Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions		Sep. 30, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 315,325	[1],[2]	$ 358,571	[3]
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		4,786		5,053
Constitutionally Guaranteed [Member] | Puerto Rico [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[4]	1,476		1,615
Constitutionally Guaranteed [Member] | Puerto Rico [Member] | Puerto Rico Public Buildings Authority [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[4]	169		188
Public Corporations, Subject To Clawback [Member] | Puerto Rico [Member] | PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[5]	918		909
Public Corporations, Subject To Clawback [Member] | Puerto Rico [Member] | PRHTA (Highway revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		350		370
Public Corporations, Subject To Clawback [Member] | Puerto Rico [Member] | PRCCDA (Puerto Rico Convention Center District Authority) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		152		164
Public Corporations, Subject To Clawback [Member] | Puerto Rico [Member] | PRIFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[4]	18		18
Public Corporations [Member] | Puerto Rico [Member] | PREPA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		724		744
Public Corporations [Member] | Puerto Rico [Member] | PRASA (Puerto Rico Aqueduct and Sewer Authority) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		373		388
Public Corporations [Member] | Puerto Rico [Member] | MFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		334		387
Public Corporations [Member] | Puerto Rico [Member] | COFINA (Puerto Rico Sales Tax Financing Corporation) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		271		269
Public Corporations [Member] | Puerto Rico [Member] | University of Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		1		$ 1
CIFG Holding Inc. [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		3,700
CIFG Holding Inc. [Member] | Public Corporations, Subject To Clawback [Member] | Puerto Rico [Member] | PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[4]	$ 46

[1] As of September 30, 2016, excludes $2.1 billion of net par as a result of loss mitigation strategies, including loss mitigation securities held in the investment portfolio, which are primarily BIG.

[2] The September 30, 2016 amounts include $3.7 billion of net par acquired from CIFG.

[3] As of December 31, 2015, excludes $1.5 billion of net par as a result of loss mitigation strategies, including loss mitigation securities held in the investment portfolio, which are primarily BIG.

[4] As of the date of this filing, the Company has paid claims on these credits.

[5] The September 30, 2016 amount includes $46 million of net par acquired from CIFG.