Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	$ 4.0	$ 522.0	$ (17.0)
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1.0)	(1.0)	(1.0)
AMPS Gain on Purchase of Shares		1.0
Net income	5.0	522.0	(16.0)
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation	2.0	2.0	2.0
Amortization of bond premium and discount	(15.0)	(11.0)	(13.0)
Share-based compensation	17.0	17.0	14.0
Unearned premiums, net	(30.0)	(58.0)	(82.0)
Losses and loss expenses, net	130.0	1,220.0	(147.0)
Ceded premiums payable	52.0	6.0	6.0
Premium receivables	(21.0)	54.0	48.0
Accrued interest payable	(1.0)	(134.0)	103.0
Amortization of intangible assets	29.0	47.0	55.0
Net investment gains (losses), including impairments	22.0	(31.0)	(7.0)
Net realized gains (losses) on extinguishment of debt	0.0	(81.0)	(33.0)
Income (loss) on variable interest entities	3.0	21.0	7.0
Other, net	13.0	(196.0)	(56.0)
Net cash provided by operating activities	200.0	1,335.0	(131.0)
Cash flows from investing activities:
Proceeds from sales of bonds	140.0	523.0	236.0
Proceeds from matured bonds	74.0	206.0	698.0
Purchases of bonds	(415.0)	(403.0)	(343.0)
Proceeds from sales of other invested assets	209.0	166.0	39.0
Purchases of other invested assets	(80.0)	(112.0)	(127.0)
Change in short-term investments	118.0	(52.0)	98.0
Change in cash collateral	(42.0)	44.0	9.0
Proceeds From Financial Guaranty Variable Interest Entity Assets	199.0	504.0	171.0
Payments to Acquire Businesses, Net of Cash Acquired	(7.0)	(18.0)	0.0
Other, net	6.0	9.0	(5.0)
Net cash provided by investing activities	435.0	866.0	776.0
Cash flows from financing activities:
Proceeds from Sale of Senior Surplus Notes			11.0
Proceeds from Issuance of Secured Debt			1,163.0
Proceeds from (Payments to) Noncontrolling Interests	(2.0)	(1.0)	(1.0)
Paydown of Ambac Note			(1,641.0)
Payments of Debt Issuance Costs			(12.0)
Payments for Repurchase of Common Stock	(5.0)	(14.0)
Payment, Tax Withholding, Share-based Payment Arrangement	(5.0)	(4.0)	(6.0)
Paydown of Financial Guaranty Variable Interest Entity Liabilities	(315.0)	(591.0)	(170.0)
Net Cash Provided by (Used in) Financing Activities	(423.0)	(2,163.0)	(657.0)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations	1.0	(1.0)	0.0
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	213.0	38.0	(12.0)
Supplemental disclosure of cash flow information
Income Taxes Paid	11.0	6.0	15.0
Cash payments related to reorganization items:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	274.0	61.0	23.0
AMPS Exchange Cash Paid		(8.0)
Sitka AAC Note
Cash payments related to reorganization items:
Repayments of Secured Debt		1,210.0
5.1 % Surplus Notes Due 2020 [Member]
Cash payments related to reorganization items:
Payments for purchase of surplus notes	0.0	(191.0)
Tier 2 Notes [Member]
Cash payments related to reorganization items:
Repayments of Secured Debt	97.0	143.0
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	4.0	522.0	(17.0)
Net income	4.0	522.0	(17.0)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	0.0	(7.0)	(9.0)
Share-based compensation	9.0	12.0	14.0
Net investment gains (losses), including impairments	0.0	14.0	5.0
Other, net	2.0	1.0	(6.0)
Net cash provided by operating activities	2.0	46.0	(10.0)
Cash flows from investing activities:
Proceeds from matured bonds	0.0	68.0	33.0
Purchases of bonds	(1.0)	(1.0)	(34.0)
Proceeds from sales of other invested assets	(3.0)	(4.0)	(8.0)
Change in short-term investments	20.0	(51.0)	105.0
Net cash provided by investing activities	16.0	12.0	95.0
Cash flows from financing activities:
Payments for Repurchase of Common Stock	5.0	14.0
Net Cash Provided by (Used in) Financing Activities	(21.0)	(57.0)	(92.0)
Supplemental disclosure of cash flow information
Income Taxes Paid	0.0	0.0	0.0
Variable Interest Entity [Member]
Adjustments to reconcile net income to net cash used in operating activities:
Net investment gains (losses), including impairments	(1.0)	(2.0)	(2.0)
Cash flows from investing activities:
Change in cash collateral	$ 235.0	$ 0.0	$ 0.0