Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Carrying Amount [Member]
Financial assets:
Other Investments	$ 61,000	$ 106,000
Cash	44,000	21,000
Loans	10,000	3,000
Total financial assets	6,537,000	9,268,000
Financial liabilities:
Liabilities for net financial guarantees written	159,000	(866,000)
Long-term Debt	1,065,000	2,806,000
Total financial liabilities	5,418,000	8,190,000
Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	17,000	2,000
Loans, at fair value	1,829,000	2,718,000
Financial liabilities:
Long-term Debt	3,107,000	4,216,000
Carrying Amount [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	568,000	690,000
Carrying Amount [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	507,000	414,000
Carrying Amount [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	1,828,000	3,320,000
Carrying Amount [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	96,000	136,000
Debt Securities, Trading	43,000
Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	38,000	94,000
Carrying Amount [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	190,000
Financial liabilities:
Derivative liabilities	1,048,000	1,940,000
Carrying Amount [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	49,000	38,000
Carrying Amount [Member] | Warrant [Member]
Financial assets:
Derivative assets	1,000
Total Fair Value [Member]
Financial assets:
Cash	44,000	21,000
Debt Securities, Available-for-sale	1,966,000
Other Investments	568,000	690,000
Derivative assets	28,000	76,000
Other assets	0
Financial liabilities:
Derivative liabilities	38,000	95,000
Credit valuation adjustment included in fair value of credit derivative liabilities	$ 32	$ 19
Estimated Future Premium Payments Weighted Average Discounted Rate	3.00%	2.20%
Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	$ 1,967,000	$ 3,455,000
Loans, at fair value	1,829,000	2,718,000
Derivative assets	239,000	38,000
Financial liabilities:
Derivative liabilities	1,048,000	1,940,000
Long-term Debt	$ 2,788,000	$ 4,056,000
Estimated Future Premium Payments Weighted Average Discounted Rate	6.80%	3.00%
Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	$ 507,000	$ 414,000
Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	1,828,000	3,320,000
Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	96,000	136,000
Debt Securities, Trading	43,000	0
Fair Value, Recurring [Member] | Warrant [Member]
Financial assets:
Derivative assets	1,000
Other Assets [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	27,000	76,000
Fair Value Measured at Net Asset Value Per Share [Member]
Financial assets:
Other Investments	494,000	577,000
Level 1 [Member]
Financial assets:
Cash	43,000	21,000
Total financial assets	833,000	750,000
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term Debt	0	0
Total financial liabilities	0	0
Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	17,000	2,000
Loans	0	0
Financial liabilities:
Long-term Debt	0	0
Level 1 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	61,000	106,000
Level 1 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	506,000	369,000
Level 1 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Level 1 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Debt Securities, Trading	0
Level 1 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 1 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	0
Financial liabilities:
Derivative liabilities	0	0
Level 1 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	0	0
Level 1 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 1 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	0	0
Level 2 [Member]
Financial assets:
Cash	1,000	1,000
Total financial assets	1,425,000	1,732,000
Financial liabilities:
Liabilities for net financial guarantees written	0	0
Long-term Debt	864,000	2,575,000
Total financial liabilities	4,942,000	8,695,000
Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	0	0
Financial liabilities:
Long-term Debt	2,992,000	4,086,000
Level 2 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	0	0
Level 2 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	1,000	46,000
Level 2 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Level 2 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	96,000	136,000
Debt Securities, Trading	43,000
Level 2 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	38,000	94,000
Level 2 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	190,000
Financial liabilities:
Derivative liabilities	1,048,000	1,940,000
Level 2 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	49,000	38,000
Level 2 [Member] | Loans Receivable [Member]
Financial assets:
Loans	0	0
Level 2 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	1,000	5,000
Level 3 [Member]
Financial assets:
Cash	0	0
Total financial assets	3,772,000	6,202,000
Financial liabilities:
Liabilities for net financial guarantees written	476,000	(112,000)
Long-term Debt	14,000	22,000
Total financial liabilities	644,000	79,000
Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	1,829,000	2,718,000
Financial liabilities:
Long-term Debt	154,000	169,000
Level 3 [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	0	0
Level 3 [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	0	0
Level 3 [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	1,828,000	3,320,000
Level 3 [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Debt Securities, Trading	0
Level 3 [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 3 [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Level 3 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	0	0
