Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012		Dec. 31, 2011
Distribution of Credit Derivative Net Par Outstanding
Premiums Receivable, at Carrying Value	$ 956	[1]	$ 1,019	[1]	$ 1,005		$ 1,003
Premium written, net	17		56
Net Par Outstanding	65,900				70,781
Percentage of total	100.00%				100.00%
Original Subordination (as a percent)	0.00%	[2]
Current Subordination (as a percent)	0.00%	[2]			0.00%	[2]
Net unrealized gains (losses)	(610)		(634)
Financial Guarantee Insurance Contracts, Premium Receivable, Premium Payments Received	53		86
U.S. RMBS
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	6,984				7,257
Original Subordination (as a percent)	24.20%	[2],[3]			24.20%	[2]
Current Subordination (as a percent)	30.20%	[2],[3]			30.40%	[2]
Net unrealized gains (losses)	(457)		(629)
U.S. RMBS | 2004 and Prior
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	119
Original Subordination (as a percent)	5.80%	[3]
Current Subordination (as a percent)	17.00%	[3]
Net unrealized gains (losses)	(1)
U.S. RMBS | 2005
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	1,909
Original Subordination (as a percent)	31.40%	[3]
Current Subordination (as a percent)	67.30%	[3]
Net unrealized gains (losses)	1
U.S. RMBS | Vintage 2006 [Member]
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	1,558
Original Subordination (as a percent)	29.40%	[3]
Current Subordination (as a percent)	34.20%	[3]
Net unrealized gains (losses)	(64)
U.S. RMBS | Vintage 2007 [Member]
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,398
Original Subordination (as a percent)	18.40%	[3]
Current Subordination (as a percent)	8.10%	[3]
Net unrealized gains (losses)	(393)
CMBS
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,983				4,094
Original Subordination (as a percent)	33.30%	[2]			33.30%	[2]
Current Subordination (as a percent)	42.00%	[2]			41.80%	[2]
Net unrealized gains (losses)	(3)		0
Super senior
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	18,184				18,908
Percentage of total	27.60%				26.70%
AAA
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	29,699				32,010
Percentage of total	45.10%				45.20%
AA
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,784				3,083
Percentage of total	5.70%				4.40%
A
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	3,316				5,487
Percentage of total	5.00%				7.80%
BBB
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	4,611				4,584
Percentage of total	7.00%				6.40%
Below investment grade (BIG)
Distribution of Credit Derivative Net Par Outstanding
Net Par Outstanding	$ 6,306				$ 6,709
Percentage of total	9.60%				9.50%

[1] )Excludes $28 million and $33 million as of March 31, 2013 and March 31, 2012, 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.