Outstanding Exposure (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Outstanding Exposure
Gross Debt Service Outstanding	$ 984,553,000,000	$ 1,029,982,000,000
Net Debt Service Outstanding	886,768,000,000	927,143,000,000
Net Par Outstanding	587,196,000,000	617,131,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Public finance
Outstanding Exposure
Gross Debt Service Outstanding	826,907,000,000	851,634,000,000
Net Debt Service Outstanding	739,493,000,000	760,167,000,000
Net Par Outstanding	454,500,000,000.00	467,739,000,000
Outstanding commitments to provide guaranties	1,700,000,000
Outstanding commitments to provide guaranties, amount expiring prior to December 31, 2011	1,300,000,000
Public finance | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	5,310,000,000	4,954,000,000
% of Total Net Par Outstanding (as a percent)	0.90%	0.80%
Public finance U.S.
Outstanding Exposure
Net Par Outstanding	413,274,000,000	426,996,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Public finance U.S. | AAA.
Outstanding Exposure
Net Par Outstanding	5,078,000,000	5,784,000,000
% of Total Net Par Outstanding (as a percent)	1.20%	1.40%
Public finance U.S. | AA.
Outstanding Exposure
Net Par Outstanding	151,571,000,000	161,906,000,000
% of Total Net Par Outstanding (as a percent)	36.70%	37.90%
Public finance U.S. | A
Outstanding Exposure
Net Par Outstanding	211,736,000,000	214,199,000,000
% of Total Net Par Outstanding (as a percent)	51.20%	50.20%
Public finance U.S. | BBB
Outstanding Exposure
Net Par Outstanding	41,939,000,000	41,948,000,000
% of Total Net Par Outstanding (as a percent)	10.20%	9.80%
Public finance U.S. | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,950,000,000	3,159,000,000
% of Total Net Par Outstanding (as a percent)	0.70%	0.70%
Public finance Non-U.S.
Outstanding Exposure
Net Par Outstanding	41,226,000,000	40,743,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Public finance Non-U.S. | Super senior
Outstanding Exposure
Net Par Outstanding	1,507,000,000	1,420,000,000
% of Total Net Par Outstanding (as a percent)	3.70%	3.50%
Public finance Non-U.S. | AAA.
Outstanding Exposure
Net Par Outstanding	1,379,000,000	1,378,000,000
% of Total Net Par Outstanding (as a percent)	3.30%	3.40%
Public finance Non-U.S. | AA.
Outstanding Exposure
Net Par Outstanding	1,145,000,000	1,330,000,000
% of Total Net Par Outstanding (as a percent)	2.80%	3.30%
Public finance Non-U.S. | A
Outstanding Exposure
Net Par Outstanding	12,517,000,000	12,482,000,000
% of Total Net Par Outstanding (as a percent)	30.40%	30.60%
Public finance Non-U.S. | BBB
Outstanding Exposure
Net Par Outstanding	22,318,000,000	22,338,000,000
% of Total Net Par Outstanding (as a percent)	54.10%	54.80%
Public finance Non-U.S. | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,360,000,000	1,795,000,000
% of Total Net Par Outstanding (as a percent)	5.70%	4.40%
Other Structured finance.
Outstanding Exposure
Gross Debt Service Outstanding	157,646,000,000	178,348,000,000
Net Debt Service Outstanding	147,275,000,000	166,976,000,000
Outstanding commitments to provide guaranties	3,900,000,000
Structured finance U.S.
Outstanding Exposure
Net Par Outstanding	103,978,000,000	118,756,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Structured finance U.S. | Super senior
Outstanding Exposure
Net Par Outstanding	19,957,000,000	21,837,000,000
% of Total Net Par Outstanding (as a percent)	19.20%	18.40%
Structured finance U.S. | AAA.
Outstanding Exposure
Net Par Outstanding	38,175,000,000	45,067,000,000
% of Total Net Par Outstanding (as a percent)	36.70%	37.90%
Structured finance U.S. | AA.
Outstanding Exposure
Net Par Outstanding	14,236,000,000	17,355,000,000
% of Total Net Par Outstanding (as a percent)	13.70%	14.60%
Structured finance U.S. | A
Outstanding Exposure
Net Par Outstanding	5,721,000,000	6,396,000,000
% of Total Net Par Outstanding (as a percent)	5.50%	5.40%
Structured finance U.S. | BBB
Outstanding Exposure
Net Par Outstanding	5,248,000,000	7,543,000,000
% of Total Net Par Outstanding (as a percent)	5.00%	6.40%
Structured finance U.S. | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	20,641,000,000	20,558,000,000
% of Total Net Par Outstanding (as a percent)	19.90%	17.30%
Structured finance Non-U.S.
Outstanding Exposure
Net Par Outstanding	28,718,000,000	30,636,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Structured finance Non-U.S. | Super senior
Outstanding Exposure
Net Par Outstanding	7,683,000,000	7,882,000,000
% of Total Net Par Outstanding (as a percent)	26.80%	25.70%
Structured finance Non-U.S. | AAA.
Outstanding Exposure
Net Par Outstanding	12,722,000,000	13,573,000,000
% of Total Net Par Outstanding (as a percent)	44.30%	44.30%
Structured finance Non-U.S. | AA.
Outstanding Exposure
Net Par Outstanding	1,606,000,000	1,969,000,000
% of Total Net Par Outstanding (as a percent)	5.60%	6.40%
Structured finance Non-U.S. | A
Outstanding Exposure
Net Par Outstanding	1,610,000,000	1,873,000,000
% of Total Net Par Outstanding (as a percent)	5.60%	6.10%
Structured finance Non-U.S. | BBB
Outstanding Exposure
Net Par Outstanding	3,273,000,000	4,045,000,000
% of Total Net Par Outstanding (as a percent)	11.30%	13.20%
Structured finance Non-U.S. | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	1,824,000,000	1,294,000,000
% of Total Net Par Outstanding (as a percent)	6.40%	4.30%
Super senior
Outstanding Exposure
Net Par Outstanding	29,147,000,000	31,139,000,000
% of Total Net Par Outstanding (as a percent)	5.00%	5.00%
AAA.
Outstanding Exposure
Net Par Outstanding	57,354,000,000	65,802,000,000
% of Total Net Par Outstanding (as a percent)	9.80%	10.70%
AA.
Outstanding Exposure
Net Par Outstanding	168,558,000,000	182,560,000,000
% of Total Net Par Outstanding (as a percent)	28.70%	29.60%
A
Outstanding Exposure
Net Par Outstanding	231,584,000,000	234,950,000,000
% of Total Net Par Outstanding (as a percent)	39.40%	38.10%
BBB
Outstanding Exposure
Net Par Outstanding	72,778,000,000	75,874,000,000
% of Total Net Par Outstanding (as a percent)	12.40%	12.30%
Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	$ 27,775,000,000	$ 26,806,000,000
% of Total Net Par Outstanding (as a percent)	4.70%	4.30%