Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	$ 522.0	$ (17.0)	$ (437.0)
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1.0)	(1.0)
AMPS Gain on Purchase of Shares	1.0
Net income	522.0	(16.0)	(437.0)
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation	2.0	2.0	1.0
Amortization of bond premium and discount	(11.0)	(13.0)	(15.0)
Share-based compensation	17.0	14.0	11.0
Unearned premiums, net	(58.0)	(82.0)	(48.0)
Losses and loss expenses, net	1,220.0	(147.0)	76.0
Ceded premiums payable	6.0	6.0	(3.0)
Premium receivables	54.0	48.0	44.0
Accrued interest payable	(134.0)	103.0	93.0
Amortization of intangible assets	47.0	55.0	57.0
Net investment gains (losses), including impairments	(31.0)	(7.0)	(22.0)
Net realized gains (losses) on extinguishment of debt	(81.0)	(33.0)	0.0
Income (loss) on variable interest entities	21.0	7.0	5.0
Increase (Decrease) in Derivative Assets and Liabilities	(44.0)	(23.0)	6.0
Other, net	(152.0)	(33.0)	67.0
Net cash provided by (used in) operating activities	1,335.0	(131.0)	(175.0)
Cash flows from investing activities:
Proceeds from sales of bonds	523.0	236.0	1,109.0
Proceeds from matured bonds	206.0	698.0	137.0
Purchases of bonds	(403.0)	(343.0)	(975.0)
Proceeds from sales of other invested assets	166.0	39.0	374.0
Purchases of other invested assets	(112.0)	(127.0)	(475.0)
Change in short-term investments	(52.0)	98.0	158.0
Change in cash collateral receivable	44.0	9.0	0.0
Proceeds From Financial Guaranty Variable Interest Entity Assets	504.0	171.0	178.0
Payments to Acquire Businesses, Net of Cash Acquired	(18.0)	0.0	(74.0)
Other, net	9.0	(5.0)	1.0
Net cash provided by investing activities	866.0	776.0	432.0
Cash flows from financing activities:
Proceeds from Sale of Senior Surplus Notes	0.0	11.0
Proceeds from Issuance of Secured Debt		1,163.0
Proceeds from (Payments to) Noncontrolling Interests	(1.0)	(1.0)
Paydown of Ambac Note		(1,641.0)	(121.0)
Payments of Debt Issuance Costs		(12.0)
Payments for Repurchase of Common Stock	(14.2)
Payment, Tax Withholding, Share-based Payment Arrangement	(4.0)	(6.0)	(3.0)
Paydown of Financial Guaranty Variable Interest Entity Liabilities	(591.0)	(170.0)	(178.0)
Net Cash Provided by (Used in) Financing Activities	(2,163.0)	(657.0)	(303.0)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations	(1.0)	0.0	0.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	38.0	(12.0)	(46.0)
Supplemental disclosure of cash flow information
Income Taxes Paid	6.0	15.0	11.0
Cash payments related to reorganization items:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	61.0	23.0	35.0
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	(191.0)
Tier 2 Notes [Member]
Cash payments related to reorganization items:
Repayments of Secured Debt	143.0
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	522.0	(17.0)	(437.0)
Net income	522.0	(17.0)	(437.0)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(7.0)	(9.0)	(6.0)
Share-based compensation	12.0	14.0	11.0
Current income taxes	(1.0)	1.0	30.0
Net investment gains (losses), including impairments	14.0	5.0	1.0
Other, net	1.0	(6.0)	(10.0)
Net cash provided by (used in) operating activities	46.0	(10.0)	11.0
Cash flows from investing activities:
Proceeds from matured bonds	68.0	33.0	46.0
Purchases of bonds	(1.0)	(34.0)	(45.0)
Proceeds from sales of other invested assets	(4.0)	(8.0)	0.0
Change in short-term investments	(51.0)	105.0	89.0
Net cash provided by investing activities	12.0	95.0	16.0
Cash flows from financing activities:
Payments for Repurchase of Common Stock	(14.0)
Net Cash Provided by (Used in) Financing Activities	(57.0)	(92.0)	(29.0)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	1.0	(6.0)	(2.0)
Supplemental disclosure of cash flow information
Income Taxes Paid	$ 0.0	$ 0.0	$ 0.0