Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 347,015	[1]	$ 358,571	[2]
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		5,054		5,053
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		2,575		2,575
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[3]	910		909
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | PREPA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		744		744
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico Aqueduct and Sewer Authority [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		388		388
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | PRHTA (Highway revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[3]	369		370
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico Convention Center District Authority [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		164		164	[3]
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		2,479		2,478
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | Commonwealth of Puerto Rico - General Obligation Bonds [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		1,615		1,615
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | MFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		387		387
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico Sales Tax Financing Corporation [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		270		269
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico Public Buildings Authority [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		188		188
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | PRIFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[3],[4]	18		18
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | University of Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1		$ 1

[1] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of March 31, 2016, which are primarily BIG.

[2] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of December 31, 2015, which are primarily BIG.

[3] The Governor issued executive orders on November 30, 2015, and December 8, 2015, directing the Puerto Rico Department of Treasury and the Puerto Rico Tourism Company to retain or transfer certain taxes and revenues pledged to secure the payment of bonds issued by PRHTA, PRIFA and PRCCDA. On January 7, 2016 the Company sued various Puerto Rico governmental officials in the United States District Court, District of Puerto Rico asserting that this attempt to “claw back” pledged taxes and revenues is unconstitutional, and demanding declaratory and injunctive relief.

[4] On January 1, 2016 PRIFA defaulted on full payment of a portion of the interest due on its bonds on that date. For those PRIFA bonds the Company had insured, the Company paid approximately $451 thousand of claims for the interest payments on which PRIFA had defaulted.