Outstanding Exposure (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 risk		Dec. 31, 2011
Financial guarantee obligations
Probability of paying more claims than being reimbursed (as a percent)	50.00%
Constant discount rate (as a percent)	5.00%
Maximum period of liquidity claims (in years)	1 year
Net Par Amount Outstanding	$ 519,893		$ 558,048
% of Total Net Par Outstanding	100.00%
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	70,781		85,047
Insured Financial Obligations Number of Contracts	14,886
Bank of America Agreement
Financial guarantee obligations
Net Par Amount Outstanding	3,200
BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	9,254		12,250
BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	5,107		4,981
BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	9,031		9,531
Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	23,392		26,762
% of Total Net Par Outstanding	4.50%		4.80%
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	16,683	[1]	18,959	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	6,709		7,803
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	371	[1],[2]	368	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	89	[2]	99	[2]
Insured Financial Obligations Number of Contracts	460	[2]	467	[2]
Below investment grade (BIG) | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	9,254		12,250
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	7,049	[1]	8,297	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,205		3,953
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	153	[1],[2]	171	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	30		40	[2]
Insured Financial Obligations Number of Contracts	183	[2]	211	[2]
Below investment grade (BIG) | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	5,107		4,981
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	2,606	[1]	3,458	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,501		1,523
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	76	[1],[2]	71	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	27		33	[2]
Insured Financial Obligations Number of Contracts	103	[2]	104	[2]
Below investment grade (BIG) | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	9,031		9,531
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	7,028	[1]	7,204	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,003		2,327
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	142	[1],[2]	126	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	32		26	[2]
Insured Financial Obligations Number of Contracts	174	[2]	152	[2]
RMBS
Financial guarantee obligations
Minimum Amount Assumed Principal Amount for Internal Rating	1
Prime first lien
Financial guarantee obligations
Net Par Amount Outstanding	641		739
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	333		398
Prime first lien | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	28		77
Prime first lien | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	436		465
Prime first lien | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	11		0
Prime first lien | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	475		542
% of Total Net Par Outstanding	0.10%		0.10%
Alt-A first lien
Financial guarantee obligations
Net Par Amount Outstanding	4,589		5,329
Alt-A first lien | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	109		1,695
Alt-A first lien | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	1,987		1,028
Alt-A first lien | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	1,479		1,540
Alt-A first lien | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	3,575		4,263
% of Total Net Par Outstanding	0.70%		0.80%
First mortgage, option adjustable rate mortgage
Financial guarantee obligations
Net Par Amount Outstanding	1,550		2,433
First mortgage, option adjustable rate mortgage | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	61		25
First mortgage, option adjustable rate mortgage | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	392		689
First mortgage, option adjustable rate mortgage | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	643		882
First mortgage, option adjustable rate mortgage | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	1,096		1,596
% of Total Net Par Outstanding	0.20%		0.30%
First mortgage, subprime
Financial guarantee obligations
Net Par Amount Outstanding	7,330		8,136
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	3,494		4,012
First mortgage, subprime | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	152		795
First mortgage, subprime | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	1,161		1,200
First mortgage, subprime | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	1,024		513
First mortgage, subprime | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	2,337		2,508
% of Total Net Par Outstanding	0.40%		0.40%
Close ended second lien
Financial guarantee obligations
Net Par Amount Outstanding	521		1,040
Close ended second lien | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	0		0
Close ended second lien | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	247		495
Close ended second lien | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	157		520
Close ended second lien | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	404		1,015
% of Total Net Par Outstanding	0.10%		0.20%
HELOCs
Financial guarantee obligations
Net Par Amount Outstanding	3,196		3,890
HELOCs | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	91		421
HELOCs | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	0		0
HELOCs | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	2,627		2,858
HELOCs | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	2,718		3,279
% of Total Net Par Outstanding	0.50%		0.60%
U.S. RMBS
Financial guarantee obligations
Net Par Amount Outstanding	17,827		21,567
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	7,257		8,532
U.S. RMBS | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	441		3,013
U.S. RMBS | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	4,223		3,877
U.S. RMBS | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	5,941		6,313
U.S. RMBS | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	10,605		13,203
% of Total Net Par Outstanding	2.00%		2.40%
TruPS
Financial guarantee obligations
Net Par Amount Outstanding	5,693		6,334
TruPS | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	1,920		2,501
TruPS | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	0		0
TruPS | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	952		951
TruPS | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	2,872		3,452
% of Total Net Par Outstanding	0.60%		0.60%
Other Structured Finance [Member]
Financial guarantee obligations
Net Par Amount Outstanding	70,866		88,028
Other Structured Finance [Member] | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	1,310		1,295
Other Structured Finance [Member] | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	384		548
Other Structured Finance [Member] | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	1,325		1,429
Other Structured Finance [Member] | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	3,019		3,272
% of Total Net Par Outstanding	0.60%		0.60%
US Public Finance
Financial guarantee obligations
Net Par Amount Outstanding	387,967		403,073
US Public Finance | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	3,290		3,395
US Public Finance | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	500		274
US Public Finance | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	813		838
US Public Finance | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	4,603		4,507
% of Total Net Par Outstanding	0.90%		0.80%
Public finance Non-U.S.
Financial guarantee obligations
Net Par Amount Outstanding	37,540		39,046	[3]
Public finance Non-U.S. | Greece
Financial guarantee obligations
Net Par Amount Outstanding			282
Public finance Non-U.S. | BIG 1
Financial guarantee obligations
Net Par Amount Outstanding	2,293		2,046	[3]
Public finance Non-U.S. | BIG 2
Financial guarantee obligations
Net Par Amount Outstanding	0		282	[3]
Public finance Non-U.S. | BIG 3
Financial guarantee obligations
Net Par Amount Outstanding	0		0	[3]
Public finance Non-U.S. | Below investment grade (BIG)
Financial guarantee obligations
Net Par Amount Outstanding	$ 2,293		$ 2,328	[3]
% of Total Net Par Outstanding	0.40%		0.40%	[3]

[1] Includes net par outstanding for FG VIEs.

[2] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making Debt Service payments.

[3] Includes $282 million in net par as of December 31, 2011, for bonds of the Hellenic Republic of Greece. See Note 6, Expected Loss to be Paid.