less an allowance for expected credit losses of $0.2 million, on the Consolidated Balance Sheets. As of December 31, 2023, the cost and estimated fair value of the investments in commercial mortgage loans were: As of December 31, 2023 December 31, 2022 (in millions) Cost Fair Value Cost Fair Value Commercial Mortgage Loans $ 144.8 $ 148.8 $ 159.9 $ 150.7

Allowance for Credit Losses

Allowance for Credit Losses	12 Months Ended
	Dec. 31, 2023
Credit Loss [Abstract]
Allowance for Credit Losses	Allowance for Credit Losses Premiums receivable The following table represents the balances of premiums receivable, net of allowance for estimated uncollectible premiums, including expected lifetime credit losses, as of December 31, 2023, 2022 and 2021, and the changes in the allowance for the period November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. Predecessor (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, December 31, 2021 $ 648.6 $ 5.7 Current period change for estimated uncollectible premiums 0.2 Write-offs of uncollectible premiums receivable (1.2) Balance, December 31, 2022 $ 292.0 $ 4.7 Current period change for estimated uncollectible premiums 5.4 Write-offs of uncollectible premiums receivable (2.7) Balance, November 15, 2023 $ 306.8 $ 7.4 Successor Balance, November 16, 2023 $ 306.8 $ — Current period change for estimated uncollectible premiums 3.3 Write-offs of uncollectible premiums receivable (0.3) Balance, December 31, 2023 $ 230.7 $ 3.0 Reinsurance Recoverables The following table presents the balances of reinsurance recoverables, net of the allowance for estimated uncollectible reinsurance, including expected credit losses, at December 31, 2023, 2022 and 2021, and changes in the allowance for the period November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. Predecessor (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, December 31, 2021 $ 2,966.4 $ 3.8 Current period change for estimated uncollectible reinsurance 1.7 Reclassified to assets held-for-sale (0.8) Balance, December 31, 2022 $ 3,029.1 $ 4.7 Balance, November 15, 2023 $ 2,981.6 $ 4.7 Successor Balance, December 31, 2023 $ 2,959.3 $ — We primarily utilize A.M. Best credit ratings when determining the allowance, adjusted as needed based on our historical experience with the reinsurers. Certain of our reinsurance recoverables are collateralized by letters of credit, funds held or trust agreements.

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	Leases Our operating lease obligations are for office facilities. Our leases have remaining lease terms ranging between less than 1 year and 10 years, some of which include options to extend the leases. The lease information is as follows: December 31, 2023 2022 (in millions) Operating leases right-of-use assets (1) $ 51.2 $ 57.7 Operating lease liabilities (2) 51.4 66.4 Operating lease weighted-average remaining lease term 7.70 8.22 Operating lease weighted-average discount rate 6.13 % 3.44 % (1) $0.5 million of Operating leases right-of-use-assets were reclassified to assets held-for-sale. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” at December 31, 2022. (2) $0.5 million of Operating lease liabilities were reclassified to liabilities held-for-sale. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” at December 31, 2022. Successor Predecessor Period from Period from November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 For the Year Ended December 31, 2022 (in millions) Operating lease costs $ 0.7 $ 5.2 $ 8.1 Variable lease costs 0.5 3.3 4.7 Sublease income (0.1) (0.9) (1.0) Total lease costs $ 1.1 $ 7.6 $ 11.8 Our short-term leases as of December 31, 2023 and 2022 were not material. Future minimum lease payments under operating leases as of December 31, 2023 were as follows: December 31, (in millions) 2023 2024 8.9 2025 9.1 2026 8.9 2027 8.3 2028 6.9 Thereafter 22.5 Total future minimum lease payments $ 64.6 Less imputed interest (13.2) Total operating lease liability $ 51.4

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2023
Insurance [Abstract]
Reinsurance	Reinsurance We reinsure certain risks with other insurance companies. Such arrangements serve to limit our maximum loss on certain individual risks as well as on catastrophes and large or unusually hazardous risks. We are liable to our insureds for reinsurance ceded in the event our reinsurers do not meet their obligations. Thus, a credit exposure exists with respect to reinsurance ceded to the extent that any reinsurer is unable or unwilling to meet the obligations assumed under the reinsurance contracts. Our allowance for uncollectible reinsurance balances receivable on paid losses and incurred claims was nil at December 31, 2023 as compared to $4.7 million at December 31, 2022 (see Note 4, “Allowance for Credit Losses” for additional information). Under certain reinsurance agreements, collateral, including letters of credit, is held to secure performance of reinsurers in meeting their obligations. The amount of such collateral was $1,212.2 million and $1,299.3 million at December 31, 2023 and December 31, 2022, respectively. The collateral we hold does not apply to our entire outstanding reinsurance recoverable. Rather, collateral is provided on an individual contract basis, as appropriate. For each individual reinsurer, the collateral held may exceed or fall below the total outstanding recoverable from that individual reinsurer. The long-term nature of the reinsurance contracts creates a credit risk to us over time arising from potentially uncollectible reinsurance. To mitigate that counterparty risk, we evaluate our reinsurers to assess their financial condition. The factors that underlie these reviews include a financial risk assessment as well as an internal assessment of the capitalization and the operational risk of the reinsurer. As a result of these reviews, we may make changes to the approved markets that are used in both our treaty and facultative reinsurance programs. In light of collateral held, we believe that no exposure to a single reinsurer represents an inappropriate concentration of credit risk to the Company. Gross reinsurance assets due from reinsurers exceeding five percent of our total reinsurance assets were approximately $945.0 million and $1,244.3 million at December 31, 2023 and 2022, respectively, of which approximately $465.1 million and $564.0 million, respectively, was secured by collateral. Estimated losses recoverable from reinsurers and the ceded portion of unearned premiums are reported as assets in our Consolidated Balance Sheets. Included in Reinsurance recoverables are paid loss recoverables of $161.9 million and $190.6 million as of December 31, 2023 and 2022, respectively. Earned premiums and losses and loss adjustment expenses are reported net of reinsurance in our Consolidated Statements of Income (Loss). Losses and loss adjustment expenses were $94.2 million for the period November 16, 2023 through December 31, 2023 (Successor), $1,043.2 million for January 1, 2023 through November 15, 2023 (Predecessor), and, $1,166.9 million and $1,314.6 million for the years ended December 31, 2022, and 2021, respectively, are net of amounts ceded to reinsurers of $79.3 million, $607.3 million, $958.8 million and $829.6 million, respectively. We are required to accept certain assigned risks and other legally mandated reinsurance obligations. Prior to the mid-1980s, we assumed various forms of casualty reinsurance for which we continue to maintain reserves for losses and loss adjustment expenses (see Note 8, “Run-off Lines”). For such assumed reinsurance transactions, we engage in various monitoring steps that are common with assumed reinsurance such as ongoing claims reviews. We assumed property related reinsurance primarily through, Argo Re and Ariel Re, and casualty related reinsurance. Premiums were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Direct written premiums $ 186.0 $ 1,907.9 $ 2,682.8 $ 2,990.6 Reinsurance ceded to other companies (66.8) (803.6) (1,106.7) (1,203.9) Reinsurance assumed from other companies 5.1 40.4 165.4 190.6 Net written premiums $ 124.3 $ 1,144.7 $ 1,741.5 $ 1,977.3 Direct earned premiums $ 252.3 $ 1,906.5 $ 2,757.8 $ 2,917.7 Reinsurance ceded to other companies (98.4) (724.9) (1,205.3) (1,272.7) Reinsurance assumed from other companies 8.4 44.3 187.9 265.1 Net earned premiums $ 162.3 $ 1,225.9 $ 1,740.4 $ 1,910.1 Percentage of reinsurance assumed to net earned premiums 5.2 % 3.6 % 10.8 % 13.9 % Loss Portfolio Transfer - U.S. On November 9, 2022, the U.S. loss portfolio transaction with Enstar covering a majority of the Company’s U.S. casualty insurance reserves, including construction, for accident years 2011 to 2019 closed. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for further discussion.

Reserves for Losses and Loss Ad

Reserves for Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2023
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 Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Net reserves beginning of the period $ 2,734.6 $ 2,213.1 $ 3,123.2 $ 2,906.1 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 94.2 775.3 1,102.2 1,176.3 Prior accident years — 267.9 64.7 138.3 Losses and LAE incurred during calendar year, net of reinsurance 94.2 1,043.2 1,166.9 1,314.6 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 33.5 100.6 171.5 180.8 Prior accident years 51.8 427.3 828.0 688.4 Losses and LAE payments made during current calendar year, net of reinsurance: 85.3 527.9 999.5 869.2 Add/(Deduct): Divestitures (1) — 24.4 (35.2) — Reclassified to liabilities held-for-sale (2) — — (313.0) — Net reserves ceded to Syndicate 1200 (2) — — (129.6) — Deferred gain on U.S. loss portfolio transfer, net of amortization — (40.9) — — Loss portfolio transfer: U.S. (3) — — (472.6) — Syndicate 1200 (for years of account 2019 and 2018) (4) — — (144.0) — Reinsurance to close transaction (for years of account 2017 and prior) (5) — — — (219.7) Retroactive reinsurance (6) — 21.7 — — Change in participation interest (7) — — 34.3 8.4 Total net reserve adjustments — 5.2 (1,060.1) (211.3) Foreign exchange adjustments 3.6 1.0 (17.4) (17.0) Net reserves - end of period 2,747.1 2,734.6 2,213.1 3,123.2 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 2,797.4 2,791.8 2,838.5 2,471.8 Gross reserves - end of period $ 5,544.5 $ 5,526.4 $ 5,051.6 $ 5,595.0 (1) For the period ended November 15, 2023, the adjustment relates to the year-to-date activity of Syndicate 1200 and on reinsurance contracts with AUA subsidiaries. Refer to the sale of Argo Underwriting Agency Limited in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. For the period ended December 31, 2022, refer to the sale of Argo Seguros and AGSE in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (2) Refer to the sale of Argo Underwriting Agency Limited in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. Additionally, the Company reduced net reserves in the amount of $129.6 million for reinsurance contracts with AUA subsidiaries, which were reclassified to held-for-sale. (3) Loss portfolio transfer of the Company’s U.S. casualty insurance reserves for accident years 2011 to 2019. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (4) Loss portfolio transfer on Syndicate 1200's reserves for the 2018 and 2019 years of account. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (5) Amount represents reserves ceded under the reinsurance to close transaction with RiverStone for Lloyd’s years of account 2017 and prior, effective January 1, 2021. (6) In connection with the sale of AUA, the Company entered into two retroactive reinsurance agreements with AUA subsidiaries. (7) Amount represents the change in reserves due to changing our participation in Syndicates 1200 and 1910. 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 Company did not incur net losses and loss adjustment expenses attributed to the COVID-19 pandemic for the year ended December 31, 2023 and December 31, 2022. Underwriting results for the years ended December 31, 2021 included net losses and loss adjustment expenses attributed to the COVID-19 pandemic of $12.4 million, primarily resulting from contingency and property exposures in the Company’s International Operations. Property losses relate to sub-limited affirmative business interruption coverage, primarily in certain International markets, as well as expected costs associated with claims handling. The impact from the net unfavorable (favorable) development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: Predecessor Period from For the Years Ended December 31, (in millions) January 1, 2023 through November 15, 2023 2022 2021 U.S. Operations $ 246.3 $ 64.5 $ 120.9 International Operations 21.4 (2.7) (26.9) Run-off Lines 0.2 2.9 44.3 Total (favorable) unfavorable prior-year development $ 267.9 $ 64.7 $ 138.3 The Company did not recognize any development of prior accident years’ losses and LAE reserves for the period November 16, 2023 through December 31, 2023 (Successor). The following describes the primary factors behind each segment’s net prior accident year reserve development for the period for January 1, 2023 through November 15, 2023 (Predecessor), and years ended December 31, 2022 and 2021: Period ended January 1, 2023 through November 15, 2023 (Predecessor): • U.S. Operations: Net unfavorable development primarily related to liability lines and professional lines, including the impact of large losses partially offset by favorable development in specialty lines. The liability lines movement was largely due to businesses we have exited. The professional lines movement largely impacted accident years 2019 through 2021. • International Operations: Net unfavorable development primarily related to unfavorable development in professional and liability lines in Argo Insurance Bermuda. • Run-off Lines: Net unfavorable development primarily related to asbestos and environmental lines largely offset by favorable loss reserve development in run-off workers compensation and liability losses excluding asbestos and environmental. Year ended December 31, 2022: • U.S. Operations: Net unfavorable development primarily related to liability lines, including the impact of large losses and claims alleging construction defect, and driven by businesses we have exited, partially offset by favorable development in specialty and professional lines. The net unfavorable prior year development relates to accident years 2019 and prior partially offset by favorable prior year development on accident years 2020 and 2021. • International Operations: Net favorable development primarily related to favorable development in liability and specialty lines, partially offset by unfavorable development from professional and property lines. The professional lines development included large claim movements in Argo Insurance Bermuda. • Run-off Lines: Net unfavorable development primarily related to asbestos and environmental lines partially offset by favorable loss reserve development in run-off liability losses excluding asbestos and environmental. Year ended December 31, 2021: • U.S. Operations: Net unfavorable development in liability and professional lines, partially offset by favorable development in specialty. The liability lines and professional lines prior-year development was largely due to movements in the fourth quarter of 2021. The liability lines movement was largely due to actual incurred loss movements greater than the expected movements in business units with significant exposure to claims alleging construction defect ($112.1 million of prior year development), driven by accident years 2017 and prior. The professional lines movement was driven by evaluations of individual management liability claims. The professional lines prior-year development of $33.0 million was driven by accident years 2018 and prior. • International Operations: Net favorable development primarily related to favorable development in liability and property lines, partially offset by unfavorable development in Argo Insurance Bermuda. The unfavorable movement in Argo Insurance Bermuda was driven by liability and professional losses. • Run-off Lines: Net unfavorable loss reserve development in run-off liability lines, including asbestos and environmental lines, and risk management workers compensation. The movement on liability exposures excluding asbestos and environmental was due to analysis of individual claims. The exposures driving the change were largely the result of claims alleging abuse. A large portion of the change was due to defense costs. The movement on asbestos and environmental lines was due to higher than expected loss activity and movements on large claims alleging environmental losses. Our reserves represent the best estimate of our ultimate liabilities, based on currently known facts, current law, 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. Actuarial models base future emergence on historic experience, with adjustments for current trends, and the appropriateness of these assumptions involved more uncertainty as of December 31, 2023. We expect there will be impacts to the timing of loss emergence and ultimate loss ratios for certain coverages we underwrite. The industry is experiencing new issues, including the temporary suspension of civil court cases in most states, the extension of certain statutes of limitations and the impact on our insureds from a significant reduction in economic activity. Our booked reserves include consideration of these factors, but legislative, regulatory or judicial actions could result in loss reserve deficiencies and reduce earnings in future periods. Short-Duration Contract Disclosures Our basis for disaggregating short-duration contracts is by each of our two ongoing reporting segments, U.S. Operations and International Operations, with International Operations further disaggregated by operating divisions. We have chosen to disaggregate the data in this way so as to not obscure useful information by otherwise aggregating items with significantly different characteristics. See Note 19, “Segment Information,” for additional information regarding our two ongoing reporting segments. Operating Divisions Our U.S. Operations reporting segment is comprised of one primary operating division (see Note 19, “Segment Information” for additional information on U.S Operations). International Operations’ primary operating division is Argo Insurance Bermuda, further described below. Argo Insurance Bermuda Argo Insurance Bermuda offers casualty, property and professional lines, which serves the needs of global clients by providing the following coverages: property, general and products liability, directors and officers liability, errors and omissions liability and employment practices liability. Lines of Business We use an underwriting committee structure to monitor and evaluate the operating performance of our lines of business. The underwriting committees are organized to allow products or coverages with similar characteristics to be managed and evaluated in distinct groups. Using this approach, our insurance business is categorized into underwriting groups, which are Property, Liability, Professional, and Specialty. Noted below are descriptions of the types of characteristics considered to disaggregate our business into these groups, as well as other qualitative factors to consider when using the information contained in the following incurred and paid claims development tables. Property Property losses are generally reported within a short period of time from the date of loss, and in most instances, property claims are settled and paid within a relatively short timeframe. However, Property can be impacted by catastrophe losses which can be more complex than non-catastrophe Property claims due to factors such as difficulty accessing impacted areas and other physical, legal and regulatory impediments potentially extending the period of time it takes to settle and pay claims. Liability Our Liability business generally covers exposures where most claims are reported without a significant time lag between the event that gives rise to a claim and the date the claim is reported to us, but certain claims like those alleging construction defect can involve a longer time period between the event and the date the claim is reported to us. Since facts and information are frequently not complete at the time claims are reported to us, and because protracted litigation is sometimes involved, it can be several years before the ultimate value of these claims is determined. In our Argo Bermuda Insurance division, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Professional Much of our Professional business is written on a claims-made basis resulting in coverage only for claims that are reported to us during the year in which the policy is effective, thus reducing the number of claims that will become known to us after the end of the policy expiration date. However, facts and information are frequently not complete at the time claims are reported to us, and protracted litigation is sometimes involved. It can be several years before the ultimate value of these claims is determined. In our Argo Bermuda Insurance division, much of the business covers higher layers, potentially increasing the time it takes to fully determine our exposure. Specialty Specialty lines losses are generally reported within a short period of time from the date of loss, and in most instances, Specialty lines claims are settled and paid within a relatively short timeframe. However, Specialty lines can be impacted by larger losses where facts and information are frequently not complete at the time claims are reported to us. These large losses can be more complex than smaller Specialty claims due to factors such as difficulty determining actual damages and other physical, legal and regulatory impediments potentially extending the period of time it takes to settle and pay claims. Descriptions of the primary types of coverages, as disclosed in the following tables, included in the significant lines of business for each operating division are noted below: U.S Operations • Liability: primary and excess specialty casualty, construction defect, general liability, commercial multi-peril, workers compensation, product liability, environmental liability, and auto liability • Professional: management liability, transaction liability and errors and omissions liability • Property: primary and excess property, inland marine and auto physical damage • Specialty: surety, animal mortality and ocean marine Argo Insurance Bermuda • Liability : general and products liability • Professional : directors and officers liability, errors and omissions liability and employment practices liability • Property: a wide range of commercial, industrial and residential property Run-off Lines Segment We have a Run-off Lines segment for certain products that we no longer underwrite, including asbestos and environmental claims. We have excluded the Run-off Lines segment from the following disaggregated short-duration contract disclosures due to its insignificance to our consolidated financial position and results of operations, both quantitatively and qualitatively. Gross reserves for losses and LAE in Run-off Lines account for less than 4% of our consolidated gross reserves for losses and LAE, and are primarily related to accident years prior to the mid-1990s. As such, claims development tables for the most recent ten Run-off Lines ,” for further information on this segment, including discussion of prior accidents years’ development. Loss Portfolio Transfers On August 8, 2022, the Company entered into a loss portfolio transfer agreement with a wholly-owned subsidiary of Enstar covering a majority of the Company’s U.S. casualty insurance reserves, including construction, for accident years 2011 to 2019. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information on the U.S. loss portfolio transfer. The activity in the claims development table includes the impact of this agreement. Reserves for IBNR Claims Reserves for IBNR claims are based on the estimated ultimate cost of settling claims, including the effects of inflation and other social and economic factors, using past experience adjusted for current trends and any other factors that would modify past experience. We use a variety of actuarial techniques to analyze current claims costs, including frequency and severity data. These actuarial techniques consider variables such as past loss experience, current claims trends, and prevailing economic, social and legal environments. Each such method has its own set of assumptions and outputs, and each has strengths and weaknesses in different areas. Since no single estimation method is superior to another method in all situations, the methods and assumptions used to project loss reserves will vary by coverage and product. We use what we believe to be the most appropriate set of actuarial methods and assumptions for each product line grouping and coverage. While the loss projection methods may vary by product line and coverage, the general approach for calculating IBNR remains the same: ultimate losses are forecasted first, and that amount is reduced by the amount of cumulative paid claims and case reserves. Reserves established in prior years are adjusted as loss experience develops and new information becomes available. Adjustments to previously estimated reserves are reflected in the results of operations in the year in which they are made. As described above, various actuarial methods are used to determine the reserves for losses and LAE recorded in our Consolidated Balance Sheets. Weightings of methods at a detailed level may change from evaluation to evaluation based on a number of observations, measures, and time elements. In comparing loss reserve methods and assumptions used at December 31, 2023 as compared with methods and assumptions used at December 31, 2022, management has not changed or adjusted methodologies or assumptions in any significant manner. Incurred & Paid Claims Development Disclosures The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2023. Reporting Segment: U.S. Operations Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 328.6 $ 337.1 $ 330.0 $ 326.3 $ 323.9 $ 321.9 $ 327.4 $ 341.3 $ 310.7 $ 312.1 2015 339.8 343.8 330.3 328.7 328.0 335.4 347.9 318.9 321.5 2016 342.6 350.5 342.4 353.0 355.3 379.0 349.1 354.5 2017 374.8 373.7 384.3 397.7 431.7 385.2 391.2 2018 426.1 430.4 414.5 420.4 366.5 390.7 2019 421.1 423.7 427.1 318.6 353.1 2020 404.2 386.7 371.1 433.9 2021 416.4 419.1 461.2 2022 439.5 466.9 2023 435.8 Total $ 3,920.9 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 32.4 $ 91.0 $ 154.6 $ 206.9 $ 240.6 $ 266.3 $ 283.2 $ 291.4 $ 304.4 $ 305.8 2015 33.7 86.9 140.2 195.6 236.4 263.9 289.3 305.6 307.2 2016 28.5 84.5 144.1 217.1 255.6 293.8 327.1 331.8 2017 27.8 83.0 158.8 238.5 295.2 348.0 354.2 2018 34.3 98.9 175.8 245.5 315.9 335.7 2019 32.4 113.6 186.1 260.1 290.6 2020 25.6 85.9 149.0 228.7 2021 27.5 83.1 164.8 2022 27.2 92.0 2023 22.4 Total $ 2,433.2 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 58.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 1,546.4 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 312.1 $ (7.0) 22,319 2015 321.5 (1.3) 20,936 2016 354.5 4.9 18,105 2017 391.2 0.1 20,982 2018 390.7 6.1 23,539 2019 353.1 (4.2) 22,976 2020 433.9 115.1 18,812 2021 461.2 211.7 15,248 2022 466.9 291.5 13,729 2023 435.8 361.0 10,514 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 22.4 $ 22.4 $ 26.0 $ 33.7 $ 36.2 $ 35.4 $ 35.1 $ 34.4 $ 32.7 $ 32.7 2015 29.9 29.5 33.2 34.0 37.1 37.9 38.3 31.3 31.3 2016 44.2 44.8 45.1 42.9 35.5 43.0 43.5 46.1 2017 60.1 61.8 78.3 87.9 99.5 87.0 87.3 2018 70.8 73.2 79.2 94.8 88.5 87.8 2019 94.4 96.8 105.0 94.5 117.7 2020 152.6 142.6 127.8 160.0 2021 177.8 159.5 159.6 2022 185.4 169.1 2023 164.0 Total 1,055.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 2.3 $ 5.4 $ 15.1 $ 24.1 $ 25.5 $ 32.3 $ 33.3 $ 33.6 $ 33.5 $ 33.6 2015 1.8 8.3 15.6 20.8 26.2 31.3 31.7 33.8 33.8 2016 2.4 11.9 24.6 28.9 30.8 34.4 38.3 43.5 2017 3.5 24.9 38.0 59.7 77.9 85.5 85.5 2018 4.5 16.7 43.8 62.6 78.8 79.7 2019 4.9 32.9 50.0 81.7 92.9 2020 13.3 36.4 70.5 81.6 2021 12.2 39.6 54.7 2022 14.3 25.7 2023 4.1 Total $ 535.1 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 11.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 532.0 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 32.7 $ (0.8) 1,044 2015 31.3 (2.5) 1,832 2016 46.1 2.2 3,264 2017 87.3 (9.7) 3,774 2018 87.8 (3.7) 4,298 2019 117.7 15.4 4,901 2020 160.0 41.6 5,012 2021 159.6 68.4 5,153 2022 169.1 122.1 5,120 2023 164.0 141.8 4,396 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Property (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 80.4 $ 82.2 $ 77.0 $ 77.1 $ 76.9 $ 76.9 $ 76.1 $ 76.0 $ 76.1 $ 74.8 2015 74.0 73.4 69.9 68.9 69.1 69.2 69.2 68.4 67.8 2016 59.4 57.6 57.1 56.6 56.6 56.5 54.2 54.4 2017 75.2 79.6 86.9 94.9 94.5 97.4 91.3 2018 89.2 93.1 95.1 96.9 102.4 101.1 2019 91.4 88.8 98.4 97.9 90.3 2020 129.5 133.2 133.1 134.0 2021 111.7 114.8 116.7 2022 103.1 104.4 2023 94.7 Total $ 929.5 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 51.6 $ 73.1 $ 75.7 $ 76.4 $ 76.3 $ 76.4 $ 76.1 $ 76.0 $ 76.0 $ 76.0 2015 44.6 67.6 68.6 67.9 68.3 68.5 69.0 68.6 68.6 2016 39.4 55.2 55.8 56.1 56.4 56.3 54.5 54.5 2017 54.4 95.3 113.9 100.8 88.4 95.1 90.5 2018 61.3 126.7 107.0 98.8 101.4 102.5 2019 55.8 82.4 90.9 94.0 96.0 2020 75.9 116.6 121.6 126.6 2021 71.3 118.3 118.2 2022 52.2 94.7 2023 59.1 Total 886.7 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 0.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 43.3 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 74.8 $ (1.2) 8,057 2015 67.8 (0.8) 7,362 2016 54.4 (0.1) 7,701 2017 91.3 (2.6) 9,930 2018 101.1 (4.3) 10,881 2019 90.3 (6.9) 11,496 2020 134.0 (6.4) 11,379 2021 116.7 (5.8) 10,312 2022 104.4 2.6 9,119 2023 94.7 16.2 7,707 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Specialty (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 13.1 $ 13.1 $ 8.9 $ 6.0 $ 4.8 $ 4.6 $ 4.6 $ 4.1 $ 4.1 $ 4.1 2015 14.8 14.3 9.5 5.5 1.2 0.5 0.3 0.2 0.2 2016 15.0 15.0 11.2 6.2 4.7 3.3 3.2 2.8 2017 16.2 16.2 7.6 0.9 0.7 0.7 0.6 2018 20.9 17.4 3.3 3.5 3.5 3.3 2019 22.7 8.5 5.6 5.9 5.8 2020 25.4 10.3 15.9 15.0 2021 27.9 5.2 2.0 2022 33.0 28.9 2023 34.6 Total $ 97.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 1.1 $ 3.3 $ 4.0 $ 4.0 $ 4.1 $ 4.1 $ 4.0 $ 4.1 $ 4.1 $ 4.1 2015 0.2 0.1 0.2 0.3 0.3 0.3 0.3 0.2 0.2 2016 1.3 1.6 2.2 2.2 2.2 2.8 2.8 2.8 2017 0.3 0.1 — 0.1 0.2 0.2 0.2 2018 — 0.7 1.7 1.2 2.4 2.9 2019 0.7 0.7 3.2 5.4 5.2 2020 0.3 7.6 10.6 10.5 2021 0.2 1.4 1.6 2022 0.1 13.4 2023 1.1 Total 42.0 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 0.6 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 55.9 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 4.1 $ — 20 2015 0.2 — 14 2016 2.8 0.1 46 2017 0.6 0.4 62 2018 3.3 0.3 82 2019 5.8 0.1 124 2020 15.0 — 274 2021 2.0 0.3 291 2022 28.9 5.6 257 2023 34.6 33.1 175 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 9.8 $ 9.8 $ 9.8 $ 6.2 $ 1.5 $ 2.3 $ 2.3 $ 1.6 $ 1.6 $ 1.6 2015 11.3 14.3 24.8 35.4 45.4 45.1 51.3 50.3 50.3 2016 13.9 14.0 14.0 6.6 6.1 0.8 2.4 6.5 2017 17.1 17.3 26.9 30.3 37.3 44.3 46.2 2018 8.9 32.1 26.6 24.2 22.9 19.8 2019 13.3 13.6 13.8 13.3 13.3 2020 23.3 24.9 12.4 12.4 2021 12.3 11.4 12.4 2022 11.1 11.1 2023 12.7 Total $ 186.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ — $ — $ 0.1 $ 0.1 $ 1.2 $ 1.2 $ 1.4 $ 1.4 $ 1.4 $ 1.4 2015 — — 16.1 20.3 26.6 34.8 38.9 50.2 50.3 2016 — — — 0.1 0.1 0.2 0.3 0.3 2017 — 3.3 3.4 18.0 19.7 22.0 27.6 2018 — 13.8 18.3 18.5 18.5 19.1 2019 — 0.1 0.7 0.6 0.9 2020 0.8 7.0 0.5 0.6 2021 — — 0.3 2022 — — 2023 — Total $ 100.5 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 2.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 88.3 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 1.6 $ (0.4) 1,361 2015 50.3 — 1,629 2016 6.5 6.0 1,969 2017 46.2 7.8 2,176 2018 19.8 0.4 1,159 2019 13.3 12.4 1,254 2020 12.4 7.0 1,434 2021 12.4 6.2 1,436 2022 11.1 11.1 1,293 2023 12.7 12.5 1,519 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 4.0 $ 4.0 $ 4.0 $ 4.0 $ 3.9 $ 10.2 $ 12.5 $ 8.1 $ 10.1 $ 10.1 2015 4.9 4.9 4.9 2.7 5.0 5.2 7.3 7.9 5.2 2016 6.7 6.7 4.8 3.1 7.3 3.1 1.9 3.8 2017 7.6 7.6 9.7 9.5 12.4 10.5 15.3 2018 8.3 8.3 8.0 6.5 21.3 36.8 2019 9.6 8.7 16.4 18.3 18.1 2020 10.4 10.4 10.4 11.1 2021 13.0 13.0 12.3 2022 9.5 9.4 2023 15.9 Total $ 138.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ — $ — $ — $ 0.3 $ 1.0 $ 0.4 $ 3.2 $ 0.4 $ 0.4 $ 0.4 2015 — — — — — — 2.9 2.9 4.0 2016 — — — — — — — 0.1 2017 0.1 0.1 4.9 9.8 9.8 9.8 9.9 2018 — — 2.0 2.1 6.0 6.1 2019 2.0 0.6 0.6 0.7 0.7 2020 — — — 6.1 2021 — — — 2022 — — 2023 — Total 27.3 Other Property outstanding liabilities including unpaid loss and AL

Run-off Lines

Run-off Lines	12 Months Ended
	Dec. 31, 2023
Discontinued Operations and Disposal Groups [Abstract]
Run-off Lines	Run-off Lines We have discontinued active underwriting of certain lines of business, including those lines that were previously recorded in Argo Group’s risk-management segment. All current activity within these lines is related to the management of claims and other administrative functions. Also included in Run-off Lines are other liability reserves, which include exposure to claims for asbestos and environmental liabilities written in past years. The other liability reserves are often characterized by long elapsed periods between the occurrence of a claim and ultimate payment to resolve the claim. We use a specialized staff dedicated to administer and settle these claims. The following table presents our gross reserves for Run-off Lines: December 31, (in millions) 2023 2022 Asbestos and Environmental: Reinsurance assumed $ 30.4 $ 31.1 Other 29.0 34.4 Total Asbestos and Environmental 59.4 65.5 Risk-management 119.0 144.6 Run-off reinsurance lines 0.4 0.4 Other run-off lines 17.3 22.6 Gross reserves - Run-off Lines $ 196.1 $ 233.1 We have received asbestos and environmental liability claims arising from other liability coverage primarily written in the 1960s, 1970s and into the early 1980s. Asbestos and environmental claims originate from policies directly underwritten by us and from reinsurance assumed during this period, including a portion assumed from the London market. Reserves for other run-off lines relate to other liability coverage primarily written in the 1970’s, with recent claim activity relating to abuse claims. The following table represents the total gross reserves for our asbestos exposure: December 31, (in millions) 2023 2022 2021 Direct written Case reserves $ 2.9 $ 3.2 $ 3.0 Unallocated loss adjustment expense 0.5 0.5 0.5 Incurred but not reported 14.3 17.4 19.9 Total direct written reserves 17.7 21.1 23.4 Assumed domestic Case reserves 7.6 6.8 7.4 Unallocated loss adjustment expense 0.8 0.8 0.8 Incurred but not reported 11.6 13.0 11.9 Total assumed domestic reserves 20.0 20.6 20.1 Assumed London Case reserves 2.8 2.4 2.1 Incurred but not reported 0.1 2.6 2.3 Total assumed London reserves 2.9 5.0 4.4 Total asbestos reserves $ 40.6 $ 46.7 $ 47.9 The following table presents our underwriting losses for Run-off Lines: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Asbestos and Environmental: Reinsurance assumed $ — $ — $ 3.5 $ 4.7 Other 0.3 1.2 7.0 10.0 Total Asbestos and Environmental 0.3 1.2 10.5 14.7 Risk-management — — 1.4 9.9 Run-off reinsurance lines — — — — Other run-off lines 0.4 2.0 (8.3) 20.1 Total underwriting loss - Run-off Lines $ 0.7 $ 3.2 $ 3.6 $ 44.7 Reserves for asbestos and environmental claims cannot be estimated with traditional loss reserving techniques that rely on historical accident year loss development factors. The uncertainty in the asbestos and environmental reserves estimates arises from several factors including lack of actuarially credible historical data, inapplicability of standard actuarial projection techniques, uncertainty with regards to claim costs, coverage interpretations and judicial, statutory and regulatory provisions under which the claims may be ultimately resolved. It is impossible to predict how the courts will interpret coverage issues and these resolutions may have a material impact on the ultimate resolution of the asbestos and environmental liabilities. We use a variety of estimation methods to calculate reserves as a whole; however, reserves for asbestos and environmental claims were determined using a variety of methods which rely on historical claim reporting and average claim cost information. We apply greatest weight to the method that projects future calendar period claims and average claim costs because it best captures the unique claim characteristics of our underlying exposures. Although management has recorded its best estimate of loss reserves, due to the uncertainties of estimation of liability that may arise as discussed herein, further deterioration of claims could occur in the future.

