Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 522.0	$ (16.0)	$ (437.0)
Adjustments to reconcile net income loss to net cash used in operating activities:
Accretion (Amortization) of Discounts and Premiums, Investments	(11.0)	(13.0)	(15.0)
Net investment gains (losses), including impairments	(31.0)	(7.0)	(22.0)
Share-based compensation	17.0	14.0	11.0
Proceeds from Contributions from Affiliates	6.0	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 matured bonds	206.0	698.0	137.0
Purchases of bonds	(403.0)	(343.0)	(975.0)
Change in short-term investments	(52.0)	98.0	158.0
Proceeds from Sale and Maturity of Other Investments	166.0	39.0	374.0
Payments for (Proceeds from) Other Investing Activities	9.0	(5.0)	1.0
Net cash provided by investing activities	866.0	776.0	432.0
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities	(2,163.0)	(657.0)	(303.0)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect	38.0	(12.0)	(46.0)
Cash and cash equivalents at beginning of period	17.0	20.0
Cash and cash equivalents end of period	31.0	17.0	20.0
Cash paid during the period for:
Income taxes	6.0	15.0	11.0
Payments to Acquire Businesses, Net of Cash Acquired	(18.0)	0.0	(74.0)
Payments for Repurchase of Common Stock	(14.2)
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income	522.0	(17.0)	(437.0)
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries	(542.0)	1.0	423.0
Accretion (Amortization) of Discounts and Premiums, Investments	(7.0)	(9.0)	(6.0)
Net investment gains (losses), including impairments	14.0	5.0	1.0
Decrease in current income taxes payable	(1.0)	1.0	30.0
Share-based compensation	12.0	14.0	11.0
Decrease in other assets	41.0	(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)
Change in short-term investments	(51.0)	105.0	89.0
Proceeds from Sale and Maturity of Other Investments	(4.0)	(8.0)	0.0
Net cash provided by investing activities	12.0	95.0	16.0
Capital Contribution to Subsidiaries	(42.0)	(92.0)	(29.0)
Cash flows from financing activities:
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)
Cash and cash equivalents at beginning of period	1.0	7.0	9.0
Cash and cash equivalents end of period	3.0	1.0	7.0
Cash paid during the period for:
Income taxes	0.0	$ 0.0	$ 0.0
Payments for Repurchase of Common Stock	(14.0)
Parent [Member]
Adjustments to reconcile net income loss to net cash used in operating activities:
Net investment gains (losses), including impairments	$ (4.0)