Outstanding Exposure - Puerto Rico Gross Par and Gross Debt Service Outstanding (Details) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding		$ 538,642	$ 559,470
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding		5,756	5,755
Gross Debt Service Outstanding		9,488	9,632
Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding	[1]	2,965	2,965
Gross Debt Service Outstanding	[1]	5,090	5,162
Not Subject to the Terms of the Recovery Act [Member] | Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross par outstanding		2,791	2,790
Gross Debt Service Outstanding		$ 4,398	$ 4,470

[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 U.S. Bankruptcy Code and is therefore void. On July 6, 2015, the U.S. Court of Appeals for the First Circuit upheld that ruling, and on December 4, 2015, the U.S. Supreme Court granted petitions for writs of certiorari relating to that ruling.