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Long-term Debt	Long-term Debt The Company recorded its debt at its fair value as of November 16, 2023 due to push-down accounting which included a discount rate to the total principal amount. The discount is being amortized to Interest expense in our Consolidated Statements of Income (Loss) using the effective yield method over the remaining period of the underlying debt obligations. Senior Unsecured Fixed Rate Notes In September 2012, Argo Group (the “Parent Guarantor”), through its subsidiary Argo Group US (the “Subsidiary Issuer”), issued $143.8 million aggregate principal amount of the Subsidiary Issuer’s 6.5% Senior Notes due September 15, 2042 (the “Notes”). The Notes are unsecured and unsubordinated obligations of the Subsidiary Issuer and rank equally in right of payment with all of the Subsidiary Issuer’s other unsecured and unsubordinated debt. The Notes are guaranteed on a full and unconditional senior unsecured basis by the Parent Guarantor. The Notes may be redeemed, for cash, in whole or in part, on or after September 15, 2017, at the Subsidiary Issuer’s option, at any time and from time to time, prior to maturity at a redemption price equal to 100% of the principal amount of the Notes to be redeemed, plus accrued but unpaid interest on the principal amount being redeemed to, but not including, the redemption date. In accordance with ASU 2015-3, “Simplifying the Presentation of Debt Issuance Costs” (Topic 835), we present the unamortized debt issuance costs in the balance sheet as a direct deduction from the carrying value of the debt liability. At December 31, 2023 and 2022, the Notes consisted of the following: (in millions) December 31, 2023 December 31, 2022 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs and fair value adjustment (15.8) (3.3) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 128.0 $ 140.5 Junior Subordinated Debentures Through a series of trusts, that are wholly-owned subsidiaries (non-consolidated), we issued debt. The debentures are variable with the rate being reset quarterly and subject to certain interest rate ceilings. Interest payments are payable quarterly. The debentures are all unsecured and are subordinated to other indebtedness. At December 31, 2023 and 2022, all debentures were eligible for redemption subject to certain terms and conditions at a price equal to 100% of the principal plus accrued and unpaid interest. A summary of our outstanding junior subordinated debentures is presented below: December 31, 2023 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2023 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M SOFR + TSA + 4.10% 9.74% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M SOFR + TSA + 3.90% 9.49% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M SOFR + TSA + 4.10% 9.74% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M SOFR + TSA + 4.10% 9.76% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M SOFR + TSA + 3.85% 9.49% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M SOFR + TSA + 3.85% 9.49% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M SOFR + TSA + 3.80% 9.47% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M SOFR + TSA + 3.60% 9.25% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M SOFR + TSA + 3.55% 9.18% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M SOFR + TSA + 3.60% 9.25% 15.5 9/15/2005 Argonaut Group Statutory Trust X 9/15/2035 3M SOFR + TSA + 3.40% 9.05% 30.9 Less: fair value adjustment (11.9) Total Outstanding $ 160.8 December 31, 2022 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2022 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 8.71% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 8.63% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 8.71% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 8.18% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 8.50% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 8.61% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 8.54% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 8.37% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 8.30% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 8.37% 15.5 9/15/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 8.17% 30.9 Total Outstanding $ 172.7 Junior Subordinated Debentures from Maybrooke Acquisition Unsecured junior subordinated debentures with a principal balance of $91.8 million were assumed through the acquisition of Maybrooke (“the acquired debt”). The acquired debt is carried on our Consolidated Balance Sheets at $80.4 million, which represents the debt’s fair value as of November 16, 2023 as required by accounting for business combinations under ASC 805. At December 31, 2023, the acquired debt was eligible for redemption at par. Interest accrues on the acquired debt based on a variable rate, which is reset quarterly. Interest payments are payable quarterly. A summary of the terms of the acquired debt outstanding is presented below: (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2023 Principal at December 31, 2023 Carrying Value at December 31, 2023 9/13/2007 9/15/2037 3M SOFR + TSA + 3.15% 8.79 % $ 91.8 $ 80.4 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2022 Principal at December 31, 2022 Carrying Value at December 31, 2022 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 7.92 % $ 91.8 $ 85.9 Other Indebtedness The following table presents interest and maturities of long-term debt as of December 31, 2023: For the Years Ended (in millions) Total 2024 2025 2026 2027 2028 Thereafter Long-term debt: Junior subordinated debentures (1) 548.3 24.6 24.6 24.6 24.6 24.6 425.3 Senior unsecured fixed rate notes (2) 316.5 9.3 9.3 9.3 9.3 9.3 270.0 (1) Interest only on Junior Subordinated Debentures through 2037. Interest calculated based on interest rate forecast. Principal due beginning May 2033. (2) Interest only on Senior Unsecured Fixed Rate Notes through 2042. Interest calculated based on the fixed rate of the notes. Principal due September 2042. Borrowing Under Revolving Credit Facility On November 2, 2018, each of Argo Group, Argo Group US, Argo International Holdings Limited, and AUA, collectively (the “Borrowers”) entered into a new $325 million credit agreement (the “Credit Agreement”) with JPMorgan Chase Bank, N.A., as administrative agent. The Credit Agreement includes a one-time borrowing of $125 million for a term loan (the “Term Loan”), and a $200 million revolving credit facility. The Company used most of the net proceeds from the Preferred Stock Offering (as defined in Note 11, “Stockholders’ Equity”) to pay off the Term Loan in September 2020. The Credit Agreement was subsequently amended to increase the revolving credit facility amount to $220 million, and to provide the removal of AIH and AUA as Borrowers upon the sale of AIH and AUA, which occurred on February 2, 2023. During July 2023, the Credit Agreement was amended to permit the acquisition of Argo Group by Brookfield Reinsurance Ltd. pursuant to the Merger Agreement and extend the maturity date of certain commitments under the revolving credit facility from November 2, 2023 to November 2, 2024. The Credit Agreement decreased from $220 million to $200 million effective November 2, 2023. Borrowings under the Credit Agreement may be used for general corporate purposes, including working capital, permitted acquisitions and letters of credit, and each of the Borrowers has agreed to be jointly and severally liable for the obligations of the other Borrowers under the Credit Agreement. The Credit Agreement contains customary events of default. If an event of default occurs and is continuing, the Borrowers could be required to immediately repay all amounts outstanding under the Credit Agreement. The lenders could elect to accelerate the maturity of the loans and/or terminate the commitments under the Credit Agreement upon the occurrence and during the continuation of an event of default. No defaults or events of defaults have occurred as of the date of this filing. The Credit Agreement allows 100% of the revolving credit facility to be used for letters of credit, subject to availability. At December 31, 2023 and 2022, there were $0.1 million and $0.3 million of letters of credit, respectively, issued against the Credit Facility. Letter of Credit Facilities - Argo Re Argo Re may be required to secure its obligations under various reinsurance contracts in certain circumstances. In order satisfy these requirements, Argo Re has entered into one committed and two uncommitted secured bilateral letters of credit facilities with commercial banks and generally uses these facilities to issue letters of credit in support of non-admitted reinsurance obligations in the U.S. and other jurisdictions. The committed letters of credit facility has a term of one year and includes customary conditions and event of default provisions. The issuance of letters of credit using the uncommitted letters of credit facilities is at the discretion of the lenders. The availability of letters of credit under these secured facilities are subject to a borrowing base requirement, determined on the basis of specified percentages of the market value of eligible categories of securities pledged to the lender. On December 31, 2023, committed and uncommitted letters of credit facilities totaled $165.0 million. On December 31, 2023, letters of credit totaling $62.0 million were outstanding, of which $27.0 million were issued against the committed, secured bilateral letters of credit facility and $35.1 million were issued by commercial banks against the uncommitted, secured bilateral letters of credit facilities. Collateral with a market value of $109.2 million was pledged to these banks as security against these letters of credit. In addition to the bilateral, secured letters of credit facilities described above, Argo Re can use other forms of collateral to secure these reinsurance obligations including trust accounts, cash deposits, letters of credit issued by commercial banks on an uncommitted basis and the Credit Agreement. On June 22, 2022, we posted collateral in the form of a $50.0 million letter of credit under the terms of the Malta sales agreement. The letter of credit is subject to reimbursement by Argo in the event of a drawdown. Other Letters of Credit Other letters of credit issued and outstanding on December 31, 2023 were $4.3 million.

Disclosures about Fair Value of

Disclosures about Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2023
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 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 their short term nature. Debt. At December 31, 2023 and 2022, the fair value of our debt instruments is determined using both Level 1 and Level 2 inputs, as previously defined in Note 3, “Investments”. We receive fair value prices from third-party pricing services for our financial instruments as well as for similar financial instruments. 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 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 December 31, 2023 and December 31, 2022. 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 and Floating Rate Loan Stock Level 2: • Our trust preferred debentures, subordinated debentures and floating rate loan stock 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: December 31, 2023 2022 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 160.8 $ 165.9 $ 172.7 $ 165.8 Subordinated debentures 80.4 83.3 85.9 88.1 Total junior subordinated debentures 241.2 249.2 258.6 253.9 Senior unsecured fixed rate notes 128.0 132.7 140.5 112.7 Floating rate loan stock (1) — — 54.7 52.5 $ 369.2 $ 381.9 $ 453.8 $ 419.1 (1) Floating rate loan stock reclassified to liabilities held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. Based on an analysis of the inputs, our financial instruments measured at fair value on a recurring basis have been categorized as follows: 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 Fair Value Measurements at Reporting Date Using (in millions) December 31, 2022 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 165.8 $ — $ 165.8 $ — Subordinated debentures 88.1 — 88.1 — Total junior subordinated debentures 253.9 — 253.9 — Senior unsecured fixed rate notes 112.7 112.7 — — Floating rate loan stock 52.5 — 52.5 — $ 419.1 $ 112.7 $ 306.4 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock At December 31, 2023, we have issued and outstanding 6,000 shares of our preferred stock (equivalent to 6,000,000 depositary shares, each representing a 1/1,000th interest in a share of preferred stock) with a $25,000 liquidation preference per share (equivalent to $25 per depositary share) (the “Preferred Stock Offering”). Dividends to the holders of the preferred stock will be payable on a non-cumulative basis only when, as and if declared by our Board of Directors (the “Board”) or a duly authorized committee thereof, quarterly in arrears on the 15th of March, June, September, and December of each year, commencing on September 15, 2020, at a rate equal to 7.00% of the liquidation preference per annum (equivalent to $1,750 per share of preferred stock and $1.75 per depositary share per annum) up to but excluding September 15, 2025. Beginning on September 15, 2025, any such dividends will be payable on a non-cumulative basis, only when, as and if declared by our Board or a duly authorized committee thereof, during each reset period, at a rate per annum equal to the Five-Year U.S. Treasury Rate as of the most recent reset dividend determination date (as described in the Company’s prospectus supplement dated July 7, 2020) plus 6.712% of the liquidation preference per annum. So long as any shares of preferred stock remain outstanding, unless dividends on all outstanding shares of preferred stock payable on a dividend payment date have been declared and paid or provided for in full, (1) no dividend shall be paid or declared on our shares of common stock or any other junior shares or any parity shares, other than a dividend payable solely in our shares of common stock, other junior shares or (solely in the case of parity shares) other parity shares, as applicable, and (2) no shares of common stock, other junior shares or parity shares shall be purchased, redeemed or otherwise acquired for consideration by us, directly or indirectly (other than (i) as a result of a reclassification of junior shares for or into other junior shares, or a reclassification of parity shares for or into other parity shares, or the exchange or conversion of one junior share for or into another junior share or the exchange or conversion of one parity share for or into another parity share, (ii) through the use of the proceeds of a substantially contemporaneous sale of junior shares or (solely in the case of parity shares) other parity shares, as applicable, or (iii) as required by or necessary to fulfill the terms of any employment contract, benefit plan or similar arrangement with or for the benefit of one or more employees, directors or consultants), in each case, during the following dividend period. Upon any voluntary or involuntary liquidation, dissolution or winding-up of Argo Group holders of the preferred stock are entitled to receive out of our assets available for distribution to stockholders, before any distribution is made to holders of our shares of common stock or other junior shares, a liquidating distribution in the amount of $25,000 per share of common stock (equivalent to $25 per depositary share) plus the amount of declared and unpaid dividends, if any, to the date fixed for distribution, without interest on such unpaid dividends. Distributions will be made pro rata in accordance with the respective aggregate liquidation preferences of the preferred stock and any parity shares, and only to the extent of our assets, if any, that are available after satisfaction of all liabilities to creditors. Neither the depositary shares nor the underlying shares of preferred stock will be convertible into, or exchangeable for, shares of any other class or series of stock or other securities of Argo Group or our subsidiaries. Neither the depositary shares nor the underlying shares of preferred stock have a stated maturity or will be subject to any sinking fund, retirement fund, or purchase fund or other obligation of ours to redeem, repurchase or retire the depositary shares or the shares of preferred stock. We may redeem the shares of preferred stock at our option, in whole or in part, from time to time, on or after September 15, 2025, at a redemption price equal to $25,000 per share (equivalent to $25 per depositary share), plus the amount of declared and unpaid dividends, if any, without interest on such unpaid dividends. In addition, we may redeem the shares of preferred stock in specified circumstances relating to certain corporate, regulatory, rating agency or tax events; provided that no such redemption may occur prior to September 15, 2025 unless one of the redemption requirements is satisfied. The depositary shares will be redeemed only if and to the extent the related shares of preferred stock are redeemed by us. The shares of preferred stock will not have voting rights, except under limited circumstances. During 2023, our Board declared quarterly cash dividends totaling $1,750 on each share of our preferred stock, or $1.75 per depositary share, outstanding to our stockholders of record. We did not declare any cash dividends during the period November 16, 2023 through December 31, 2023. For the period January 1, 2023 through November 15, 2023 we declared cash dividends totaling $10.5 million to our preferred stockholders. We are authorized to issue 30 million shares of $1.00 par value preferred stock. As of December 31, 2023 and 2022, 6,000 shares of preferred stock were issued and outstanding. Common Stock On February 8, 2023, the Company entered into the Merger Agreement with Brookfield Reinsurance Ltd. and Merger Sub. As part of the Merger Agreement, the Company has agreed to suspend any dividends that would otherwise be declared and paid on the Company Shares during the period from the date of the Merger Agreement through the earlier of the closing of the transaction and the termination of the Merger Agreement. As of November 16, 2023, pursuant to the Merger Agreement, each share of common stock of the Company issued and outstanding immediately prior to the Merger was automatically canceled and converted into the right to receive an amount in cash equal to $30.00. As a result of the Merger, the Company’s new authorized share capital is 2,000,000,000 shares of common stock with a par value of $1.00 per share. All 1,056,638,730 outstanding shares are owned by BNRE Triangle Acquisition Inc. During 2022, our Board declared quarterly cash dividends totaling $1.24 on each share of common stock outstanding to our stockholders of record. For the year ended December 31, 2022, we paid cash dividends totaling $43.4 million to our common stockholders. During 2021, our Board declared quarterly cash dividends totaling $1.24 on each share of common stock outstanding. For the year ended December 31, 2021, we paid cash dividends totaling $43.9 million to our stockholders. On May 3, 2016, our Board authorized the repurchase of up to $150.0 million of our shares of common stock (“2016 Repurchase Authorization”). The 2016 Repurchase Authorization supersedes all the previous Repurchase Authorizations. As of December 31, 2022, availability under the 2016 Repurchase Authorization for future repurchases of our shares of common stock was $53.3 million. For the period January 1, 2023 through November 15, 2023 (Predecessor) and December 31, 2022, we did not repurchase any shares of common stock . The repurchase of common stock is also subject to the terms of our preferred stock, pursuant to which we may not (other than in limited circumstances) purchase, redeem or otherwise acquire our common stock unless the full dividends for the latest completed dividend period on all outstanding shares of our preferred stock have been declared and paid or provided for.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2023
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 periods November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Predecessor Balance, December 31, 2021 $ (35.3) $ 19.7 $ (7.1) $ (22.7) Other comprehensive loss before reclassifications (0.7) (347.2) (0.7) (348.6) Amounts reclassified from accumulated other comprehensive loss 31.8 34.4 — 66.2 Net current-period other comprehensive income (loss) 31.1 (312.8) (0.7) (282.4) Balance, December 31, 2022 (4.2) (293.1) (7.8) (305.1) Other comprehensive income before reclassifications 1.0 13.7 0.8 15.5 Amounts reclassified from accumulated other comprehensive loss — 22.1 — 22.1 Net current-period other comprehensive income 1.0 35.8 0.8 37.6 Balance, November 15, 2023 $ (3.2) $ (257.3) $ (7.0) $ (267.5) Successor Balance, November 16, 2023 — — — — Other comprehensive income before reclassifications 0.1 51.2 0.6 51.9 Amounts reclassified from accumulated other comprehensive income — (0.1) — (0.1) Net current-period other comprehensive income 0.1 51.1 0.6 51.8 Balance, December 31, 2023 $ 0.1 $ 51.1 $ 0.6 $ 51.8 The amounts reclassified from accumulated other comprehensive (loss) income shown in the above table have been included in the following captions in our Consolidated Statements of Income (Loss): Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Unrealized gains and losses on securities: Net realized investment and other losses (gains) (1) $ (0.1) $ 28.0 $ 43.6 $ (12.2) (Benefit) provision for income taxes — (5.9) (9.2) 4.2 Foreign currency translation adjustments: Net realized investment and other losses (gains) (2) — — 31.8 — Total, net of taxes $ (0.1) $ 22.1 $ 66.2 $ (8.0) (1) Net realized investment and other losses (gains) in the Predecessor periods include losses realized as a result of the Loss Portfolio Transfer - U.S. and the sale of Argo Underwriting Agency Limited. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (2) Foreign currency translation losses were realized as a result of the sale of Argo Seguros and AGSE in 2022. Refer to the sale of Argo Seguros and AGSE in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. 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.

Net (Loss) Income Per Common St

Net (Loss) Income Per Common Stock	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net (Loss) Income Per Common Stock	Net (Loss) Income Per Common Stock As a result of the Merger, all Argo Group common stock ceased to be traded on the New York Stock Exchange as of November 16, 2023. In accordance with ASC 260, Earnings Per Share , calculation of earnings per share is not required for entities whose publicly traded securities only include nonconvertible debt. For the Successor period of November 16, 2023 through December 31, 2023, the earnings per share calculation is not required. The following table presents the calculation of net (loss) income per shares of common stock on a basic and diluted basis for the Predecessor period: Predecessor Period from For the Years Ended December 31, January 1, 2023 through November 15, 2023 2022 2021 (in millions, except number of shares and per share amounts) Net income (loss) $ (210.4) $ (175.2) $ 6.7 Less: Preferred stock dividends 10.5 10.5 10.5 Net income (loss) attributable to common stockholders (220.9) (185.7) (3.8) Weighted average common stock outstanding - basic 35,166,679 34,980,608 34,816,160 Effect of dilutive securities: Equity compensation awards — — — Weighted average common stock outstanding - diluted 35,166,679 34,980,608 34,816,160 Net income (loss) per common stock: Basic $ (6.28) $ (5.31) $ (0.11) Diluted $ (6.28) $ (5.31) $ (0.11)

Share-based Compensation

Share-based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Share-based Compensation	Share-based Compensation The fair value method of accounting was used for share-based compensation plans. Under the fair value method, compensation cost is measured based on the fair value of the award at the measurement date and recognized over the requisite service period, less estimated forfeitures. We estimated forfeitures based on historical forfeitures patterns, thereby recognizing expense only for those awards that are expected to vest. The estimate of forfeitures was adjusted as actual forfeitures differed from our estimate, resulting in recognition of compensation expense only for those awards that actually vest. In conjunction with the Merger, the vesting of all outstanding restricted share awards were accelerated and converted to cash at $30 per share in accordance with the Merger Agreement, contributing $2.2 million to the purchase price. The performance shares were evaluated to determine the assumed level of performance. As a result of this evaluation, 5,031 shares were converted to cash at $30 per share, resulting in $0.1 million being included as part of the purchase price. Total expense for all share-based payment compensation agreements totaled $4.3 million, with $1.5 million being reported as Underwriting, acquisition and general expenses in the Predecessor period and $2.8 million being included in Non-operating expenses in the Consolidated Statements of Income (Loss) in the Successor period. The non-operating expense classification represents the expense recorded on the acceleration of non-vested share awards as a result of the Merger. We present all tax benefits resulting from the exercise of stock options and vesting of non-vested shares as cash flows from operating activities. Excess tax benefits are realized tax benefits from tax deductions for exercised options and vested shares in excess of the deferred tax asset attributable to stock compensation costs for such options. Such tax benefits and cash flows were immaterial for all reporting periods. Performance Shares We issued to certain key employees non-vested restricted stock awards whose vesting is subject to the achievement of certain performance measures. The non-vested performance share awards generally vest over one A summary of non-vested performance share activity as of December 31, 2023 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2023 124,974 $ 46.41 Expired or forfeited (119,943) $ 46.64 Converted to cash (5,031) $ 41.00 Outstanding at December 31, 2023 — $ — Included in the awards expired or forfeited were 102,891 shares that were canceled due to the performance measures not being achieved. Restricted Shares A summary of restricted share activity as of December 31, 2023 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2023 341,670 $ 42.19 Vested and issued (114,101) $ 41.66 Expired or forfeited (87,309) $ 43.78 Converted to cash (140,260) $ 41.64 Outstanding at December 31, 2023 — $ — Fair value of shares vested during the year was $4.8 million. Stock-settled Share Appreciation Rights In June 2022, we issued 135,000 stock-settled share appreciation rights (“SSARs”) to our former Chief Executive Officer. The SSARs were to vest on a pro rata basis over a three year period, and had an exercise price of $43.80 per share. We valued the shares using the Black Scholes model, which resulted in a grant date fair value of $8.28 per share. Immediately prior to the Merger, the awards were forfeited with the resignation of the former Chief Executive Officer. Prior to the forfeiture of the awards, 45,000 awards had vested. Expense recognized on these awards for the year ended December 31, 2023 was $0.3 million in the Predecessor period. Employee Stock Purchase Plans We had established an employee stock purchase plan for eligible employees (Argo Group’s 2007 Employee Share Purchase Plan). Under this plan, newly issued shares of our common stock could be purchased over an offering period of three months at 85% of the lower of the market value on the first day of the offering period or on the designated purchase date at the end of the offering period. We had also established a “Save As You Earn Plan” for our United Kingdom (“U.K.”) employees. Under this plan, newly issued shares of our common stock could be purchased over an offering period of three , 2022 and 2021 was $0.2 million , $0.7 million and $0.5 million, respectively. In connection with the Merger, Argo Group common stock ceased to be traded on the NYSE.

Underwriting, Acquisition and G

Underwriting, Acquisition and General Expenses	12 Months Ended
	Dec. 31, 2023
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 Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Commissions $ 12.7 $ 141.7 $ 280.2 $ 289.5 Other underwriting and insurance expenses 33.8 268.3 401.0 428.6 Amortization of value of business acquired and other intangible assets 37.9 — — — Total 84.4 410.0 681.2 718.1 Net deferral of policy acquisition costs (7.2) 9.0 (10.5) (15.8) Total underwriting, acquisition and general expenses $ 77.2 $ 419.0 $ 670.7 $ 702.3

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
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 taxes 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 pre-tax loss is reported in Bermuda for the predecessor period. No tax is associated with this entity during the predecessor period. Subsequent to redomiciling, the Company pre-tax loss and tax benefit is reported in the United States for the successor period. 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 loss and tax benefit is reported in the United States for the successor period. We have subsidiaries based in the U.K. that are subject to the tax laws of that country. Under current law, these subsidiaries are taxed at the applicable corporate tax rates. Certain U.K. subsidiaries are deemed to be engaged in business in the U.S., and therefore, are subject to U.S. corporate tax in respect of a proportion of their U.S. underwriting business only. Relief is available against the U.K. tax liabilities in respect of overseas taxes paid that arise from the underwriting business. Our U.K. subsidiaries file separate U.K. income tax returns. On February 2, 2023, Argo International Holdings Limited, a wholly-owned U.K. subsidiary of the Company, sold AUA. See Note 2, “Recent Acquisitions, Disposal & Transactions” for additional information related this transaction. 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. Our U.S. subsidiaries generally file a consolidated U.S. federal income tax return. We also have operations in Ireland and Italy which are subject to income taxes imposed by the jurisdiction in which they operate. In addition, we have an operation in Barbados which is not subject to income tax under the laws of that country. On June 10, 2021, U.K. tax legislation referred to as Finance Act 2021 received Royal Assent and was enacted. The effects of changes in tax laws and tax rates are recognized in the period of enactment. Accordingly, we recorded the impacts of Finance Act 2021 in our June 30, 2021 consolidated financial statements which primarily includes the remeasurement of our deferred tax assets and liabilities for the increased U.K. tax rate from 19% to 25% beginning on April 1, 2023. 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 December 31, 2023, that it is not a CAMT taxpayer or subject to Excise Tax on Repurchases of Corporate Stock. The following table presents the components of income tax provision (benefit) included in the amounts reported in our consolidated financial statements: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Current income tax provision (benefit) related to: United States (Federal) $ 4.2 $ 15.1 $ (21.0) $ 35.4 United States (State) (4.2) 0.1 0.1 2.4 United Kingdom — (0.1) (0.8) (2.2) Other jurisdictions — 0.1 (1.7) 1.6 Total current income tax provision — 15.2 (23.4) 37.2 Deferred income tax provision (benefit) related to: United States 1.3 (7.9) 6.0 (26.3) United Kingdom — (7.0) 7.3 (12.3) Other jurisdictions — — 2.1 — Total deferred income tax (benefit) 1.3 (14.9) 15.4 (38.6) Income tax provision (benefit) $ 1.3 $ 0.3 $ (8.0) $ (1.4) Our expected income tax provision (benefit) 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 years ended December 31, 2023, 2022 and 2021, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Bermuda $ (11.3) — % $ (90.3) — % $ (76.0) — % $ (18.0) — % United States 14.3 9.0 % (96.9) (7.5) % (83.2) 17.9 % 65.6 18.1 % United Kingdom (1.3) — % (23.2) 30.4 % 23.4 27.9 % (61.1) 24.4 % Barbados — — % — — % (4.5) — % — (1) — % Brazil — — % — — % (0.1) (422.4) % 15.3 10.4 % United Arab Emirates — — % 0.3 — % 1.4 — % 1.4 — % Ireland 0.5 — % (0.1) — % (39.1) — % (0.2) — % Italy — 2.1 % 0.1 50.3 % (0.9) (4.8) % 1.4 — % Malta — — % — — % (4.2) — % 0.9 — % Pre-tax income (loss) $ 2.2 59.1 % $ (210.1) 0.1 % $ (183.2) 4.3 % $ 5.3 (26.4) % (1) Pre-tax income for the respective year was less than $0.1 million. Our effective tax rate may vary significantly from period to period depending on the jurisdiction generating the pre-tax income (loss) and its corresponding statutory tax rate. The geographic distribution of pre-tax income (loss) can fluctuate significantly between periods given the inherent nature of our business. A reconciliation of the difference between the provision for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Income tax provision (benefit) at expected rate $ 2.9 $ (24.7) $ (14.7) $ 9.8 Tax effect of: Nontaxable investment income — (0.1) (0.4) (0.5) Foreign exchange adjustments — (2.6) (2.1) (0.7) Impairment of goodwill — — 5.4 8.2 Base Erosion and Anti-Abuse Tax — 23.5 — — Withholding taxes — 0.1 2.7 0.1 U.S. state tax expense, net of federal income tax effect 0.1 (1.2) — — Change in uncertain tax position liability (3.4) 1.2 (1.4) (4.5) Change in valuation allowance 1.8 (1.4) (7.6) (0.7) Impact of change in tax rate related to Finance Act 2021 (0.2) (0.2) 1.7 (8.3) Brazil Premiums and Underwriting — — 0.3 (5.3) Sale of Brazil and Malta Operations — — 6.6 — Excess Executive Compensation — 2.0 — — Other 0.1 3.7 1.5 0.5 Income tax provision (benefit) $ 1.3 $ 0.3 $ (8.0) $ (1.4) The net deferred tax asset (liability) comprises the tax effects of temporary differences related to the following assets and liabilities: As of December 31, (in millions) 2023 2022 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 45.5 $ 31.4 Unearned premiums 23.9 26.5 Net operating loss carryforwards 36.3 26.5 Investment in limited partnership interests 9.3 14.0 Unrealized losses on equity securities 6.9 8.2 Unrealized losses on fixed maturities and other investment securities 42.3 63.6 Investments 4.9 — Right of use assets 10.6 12.8 Accrued bonus 5.5 6.9 Stock option expense — 0.9 Bad debt 3.2 1.9 Other 2.6 4.3 Deferred tax assets, gross 191.0 197.0 Deferred tax liabilities: Debt obligations (6.4) — Unrealized gains on limited partnership interests (24.8) (25.3) Investments (5.8) Depreciable fixed assets (7.3) (7.1) Deferred acquisition costs (0.5) (23.0) Lease liability (12.1) (11.0) TCJA reserve transitional liability (1.1) (1.6) Value of business acquired (32.2) — Other intangible assets (37.1) — Underwriting results (9.1) — Other (0.6) (1.7) Deferred tax liabilities, gross (131.2) (75.5) Deferred tax assets, net before valuation allowance $ 59.8 $ 121.5 Valuation allowance (20.7) (20.3) Deferred tax asset (liabilities), net $ 39.1 $ 101.2 Net deferred tax assets (liabilities) - United States 39.1 101.2 Deferred tax asset (liabilities), net $ 39.1 $ 101.2 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. The valuation allowance for deferred tax assets increased by $0.4 million in 2023 and primarily related to the following: ($1.3) million Internal Revenue Code Section 382 limited net operating loss carryforwards within the U.S., and $1.7 million of losses incurred in the United Kingdom. Based upon a review of our available evidence, our management concluded that it is more-likely-than-not that $39.1 million of our deferred tax assets will be realized. For tax return purposes, as of December 31, 2023, we had NOL carryforwards in Italy, United States, and United Kingdom. The amount and timing of realizing the benefits of NOL carryforwards depend on future taxable income and limitations imposed by tax laws. Only a portion of the United States NOL carryforwards has been recognized as mentioned above in the consolidated financial statements and is included in net deferred tax assets. The NOL amounts by jurisdiction and year of expiration are as follows: (in millions) December 31, 2023 Expiration Net operating loss carryforwards by jurisdiction: Ireland 9.8 Indefinite Italy 49.7 Indefinite United Kingdom 6.9 Indefinite United States 92.3 2025-2043 For any uncertain tax positions not meeting the “more-likely-than-not” recognition threshold, accounting standards require recognition, measurement and disclosure in a company’s financial statements. Included in the balances at December 31, 2023 and 2022 were $0.0 million and $4.6 million, respectively, of unrecognized tax benefits that, if recognized, would affect the annual effective tax rate. A net increase (decrease) of interest in the amount of $(0.4) million, $0.6 million, and $(1.0) million has been recorded in the line item Interest Expense in our Consolidated Statements of Income (Loss) for the twelve months ended December 31, 2023, 2022, and 2021, respectively. A net increase (decrease) of penalty in the amount of $0.0 million, $0.1 million, and $(0.8) million has been recorded in the line item Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss) for the twelve months ended December 31, 2023, 2022, and 2021, respectively. The following is a reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2023 and 2022: (in millions) 2023 2022 Balance at January 1 $ 4.6 $ 3.6 Additions for tax positions of prior years — 3.0 Reductions for tax positions of prior years (1.0) (1.4) Reductions based on settlements with taxing authorities (2.4) — Expiration of statute of limitations (1.2) (0.6) Balance at December 31 $ — $ 4.6 Our U.S. subsidiaries are no longer subject to U.S. federal and state income tax examinations by tax authorities for years before 2020. Our U.K. subsidiary is no longer subject to U.K. income tax examinations by His Majesty’s Revenue and Customs for years before 2021.

Pension Benefits and Savings Pl

Pension Benefits and Savings Plans	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Pension Benefits and Savings Plans	Pension Benefits and Savings Plans Argo Group US sponsors a qualified defined benefit plan and non-qualified unfunded supplemental defined benefit plans, all of which were curtailed effective February 2004. As of December 31, 2023 and 2022, the qualified pension plan was underfunded by $2.8 million and $3.2 million, respectively. The non-qualified pension plans were unfunded by $1.4 million and $1.5 million at December 31, 2023 and 2022, respectively. Underfunded and unfunded amounts are included in Accrued underwriting expenses and other liabilities in our Consolidated Balance Sheets. Based on the current funding status of the pension plan, effects of the curtailment and expected changes in pension plan asset values and pension obligations, we do not believe any significant funding of the pension plan will be required during the year ending December 31, 2024. Net periodic benefit costs were $0.1 million for the period November 16, 2023 through December 31, 2023 (Successor), and $0.8 million from January 1, 2023 through November 15, 2023 (Predecessor). Net periodic benefit costs were $0.1 million for both the years ended December 31, 2022 and 2021. Substantially all of our employees are either eligible or mandated by applicable laws to participate in employee savings plans. Under these plans, a percentage of an employee’s pay may be or is mandated based on applicable laws to be contributed to various savings alternatives. The plans also call for our contributions under several formulae. Charges to income related to our contributions were $0.8 million for the period November 16, 2023 through December 31, 2023 (Successor), and $5.3 million from January 1, 2023 through November 15, 2023 (Predecessor). Charges to income related to our contributions were $8.5 million and $9.3 million in 2022 and 2021, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
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 December 31, 2023, 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. Transaction-Related Stockholder Litigation Following the announcement of the proposed transaction with Brookfield Reinsurance Ltd. and Merger Sub, the following complaints were filed in the United Stated District Court for the Southern District of New York: Stein v. Argo Group Int’l Holdings. Ltd., et al., 1:23-cv -01947 (S.D.N.Y); O’Dell v. Argo Group Int’l Holdings, Ltd., et al., C.A. No. 1:23-cv-1999 (S.D.N.Y.); Jones v. Argo Group Int’l Holdings. Ltd., et al., 1:23-cv-02606 (S.D.N.Y); Ballard v. Argo Group Int’l Holdings, Ltd., et al., 1:23-cv-02635 (S.D.N.Y); Montgomery v. Argo Group Int’l Holdings, Ltd., et al., 1:23-cv-02749 (S.D.N.Y). The complaints each asserted violations of Section 14(a) and Section 20(a) of the Exchange Act and alleged that the proxy statement filed in connection with the proposed transaction between the Company, Brookfield Reinsurance Ltd. and Merger Sub omitted certain purportedly material information that rendered the proxy statement incomplete and misleading. The complaints sought, among other things, an order to enjoin the transaction unless additional disclosures were issued; and, if the transaction closes, damages. All of the complaints were voluntarily dismissed. 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.” The summons is still pending before the Court. In addition, trial in this action has not been set and the outcome remains uncertain. The Company intends to defend this matter vigorously. Contractual Commitments We have contractual commitments to invest up to $93.4 million related to our limited partnership investments at December 31, 2023. 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.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2023
Segment Reporting [Abstract]
Segment Information	Segment Information We are primarily engaged in underwriting property and casualty insurance and reinsurance. We have two ongoing reporting segments: U.S. Operations and International Operations. Additionally, we have a Run-off Lines segment 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. Transactions between segments are reported in the segment that initiated the transaction. 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 the sales of investments. Realized investment gains 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 before income taxes for each segment were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Revenue: Net earned premiums U.S. Operations $ 147.2 $ 1,101.6 $ 1,209.0 $ 1,283.7 International Operations 14.9 124.0 530.5 625.8 Run-off Lines 0.2 0.3 0.9 0.6 Total net earned premiums 162.3 1,225.9 1,740.4 1,910.1 Net investment income U.S. Operations 23.5 99.9 88.4 119.4 International Operations 4.4 18.7 39.1 50.6 Run-off Lines 0.7 2.7 2.3 3.6 Corporate and Other — — — 14.0 Total net investment income 28.6 121.3 129.8 187.6 Net investment and other gains (losses) (0.3) (22.7) (115.3) 32.6 Total revenue $ 190.6 $ 1,324.5 $ 1,754.9 $ 2,130.3 Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Income (loss) before income taxes U.S. Operations $ 17.3 $ (127.5) $ (22.9) $ 61.1 International Operations 0.9 6.7 63.8 64.1 Run-off Lines (0.1) (1.2) (1.8) (41.5) Total segment income before income taxes 18.1 (122.0) 39.1 83.7 Corporate and Other (1.9) (22.5) (32.0) (22.5) Net investment and other gains (losses) (0.3) (22.7) (115.3) 32.6 Foreign currency exchange gains (losses) (0.6) (1.8) 5.0 (1.6) Impairment of goodwill and intangible assets — — (28.5) (43.2) Non-operating expense (13.1) (41.1) (51.5) (43.7) Total income (loss) before income taxes $ 2.2 $ (210.1) $ (183.2) $ 5.3 The table below presents net earned premiums by geographic location for the periods November 16, 2023 through December 31, 2023 (Successor), and January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. 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 Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 United States $ 147.4 $ 1,101.9 $ 1,209.9 $ 1,277.0 United Kingdom — 48.3 480.2 475.3 Bermuda 14.9 75.7 38.0 54.8 Malta — — 3.9 35.4 All other jurisdictions — — 8.4 67.6 Total net earned premiums $ 162.3 $ 1,225.9 $ 1,740.4 $ 1,910.1 The following table represents identifiable assets: As of December 31, (in millions) 2023 2022 U.S. Operations $ 6,279.0 $ 5,815.0 International Operations (1) 1,888.9 3,791.6 Run-off Lines 221.4 284.4 Corporate and Other 113.8 143.4 Total $ 8,503.1 $ 10,034.4 (1) $2,066.2 million of International assets were reclassified to assets held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. Included in total assets at December 31, 2022 are $303.7 million in assets associated with trade capital providers that are classified as held-for-sale. The following table represents goodwill and intangible assets, net of accumulated amortization, as of December 31, 2023 and 2022: Goodwill Intangible Assets, Net of As of December 31, As of December 31, (in millions) 2023 2022 2023 2022 U.S. Operations $ — $ 118.6 $ 293.8 $ — International Operations (1) — — 30.4 — Total $ — $ 118.6 $ 324.2 $ — (1) $17.5 million of International goodwill was reclassified to assets held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. The Merger resulted in a bargain purchase that eliminated goodwill as of November 16, 2023. As of November 16, 2023, we recorded $362.1 million in intangible assets, including value of business acquired, resulting from push-down accounting from the Merger with Brookfield Reinsurance Ltd. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. During the year ended December 31, 2022, we recorded a $28.5 million impairment charge for the sale of Argo Underwriting Agency Limited, 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. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information.

