Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Details) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2024	Jun. 30, 2024 USD ($) Policies	Dec. 31, 2023 USD ($) Policies	Jun. 30, 2023 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered				$ 5
Number of policies | Policies		143	141
Remaining weighted-average contract period (in years)	12 years	11 years
Gross insured contractual payments outstanding:
Principal		$ 2,581	$ 3,838
Interest		1,141	1,421
Total		3,722	5,259
Gross undiscounted claim liability		1,126	1,202
Discount, gross claim liability		452	426
Gross claim liability before all subrogation and before reinsurance		(674)	777
Less:
Gross other subrogation		(263)	(263)
Discount, other subrogation		77	69
Discounted other subrogation, before reinsurance		(186)	(194)
Gross claim liability, net of all subrogation and discounts, before reinsurance		(487)	583
Less: Unearned premium reserves		(14)	(28)
Plus: Loss adjustment expenses reserves		3	4
Claim liability reported on Balance Sheet, before reinsurance		476	559
Reinsurance recoverable reported on Balance Sheet		26	30
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		35
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers		26	30
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 0	$ (1)
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		24	18
Remaining weighted-average contract period (in years)	9 years	5 years
Gross insured contractual payments outstanding:
Principal		$ 219	$ 429
Interest		18	75
Total		237	505
Gross undiscounted claim liability		0	1
Discount, gross claim liability		0	0
Gross claim liability before all subrogation and before reinsurance		0	1
Less:
Gross other subrogation		(13)	(13)
Discount, other subrogation		2	2
Discounted other subrogation, before reinsurance		(10)	(11)
Gross claim liability, net of all subrogation and discounts, before reinsurance		10	10
Less: Unearned premium reserves		0	0
Plus: Loss adjustment expenses reserves		1	0
Claim liability reported on Balance Sheet, before reinsurance		(9)	(10)
Reinsurance recoverable reported on Balance Sheet		$ 0	$ 1
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		3	8
Remaining weighted-average contract period (in years)	9 years	18 years
Gross insured contractual payments outstanding:
Principal		$ 194	$ 1,084
Interest		182	328
Total		376	1,412
Gross undiscounted claim liability		9	19
Discount, gross claim liability		2	2
Gross claim liability before all subrogation and before reinsurance		(7)	17
Less:
Gross other subrogation		(3)	(2)
Discount, other subrogation		0	0
Discounted other subrogation, before reinsurance		(3)	(2)
Gross claim liability, net of all subrogation and discounts, before reinsurance		(4)	(15)
Less: Unearned premium reserves		(2)	(12)
Plus: Loss adjustment expenses reserves		1	3
Claim liability reported on Balance Sheet, before reinsurance		2	6
Reinsurance recoverable reported on Balance Sheet		$ 0	$ 0
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		10	9
Remaining weighted-average contract period (in years)	13 years	12 years
Gross insured contractual payments outstanding:
Principal		$ 439	$ 430
Interest		253	262
Total		692	692
Gross undiscounted claim liability		39	41
Discount, gross claim liability		7	7
Gross claim liability before all subrogation and before reinsurance		(32)	34
Less:
Gross other subrogation		(1)	0
Discount, other subrogation		0	0
Discounted other subrogation, before reinsurance		0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance		(32)	34
Less: Unearned premium reserves		(4)	(4)
Plus: Loss adjustment expenses reserves		0	0
Claim liability reported on Balance Sheet, before reinsurance		28	30
Reinsurance recoverable reported on Balance Sheet		$ 8	$ 8
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		11	13
Remaining weighted-average contract period (in years)	13 years	11 years
Gross insured contractual payments outstanding:
Principal		$ 269	$ 394
Interest		99	139
Total		368	534
Gross undiscounted claim liability		231	324
Discount, gross claim liability		77	86
Gross claim liability before all subrogation and before reinsurance		(155)	239
Less:
Gross other subrogation		(25)	(27)
Discount, other subrogation		4	4
Discounted other subrogation, before reinsurance		(21)	(23)
Gross claim liability, net of all subrogation and discounts, before reinsurance		(134)	215
Less: Unearned premium reserves		2	0
Plus: Loss adjustment expenses reserves		0	0
Claim liability reported on Balance Sheet, before reinsurance		136	215
Reinsurance recoverable reported on Balance Sheet		$ 14	$ 18
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		91	88
Remaining weighted-average contract period (in years)	12 years	12 years
Gross insured contractual payments outstanding:
Principal		$ 1,439	$ 1,473
Interest		573	600
Total		2,012	2,073
Gross undiscounted claim liability		809	772
Discount, gross claim liability		359	323
Gross claim liability before all subrogation and before reinsurance		(450)	450
Less:
Gross other subrogation		(211)	(208)
Discount, other subrogation		67	60
Discounted other subrogation, before reinsurance		(144)	(149)
Gross claim liability, net of all subrogation and discounts, before reinsurance		(307)	301
Less: Unearned premium reserves		(9)	(10)
Plus: Loss adjustment expenses reserves		1	1
Claim liability reported on Balance Sheet, before reinsurance		298	292
Reinsurance recoverable reported on Balance Sheet		$ 4	$ 3
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies		4	5
Remaining weighted-average contract period (in years)	7 years	8 years
Gross insured contractual payments outstanding:
Principal		$ 21	$ 27
Interest		16	17
Total		37	44
Gross undiscounted claim liability		37	44
Discount, gross claim liability		8	8
Gross claim liability before all subrogation and before reinsurance		(29)	36
Less:
Gross other subrogation		(11)	(11)
Discount, other subrogation		3	3
Discounted other subrogation, before reinsurance		(8)	(8)
Gross claim liability, net of all subrogation and discounts, before reinsurance		(21)	28
Less: Unearned premium reserves		(1)	(1)
Plus: Loss adjustment expenses reserves		0	0
Claim liability reported on Balance Sheet, before reinsurance		21	27
Reinsurance recoverable reported on Balance Sheet		$ 0	$ 0