Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011		Dec. 31, 2010
Distribution of Credit Derivative Net Par Outstanding
Premiums Receivable, at Carrying Value	$ 944	[1]	$ 987	[1]	$ 944	[1]	$ 987	[1]	$ 1,003		$ 1,168
Premium written, net					134		153
Net Par Outstanding	74,684				74,684				85,047
Percentage of total	100.00%				100.00%				100.00%
Original Subordination (as a percent)	0.00%	[2]			0.00%	[2]
Current Subordination (as a percent)	0.00%	[2]			0.00%	[2]			0.00%	[2]
Unrealized Gains (Losses)	(38)		1,156		(388)		830
U.S. RMBS
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	7,576				7,576				8,532
Original Subordination (as a percent)	24.20%	[2],[3]			24.20%	[2],[3]			24.10%	[2]
Current Subordination (as a percent)	30.80%	[2],[3]			30.80%	[2],[3]			32.20%	[2]
Unrealized Gains (Losses)	(78)		1,000		(457)		658
U.S. RMBS | 2004 and Prior
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	130				130
Original Subordination (as a percent)	6.40%	[3]			6.40%	[3]
Current Subordination (as a percent)	19.40%	[3]			19.40%	[3]
Unrealized Gains (Losses)	3				3
U.S. RMBS | 2005
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	2,175				2,175
Original Subordination (as a percent)	30.90%	[3]			30.90%	[3]
Current Subordination (as a percent)	66.30%	[3]			66.30%	[3]
Unrealized Gains (Losses)	11				10
U.S. RMBS | Vintage 2006 [Member]
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	1,589				1,589
Original Subordination (as a percent)	29.40%	[3]			29.40%	[3]
Current Subordination (as a percent)	34.70%	[3]			34.70%	[3]
Unrealized Gains (Losses)	(24)				(38)
U.S. RMBS | Vintage 2007 [Member]
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,682				3,682
Original Subordination (as a percent)	18.50%	[3]			18.50%	[3]
Current Subordination (as a percent)	8.60%	[3]			8.60%	[3]
Unrealized Gains (Losses)	(68)				(432)
CMBS
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	4,195				4,195				4,612
Original Subordination (as a percent)	33.50%	[2]			33.50%	[2]			32.60%	[2]
Current Subordination (as a percent)	41.50%	[2]			41.50%	[2]			38.90%	[2]
Unrealized Gains (Losses)	0		0		0		10
Super senior
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	18,984				18,984				21,802
Percentage of total	25.40%				25.40%				25.60%
AAA
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	34,877				34,877				40,240
Percentage of total	46.70%				46.70%				47.30%
AA
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,422				3,422				4,342
Percentage of total	4.60%				4.60%				5.10%
A
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	5,786				5,786				5,830
Percentage of total	7.80%				7.80%				6.90%
BBB
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	4,721				4,721				5,030
Percentage of total	6.30%				6.30%				5.90%
Below investment grade (BIG)
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	$ 6,894				$ 6,894				$ 7,803
Percentage of total	9.20%				9.20%				9.20%

[1] Excludes $30 million and $29 million as of September 30, 2012 and 2011, respectively, related to consolidated FG VIEs.

[2] Represents the sum of subordinate tranches and over-collateralization and does not include any benefit from excess interest collections that may be used to absorb losses.

[3] Represents the sum of subordinate tranches and overcollateralization and does not include any benefit from excess interest collections that may be used to absorb losses.