Statutory Accounting Principles

Statutory Accounting Principles	12 Months Ended
	Dec. 31, 2023
Statutory Accounting Principles [Abstract]
Statutory Accounting Principles	Statutory Accounting Principles Financial Information The statutory capital and surplus for our principal operating subsidiaries was as follows: Statutory capital and surplus (1) December 31, (in millions) 2023 2022 Bermuda $ 1,150.6 $ 1,024.9 United Kingdom (2) — 370.0 United States 1,410.4 1,111.1 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) Sold on February 2, 2023. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information related to this transaction. The statutory net income (loss) for our principal operating subsidiaries was as follows: Statutory net income (loss) (1) For the Years Ended December 31, (in millions) 2023 2022 2021 Bermuda $ 0.8 $ (29.1) $ 14.2 United Kingdom — 21.4 8.6 United States 39.5 (117.8) 103.5 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. Dividends As an insurance holding company, we are largely dependent on dividends and other permitted payments from our insurance subsidiaries to pay cash dividends to our stockholders, for debt service and for our operating expenses. The ability of our insurance subsidiaries to pay dividends to us is subject to certain restrictions imposed by the jurisdictions of domicile that regulate our insurance subsidiaries and each jurisdiction has calculations for the amount of dividends that an insurance company can pay without the approval of the insurance regulator. The payment of dividends to our stockholders is permitted so long as (i) we are not, or would not be after the payment, unable to pay our liabilities as they become due and (ii) the realizable value of our assets is in excess of our liabilities after taking such payment into account. In light of these restrictions, we have no material restrictions on dividend payments that may be made to our stockholders at December 31, 2023. Argo Re is the direct subsidiary of Argo Group, and therefore, has direct dividend paying capabilities to the parent. As of December 31, 2023, Argo Re’s solvency and liquidity margins and statutory capital and surplus were in excess of the minimum levels required by the Insurance Act. As of December 31, 2023 and 2022, the minimum statutory capital and surplus required to be maintained by Argo Re was $106.6 million and $100.0 million, respectively. Argo Re is generally prohibited from declaring or paying, in any financial year, dividends of more than 25% of its total statutory capital and surplus (as shown on its previous financial year’s statutory balance sheet) unless it files (at least seven days before payment of such dividends) with the Bermuda Monetary Authority (“BMA”) an affidavit signed by at least two directors (one of whom must be a Bermuda resident director if any of the insurer’s directors are resident in Bermuda) and the principal representative stating that it will continue to meet its solvency margin and minimum liquidity ratio. Argo Re may not reduce its total statutory capital by 15% or more, as set out in its previous year’s financial statements, unless it has received the prior approval of the BMA. Based on these regulatory restrictions, the maximum amount available for payment of dividends to Argo Group by Argo Re during 2023 without prior regulatory approval is $287.7 million. In 2023, Argo Re did not pay any dividends to Argo Group. In 2022, and 2021 Argo Re paid cash dividends of $33.0 million, and $85.0 million respectively, to Argo Group. The proceeds of the dividends were used to repay intercompany balances related primarily to the funding of dividend and interest payments and other corporate expenses. In 2022, it also included the dividend of the proceeds from the sale of Argo Seguros. Our U.S. insurance subsidiaries file financial statements prepared in accordance with statutory accounting principles prescribed or permitted by insurance regulatory authorities of the state in which they are domiciled. The differences between statutory-based financial statements and financial statements prepared in accordance with GAAP vary between jurisdictions. The principal differences are that for statutory-based financial statements, deferred policy acquisition costs are not recognized, a portion of the deferred federal income tax asset is non-admitted, bonds are generally carried at amortized cost, certain assets are non-admitted and charged directly to surplus, a collectability allowance related to reinsurance recoverables is charged directly to surplus and outstanding losses and unearned premium are presented net of reinsurance. As an intermediate insurance holding company, Argo Group US, Inc. is largely dependent on dividends and other permitted payments from its insurance subsidiaries to service its debt, fund operating expenses and pay dividends to Argo Ireland. Various state insurance laws restrict the amount that may be transferred to Argo Group US from its subsidiaries in the form of dividends without prior approval of regulatory authorities. In addition, that portion of the insurance subsidiaries’ net equity that results from the difference between statutory insurance principles and GAAP would not be available for dividends. During 2023, Argo Group US, Inc. received a dividend of $21.3 million from Rockwood. Argonaut Insurance Company is a direct subsidiary of Argo Group US, Inc. and is regulated by the Illinois Division of Insurance. During 2024, Argonaut Insurance Company may be permitted to pay dividends of up to $120.7 million without approval from the Illinois Division of Insurance. Rockwood, a direct subsidiary of Argo Group US, Inc., is regulated by the Pennsylvania Department of Insurance. Rockwood may be permitted to pay ordinary dividends of up to $25.0 million with approval from the Pennsylvania Department of Insurance during 2024. Each department of insurance may require prior approval for the payment of all dividends, based on business and regulatory conditions of the insurance companies.

Insurance Assessments

Insurance Assessments	12 Months Ended
	Dec. 31, 2023
Insurance [Abstract]
Insurance Assessments	Insurance Assessments We participate in statutorily created insolvency guarantee and weather-related loss protection associations in all states where we are authorized to transact business. These associations were formed for the purpose of paying the claims of insolvent companies. We are assessed a pro-rata share of such claims based upon our premium writings, subject to a maximum annual assessment per line of insurance. Certain of these assessments can be recovered through premium tax offsets or policy surcharges. We do not believe that assessments on current insolvencies will have a material impact on our financial condition or results of operations. We have accrued assessments of $6.9 million and $5.2 million at December 31, 2023 and 2022, respectively.

Transactions with Related Parti

Transactions with Related Parties	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Transactions with Related Parties	Transactions with Related Parties There were no material transactions with related parties for the periods November 16, 2023 through December 31, 2023 (Successor), and January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021.

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Event	Subsequent Events On February 20, 2024, Brookfield Reinsurance Ltd. made a $100.0 million capital contribution to the Company. On February 21, 2024, the Company entered into Amendment No. 6 to the Credit Agreement with the financial institutions party thereto. Amendment No. 6, among other things, replaced the minimum Tangible Net Worth covenant in the Credit Agreement with a minimum Consolidated Net Worth covenant that no longer excludes the value of intangible assets. The Consolidated Net Worth covenant is tested at the end of each fiscal quarter (commencing with the fiscal quarter ended December 31, 2023) and has been set at an amount equal to the sum of (i) $872.0 millions plus (ii) 50% of positive net income for each fiscal quarter ending after December 31, 2023 plus (iii) 50% of net proceeds received from the issuance and sale of certain equity interests after December 31, 2023. On February 22, 2024, the Company borrowed $100.0 million through the revolving credit facility, payable in 30 days, under the terms of the Credit Agreement.

Schedule II Condensed Financial

Schedule II Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2023
Condensed Financial Information Disclosure [Abstract]
Schedule II Condensed Financial Information of Registrant	ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (in millions) As of BALANCE SHEETS December 31, 2023 2022 Assets Short-term investments $ — $ 1.8 Investment in subsidiaries 1,363.3 1,281.7 Cash, restricted cash and cash equivalents 2.2 5.2 Operating lease right-of-use assets — 4.6 Other assets 0.9 6.7 Total assets $ 1,366.4 $ 1,300.0 Liabilities and Stockholders' Equity Junior subordinated debentures $ 14.3 $ 28.4 Accrued underwriting expenses and other liabilities 2.2 10.0 Operating lease liabilities — 4.6 Due to subsidiaries 21.3 14.0 Intercompany notes payable 31.1 10.1 Total liabilities 68.9 67.1 Stockholders' equity 1,297.5 1,232.9 Total liabilities and stockholders' equity $ 1,366.4 $ 1,300.0 STATEMENTS OF INCOME (LOSS) Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Revenue: Net investment expense $ (0.1) $ — $ — $ — Total revenue (0.1) — — — Expenses: Interest expense 0.4 2.3 1.6 1.2 Operating expenses (1.3) 6.8 (0.6) 6.2 Non-operating expenses 2.7 21.3 26.2 0.2 Total expenses 1.8 30.4 27.2 7.6 Net loss before equity in earnings of subsidiaries (1) (1.9) (30.4) (27.2) (7.6) Equity in undistributed earnings of subsidiaries 2.8 (180.0) (148.0) 14.3 Net (loss) income $ 0.9 $ (210.4) $ (175.2) $ 6.7 Dividends on preferred stock — 10.5 10.5 10.5 Net (loss) income attributable to common stockholders $ 0.9 $ (220.9) $ (185.7) $ (3.8) (1) Argo Group is not subject to taxation. See the Report of the Independent Registered Public Accounting Firm. ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE II CONDENSED FINANCIAL INFORMATION OF REGISTRANT (in millions) Successor Predecessor STATEMENTS OF CASH FLOWS Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Cash flows from operating activities: Net (loss) income $ 0.9 $ (210.4) $ (175.2) $ 6.7 Adjustments to reconcile net income to net cash provided by (used in) operating activities: Amortization and depreciation — — 1.5 1.5 Share-based payments expense — 1.0 2.8 2.3 Loss on disposal of fixed assets — — (3.5) (3.0) Undistributed earnings of subsidiaries (2.8) 180.0 148.0 (14.3) Change in: Prepaid assets — 0.2 (1.8) 7.2 Accrued expenses (8.0) 10.6 6.0 (4.1) Due to subsidiaries 5.6 22.7 28.8 (12.1) Other, net (2.2) 5.1 4.7 (3.9) Cash provided by (used in) operating activities (6.5) 9.2 11.3 (19.7) Cash flows from investing activities: Change in short-term investments — (3.8) 12.7 (13.9) Settlements of foreign currency exchange forward contracts — 2.0 (2.0) 0.5 Dividend received from subsidiaries — — 33.3 85.0 Cash provided by (used in) investing activities — (1.8) 44.0 71.6 Cash flows from financing activities: Activity under stock incentive plans — 0.7 1.8 1.3 Payment of cash dividend to preferred stockholders — (10.5) (10.5) (10.5) Payment of cash dividend to common stockholders — 0.3 (43.4) (43.7) Cash used in financing activities — (9.5) (52.1) (52.9) Change in cash (6.5) (2.1) 3.2 (1.0) Cash, beginning of period 8.7 5.2 2.0 3.0 Cash, end of year $ 2.2 $ 3.1 $ 5.2 $ 2.0 See the Report of the Independent Registered Public Accounting Firm.

Schedule III Supplemental Insur

Schedule III Supplemental Insurance Information	12 Months Ended
	Dec. 31, 2023
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Schedule III Supplemental Insurance Information	ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE III SUPPLEMENTAL INSURANCE INFORMATION AS OF DECEMBER 31, 2023, 2022 AND 2021 (in millions) Segment DAC (1) Reserves for Losses and Loss Adjustment Expenses (2) UPR (3) Period Ended December 31, 2023 U.S. Operations 7.4 4,224.1 763.2 International Operations (0.2) 1,124.3 153.4 Run-off Lines — 196.1 — Total $ 7.2 $ 5,544.5 $ 916.6 Year Ended December 31, 2022 U.S. Operations 109.4 3,718.1 893.4 International Operations (4) (2.4) 1,100.4 146.5 Run-off Lines — 233.1 — Total $ 107.0 $ 5,051.6 $ 1,039.9 Year Ended December 31, 2021 U.S. Operations 103.7 3,422.4 973.7 International Operations 64.3 1,911.4 493.1 Run-off Lines — 261.2 — Total $ 168.0 $ 5,595.0 $ 1,466.8 (1) Deferred policy acquisition costs. (2) Future policy benefits, losses, claims and loss expenses. (3) Unearned premiums. (4) $993.4 million of gross reserves were reclassified as liabilities held-for-sale at December 31, 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE III SUPPLEMENTAL INSURANCE INFORMATION FOR THE PERIOD NOVEMBER 16, 2023 THROUGH DECEMBER 31, 2023, JANUARY 1, 2023 THROUGH NOVEMBER 15, 2023, AND FOR THE YEARS ENDED DECEMBER 31, 2022 AND 2021 (in millions) Segment Premium Revenue (1) Net Investment Income (2) Loss & LAE (3) Amortization (Deferral) DAC (4) (5) Other Operating Expenses (6) Net Premiums Written (7) The Period from November 16, 2023 through December 31, 2023 (Successor) U.S. Operations 147.2 23.5 81.7 (7.5) 76.1 114.9 International Operations 14.9 4.4 12.0 0.3 6.0 9.2 Run-off Lines 0.2 0.7 0.5 — 0.4 0.2 Corporate and Other — — — — 1.9 — Total $ 162.3 $ 28.6 $ 94.2 $ (7.2) $ 84.4 $ 124.3 The Period from January 1, 2023 through November 15, 2023 (Predecessor) U.S. Operations 1,101.6 99.9 935.1 19.9 349.7 1,002.7 International Operations 124.0 18.7 105.5 (10.9) 36.9 141.8 Run-off Lines 0.3 2.7 2.6 — 0.9 0.2 Corporate and Other — — — — 22.5 — Total $ 1,225.9 $ 121.3 $ 1,043.2 $ 9.0 $ 410.0 $ 1,144.7 Year Ended December 31, 2022 U.S. Operations 1,209.0 88.4 870.1 (3.5) 436.3 1,196.2 International Operations 530.5 39.1 293.9 (7.0) 212.3 544.5 Run-off Lines 0.9 2.3 2.9 — 1.6 0.8 Corporate and Other — — — — 31.0 — Total $ 1,740.4 $ 129.8 $ 1,166.9 $ (10.5) $ 681.2 $ 1,741.5 Year Ended December 31, 2021 U.S. Operations 1,283.7 119.4 908.2 (5.8) 425.1 1,304.8 International Operations 625.8 50.6 362.1 (10.0) 256.3 671.7 Run-off Lines 0.6 3.6 44.3 — 1.0 0.8 Corporate and Other — 14.0 — — 35.7 — Total $ 1,910.1 $ 187.6 $ 1,314.6 $ (15.8) $ 718.1 $ 1,977.3 (1) Premium revenue, net (premiums earned). (2) Net investment income allocated based upon each segment’s share of investable funds. (3) Benefits, claims, losses and settlement expenses. (4) Amortization (deferral) of deferred policy acquisition costs. (5) The amortization (deferral) of DAC will not equal the change in the balance sheet. See Note 1, “Business and Significant Accounting Policies” for further discussion. (6) Other insurance expenses allocated based on specific identification, where possible, and related activities. (7) Premiums written, net. See the Report of the Independent Registered Public Accounting Firm.

Schedule V Valuation and Qualif

Schedule V Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2023
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule V Valuation and Qualifying Accounts	ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (in millions) Balance at Charged to Capital Loss Net Operating Charged to Deductions Balance at Year Ended December 31, 2023 Deducted from assets: Valuation allowance for deferred tax asset $ 20.3 $ — $ — $ 0.4 $ — $ — $ 20.7 Year Ended December 31, 2022 Deducted from assets: Valuation allowance for deferred tax asset $ 27.9 $ — $ 3.3 $ (10.9) $ — $ — $ 20.3 Year Ended December 31, 2021 Deducted from assets: Valuation allowance for deferred tax asset $ 28.6 $ (0.7) $ — $ — $ — $ — $ 27.9 See the Report of the Independent Registered Public Accounting Firm.

Schedule VI Supplemental Inform

Schedule VI Supplemental Information for Property-Casualty Insurance Companies	12 Months Ended
	Dec. 31, 2023
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Schedule VI Supplemental Information for Property-Casualty Insurance Companies	ARGO GROUP INTERNATIONAL HOLDINGS, INC. SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY-CASUALTY INSURANCE COMPANIES (in millions) Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Deferred acquisition costs (1) $ 7.2 $ 88.7 $ 107.0 $ 168.0 Reserves for losses and loss adjustment expenses (1) $ 5,544.5 $ 5,526.4 $ 5,051.6 $ 5,595.0 Unamortized discount in reserves for losses (1) $ 20.8 $ 20.4 $ 19.3 $ 18.8 Unearned premiums (1) $ 916.6 $ 986.2 $ 1,039.9 $ 1,466.8 Premiums earned $ 162.3 $ 1,225.9 $ 1,740.4 $ 1,910.1 Net investment income $ 28.6 $ 121.3 $ 129.8 $ 187.6 Losses and loss adjustment expenses incurred: Current year $ 94.2 $ 775.3 $ 1,102.2 $ 1,176.3 Prior years — 267.9 64.7 138.3 Losses and loss adjustment expenses incurred $ 94.2 $ 1,043.2 $ 1,166.9 $ 1,314.6 (Deferral) amortization of policy acquisition costs (2) $ (7.2) $ 9.0 $ (10.5) $ (15.8) Paid losses and loss adjustment expenses, net of reinsurance $ 85.3 $ 527.9 $ 999.5 $ 869.2 Gross premiums written $ 191.2 $ 1,948.4 $ 2,848.1 $ 3,181.2 (1) As of December 31, 2022, balances related to AUA were reclassified held-for-sale. See Note 2, “Recent Acquisitions, Disposals & Other Transactions.” (2) The amortization (deferral) of policy acquisition costs will not equal the change in the balance sheet. For further discussion, see Note 1, “Business and Significant Accounting Policies.” See the Report of the Independent Registered Public Accounting Firm.

Business and Significant Acco_2

Business and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Business	Business Argo Group International Holdings, Inc. (“Argo Group,” “we” or the “Company”) is an underwriter of specialty insurance products in the property and casualty market. Argo Group US, Inc. (“Argo Group US”) is a subsidiary of Argo Financial Holding (Ireland) UC (“Argo Ireland”). Argo Re Ltd. (“Argo Re”), a Bermuda based company, is the parent of both Argo Ireland and Argo International Holdings, Ltd. Argo Re is directly owned by Argo Group. We conduct our ongoing business through two primary segments - U.S. Operations and International Operations. In addition to these main business segments, we have a Run-off Lines segment for certain products we no longer underwrite. U.S. Operations is comprised of the Excess and Surplus Lines businesses focusing on the U.S.-based risks that the standard, admitted insurance market is unwilling or unable to underwrite, and through other specialized admitted and non-admitted business distributed through retail, wholesale, and managing general brokers/agents in the specialty insurance market. Excess and Surplus Lines products are underwritten by Colony Insurance Company (“Colony”). The other U.S. specialized admitted and non-admitted businesses consist of the following operations: Argo Pro, U.S. Specialty Programs, Argo Surety, Rockwood Casualty Insurance Company (“Rockwood”), Argo Insurance and Inland Marine. International Operations is comprised of Argo Insurance Bermuda and Italy. This business provides a broad range of commercial property, casualty, professional liability and specialty coverages. Our Run-off Lines segment includes liabilities associated with other liability policies that were issued in the 1960s, 1970s and into the 1980s, as well as the former risk-management business and other business no longer underwritten. On February 2, 2023, we completed the sale of Argo Underwriting Agency Limited (“Syndicate 1200” or “AUA”) to Ohio Farmers Insurance Company (the “Buyer”), part of the Westfield group of insurance companies. AUA was a subsidiary of Argo International Holdings, Ltd. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for further information.
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The Consolidated Financial Statements of Argo Group and its subsidiaries have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The preparation of Consolidated 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 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 goodwill and intangibles, including those identified as part of purchase accounting related to the Merger, and our deferred tax asset valuation allowance. Actual results could differ from those estimates. Specifically, estimates for reserves for losses and loss adjustment expenses are based upon past claim experience modified for current trends as well as prevailing economic, legal and social conditions. Although management believes that amounts included in the accompanying Consolidated Financial Statements are reasonable, such estimates may be more or less than the amounts ultimately paid when the claims are settled. The estimates are continually reviewed and any changes are reflected in current operating results. Further, the nature of loss exposures involves significant variability due to the nature of the long-tailed payments on certain claims. As such, losses and loss adjustment expenses could vary significantly from the recorded amounts. Accounting for business combinations requires significant estimates and assumptions, especially at the acquisition date. In determining the Company’s estimated fair value of assets acquired and liabilities assumed by Brookfield Reinsurance as part of the Merger, we used various recognized valuation methods including the income, market and cost approaches. Valuations were performed by independent valuation specialists under the Company’s supervision. The value of business acquired represents the fair value of the expected future profits in unearned premiums, net of reinsurance, utilizing primarily ultimate loss and expense related assumptions, for insurance contracts acquired as a result of the Merger. The fair value adjustment for reserves for losses and loss adjustment expenses represents the difference between the fair value and book value of unpaid incurred claims net of reinsurance recoveries. Value of business acquired is classified separately on our Consolidated Balances Sheets, while the fair value adjustment for reserves for losses and loss adjustment expenses is included in our other intangible assets. These intangible assets were based primarily on an income valuation technique with assumptions for: (i) settlement patterns that reflect an actuarial estimate of the expected future net cash flows, (ii) a discount rate that reflect a market participant’s view of (a) a reduction to those cash flows for the time value of money and (b) a risk component to reflect the net present value of profit that an investor would demand in return for the assumption of the development risk. The Consolidated Financial Statements include the accounts and operations of Argo Group and its subsidiaries. All material intercompany accounts and transactions have been eliminated. Certain reclassifications have been made to financial information presented for prior years to conform to the current year’s presentation. Amounts related to trade capital providers, who are third-party capital participants that provided underwriting capital to the sold Syndicate 1200 are included in the balance sheet as held-for-sale at December 31, 2022. Trade capital providers participated on a quota share basis, assuming 100% of their contractual participation in the underwriting syndicate results and with such results settled on a year of account basis. We have evaluated our investment in our eleven statutory trusts (collectively, the “Trusts”) under the Financial Accounting Standards Board’s (“FASB’s”) provisions for consolidation of variable interest entities under Accounting Standards Codification (“ASC”) Topic 810-10, “Consolidation,” as amended. We determined that the Trusts are variable interest entities due to the fact that the Trusts do not have sufficient equity to finance their activities without additional subordinate financial support from other parties. We do not have any power to direct the activities that impact the Trusts’ economic performance. We are not entitled to receive a majority of the residual returns of the Trusts. Additionally, we are not responsible for absorbing the majority of the expected losses of the Trusts; therefore, we are not the primary beneficiary and, accordingly, the Trusts are not included in our Consolidated Financial Statements.
Investments	Investments Investments in fixed maturities at December 31, 2023 and 2022 include bonds and structured securities. Equity securities include common stocks, preferred stocks and mutual funds. Other investments consist of foreign regulatory deposits, hedge funds, private equity funds, private equity direct investments, and voluntary pools. Short-term investments consist of money market funds, certificates of deposit, bonds, sovereign debt and interest-bearing cash accounts. Investments with original maturities of over 90 days and less than one year are classified as short-term investments in our Consolidated Financial Statements as they are part of our investing activities. Previous to the Merger and the application of push-down accounting, the Company classified interest-bearing cash accounts and short-term investments with original maturities of 90 days or less as Short-term investments in our Consolidated Balance Sheets. Post Merger, these securities are classified in Cash, restricted cash and cash equivalents in our Consolidated Balance Sheets. The amortized cost of fixed maturity securities is adjusted for amortization of premiums and accretion of discounts. This amortization or accretion is included in Net investment income in our Consolidated Statements of Income (Loss). For the structured securities portion of the fixed maturity securities portfolio, we recognize income using a constant effective yield based on anticipated prepayments and the estimated economic life of the securities. Premium or discount is amortized into income using the retrospective method. Our investments in fixed maturities are considered available-for-sale and are carried at fair value. As available-for-sale investments, changes in the fair value of fixed maturities are not recognized in income during the period, but rather are recognized as a separate component of stockholders’ equity until realized. Fair value of these investments is estimated using prices obtained from third-party pricing services, where available. For securities where we were unable to obtain fair values from a pricing service or broker, fair values were estimated using information obtained from investment advisors. We performed several processes to ascertain the reasonableness of these investment values by (1) obtaining and reviewing internal control reports for our service providers that obtain fair values from third-party pricing services, (2) obtaining and reviewing evaluated pricing methodology documentation from third-party pricing services and (3) comparing the security pricing received from a secondary third-party pricing service versus the prices used in the Consolidated Financial Statements and obtaining additional information for variances that exceeded a defined threshold. As of December 31, 2023, investments reported at fair value for which we did not receive a fair value from a pricing service or broker accounted for less than 2% of our investment portfolio. The actual value at which such securities could be sold or settled with a willing buyer or seller may differ from such estimated fair values depending on a number of factors including, but not limited to, current and future economic conditions, the quantity sold or settled, the presence of an active market and the availability of a willing buyer or seller. The cost of securities sold is based on the specific identification method. Commercial mortgage loans are carried at unpaid principal balances less allowance for credit losses, plus or minus adjustments for the accretion or amortization of discount or premium. Interest income on such loans is accrued as earned. Our investments in equity securities are reported at fair value, changes in the fair value of equity securities are included in Net realized investment and other gains (losses) in the Consolidated Statements of Income (Loss). Changes in the value of other investments consisting of hedge funds, private equity funds, private equity direct investments and voluntary pools are principally recognized in income during the period using the equity method of accounting. Our foreign regulatory deposits are assets held in trust in jurisdictions where there is a legal and regulatory requirement to maintain funds locally in order to protect policyholders. Lloyd’s was the appointed investment manager for the funds. The underlying assets were invested in government securities, agency securities and corporate bonds whose values were obtained from Lloyd’s. Our AUA business was sold in February 2023. Foreign currency future contracts held by us are valued by our counterparties using market driven foreign currency exchanges rates. We regularly review our investments to identify and evaluate those that may be credit impaired. For fixed maturity securities, the evaluation for credit losses is generally based on the present value of expected cash flows of the security as compared to the amortized book value, the financial condition, near-term and long-term prospects for the issuer, including industry conditions, implications of rating agency actions, the likelihood of principal and interest recoverability and whether it is more likely than not we will be required to sell the investment prior to the anticipated recovery in value. Effective January 1, 2020 with the adoption of ASU 2016-13 Financial Instruments-Credit Losses, we recognize credit losses on fixed maturities through an allowance account. For fixed maturities that we do not intend to sell or for which it is more likely than not we will not be required to sell prior to the anticipated recovery in value, we separate the credit component of the impairment from the component related to all other market factors and report the credit loss component to net realized investment gains (losses) in the Consolidated Statement of Income (Loss). The impairment related to all other market factors is reported as a separate component of stockholder’s equity in other comprehensive income (loss). The credit loss allowance account is adjusted for any additional credit losses or subsequent recoveries and the cost basis of the fixed maturity security is not adjusted. For fixed maturity securities that we intend to sell or for which it is more likely than not that we will be required to sell before an anticipated recovery in value, the full amount of the impairment is recognized in Net realized investment and other gains (losses) in the Consolidated Statements of Income (Loss) and the cost basis of the fixed maturity security is adjusted to reflect the recognized realized loss. The new cost basis is not adjusted for any recoveries in fair value. We report accrued investment income separately from fixed maturity securities and have elected to not measure an allowance for credit losses for accrued investment income. The write-off of investment income accrued for fixed maturities that have defaulted on interest payments is recognized as a loss in Net realized investment and other gains (losses) , in the period of the default, in the Consolidated Statements of Income (Loss). At December 31, 2022, amounts relating to Syndicate 1200 trade capital providers were reclassified to Assets held-for-sale
Cash, restricted cash, and cash equivalents	Cash, restricted cash, and cash equivalents Cash, restricted cash, and cash equivalents consists of cash deposited in operating accounts with commercial banks and short-term investments with original maturities of 90 days or less. Previous to the Merger and the application of push-down accounting, the Company classified short-term investments with original maturities of 90 days or less as Short-term investments in our Consolidated Balance Sheets.
Premiums Receivables and Reinsurance Recoverables	Premiums Receivables and Reinsurance Recoverables Premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected lifetime credit losses, both dispute and credit related. The allowance is based upon our ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by our ability to cancel the policy if the policyholder does not pay the premium. Reinsurance recoverables represent amounts of paid losses and loss adjustment expenses, case reserves and incurred but not reported (“IBNR”) amounts ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. We report our reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses. The allowance is based upon our ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors. We use the rating-based method to estimate the uncollectible reinsurance reserves due to credit losses. Under this method, reinsurance credit risk is estimated by considering the reinsurers probability of default. Reinsurance recoverables are forecasted out of the assumed billing periods and a liquidation factor is applied based on the rating of the reinsurer and adjusted as needed based on our historical experience with the reinsurers. Additionally, reinsurance recoverable balances are evaluated to identify any dispute risk and when required, an additional reserve is recorded. Amounts deemed to be uncollectible, including amounts due from known insolvent reinsurers, are written off against the allowance. Changes in the allowance, as well as any subsequent collections of amounts previously written off, are reported as part of underwriting expense. We evaluate and monitor the financial condition of our reinsurers under voluntary reinsurance arrangements to minimize our exposure to significant losses from reinsurer insolvencies. As a result of push-down accounting due to the Merger, the fair value of the allowance for uncollectible premiums as well as reinsurance recoverables were nil as of November 16, 2023. The previous allowances were applied to the premium receivable or reinsurance recoverable balance, resulting in no net change in the asset. At December 31, 2022, premiums receivable and reinsurance recoverables include amounts relating to the trade capital providers’ quota share, which were reclassified to Assets held-for-sale in our Consolidated Balance Sheets.
Deferred Acquisition Costs	Deferred Acquisition Costs Policy acquisition costs, which include commissions, premium taxes, fees and certain other costs of underwriting policies, are deferred, when such class of policies are profitable, and amortized over the same period in which the related premiums are earned. To qualify for capitalization, the policy acquisition cost must be directly related to the successful acquisition of an insurance contract. We continually review the methods of making such estimates and establishing the deferred costs with any adjustments made in the accounting period in which it arose. The amortization of deferred acquisition costs is included in Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss). The Company evaluates the recoverability of deferred acquisition costs by determining if the future-earned premiums is greater than the expected future claims and expenses. The Company considers anticipated investment income in this determination. If a loss is probable on the unexpired portion of policies in force, a premium deficiency reserve is recognized. At December 31, 2023 and 2022, the deferred acquisition costs were considered fully recoverable and no premium deficiency reserve was recorded. As a result of push-down accounting due to the Merger, the fair value of our deferred acquisition costs was nil as of November 16, 2023. Our deferred acquisition costs as of December 31, 2023 relates to policy acquisition costs incurred after November 16, 2023. The 2022 net amortization of policy acquisition costs will not equal the change in our Consolidated Balance Sheets as Syndicate 1200 deferred acquisition costs were reclassified to Assets held-for-sale on our Consolidated Balance Sheets at December 31, 2022. The 2022 net amortization of policy acquisition costs will not equal the change in our Consolidated Balance Sheets as the trade capital providers’ share is not reflected in our Consolidated Statements of Income (Loss) and differences arise from foreign currency exchange rates applied to deferred acquisition costs which are treated as a nonmonetary asset.
Goodwill, Value of Business Acquired and Other Intangible Assets	Goodwill, Value of Business Acquired and Other Intangible Assets Goodwill and intangible assets are allocated to reporting units in which the results of operations for the acquired company are reported (see Note 19, “Segment Information” for further discussion). Intangible assets with a finite life are amortized over the estimated useful life of the asset. Goodwill and intangible assets with an indefinite useful life are not amortized. Goodwill and intangible assets are tested for impairment on an annual basis or more frequently if events or changes in circumstances indicate that the carrying amount may not be recoverable. We perform our annual goodwill and intangible asset impairment test on October 1 of each year. The intangible asset amortization expense is reflected in Underwriting, acquisition and general expenses in our Consolidated Statements of Income (Loss).
Leases	Leases We determine if a contract contains a lease at inception and recognize operating lease right-of-use assets and operating lease liabilities based on the present value of the future minimum lease payments at the commencement date. As our leases do not provide an implicit interest rate, we use our incremental borrowing rate based on the information available at the commencement date to determine the present value of future payments. Lease agreements have lease and non-lease components. We account for these components separately, therefore our operating lease right-of-use asset and operating lease liabilities represent base rent only. Lease expense is recognized on a straight-line basis over the lease term. Renewal options are evaluated prior to the expiration date and recorded upon exercise.
Property and Equipment	Property and Equipment Property and equipment used in operations, including certain costs incurred to develop or obtain computer software for internal use, are capitalized and carried at cost less accumulated depreciation and are reported in Other assets three
Derivative Instruments	Derivative Instruments We enter into short-term, currency spot and forward contracts to manage operational currency exposure from our non-USD insurance operations. The forward contracts are typically thirty to ninety days and are renewed as management deems necessary to accomplish the objectives of the contracts. These foreign currency forward contracts are carried at fair value in Other assets on our Consolidated Balance Sheets at December 31, 2023 and 2022, respectively. The realized and unrealized gains and losses are included in Net realized investment and other gains (losses) in our Consolidated Statements of Income (Loss). The forwards contracts are not designated as hedges for accounting purposes.
Assets held-for-sale and Liabilities held-for-sale	Assets held-for-sale Liabilities held-for-sale
Reserves for Losses and Loss Adjustment Expenses	Reserves for Losses and Loss Adjustment Expenses Liabilities for unpaid losses and loss adjustment expenses include the accumulation of individual case estimates for claims reported as well as estimates of IBNR claims and estimates of claim settlement expenses. Reserves for loss and loss adjustment expenses represents management's best estimate of the ultimate liability to settle these claims as of the balance sheet date. The effects of changes in this estimate are included in results of operations in the period in which the estimates are changed. Reinsurance recoverables on unpaid claims and claim expenses represent estimates of the portion of such liabilities that will be recoverable from reinsurers. Amounts recoverable from reinsurers are recognized as assets at the same time and in a manner consistent with the unpaid claims liabilities associated with the reinsurance policy.
Reinsurance	Reinsurance In the normal course of business, our insurance subsidiaries cede risks above certain retention levels to other insurance companies. Reinsurance recoverables include claims we paid and estimates of unpaid losses and loss adjustment expenses that are subject to reimbursement under reinsurance and retrocessional contracts. The method for determining reinsurance recoverables for unpaid losses and loss adjustment expenses involves reviewing actuarial estimates of gross unpaid losses and loss adjustment expenses to determine our ability to cede unpaid losses and loss adjustment expenses under our existing reinsurance contracts. This method is continually reviewed and updated and any resulting adjustments are reflected in earnings in the period identified. Reinsurance premiums, commissions and expense reimbursements are accounted for on a basis consistent with those used in accounting for the original policies issued and the term of the reinsurance contracts. Amounts recoverable from reinsurers for losses and loss adjustment expenses for which our insurance and reinsurance subsidiaries have not been relieved of their legal obligations to the policyholder are reported as assets.
Earned Premiums	Earned Premiums Premium revenue is generally recognized ratably over the policy period. Premiums that have yet to be earned are reported as Unearned premiums in our Consolidated Balance Sheets. At December 31, 2022, trade capital providers balances were reclassified to Assets held-for-sale. Assumed reinstatement premiums that reinstate coverage are written and earned at the time the associated loss event occurs. The original premium is earned over the remaining exposure period of the contract. Reinstatement premiums are estimated based upon contract terms for reported losses and estimated for incurred but not reported losses.
Retrospectively Rated Policies	Retrospectively Rated Policies
Non-Operating Expenses	Non-Operating Expenses Non-operating expenses represent costs not associated with our ongoing insurance or other operations, including severance expenses, certain legal costs, merger and acquisition and other transaction-related expenses, and certain non-recurring expenses. As such, non-operating expenses have been excluded from the calculation of our expense ratio. These non-recurring costs are included in the line item Non-operating expenses in the Company’s Consolidated Statements of Income (Loss).
Share-Based Payments	Share-Based Payments
Foreign Currency Exchange Gain (Loss)	Foreign Currency Exchange Gain (Loss) The reporting currency of the Company is the U.S. dollar (“USD”). USD is the functional currency of all but one of our remaining foreign operations. For foreign operations with the U.S. dollar as the functional currency, monetary assets and liabilities that are denominated in local currencies are remeasured at the exchange rates in effect at the balance sheet date. The resulting gains and losses from changes in the foreign exchange rates are reflected in net income. Non-monetary assets and liabilities are not remeasured. In the case of our non-USD denominated available-for-sale investments, the change in exchange rates between the local currency and USD at each balance sheet date represents an unrealized appreciation or depreciation in value of these securities and is included as a component of Accumulated other comprehensive income (loss)
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates in effect for the year in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in net income or loss in the period in which the change is enacted. We recognize interest expense and penalties related to the unrecognized tax benefits in Interest expense and Underwriting, acquisition and general expenses , respectively, in our Consolidated Statements of Income (Loss). We recognize valuation allowance in Income tax provision (benefit) in our
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements On October 9, 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update 2023-06— Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative (“ASU 2023-06”). The amendments modify the disclosure or presentation requirements on a variety of Topics in the Codification. Certain of the amendments represent clarifications to or technical corrections of the current requirements and also facilitate the comparison of entities subject to the SEC’s existing disclosures with those entities that were not previously subject to the SEC’s requirements. Further, the amendments align the requirements in the Codification with the SEC’s regulations. The effective date for each amendment will be the date on which the SEC’s removal of that related disclosure from Regulation S-X or Regulation S-K becomes effective, with early adoption prohibited. The amendments in this Update should be applied prospectively. We are currently evaluating the requirements of ASU 2023-06. However, as they apply to disclosure requirements, the adoption of the standard is not anticipated to have a material impact on our profitability, financial position or cash flows. On November 27, 2023, the FASB issued Accounting Standards Update 2023-07— Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (“ASU 2023-07”). The amendments improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. In addition, the amendments enhance interim disclosure requirements, clarify circumstances in which an entity can disclose multiple segment measures of profit or loss, provide new segment disclosure requirements for entities with a single reportable segment, and contain other disclosure requirements. The amendments in ASU 2023-07 are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. Early adoption is permitted. We plan to adopt ASU 2023-07 effective January 1, 2024. As ASU 2023-07 applies to disclosure requirements, the adoption of the standard is not anticipated to have a material impact on our profitability, financial position or cash flows. On December 14, 2023, the FASB issued Accounting Standards Update 2023-09— Income Taxes (Topic 740): Improvements to Income Tax Disclosures (“ASU 2023-09”). The amendments improve income tax disclosures by requiring (1) consistent categories and greater disaggregation of information in the rate reconciliation and (2) income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. The amendments in ASU 2023-09 are effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. We are currently evaluating the requirements of ASU 2023-09. However, as they apply to disclosure requirements, the adoption of the standard is not anticipated to have a material impact on our profitability, financial position or cash flows.

