Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) Policies	Dec. 31, 2021 USD ($) Policies	Mar. 31, 2021 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered			$ 0
Number of policies | Policies	199	205
Remaining weighted-average contract period (in years)	14 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 5,469	$ 6,302
Interest	2,143	2,984
Total	7,612	9,286
Gross undiscounted claim liability	1,559	2,095
Discount, gross claim liability	377	303
Gross claim liability before all subrogation and before reinsurance	1,182	1,792
Less:
Gross RMBS subrogation	(1,537)	(1,737)
Discount, RMBS subrogation	35	7
Discounted RMBS subrogation, before reinsurance	(1,502)	(1,730)
Less:
Gross other subrogation	(401)	(633)
Discount, other subrogation	41	28
Discounted other subrogation, before reinsurance	(360)	(605)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(680)	(543)
Less: Unearned premium reserves	(42)	(56)
Plus: Loss adjustment expenses reserves	39	45
Claim liability reported on Balance Sheet, before reinsurance	(683)	(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		24
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 0
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	34	34
Remaining weighted-average contract period (in years)	9 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 1,297	$ 904
Interest	608	589
Total	1,905	1,493
Gross undiscounted claim liability	8	5
Discount, gross claim liability	1	0
Gross claim liability before all subrogation and before reinsurance	7	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	7	5
Less: Unearned premium reserves	(5)	(3)
Plus: Loss adjustment expenses reserves	1	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	14	15
Remaining weighted-average contract period (in years)	17 years	12 years
Gross insured contractual payments outstanding:
Principal	$ 305	$ 840
Interest	348	612
Total	653	1,452
Gross undiscounted claim liability	5	16
Discount, gross claim liability	1	1
Gross claim liability before all subrogation and before reinsurance	5	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	(5)	(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	$ 457	$ 459
Interest	308	308
Total	766	767
Gross undiscounted claim liability	45	45
Discount, gross claim liability	5	3
Gross claim liability before all subrogation and before reinsurance	40	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	40	42
Less: Unearned premium reserves	(5)	(5)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	35	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	14	14
Remaining weighted-average contract period (in years)	15 years	15 years
Gross insured contractual payments outstanding:
Principal	$ 1,265	$ 1,300
Interest	174	169
Total	1,439	1,469
Gross undiscounted claim liability	572	544
Discount, gross claim liability	155	109
Gross claim liability before all subrogation and before reinsurance	416	435
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(33)	(33)
Discount, other subrogation	4	2
Discounted other subrogation, before reinsurance	(29)	(31)
Gross claim liability, net of all subrogation and discounts, before reinsurance	387	404
Less: Unearned premium reserves	(12)	(14)
Plus: Loss adjustment expenses reserves	3	4
Claim liability reported on Balance Sheet, before reinsurance	378	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	124	130
Remaining weighted-average contract period (in years)	14 years	13 years
Gross insured contractual payments outstanding:
Principal	$ 2,105	$ 2,759
Interest	683	1,284
Total	2,788	4,043
Gross undiscounted claim liability	867	1,423
Discount, gross claim liability	208	185
Gross claim liability before all subrogation and before reinsurance	659	1,238
Less:
Gross RMBS subrogation	(1,537)	(1,737)
Discount, RMBS subrogation	35	7
Discounted RMBS subrogation, before reinsurance	(1,502)	(1,730)
Less:
Gross other subrogation	(350)	(583)
Discount, other subrogation	34	24
Discounted other subrogation, before reinsurance	(316)	(559)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(1,159)	(1,051)
Less: Unearned premium reserves	(16)	(24)
Plus: Loss adjustment expenses reserves	35	40
Claim liability reported on Balance Sheet, before reinsurance	(1,140)	(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	$ 40	$ 40
Interest	22	22
Total	62	62
Gross undiscounted claim liability	62	62
Discount, gross claim liability	7	4
Gross claim liability before all subrogation and before reinsurance	55	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	(10)	(10)
Gross claim liability, net of all subrogation and discounts, before reinsurance	45	47
Less: Unearned premium reserves	(1)	(1)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	44	46
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0