Outstanding Exposure (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Outstanding Exposure
Mortgage Guaranty Insured Obligations Outstanding Principal Amount	$ 148
Gross Debt Service Outstanding	890,592	936,132
Net Debt Service Outstanding	835,088	845,665
Public finance
Outstanding Exposure
Gross Debt Service Outstanding	767,155	798,471
Net Debt Service Outstanding	719,301	716,890
Structured finance
Outstanding Exposure
Gross Debt Service Outstanding	123,437	137,661
Net Debt Service Outstanding	115,787	128,775
Public finance Ireland
Outstanding Exposure
Mortgage Guaranty Insured Obligations Outstanding Principal Amount	$ 133