Business and Significant Acco_3

Business and Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Intangible Assets And Accumulated Amortization	The following table presents our intangible assets recognized on our Consolidated Balance Sheets as result of push-down accounting and the accumulated amortization: As of December 31, 2023 (in millions) Gross Carrying Accumulated Net Value Useful Life Value of business acquired $ 176.3 $ (32.7) $ 143.6 (a) Other intangible assets: Broker relations 21.5 (0.2) 21.3 13 to 16 years Trade names 12.9 (0.3) 12.6 5 years Insurance licenses 25.0 — 25.0 Indefinite Leases 7.1 (0.1) 7.0 9 years Internally developed software 16.5 (0.3) 16.2 5 to 7 years Fair value adjustment for reserves for losses and loss adjustment expenses 102.8 (4.3) 98.5 (b) Total other intangible assets 185.8 (5.2) 180.6 Total intangible assets $ 362.1 $ (37.9) $ 324.2 (a) Amortized based on unearned premium earnout pattern. (b) Amortized based on settlement pattern.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table outlines the estimated future amortization expense related to definite lived intangible assets held as of December 31, 2023: (in millions) Years As of December 31, 2024 $ 171.7 2025 39.8 2026 25.7 2027 17.4 2028 13.3 Thereafter 31.3 Total amortization expense $ 299.2
Supplemental Cash Flow Information	Interest paid and income taxes paid (recovered) were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Senior unsecured fixed rate notes $ 1.2 $ 8.2 $ 9.3 $ 9.3 Junior subordinated debentures 4.1 19.3 13.5 10.0 Other indebtedness — 0.8 1.3 2.5 Total interest paid $ 5.3 $ 28.3 $ 24.1 $ 21.8 Income taxes paid 0.1 0.2 26.2 43.0 Income taxes recovered — (0.1) (2.1) (2.6) Income taxes paid, net $ 0.1 $ 0.1 $ 24.1 $ 40.4

Recent Acquisitions, Disposal_2

Recent Acquisitions, Disposals & Other Transactions (Tables)	12 Months Ended
	Dec. 31, 2023
Business Combination and Asset Acquisition [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The following table is a summary of the purchase price and the fair value of assets acquired and liabilities assumed as part of the Merger as of November 16, 2023: As of (in millions) November 16, 2023 Consideration transferred settling 35,221,291 shares of outstanding common stock $ 1,056.6 Consideration transferred settling unvested employee stock 2.3 Total consideration $ 1,058.9 Assets Investments: Fixed maturities available-for-sale, at fair value $ 2,525.3 Commercial mortgage loans 144.9 Equity securities, at fair value 11.7 Other investments 327.8 Short-term investments, at fair value 450.1 Total investments 3,459.8 Cash 712.9 Accrued investment income 17.1 Premiums receivable 306.8 Reinsurance recoverables 2,981.6 Other intangible assets 186.1 Current income taxes receivable, net 53.2 Deferred tax asset, net 54.0 Ceded unearned premiums 387.6 Operating lease right-of-use assets 51.6 Other assets 190.8 Value of business acquired 176.3 Total assets (1) $ 8,577.8 Liabilities Reserves for losses and loss adjustment expenses 5,526.4 Unearned premiums 986.2 Accrued underwriting expenses and other liabilities 92.0 Ceded reinsurance payable, net 257.4 Funds held 49.9 Senior unsecured fixed rate notes 127.9 Junior subordinated debentures 241.0 Operating lease liabilities 52.1 Total liabilities assumed (2) $ 7,332.9 Fair value of net assets acquired $ 1,244.9 Other claims on net assets: Preferred stock $ 137.1 Bargain purchase recognized in Additional paid-in capital $ 48.9 (1) Reflects net fair value adjustments of $114.2 million to increase the total assets acquired, including value of business acquired and other intangible assets. (2) Reflects net fair value adjustments of $80.9 million to reduce the total liabilities assumed.
Disposal Groups, Including Discontinued Operations	The table below reflects the carrying amounts of assets and liabilities held-for-sale related to the pending disposition described above: As of (in millions) December 31, 2022 Assets Investments: Fixed maturities available-for-sale, at fair value $ 490.6 Other investments 81.6 Short-term investments, at fair value 114.1 Total investments 686.4 Cash 70.8 Accrued investment income 2.1 Premiums receivable 331.9 Reinsurance recoverables 733.1 Current income taxes receivable, net 6.3 Deferred tax asset, net 28.1 Deferred acquisition costs, net 69.4 Ceded unearned premiums 76.1 Other assets 62.0 Total assets $ 2,066.2 Liabilities Reserves for losses and loss adjustment expenses 993.4 Unearned premiums 335.6 Accrued underwriting expenses and other liabilities 34.4 Ceded reinsurance payable, net 323.5 Funds held 172.9 Other indebtedness 54.7 Total liabilities $ 1,914.5 The following table presents our gross reserves for Run-off Lines: December 31, (in millions) 2023 2022 Asbestos and Environmental: Reinsurance assumed $ 30.4 $ 31.1 Other 29.0 34.4 Total Asbestos and Environmental 59.4 65.5 Risk-management 119.0 144.6 Run-off reinsurance lines 0.4 0.4 Other run-off lines 17.3 22.6 Gross reserves - Run-off Lines $ 196.1 $ 233.1

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2023
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 in fixed maturity investments were as follows: 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 December 31, 2022 (in millions) Amortized Gross Gross Allowance for Credit Losses Fair Fixed maturities U.S. Governments $ 410.9 $ — $ 30.2 $ — $ 380.7 Foreign Governments 35.6 0.3 6.7 0.8 28.4 Obligations of states and political subdivisions 109.9 0.4 10.1 0.4 99.8 Corporate bonds 1,394.8 0.9 160.0 1.6 1,234.1 Commercial mortgage-backed securities 337.4 — 52.0 — 285.4 Residential mortgage-backed securities 320.0 0.2 50.2 — 270.0 Asset-backed securities 153.4 — 14.2 — 139.2 Collateralized loan obligations 254.4 0.3 16.8 — 237.9 Total fixed maturities $ 3,016.4 $ 2.1 $ 340.2 $ 2.8 $ 2,675.5
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 December 31, 2023, by contractual maturity, were as follows: (in millions) Amortized Fair Due in one year or less $ 290.2 $ 290.8 Due after one year through five years 1,019.7 1,037.4 Due after five years through ten years 322.1 337.7 Due after ten years 30.9 34.1 Structured securities 858.6 885.4 Total $ 2,521.5 $ 2,585.4
Schedule of Carrying Value Redemption Characteristics and Unfunded Investment Commitments of Other Invested Assets Portfolio	Details regarding the carrying value and unfunded investment commitments of other investments as of December 31, 2023 and 2022 were as follows: 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 December 31, 2022 (in millions) Carrying Unfunded Investment Type Hedge funds $ 54.0 $ — Private equity 264.6 108.9 Other 4.6 — Total other investments $ 323.2 $ 108.9
Schedule of Aging of Unrealized Losses	An aging of unrealized losses on our investments in fixed maturities is presented below: December 31, 2023 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ — $ — $ — $ — $ — $ — 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 December 31, 2022 Less Than One Year One Year or Greater Total (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Fixed maturities U.S. Governments $ 271.0 $ 18.1 $ 109.8 $ 12.1 $ 380.8 $ 30.2 Foreign Governments 16.7 4.9 2.6 1.8 19.3 6.7 Obligations of states and political subdivisions 67.4 4.1 24.3 6.0 91.7 10.1 Corporate bonds 695.1 68.3 519.6 91.7 1,214.7 160.0 Commercial mortgage-backed securities 144.2 18.6 141.2 33.4 285.4 52.0 Residential mortgage-backed securities 88.7 8.8 178.8 41.4 267.5 50.2 Asset-backed securities 93.3 7.5 45.9 6.7 139.2 14.2 Collateralized loan obligations 181.1 13.3 44.2 3.5 225.3 16.8 Total fixed maturities $ 1,557.5 $ 143.6 $ 1,066.4 $ 196.6 $ 2,623.9 $ 340.2
Schedule of 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 months ending December 31, 2023 and 2022, respectively: Predecessor Foreign Governments Obligations of states and political subdivisions Corporate bonds Asset backed securities Total Balance, January 1, 2022 $ 0.2 $ — $ 2.2 $ 0.1 $ 2.5 Securities for which allowance was not previously recorded 0.4 — 1.8 — 2.2 Securities sold during the period (0.1) — (0.7) — (0.8) Reductions for credit impairments — — (1.4) — (1.4) Additional net increases (decreases) in existing allowance 0.2 0.4 (0.3) — 0.3 Balance, December 31, 2022 $ 0.7 $ 0.4 $ 1.6 $ 0.1 $ 2.8 Additions-initial adoption of accounting standard — — — — — Securities for which allowance was not previously recorded 0.1 0.5 2.1 — 2.7 Securities sold during the period — — (0.7) — (0.7) Reductions for credit impairments — — — — — Additional net increases (decreases) in existing allowance 0.3 (0.4) (0.4) — (0.5) Balance, November 15, 2023 $ 1.1 $ 0.5 $ 2.6 $ 0.1 $ 4.3 Successor Balance, November 16, 2023 $ — $ — $ — $ — $ — Additional net increases (decreases) in existing allowance — — 0.2 — 0.2 Balance, December 31, 2023 $ — $ — $ 0.2 $ — $ 0.2
Schedule of Loans by Property Type	The following table presents loans by property type: 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 December 31, 2022 (in millions) Cost Composition Loan Count Apartments $ 87.4 54.5 % 16 Hotel 25.0 15.6 % 4 Industrial 26.0 16.3 % 4 Retail 21.5 13.6 % 4 Total $ 159.9 100.0 % 28
Schedule of Loans by Debt Service Covenant Ratio	The following table presents our loans by Debt Service Coverage Ratio (“DSCR”): 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 December 31, 2022 (in millions) Cost Loan Count 1.00 to 1.50 $ 10.4 2 Greater than 1.5 to 2.0 60.4 10 Greater than 2.0 to 3.0 52.0 10 Greater than 3.0 to 4.0 25.8 4 Greater than 4.0 11.3 2 Total $ 159.9 28 The following table presents loans by Loan To Value (“LTV”): 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 December 31, 2022 (in millions) Cost Loan Count Equal to or less than 50.0% $ 36.7 6 Greater than 50.0% to 55.0% 9.1 2 Greater than 55.0% to 60.0% 42.6 8 Greater than 60.0% to 70.0% 71.5 12 Total $ 159.9 28
Schedule of Loans by Maturity	The following table presents loans by maturity: 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 December 31, 2022 (in millions) Cost Loan Count Greater than One Year and Less than Three $ 54.8 $ 10 Greater than Three Years and Less than Five Years 33.8 6 Greater than Five Years and Less than Seven Years 20.4 4 Greater than Seven Years and Less than Ten Years 50.9 8 Total $ 159.9 28
Schedule of Company's Gross Realized Investment Gains (Losses)	The following table presents our gross realized investment gains and losses: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Realized gains on fixed maturities and other: Fixed maturities $ 0.1 $ 0.6 $ 20.5 $ 30.6 Other investments, including short-terms 5.4 14.9 34.8 9.8 Other assets — — — 3.3 5.5 15.5 55.3 43.7 Realized losses on fixed maturities and other: Fixed maturities — (25.7) (29.9) (11.8) Other investments, including short-terms (5.4) (11.3) (51.1) (18.5) Other assets — — — (12.5) (5.4) (37.0) (81.0) (42.8) Other net losses recognized on fixed maturities and other: Credit gains (losses) on fixed maturities (0.2) (2.2) (4.6) 0.6 Impairment related to change in intent (1) — (2.9) (34.2) — Other (2) — (8.4) (55.1) (6.3) (0.2) (13.5) (93.9) (5.7) Equity securities Net realized gains (losses) on equity securities — 6.8 1.2 71.5 Change in unrealized gains (losses) on equity securities held at the end of the period (0.2) 5.5 3.1 (34.1) Net gains (losses) on equity securities (0.2) 12.3 4.3 37.4 Net investment and other gains (losses) before income taxes (0.3) (22.7) (115.3) 32.6 Income tax (benefit) provision (0.1) (6.8) (10.0) 6.2 Net investment and other gains (losses), net of income taxes $ (0.2) $ (15.9) $ (105.3) $ 26.4 (1) Refer to the Loss Portfolio Transfer - U.S. in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for the year ended December 31, 2022. (2) Refer to the sale of AGSE and Argo Seguros in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for the year ended December 31, 2022.
Schedule of Changes in Unrealized Appreciation (Depreciation)	Changes in unrealized gains (losses) related to investments are summarized as follows: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Change in unrealized gains (losses) Fixed maturities $ 64.2 $ 41.2 $ (383.7) $ (105.9) Other and short-term investments 0.4 2.0 (0.8) (1.0) Net unrealized investment gains (losses) before income taxes 64.6 43.2 (384.5) (106.9) Income tax provision (benefit) 13.5 7.4 (71.7) (21.5) Net unrealized investment gains (losses), net of income taxes $ 51.1 $ 35.8 $ (312.8) $ (85.4)
Schedule of Fair Value of Foreign Currency Exchange Forward Contracts	The fair value of our foreign currency exchange forward contracts as of December 31, 2023 and 2022 was as follows: As of (in millions) December 31, 2023 December 31, 2022 Operational currency exposure $ 1.8 $ 5.8 Asset manager investment exposure (0.5) (0.6) Total $ 1.3 $ 5.2
Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts	The following table presents our gross investment realized gains and losses on our foreign currency exchange forward contracts: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Realized gains Operational currency exposure $ 4.5 $ 12.0 $ 30.0 $ 16.5 Asset manager investment exposure — 1.5 3.9 3.7 Total return strategy — — — 13.0 Gross realized investment gains 4.5 13.5 33.9 33.2 Realized losses Operational currency exposure (2.9) (11.4) (46.3) (28.9) Asset manager investment exposure (0.7) (1.0) (0.9) (1.0) Total return strategy — — — (12.0) Gross realized investment losses (3.6) (12.4) (47.2) (41.9) Net realized investment gains (losses) on foreign $ 0.9 $ 1.1 $ (13.3) $ (8.7)
Schedule of Restricted Assets	The following table presents our components of restricted assets: As of (in millions) December 31, 2023 December 31, 2022 Securities and cash on deposit for regulatory and other purposes $ 153.4 $ 149.3 Securities pledged as collateral for letters of credit and other 109.2 169.8 Securities on deposit supporting Lloyd’s business (1) — 171.4 Total restricted investments $ 262.6 $ 490.5 (1) Argo Group was required to maintain Funds at Lloyd’s (“FAL”) to support its business for Syndicate 1200 and Syndicate 1910. At December 31, 2022 the amount of securities pledged for FAL was $171.4 million, which was provided by Argo Re, Ltd. FAL of $123.7 million held by Syndicate 1200 and 1910 was reclassified to Assets held-for-sale . During the second quarter 2023, the funds at Lloyd’s (FAL) previously used to support the activities of AUA and its subsidiaries, were released to the Company. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information.
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) December 31, 2023 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 asset (2) Significant other observable inputs (3) Significant unobservable inputs Fair Value Measurements at Reporting Date Using (in millions) December 31, 2022 Level 1 (1) Level 2 (2) Level 3 (3) Fixed maturities U.S. Governments $ 380.7 $ 378.7 $ 2.0 $ — Foreign Governments 28.4 — 28.4 — Obligations of states and political subdivisions 99.8 — 99.8 — Corporate bonds 1,234.1 — 1,212.1 22.0 Commercial mortgage-backed securities 285.4 — 285.4 — Residential mortgage-backed securities 270.0 — 270.0 — Asset-backed securities 139.2 — 120.5 18.7 Collateralized loan obligations 237.9 — 237.9 — Total fixed maturities 2,675.5 378.7 2,256.1 40.7 Equity securities 43.9 28.4 — 15.5 Other investments 0.3 — 0.3 — Short-term investments 449.6 449.3 0.3 — Derivatives 5.2 — 5.2 — Total assets $ 3,174.5 $ 856.4 $ 2,261.9 $ 56.2 (1) Quoted prices in active markets for identical asset (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 Observable Inputs (Level 3) (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 income 0.8 — 0.8 Purchases, issuances, sales, and settlements: Purchases 10.6 — 10.6 Issuances — — — 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) (in millions) Credit Financial Equity Total Beginning balance, January 1, 2022 $ 2.8 $ 14.7 $ 17.5 Transfers into Level 3 36.1 1.5 37.6 Transfers out of Level 3 — — — Total gains or losses (realized/unrealized): Included in net income (0.4) (0.7) (1.1) Included in other comprehensive loss (4.8) — (4.8) Purchases, issuances, sales, and settlements: Purchases 9.0 1.0 10.0 Issuances — — — Sales (2.0) (1.0) (3.0) Settlements — — — Ending balance, December 31, 2022 $ 40.7 $ 15.5 $ 56.2 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, 2022 $ — $ (4.4) $ (4.4)
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	As of December 31, 2023, the cost and estimated fair value of the investments in commercial mortgage loans were: As of December 31, 2023 December 31, 2022 (in millions) Cost Fair Value Cost Fair Value Commercial Mortgage Loans $ 144.8 $ 148.8 $ 159.9 $ 150.7 A summary of our financial instruments whose carrying value did not equal fair value is shown below: December 31, 2023 2022 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 160.8 $ 165.9 $ 172.7 $ 165.8 Subordinated debentures 80.4 83.3 85.9 88.1 Total junior subordinated debentures 241.2 249.2 258.6 253.9 Senior unsecured fixed rate notes 128.0 132.7 140.5 112.7 Floating rate loan stock (1) — — 54.7 52.5 $ 369.2 $ 381.9 $ 453.8 $ 419.1 (1) Floating rate loan stock reclassified to liabilities held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. Based on an analysis of the inputs, our financial instruments measured at fair value on a recurring basis have been categorized as follows: 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 Fair Value Measurements at Reporting Date Using (in millions) December 31, 2022 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 165.8 $ — $ 165.8 $ — Subordinated debentures 88.1 — 88.1 — Total junior subordinated debentures 253.9 — 253.9 — Senior unsecured fixed rate notes 112.7 112.7 — — Floating rate loan stock 52.5 — 52.5 — $ 419.1 $ 112.7 $ 306.4 $ — (1) Quoted prices in active markets for identical assets (2) Significant other observable inputs (3) Significant unobservable inputs

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2023
Credit Loss [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table represents the balances of premiums receivable, net of allowance for estimated uncollectible premiums, including expected lifetime credit losses, as of December 31, 2023, 2022 and 2021, and the changes in the allowance for the period November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. Predecessor (in millions) Premiums Receivable, Net of Allowance for Estimated Uncollectible Premiums Allowance for Estimated Uncollectible Premiums Balance, December 31, 2021 $ 648.6 $ 5.7 Current period change for estimated uncollectible premiums 0.2 Write-offs of uncollectible premiums receivable (1.2) Balance, December 31, 2022 $ 292.0 $ 4.7 Current period change for estimated uncollectible premiums 5.4 Write-offs of uncollectible premiums receivable (2.7) Balance, November 15, 2023 $ 306.8 $ 7.4 Successor Balance, November 16, 2023 $ 306.8 $ — Current period change for estimated uncollectible premiums 3.3 Write-offs of uncollectible premiums receivable (0.3) Balance, December 31, 2023 $ 230.7 $ 3.0
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, at December 31, 2023, 2022 and 2021, and changes in the allowance for the period November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. Predecessor (in millions) Reinsurance Recoverables, Net of Allowance for Estimated Uncollectible Reinsurance Allowance for Estimated Uncollectible Reinsurance Balance, December 31, 2021 $ 2,966.4 $ 3.8 Current period change for estimated uncollectible reinsurance 1.7 Reclassified to assets held-for-sale (0.8) Balance, December 31, 2022 $ 3,029.1 $ 4.7 Balance, November 15, 2023 $ 2,981.6 $ 4.7 Successor Balance, December 31, 2023 $ 2,959.3 $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Lease Components	The lease information is as follows: December 31, 2023 2022 (in millions) Operating leases right-of-use assets (1) $ 51.2 $ 57.7 Operating lease liabilities (2) 51.4 66.4 Operating lease weighted-average remaining lease term 7.70 8.22 Operating lease weighted-average discount rate 6.13 % 3.44 % (1) $0.5 million of Operating leases right-of-use-assets were reclassified to assets held-for-sale. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” at December 31, 2022. (2) $0.5 million of Operating lease liabilities were reclassified to liabilities held-for-sale. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” at December 31, 2022.
Schedule of Lease Cost	Successor Predecessor Period from Period from November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 For the Year Ended December 31, 2022 (in millions) Operating lease costs $ 0.7 $ 5.2 $ 8.1 Variable lease costs 0.5 3.3 4.7 Sublease income (0.1) (0.9) (1.0) Total lease costs $ 1.1 $ 7.6 $ 11.8
Schedule of Operating Lease Maturity	Future minimum lease payments under operating leases as of December 31, 2023 were as follows: December 31, (in millions) 2023 2024 8.9 2025 9.1 2026 8.9 2027 8.3 2028 6.9 Thereafter 22.5 Total future minimum lease payments $ 64.6 Less imputed interest (13.2) Total operating lease liability $ 51.4

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2023
Insurance [Abstract]
Schedule of Reinsurance Premiums	Premiums were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Direct written premiums $ 186.0 $ 1,907.9 $ 2,682.8 $ 2,990.6 Reinsurance ceded to other companies (66.8) (803.6) (1,106.7) (1,203.9) Reinsurance assumed from other companies 5.1 40.4 165.4 190.6 Net written premiums $ 124.3 $ 1,144.7 $ 1,741.5 $ 1,977.3 Direct earned premiums $ 252.3 $ 1,906.5 $ 2,757.8 $ 2,917.7 Reinsurance ceded to other companies (98.4) (724.9) (1,205.3) (1,272.7) Reinsurance assumed from other companies 8.4 44.3 187.9 265.1 Net earned premiums $ 162.3 $ 1,225.9 $ 1,740.4 $ 1,910.1 Percentage of reinsurance assumed to net earned premiums 5.2 % 3.6 % 10.8 % 13.9 %

