Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, shares issued	46,659,144	46,658,990
Treasury Stock, Common, Shares	1,463,774	1,685,233
Common Stock, Shares, Outstanding	45,195,370
Assets:
Debt Securities, Available-for-sale	$ 1,710	$ 1,395
Short-term investments, at cost (approximates fair value)	2,197	2,041
Other Investments	475	568
Debt Securities, Available-for-sale, Allowance for Credit Loss	3	0
Investments, Total	2,664	2,593
Investment income due and accrued	14	10
Other assets	129	112
Assets	8,428	7,973	$ 12,303
Liabilities:
Liabilities	6,997	6,647
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	0	0
Additional paid-in capital	292	274
Accumulated other comprehensive income (loss)	(160)	(253)	58
Retained earnings	1,246	1,245
Common stock held in treasury at cost	(17)	(15)
Total Ambac Financial Group, Inc. stockholders’ equity	1,362	1,252
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	8,428	7,973
Short-term investments, amortized cost	426	507
Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Debt Securities, Available-for-sale	14	12
Short-term investments, at cost (approximates fair value)	14	13
Other Investments	18	16
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Investments, Total	188	203
Cash	0	3
Investment in subsidiaries	1,150	1,029
Investment income due and accrued	1	1
Other assets	24	19
Assets	1,365	1,255
Taxes Payable, Current	0	1
Liabilities:
Accounts payable and other liabilities	3	3
Liabilities	4	3
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	0	0
Additional paid-in capital	292	274
Accumulated other comprehensive income (loss)	(160)	(253)
Retained earnings	1,246	1,245
Common stock held in treasury at cost	(17)	(15)
Total Ambac Financial Group, Inc. stockholders’ equity	1,362	1,252	$ 1,038	$ 1,080
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	1,365	1,255
Short-term investments, amortized cost	156	175
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	426	507
Short-term investments, at cost (approximates fair value)	426	507
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Short-term Investments [Member] | Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Short-term investments, at cost (approximates fair value)	$ 156	$ 175