Outstanding Exposure - Puerto Rico Gross Par and Gross Debt Service Outstanding (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 397,233	$ 408,492
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Par Outstanding	5,187	5,186
Gross Debt Service Outstanding	$ 8,385	$ 8,514