Financial Guarantee Insurance Contracts - Additional Information (Detail) $ in Thousands, £ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2021 GBP (£)	Dec. 31, 2020 GBP (£)	Dec. 31, 2019 GBP (£)	Dec. 31, 2018 USD ($)
Insurance [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 1,000	$ 0
Net par amount of financial guarantees	$ 28,020,000	33,888,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,098,000	$ 1,140,000	1,536,000				$ 1,633,000
Stockholders Equity After Possible Increase in Domestic Public Finance Loss Reserves	743,000
Possible Increase in Domestic Public Finance Loss Reserves	$ 355,000
Estimated Future Premium Payments Weighted Average Discounted Rate	2.20%	2.20%		2.20%	2.20%
Financial Guarantee Insurance Contracts, Premium Receivable	$ 320,000	$ 370,000	416,000				$ 495,000
Amount Of Insured Par Outstanding Ceded To Reinsurer	$ 2,695,000
Ceded Principal Outstanding Major Reinsurer Percentage	7.90%
Deferred Ceded Premiums And Reinsurance Recoverables	$ 145,000
Reinsurance Payable	$ 33,000	$ 27,000
Weighted average period of future premiums	8 years	8 years 3 months 18 days
Uncollectable premium receivables	$ 9,000	$ 17,000
Accelerated premium revenue for retired obligations	1,000	12,000	10,000
Reinsurance recoveries of losses included in losses and loss expenses	5,000	(11,000)	(7,000)
Losses and loss expense reserves ceded to reinsurers		33,000
Subrogation recoveries, net of reinsurance	(1,704,000)	(1,725,000)
Amortization of intangible assets	55,000	57,000	295,000
Intangible assets	362,000	409,000
Letters of Credit Outstanding, Amount	111,000
Financial Guarantee Outstanding Principal Ceded To Third Parties	6,102,000
Public Finance Puerto Rico Net Par Outstanding	1,054,000
Premiums Receivable, Gross	329,000	387,000
Allowance for Doubtful Accounts, Premiums and Other Receivables	9,000	17,000	9,000
Premium Receivable, Credit Loss Expense (Reversal)	(6,000)	9,000
Premium Receivable, Allowance for Credit Loss, Writeoff	(2,000)	(2,000)
Reinsurance Recoverable, Allowance for Credit Loss	0	0
Net Incurred RMBS Subrogation Recoveries	20,000	(23,000)	42,000
Eighth Amended POA Proposed Debt Restructure Amount	33,000,000
Eighth Amended POA Proposed Pension Obligation Restructure Amount	$ 50,000,000
PHIFA Trust funded Share of Clawback CVI	27.00%			27.00%
PRHTA Share of Contingent Value Instrument	69.00%			69.00%
CCDA Share of Contingent Value Instrument	4.00%			4.00%
Nominal Cap of Allowed PRIGA and CCDA Under Eighth Amended POA	75.00%			75.00%
Stockholderes Equity After Possible Increase in Domestic Public Finance Loss Reserves	$ (607,000)
Financial Guarantee
Insurance [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	0
Losses and loss expense reserves ceded to reinsurers	24,000
Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	277,000	302,000
IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000	40,000
II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	6,000	3,000
III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	22,000	27,000
IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	$ 12,000	$ 15,000
Maximum [Member] | Furniture and Fixtures [Member]
Insurance [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Loss Reserves [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves	1.20%	1.10%
United Kingdom, Pounds
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable	$ 108,000	$ 117,000	$ 129,000	£ 80	£ 86	£ 97
Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	12,360,000	15,497,000
Premiums Receivable, Gross	159,000	185,000
Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	151,000	157,000
Public Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000	27,000
Public Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	5,000	0
Public Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Public Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Structured Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	4,904,000	6,337,000
Premiums Receivable, Gross	45,000	59,000
Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	19,000	27,000
Structured Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	0
Structured Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	3,000
Structured Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000	14,000
Structured Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000	15,000
International Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	10,756,000	12,054,000
Premiums Receivable, Gross	125,000	144,000
International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	107,000	118,000
International Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	8,000	13,000
International Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
International Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	11,000	13,000
International Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Housing Revenue [Member] | Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	5,610,000	5,855,000
Premiums Receivable, Gross	157,000	168,000
Housing Revenue [Member] | Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	149,000	155,000
Housing Revenue [Member] | Public Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	3,000	13,000
Housing Revenue [Member] | Public Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	5,000	0
Housing Revenue [Member] | Public Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Housing Revenue [Member] | Public Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Housing Revenue [Member] | Military Housing [Member] | Public Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	5,490,000	5,575,000
