Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (16)	$ (437)	$ (216)
Adjustments to reconcile net income loss to net cash used in operating activities:
Accretion (Amortization) of Discounts and Premiums, Investments	(13)	(15)	(63)
Net realized investment gains	(7)	(22)	(81)
Decrease in current income taxes payable	(4)	17	35
Share-based compensation	14	11	12
Proceeds from Contributions from Affiliates	6
Other, net	(35)	59	79
Net cash used in operating activities	(131)	(175)	(311)
Cash flows from investing activities:
Proceeds from matured bonds	698	137	379
Purchases of bonds	(343)	(975)	(959)
Change in short-term investments	98	158	(218)
Proceeds from Sale and Maturity of Other Investments	39	374	81
Payments for (Proceeds from) Other Investing Activities	(5)	1	(2)
Net cash provided by investing activities	776	432	1,000
AMPS Proceeds	0	0	19
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities	(657)	(303)	(691)
Cash and cash equivalents at beginning of period	20	24
Cash and cash equivalents end of period	17	20	24
Cash paid during the period for:
Income taxes	15	11	21
Payments to Acquire Businesses, Net of Cash Acquired		(74)
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss)	(17)	(437)	(216)
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries	1	423	223
Accretion (Amortization) of Discounts and Premiums, Investments	(9)	(6)	(6)
Net realized investment gains	5	1	2
Decrease in current income taxes payable	1	30	15
Share-based compensation	14	11	12
Decrease in other assets	(5)	(1)	(8)
Other, net	(6)	(10)	(6)
Net cash used in operating activities	(10)	11	16
Cash flows from investing activities:
Proceeds from matured bonds	33	46	86
Purchases of bonds	(34)	(45)	(2)
Change in short-term investments	105	89	(125)
Proceeds from Sale and Maturity of Other Investments	(8)	0	0
Net cash provided by investing activities	95	16	(22)
Capital Contribution to Subsidiaries	(92)	(29)	0
AMPS Proceeds	0	0	19
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities	(92)	(29)	0
Cash and Cash Equivalents, Period Increase (Decrease)	(6)	(2)	(6)
Cash and cash equivalents at beginning of period	7	9	15
Cash and cash equivalents end of period	1	7	9
Cash paid during the period for:
Income taxes	0	0	$ 1
Payments to Acquire Businesses, Net of Cash Acquired		$ (74)
Parent [Member]
Adjustments to reconcile net income loss to net cash used in operating activities:
Net realized investment gains	$ (4)