Outstanding Exposure - Puerto Rico Net Par Outstanding (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	$ 403,729	[1]	$ 459,107	[2]
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	4,939		5,441
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	2,447		2,647
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	844		872
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	772		860
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	384		384
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	273		302
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	174		185
Puerto Rico [Member] | Subject to the Terms of the Recovery Act [Member] | Puerto Rico Public Finance Corporation [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	0		44
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	2,492		2,794
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	1,672		1,885
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico Municipal Finance Agency [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	399		450
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	269		268
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	100		139
Puerto Rico [Member] | Not Subject to the Terms of the Recovery Act [Member] | GDB [Member]
Schedule of Insured Financial Obligations [Line Items]
Net par amount outstanding	33		33
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	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 $1.3 billion of loss mitigation securities insured and held by the Company as of December 31, 2014, which are primarily in the BIG category.

[2] Excludes $1.2 billion of loss mitigation securities insured and held by the Company as of December 31, 2013, which are primarily in the BIG category.