Other Public Finance Sectors [Member] | Public Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	2,000	17,000
Other Public Finance Sectors [Member] | Public Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	2,000	2,000
Other Public Finance Sectors [Member] | Public Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	15,000
Other Public Finance Sectors [Member] | Public Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Public Finance Sectors [Member] | Public Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Public Finance Sectors [Member] | Public Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Mortgage-backed and Home Equity [Member] | Structured Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	2,724,000	3,635,000
Premiums Receivable, Gross	16,000	22,000
Mortgage-backed and Home Equity [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	3,000
Mortgage-backed and Home Equity [Member] | Structured Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Mortgage-backed and Home Equity [Member] | Structured Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	1,000
Mortgage-backed and Home Equity [Member] | Structured Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	2,000	3,000
Mortgage-backed and Home Equity [Member] | Structured Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000	15,000
Structured Insurance [Member] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	10,000	14,000
Structured Insurance [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	10,000	14,000
Structured Insurance [Member] | Structured Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Structured Insurance [Member] | Structured Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Structured Insurance [Member] | Structured Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Structured Insurance [Member] | Structured Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Student Loan [Member] | Structured Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	12,000	16,000
Student Loan [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	3,000
Student Loan [Member] | Structured Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	1,000	0
Student Loan [Member] | Structured Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	2,000
Student Loan [Member] | Structured Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	9,000	11,000
Student Loan [Member] | Structured Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Structured Finance [Member] | Structured Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	624,000	1,085,000
Premiums Receivable, Gross	7,000	7,000
Other Structured Finance [Member] | Structured Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	7,000	7,000
Other Structured Finance [Member] | Structured Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Structured Finance [Member] | Structured Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Structured Finance [Member] | Structured Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other Structured Finance [Member] | Structured Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Sovereign/Sub-sovereign [Member] | International Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	5,141,000	5,270,000
Premiums Receivable, Gross	93,000	108,000
Sovereign/Sub-sovereign [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	74,000	82,000
Sovereign/Sub-sovereign [Member] | International Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	8,000	13,000
Sovereign/Sub-sovereign [Member] | International Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Sovereign/Sub-sovereign [Member] | International Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	11,000	13,000
Sovereign/Sub-sovereign [Member] | International Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Investor-owned and Public Utilities [Member] | International Finance [Member]
Insurance [Line Items]
Net par amount of financial guarantees	3,283,000	3,899,000
Premiums Receivable, Gross	28,000	31,000
Investor-owned and Public Utilities [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	28,000	31,000
Investor-owned and Public Utilities [Member] | International Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Investor-owned and Public Utilities [Member] | International Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Investor-owned and Public Utilities [Member] | International Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Investor-owned and Public Utilities [Member] | International Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other International [Member] | International Finance [Member]
Insurance [Line Items]
Premiums Receivable, Gross	5,000	5,000
Other International [Member] | International Finance [Member] | Surveillance Category One [Member]
Insurance [Line Items]
Premiums Receivable, Gross	5,000	5,000
Other International [Member] | International Finance [Member] | IA [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other International [Member] | International Finance [Member] | II [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other International [Member] | International Finance [Member] | III [Member]
Insurance [Line Items]
Premiums Receivable, Gross	0	0
Other International [Member] | International Finance [Member] | IV [Member]
Insurance [Line Items]
Premiums Receivable, Gross	$ 0	$ 0