Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022 USD ($) Policies	Dec. 31, 2021 USD ($) Policies	Sep. 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	180	205
Remaining weighted-average contract period (in years)	13 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 4,813	$ 6,302
Interest	1,847	2,984
Total	6,660	9,286
Gross undiscounted claim liability	1,694	2,095
Discount, gross claim liability	521	303
Gross claim liability before all subrogation and before reinsurance	1,173	1,792
Less:
Gross RMBS subrogation	(1,814)	(1,737)
Discount, RMBS subrogation	3	7
Discounted RMBS subrogation, before reinsurance	(1,811)	(1,730)
Less:
Gross other subrogation	(436)	(633)
Discount, other subrogation	56	28
Discounted other subrogation, before reinsurance	(380)	(605)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(1,019)	(543)
Less: Unearned premium reserves	(34)	(56)
Plus: Loss adjustment expenses reserves	38	45
Claim liability reported on Balance Sheet, before reinsurance	(1,015)	(554)
Reinsurance recoverable reported on Balance Sheet	10	23
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	1
Financial Guarantee
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	10	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	27	34
Remaining weighted-average contract period (in years)	7 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 1,046	$ 904
Interest	417	589
Total	1,464	1,493
Gross undiscounted claim liability	4	5
Discount, gross claim liability	1	0
Gross claim liability before all subrogation and before reinsurance	3	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	3	5
Less: Unearned premium reserves	(2)	(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	8	15
Remaining weighted-average contract period (in years)	19 years	12 years
Gross insured contractual payments outstanding:
Principal	$ 215	$ 840
Interest	203	612
Total	419	1,452
Gross undiscounted claim liability	4	16
Discount, gross claim liability	1	1
Gross claim liability before all subrogation and before reinsurance	3	15
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(4)	(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	$ 459	$ 459
Interest	296	308
Total	755	767
Gross undiscounted claim liability	45	45
Discount, gross claim liability	7	3
Gross claim liability before all subrogation and before reinsurance	37	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	37	42
Less: Unearned premium reserves	(5)	(5)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	33	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	$ 974	$ 1,300
Interest	159	169
Total	1,134	1,469
Gross undiscounted claim liability	444	544
Discount, gross claim liability	161	109
Gross claim liability before all subrogation and before reinsurance	283	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	5	2
Discounted other subrogation, before reinsurance	(26)	(31)
Gross claim liability, net of all subrogation and discounts, before reinsurance	257	404
Less: Unearned premium reserves	(8)	(14)
Plus: Loss adjustment expenses reserves	3	4
Claim liability reported on Balance Sheet, before reinsurance	252	394
Reinsurance recoverable reported on Balance Sheet	$ 21	$ 22
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	119	130
Remaining weighted-average contract period (in years)	12 years	13 years
Gross insured contractual payments outstanding:
Principal	$ 2,084	$ 2,759
Interest	751	1,284
Total	2,834	4,043
Gross undiscounted claim liability	1,142	1,423
Discount, gross claim liability	342	185
Gross claim liability before all subrogation and before reinsurance	800	1,238
Less:
Gross RMBS subrogation	(1,814)	(1,737)
Discount, RMBS subrogation	3	7
Discounted RMBS subrogation, before reinsurance	(1,811)	(1,730)
Less:
Gross other subrogation	(388)	(583)
Discount, other subrogation	46	24
Discounted other subrogation, before reinsurance	(342)	(559)
Gross claim liability, net of all subrogation and discounts, before reinsurance	(1,353)	(1,051)
Less: Unearned premium reserves	(16)	(24)
Plus: Loss adjustment expenses reserves	34	40
Claim liability reported on Balance Sheet, before reinsurance	(1,336)	(1,036)
Reinsurance recoverable reported on Balance Sheet	$ (21)	$ (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	55	62
Gross undiscounted claim liability	55	62
Discount, gross claim liability	10	4
Gross claim liability before all subrogation and before reinsurance	45	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	4	2
Discounted other subrogation, before reinsurance	(8)	(10)
Gross claim liability, net of all subrogation and discounts, before reinsurance	37	47
Less: Unearned premium reserves	(1)	(1)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	36	46
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0