Outstanding Exposure (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Outstanding Exposure
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 Outstanding	$ 552,934		$ 558,048
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	78,443		85,047
BIG 1
Outstanding Exposure
Net Par Outstanding	10,041		12,250
BIG 2
Outstanding Exposure
Net Par Outstanding	5,808		4,981
BIG 3
Outstanding Exposure
Net Par Outstanding	8,965		9,531
Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	24,814		26,762
% of Total Net Par Outstanding	4.50%		4.80%
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	17,714	[1]	18,959	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	7,100		7,803
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	375	[1],[2]	368	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	94	[2]	99	[2]
Insured Financial Obligations Number of Contracts	469	[2]	467	[2]
Below investment grade ("BIG") | BIG 1
Outstanding Exposure
Net Par Outstanding	10,041		12,250
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	7,467	[1]	8,297	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,574		3,953
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	164	[1],[2]	171	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	35		40	[2]
Insured Financial Obligations Number of Contracts	199	[2]	211	[2]
Below investment grade ("BIG") | BIG 2
Outstanding Exposure
Net Par Outstanding	5,808		4,981
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	3,353	[1]	3,458	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,455		1,523
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	79	[1],[2]	71	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	34		33	[2]
Insured Financial Obligations Number of Contracts	113	[2]	104	[2]
Below investment grade ("BIG") | BIG 3
Outstanding Exposure
Net Par Outstanding	8,965		9,531
Financial Guaranty Contracts Accounted for as Insurance Outstanding Principal Amount	6,894	[1]	7,204	[1]
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	2,071		2,327
Financial Guaranty Contracts Accounted for as Insurance Number of Contracts	132	[1],[2]	126	[1],[2]
Financial Guaranty Contracts Accounted for as Credit Derivatives Number of Contracts	25		26	[2]
Insured Financial Obligations Number of Contracts	157	[2]	152	[2]
RMBS
Outstanding Exposure
Minimum Amount Assumed Principal Amount for Internal Rating	1
Residential, Prime, Financing Receivable [Member]
Outstanding Exposure
Net Par Outstanding	690		739
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	367		398
Residential, Prime, Financing Receivable [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	76		77
Residential, Prime, Financing Receivable [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	430		465
Residential, Prime, Financing Receivable [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	3		0
Residential, Prime, Financing Receivable [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	509		542
% of Total Net Par Outstanding	0.10%		0.10%
Alt-A First Mortgage [Member]
Outstanding Exposure
Net Par Outstanding	4,939		5,329
Alt-A First Mortgage [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	436		1,695
Alt-A First Mortgage [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	2,039		1,028
Alt-A First Mortgage [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	1,374		1,540
Alt-A First Mortgage [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	3,849		4,263
% of Total Net Par Outstanding	0.70%		0.80%
First Mortgage Option Adjustable Rate Mortgage [Member]
Outstanding Exposure
Net Par Outstanding	1,991		2,433
First Mortgage Option Adjustable Rate Mortgage [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	61		25
First Mortgage Option Adjustable Rate Mortgage [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	471		689
First Mortgage Option Adjustable Rate Mortgage [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	827		882
First Mortgage Option Adjustable Rate Mortgage [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	1,359		1,596
% of Total Net Par Outstanding	0.30%		0.30%
Residential, Subprime, Financing Receivable [Member]
Outstanding Exposure
Net Par Outstanding	7,754		8,136
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	3,778		4,012
Residential, Subprime, Financing Receivable [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	218		795
Residential, Subprime, Financing Receivable [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	1,276		1,200
Residential, Subprime, Financing Receivable [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	864		513
Residential, Subprime, Financing Receivable [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,358		2,508
% of Total Net Par Outstanding	0.40%		0.40%
Close Ended Second Mortgage [Member]
Outstanding Exposure
Net Par Outstanding	997		1,040
Close Ended Second Mortgage [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	0		0
Close Ended Second Mortgage [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	450		495
Close Ended Second Mortgage [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	419		520
Close Ended Second Mortgage [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	869		1,015
% of Total Net Par Outstanding	0.20%		0.20%
Home Equity Line of Credit [Member]
Outstanding Exposure
Net Par Outstanding	3,521		3,890
Home Equity Line of Credit [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	394		421
Home Equity Line of Credit [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	0		0
Home Equity Line of Credit [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	2,587		2,858
Home Equity Line of Credit [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,981		3,279
% of Total Net Par Outstanding	0.50%		0.60%
US Residential Mortgage Backed Securities [Member]
Outstanding Exposure
Net Par Outstanding	19,892		21,567
Financial Guaranty Contracts Accounted for as Credit Derivatives Outstanding Principal Amount	7,902		8,532
US Residential Mortgage Backed Securities [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	1,185		3,013
US Residential Mortgage Backed Securities [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	4,666		3,877
US Residential Mortgage Backed Securities [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	6,074		6,313
US Residential Mortgage Backed Securities [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	11,925		13,203
% of Total Net Par Outstanding	2.20%		2.40%
TruPS [Member]
Outstanding Exposure
Net Par Outstanding	6,006		6,334
TruPS [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	2,071		2,501
TruPS [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	0		0
TruPS [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	952		951
TruPS [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	3,023		3,452
% of Total Net Par Outstanding	0.50%		0.60%
Other Structured Finance [Member]
Outstanding Exposure
Net Par Outstanding	78,390		88,028
Other Structured Finance [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	1,261		1,295
Other Structured Finance [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	459		548
Other Structured Finance [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	1,224		1,429
Other Structured Finance [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	2,944		3,272
% of Total Net Par Outstanding	0.50%		0.60%
US Public Finance [Member]
Outstanding Exposure
Net Par Outstanding	409,877		403,073
US Public Finance [Member] | BIG 1
Outstanding Exposure
Net Par Outstanding	3,285		3,395
US Public Finance [Member] | BIG 2
Outstanding Exposure
Net Par Outstanding	407		274
US Public Finance [Member] | BIG 3
Outstanding Exposure
Net Par Outstanding	715		838
US Public Finance [Member] | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	4,407		4,507
% of Total Net Par Outstanding	0.80%		0.80%
Public finance Non-U.S.
Outstanding Exposure
Net Par Outstanding	38,769	[3]	39,046	[3]
Public finance Non-U.S. | Greece
Outstanding Exposure
Net Par Outstanding			282
Public finance Non-U.S. | BIG 1
Outstanding Exposure
Net Par Outstanding	2,239	[3]	2,046	[3]
Public finance Non-U.S. | BIG 2
Outstanding Exposure
Net Par Outstanding	276	[3]	282	[3]
Public finance Non-U.S. | BIG 3
Outstanding Exposure
Net Par Outstanding	0	[3]	0	[3]
Public finance Non-U.S. | Below investment grade ("BIG")
Outstanding Exposure
Net Par Outstanding	$ 2,515	[3]	$ 2,328	[3]
% of Total Net Par Outstanding	0.50%	[3]	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 $276 million and $282 million in net par as of June 30, 2012 and December 31, 2011, respectively, for bonds of the Hellenic Republic of Greece, a portion of which was accelerated in July 2012 and a portion of which the Company intends to accelerate on or after September 2012. See Note 4, Financial Guaranty Insurance Contracts.