Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($) Policies	Dec. 31, 2021 USD ($) Policies	Jun. 30, 2021 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered			$ 1
Number of policies | Policies	197	205
Remaining weighted-average contract period (in years)	13 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 4,871	$ 6,302
Interest	1,890	2,984
Total	6,761	9,286
Gross undiscounted claim liability	1,553	2,095
Discount, gross claim liability	440	303
Gross claim liability before all subrogation and before reinsurance	1,112	1,792
Less:
Gross RMBS subrogation	(1,531)	(1,737)
Discount, RMBS subrogation	47	7
Discounted RMBS subrogation, before reinsurance	(1,484)	(1,730)
Less:
Gross other subrogation	(361)	(633)
Discount, other subrogation	45	28
Discounted other subrogation, before reinsurance	(316)	(605)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(687)	(543)
Less: Unearned premium reserves	(38)	(56)
Plus: Loss adjustment expenses reserves	34	45
Claim liability reported on Balance Sheet, before reinsurance	(691)	(554)
Reinsurance recoverable reported on Balance Sheet	14	23
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	0
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	14	24
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ 0	$ 0
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	30	34
Remaining weighted-average contract period (in years)	8 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 922	$ 904
Interest	515	589
Total	1,437	1,493
Gross undiscounted claim liability	6	5
Discount, gross claim liability	0	0
Gross claim liability before all subrogation and before reinsurance	6	5
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	6	5
Less: Unearned premium reserves	(4)	(3)
Plus: Loss adjustment expenses reserves	0	1
Claim liability reported on Balance Sheet, before reinsurance	3	3
Reinsurance recoverable reported on Balance Sheet	$ 1	$ 1
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	9	15
Remaining weighted-average contract period (in years)	19 years	12 years
Gross insured contractual payments outstanding:
Principal	$ 241	$ 840
Interest	210	612
Total	451	1,452
Gross undiscounted claim liability	5	16
Discount, gross claim liability	1	1
Gross claim liability before all subrogation and before reinsurance	4	15
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(5)	(5)
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	(4)	(5)
Gross claim liability, net of all subrogation and discounts, before reinsurance	0	10
Less: Unearned premium reserves	(3)	(10)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	(3)	1
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 1
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	8	7
Remaining weighted-average contract period (in years)	14 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 464	$ 459
Interest	297	308
Total	760	767
Gross undiscounted claim liability	44	45
Discount, gross claim liability	6	3
Gross claim liability before all subrogation and before reinsurance	38	42
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	38	42
Less: Unearned premium reserves	(5)	(5)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	34	38
Reinsurance recoverable reported on Balance Sheet	$ 9	$ 10
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	13	14
Remaining weighted-average contract period (in years)	14 years	15 years
Gross insured contractual payments outstanding:
Principal	$ 1,027	$ 1,300
Interest	158	169
Total	1,185	1,469
Gross undiscounted claim liability	430	544
Discount, gross claim liability	132	109
Gross claim liability before all subrogation and before reinsurance	298	435
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(32)	(33)
Discount, other subrogation	4	2
Discounted other subrogation, before reinsurance	(28)	(31)
Gross claim liability, net of all subrogation and discounts, before reinsurance	270	404
Less: Unearned premium reserves	(9)	(14)
Plus: Loss adjustment expenses reserves	2	4
Claim liability reported on Balance Sheet, before reinsurance	264	394
Reinsurance recoverable reported on Balance Sheet	$ 22	$ 22
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	132	130
Remaining weighted-average contract period (in years)	13 years	13 years
Gross insured contractual payments outstanding:
Principal	$ 2,184	$ 2,759
Interest	690	1,284
Total	2,873	4,043
Gross undiscounted claim liability	1,012	1,423
Discount, gross claim liability	293	185
Gross claim liability before all subrogation and before reinsurance	719	1,238
Less:
Gross RMBS subrogation	(1,531)	(1,737)
Discount, RMBS subrogation	47	7
Discounted RMBS subrogation, before reinsurance	(1,484)	(1,730)
Less:
Gross other subrogation	(312)	(583)
Discount, other subrogation	38	24
Discounted other subrogation, before reinsurance	(274)	(559)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(1,040)	(1,051)
Less: Unearned premium reserves	(17)	(24)
Plus: Loss adjustment expenses reserves	31	40
Claim liability reported on Balance Sheet, before reinsurance	(1,026)	(1,036)
Reinsurance recoverable reported on Balance Sheet	$ (18)	$ (11)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	5	5
Remaining weighted-average contract period (in years)	7 years	7 years
Gross insured contractual payments outstanding:
Principal	$ 34	$ 40
Interest	21	22
Total	56	62
Gross undiscounted claim liability	56	62
Discount, gross claim liability	8	4
Gross claim liability before all subrogation and before reinsurance	47	57
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(12)	(12)
Discount, other subrogation	3	2
Discounted other subrogation, before reinsurance	(9)	(10)
Gross claim liability, net of all subrogation and discounts, before reinsurance	38	47
Less: Unearned premium reserves	(1)	(1)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	38	46
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0