Consolidated Balance Sheets - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets:
Fixed maturity securities, at fair value	$ 2,043,000	$ 2,043,000
Total investments (net of allowance for credit losses of $3 and $3)	2,632,000	2,632,000	$ 2,664,000
Restricted Cash	11,000	11,000	12,000
Premiums Receivable, Net	317,000	317,000	290,000
Premium Receivable, Allowance for Credit Loss	3,000	3,000	4,000
Reinsurance Recoverables on Unpaid Losses, Allowance	0	0	0
Reinsurance Recoverables, Including Reinsurance Premium Paid	277,000	277,000	195,000
Deferred ceded premium	232,000	232,000	204,000
Subrogation recoverable	128,000	128,000	137,000
Derivative assets	18,000	18,000	26,000
Intangible assets, less accumulated amortization	285,000	285,000	307,000
Goodwill	70,000	70,000	70,000	$ 61,000
Other assets	163,000	163,000	129,000
Total assets	8,184,000	8,184,000	8,428,000
Liabilities:
Unearned premiums	445,000	445,000	422,000
Liability for Claims and Claims Adjustment Expense	890,000	890,000	893,000
Ceded premiums payable	140,000	140,000	90,000
Long-term debt	515,000	515,000	508,000
Accrued interest payable	500,000	500,000	475,000
Derivative Liability	26,000	26,000	35,000
Other liabilities	203,000	203,000	199,000
Total liabilities	6,748,000	6,748,000	6,997,000
Redeemable Noncontrolling Interest, Equity, Redemption Value	17,000	17,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount	17,000	17,000	17,000	20,000
Liabilities	6,748,000	6,748,000	6,997,000
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0	0	0
Common Stock, Value, Issued	0	0	0
Additional paid-in capital	295,000	295,000	292,000
Accumulated other comprehensive income	(175,000)	(175,000)	(160,000)	(253,000)
Retained earnings	1,265,000	1,265,000	1,246,000
Treasury stock, shares at cost: 0 and 8,202	(17,000)	(17,000)	(17,000)
Total Ambac Financial Group, Inc. stockholders’ equity	1,368,000	1,368,000	1,362,000
Noncontrolling interest	51,000	51,000	53,000
Total stockholders’ equity	1,419,000	1,419,000	1,415,000	1,305,000
Total liabilities and stockholders’ equity	8,184,000	8,184,000	8,428,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	3,000	3,000	3,000
Debt Securities, Available-for-sale, Amortized Cost	2,078,000	2,078,000	2,197,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	97,000	97,000	274,000	$ 61,000
Deferred Policy Acquisition Cost	12,000	12,000	11,000
Capitalized Contract Cost, Net	$ 7,000	$ 7,000	$ 6,000
Treasury Stock, Common, Shares	1,434,172	1,434,172	1,463,774
Preferred Stock, Shares Issued	0	0	0
Afg [Member]
Stockholders’ equity:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 35,000	$ 35,000	$ 28,000
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	314,000	314,000	426,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Amortized Cost	314,000	314,000	426,000
Variable Interest Entity, Primary Beneficiary [Member]
Assets:
Fixed maturity securities, at fair value	2,101,000	2,101,000	2,167,000
Restricted Cash	62,000	62,000	246,000
Derivative assets	208,000	208,000	226,000
Other assets	95,000	95,000	92,000
Total assets	4,033,000	4,033,000	4,394,000
Liabilities:
Long-term debt	2,853,000	2,853,000	2,967,000
Derivative Liability	1,136,000	1,136,000	1,197,000
Other Sundry Liabilities, Current	59,000	59,000	240,000
Other liabilities	7,000	7,000	5,000
Total liabilities	4,048,000	4,048,000	4,404,000
Liabilities	4,048,000	4,048,000	4,404,000
Stockholders’ equity:
Financing Receivable, after Allowance for Credit Loss	1,567,000	1,567,000	1,663,000
Gross Investment Income, Operating	2,000
Derivative and other assets	303,000	303,000	318,000
Fixed Income Securities [Member]
Assets:
Fixed maturity securities, at fair value	1,703,000	1,703,000	1,710,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	3,000	3,000	3,000
Debt Securities, Available-for-sale, Amortized Cost	1,737,000	1,737,000	1,744,000
Debt Securities, Available-for-Sale, Excluding Accrued Interest	1,703,000	1,703,000	1,710,000
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	1,737,000	1,737,000	1,744,000
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	314,000	314,000	426,000
Stockholders’ equity:
Gross Investment Income, Operating	5,000	10,000
Other Investments [Member]
Stockholders’ equity:
Other Investment Not Readily Marketable, Fair Value	558,000	558,000	475,000
Gross Investment Income, Operating	8,000	21,000
Fixed Income Securities, Trading
Stockholders’ equity:
Gross Investment Income, Operating	2,000	4,000
Debt Securities, Available-for-Sale, Excluding Accrued Interest	31,000	31,000	27,000
Collateral Pledged [Member] | Fixed Income Securities [Member]
Assets:
Fixed maturity securities, at fair value	25,000	25,000	27,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Amortized Cost	27,000	27,000	0
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	0	0	27,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Amortized Cost	0	0	27,000
Collateral Pledged [Member] | Short-term Investments
Stockholders’ equity:
Debt Securities, Available-for-sale, Amortized Cost	0	0	27,000
Collateralized Securities | Fixed Income Securities [Member]
Stockholders’ equity:
Debt Securities, Available-for-Sale, Excluding Accrued Interest	25,000	25,000	0
Collateralized Securities | Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	$ 0	$ 0	$ 27,000