Outstanding Exposure - Puerto Rico Gross Par and Gross Debt Service Outstanding (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 619,932		$ 646,722
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	6,036		6,035
Gross Debt Service Outstanding	9,927		10,074
Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	3,059	[1]	3,058	[1]
Gross Debt Service Outstanding	5,252	[1]	5,326	[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		2,977
Gross Debt Service Outstanding	$ 4,675		$ 4,748

[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.