Reserves for Losses and Loss _2

Reserves for Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2023
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 Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Net reserves beginning of the period $ 2,734.6 $ 2,213.1 $ 3,123.2 $ 2,906.1 Add: Losses and LAE incurred during current calendar year, net of reinsurance: Current accident year 94.2 775.3 1,102.2 1,176.3 Prior accident years — 267.9 64.7 138.3 Losses and LAE incurred during calendar year, net of reinsurance 94.2 1,043.2 1,166.9 1,314.6 Deduct: Losses and LAE payments made during current calendar year, net of reinsurance: Current accident year 33.5 100.6 171.5 180.8 Prior accident years 51.8 427.3 828.0 688.4 Losses and LAE payments made during current calendar year, net of reinsurance: 85.3 527.9 999.5 869.2 Add/(Deduct): Divestitures (1) — 24.4 (35.2) — Reclassified to liabilities held-for-sale (2) — — (313.0) — Net reserves ceded to Syndicate 1200 (2) — — (129.6) — Deferred gain on U.S. loss portfolio transfer, net of amortization — (40.9) — — Loss portfolio transfer: U.S. (3) — — (472.6) — Syndicate 1200 (for years of account 2019 and 2018) (4) — — (144.0) — Reinsurance to close transaction (for years of account 2017 and prior) (5) — — — (219.7) Retroactive reinsurance (6) — 21.7 — — Change in participation interest (7) — — 34.3 8.4 Total net reserve adjustments — 5.2 (1,060.1) (211.3) Foreign exchange adjustments 3.6 1.0 (17.4) (17.0) Net reserves - end of period 2,747.1 2,734.6 2,213.1 3,123.2 Add: Reinsurance recoverables on unpaid losses and LAE, end of year 2,797.4 2,791.8 2,838.5 2,471.8 Gross reserves - end of period $ 5,544.5 $ 5,526.4 $ 5,051.6 $ 5,595.0 (1) For the period ended November 15, 2023, the adjustment relates to the year-to-date activity of Syndicate 1200 and on reinsurance contracts with AUA subsidiaries. Refer to the sale of Argo Underwriting Agency Limited in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. For the period ended December 31, 2022, refer to the sale of Argo Seguros and AGSE in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (2) Refer to the sale of Argo Underwriting Agency Limited in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. Additionally, the Company reduced net reserves in the amount of $129.6 million for reinsurance contracts with AUA subsidiaries, which were reclassified to held-for-sale. (3) Loss portfolio transfer of the Company’s U.S. casualty insurance reserves for accident years 2011 to 2019. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (4) Loss portfolio transfer on Syndicate 1200's reserves for the 2018 and 2019 years of account. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (5) Amount represents reserves ceded under the reinsurance to close transaction with RiverStone for Lloyd’s years of account 2017 and prior, effective January 1, 2021. (6) In connection with the sale of AUA, the Company entered into two retroactive reinsurance agreements with AUA subsidiaries. (7) Amount represents the change in reserves due to changing our participation in Syndicates 1200 and 1910.
Impact from (Favorable) Unfavorable Development of Prior Accident Years’ Loss and LAE Reserves on Each Reporting Segment	The impact from the net unfavorable (favorable) development of prior accident years’ losses and LAE reserves on each reporting segment is presented below: Predecessor Period from For the Years Ended December 31, (in millions) January 1, 2023 through November 15, 2023 2022 2021 U.S. Operations $ 246.3 $ 64.5 $ 120.9 International Operations 21.4 (2.7) (26.9) Run-off Lines 0.2 2.9 44.3 Total (favorable) unfavorable prior-year development $ 267.9 $ 64.7 $ 138.3
Summary of Information About Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	The following tables provide information about incurred and cumulative paid losses and allocated loss adjustment expenses (“ALAE”), net of reinsurance. The following tables also include IBNR reserves plus expected development on reported claims and the cumulative number of reported claims as of December 31, 2023. Reporting Segment: U.S. Operations Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 328.6 $ 337.1 $ 330.0 $ 326.3 $ 323.9 $ 321.9 $ 327.4 $ 341.3 $ 310.7 $ 312.1 2015 339.8 343.8 330.3 328.7 328.0 335.4 347.9 318.9 321.5 2016 342.6 350.5 342.4 353.0 355.3 379.0 349.1 354.5 2017 374.8 373.7 384.3 397.7 431.7 385.2 391.2 2018 426.1 430.4 414.5 420.4 366.5 390.7 2019 421.1 423.7 427.1 318.6 353.1 2020 404.2 386.7 371.1 433.9 2021 416.4 419.1 461.2 2022 439.5 466.9 2023 435.8 Total $ 3,920.9 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 32.4 $ 91.0 $ 154.6 $ 206.9 $ 240.6 $ 266.3 $ 283.2 $ 291.4 $ 304.4 $ 305.8 2015 33.7 86.9 140.2 195.6 236.4 263.9 289.3 305.6 307.2 2016 28.5 84.5 144.1 217.1 255.6 293.8 327.1 331.8 2017 27.8 83.0 158.8 238.5 295.2 348.0 354.2 2018 34.3 98.9 175.8 245.5 315.9 335.7 2019 32.4 113.6 186.1 260.1 290.6 2020 25.6 85.9 149.0 228.7 2021 27.5 83.1 164.8 2022 27.2 92.0 2023 22.4 Total $ 2,433.2 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 58.7 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 1,546.4 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 312.1 $ (7.0) 22,319 2015 321.5 (1.3) 20,936 2016 354.5 4.9 18,105 2017 391.2 0.1 20,982 2018 390.7 6.1 23,539 2019 353.1 (4.2) 22,976 2020 433.9 115.1 18,812 2021 461.2 211.7 15,248 2022 466.9 291.5 13,729 2023 435.8 361.0 10,514 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 22.4 $ 22.4 $ 26.0 $ 33.7 $ 36.2 $ 35.4 $ 35.1 $ 34.4 $ 32.7 $ 32.7 2015 29.9 29.5 33.2 34.0 37.1 37.9 38.3 31.3 31.3 2016 44.2 44.8 45.1 42.9 35.5 43.0 43.5 46.1 2017 60.1 61.8 78.3 87.9 99.5 87.0 87.3 2018 70.8 73.2 79.2 94.8 88.5 87.8 2019 94.4 96.8 105.0 94.5 117.7 2020 152.6 142.6 127.8 160.0 2021 177.8 159.5 159.6 2022 185.4 169.1 2023 164.0 Total 1,055.6 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 2.3 $ 5.4 $ 15.1 $ 24.1 $ 25.5 $ 32.3 $ 33.3 $ 33.6 $ 33.5 $ 33.6 2015 1.8 8.3 15.6 20.8 26.2 31.3 31.7 33.8 33.8 2016 2.4 11.9 24.6 28.9 30.8 34.4 38.3 43.5 2017 3.5 24.9 38.0 59.7 77.9 85.5 85.5 2018 4.5 16.7 43.8 62.6 78.8 79.7 2019 4.9 32.9 50.0 81.7 92.9 2020 13.3 36.4 70.5 81.6 2021 12.2 39.6 54.7 2022 14.3 25.7 2023 4.1 Total $ 535.1 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 11.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 532.0 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 32.7 $ (0.8) 1,044 2015 31.3 (2.5) 1,832 2016 46.1 2.2 3,264 2017 87.3 (9.7) 3,774 2018 87.8 (3.7) 4,298 2019 117.7 15.4 4,901 2020 160.0 41.6 5,012 2021 159.6 68.4 5,153 2022 169.1 122.1 5,120 2023 164.0 141.8 4,396 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Property (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 80.4 $ 82.2 $ 77.0 $ 77.1 $ 76.9 $ 76.9 $ 76.1 $ 76.0 $ 76.1 $ 74.8 2015 74.0 73.4 69.9 68.9 69.1 69.2 69.2 68.4 67.8 2016 59.4 57.6 57.1 56.6 56.6 56.5 54.2 54.4 2017 75.2 79.6 86.9 94.9 94.5 97.4 91.3 2018 89.2 93.1 95.1 96.9 102.4 101.1 2019 91.4 88.8 98.4 97.9 90.3 2020 129.5 133.2 133.1 134.0 2021 111.7 114.8 116.7 2022 103.1 104.4 2023 94.7 Total $ 929.5 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 51.6 $ 73.1 $ 75.7 $ 76.4 $ 76.3 $ 76.4 $ 76.1 $ 76.0 $ 76.0 $ 76.0 2015 44.6 67.6 68.6 67.9 68.3 68.5 69.0 68.6 68.6 2016 39.4 55.2 55.8 56.1 56.4 56.3 54.5 54.5 2017 54.4 95.3 113.9 100.8 88.4 95.1 90.5 2018 61.3 126.7 107.0 98.8 101.4 102.5 2019 55.8 82.4 90.9 94.0 96.0 2020 75.9 116.6 121.6 126.6 2021 71.3 118.3 118.2 2022 52.2 94.7 2023 59.1 Total 886.7 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 0.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 43.3 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 74.8 $ (1.2) 8,057 2015 67.8 (0.8) 7,362 2016 54.4 (0.1) 7,701 2017 91.3 (2.6) 9,930 2018 101.1 (4.3) 10,881 2019 90.3 (6.9) 11,496 2020 134.0 (6.4) 11,379 2021 116.7 (5.8) 10,312 2022 104.4 2.6 9,119 2023 94.7 16.2 7,707 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: U.S. Operations Line of Business: Specialty (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 13.1 $ 13.1 $ 8.9 $ 6.0 $ 4.8 $ 4.6 $ 4.6 $ 4.1 $ 4.1 $ 4.1 2015 14.8 14.3 9.5 5.5 1.2 0.5 0.3 0.2 0.2 2016 15.0 15.0 11.2 6.2 4.7 3.3 3.2 2.8 2017 16.2 16.2 7.6 0.9 0.7 0.7 0.6 2018 20.9 17.4 3.3 3.5 3.5 3.3 2019 22.7 8.5 5.6 5.9 5.8 2020 25.4 10.3 15.9 15.0 2021 27.9 5.2 2.0 2022 33.0 28.9 2023 34.6 Total $ 97.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 1.1 $ 3.3 $ 4.0 $ 4.0 $ 4.1 $ 4.1 $ 4.0 $ 4.1 $ 4.1 $ 4.1 2015 0.2 0.1 0.2 0.3 0.3 0.3 0.3 0.2 0.2 2016 1.3 1.6 2.2 2.2 2.2 2.8 2.8 2.8 2017 0.3 0.1 — 0.1 0.2 0.2 0.2 2018 — 0.7 1.7 1.2 2.4 2.9 2019 0.7 0.7 3.2 5.4 5.2 2020 0.3 7.6 10.6 10.5 2021 0.2 1.4 1.6 2022 0.1 13.4 2023 1.1 Total 42.0 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 0.6 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 55.9 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 4.1 $ — 20 2015 0.2 — 14 2016 2.8 0.1 46 2017 0.6 0.4 62 2018 3.3 0.3 82 2019 5.8 0.1 124 2020 15.0 — 274 2021 2.0 0.3 291 2022 28.9 5.6 257 2023 34.6 33.1 175 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) During 2021, the Company revised the manner in which it measures reported claims. The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. During 2021, we implemented additional processes to consolidate multiple data sources for U.S. Operations reserving. As part of that process, the level of detail used to determine the number of reported claims for some of the business units in US Operations changed. As a result, the cumulative number of reported claims for each accident year presented above as of December 31, 2021 is not comparable to the cumulative number of reported claims disclosed in previously issued financial statements. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Liability (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 9.8 $ 9.8 $ 9.8 $ 6.2 $ 1.5 $ 2.3 $ 2.3 $ 1.6 $ 1.6 $ 1.6 2015 11.3 14.3 24.8 35.4 45.4 45.1 51.3 50.3 50.3 2016 13.9 14.0 14.0 6.6 6.1 0.8 2.4 6.5 2017 17.1 17.3 26.9 30.3 37.3 44.3 46.2 2018 8.9 32.1 26.6 24.2 22.9 19.8 2019 13.3 13.6 13.8 13.3 13.3 2020 23.3 24.9 12.4 12.4 2021 12.3 11.4 12.4 2022 11.1 11.1 2023 12.7 Total $ 186.3 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ — $ — $ 0.1 $ 0.1 $ 1.2 $ 1.2 $ 1.4 $ 1.4 $ 1.4 $ 1.4 2015 — — 16.1 20.3 26.6 34.8 38.9 50.2 50.3 2016 — — — 0.1 0.1 0.2 0.3 0.3 2017 — 3.3 3.4 18.0 19.7 22.0 27.6 2018 — 13.8 18.3 18.5 18.5 19.1 2019 — 0.1 0.7 0.6 0.9 2020 0.8 7.0 0.5 0.6 2021 — — 0.3 2022 — — 2023 — Total $ 100.5 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 2.5 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 88.3 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 1.6 $ (0.4) 1,361 2015 50.3 — 1,629 2016 6.5 6.0 1,969 2017 46.2 7.8 2,176 2018 19.8 0.4 1,159 2019 13.3 12.4 1,254 2020 12.4 7.0 1,434 2021 12.4 6.2 1,436 2022 11.1 11.1 1,293 2023 12.7 12.5 1,519 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims. Reporting Segment: International Operations Operating Division: Argo Insurance Bermuda Line of Business: Professional (in millions, except number of claims reported) Incurred Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ 4.0 $ 4.0 $ 4.0 $ 4.0 $ 3.9 $ 10.2 $ 12.5 $ 8.1 $ 10.1 $ 10.1 2015 4.9 4.9 4.9 2.7 5.0 5.2 7.3 7.9 5.2 2016 6.7 6.7 4.8 3.1 7.3 3.1 1.9 3.8 2017 7.6 7.6 9.7 9.5 12.4 10.5 15.3 2018 8.3 8.3 8.0 6.5 21.3 36.8 2019 9.6 8.7 16.4 18.3 18.1 2020 10.4 10.4 10.4 11.1 2021 13.0 13.0 12.3 2022 9.5 9.4 2023 15.9 Total $ 138.0 Cumulative Paid Losses & ALAE, Net of Reinsurance Accident For the Years Ended December 31, 2014 (1) 2015 (1) 2016 (1) 2017 (1) 2018 (1) 2019 (1) 2020 (1) 2021 (1) 2022 (1) 2023 (1) 2014 $ — $ — $ — $ 0.3 $ 1.0 $ 0.4 $ 3.2 $ 0.4 $ 0.4 $ 0.4 2015 — — — — — — 2.9 2.9 4.0 2016 — — — — — — — 0.1 2017 0.1 0.1 4.9 9.8 9.8 9.8 9.9 2018 — — 2.0 2.1 6.0 6.1 2019 2.0 0.6 0.6 0.7 0.7 2020 — — — 6.1 2021 — — — 2022 — — 2023 — Total 27.3 Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance 3.2 Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance $ 113.9 As of December 31, 2023 Accident Year Incurred Losses & ALAE, Net of Reinsurance IBNR & Expected Development on Reported Claims Cumulative Number of Reported Claims (2) 2014 $ 10.1 $ 2.3 1,130 2015 5.2 1.1 1,158 2016 3.8 3.7 1,280 2017 15.3 5.3 1,471 2018 36.8 23.0 1,101 2019 18.1 7.1 1,111 2020 11.1 5.0 965 2021 12.3 11.5 858 2022 9.4 9.4 844 2023 15.9 15.8 883 (1) Information presented for calendar years prior to 2023 is required supplementary information and is unaudited. (2) The cumulative number of reported claims is measured by individual claimant at a coverage level. Reported occurrences that do not result in a liability are included as reported claims.
Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets	The reconciliation of the net incurred and paid development tables to the liability for unpaid losses and LAE in our Consolidated Balance Sheets is as follows: (in millions) As of December 31, 2023 Liabilities for unpaid losses and ALAE: US Operations: Liability $ 1,546.4 Professional 532.0 Property 43.3 Specialty 55.9 International Operations: Argo Insurance Bermuda- Liability 88.3 Argo Insurance Bermuda- Professional 113.9 Run-off Lines 147.7 Other lines 169.7 Total liabilities for unpaid losses and ALAE, net of reinsurance 2,697.2 Reinsurance recoverables on unpaid losses and LAE: US Operations: Liability 1,382.6 Professional 424.4 Property 169.9 Specialty 25.5 International Operations: Argo Insurance Bermuda- Liability 246.3 Argo Insurance Bermuda- Professional 181.7 Run-off Lines 53.2 Other lines 313.8 Total reinsurance recoverables on unpaid losses and LAE 2,797.4 Unallocated loss adjustment expenses 70.7 Unamortized reserve discount (20.8) Gross liability for unpaid losses and LAE $ 5,544.5
Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance	The following table provides supplementary unaudited information about the annual percentage payout of incurred losses and ALAE, net of reinsurance, as of December 31, 2023: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (1) Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9 Year 10 Remainder U.S. Operations: U.S. Liability 8.6% 18.8% 20.8% 21.4% 11.8% 7.1% 4.2% 2.5% 1.6% 1.0% 2.2% U.S. Professional 7.1% 17.5% 19.6% 17.3% 13.2% 9.2% 6.1% 3.9% 2.4% 1.5% 2.2% U.S. Property 56.4% 35.8% 5.7% 1.6% 0.4% 0.1% —% —% —% —% —% U.S. Specialty 15.2% 47.8% 23.8% 8.6% 2.5% 1.1% 0.5% 0.2% 0.1% 0.1% 0.1% International Operations: Bermuda Insurance Professional 2.7% 7.6% 11.8% 13.7% 13.5% 11.9% 9.8% 7.7% 5.9% 4.4% 11.1% Bermuda Insurance Liability 0.5% 13.5% 18.4% 14.7% 10.7% 7.8% 5.9% 4.5% 3.6% 2.9% 17.5% (1) The average annual percentage payout is calculated from a paid losses and ALAE development pattern based on an actuarial analysis of the paid losses and ALAE movements by accident year for each disaggregation category. The paid losses and ALAE development pattern provides the expected percentage of ultimate losses and ALAE to be paid in each year. The pattern considers all accident years included in the claim’s development tables .
Schedule of Information About Discounted Liabilities for Unpaid Losses and LAE	The following tables provide information about these discounted liabilities for unpaid losses and LAE: Carrying Amount of Reserves for Losses & LAE Aggregate Amount of Discount As of December 31, As of December 31, (in millions, except discount percentages) 2023 2022 2021 2023 2022 2021 US Operations: Commercial Specialty - Liability $ 182.6 $ 168.0 $ 163.1 $ 16.1 $ 14.7 $ 14.1 Run-off Lines 76.8 93.0 114.3 4.7 4.6 4.7 Total $ 259.4 $ 261.0 $ 277.4 $ 20.8 $ 19.3 $ 18.8 Interest Accretion (1) Discount Rate Successor Predecessor Period from Period from For the Years Ended December 31, As of December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 2023 2022 2021 US Operations: Commercial Specialty - Liability $ 0.1 $ 1.3 $ 1.7 $ 0.9 2.25% 2.25% 2.25% Run-off Lines — 0.1 0.1 0.2 3.50% 3.50% 3.50% Total $ 0.1 $ 1.4 $ 1.8 $ 1.1 (1) Interest accretion is recorded in the line item Losses and loss adjustment expenses in our Consolidated Statements of Income (Loss).

Run-off Lines (Tables)

Run-off Lines (Tables)	12 Months Ended
	Dec. 31, 2023
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations	The table below reflects the carrying amounts of assets and liabilities held-for-sale related to the pending disposition described above: As of (in millions) December 31, 2022 Assets Investments: Fixed maturities available-for-sale, at fair value $ 490.6 Other investments 81.6 Short-term investments, at fair value 114.1 Total investments 686.4 Cash 70.8 Accrued investment income 2.1 Premiums receivable 331.9 Reinsurance recoverables 733.1 Current income taxes receivable, net 6.3 Deferred tax asset, net 28.1 Deferred acquisition costs, net 69.4 Ceded unearned premiums 76.1 Other assets 62.0 Total assets $ 2,066.2 Liabilities Reserves for losses and loss adjustment expenses 993.4 Unearned premiums 335.6 Accrued underwriting expenses and other liabilities 34.4 Ceded reinsurance payable, net 323.5 Funds held 172.9 Other indebtedness 54.7 Total liabilities $ 1,914.5 The following table presents our gross reserves for Run-off Lines: December 31, (in millions) 2023 2022 Asbestos and Environmental: Reinsurance assumed $ 30.4 $ 31.1 Other 29.0 34.4 Total Asbestos and Environmental 59.4 65.5 Risk-management 119.0 144.6 Run-off reinsurance lines 0.4 0.4 Other run-off lines 17.3 22.6 Gross reserves - Run-off Lines $ 196.1 $ 233.1
Total Gross Reserves for Asbestos Exposure	The following table represents the total gross reserves for our asbestos exposure: December 31, (in millions) 2023 2022 2021 Direct written Case reserves $ 2.9 $ 3.2 $ 3.0 Unallocated loss adjustment expense 0.5 0.5 0.5 Incurred but not reported 14.3 17.4 19.9 Total direct written reserves 17.7 21.1 23.4 Assumed domestic Case reserves 7.6 6.8 7.4 Unallocated loss adjustment expense 0.8 0.8 0.8 Incurred but not reported 11.6 13.0 11.9 Total assumed domestic reserves 20.0 20.6 20.1 Assumed London Case reserves 2.8 2.4 2.1 Incurred but not reported 0.1 2.6 2.3 Total assumed London reserves 2.9 5.0 4.4 Total asbestos reserves $ 40.6 $ 46.7 $ 47.9
Underwriting Losses for Run-Off Lines	The following table presents our underwriting losses for Run-off Lines: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Asbestos and Environmental: Reinsurance assumed $ — $ — $ 3.5 $ 4.7 Other 0.3 1.2 7.0 10.0 Total Asbestos and Environmental 0.3 1.2 10.5 14.7 Risk-management — — 1.4 9.9 Run-off reinsurance lines — — — — Other run-off lines 0.4 2.0 (8.3) 20.1 Total underwriting loss - Run-off Lines $ 0.7 $ 3.2 $ 3.6 $ 44.7

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Schedule Of Unamortized Debt Issuance Costs Deducted From Carrying Value Of Debt Liability	At December 31, 2023 and 2022, the Notes consisted of the following: (in millions) December 31, 2023 December 31, 2022 Senior unsecured fixed rate notes Principal $ 143.8 $ 143.8 Less: unamortized debt issuance costs and fair value adjustment (15.8) (3.3) Senior unsecured fixed rate notes, less unamortized debt issuance costs $ 128.0 $ 140.5
Schedule of Long-term Debt	A summary of our outstanding junior subordinated debentures is presented below: December 31, 2023 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2023 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M SOFR + TSA + 4.10% 9.74% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M SOFR + TSA + 3.90% 9.49% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M SOFR + TSA + 4.10% 9.74% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M SOFR + TSA + 4.10% 9.76% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M SOFR + TSA + 3.85% 9.49% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M SOFR + TSA + 3.85% 9.49% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M SOFR + TSA + 3.80% 9.47% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M SOFR + TSA + 3.60% 9.25% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M SOFR + TSA + 3.55% 9.18% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M SOFR + TSA + 3.60% 9.25% 15.5 9/15/2005 Argonaut Group Statutory Trust X 9/15/2035 3M SOFR + TSA + 3.40% 9.05% 30.9 Less: fair value adjustment (11.9) Total Outstanding $ 160.8 December 31, 2022 (in millions) Issue Date Trust Preferred Pools Maturity Rate Structure Interest Rate at December 31, 2022 Amount Argo Group 5/15/2003 PXRE Capital Statutory Trust II 5/15/2033 3M LIBOR + 4.10% 8.71% $ 18.0 11/6/2003 PXRE Capital Trust VI 9/30/2033 3M LIBOR + 3.90% 8.63% 10.3 Argo Group US 5/15/2003 Argonaut Group Statutory Trust I 5/15/2033 3M LIBOR + 4.10% 8.71% 15.5 12/16/2003 Argonaut Group Statutory Trust III 1/8/2034 3M LIBOR + 4.10% 8.18% 12.3 4/29/2004 Argonaut Group Statutory Trust IV 4/29/2034 3M LIBOR + 3.85% 8.50% 13.4 5/26/2004 Argonaut Group Statutory Trust V 5/24/2034 3M LIBOR + 3.85% 8.61% 12.4 5/12/2004 Argonaut Group Statutory Trust VI 6/17/2034 3M LIBOR + 3.80% 8.54% 13.4 9/17/2004 Argonaut Group Statutory Trust VII 12/15/2034 3M LIBOR + 3.60% 8.37% 15.5 9/22/2004 Argonaut Group Statutory Trust VIII 9/22/2034 3M LIBOR + 3.55% 8.30% 15.5 10/22/2004 Argonaut Group Statutory Trust IX 12/15/2034 3M LIBOR + 3.60% 8.37% 15.5 9/15/2005 Argonaut Group Statutory Trust X 9/15/2035 3M LIBOR + 3.40% 8.17% 30.9 Total Outstanding $ 172.7 A summary of the terms of the acquired debt outstanding is presented below: (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2023 Principal at December 31, 2023 Carrying Value at December 31, 2023 9/13/2007 9/15/2037 3M SOFR + TSA + 3.15% 8.79 % $ 91.8 $ 80.4 (in millions) Issue Date Maturity Rate Structure Interest Rate at December 31, 2022 Principal at December 31, 2022 Carrying Value at December 31, 2022 9/13/2007 9/15/2037 3 month LIBOR + 3.15% 7.92 % $ 91.8 $ 85.9
Schedule of Outstanding Balance	The following table presents interest and maturities of long-term debt as of December 31, 2023: For the Years Ended (in millions) Total 2024 2025 2026 2027 2028 Thereafter Long-term debt: Junior subordinated debentures (1) 548.3 24.6 24.6 24.6 24.6 24.6 425.3 Senior unsecured fixed rate notes (2) 316.5 9.3 9.3 9.3 9.3 9.3 270.0 (1) Interest only on Junior Subordinated Debentures through 2037. Interest calculated based on interest rate forecast. Principal due beginning May 2033. (2) Interest only on Senior Unsecured Fixed Rate Notes through 2042. Interest calculated based on the fixed rate of the notes. Principal due September 2042.

Disclosures about Fair Value _2

Disclosures about Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Summary of Company's Financial Instruments Whose Carrying Amount Did Not Equal Fair Value	As of December 31, 2023, the cost and estimated fair value of the investments in commercial mortgage loans were: As of December 31, 2023 December 31, 2022 (in millions) Cost Fair Value Cost Fair Value Commercial Mortgage Loans $ 144.8 $ 148.8 $ 159.9 $ 150.7 A summary of our financial instruments whose carrying value did not equal fair value is shown below: December 31, 2023 2022 (in millions) Carrying Fair Carrying Fair Junior subordinated debentures: Trust preferred debentures $ 160.8 $ 165.9 $ 172.7 $ 165.8 Subordinated debentures 80.4 83.3 85.9 88.1 Total junior subordinated debentures 241.2 249.2 258.6 253.9 Senior unsecured fixed rate notes 128.0 132.7 140.5 112.7 Floating rate loan stock (1) — — 54.7 52.5 $ 369.2 $ 381.9 $ 453.8 $ 419.1 (1) Floating rate loan stock reclassified to liabilities held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”. Based on an analysis of the inputs, our financial instruments measured at fair value on a recurring basis have been categorized as follows: 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 Fair Value Measurements at Reporting Date Using (in millions) December 31, 2022 Level 1 (1) Level 2 (2) Level 3 (3) Junior subordinated debentures: Trust preferred debentures $ 165.8 $ — $ 165.8 $ — Subordinated debentures 88.1 — 88.1 — Total junior subordinated debentures 253.9 — 253.9 — Senior unsecured fixed rate notes 112.7 112.7 — — Floating rate loan stock 52.5 — 52.5 — $ 419.1 $ 112.7 $ 306.4 $ — (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)	12 Months Ended
	Dec. 31, 2023
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income (Loss)	A summary of changes in accumulated other comprehensive income (loss), net of taxes (where applicable) by component for the periods November 16, 2023 through December 31, 2023 (Successor), January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021 is presented below: (in millions) Foreign Currency Translation Adjustments Unrealized Defined Benefit Pension Plans Total Predecessor Balance, December 31, 2021 $ (35.3) $ 19.7 $ (7.1) $ (22.7) Other comprehensive loss before reclassifications (0.7) (347.2) (0.7) (348.6) Amounts reclassified from accumulated other comprehensive loss 31.8 34.4 — 66.2 Net current-period other comprehensive income (loss) 31.1 (312.8) (0.7) (282.4) Balance, December 31, 2022 (4.2) (293.1) (7.8) (305.1) Other comprehensive income before reclassifications 1.0 13.7 0.8 15.5 Amounts reclassified from accumulated other comprehensive loss — 22.1 — 22.1 Net current-period other comprehensive income 1.0 35.8 0.8 37.6 Balance, November 15, 2023 $ (3.2) $ (257.3) $ (7.0) $ (267.5) Successor Balance, November 16, 2023 — — — — Other comprehensive income before reclassifications 0.1 51.2 0.6 51.9 Amounts reclassified from accumulated other comprehensive income — (0.1) — (0.1) Net current-period other comprehensive income 0.1 51.1 0.6 51.8 Balance, December 31, 2023 $ 0.1 $ 51.1 $ 0.6 $ 51.8
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	The amounts reclassified from accumulated other comprehensive (loss) income shown in the above table have been included in the following captions in our Consolidated Statements of Income (Loss): Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Unrealized gains and losses on securities: Net realized investment and other losses (gains) (1) $ (0.1) $ 28.0 $ 43.6 $ (12.2) (Benefit) provision for income taxes — (5.9) (9.2) 4.2 Foreign currency translation adjustments: Net realized investment and other losses (gains) (2) — — 31.8 — Total, net of taxes $ (0.1) $ 22.1 $ 66.2 $ (8.0) (1) Net realized investment and other losses (gains) in the Predecessor periods include losses realized as a result of the Loss Portfolio Transfer - U.S. and the sale of Argo Underwriting Agency Limited. Refer to Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information. (2) Foreign currency translation losses were realized as a result of the sale of Argo Seguros and AGSE in 2022. Refer to the sale of Argo Seguros and AGSE in Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information.

Net (Loss) Income Per Common _2

Net (Loss) Income Per Common Stock (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Income Per Common Share on Basic and Diluted Basis	The following table presents the calculation of net (loss) income per shares of common stock on a basic and diluted basis for the Predecessor period: Predecessor Period from For the Years Ended December 31, January 1, 2023 through November 15, 2023 2022 2021 (in millions, except number of shares and per share amounts) Net income (loss) $ (210.4) $ (175.2) $ 6.7 Less: Preferred stock dividends 10.5 10.5 10.5 Net income (loss) attributable to common stockholders (220.9) (185.7) (3.8) Weighted average common stock outstanding - basic 35,166,679 34,980,608 34,816,160 Effect of dilutive securities: Equity compensation awards — — — Weighted average common stock outstanding - diluted 35,166,679 34,980,608 34,816,160 Net income (loss) per common stock: Basic $ (6.28) $ (5.31) $ (0.11) Diluted $ (6.28) $ (5.31) $ (0.11)

Share-based Compensation (Table

Share-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Summary of Performance Share Activity	A summary of non-vested performance share activity as of December 31, 2023 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2023 124,974 $ 46.41 Expired or forfeited (119,943) $ 46.64 Converted to cash (5,031) $ 41.00 Outstanding at December 31, 2023 — $ —
Summary of Restricted Share Activity	A summary of restricted share activity as of December 31, 2023 and changes during the year then ended is as follows: Shares Weighted-Average Outstanding at January 1, 2023 341,670 $ 42.19 Vested and issued (114,101) $ 41.66 Expired or forfeited (87,309) $ 43.78 Converted to cash (140,260) $ 41.64 Outstanding at December 31, 2023 — $ —

Underwriting, Acquisition and_2

Underwriting, Acquisition and General Expenses (Tables)	12 Months Ended
	Dec. 31, 2023
Underwriting Acquisition And Insurance Expenses [Abstract]
Underwriting, Acquisition and Insurance Expenses	Underwriting, acquisition and general expenses were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Commissions $ 12.7 $ 141.7 $ 280.2 $ 289.5 Other underwriting and insurance expenses 33.8 268.3 401.0 428.6 Amortization of value of business acquired and other intangible assets 37.9 — — — Total 84.4 410.0 681.2 718.1 Net deferral of policy acquisition costs (7.2) 9.0 (10.5) (15.8) Total underwriting, acquisition and general expenses $ 77.2 $ 419.0 $ 670.7 $ 702.3

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Tax Provision (Benefit) Expense	The following table presents the components of income tax provision (benefit) included in the amounts reported in our consolidated financial statements: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Current income tax provision (benefit) related to: United States (Federal) $ 4.2 $ 15.1 $ (21.0) $ 35.4 United States (State) (4.2) 0.1 0.1 2.4 United Kingdom — (0.1) (0.8) (2.2) Other jurisdictions — 0.1 (1.7) 1.6 Total current income tax provision — 15.2 (23.4) 37.2 Deferred income tax provision (benefit) related to: United States 1.3 (7.9) 6.0 (26.3) United Kingdom — (7.0) 7.3 (12.3) Other jurisdictions — — 2.1 — Total deferred income tax (benefit) 1.3 (14.9) 15.4 (38.6) Income tax provision (benefit) $ 1.3 $ 0.3 $ (8.0) $ (1.4)
Schedule of Earned Premiums by Geographic Location	For the years ended December 31, 2023, 2022 and 2021, pre-tax income (loss) attributable to our operations and the operations’ effective tax rates were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Pre-Tax Effective Bermuda $ (11.3) — % $ (90.3) — % $ (76.0) — % $ (18.0) — % United States 14.3 9.0 % (96.9) (7.5) % (83.2) 17.9 % 65.6 18.1 % United Kingdom (1.3) — % (23.2) 30.4 % 23.4 27.9 % (61.1) 24.4 % Barbados — — % — — % (4.5) — % — (1) — % Brazil — — % — — % (0.1) (422.4) % 15.3 10.4 % United Arab Emirates — — % 0.3 — % 1.4 — % 1.4 — % Ireland 0.5 — % (0.1) — % (39.1) — % (0.2) — % Italy — 2.1 % 0.1 50.3 % (0.9) (4.8) % 1.4 — % Malta — — % — — % (4.2) — % 0.9 — % Pre-tax income (loss) $ 2.2 59.1 % $ (210.1) 0.1 % $ (183.2) 4.3 % $ 5.3 (26.4) % (1)
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 for income taxes and the expected tax provision (benefit) at the weighted average tax rate is as follows: Successor Predecessor Period from Period from For the Years Ended December 31, November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 (in millions) Income tax provision (benefit) at expected rate $ 2.9 $ (24.7) $ (14.7) $ 9.8 Tax effect of: Nontaxable investment income — (0.1) (0.4) (0.5) Foreign exchange adjustments — (2.6) (2.1) (0.7) Impairment of goodwill — — 5.4 8.2 Base Erosion and Anti-Abuse Tax — 23.5 — — Withholding taxes — 0.1 2.7 0.1 U.S. state tax expense, net of federal income tax effect 0.1 (1.2) — — Change in uncertain tax position liability (3.4) 1.2 (1.4) (4.5) Change in valuation allowance 1.8 (1.4) (7.6) (0.7) Impact of change in tax rate related to Finance Act 2021 (0.2) (0.2) 1.7 (8.3) Brazil Premiums and Underwriting — — 0.3 (5.3) Sale of Brazil and Malta Operations — — 6.6 — Excess Executive Compensation — 2.0 — — Other 0.1 3.7 1.5 0.5 Income tax provision (benefit) $ 1.3 $ 0.3 $ (8.0) $ (1.4)
Schedule of Net Deferred Tax Liability Comprises Tax Effect Related to Assets and Liabilities	The net deferred tax asset (liability) comprises the tax effects of temporary differences related to the following assets and liabilities: As of December 31, (in millions) 2023 2022 Deferred tax assets: Losses and loss adjustment expense reserve discounting $ 45.5 $ 31.4 Unearned premiums 23.9 26.5 Net operating loss carryforwards 36.3 26.5 Investment in limited partnership interests 9.3 14.0 Unrealized losses on equity securities 6.9 8.2 Unrealized losses on fixed maturities and other investment securities 42.3 63.6 Investments 4.9 — Right of use assets 10.6 12.8 Accrued bonus 5.5 6.9 Stock option expense — 0.9 Bad debt 3.2 1.9 Other 2.6 4.3 Deferred tax assets, gross 191.0 197.0 Deferred tax liabilities: Debt obligations (6.4) — Unrealized gains on limited partnership interests (24.8) (25.3) Investments (5.8) Depreciable fixed assets (7.3) (7.1) Deferred acquisition costs (0.5) (23.0) Lease liability (12.1) (11.0) TCJA reserve transitional liability (1.1) (1.6) Value of business acquired (32.2) — Other intangible assets (37.1) — Underwriting results (9.1) — Other (0.6) (1.7) Deferred tax liabilities, gross (131.2) (75.5) Deferred tax assets, net before valuation allowance $ 59.8 $ 121.5 Valuation allowance (20.7) (20.3) Deferred tax asset (liabilities), net $ 39.1 $ 101.2 Net deferred tax assets (liabilities) - United States 39.1 101.2 Deferred tax asset (liabilities), net $ 39.1 $ 101.2
Schedule of Net Operating Loss Carryforwards Amounts by Jurisdiction and Year of Expiration	The NOL amounts by jurisdiction and year of expiration are as follows: (in millions) December 31, 2023 Expiration Net operating loss carryforwards by jurisdiction: Ireland 9.8 Indefinite Italy 49.7 Indefinite United Kingdom 6.9 Indefinite United States 92.3 2025-2043
Schedule of Unrecognized Tax Benefits	The following is a reconciliation of the beginning and ending amount of unrecognized tax benefits for the years ended December 31, 2023 and 2022: (in millions) 2023 2022 Balance at January 1 $ 4.6 $ 3.6 Additions for tax positions of prior years — 3.0 Reductions for tax positions of prior years (1.0) (1.4) Reductions based on settlements with taxing authorities (2.4) — Expiration of statute of limitations (1.2) (0.6) Balance at December 31 $ — $ 4.6

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2023
Segment Reporting [Abstract]
Revenue and Income (Loss) Before Income Taxes for Each Segment	Revenue and income before income taxes for each segment were as follows: Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Revenue: Net earned premiums U.S. Operations $ 147.2 $ 1,101.6 $ 1,209.0 $ 1,283.7 International Operations 14.9 124.0 530.5 625.8 Run-off Lines 0.2 0.3 0.9 0.6 Total net earned premiums 162.3 1,225.9 1,740.4 1,910.1 Net investment income U.S. Operations 23.5 99.9 88.4 119.4 International Operations 4.4 18.7 39.1 50.6 Run-off Lines 0.7 2.7 2.3 3.6 Corporate and Other — — — 14.0 Total net investment income 28.6 121.3 129.8 187.6 Net investment and other gains (losses) (0.3) (22.7) (115.3) 32.6 Total revenue $ 190.6 $ 1,324.5 $ 1,754.9 $ 2,130.3 Successor Predecessor Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 Income (loss) before income taxes U.S. Operations $ 17.3 $ (127.5) $ (22.9) $ 61.1 International Operations 0.9 6.7 63.8 64.1 Run-off Lines (0.1) (1.2) (1.8) (41.5) Total segment income before income taxes 18.1 (122.0) 39.1 83.7 Corporate and Other (1.9) (22.5) (32.0) (22.5) Net investment and other gains (losses) (0.3) (22.7) (115.3) 32.6 Foreign currency exchange gains (losses) (0.6) (1.8) 5.0 (1.6) Impairment of goodwill and intangible assets — — (28.5) (43.2) Non-operating expense (13.1) (41.1) (51.5) (43.7) Total income (loss) before income taxes $ 2.2 $ (210.1) $ (183.2) $ 5.3
Schedule of Earned Premiums by Geographic Location	The table below presents net earned premiums by geographic location for the periods November 16, 2023 through December 31, 2023 (Successor), and January 1, 2023 through November 15, 2023 (Predecessor), and for the years ended December 31, 2022 and 2021. 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 Period from Period from For the Years Ended December 31, (in millions) November 16, 2023 through December 31, 2023 January 1, 2023 through November 15, 2023 2022 2021 United States $ 147.4 $ 1,101.9 $ 1,209.9 $ 1,277.0 United Kingdom — 48.3 480.2 475.3 Bermuda 14.9 75.7 38.0 54.8 Malta — — 3.9 35.4 All other jurisdictions — — 8.4 67.6 Total net earned premiums $ 162.3 $ 1,225.9 $ 1,740.4 $ 1,910.1
Identifiable Assets	The following table represents identifiable assets: As of December 31, (in millions) 2023 2022 U.S. Operations $ 6,279.0 $ 5,815.0 International Operations (1) 1,888.9 3,791.6 Run-off Lines 221.4 284.4 Corporate and Other 113.8 143.4 Total $ 8,503.1 $ 10,034.4 (1) $2,066.2 million of International assets were reclassified to assets held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”.
Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization	The following table represents goodwill and intangible assets, net of accumulated amortization, as of December 31, 2023 and 2022: Goodwill Intangible Assets, Net of As of December 31, As of December 31, (in millions) 2023 2022 2023 2022 U.S. Operations $ — $ 118.6 $ 293.8 $ — International Operations (1) — — 30.4 — Total $ — $ 118.6 $ 324.2 $ — (1) $17.5 million of International goodwill was reclassified to assets held-for-sale in 2022. See Note 2, “Recent Acquisitions, Disposals & Other Transactions”.

Statutory Accounting Principl_2

Statutory Accounting Principles (Tables)	12 Months Ended
	Dec. 31, 2023
Statutory Accounting Principles [Abstract]
Statutory Capital and Surplus for Principal Operating Subsidiaries	The statutory capital and surplus for our principal operating subsidiaries was as follows: Statutory capital and surplus (1) December 31, (in millions) 2023 2022 Bermuda $ 1,150.6 $ 1,024.9 United Kingdom (2) — 370.0 United States 1,410.4 1,111.1 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries. (2) Sold on February 2, 2023. See Note 2, “Recent Acquisitions, Disposals & Other Transactions” for additional information related to this transaction.
Statutory Net Income (Loss) for Principal Operating Subsidiaries	The statutory net income (loss) for our principal operating subsidiaries was as follows: Statutory net income (loss) (1) For the Years Ended December 31, (in millions) 2023 2022 2021 Bermuda $ 0.8 $ (29.1) $ 14.2 United Kingdom — 21.4 8.6 United States 39.5 (117.8) 103.5 (1) Such amounts include ownership interests in affiliate insurance and reinsurance subsidiaries.

