Outstanding Exposure - Debt Service Outstanding (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 356,280	$ 375,080
Net Debt Service Outstanding	354,612	371,586
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	343,956	361,511
Net Debt Service Outstanding	342,801	358,438
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	12,324	13,569
Net Debt Service Outstanding	$ 11,811	$ 13,148