Outstanding Exposure - Puerto Rico Gross Par and Gross Debt Service Outstanding (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	$ 426,704		$ 487,895
Gross Debt Service Outstanding	646,722		737,380
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	6,035		6,796
Gross Debt Service Outstanding	10,074		11,347
Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	3,058	[1]	3,279	[1]
Gross Debt Service Outstanding	5,326	[1]	5,748	[1]
Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	2,977		3,517
Gross Debt Service Outstanding	$ 4,748		$ 5,599

[1] On February 6, 2015, the U.S. District Court for the District of Puerto Rico ruled that the Recovery Act is preempted by the Federal Bankruptcy Code and is therefore void. On February 19, 2015, the Commonwealth appealed the ruling to the U.S. Court of Appeals for the First Circuit.