Business and Significant Acco_4

Business and Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Millions		2 Months Ended	11 Months Ended	12 Months Ended
	Nov. 16, 2023 USD ($) $ / shares	Dec. 31, 2023 USD ($) $ / shares	Nov. 15, 2023 USD ($)	Dec. 31, 2023 USD ($) segment trust $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($)	Oct. 01, 2022 USD ($)
Business And Significant Accounting Policies [Line Items]
Number of reportable segments | segment				2
Preferred stock, dividend rate (in percentage)	7%
Preferred shares, par value (in dollars per share) | $ / shares	$ 1	$ 1		$ 1	$ 1
Percentage of contractual participation				100%
Number of statutory trusts | trust				11
Value of business acquired amortization expense		$ (37.9)
Amortization of intangible assets					$ 0	$ 0
Impairment of goodwill and intangibles		0	$ 0		28.5	43.2
Impairment of indefinite lived intangible assets					17.3
Impairment of goodwill					11.2
Goodwill		0		$ 0	118.6
Accumulated depreciation for property and equipment		2.3		2.3	144.7
Net book value of property and equipment		31.1		$ 31.1	43.6
Depreciation expense		$ 2.3	$ 9.1		$ 22.3	23.9
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Other assets		Other assets	Other assets
Estimated liability for return of premiums				$ 0	$ 0.2
Estimated amount of premiums receivables due				0.2	0.2
Foreign currency translation adjustment gain (loss)		$ (0.1)		(0.1)	(4.2)
Argo Group International Holdings, Inc. | Brookfield Reinsurance
Business And Significant Accounting Policies [Line Items]
Interest in preferred stock	0.001
Bargain purchase gain	$ 48.9	48.9		48.9
Argo Group International Holdings, Inc. | Brookfield Reinsurance | Common Stock
Business And Significant Accounting Policies [Line Items]
Equity interests issued and issuable (in dollars per share) | $ / shares	$ 30
International Operations
Business And Significant Accounting Policies [Line Items]
Carrying value of reporting unit in excess of fair value						43.2
Goodwill		$ 0		$ 0	$ 0	28.7
Indefinite-lived intangible asset carrying value						$ 60.5	$ 17.3
Minimum
Business And Significant Accounting Policies [Line Items]
Useful life		3 years		3 years
Maximum
Business And Significant Accounting Policies [Line Items]
Useful life		39 years		39 years

Business and Significant Acco_5

Business and Significant Accounting Policies - Intangible Assets and Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 16, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Total other gross carrying amount	$ 185.8
Gross Carrying Amount	362.1
Other accumulated amortization	(5.2)
Accumulated Amortization	(37.9)
Net Value	299.2
Other intangible assets, net	180.6		$ 0
Total intangible assets	324.2	$ 362.1	$ 0
Insurance licenses
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible asset carrying value	25
Value of Business Acquired
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	176.3
Accumulated Amortization	(32.7)
Net Value	143.6
Broker relations
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	21.5
Accumulated Amortization	(0.2)
Net Value	$ 21.3
Broker relations | Minimum
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	13 years
Broker relations | Maximum
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	16 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 12.9
Accumulated Amortization	(0.3)
Net Value	$ 12.6
Weighted average useful life	5 years
Leases
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7.1
Accumulated Amortization	(0.1)
Net Value	$ 7
Weighted average useful life	9 years
Internally developed software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 16.5
Accumulated Amortization	(0.3)
Net Value	$ 16.2
Internally developed software | Minimum
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	5 years
Internally developed software | Maximum
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	7 years
Fair Value Adjustment For Loss And LAE Reserves
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 102.8
Accumulated Amortization	(4.3)
Net Value	$ 98.5

Business and Significant Acco_6

Business and Significant Accounting Policies - Future Amortization Expense (Details) $ in Millions	Dec. 31, 2023 USD ($)
Accounting Changes and Error Corrections [Abstract]
2024	$ 171.7
2025	39.8
2026	25.7
2027	17.4
2028	13.3
Thereafter	31.3
Net Value	$ 299.2

Business and Significant Acco_7

Business and Significant Accounting Policies - Schedule of Interest Paid (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 5.3	$ 28.3	$ 24.1	$ 21.8
Income taxes paid	0.1	0.2	26.2	43
Income taxes recovered	0	(0.1)	(2.1)	(2.6)
Income taxes paid, net	0.1	0.1	24.1	40.4
Senior unsecured fixed rate notes
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	1.2	8.2	9.3	9.3
Junior subordinated debentures
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	4.1	19.3	13.5	10
Other indebtedness
Disclosure - Business and Significant Accounting Policies - Supplemental Cash Flow Information - Schedule of Interest Paid (Detail) [Line Items]
Total interest paid	$ 0	$ 0.8	$ 1.3	$ 2.5

Recent Acquisitions, Disposal_3

Recent Acquisitions, Disposals & Other Transactions - Merger (Details) - Argo Group International Holdings, Inc. - Brookfield Reinsurance - USD ($) $ / shares in Units, $ in Millions			2 Months Ended
	Nov. 16, 2023	Nov. 15, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Consideration transferred	$ 1,058.9
Number of common stock shares canceled (in shares)		35,221,291	35,221,291
Bargain purchase gain	48.9		$ 48.9
Employee Stock
Business Acquisition [Line Items]
Equity interests issued and issuable	2.3
Common Stock
Business Acquisition [Line Items]
Equity interests issued and issuable	$ 1,056.6
Equity interests issued and issuable (in dollars per share)	$ 30

Recent Acquisitions, Disposal_4

Recent Acquisitions, Disposals & Other Transactions - Merger Identifiable Assets and Liabilities (Details) - Argo Group International Holdings, Inc. - Brookfield Reinsurance - USD ($) $ in Millions			2 Months Ended
	Nov. 16, 2023	Nov. 15, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Number of common stock shares canceled (in shares)		35,221,291	35,221,291
Consideration transferred	$ 1,058.9
Assets
Fixed maturities available-for-sale, at fair value	2,525.3
Commercial mortgage loans	144.9
Equity securities, at fair value	11.7
Other investments	327.8
Short-term investments, at fair value	450.1
Total investments	3,459.8
Cash	712.9
Accrued investment income	17.1
Premiums receivable	306.8
Reinsurance recoverables	2,981.6
Other intangible assets	186.1
Current income taxes receivable, net	53.2
Deferred tax asset, net	54
Ceded unearned premiums	387.6
Operating lease right-of-use assets	51.6
Other assets	190.8
Value of business acquired	176.3
Total assets	8,577.8
Liabilities
Reserves for losses and loss adjustment expenses	5,526.4
Unearned premiums	986.2
Accrued underwriting expenses and other liabilities	92
Ceded reinsurance payable, net	257.4
Funds held	49.9
Senior unsecured fixed rate notes	127.9
Junior subordinated debentures	241
Operating lease liabilities	52.1
Total liabilities assumed	7,332.9
Fair value of net assets acquired	1,244.9
Preferred stock	137.1
Bargain purchase gain	48.9		$ 48.9
Fair value adjustment to assets acquired	114.2
Fair value adjustment to liabilities assumed	80.9
Common Stock
Business Acquisition [Line Items]
Equity interests issued and issuable	1,056.6
Employee Stock
Business Acquisition [Line Items]
Equity interests issued and issuable	$ 2.3

Recent Acquisitions, Disposal_5

Recent Acquisitions, Disposals & Other Transactions - Sale of Argo Underwriting Agency Limited (Details) - USD ($) $ in Millions			1 Months Ended	2 Months Ended	3 Months Ended	9 Months Ended	11 Months Ended	12 Months Ended
	Feb. 02, 2023	Sep. 08, 2022	Jul. 31, 2023	Dec. 31, 2023	Mar. 31, 2023	Sep. 30, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of goodwill and intangibles				$ 0			$ 0	$ 28.5	$ 43.2
Impairment of indefinite lived intangible assets								17.3
Impairment of goodwill								11.2
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale	$ 155.7	$ 125				$ 161.3
Impairment of goodwill and intangibles		28.5
Impairment of indefinite lived intangible assets		17.3
Impairment of goodwill		$ 11.2
Consideration placed in escrow	$ 30.6
Period for which consideration can be released to Seller	2 years
Proceeds from sale of business unit	$ 125.1		$ 5.6
Pretax net income (loss)							$ 15.6	$ 66.8	$ 22.4
Gain (loss) on disposal, pre-tax					$ (20.3)
Consideration placed in escrow, released						$ 12.9

Recent Acquisitions, Disposal_6

Recent Acquisitions, Disposals & Other Transactions - Assets and Liabilities Held-for-Sale (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments:
Assets held-for-sale	$ 0	$ 2,066.2
Liabilities
Liabilities held-for-sale	$ 0	1,914.5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Investments:
Fair Value		490.6
Other investments		81.6
Short-term investments, at fair value		114.1
Investments		686.4
Cash, restricted cash and cash equivalents		70.8
Accrued investment income		2.1
Premiums receivable		331.9
Reinsurance recoverables		733.1
Current income taxes receivable, net		6.3
Deferred tax assets, net		28.1
Deferred acquisition costs, net		69.4
Ceded unearned premiums		76.1
Other assets		62
Assets held-for-sale		2,066.2
Liabilities
Reserves for losses and loss adjustment expenses		993.4
Unearned premiums		335.6
Accrued underwriting expenses and other liabilities		34.4
Ceded reinsurance payable, net		323.5
Funds held		172.9
Other indebtedness		54.7
Liabilities held-for-sale		$ 1,914.5

Recent Acquisitions, Disposal_7

Recent Acquisitions, Disposals & Other Transactions - Sale of ArgoGlobal SE (Details) - Jun. 22, 2022 - Disposal Group, Disposed of by Sale, Not Discontinued Operations - ArgoGlobal Holdings Ltd. € in Millions, $ in Millions	USD ($)	EUR (€)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale	$ 5.2	€ 4.9
Loss on disposal	21.3
Losses from the realization of historical foreign currency translation losses	$ 4.5

Recent Acquisitions, Disposal_8

Recent Acquisitions, Disposals & Other Transactions - Sale of Argo Seguros Brasil S.A. (Details) - Disposal Group, Disposed of by Sale, Not Discontinued Operations - Argo Seguros Brasil S.A. R$ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Feb. 15, 2022 USD ($)	Feb. 15, 2022 BRL (R$)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration received from sale			$ 26.9	R$ 140
Loss on disposal	$ 33.8	$ 6.3
Location of loss on disposal	Net realized investment and other gains (losses)
Losses from the realization of historical foreign currency translation losses	$ 27.3

Recent Acquisitions, Disposal_9

Recent Acquisitions, Disposals & Other Transactions - Loss Portfolio Transfer - U.S. (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended		11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021	Nov. 09, 2022	Aug. 08, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio transfer reserves cover							$ 746	$ 746
Additional cover in excess of threshold		$ 275			$ 275			275
Additional cover threshold								821
Policy limit								1,096
Recognized loss					75
Loss portfolio transfer,available		188.6			188.6
Recognized loss related to impaired assets		3.4	$ 34.2
Reserves transferred on closing date							509
Cash and investments transferred							$ 630
Increase in reinsurance recoverables		509
Reduction to cash and investments		630
Estimated after-tax expense		100
Ceded premiums earned	$ 98.4	$ 121		$ 724.9	$ 1,205.3	$ 1,272.7
Deferred gain on ceded premiums reserve	$ 82.4
Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss corridor retained								75
Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss corridor retained								$ 821

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($) security	Nov. 15, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Fair value of investments, assets managed on behalf of the trade capital providers | $			$ 55.9
Debt securities, available-for-sale, term	2 years 8 months 4 days		3 years 3 months 14 days
Number of securities in an unrealized loss position, total | security	1,431
Number of securities in an unrealized loss position for less than one year | security	104
Number of securities in an unrealized loss position for a period of one year or greater | security	0
Change in allowance for credit losses on fixed maturity securities | $	$ (0.2)	$ (2.1)	$ (2.5)	$ 0.6
Gain (Loss) on Investments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Change in allowance for credit losses on fixed maturity securities | $	$ 0.2	$ 2.2	$ 2.5

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses and Fair Value of Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 16, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Invested Assets [Line Items]
Amortized Cost	$ 2,521.5			$ 3,016.4
Gross Unrealized Gains	65.5			2.1
Gross Unrealized Losses	1.4			340.2
Allowance for Credit Losses	0.2	$ 0	$ 4.3	2.8	$ 2.5
Fair Value	2,585.4			2,675.5
U.S. Governments
Schedule of Invested Assets [Line Items]
Amortized Cost	357.7			410.9
Gross Unrealized Gains	4.5			0
Gross Unrealized Losses	0			30.2
Allowance for Credit Losses	0			0
Fair Value	362.2			380.7
Foreign Governments
Schedule of Invested Assets [Line Items]
Amortized Cost	27.9			35.6
Gross Unrealized Gains	2.6			0.3
Gross Unrealized Losses	0			6.7
Allowance for Credit Losses	0.2			0.8
Fair Value	30.3			28.4
Obligations of states and political subdivisions
Schedule of Invested Assets [Line Items]
Amortized Cost	92.4			109.9
Gross Unrealized Gains	2			0.4
Gross Unrealized Losses	0			10.1
Allowance for Credit Losses	0			0.4
Fair Value	94.4			99.8
Corporate bonds
Schedule of Invested Assets [Line Items]
Amortized Cost	1,185			1,394.8
Gross Unrealized Gains	28.9			0.9
Gross Unrealized Losses	0.8			160
Allowance for Credit Losses	0			1.6
Fair Value	1,213.1			1,234.1
Commercial mortgage-backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	270.9			337.4
Gross Unrealized Gains	10.1			0
Gross Unrealized Losses	0.5			52
Allowance for Credit Losses	0			0
Fair Value	280.5			285.4
Residential mortgage-backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	235.2			320
Gross Unrealized Gains	13.6			0.2
Gross Unrealized Losses	0			50.2
Allowance for Credit Losses	0			0
Fair Value	248.8			270
Asset-backed securities
Schedule of Invested Assets [Line Items]
Amortized Cost	140.4			153.4
Gross Unrealized Gains	1.7			0
Gross Unrealized Losses	0.1			14.2
Allowance for Credit Losses	0			0
Fair Value	142			139.2
Collateralized loan obligations
Schedule of Invested Assets [Line Items]
Amortized Cost	212			254.4
Gross Unrealized Gains	2.1			0.3
Gross Unrealized Losses	0			16.8
Allowance for Credit Losses	0			0
Fair Value	$ 214.1			$ 237.9

Investments - Schedule of Amo_2

Investments - Schedule of Amortized Cost and Fair Values of Fixed Maturity Investments, by Contractual Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 290.2
Due after one year through five years	1,019.7
Due after five years through ten years	322.1
Due after ten years	30.9
Total	2,521.5	$ 3,016.4
Fair Value
Due in one year or less	290.8
Due after one year through five years	1,037.4
Due after five years through ten years	337.7
Due after ten years	34.1
Total	2,585.4	$ 2,675.5
Structured Securities
Amortized Cost
Structured securities	858.6
Fair Value
Structured securities	$ 885.4

Investments - Schedule of Carry

Investments - Schedule of Carrying Value and Unfunded Investment Commitments of Other Invested Assets Portfolio (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Other investments	$ 311	$ 323.2
Unfunded Commitments	93.4	108.9
Hedge funds
Schedule of Investments [Line Items]
Other investments	56.2	54
Unfunded Commitments	0	0
Private equity
Schedule of Investments [Line Items]
Other investments	250.3	264.6
Unfunded Commitments	93.4	108.9
Other
Schedule of Investments [Line Items]
Other investments	4.5	4.6
Unfunded Commitments	$ 0	$ 0

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	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Fair value, less than one year	$ 107.2	$ 1,557.5
Unrealized losses, less than one year	1.4	143.6
Fair value, one year or greater	0	1,066.4
Unrealized losses, one year or greater	0	196.6
Fair value, total	107.2	2,623.9
Unrealized losses, total	1.4	340.2
U.S. Governments
Schedule of Investments [Line Items]
Fair value, less than one year	0	271
Unrealized losses, less than one year	0	18.1
Fair value, one year or greater	0	109.8
Unrealized losses, one year or greater	0	12.1
Fair value, total	0	380.8
Unrealized losses, total	0	30.2
Foreign Governments
Schedule of Investments [Line Items]
Fair value, less than one year	0.1	16.7
Unrealized losses, less than one year	0	4.9
Fair value, one year or greater	0	2.6
Unrealized losses, one year or greater	0	1.8
Fair value, total	0.1	19.3
Unrealized losses, total	0	6.7
Obligations of states and political subdivisions
Schedule of Investments [Line Items]
Fair value, less than one year	0.5	67.4
Unrealized losses, less than one year	0	4.1
Fair value, one year or greater	0	24.3
Unrealized losses, one year or greater	0	6
Fair value, total	0.5	91.7
Unrealized losses, total	0	10.1
Corporate bonds
Schedule of Investments [Line Items]
Fair value, less than one year	38.7	695.1
Unrealized losses, less than one year	0.8	68.3
Fair value, one year or greater	0	519.6
Unrealized losses, one year or greater	0	91.7
Fair value, total	38.7	1,214.7
Unrealized losses, total	0.8	160
Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Fair value, less than one year	32.2	144.2
Unrealized losses, less than one year	0.5	18.6
Fair value, one year or greater	0	141.2
Unrealized losses, one year or greater	0	33.4
Fair value, total	32.2	285.4
Unrealized losses, total	0.5	52
Residential mortgage-backed securities
Schedule of Investments [Line Items]
Fair value, less than one year	2.9	88.7
Unrealized losses, less than one year	0	8.8
Fair value, one year or greater	0	178.8
Unrealized losses, one year or greater	0	41.4
Fair value, total	2.9	267.5
Unrealized losses, total	0	50.2
Asset-backed securities
Schedule of Investments [Line Items]
Fair value, less than one year	11.4	93.3
Unrealized losses, less than one year	0.1	7.5
Fair value, one year or greater	0	45.9
Unrealized losses, one year or greater	0	6.7
Fair value, total	11.4	139.2
Unrealized losses, total	0.1	14.2
Collateralized loan obligations
Schedule of Investments [Line Items]
Fair value, less than one year	21.4	181.1
Unrealized losses, less than one year	0	13.3
Fair value, one year or greater	0	44.2
Unrealized losses, one year or greater	0	3.5
Fair value, total	21.4	225.3
Unrealized losses, total	$ 0	$ 16.8

Investments - Allowance for Cre

Investments - Allowance for Credit Losses (Detail) - USD ($) $ in Millions	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 0	$ 2.8	$ 2.5
Securities for which allowance was not previously recorded		2.7	2.2
Securities sold during the period		(0.7)	(0.8)
Reductions for credit impairments		0	(1.4)
Additional net increases (decreases) in existing allowance	0.2	(0.5)	0.3
Ending balance	0.2	4.3	2.8
Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		0
Ending balance			0
Foreign Governments
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0.7	0.2
Securities for which allowance was not previously recorded		0.1	0.4
Securities sold during the period		0	(0.1)
Reductions for credit impairments		0	0
Additional net increases (decreases) in existing allowance	0	0.3	0.2
Ending balance	0	1.1	0.7
Foreign Governments | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		0
Ending balance			0
Obligations of states and political subdivisions
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0.4	0
Securities for which allowance was not previously recorded		0.5	0
Securities sold during the period		0	0
Reductions for credit impairments		0	0
Additional net increases (decreases) in existing allowance	0	(0.4)	0.4
Ending balance	0	0.5	0.4
Obligations of states and political subdivisions | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		0
Ending balance			0
Corporate bonds
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	1.6	2.2
Securities for which allowance was not previously recorded		2.1	1.8
Securities sold during the period		(0.7)	(0.7)
Reductions for credit impairments		0	(1.4)
Additional net increases (decreases) in existing allowance	0.2	(0.4)	(0.3)
Ending balance	0.2	2.6	1.6
Corporate bonds | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		0
Ending balance			0
Asset-backed securities
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance	0	0.1	0.1
Securities for which allowance was not previously recorded		0	0
Securities sold during the period		0	0
Reductions for credit impairments		0	0
Additional net increases (decreases) in existing allowance	0	0	0
Ending balance	$ 0	0.1	0.1
Asset-backed securities | Cumulative Effect, Period of Adoption, Adjustment
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]
Beginning balance		$ 0
Ending balance			$ 0

Investments - Schedule of Loans

Investments - Schedule of Loans by Property Type (Details) $ in Millions	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 144.8	$ 159.9
Composition	100%	100%
Loan Count | loan	28	28
Apartments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 76.1	$ 87.4
Composition	52.60%	54.50%
Loan Count | loan	16	16
Hotel
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 22.4	$ 25
Composition	15.40%	15.60%
Loan Count | loan	4	4
Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 26	$ 26
Composition	18%	16.30%
Loan Count | loan	4	4
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 20.3	$ 21.5
Composition	14%	13.60%
Loan Count | loan	4	4

Investments - Schedule of Loa_2

Investments - Schedule of Loans by Debt Service Covenant Ratio (Details) $ in Millions	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 144.8	$ 159.9
Loan Count | loan	28	28
Equal to or less than 50.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 12.3	$ 36.7
Loan Count | loan	2	6
Greater than 50.0% to 55.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 9.1	$ 9.1
Loan Count | loan	2	2
Greater than 55.0% to 60.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 18.9	$ 42.6
Loan Count | loan	4	8
Greater than 60.0% to 70.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 37.3	$ 71.5
Loan Count | loan	6	12
Greater than 70.0%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 67.2
Loan Count | loan	14
Less than 1.00
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 36.2
Loan Count | loan	8
1.00 to 1.50
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 29.4	$ 10.4
Loan Count | loan	6	2
Greater than 1.5 to 2.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 30.9	$ 60.4
Loan Count | loan	6	10
Greater than 2.0 to 3.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 36	$ 52
Loan Count | loan	6	10
Greater than 3.0 to 4.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $	$ 12.3	$ 25.8
Loan Count | loan	2	4
Greater than 4.0
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost | $		$ 11.3
Loan Count | loan		2

Investments - Schedule of Loa_3

Investments - Schedule of Loans by Maturity (Details) $ in Millions	Dec. 31, 2023 USD ($) loan	Dec. 31, 2022 USD ($) loan
Investments, Debt and Equity Securities [Abstract]
One Year or Less | $	$ 19.7
Greater than One Year and Less than Three | $	34.9	$ 54.8
Greater than Three Years and Less than Five Years | $	32.4	33.8
Greater than Five Years and Less than Seven Years | $	17.2	20.4
Greater than Seven Years and Less than Ten Years | $	40.6	50.9
Total | $	$ 144.8	$ 159.9
One Year or Less | loan	4
Greater than One Year and Less than Three | loan	6	10
Greater than Three Years and Less than Five Years | loan	6	6
Greater than Five Years and Less than Seven Years | loan	4	4
Greater than Seven Years and Less than Ten Years | loan	8	8
Total | loan	28	28

Investments - Schedule of Compa

Investments - Schedule of Company's Gross Realized Investment Gains (Losses) (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	$ 5.5	$ 15.5	$ 55.3	$ 43.7
Realized losses on fixed maturities and other:	(5.4)	(37)	(81)	(42.8)
Other	0	(8.4)	(55.1)	(6.3)
Other net losses recognized on fixed maturities and other:	(0.2)	(13.5)	(93.9)	(5.7)
Net realized gains (losses) on equity securities	0	6.8	1.2	71.5
Change in fair value recognized	(0.2)	5.5	3.1	(34.1)
Net gains (losses) on equity securities	(0.2)	12.3	4.3	37.4
Net investment and other (gains) losses	(0.3)	(22.7)	(115.3)	32.6
Income tax (benefit) provision	(0.1)	(6.8)	(10)	6.2
Net investment and other gains (losses), net of income taxes	(0.2)	(15.9)	(105.3)	26.4
Fixed maturities
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	0.1	0.6	20.5	30.6
Realized losses on fixed maturities and other:	0	(25.7)	(29.9)	(11.8)
Other investments, including short-terms
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	5.4	14.9	34.8	9.8
Realized losses on fixed maturities and other:	(5.4)	(11.3)	(51.1)	(18.5)
Other assets
Schedule of Investments [Line Items]
Realized gains on fixed maturities and other:	0	0	0	3.3
Realized losses on fixed maturities and other:	0	0	0	(12.5)
Other Than Temporary Impairment Losses On Fixed Maturities
Schedule of Investments [Line Items]
Credit gains (losses) on fixed maturities	(0.2)	(2.2)	(4.6)	0.6
Impairment Related to Change in Intent
Schedule of Investments [Line Items]
Impairment related to change in intent	$ 0	$ (2.9)	$ (34.2)	$ 0

Investments - Schedule of Chang

Investments - Schedule of Changes in Unrealized Appreciation (Depreciation) (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ 64.6	$ 43.2	$ (384.5)	$ (106.9)
Income tax provision (benefit)	13.5	7.4	(71.7)	(21.5)
Net unrealized investment gains (losses), net of income taxes	51.1	35.8	(312.8)	(85.4)
Fixed maturities
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	64.2	41.2	(383.7)	(105.9)
Other and short-term investments
Schedule of Investments [Line Items]
Net unrealized investment gains (losses) before income taxes	$ 0.4	$ 2	$ (0.8)	$ (1)

Investments - Schedule of Fair

Investments - Schedule of Fair Value of Foreign Currency Exchange Forward Contracts (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ 1.3	$ 5.2
Foreign Currency Exchange Forward Contracts | Operational currency exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	1.8	5.8
Foreign Currency Exchange Forward Contracts | Asset manager investment exposure
Schedule of Investments [Line Items]
Derivative assets (liabilities), at fair value, net	$ (0.5)	$ (0.6)

Investments - Schedule of Reali

Investments - Schedule of Realized Gains and Losses of Investment on Foreign Currency Exchange Forward Contracts (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Gross realized investment gains	$ 4.5	$ 13.5	$ 33.9	$ 33.2
Gross realized investment losses	(3.6)	(12.4)	(47.2)	(41.9)
Foreign Currency Exchange Forward Contracts
Schedule of Investments [Line Items]
Net realized investment gains (losses) on foreign    currency exchange forward contracts	0.9	1.1	(13.3)	(8.7)
Foreign Currency Exchange Forward Contracts | Operational currency exposure
Schedule of Investments [Line Items]
Gross realized investment gains	4.5	12	30	16.5
Gross realized investment losses	(2.9)	(11.4)	(46.3)	(28.9)
Foreign Currency Exchange Forward Contracts | Asset manager investment exposure
Schedule of Investments [Line Items]
Gross realized investment gains	0	1.5	3.9	3.7
Gross realized investment losses	(0.7)	(1)	(0.9)	(1)
Foreign Currency Exchange Forward Contracts | Total return strategy
Schedule of Investments [Line Items]
Gross realized investment gains	0	0	0	13
Gross realized investment losses	$ 0	$ 0	$ 0	$ (12)

Investments - Components of Res

Investments - Components of Restricted Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities required to be maintained at Lloyd's		$ 171.4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities required to be maintained at Lloyd's		123.7
Asset Pledged as Collateral
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	$ 262.6	490.5
Asset Pledged as Collateral | Securities and cash on deposit for regulatory and other purposes
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	153.4	149.3
Asset Pledged as Collateral | Letter of Credit
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	109.2	169.8
Asset Pledged as Collateral | Deposits
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Restricted investments	$ 0	$ 171.4

Investments - Financial Assets

Investments - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 3,481.2	$ 3,651.9
Recurring fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	1.3	5.2
Total assets	3,027.1	3,174.5
Recurring fair value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0	0
Total assets	793.4	856.4
Recurring fair value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	1.3	5.2
Total assets	2,176.9	2,261.9
Recurring fair value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivatives	0	0
Total assets	56.8	56.2
Recurring fair value | Fixed maturities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	2,585.4	2,675.5
Recurring fair value | Fixed maturities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	360.1	378.7
Recurring fair value | Fixed maturities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	2,174.9	2,256.1
Recurring fair value | Fixed maturities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	50.4	40.7
Recurring fair value | Fixed maturities | Collateralized loan obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	214.1	237.9
Recurring fair value | Fixed maturities | Collateralized loan obligations | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Collateralized loan obligations | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	214.1	237.9
Recurring fair value | Fixed maturities | Collateralized loan obligations | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | U.S. Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	362.2	380.7
Recurring fair value | Fixed maturities | U.S. Governments | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	360.1	378.7
Recurring fair value | Fixed maturities | U.S. Governments | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	2.1	2
Recurring fair value | Fixed maturities | U.S. Governments | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Foreign Governments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	30.3	28.4
Recurring fair value | Fixed maturities | Foreign Governments | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Foreign Governments | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	30.3	28.4
Recurring fair value | Fixed maturities | Foreign Governments | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Obligations of states and political subdivisions
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	94.4	99.8
Recurring fair value | Fixed maturities | Obligations of states and political subdivisions | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Obligations of states and political subdivisions | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	94.4	99.8
Recurring fair value | Fixed maturities | Obligations of states and political subdivisions | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,213.1	1,234.1
Recurring fair value | Fixed maturities | Corporate bonds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Corporate bonds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,180.5	1,212.1
Recurring fair value | Fixed maturities | Corporate bonds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	32.6	22
Recurring fair value | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	280.5	285.4
Recurring fair value | Fixed maturities | Commercial mortgage-backed securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Commercial mortgage-backed securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	280.5	285.4
Recurring fair value | Fixed maturities | Commercial mortgage-backed securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Residential mortgage-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	248.8	270
Recurring fair value | Fixed maturities | Residential mortgage-backed securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Residential mortgage-backed securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	248.8	270
Recurring fair value | Fixed maturities | Residential mortgage-backed securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Asset-backed securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	142	139.2
Recurring fair value | Fixed maturities | Asset-backed securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Fixed maturities | Asset-backed securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	124.2	120.5
Recurring fair value | Fixed maturities | Asset-backed securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	17.8	18.7
Recurring fair value | Equity securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	10.7	43.9
Recurring fair value | Equity securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	4.3	28.4
Recurring fair value | Equity securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Equity securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	6.4	15.5
Recurring fair value | Other investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0.2	0.3
Recurring fair value | Other investments | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Other investments | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0.2	0.3
Recurring fair value | Other investments | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0	0
Recurring fair value | Short-term investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	429.5	449.6
Recurring fair value | Short-term investments | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	429	449.3
Recurring fair value | Short-term investments | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	0.5	0.3
Recurring fair value | Short-term investments | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
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	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 56.2
Beginning balance	$ 56.2	17.5
Transfers into Level 3	5.6	37.6
Transfers out of Level 3	$ (13.2)	0
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Income Extensible List Not Disclosed Flag	Included in net income
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Other Comprehensive Income Extensible List Not Disclosed Flag	Included in other comprehensive income
Total gains or losses (realized/unrealized):
Included in net income	$ (0.5)	(1.1)
Included in other comprehensive income	0.8	(4.8)
Purchases, issuances, sales, and settlements:
Purchases	10.6	10
Issuances	0	0
Sales	(1.6)	(3)
Settlements	(1.1)	0
Ending balance	56.8	56.2
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	(0.8)	(4.4)
Credit Financial
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		40.7
Beginning balance	40.7	2.8
Transfers into Level 3	5.6	36.1
Transfers out of Level 3	(5.6)	0
Total gains or losses (realized/unrealized):
Included in net income	(0.1)	(0.4)
Included in other comprehensive income	0.8	(4.8)
Purchases, issuances, sales, and settlements:
Purchases	10.6	9
Issuances	0	0
Sales	(0.5)	(2)
Settlements	(1.1)	0
Ending balance	50.4	40.7
Amount of total gains or losses for the year included in net income (loss) 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		15.5
Beginning balance	15.5	14.7
Transfers into Level 3	0	1.5
Transfers out of Level 3	(7.6)	0
Total gains or losses (realized/unrealized):
Included in net income	(0.4)	(0.7)
Included in other comprehensive income	0	0
Purchases, issuances, sales, and settlements:
Purchases	0	1
Issuances	0	0
Sales	(1.1)	(1)
Settlements	0	0
Ending balance	6.4	15.5
Amount of total gains or losses for the year included in net income (loss) attributable to the change in unrealized gains or losses relating to assets still held at end of period	$ (0.8)	$ (4.4)

Investments - Commercial Mortga

Investments - Commercial Mortgage Loans (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost	$ 144.8	$ 159.9
Fair Value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cost	$ 148.8	$ 150.7

Allowance for Credit Losses - P

Allowance for Credit Losses - Premium Receivables (Details) - USD ($) $ in Millions	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Nov. 16, 2023	Dec. 31, 2021
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premiums receivable	$ 230.7	$ 306.8	$ 292	$ 306.8	$ 648.6
Balance, December 31, 2022	0	4.7	5.7
Current period change for estimated uncollectible premiums	3.3	5.4	0.2
Write-offs of uncollectible premiums receivable	(0.3)	(2.7)	(1.2)
Balance, December 31, 2023	$ 3	$ 7.4	$ 4.7

Allowance for Credit Losses - R

Allowance for Credit Losses - Reinsurance Recoverables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2021
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance recoverables, net	$ 3,029.1	$ 2,959.3	$ 2,981.6	$ 2,966.4
Balance, December 31, 2022	3.8
Current period change for estimated uncollectible reinsurance	1.7
Reclassified to assets held-for-sale	(0.8)
Balance, December 31, 2023	$ 4.7

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Lease cost	$ 1.1	$ 7.6	$ 11.8
Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term	10 years

Leases - Components of Leases (

Leases - Components of Leases (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 51.2	$ 57.7
Operating lease liabilities	$ 51.4	$ 66.4
Operating lease weighted-average remaining lease term	7 years 8 months 12 days	8 years 2 months 19 days
Operating lease weighted-average discount rate	6.13%	3.44%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Lessee, Lease, Description [Line Items]
Operating lease right-of-use asset reclassified		$ 0.5
Operating lease liabilities reclassified		$ 0.5

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease costs	$ 0.7	$ 5.2	$ 8.1
Variable lease costs	0.5	3.3	4.7
Sublease income	(0.1)	(0.9)	(1)
Total lease costs	$ 1.1	$ 7.6	$ 11.8

Leases - Lease Maturity (Detail

Leases - Lease Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2024	$ 8.9
2025	9.1
2026	8.9
2027	8.3
2028	6.9
Thereafter	22.5
Total future minimum lease payments	64.6
Less imputed interest	(13.2)
Total operating lease liability	$ 51.4	$ 66.4

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Ceded Credit Risk [Line Items]
Reinsurance recoverables, allowance for doubtful accounts	$ 0	$ 4.7	$ 4.7	$ 3.8
Amount of collateral under reinsurance agreement	1,212.2		1,299.3
Reinsurance recoverables	2,959.3		3,029.1
Paid loss recoverables in insurance recoverables	161.9		190.6
Loss & LAE	94.2	1,043.2	1,166.9	1,314.6
Net of amounts ceded to reinsurers	79.3	$ 607.3	958.8	$ 829.6
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables	945		1,244.3
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Ceded Credit Risk, Unsecured | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables	$ 465.1		$ 564

