Outstanding Exposure (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Outstanding Exposure
Gross Debt Service Outstanding	$ 917,175	$ 936,132
Net Debt Service Outstanding	858,527	845,665
Public finance
Outstanding Exposure
Gross Debt Service Outstanding	786,373	798,471
Net Debt Service Outstanding	735,829	716,890
Structured Finance
Outstanding Exposure
Gross Debt Service Outstanding	130,802	137,661
Net Debt Service Outstanding	$ 122,698	$ 128,775