Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, shares issued	46,658,990	46,477,068
Treasury stock, shares	1,685,233	172,929
Common Stock, Shares, Outstanding	44,973,757
Assets:
Debt Securities, Available-for-sale	$ 1,966
Short-term investments, at cost (approximates fair value)	2,041
Other Investments	568	$ 690
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Investments, Total	2,593	2,955
Other assets	84	68
Total assets	7,973	12,303
Liabilities:
Total liabilities	6,647	11,187
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	0	0
Additional paid-in capital	274	257
Accumulated other comprehensive income (loss)	(253)	58	$ 79
Retained earnings	1,245	726
Common stock held in treasury at cost	(15)	(3)
Total Ambac Financial Group, Inc. stockholders’ equity	1,252	1,038
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	7,973	12,303
Short-term investments, amortized cost	507	415
Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Short-term investments, at cost (approximates fair value)	13	130
Other Investments	16	11
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	3
Investments, Total	203	254
Cash	3	1
Investment in subsidiaries	1,029	769
Investment income due and accrued	1	1
Other assets	19	17
Total assets	1,255	1,041
Taxes Payable, Current	1	1
Liabilities:
Accounts payable and other liabilities	3	2
Total liabilities	3	3
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	0	0
Additional paid-in capital	274	257
Accumulated other comprehensive income (loss)	(253)	58
Retained earnings	1,245	726
Common stock held in treasury at cost	(15)	(3)
Total Ambac Financial Group, Inc. stockholders’ equity	1,252	1,038	$ 1,080	$ 1,477
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	1,255	1,041
Short-term investments, amortized cost	175	124
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	507	414
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)	175	124
Fixed Income Securities [Member]
Assets:
Debt Securities, Available-for-sale	1,395	1,730
Short-term investments, at cost (approximates fair value)	1,469	1,605
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Investment income due and accrued	10	10
Fixed Income Securities [Member] | Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Debt Securities, Available-for-sale	$ 12	$ 119