Reinsurance - Schedule of Reins

Reinsurance - Schedule of Reinsurance Premium (Detail) - USD ($) $ in Millions	2 Months Ended	3 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Insurance [Abstract]
Direct written premiums	$ 186		$ 1,907.9	$ 2,682.8	$ 2,990.6
Reinsurance ceded to other companies	(66.8)		(803.6)	(1,106.7)	(1,203.9)
Reinsurance assumed from other companies	5.1		40.4	165.4	190.6
Net written premiums	124.3		1,144.7	1,741.5	1,977.3
Direct earned premiums	252.3		1,906.5	2,757.8	2,917.7
Reinsurance ceded to other companies	(98.4)	$ (121)	(724.9)	(1,205.3)	(1,272.7)
Reinsurance assumed from other companies	8.4		44.3	187.9	265.1
Net earned premiums	$ 162.3		$ 1,225.9	$ 1,740.4	$ 1,910.1
Percentage of reinsurance assumed to net earned premiums	5.20%		3.60%	10.80%	13.90%

Reserves for Losses and Loss _3

Reserves for Losses and Loss Adjustment Expenses - Reserves for Losses and Loss Adjustment Expenses (Detail) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($)	Nov. 15, 2023 USD ($) agreement	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves beginning of the year	$ 2,734.6	$ 2,213.1	$ 2,213.1	$ 3,123.2	$ 2,906.1
Losses and LAE incurred during current calendar year, net of reinsurance:
Current accident year	94.2	775.3		1,102.2	1,176.3
Prior accident years	0	267.9		64.7	138.3
Losses and LAE incurred during calendar year, net of reinsurance	94.2	1,043.2		1,166.9	1,314.6
Losses and LAE payments made during current calendar year, net of reinsurance:
Current accident year	33.5	100.6		171.5	180.8
Prior accident years	51.8	427.3		828	688.4
Losses and LAE payments made during current calendar year, net of reinsurance:	85.3	527.9		999.5	869.2
Add/(Deduct):
Divestitures	0	24.4		(35.2)	0
Reclassified to liabilities held-for-sale	0	0		(313)	0
Net reserves ceded to Syndicate 1200	0	0		(129.6)	0
Deferred gain on U.S. loss portfolio transfer, net of amortization	0	(40.9)		0	0
Loss portfolio transfer:
Reinsurance to close transaction (for years of account 2017 and prior)	0	0		0	(219.7)
Retroactive reinsurance	0	21.7		0	0
Total deductions	0	5.2		(1,060.1)	(211.3)
Change in participation interest	0	0		34.3	8.4
Foreign exchange adjustments	3.6	1		(17.4)	(17)
Net reserves - end of period	2,747.1	2,734.6	2,747.1	2,213.1	3,123.2
Reinsurance recoverables on unpaid losses and LAE, end of year	2,797.4	2,791.8	2,797.4	2,838.5	2,471.8
Reserves for losses and loss adjustment expenses	5,544.5	$ 5,526.4	$ 5,544.5	5,051.6	5,595
Number of retroactive reinsurance agreements entered into | agreement		2
United States (Federal)
Loss portfolio transfer:
Loss portfolio transfer (for years of account 2019 and 2018)	0	$ 0		(472.6)	0
Syndicate 1200
Loss portfolio transfer:
Loss portfolio transfer (for years of account 2019 and 2018)	$ 0	$ 0		$ (144)	$ 0

Reserves for Losses and Loss _4

Reserves for Losses and Loss Adjustment Expenses - Additional Information (Detail) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($)	Nov. 15, 2023 USD ($)	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Loss adjustment expenses related to pandemic			$ 0	$ 0	$ 12.4
Prior years	$ 0	$ 267.9		64.7	138.3
Number of reportable segments | segment			2
Claims remain outstanding period			10 years
Number of reporting segments | segment			2
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Prior years		246.3		64.5	120.9
U.S. Operations | Liability
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Prior years			$ 112.1
U.S. Operations | Professional
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Prior years			$ 33
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Prior years		$ 0.2		$ 2.9	$ 44.3
Percentage of gross reserves for losses			4%

Reserves for Losses and Loss _5

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	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total (favorable) unfavorable prior-year development	$ 0	$ 267.9	$ 64.7	$ 138.3
U.S. Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total (favorable) unfavorable prior-year development		246.3	64.5	120.9
International Operations
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total (favorable) unfavorable prior-year development		21.4	(2.7)	(26.9)
Run-off Lines
Schedule Of Prior Accident Years Loss And Loss Adjustment Expense Reserves Development [Line Items]
Total (favorable) unfavorable prior-year development		$ 0.2	$ 2.9	$ 44.3

Reserves for Losses and Loss _6

Reserves for Losses and Loss Adjustment Expenses - Summary of Information about Incurred and Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance (Detail) $ in Millions	Dec. 31, 2023 USD ($) claim	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,697.2
U.S. Operations | Liability
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	3,920.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	2,433.2
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	58.7
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	1,546.4
U.S. Operations | Liability | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	312.1	$ 310.7	$ 341.3	$ 327.4	$ 321.9	$ 323.9	$ 326.3	$ 330	$ 337.1	$ 328.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	305.8	304.4	291.4	283.2	266.3	240.6	206.9	154.6	91	32.4
IBNR & Expected Development on Reported Claims	$ (7)
Cumulative number of reported claims | claim	22,319
U.S. Operations | Liability | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 321.5	318.9	347.9	335.4	328	328.7	330.3	343.8	339.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	307.2	305.6	289.3	263.9	236.4	195.6	140.2	86.9	33.7
IBNR & Expected Development on Reported Claims	$ (1.3)
Cumulative number of reported claims | claim	20,936
U.S. Operations | Liability | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 354.5	349.1	379	355.3	353	342.4	350.5	342.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	331.8	327.1	293.8	255.6	217.1	144.1	84.5	28.5
IBNR & Expected Development on Reported Claims	$ 4.9
Cumulative number of reported claims | claim	18,105
U.S. Operations | Liability | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 391.2	385.2	431.7	397.7	384.3	373.7	374.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	354.2	348	295.2	238.5	158.8	83	27.8
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative number of reported claims | claim	20,982
U.S. Operations | Liability | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 390.7	366.5	420.4	414.5	430.4	426.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	335.7	315.9	245.5	175.8	98.9	34.3
IBNR & Expected Development on Reported Claims	$ 6.1
Cumulative number of reported claims | claim	23,539
U.S. Operations | Liability | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 353.1	318.6	427.1	423.7	421.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	290.6	260.1	186.1	113.6	32.4
IBNR & Expected Development on Reported Claims	$ (4.2)
Cumulative number of reported claims | claim	22,976
U.S. Operations | Liability | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 433.9	371.1	386.7	404.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	228.7	149	85.9	25.6
IBNR & Expected Development on Reported Claims	$ 115.1
Cumulative number of reported claims | claim	18,812
U.S. Operations | Liability | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 461.2	419.1	416.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	164.8	83.1	27.5
IBNR & Expected Development on Reported Claims	$ 211.7
Cumulative number of reported claims | claim	15,248
U.S. Operations | Liability | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 466.9	439.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	92	27.2
IBNR & Expected Development on Reported Claims	$ 291.5
Cumulative number of reported claims | claim	13,729
U.S. Operations | Liability | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 435.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	22.4
IBNR & Expected Development on Reported Claims	$ 361
Cumulative number of reported claims | claim	10,514
U.S. Operations | Professional
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 1,055.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	535.1
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	11.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	532
U.S. Operations | Professional | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	32.7	32.7	34.4	35.1	35.4	36.2	33.7	26	22.4	22.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	33.6	33.5	33.6	33.3	32.3	25.5	24.1	15.1	5.4	2.3
IBNR & Expected Development on Reported Claims	$ (0.8)
Cumulative number of reported claims | claim	1,044
U.S. Operations | Professional | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 31.3	31.3	38.3	37.9	37.1	34	33.2	29.5	29.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	33.8	33.8	31.7	31.3	26.2	20.8	15.6	8.3	1.8
IBNR & Expected Development on Reported Claims	$ (2.5)
Cumulative number of reported claims | claim	1,832
U.S. Operations | Professional | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 46.1	43.5	43	35.5	42.9	45.1	44.8	44.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	43.5	38.3	34.4	30.8	28.9	24.6	11.9	2.4
IBNR & Expected Development on Reported Claims	$ 2.2
Cumulative number of reported claims | claim	3,264
U.S. Operations | Professional | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 87.3	87	99.5	87.9	78.3	61.8	60.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	85.5	85.5	77.9	59.7	38	24.9	3.5
IBNR & Expected Development on Reported Claims	$ (9.7)
Cumulative number of reported claims | claim	3,774
U.S. Operations | Professional | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 87.8	88.5	94.8	79.2	73.2	70.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	79.7	78.8	62.6	43.8	16.7	4.5
IBNR & Expected Development on Reported Claims	$ (3.7)
Cumulative number of reported claims | claim	4,298
U.S. Operations | Professional | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 117.7	94.5	105	96.8	94.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	92.9	81.7	50	32.9	4.9
IBNR & Expected Development on Reported Claims	$ 15.4
Cumulative number of reported claims | claim	4,901
U.S. Operations | Professional | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 160	127.8	142.6	152.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	81.6	70.5	36.4	13.3
IBNR & Expected Development on Reported Claims	$ 41.6
Cumulative number of reported claims | claim	5,012
U.S. Operations | Professional | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 159.6	159.5	177.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	54.7	39.6	12.2
IBNR & Expected Development on Reported Claims	$ 68.4
Cumulative number of reported claims | claim	5,153
U.S. Operations | Professional | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 169.1	185.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	25.7	14.3
IBNR & Expected Development on Reported Claims	$ 122.1
Cumulative number of reported claims | claim	5,120
U.S. Operations | Professional | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 164
Cumulative Paid Losses & ALAE, Net of Reinsurance	4.1
IBNR & Expected Development on Reported Claims	$ 141.8
Cumulative number of reported claims | claim	4,396
U.S. Operations | Property
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 929.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	886.7
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	0.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	43.3
U.S. Operations | Property | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	74.8	76.1	76	76.1	76.9	76.9	77.1	77	82.2	80.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	76	76	76	76.1	76.4	76.3	76.4	75.7	73.1	51.6
IBNR & Expected Development on Reported Claims	$ (1.2)
Cumulative number of reported claims | claim	8,057
U.S. Operations | Property | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 67.8	68.4	69.2	69.2	69.1	68.9	69.9	73.4	74
Cumulative Paid Losses & ALAE, Net of Reinsurance	68.6	68.6	69	68.5	68.3	67.9	68.6	67.6	44.6
IBNR & Expected Development on Reported Claims	$ (0.8)
Cumulative number of reported claims | claim	7,362
U.S. Operations | Property | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 54.4	54.2	56.5	56.6	56.6	57.1	57.6	59.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	54.5	54.5	56.3	56.4	56.1	55.8	55.2	39.4
IBNR & Expected Development on Reported Claims	$ (0.1)
Cumulative number of reported claims | claim	7,701
U.S. Operations | Property | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 91.3	97.4	94.5	94.9	86.9	79.6	75.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	90.5	95.1	88.4	100.8	113.9	95.3	54.4
IBNR & Expected Development on Reported Claims	$ (2.6)
Cumulative number of reported claims | claim	9,930
U.S. Operations | Property | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 101.1	102.4	96.9	95.1	93.1	89.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	102.5	101.4	98.8	107	126.7	61.3
IBNR & Expected Development on Reported Claims	$ (4.3)
Cumulative number of reported claims | claim	10,881
U.S. Operations | Property | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 90.3	97.9	98.4	88.8	91.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	96	94	90.9	82.4	55.8
IBNR & Expected Development on Reported Claims	$ (6.9)
Cumulative number of reported claims | claim	11,496
U.S. Operations | Property | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 134	133.1	133.2	129.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	126.6	121.6	116.6	75.9
IBNR & Expected Development on Reported Claims	$ (6.4)
Cumulative number of reported claims | claim	11,379
U.S. Operations | Property | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 116.7	114.8	111.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	118.2	118.3	71.3
IBNR & Expected Development on Reported Claims	$ (5.8)
Cumulative number of reported claims | claim	10,312
U.S. Operations | Property | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 104.4	103.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	94.7	52.2
IBNR & Expected Development on Reported Claims	$ 2.6
Cumulative number of reported claims | claim	9,119
U.S. Operations | Property | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 94.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	59.1
IBNR & Expected Development on Reported Claims	$ 16.2
Cumulative number of reported claims | claim	7,707
U.S. Operations | Specialty
Claims Development [Line Items]
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	$ 55.9
U.S. Operations | Specialty Admitted | Specialty
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	97.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	42
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	0.6
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	55.9
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	4.1	4.1	4.1	4.6	4.6	4.8	6	8.9	13.1	13.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	4.1	4.1	4.1	4	4.1	4.1	4	4	3.3	1.1
IBNR & Expected Development on Reported Claims	$ 0
Cumulative number of reported claims | claim	20
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.2	0.2	0.3	0.5	1.2	5.5	9.5	14.3	14.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.2	0.2	0.3	0.3	0.3	0.3	0.2	0.1	0.2
IBNR & Expected Development on Reported Claims	$ 0
Cumulative number of reported claims | claim	14
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 2.8	3.2	3.3	4.7	6.2	11.2	15	15
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.8	2.8	2.8	2.2	2.2	2.2	1.6	1.3
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative number of reported claims | claim	46
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 0.6	0.7	0.7	0.9	7.6	16.2	16.2
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.2	0.2	0.2	0.1	0	0.1	0.3
IBNR & Expected Development on Reported Claims	$ 0.4
Cumulative number of reported claims | claim	62
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 3.3	3.5	3.5	3.3	17.4	20.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	2.9	2.4	1.2	1.7	0.7	0
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative number of reported claims | claim	82
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 5.8	5.9	5.6	8.5	22.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	5.2	5.4	3.2	0.7	0.7
IBNR & Expected Development on Reported Claims	$ 0.1
Cumulative number of reported claims | claim	124
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 15	15.9	10.3	25.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	10.5	10.6	7.6	0.3
IBNR & Expected Development on Reported Claims	$ 0
Cumulative number of reported claims | claim	274
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 2	5.2	27.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.6	1.4	0.2
IBNR & Expected Development on Reported Claims	$ 0.3
Cumulative number of reported claims | claim	291
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 28.9	33
Cumulative Paid Losses & ALAE, Net of Reinsurance	13.4	0.1
IBNR & Expected Development on Reported Claims	$ 5.6
Cumulative number of reported claims | claim	257
U.S. Operations | Specialty Admitted | Specialty | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 34.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.1
IBNR & Expected Development on Reported Claims	$ 33.1
Cumulative number of reported claims | claim	175
International Operations | Argo Insurance Bermuda- Liability | Liability
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 186.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	100.5
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	2.5
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	88.3
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	1.6	1.6	1.6	2.3	2.3	1.5	6.2	9.8	9.8	9.8
Cumulative Paid Losses & ALAE, Net of Reinsurance	1.4	1.4	1.4	1.4	1.2	1.2	0.1	0.1	0	0
IBNR & Expected Development on Reported Claims	$ (0.4)
Cumulative number of reported claims | claim	1,361
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 50.3	50.3	51.3	45.1	45.4	35.4	24.8	14.3	11.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	50.3	50.2	38.9	34.8	26.6	20.3	16.1	0	0
IBNR & Expected Development on Reported Claims	$ 0
Cumulative number of reported claims | claim	1,629
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 6.5	2.4	0.8	6.1	6.6	14	14	13.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.3	0.3	0.2	0.1	0.1	0	0	0
IBNR & Expected Development on Reported Claims	$ 6
Cumulative number of reported claims | claim	1,969
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 46.2	44.3	37.3	30.3	26.9	17.3	17.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	27.6	22	19.7	18	3.4	3.3	0
IBNR & Expected Development on Reported Claims	$ 7.8
Cumulative number of reported claims | claim	2,176
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 19.8	22.9	24.2	26.6	32.1	8.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	19.1	18.5	18.5	18.3	13.8	0
IBNR & Expected Development on Reported Claims	$ 0.4
Cumulative number of reported claims | claim	1,159
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 13.3	13.3	13.8	13.6	13.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.9	0.6	0.7	0.1	0
IBNR & Expected Development on Reported Claims	$ 12.4
Cumulative number of reported claims | claim	1,254
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 12.4	12.4	24.9	23.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.6	0.5	7	0.8
IBNR & Expected Development on Reported Claims	$ 7
Cumulative number of reported claims | claim	1,434
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 12.4	11.4	12.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.3	0	0
IBNR & Expected Development on Reported Claims	$ 6.2
Cumulative number of reported claims | claim	1,436
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 11.1	11.1
Cumulative Paid Losses & ALAE, Net of Reinsurance	0	0
IBNR & Expected Development on Reported Claims	$ 11.1
Cumulative number of reported claims | claim	1,293
International Operations | Argo Insurance Bermuda- Liability | Liability | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 12.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	0
IBNR & Expected Development on Reported Claims	$ 12.5
Cumulative number of reported claims | claim	1,519
International Operations | Argo Insurance Bermuda- Liability | Professional
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 138
Cumulative Paid Losses & ALAE, Net of Reinsurance	27.3
Other Property outstanding liabilities including unpaid loss and ALAE prior to 2014, net of reinsurance	3.2
Total outstanding liabilities for unpaid losses and ALAE, net of reinsurance	113.9
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	10.1	10.1	8.1	12.5	10.2	3.9	4	4	4	4
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.4	0.4	0.4	3.2	0.4	1	0.3	0	0	$ 0
IBNR & Expected Development on Reported Claims	$ 2.3
Cumulative number of reported claims | claim	1,130
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 5.2	7.9	7.3	5.2	5	2.7	4.9	4.9	4.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	4	2.9	2.9	0	0	0	0	0	$ 0
IBNR & Expected Development on Reported Claims	$ 1.1
Cumulative number of reported claims | claim	1,158
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 3.8	1.9	3.1	7.3	3.1	4.8	6.7	6.7
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.1	0	0	0	0	0	0	$ 0
IBNR & Expected Development on Reported Claims	$ 3.7
Cumulative number of reported claims | claim	1,280
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 15.3	10.5	12.4	9.5	9.7	7.6	7.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	9.9	9.8	9.8	9.8	4.9	0.1	$ 0.1
IBNR & Expected Development on Reported Claims	$ 5.3
Cumulative number of reported claims | claim	1,471
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contracts, Accident Year 2018
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 36.8	21.3	6.5	8	8.3	8.3
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.1	6	2.1	2	0	$ 0
IBNR & Expected Development on Reported Claims	$ 23
Cumulative number of reported claims | claim	1,101
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contract, Accident Year 2019
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 18.1	18.3	16.4	8.7	9.6
Cumulative Paid Losses & ALAE, Net of Reinsurance	0.7	0.7	0.6	0.6	$ 2
IBNR & Expected Development on Reported Claims	$ 7.1
Cumulative number of reported claims | claim	1,111
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contract, Accident Year 2020
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 11.1	10.4	10.4	10.4
Cumulative Paid Losses & ALAE, Net of Reinsurance	6.1	0	0	$ 0
IBNR & Expected Development on Reported Claims	$ 5
Cumulative number of reported claims | claim	965
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contract, Accident Year 2021
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 12.3	13	13
Cumulative Paid Losses & ALAE, Net of Reinsurance	0	0	$ 0
IBNR & Expected Development on Reported Claims	$ 11.5
Cumulative number of reported claims | claim	858
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contract, Accident Year 2022
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 9.4	9.5
Cumulative Paid Losses & ALAE, Net of Reinsurance	0	$ 0
IBNR & Expected Development on Reported Claims	$ 9.4
Cumulative number of reported claims | claim	844
International Operations | Argo Insurance Bermuda- Liability | Professional | Short-Duration Insurance Contract, Accident Year 2023
Claims Development [Line Items]
Incurred Losses & ALAE, Net of Reinsurance	$ 15.9
Cumulative Paid Losses & ALAE, Net of Reinsurance	0
IBNR & Expected Development on Reported Claims	$ 15.8
Cumulative number of reported claims | claim	883

Reserves for Losses and Loss _7

Reserves for Losses and Loss Adjustment Expenses - Summary of Reconciliation of Net Incurred and Paid Development to Liability for Unpaid Losses and LAE in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	$ 2,697.2
Total reinsurance recoverables on unpaid losses and LAE	2,797.4
Unallocated loss adjustment expenses	70.7
Unamortized reserve discount	(20.8)		$ (19.3)	$ (18.8)
Reserves for losses and loss adjustment expenses	5,544.5	$ 5,526.4	5,051.6	5,595
U.S. Operations | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	1,546.4
Total reinsurance recoverables on unpaid losses and LAE	1,382.6
U.S. Operations | Professional
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	532
Total reinsurance recoverables on unpaid losses and LAE	424.4
U.S. Operations | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	43.3
Total reinsurance recoverables on unpaid losses and LAE	169.9
U.S. Operations | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	55.9
Total reinsurance recoverables on unpaid losses and LAE	25.5
International Operations | Argo Insurance Bermuda- Liability | Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	88.3
Total reinsurance recoverables on unpaid losses and LAE	246.3
International Operations | Argo Insurance Bermuda- Liability | Professional
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	113.9
Total reinsurance recoverables on unpaid losses and LAE	181.7
Run-off Lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	147.7
Total reinsurance recoverables on unpaid losses and LAE	53.2
Unamortized reserve discount	(4.7)		$ (4.6)	$ (4.7)
Other Lines
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total liabilities for unpaid losses and ALAE, net of reinsurance	169.7
Total reinsurance recoverables on unpaid losses and LAE	$ 313.8

Reserves for Losses and Loss _8

Reserves for Losses and Loss Adjustment Expenses - Schedule of Supplementary Unaudited Information About Annual Percentage Payout of Incurred Losses and ALAE, Net of Reinsurance (Detail)	Dec. 31, 2023
U.S. Operations | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	8.60%
Year 2	18.80%
Year 3	20.80%
Year 4	21.40%
Year 5	11.80%
Year 6	7.10%
Year 7	4.20%
Year 8	2.50%
Year 9	1.60%
Year 10	1%
Remainder	2.20%
U.S. Operations | Professional
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	7.10%
Year 2	17.50%
Year 3	19.60%
Year 4	17.30%
Year 5	13.20%
Year 6	9.20%
Year 7	6.10%
Year 8	3.90%
Year 9	2.40%
Year 10	1.50%
Remainder	2.20%
U.S. Operations | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	56.40%
Year 2	35.80%
Year 3	5.70%
Year 4	1.60%
Year 5	0.40%
Year 6	0.10%
Year 7	0%
Year 8	0%
Year 9	0%
Year 10	0%
Remainder	0%
U.S. Operations | Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	15.20%
Year 2	47.80%
Year 3	23.80%
Year 4	8.60%
Year 5	2.50%
Year 6	1.10%
Year 7	0.50%
Year 8	0.20%
Year 9	0.10%
Year 10	0.10%
Remainder	0.10%
International Operations | Argo Insurance Bermuda- Liability | Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	0.50%
Year 2	13.50%
Year 3	18.40%
Year 4	14.70%
Year 5	10.70%
Year 6	7.80%
Year 7	5.90%
Year 8	4.50%
Year 9	3.60%
Year 10	2.90%
Remainder	17.50%
International Operations | Argo Insurance Bermuda- Liability | Professional
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Year 1	2.70%
Year 2	7.60%
Year 3	11.80%
Year 4	13.70%
Year 5	13.50%
Year 6	11.90%
Year 7	9.80%
Year 8	7.70%
Year 9	5.90%
Year 10	4.40%
Remainder	11.10%

Reserves for Losses and Loss _9

Reserves for Losses and Loss Adjustment Expenses - Schedule of Information About Discounted Liabilities For Unpaid Losses and LAE (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	$ 259.4		$ 261	$ 277.4
Aggregate Amount of Discount	20.8		19.3	18.8
Interest Accretion	0.1	$ 1.4	1.8	1.1
U.S. Operations | Specialty Admitted | Liability
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	182.6		168	163.1
Aggregate Amount of Discount	16.1		14.7	14.1
Interest Accretion	$ 0.1	1.3	$ 1.7	$ 0.9
Discount Rate	2.25%		2.25%	2.25%
Run-off Lines
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Carrying Amount of Reserves for Losses & LAE	$ 76.8		$ 93	$ 114.3
Aggregate Amount of Discount	4.7		4.6	4.7
Interest Accretion	$ 0	$ 0.1	$ 0.1	$ 0.2
Discount Rate	3.50%		3.50%	3.50%

Run-off Lines - Gross Reserves

Run-off Lines - Gross Reserves for Run-Off Lines (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ 59.4	$ 65.5
Gross reserves - Run-off Lines	196.1	233.1
Reinsurance assumed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	30.4	31.1
Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	29	34.4
Risk-management
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	119	144.6
Run-off reinsurance lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	0.4	0.4
Other run-off lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross reserves - Run-off Lines	$ 17.3	$ 22.6

Run-off Lines - Total Gross Res

Run-off Lines - Total Gross Reserves for Asbestos Exposure (Detail) - Asbestos and Environmental Claims - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	$ 17.7	$ 21.1	$ 23.4
Total asbestos reserves	40.6	46.7	47.9
Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	2.9	3.2	3
Unallocated loss adjustment expense
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	0.5	0.5	0.5
Incurred but not reported
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total direct written reserves	14.3	17.4	19.9
Assumed domestic
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	20	20.6	20.1
Assumed domestic | Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	7.6	6.8	7.4
Assumed domestic | Unallocated loss adjustment expense
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	0.8	0.8	0.8
Assumed domestic | Incurred but not reported
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	11.6	13	11.9
Assumed London
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	2.9	5	4.4
Assumed London | Case reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	2.8	2.4	2.1
Assumed London | Incurred but not reported
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total assumed reserves	$ 0.1	$ 2.6	$ 2.3

Run-off Lines - Underwriting Lo

Run-off Lines - Underwriting Losses for Run-Off Lines (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	$ 0.3	$ 1.2	$ 10.5	$ 14.7
Total underwriting loss - Run-off Lines	0.7	3.2	3.6	44.7
Reinsurance assumed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	0	0	3.5	4.7
Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total Asbestos and Environmental	0.3	1.2	7	10
Risk-management
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	0	0	1.4	9.9
Run-off reinsurance lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	0	0	0	0
Other run-off lines
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total underwriting loss - Run-off Lines	$ 0.4	$ 2	$ (8.3)	$ 20.1

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Sep. 30, 2012 USD ($)	Dec. 31, 2023 USD ($) debtInstrument	Dec. 31, 2022 USD ($)	Nov. 02, 2023 USD ($)	Feb. 02, 2023 USD ($)	Jun. 22, 2022 USD ($)	Nov. 02, 2018 USD ($)
Debt Instrument [Line Items]
Principal		$ 143,800,000	$ 143,800,000
Amount of collateral under reinsurance agreement		1,212,200,000	1,299,300,000
Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		62,000,000
Amount of collateral under reinsurance agreement		$ 109,200,000
New Credit Agreement
Debt Instrument [Line Items]
Line of credit, maximum borrowing amount							$ 325,000,000
New Credit Agreement | Term Loan
Debt Instrument [Line Items]
Principal							125,000,000
New Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Principal				$ 200,000,000	$ 220,000,000		$ 200,000,000
New Credit Agreement | Letter of Credit
Debt Instrument [Line Items]
Percentage of revolving credit facility allowed to be used for letters of credit		100%
Letter of credit facility amount outstanding		$ 100,000	$ 300,000
Reinsurance Credit Facilities, Secured Bilateral Line of Credit Facilities | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		165,000,000
Committed Secured Bilateral Facility | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		$ 27,000,000
Number of letters of credit | debtInstrument		1
Debt instrument, term		1 year
Uncommitted Secured Bilateral Facility | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		$ 35,100,000
Number of letters of credit | debtInstrument		2
Malta Sales Agreement | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding						$ 50,000,000
Other Letters of Credit | Letter of Credit
Debt Instrument [Line Items]
Letter of credit facility amount outstanding		$ 4,300,000
Senior unsecured fixed rate notes
Debt Instrument [Line Items]
Principal	$ 143,800,000
Debt instrument interest rate stated percentage	6.50%
Redemption price, percentage	100%
Junior subordinated debentures
Debt Instrument [Line Items]
Redemption price, percentage		100%	100%
Subordinated debentures
Debt Instrument [Line Items]
Principal		$ 91,800,000	$ 91,800,000
Debt instrument interest rate stated percentage		8.79%	7.92%
Unsecured debentures		$ 80,400,000	$ 85,900,000

Long-term Debt - Schedule of Un

Long-term Debt - Schedule of Unamortized Debt Issuance Costs Deducted from Carrying Value of Debt Liability (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Senior unsecured fixed rate notes	$ 143.8	$ 143.8
Less: unamortized debt issuance costs and fair value adjustment	(15.8)	(3.3)
Senior unsecured fixed rate notes, less unamortized debt issuance costs	$ 128	$ 140.5

Long-term Debt - Schedule of Ju

Long-term Debt - Schedule of Junior Subordinated Debentures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 241.2	$ 258.6
Argo Group
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	$ 14.3	$ 28.4
Trust preferred debentures | Argo Group | PXRE Capital Statutory Trust II
Debt Instrument [Line Items]
Interest rate	9.74%	8.71%
Junior subordinated debentures, Amount	$ 18	$ 18
Trust preferred debentures | Argo Group | PXRE Capital Trust VI
Debt Instrument [Line Items]
Interest rate	9.49%	8.63%
Junior subordinated debentures, Amount	$ 10.3	$ 10.3
Trust preferred debentures | Argo Group US
Debt Instrument [Line Items]
Junior subordinated debentures, Amount	160.8	$ 172.7
Less: fair value adjustment	$ (11.9)
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust I
Debt Instrument [Line Items]
Interest rate	9.74%	8.71%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust III
Debt Instrument [Line Items]
Interest rate	9.76%	8.18%
Junior subordinated debentures, Amount	$ 12.3	$ 12.3
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IV
Debt Instrument [Line Items]
Interest rate	9.49%	8.50%
Junior subordinated debentures, Amount	$ 13.4	$ 13.4
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust V
Debt Instrument [Line Items]
Interest rate	9.49%	8.61%
Junior subordinated debentures, Amount	$ 12.4	$ 12.4
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VI
Debt Instrument [Line Items]
Interest rate	9.47%	8.54%
Junior subordinated debentures, Amount	$ 13.4	$ 13.4
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VII
Debt Instrument [Line Items]
Interest rate	9.25%	8.37%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VIII
Debt Instrument [Line Items]
Interest rate	9.18%	8.30%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IX
Debt Instrument [Line Items]
Interest rate	9.25%	8.37%
Junior subordinated debentures, Amount	$ 15.5	$ 15.5
Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust X
Debt Instrument [Line Items]
Interest rate	9.05%	8.17%
Junior subordinated debentures, Amount	$ 30.9	$ 30.9
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group | PXRE Capital Statutory Trust II
Debt Instrument [Line Items]
Interest rate basis spread	4.10%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group | PXRE Capital Trust VI
Debt Instrument [Line Items]
Interest rate basis spread	3.90%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust I
Debt Instrument [Line Items]
Interest rate basis spread	4.10%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust III
Debt Instrument [Line Items]
Interest rate basis spread	4.10%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IV
Debt Instrument [Line Items]
Interest rate basis spread	3.85%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust V
Debt Instrument [Line Items]
Interest rate basis spread	3.85%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VI
Debt Instrument [Line Items]
Interest rate basis spread	3.80%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VII
Debt Instrument [Line Items]
Interest rate basis spread	3.60%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VIII
Debt Instrument [Line Items]
Interest rate basis spread	3.55%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IX
Debt Instrument [Line Items]
Interest rate basis spread	3.60%
Secured Overnight Financing Rate (SOFR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust X
Debt Instrument [Line Items]
Interest rate basis spread	3.40%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group | PXRE Capital Statutory Trust II
Debt Instrument [Line Items]
Interest rate basis spread		4.10%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group | PXRE Capital Trust VI
Debt Instrument [Line Items]
Interest rate basis spread		3.90%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust I
Debt Instrument [Line Items]
Interest rate basis spread		4.10%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust III
Debt Instrument [Line Items]
Interest rate basis spread		4.10%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IV
Debt Instrument [Line Items]
Interest rate basis spread		3.85%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust V
Debt Instrument [Line Items]
Interest rate basis spread		3.85%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VI
Debt Instrument [Line Items]
Interest rate basis spread		3.80%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VII
Debt Instrument [Line Items]
Interest rate basis spread		3.60%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust VIII
Debt Instrument [Line Items]
Interest rate basis spread		3.55%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust IX
Debt Instrument [Line Items]
Interest rate basis spread		3.60%
London Interbank Offered Rate (LIBOR) | Trust preferred debentures | Argo Group US | Argonaut Group Statutory Trust X
Debt Instrument [Line Items]
Interest rate basis spread		3.40%

Long-term Debt - Schedule of Ma

Long-term Debt - Schedule of Maybrooke Junior Subordinated Debentures (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Principal	$ 143.8	$ 143.8
Subordinated debentures
Debt Instrument [Line Items]
Interest rate	8.79%	7.92%
Principal	$ 91.8	$ 91.8
Carrying Value	$ 80.4	$ 85.9
Secured Overnight Financing Rate (SOFR) | Subordinated debentures
Debt Instrument [Line Items]
Interest rate basis spread	3.15%
London Interbank Offered Rate (LIBOR) | Subordinated debentures
Debt Instrument [Line Items]
Interest rate basis spread		3.15%

Long-term Debt - Schedule of Lo

Long-term Debt - Schedule of Long-term Debt Maturity (Details) $ in Millions	Dec. 31, 2023 USD ($)
Junior subordinated debentures
Debt Instrument [Line Items]
Total	$ 548.3
2024	24.6
2025	24.6
2026	24.6
2027	24.6
2028	24.6
Thereafter	425.3
Senior unsecured fixed rate notes
Debt Instrument [Line Items]
Total	316.5
2024	9.3
2025	9.3
2026	9.3
2027	9.3
2028	9.3
Thereafter	$ 270

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	Dec. 31, 2023	Dec. 31, 2022
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 369.2	$ 453.8
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	381.9	419.1
Junior subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	241.2	258.6
Junior subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	249.2	253.9
Junior subordinated debentures | Trust preferred debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	160.8	172.7
Junior subordinated debentures | Trust preferred debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	165.9	165.8
Junior subordinated debentures | Subordinated debentures | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	80.4	85.9
Junior subordinated debentures | Subordinated debentures | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	83.3	88.1
Senior unsecured fixed rate notes | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	128	140.5
Senior unsecured fixed rate notes | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	132.7	112.7
Floating rate loan stock | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	0	54.7
Floating rate loan stock | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments	$ 0	$ 52.5

