Outstanding Exposure - Puerto Rico Gross Par and Gross Debt Service Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Insured Financial Obligations [Line Items]
Gross Par Outstanding	$ 244,191	$ 269,386
Gross Debt Service Outstanding	375,080	408,492
Puerto Rico [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Par Outstanding	4,971	5,186
Gross Debt Service Outstanding	$ 8,035	$ 8,514