Outstanding Exposure - Debt Service Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 455,000	$ 559,470
Net Debt Service Outstanding	437,535	536,341
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	425,849	515,494
Net Debt Service Outstanding	409,447	494,426
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	29,151	43,976
Net Debt Service Outstanding	$ 28,088	$ 41,915