Disclosures about Fair Value _4

Disclosures about Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value (Details) - Recurring fair value - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	$ 381.9	$ 419.1
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	132.7	112.7
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	249.2	306.4
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	249.2	253.9
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	249.2	253.9
Junior 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	132.7	112.7
Senior unsecured fixed rate notes | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	132.7	112.7
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
Floating rate loan stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments		52.5
Floating rate loan stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments		0
Floating rate loan stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments		52.5
Floating rate loan stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments		0
Trust preferred debentures | Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	165.9	165.8
Trust preferred debentures | Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Trust preferred debentures | Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	165.9	165.8
Trust preferred debentures | Junior subordinated debentures | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Subordinated debentures | Junior subordinated debentures
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	83.3	88.1
Subordinated debentures | Junior subordinated debentures | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	0	0
Subordinated debentures | Junior subordinated debentures | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments	83.3	88.1
Subordinated debentures | Junior subordinated debentures | 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)	11 Months Ended	12 Months Ended
	Nov. 15, 2023 USD ($) $ / shares shares	Dec. 31, 2023 $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares	Nov. 16, 2023 USD ($) $ / shares shares	Jul. 09, 2020 $ / shares	May 03, 2016 USD ($)
Class of Stock [Line Items]
Preferred shares, issued (in shares) | shares		6,000	6,000
Depositary shares issued (in shares) | shares		6,000,000
Fractional interest per preference share		0.001
Preferred stock, liquidation preference (in dollars per share)		$ 25,000	$ 25,000
Depositary share, liquidation preference (in dollars per share)		25				$ 25
Preferred stock, per depositary share amounts of preferred dividends (in dollars per share)		$ 1.75
Preferred shares, authorized (in shares) | shares		30,000,000	30,000,000
Preferred shares, par value (in dollars per share)		$ 1	$ 1		$ 1
Preferred shares, outstanding (in shares) | shares		6,000	6,000
Common shares, shares authorized (in shares) | shares		2,000,000,000	500,000,000		2,000,000,000
Common shares, par value (in dollars per share)		$ 1	$ 1		$ 1
Dividend declared per common share (in dollars per share)	$ 0		$ 1.24	$ 1.24
Cash dividends paid to common stockholders | $	$ (300,000)		$ 43,400,000	$ 43,900,000
Common shares repurchased on open market (in shares) | shares	0		0
BNRE Triangle Acquisition Inc.
Class of Stock [Line Items]
Common stock | $					$ 1,056,638,730
2016 Repurchase Authorization
Class of Stock [Line Items]
Remaining number of shares available under repurchase authorization, value | $			$ 53,300,000
2016 Repurchase Authorization | Maximum
Class of Stock [Line Items]
Total number of shares authorized for purchase, value | $							$ 150,000,000
Preferred Stock and Additional Paid-in Capital
Class of Stock [Line Items]
Preferred shares, issued (in shares) | shares		6,000
Preferred stock, liquidation preference (in dollars per share)		$ 25,000				$ 25,000
Dividends declared per preferred share (in dollars per share)		0.0700
Preferred stock dividends (in dollars per share)		$ 1,750
Preferred shares, outstanding (in shares) | shares		6,000
Preferred Stock and Additional Paid-in Capital | US Treasury (UST) Interest Rate
Class of Stock [Line Items]
Preferred stock, dividend payment rate, Basis spread on variable rate (in percentage)		0.06712

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,244.8	$ 1,232.9	$ 1,735.2
Other comprehensive income before reclassifications	51.9	15.5	(348.6)
Amounts reclassified from accumulated other comprehensive loss	(0.1)	22.1	66.2
Net current-period other comprehensive income (loss)	51.8	37.6	(282.4)
Ending Balance	1,297.5	1,049.9	1,232.9
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	(4.2)	(35.3)
Other comprehensive income before reclassifications	0.1	1	(0.7)
Amounts reclassified from accumulated other comprehensive loss	0	0	31.8
Net current-period other comprehensive income (loss)	0.1	1	31.1
Ending Balance	0.1	(3.2)	(4.2)
Unrealized Holding Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	(293.1)	19.7
Other comprehensive income before reclassifications	51.2	13.7	(347.2)
Amounts reclassified from accumulated other comprehensive loss	(0.1)	22.1	34.4
Net current-period other comprehensive income (loss)	51.1	35.8	(312.8)
Ending Balance	51.1	(257.3)	(293.1)
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	(7.8)	(7.1)
Other comprehensive income before reclassifications	0.6	0.8	(0.7)
Amounts reclassified from accumulated other comprehensive loss	0	0	0
Net current-period other comprehensive income (loss)	0.6	0.8	(0.7)
Ending Balance	0.6	(7)	(7.8)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	0	(305.1)	(22.7)
Ending Balance	$ 51.8	$ (267.5)	$ (305.1)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Unrealized gains and losses on securities:
Net investment and other (gains) losses		$ (0.1)	$ 20.4	$ 115.9	$ (72.4)
Income tax provision (benefit)		1.3	0.3	(8)	(1.4)
Total, net of taxes	$ (0.9)	(0.9)	210.4	175.2	(6.7)
Reclassification out of accumulated other comprehensive income
Unrealized gains and losses on securities:
Total, net of taxes		(0.1)	22.1	66.2	(8)
Unrealized Holding Gains (Losses) on Securities | Reclassification out of accumulated other comprehensive income
Unrealized gains and losses on securities:
Net investment and other (gains) losses		(0.1)	28	43.6	(12.2)
Income tax provision (benefit)		0	(5.9)	(9.2)	4.2
Foreign Currency Translation Adjustments | Reclassification out of accumulated other comprehensive income
Unrealized gains and losses on securities:
Net investment and other (gains) losses		$ 0	$ 0	$ (31.8)	$ 0

Net (Loss) Income Per Common _3

Net (Loss) Income Per Common Stock - Net (Loss) Income Per Common Share on Basic and Diluted Basis (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net income (loss)	$ 0.9	$ 0.9	$ (210.4)	$ (175.2)	$ 6.7
Dividends on Series A Preferred stock		0	10.5	10.5	10.5
Net income (loss) attributable to common shareholders, diluted		0.9	(220.9)	(185.7)	(3.8)
Net income (loss) attributable to common shareholders, basic		$ 0.9	$ (220.9)	$ (185.7)	$ (3.8)
Weighted average common shares outstanding - basic (in shares)			35,166,679	34,980,608	34,816,160
Effect of dilutive securities:
Equity compensation awards (in shares)			0	0	0
Weighted average common shares outstanding - diluted (in shares)			35,166,679	34,980,608	34,816,160
Net income (loss) per common stock:
Basic (in dollars per share)			$ (6.28)	$ (5.31)	$ (0.11)
Diluted (in dollars per share)			$ (6.28)	$ (5.31)	$ (0.11)

Net (Loss) Income Per Common _4

Net (Loss) Income Per Common Stock - Additional Information (Detail) - shares	11 Months Ended	12 Months Ended
	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2023
Earnings Per Share [Abstract]
Treasury shares (in shares)	11,318,339	11,318,339	11,318,339	0
Anti-dilutive securities excluded from computation of diluted net income per common share (in shares)	47,571	79,276	208,524

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	2 Months Ended	11 Months Ended	12 Months Ended
	Nov. 16, 2023	Jun. 30, 2022	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense			$ 2.8	$ 1.5	$ 4.3
Argo Group International Holdings, Inc. | Common Stock | Brookfield Reinsurance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity interests issued and issuable (in dollars per share)	$ 30
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Converted To Cash, Value	$ 2.2
Converted to cash (in shares)					140,260
Share-based compensation, restricted shares , vested in period, fair value					$ 4.8
Vested in period (in shares)					114,101
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Converted To Cash, Value	$ 0.1
Converted to cash (in shares)	5,031				5,031
Canceled in period (in shares)					102,891
Performance Shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years					1 year
Performance Shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years					4 years
Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense				$ 0.3
Awards granted (in shares)		135,000
Share-based compensation arrangement by share-based payment award, award vesting period, years		3 years
Weighted average exercise price (in dollars per share)		$ 43.80
Weighted average grant date fair value (in dollars per share)		$ 8.28
Vested in period (in shares)		45,000
Share-based Payment Arrangement
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment expense					$ 0.2	$ 0.7	$ 0.5
2007 Employee Share Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years					3 months
Discount from market price					85%
Earn Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount from market price					85%
Earn Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years					3 years
Earn Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting period, years					5 years

Share-based Compensation - Summ

Share-based Compensation - Summary of Performance Share Activity (Details) - Performance Shares - $ / shares		12 Months Ended
	Nov. 16, 2023	Dec. 31, 2023	Dec. 31, 2022
Shares
Options outstanding (in shares)		0	124,974
Expired or forfeited (in shares)		(119,943)
Converted to cash (in shares)	(5,031)	(5,031)
Outstanding, ending balance (in shares)		0
Weighted-Average Grant Date Fair Value
Outstanding, weighted-average grant date fair value, beginning balance (in dollars per share)		$ 46.41
Expired or forfeited (in dollars per share)		46.64
Converted to cash (in dollars per share)		41
Outstanding, weighted-average grant date fair value, ending balance (in dollars per share)		$ 0

Share-based Compensation - Su_2

Share-based Compensation - Summary of Restricted Share Activity (Detail) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Shares
Outstanding, beginning balance (in shares) | shares	341,670
Vested and issued (in shares) | shares	(114,101)
Expired or forfeited (in shares) | shares	(87,309)
Converted to cash (in shares) | shares	(140,260)
Outstanding, ending balance (in shares) | shares	0
Weighted-Average Grant Date Fair Value
Outstanding, weighted-average grant date fair value, beginning balance (in dollars per share) | $ / shares	$ 42.19
Vested and issued (in dollars per share) | $ / shares	41.66
Expired or forfeited (in dollars per share) | $ / shares	43.78
Converted to cash (in dollars per share) | $ / shares	41.64
Outstanding, weighted-average grant date fair value, ending balance (in dollars per share) | $ / shares	$ 0

Underwriting, Acquisition and_3

Underwriting, Acquisition and General Expenses (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Underwriting Acquisition And Insurance Expenses [Abstract]
Commissions	$ 12.7	$ 141.7	$ 280.2	$ 289.5
Other underwriting and insurance expenses	33.8	268.3	401	428.6
Amortization of value of business acquired and other intangible assets	37.9	0	0	0
Underwriting, acquisition and insurance expenses, total	84.4	410	681.2	718.1
Net deferral of policy acquisition costs	(7.2)	9	(10.5)	(15.8)
Total underwriting, acquisition and general expenses	$ 77.2	$ 419	$ 670.7	$ 702.3

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Net operating losses carryback period	2 years
Capital losses carryback period	3 years
Net change in valuation allowance, for deferred tax asset	$ 0.4
Net deferred assets	39.1	$ 101.2
Valuation allowance	(20.7)	(20.3)
Unrecognized tax benefits	0	4.6	$ 3.6
Unrecognized tax benefits, interest expense (benefit) on income taxes	(0.4)	0.6	(1)
Tax penalty expense (benefit)	0	$ 0.1	$ (0.8)
United States (Federal)
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	(1.3)
United Kingdom
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ (1.7)

Income Taxes - Income Tax (Bene

Income Taxes - Income Tax (Benefit) Provision Expense (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Current income tax provision (benefit) related to:
United States (Federal)	$ 4.2	$ 15.1	$ (21)	$ 35.4
United States (State)	(4.2)	0.1	0.1	2.4
United Kingdom	0	(0.1)	(0.8)	(2.2)
Other jurisdictions	0	0.1	(1.7)	1.6
Total current income tax provision	0	15.2	(23.4)	37.2
Deferred income tax provision (benefit) related to:
United States	1.3	(7.9)	6	(26.3)
United Kingdom	0	(7)	7.3	(12.3)
Other jurisdictions	0	0	2.1	0
Total deferred income tax (benefit)	1.3	(14.9)	15.4	(38.6)
Income tax provision (benefit)	$ 1.3	$ 0.3	$ (8)	$ (1.4)

Income Taxes - Schedule of Pre-

Income Taxes - Schedule of Pre-Tax Income (Loss) and Effective Income Tax Rates (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 2.2	$ (210.1)	$ (183.2)	$ 5.3
Effective Tax Rate	59.10%	0.10%	4.30%	(26.40%)
Bermuda
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (11.3)	$ (90.3)	$ (76)	$ (18)
Effective Tax Rate	0%	0%	0%	0%
United States (Federal)
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 14.3	$ (96.9)	$ (83.2)	$ 65.6
Effective Tax Rate	9%	(7.50%)	17.90%	18.10%
United Kingdom
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ (1.3)	$ (23.2)	$ 23.4	$ (61.1)
Effective Tax Rate	0%	30.40%	27.90%	24.40%
Barbados
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ (4.5)	$ 0.1
Effective Tax Rate	0%	0%	0%	0%
Brazil
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ (0.1)	$ 15.3
Effective Tax Rate	0%	0%	(422.40%)	10.40%
United Arab Emirates
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0.3	$ 1.4	$ 1.4
Effective Tax Rate	0%	0%	0%	0%
Ireland
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0.5	$ (0.1)	$ (39.1)	$ (0.2)
Effective Tax Rate	0%	0%	0%	0%
Italy
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0.1	$ (0.9)	$ 1.4
Effective Tax Rate	2.10%	50.30%	(4.80%)	0%
Malta
Income Tax Examination [Line Items]
Pre-Tax Income (Loss)	$ 0	$ 0	$ (4.2)	$ 0.9
Effective Tax Rate	0%	0%	0%	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	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income tax provision (benefit) at expected rate	$ 2.9	$ (24.7)	$ (14.7)	$ 9.8
Tax effect of:
Nontaxable investment income	0	(0.1)	(0.4)	(0.5)
Foreign exchange adjustments	0	(2.6)	(2.1)	(0.7)
Impairment of goodwill	0	0	5.4	8.2
Base Erosion and Anti-Abuse Tax	0	23.5	0	0
Withholding taxes	0	0.1	2.7	0.1
U.S. state tax expense, net of federal income tax effect	0.1	(1.2)	0	0
Change in uncertain tax position liability	(3.4)	1.2	(1.4)	(4.5)
Change in valuation allowance	1.8	(1.4)	(7.6)	(0.7)
Impact of change in tax rate related to Finance Act 2021	(0.2)	(0.2)	1.7	(8.3)
Brazil Premiums and Underwriting	0	0	0.3	(5.3)
Sale of Brazil and Malta Operations	0	0	6.6	0
Excess Executive Compensation	0	2	0	0
Other	0.1	3.7	1.5	0.5
Income tax provision (benefit)	$ 1.3	$ 0.3	$ (8)	$ (1.4)

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Deferred Tax Liability Comprises Tax Effect Related to Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Losses and loss adjustment expense reserve discounting	$ 45.5	$ 31.4
Unearned premiums	23.9	26.5
Net operating loss carryforwards	36.3	26.5
Investment in limited partnership interests	9.3	14
Unrealized losses on equity securities	6.9	8.2
Unrealized losses on fixed maturities and other investment securities	42.3	63.6
Investments	4.9	0
Right of use assets	10.6	12.8
Accrued bonus	5.5	6.9
Stock option expense	0	0.9
Bad debt	3.2	1.9
Other	2.6	4.3
Deferred tax assets, gross	191	197
Deferred tax liabilities:
Debt obligations	6.4	0
Unrealized gains on limited partnership interests	(24.8)	(25.3)
Investments		(5.8)
Depreciable fixed assets	(7.3)	(7.1)
Deferred acquisition costs	(0.5)	(23)
Lease liability	(12.1)	(11)
TCJA reserve transitional liability	(1.1)	(1.6)
Value of business acquired	(32.2)	0
Other intangible assets	(37.1)	0
Underwriting results	(9.1)	0
Other	(0.6)	(1.7)
Deferred tax liabilities, gross	(131.2)	(75.5)
Deferred tax assets, net before valuation allowance	59.8	121.5
Valuation allowance	(20.7)	(20.3)
Deferred tax asset (liabilities), net	39.1	101.2
Domestic Tax Authority
Deferred tax liabilities:
Deferred tax asset (liabilities), net	$ 39.1	$ 101.2

Income Taxes - Schedule of Ne_2

Income Taxes - Schedule of Net Operating Loss Carryforwards Amounts by Jurisdiction and Year of Expiration (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Ireland | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	$ 9.8
Italy | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	49.7
United Kingdom
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	1.7
United Kingdom | Indefinite Expiration
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	6.9
United States (Federal)
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	1.3
United States (Federal) | Expiration Year, 2025-2043
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards by jurisdiction:	$ 92.3

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at January 1	$ 4.6	$ 3.6
Additions for tax positions of prior years	0	3
Reductions for tax positions of prior years	(1)	(1.4)
Reductions based on settlements with taxing authorities	(2.4)	0
Expiration of statute of limitations	(1.2)	(0.6)
Balance at December 31	$ 0	$ 4.6

Pension Benefits and Savings _2

Pension Benefits and Savings Plans (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 0.1	$ 0.8	$ 0.1	$ 0.1
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer towards savings plan	0.8	$ 5.3	8.5	$ 9.3
Qualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Underfunded amount	2.8		3.2
Nonqualified Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Underfunded amount	$ 1.4		$ 1.5

Commitments and Contingencies (

Commitments and Contingencies (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Nov. 16, 2023	Dec. 31, 2023
Argo Group International Holdings, Inc. | Common Stock | Brookfield Reinsurance
Commitments And Contingencies [Line Items]
Equity interests issued and issuable (in dollars per share)	$ 30
Maximum
Commitments And Contingencies [Line Items]
Contractual commitments related to its limited partnership investments, up to		$ 93.4
Contractual commitments period		12 years

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023 USD ($)	Nov. 15, 2023 USD ($)	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Nov. 16, 2023 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of reportable segments | segment			2
Assets associated with trade capital providers				$ 303.7
Other intangible assets, net of accumulated amortization	$ 324.2		$ 324.2	0		$ 362.1
Impairment of goodwill and intangibles	$ 0	$ 0		28.5	$ 43.2
Impairment of indefinite lived intangible assets				17.3
Impairment of goodwill and intangibles				11.2
ArgoGlobal Syndicate 1200
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of goodwill and intangibles				$ 28.5

Segment Information - Revenue a

Segment Information - Revenue and Income (Loss) Before Income Taxes for Each Segment (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net earned premiums	$ 162.3	$ 1,225.9	$ 1,740.4	$ 1,910.1
Net investment income	28.6	121.3	129.8	187.6
Net investment and other gains (losses)	(0.3)	(22.7)	(115.3)	32.6
Total revenue	190.6	1,324.5	1,754.9	2,130.3
Foreign currency exchange gains (losses)	(0.6)	(1.8)	5	(1.6)
Impairment of goodwill and intangibles	0	0	(28.5)	(43.2)
Non-operating expenses	(13.1)	(41.1)	(51.5)	(43.7)
Pre-Tax Income (Loss)	2.2	(210.1)	(183.2)	5.3
U.S. Operations
Segment Reporting Information [Line Items]
Net earned premiums	147.2	1,101.6	1,209	1,283.7
Net investment income	23.5	99.9	88.4	119.4
International Operations
Segment Reporting Information [Line Items]
Net earned premiums	14.9	124	530.5	625.8
Net investment income	4.4	18.7	39.1	50.6
Run-off Lines
Segment Reporting Information [Line Items]
Net earned premiums	0.2	0.3	0.9	0.6
Net investment income	0.7	2.7	2.3	3.6
Operating Segments
Segment Reporting Information [Line Items]
Pre-Tax Income (Loss)	18.1	(122)	39.1	83.7
Operating Segments | U.S. Operations
Segment Reporting Information [Line Items]
Net earned premiums	147.2	1,101.6	1,209	1,283.7
Net investment income	23.5	99.9	88.4	119.4
Pre-Tax Income (Loss)	17.3	(127.5)	(22.9)	61.1
Operating Segments | International Operations
Segment Reporting Information [Line Items]
Net earned premiums	14.9	124	530.5	625.8
Net investment income	4.4	18.7	39.1	50.6
Pre-Tax Income (Loss)	0.9	6.7	63.8	64.1
Operating Segments | Run-off Lines
Segment Reporting Information [Line Items]
Net earned premiums	0.2	0.3	0.9	0.6
Net investment income	0.7	2.7	2.3	3.6
Pre-Tax Income (Loss)	(0.1)	(1.2)	(1.8)	(41.5)
Corporate and Other
Segment Reporting Information [Line Items]
Net investment income	0	0	0	14
Pre-Tax Income (Loss)	$ (1.9)	$ (22.5)	$ (32)	$ (22.5)

Segment Information - Schedule

Segment Information - Schedule of Earned Premiums by Geographic Location (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 162.3	$ 1,225.9	$ 1,740.4	$ 1,910.1
United States (Federal)
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	147.4	1,101.9	1,209.9	1,277
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	0	48.3	480.2	475.3
Bermuda
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	14.9	75.7	38	54.8
Malta
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	0	0	3.9	35.4
All other jurisdictions
Revenues from External Customers and Long-Lived Assets [Line Items]
Total earned premiums	$ 0	$ 0	$ 8.4	$ 67.6

Segment Information - Identifia

Segment Information - Identifiable Assets (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 8,503.1		$ 10,034.4
Assets held-for-sale	0		2,066.2
Net earned premiums	162.3	$ 1,225.9	1,740.4	$ 1,910.1
United States (Federal)
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	147.4	1,101.9	1,209.9	1,277
United Kingdom
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	0	48.3	480.2	475.3
Bermuda
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	14.9	75.7	38	54.8
Malta
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	0	0	3.9	35.4
All other jurisdictions
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	0	0	8.4	67.6
Argo Underwriting Agency Limited | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Assets held-for-sale			2,066.2
U.S. Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	147.2	1,101.6	1,209	1,283.7
International Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	14.9	124	530.5	625.8
Run-off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Net earned premiums	0.2	0.3	0.9	0.6
Operating Segments | U.S. Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	6,279		5,815
Net earned premiums	147.2	1,101.6	1,209	1,283.7
Operating Segments | International Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	1,888.9		3,791.6
Net earned premiums	14.9	124	530.5	625.8
Operating Segments | International Operations | Argo Underwriting Agency Limited | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment Reporting, Asset Reconciling Item [Line Items]
Assets held-for-sale	2,066.2
Operating Segments | Run-off Lines
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	221.4		284.4
Net earned premiums	0.2	$ 0.3	0.9	$ 0.6
Corporate and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Identifiable assets	$ 113.8		$ 143.4

Segment Information - Schedul_2

Segment Information - Schedule of Goodwill and Intangible Assets Net of Accumulated Amortization (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 16, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Goodwill	$ 0		$ 118.6
Intangible Assets, Net of Accumulated Amortization	324.2	$ 362.1	0
U.S. Operations
Segment Reporting Information [Line Items]
Goodwill	0		118.6
Intangible Assets, Net of Accumulated Amortization	293.8		0
International Operations
Segment Reporting Information [Line Items]
Goodwill	0		0	$ 28.7
Intangible Assets, Net of Accumulated Amortization	30.4		$ 0
International Operations | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
Segment Reporting Information [Line Items]
Goodwill derecognized	$ 17.5

Statutory Accounting Principl_3

Statutory Accounting Principles - Statutory Capital and Surplus for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Bermuda
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 1,150.6	$ 1,024.9
United Kingdom
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	0	370
United States (Federal)
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	$ 1,410.4	$ 1,111.1

Statutory Accounting Principl_4

Statutory Accounting Principles - Statutory Net Income (Loss) for Principal Operating Subsidiaries (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Bermuda
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 0.8	$ (29.1)	$ 14.2
United Kingdom
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	0	21.4	8.6
United States (Federal)
Statutory Accounting Practices [Line Items]
Statutory net income (loss)	$ 39.5	$ (117.8)	$ 103.5

Statutory Accounting Principl_5

Statutory Accounting Principles - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Argo Re
Statutory Accounting Practices [Line Items]
Maximum permissible limit for dividend		25%
Reduction in total statutory capital		15%
Maximum permitted amount of dividends		$ 287.7
Cash dividends			$ 33	$ 85
Rockwood Casualty Insurance Company
Statutory Accounting Practices [Line Items]
Cash dividends		21.3
Rockwood Casualty Insurance Company | Forecast
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends	$ 25
Argonaut Insurance Company | Forecast
Statutory Accounting Practices [Line Items]
Maximum permitted amount of dividends	$ 120.7
Minimum
Statutory Accounting Practices [Line Items]
Minimum statutory capital and surplus balance		$ 106.6	$ 100

Insurance Assessments (Detail)

Insurance Assessments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Insurance [Abstract]
Insurance assessments on current insolvencies	$ 6.9	$ 5.2

Subsequent Event (Detail)

Subsequent Event (Detail) - Subsequent Event - USD ($) $ in Millions	Feb. 22, 2024	Feb. 20, 2024	Feb. 21, 2024
Argo Group International Holdings, Inc. | Brookfield Reinsurance
Subsequent Event [Line Items]
Capital contribution		$ 100
New Credit Agreement
Subsequent Event [Line Items]
Debt covenant, consolidated net worth			$ 872
Percent of net income added to consolidated net worth			50%
Percent of net proceeds from equity interests added to consolidated net worth			50%
New Credit Agreement | Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Borrowings from revolving credit facility	$ 100

Schedule II Condensed Financi_2

Schedule II Condensed Financial Information of Registrant - Schedule of Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 16, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets
Cash, restricted cash and cash equivalents	$ 791.6	$ 712.9	$ 45.8	$ 50.2	$ 146.1	$ 148.8
Operating lease right-of-use assets	51.2			57.7
Other assets	189.1			121.5
Total assets	8,503.1			10,034.4
Liabilities and Stockholders' Equity
Junior subordinated debentures	241.2			258.6
Accrued underwriting expenses and other liabilities	73.9			121.3
Operating lease liabilities	51.4			66.4
Total liabilities	7,205.6			8,801.5
Stockholders' equity	1,297.5	$ 1,244.8	$ 1,049.9	1,232.9	$ 1,735.2	$ 1,857.8
Total liabilities and stockholders' equity	8,503.1			10,034.4
Argo Group International Holdings, Ltd (Parent  Guarantor)
Assets
Short-term investments	0			1.8
Investment in subsidiaries	1,363.3			1,281.7
Cash, restricted cash and cash equivalents	2.2			5.2
Operating lease right-of-use assets	0			4.6
Other assets	0.9			6.7
Total assets	1,366.4			1,300
Liabilities and Stockholders' Equity
Junior subordinated debentures	14.3			28.4
Accrued underwriting expenses and other liabilities	2.2			10
Operating lease liabilities	0			4.6
Total liabilities	68.9			67.1
Stockholders' equity	1,297.5			1,232.9
Total liabilities and stockholders' equity	1,366.4			1,300
Argo Group International Holdings, Ltd (Parent  Guarantor) | Argo Group US
Liabilities and Stockholders' Equity
Due to subsidiaries	21.3			14
Argo Group International Holdings, Ltd (Parent  Guarantor) | Related Party
Liabilities and Stockholders' Equity
Due to subsidiaries	$ 31.1			$ 10.1

Schedule II Condensed Financi_3

Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Income (Detail) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue:
Net investment expense		$ 28.6	$ 121.3	$ 129.8	$ 187.6
Net investment and other (gains) losses		(0.3)	(22.7)	(115.3)	32.6
Total revenue		190.6	1,324.5	1,754.9	2,130.3
Expenses:
Interest expense		3.5	29.8	26.8	21.6
Non-operating expenses		13.1	41.1	51.5	43.7
Total expenses		188.4	1,534.6	1,938.1	2,125
Net income (loss)	$ 0.9	0.9	(210.4)	(175.2)	6.7
Dividends on Series A Preferred stock		0	10.5	10.5	10.5
Net income (loss) attributable to common shareholders, basic		0.9	(220.9)	(185.7)	(3.8)
Argo Group International Holdings, Ltd (Parent  Guarantor)
Revenue:
Net investment expense		(0.1)	0	0	0
Total revenue		(0.1)	0	0	0
Expenses:
Interest expense		0.4	2.3	1.6	1.2
Operating expenses		(1.3)	6.8	(0.6)	6.2
Non-operating expenses		2.7	21.3	26.2	0.2
Total expenses		1.8	30.4	27.2	7.6
Net income before equity in earnings of subsidiaries		(1.9)	(30.4)	(27.2)	(7.6)
Equity in undistributed earnings of subsidiaries		2.8	(180)	(148)	14.3
Net income (loss)		0.9	(210.4)	(175.2)	6.7
Dividends on Series A Preferred stock		0	10.5	10.5	10.5
Net income (loss) attributable to common shareholders, basic		$ 0.9	$ (220.9)	$ (185.7)	$ (3.8)

Schedule II Condensed Financi_4

Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Cash Flows (Detail) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows provided by (used in) operating activities:
Net income (loss)	$ 0.9	$ 0.9	$ (210.4)	$ (175.2)	$ 6.7
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation		39.6	12.2	18.5	43.4
Share-based payments expense		0	1.5	9.6	8
Loss on disposals of long-lived assets, net		0	1.2	0.6	23.3
Change in:
Other, net		(14.3)	(77.2)	0	17.9
Net cash flows from operating activities		16.9	293.7	53.2	99.7
Cash flows provided by (used in) investing activities:
Change in short-term investments		24.1	(627)	26.1	(116.4)
Settlements of foreign currency exchange forward contracts		1.3	4.5	(22)	(1.2)
Cash provided by (used in) investing activities		61.8	(359.7)	(26.6)	(55.9)
Cash flows provided by (used in) financing activities:
Activity under stock incentive plans		0	0.7	1.8	1.3
Payment of cash dividends to preferred stockholders		0	(10.5)	(10.5)	(10.5)
Payment of cash dividends to common stockholders		0	0.3	(43.4)	(43.7)
Cash used in financing activities		0	(9.5)	(52.1)	(52.9)
Change in cash		78.7	(75.2)	(25.1)	(2.7)
Argo Group International Holdings, Ltd (Parent  Guarantor)
Cash flows provided by (used in) operating activities:
Net income (loss)		0.9	(210.4)	(175.2)	6.7
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation		0	0	1.5	1.5
Share-based payments expense		0	1	2.8	2.3
Loss on disposals of long-lived assets, net		0	0	(3.5)	(3)
Undistributed earnings of subsidiaries		(2.8)	180	148	(14.3)
Change in:
Prepaid assets		0	0.2	(1.8)	7.2
Accrued expenses		(8)	10.6	6	(4.1)
Due to subsidiaries		5.6	22.7	28.8	(12.1)
Other, net		(2.2)	5.1	4.7	(3.9)
Net cash flows from operating activities		(6.5)	9.2	11.3	(19.7)
Cash flows provided by (used in) investing activities:
Change in short-term investments		0	(3.8)	12.7	(13.9)
Settlements of foreign currency exchange forward contracts		0	2	(2)	0.5
Dividend received from subsidiaries		0	0	33.3	85
Cash provided by (used in) investing activities		0	(1.8)	44	71.6
Cash flows provided by (used in) financing activities:
Activity under stock incentive plans		0	0.7	1.8	1.3
Payment of cash dividends to preferred stockholders		0	(10.5)	(10.5)	(10.5)
Payment of cash dividends to common stockholders		0	0.3	(43.4)	(43.7)
Cash used in financing activities		0	(9.5)	(52.1)	(52.9)
Change in cash		(6.5)	(2.1)	3.2	(1)
Cash, beginning of year	8.7	3.1	5.2	2	3
Cash, end of period	$ 2.2	$ 2.2	$ 3.1	$ 5.2	$ 2

Schedule III Supplemental Ins_2

Schedule III Supplemental Insurance Information (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC	$ 7.2	$ 88.7	$ 107	$ 168
Reserves for Losses and Loss Adjustment Expenses	5,544.5		5,051.6	5,595
UPR	916.6		1,039.9	1,466.8
Premium Revenue	162.3	1,225.9	1,740.4	1,910.1
Net investment income	28.6	121.3	129.8	187.6
Loss & LAE	94.2	1,043.2	1,166.9	1,314.6
Amortization (Deferral) DAC	(7.2)	9	(10.5)	(15.8)
Other Operating Expenses	84.4	410	681.2	718.1
Net Premiums Written	124.3	1,144.7	1,741.5	1,977.3
U.S. Operations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC	7.4		109.4	103.7
Reserves for Losses and Loss Adjustment Expenses	4,224.1		3,718.1	3,422.4
UPR	763.2		893.4	973.7
Premium Revenue	147.2	1,101.6	1,209	1,283.7
Net investment income	23.5	99.9	88.4	119.4
Loss & LAE	81.7	935.1	870.1	908.2
Amortization (Deferral) DAC	(7.5)	19.9	(3.5)	(5.8)
Other Operating Expenses	76.1	349.7	436.3	425.1
Net Premiums Written	114.9	1,002.7	1,196.2	1,304.8
International Operations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC	(0.2)		(2.4)	64.3
Reserves for Losses and Loss Adjustment Expenses	1,124.3		1,100.4	1,911.4
UPR	153.4		146.5	493.1
Premium Revenue	14.9	124	530.5	625.8
Net investment income	4.4	18.7	39.1	50.6
Loss & LAE	12	105.5	293.9	362.1
Amortization (Deferral) DAC	0.3	(10.9)	(7)	(10)
Other Operating Expenses	6	36.9	212.3	256.3
Net Premiums Written	9.2	141.8	544.5	671.7
International Operations | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Argo Underwriting Agency Limited
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Gross reserves, net of intercompany gross ups			993.4
Run-off Lines
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
DAC	0		0	0
Reserves for Losses and Loss Adjustment Expenses	196.1		233.1	261.2
UPR	0		0	0
Premium Revenue	0.2	0.3	0.9	0.6
Net investment income	0.7	2.7	2.3	3.6
Loss & LAE	0.5	2.6	2.9	44.3
Amortization (Deferral) DAC	0	0	0	0
Other Operating Expenses	0.4	0.9	1.6	1
Net Premiums Written	0.2	0.2	0.8	0.8
Corporate and Other
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium Revenue	0	0	0	0
Net investment income	0	0	0	14
Loss & LAE	0	0	0	0
Amortization (Deferral) DAC	0	0	0	0
Other Operating Expenses	1.9	22.5	31	35.7
Net Premiums Written	$ 0	$ 0	$ 0	$ 0

Schedule V Valuation and Qual_2

Schedule V Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 20.3	$ 27.9	$ 28.6
Charged to Cost and Expense	0	0	(0.7)
Capital Loss Carryforward	0	3.3	0
Net Operating Loss Carryforward	0.4	(10.9)	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Year	$ 20.7	$ 20.3	$ 27.9

Schedule VI Supplemental Info_2

Schedule VI Supplemental Information for Property-Casualty Insurance Companies (Detail) - USD ($) $ in Millions	2 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2023	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs	$ 7.2	$ 88.7	$ 107	$ 168
Reserves for losses and loss adjustment expenses	5,544.5	5,526.4	5,051.6	5,595
Unamortized discount in reserves for losses	20.8	20.4	19.3	18.8
Unearned premiums	916.6	986.2	1,039.9	1,466.8
Premiums earned	162.3	1,225.9	1,740.4	1,910.1
Net investment income	28.6	121.3	129.8	187.6
Current year	94.2	775.3	1,102.2	1,176.3
Prior years	0	267.9	64.7	138.3
Losses and loss adjustment expenses incurred	94.2	1,043.2	1,166.9	1,314.6
Amortization (Deferral) DAC	(7.2)	9	(10.5)	(15.8)
Paid losses and loss adjustment expenses, net of reinsurance	85.3	527.9	999.5	869.2
Gross premiums written	$ 191.2	$ 1,948.4	$ 2,848.1	$ 3,181.2