Level 3 [Member] | Loans Receivable [Member]
Financial assets:
Loans	10,000	3,000
Level 3 [Member] | Warrant [Member]
Financial assets:
Derivative assets	1,000
Level 3 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	26,000	71,000
Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	102,000	340,000
Corporate Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	598,000	613,000
Debt Security, Government, Non-US [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	76,000	87,000
US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	65,000	45,000
Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	238,000	252,000
Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	137,000	128,000
Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	224,000	265,000
Commercial Mortgage Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	15,000
Fair Value, Recurring [Member]
Financial assets:
Total financial assets	6,525,000	9,261,000
Financial liabilities:
Liabilities for net financial guarantees written	476,000	(112,000)
Long-term Debt	878,000	2,598,000
Total financial liabilities	5,586,000	8,775,000
Fair Value, Recurring [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	17,000	2,000
Loans	1,829,000	2,718,000
Financial liabilities:
Long-term Debt	3,145,000	4,255,000
Fair Value, Recurring [Member] | Other Debt Obligations [Member]
Financial assets:
Other Investments	556,000	683,000
Fair Value, Recurring [Member] | Short-term Investments [Member]
Financial assets:
Short term investments	507,000	414,000
Fair Value, Recurring [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	224,000	265,000
Fair Value, Recurring [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	137,000	128,000
Fair Value, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	238,000	252,000
Fair Value, Recurring [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	65,000	45,000
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	76,000	87,000
Fair Value, Recurring [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	598,000	613,000
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	1,828,000	3,320,000
Fair Value, Recurring [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	102,000	340,000
Fair Value, Recurring [Member] | Municipal Bonds [Member] | Variable Interest Entity [Member]
Financial assets:
Debt Securities, Available-for-sale	96,000	136,000
Debt Securities, Trading	43,000
Fair Value, Recurring [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	38,000	94,000
Fair Value, Recurring [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	190,000
Financial liabilities:
Derivative liabilities	1,048,000	1,940,000
Fair Value, Recurring [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial assets:
Derivative assets	49,000	38,000
Fair Value, Recurring [Member] | Loans Receivable [Member]
Financial assets:
Loans	10,000	3,000
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	15,000
Fair Value, Recurring [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	27,000	76,000
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	65,000	45,000
Fair Value, Recurring [Member] | Level 1 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	76,000	87,000
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	1,000
Fair Value, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	157,000	187,000
Fair Value, Recurring [Member] | Level 2 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	137,000	128,000
Fair Value, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	238,000	252,000
Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	585,000	600,000
Fair Value, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	102,000	340,000
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	15,000
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	67,000	79,000
Fair Value, Recurring [Member] | Level 3 [Member] | Collateralized Debt Obligations [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Debt Security, Government, Non-US [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	12,000	12,000
Fair Value, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Financial assets:
Debt Securities, Available-for-sale	0
Collateral Pledged [Member]
Financial assets:
Debt Securities, Available-for-sale	64,000	120,000
Collateral Pledged [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale		15,000
Collateral Pledged [Member] | Short-term Investments [Member] | Carrying Amount [Member]
Financial assets:
Debt Securities, Available-for-sale	64,000	105,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	64,000	105,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale		15,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 1 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	64,000	105,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 1 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale		15,000
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 2 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	0	0
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 2 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale		0
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | Short-term Investments [Member]
Financial assets:
Debt Securities, Available-for-sale	$ 0	0
Collateral Pledged [Member] | Fair Value, Recurring [Member] | Level 3 [Member] | US Government Debt Securities [Member]
Financial assets:
Debt Securities, Available-for-sale		$ 0