Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) - USD ($) $ in Millions		Dec. 31, 2016		Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 296,318	[1]	$ 358,571	[2]
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		4,786		5,053
CIFG Holding Inc. [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		2,900
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	[3]	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	[3]	169		188
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | Puerto Rico [Member] | PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[3],[4]	918		909
Public Corporations - Certain Revenues Potentially 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 - Certain Revenues Potentially Subject to Clawback [Member] | Puerto Rico [Member] | PRCCDA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		152		164
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | Puerto Rico [Member] | PRIFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	[3]	18		18
Public Corporations - Certain Revenues Potentially Subject to Clawback [Member] | CIFG Holding Inc. [Member] | Puerto Rico [Member] | PRHTA (Transportation revenue) [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		46
Other Public Corporations [Member] | Puerto Rico [Member] | PREPA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		724		744
Other Public Corporations [Member] | Puerto Rico [Member] | PRASA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		373		388
Other Public Corporations [Member] | Puerto Rico [Member] | MFA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		334		387
Other Public Corporations [Member] | Puerto Rico [Member] | COFINA [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		271		269
Other Public Corporations [Member] | Puerto Rico [Member] | U of PR [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding		$ 1		$ 1

[1] The December 31, 2016 amounts include $2.9 billion of net par from the CIFG Acquisition.

[2] The December 31, 2015 amounts include $10.9 billion of net par from the Radian Asset Acquisition.

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

[4] The December 31, 2016 amount includes $46 million of net par from the CIFG Acquisition.