Outstanding Exposure - Debt Service Outstanding (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	$ 484,571,000,000	$ 559,470,000,000
Net Debt Service Outstanding	465,559,000,000	536,341,000,000
Excess Of Loss Reinsurance [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Debt Service Outstanding	275,000,000	0
Public Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	451,287,000,000	515,494,000,000
Net Debt Service Outstanding	433,621,000,000	494,426,000,000
Structured Finance [Member]
Schedule of Insured Financial Obligations [Line Items]
Gross Debt Service Outstanding	33,284,000,000	43,976,000,000
Net Debt Service Outstanding	$ 31,938,000,000	$ 41,915,000,000