Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Proceeds From Issuance of Tier II Notes		$ 240,000
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	$ (216,000)	186,000	$ (329,000)
AMPS Exchange Loss Based on Carry Value	0	82,000	0
Net income (loss)	(216,000)	267,000	(329,000)
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	0	1,000	1,000
Amortization of bond premium and discount	(63,000)	(137,000)	(183,000)
Share-based compensation	12,000	12,000	4,000
Deferred income taxes	1,000	7,000	32,000
Current income taxes	35,000	(35,000)	(26,000)
Unearned premiums, net	(132,000)	(163,000)	(168,000)
Losses and loss expenses, net	(364,000)	(1,633,000)	400,000
Ceded premiums payable	(4,000)	(5,000)	(5,000)
Premium receivables	77,000	91,000	77,000
Accrued interest payable	87,000	9,000	50,000
Amortization of insurance intangible assets	295,000	107,000	151,000
Net mark-to-market (gains) losses	(1,000)	1,000	(15,000)
Net realized investment gains	(81,000)	(112,000)	(5,000)
Other-than-temporary impairment charges	0	3,000	20,000
Net realized gains (losses) on extinguishment of debt	0	(3,000)	(5,000)
Other, net	80,000	67,000	22,000
Net cash used in operating activities	(311,000)	(1,543,000)	(221,000)
Cash flows from investing activities:
Proceeds from sales of bonds	1,212,000	1,248,000	2,139,000
Proceeds from matured bonds	379,000	432,000	814,000
Purchases of bonds	(959,000)	(528,000)	(2,054,000)
Proceeds from sales of other invested assets	81,000	159,000	350,000
Purchases of other invested assets	(137,000)	(140,000)	(299,000)
Change in short-term investments	(218,000)	127,000	(127,000)
Change in cash collateral receivable	100,000	(58,000)	123,000
Proceeds From Financial Guaranty Variable Interest Entity Assets	543,000	349,000	235,000
Other, net	(2,000)	0	(17,000)
Net cash provided by investing activities	1,000,000	1,588,000	1,163,000
Cash flows from financing activities:
Proceeds from Sale of Senior Surplus Notes	0	24,000
Paydown of Ambac Note	(178,000)	(214,000)
Paydown Of Variable Interest Entity Secured Borrowing	0	74,000	29,000
Payments From Drawdowns Of Borrowings Under Guaranteed Investment Agreements			82,000
Payments for extinguishment of surplus notes	0	(191,000)	(69,000)
Payments of Debt Issuance Costs		(9,000)
AMPS Proceeds	19,000
AMPS Exchange Cash Paid	0	(11,000)
Payment, Tax Withholding, Share-based Payment Arrangement	(3,000)	(1,000)	(1,000)
Paydown of Financial Guaranty Variable Interest Entity Liabilities	(542,000)	(349,000)	(230,000)
Net Cash Provided by (Used in) Financing Activities	(691,000)	(585,000)	(412,000)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0	(1,000)
Cash and Cash Equivalents, Period Increase (Decrease)	(2,000)	(541,000)	529,000
Cash and cash equivalents end of period	24,000	63,000	624,000
Supplemental disclosure of cash flow information
Income Taxes Paid	21,000	35,000	40,000
Cash payments related to reorganization items:
Variable interest entity activities	(38,000)	(3,000)	(20,000)
Increase (Decrease) in Derivative Assets and Liabilities	(1,000)	(17,000)	(223,000)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	81,000	83,000	625,000
Proceeds From Issuance of Ambac UK Debt	12,000
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss) attributable to common stockholders	(216,000)	186,000	(329,000)
Net income (loss)	(216,000)	186,000	(329,000)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(6,000)	(7,000)	(17,000)
Share-based compensation	12,000	12,000	4,000
Current income taxes	15,000	(15,000)	(1,000)
Net realized investment gains	(1,000)	1,000	7,000
Other, net	(6,000)	0	(10,000)
Net cash used in operating activities	16,000	32,000	16,000
Cash flows from investing activities:
Proceeds from matured bonds	86,000	230,000	187,000
Purchases of bonds	(2,000)	(137,000)	(196,000)
Change in short-term investments	(125,000)	(123,000)	(3,000)
Net cash provided by investing activities	(22,000)	(21,000)	(44,000)
Cash flows from financing activities:
AMPS Exchange Cash Paid	0
Cash and Cash Equivalents, Period Increase (Decrease)	(6,000)	11,000	(28,000)
Cash and cash equivalents end of period	9,000	15,000	4,000
Supplemental disclosure of cash flow information
Income Taxes Paid	$ 1,000	$ 4,000	$ 1,000