Business Combinations and Assumption of Insured Portfolio - Narrative (Details)				1 Months Ended	3 Months Ended	12 Months Ended				36 Months Ended
	Oct. 01, 2019 USD ($)	Jun. 01, 2018 USD ($)	Jan. 10, 2017 USD ($)	Feb. 28, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($) Company
Business Acquisition [Line Items]
Principal					$ 1,453,000,000	$ 1,453,000,000	$ 1,457,000,000			$ 1,453,000,000
Acquisition, net of cash acquired						(145,000,000)	0	$ 95,000,000
Net par amount outstanding					236,807,000,000	236,807,000,000	241,802,000,000			236,807,000,000
Net Par Outstanding					5,956,000,000	5,956,000,000	6,182,000,000			5,956,000,000
Gross written premiums on new business, net of commissions						689,000,000	610,000,000	301,000,000
Financial Guarantee Insurance Contracts, Premium Receivable, Proceeds from Premiums Received						318,000,000	577,000,000	301,000,000
Cash					169,000,000	169,000,000	104,000,000	144,000,000	$ 144,000,000	169,000,000
Premiums receivable, net of commissions payable					1,286,000,000	1,286,000,000	904,000,000			1,286,000,000
Fair value of credit derivative asset (liability), net					(185,000,000)	(185,000,000)	(207,000,000)			$ (185,000,000)
Net expected loss to be paid							$ 131,000,000
BlueMountain Capital Management, LLC [Member]
Business Acquisition [Line Items]
Number of business acquired | Company										1
Cash purchase price	$ 157,000,000
Other payments to acquire businesses	$ 60,000,000
Revenue					32,000,000
Acquisition cost expensed						9,000,000
Net income (loss)					(10,000,000)
MBIA UK [Member]
Business Acquisition [Line Items]
Number of business acquired | Company										1
Cash purchase price			$ 329,000,000
Cash purchase price			334,000,000
Revenue									192,000,000
Net income (loss)									$ 139,000,000
Acquisition related costs								$ 7,000,000
Reinsurance of SGI Insured Portfolio [Member]
Business Acquisition [Line Items]
Number of business acquired | Company										1
Net expected loss to be paid		$ 131,000,000
Subsidiaries [Member] | MBIA UK [Member]
Business Acquisition [Line Items]
Cash acquired from acquisition			23,000,000
Bond exchanged amount			347,000,000
Gross Par Outstanding, Fair Value			334,000,000
MBIA UK [Member]
Business Acquisition [Line Items]
Net par amount outstanding			$ 12,000,000,000
AGM, AGC and MAC [Member] | BlueMountain Capital Management, LLC [Member]
Business Acquisition [Line Items]
Debt Instrument, term	10 years
Interest rate of debt (as a percent)	3.50%
Principal	$ 250,000,000
Reinsurance of SGI Insured Portfolio [Member]
Business Acquisition [Line Items]
Gross written premiums on new business, net of commissions		$ 330,000,000
Reinsurance of SGI Insured Portfolio [Member] | AGC [Member]
Business Acquisition [Line Items]
Reinsurance Retention Policy Quota Share Basis Percent		100.00%
Net par amount outstanding		$ 12,000,000,000
Cash		363,000,000
Premiums receivable, net of commissions payable		61,000,000
Professional Fees		4,000,000
United States [Member]
Business Acquisition [Line Items]
Net par amount outstanding					$ 184,787,000,000	$ 184,787,000,000				$ 184,787,000,000
United States [Member] | Syncora Guarantee Inc [Member] | Reinsurance of SGI Insured Portfolio [Member]
Business Acquisition [Line Items]
Net Par Outstanding		1,500,000,000
Insurance Contracts Assumed [Member] | Reinsurance of SGI Insured Portfolio [Member] | AGC [Member]
Business Acquisition [Line Items]
Cash		343,000,000
Premiums receivable, net of commissions payable		45,000,000
Fair value of credit derivative asset (liability), net		$ 17,000,000
Subsequent Event [Member] | BlueMountain Capital Management, LLC [Member]
Business Acquisition [Line Items]
Other payments to acquire businesses				$ 30,000,000