Outstanding Exposure (Details 2) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Outstanding Exposure
Net Par Outstanding	$ 587,196,000,000	$ 617,131,000,000
% of Total Net Par Outstanding (as a percent)	100.00%	100.00%
Net Par Outstanding Credit Derivatives	98,005,000,000	109,771,000,000
RMBS
Outstanding Exposure
Minimum par of assumed credits	1,000,000
Net par outstanding of transactions covered by the Bank of America Agreement	4,400,000,000
Percentage of Assured Guaranty's total below-investment-grade ("BIG") RMBS net par outstanding covered by the Bank of America Agreement (as a percent)	28.00%
U.S. RMBS
Outstanding Exposure
Net Par Outstanding	23,266,000,000	25,130,000,000
U.S. RMBS | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	15,857,000,000	16,355,000,000
% of Total Net Par Outstanding (as a percent)	2.70%	2.60%
U.S. RMBS | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	2,110,000,000	2,252,000,000
U.S. RMBS | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	7,187,000,000	8,528,000,000
U.S. RMBS | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	6,560,000,000	5,575,000,000
Prime first lien
Outstanding Exposure
Net Par Outstanding	786,000,000	849,000,000
Prime first lien | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	608,000,000	624,000,000
% of Total Net Par Outstanding (as a percent)	0.10%	0.10%
Prime first lien | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	26,000,000	82,000,000
Prime first lien | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	582,000,000	542,000,000
Alt-A first lien
Outstanding Exposure
Net Par Outstanding	5,731,000,000	6,134,000,000
Alt-A first lien | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	5,011,000,000	4,657,000,000
% of Total Net Par Outstanding (as a percent)	0.90%	0.80%
Alt-A first lien | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	1,127,000,000	976,000,000
Alt-A first lien | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	2,397,000,000	3,108,000,000
Alt-A first lien | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	1,487,000,000	573,000,000
Option ARM
Outstanding Exposure
Net Par Outstanding	2,809,000,000	3,214,000,000
Option ARM | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,562,000,000	2,859,000,000
% of Total Net Par Outstanding (as a percent)	0.40%	0.50%
Option ARM | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding		33,000,000
Option ARM | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	1,302,000,000	2,186,000,000
Option ARM | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	1,260,000,000	640,000,000
Subprime
Outstanding Exposure
Net Par Outstanding	8,572,000,000	9,039,000,000
Subprime | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	3,014,000,000	3,083,000,000
% of Total Net Par Outstanding (as a percent)	0.50%	0.40%
Subprime | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	334,000,000	729,000,000
Subprime | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	2,468,000,000	2,248,000,000
Subprime | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	212,000,000	106,000,000
CES
Outstanding Exposure
Net Par Outstanding	1,087,000,000	1,164,000,000
CES | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	1,058,000,000	1,131,000,000
% of Total Net Par Outstanding (as a percent)	0.20%	0.20%
CES | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	153,000,000	63,000,000
CES | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	438,000,000	444,000,000
CES | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	467,000,000	624,000,000
HELOCs
Outstanding Exposure
Net Par Outstanding	4,281,000,000	4,730,000,000
HELOCs | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	3,604,000,000	4,001,000,000
% of Total Net Par Outstanding (as a percent)	0.60%	0.60%
HELOCs | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	470,000,000	369,000,000
HELOCs | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	3,134,000,000	3,632,000,000
Other structured finance
Outstanding Exposure
Net Par Outstanding	109,430,000,000.00	124,262,000,000
Other structured finance | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	6,608,000,000	5,497,000,000
% of Total Net Par Outstanding (as a percent)	1.10%	0.90%
Other structured finance | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	3,756,000,000	2,758,000,000
Other structured finance | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	424,000,000	292,000,000
Other structured finance | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	2,428,000,000	2,447,000,000
Public finance
Outstanding Exposure
Net Par Outstanding	454,500,000,000.00	467,739,000,000
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 | Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	4,241,000,000	3,752,000,000
Public finance | Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	204,000,000	283,000,000
Public finance | Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	865,000,000	919,000,000
Total first lien
Outstanding Exposure
Net par outstanding of transactions covered by the Bank of America Agreement	1,900,000,000
Percentage of Assured Guaranty's total below-investment-grade ("BIG") RMBS net par outstanding covered by the Bank of America Agreement (as a percent)	17.00%
Loss sharing agreement (as a percent)	80.00%
Maximum aggregate collateral losses	6,600,000,000
Below investment grade ("BIG")
Outstanding Exposure
Probability of paying more claims than being reimbursed	more than 50%
Constant discount rate (as a percent)	5.00%
Maximum period of liquidity claims (in years)	1
Net Par Outstanding	27,775,000,000	26,806,000,000
% of Total Net Par Outstanding (as a percent)	4.70%	4.30%
Net Par Outstanding Financial Guaranty Insurance	19,339,000,000	18,448,000,000
Net Par Outstanding Credit Derivatives	8,436,000,000	8,358,000,000
Number of Risks in Financial Guaranty Insurance	364	332
Number of Risks in Credit Derivative	97	94
Number of Risks in Category	461	426
Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	10,107,000,000	8,762,000,000
Net Par Outstanding Financial Guaranty Insurance	6,877,000,000	5,521,000,000
Net Par Outstanding Credit Derivatives	3,230,000,000	3,241,000,000
Number of Risks in Financial Guaranty Insurance	151	120
Number of Risks in Credit Derivative	30	31
Number of Risks in Category	181	151
Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	7,815,000,000	9,103,000,000
Net Par Outstanding Financial Guaranty Insurance	5,038,000,000	5,646,000,000
Net Par Outstanding Credit Derivatives	2,777,000,000	3,457,000,000
Number of Risks in Financial Guaranty Insurance	84	97
Number of Risks in Credit Derivative	44	50
Number of Risks in Category	128	147
Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	9,853,000,000	8,941,000,000
Net Par Outstanding Financial Guaranty Insurance	7,424,000,000	7,281,000,000
Net Par Outstanding Credit Derivatives	$ 2,429,000,000	$ 1,660,000,000
Number of Risks in Financial Guaranty Insurance	129	115
Number of Risks in Credit Derivative	23	13
Number of Risks in Category	152	128