Outstanding Exposure - Debt Service Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 375,080	$ 408,492
Net debt service outstanding	371,586	401,118
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	361,511	393,010
Net debt service outstanding	358,438	386,092
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	13,569	15,482
Net debt service outstanding	$ 13,148	$ 15,026