Financial Guaranty Contracts Accounted for as Credit Derivatives (Details) (USD $)	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Financial Guaranty Contracts Accounted for as Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	3 years 8 months 12 days		3 years 8 months 12 days
Net par of terminated CDS transactions	$ 1,000,000,000				$ 200,000,000
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	65,900,000,000		70,781,000,000
Original Subordination (as a percent)	0.00%	[1]
Current Subordination (as a percent)	0.00%	[1]	0.00%	[1]
Proceeds from Termination of Financial Guaranty Contracts Accounted for as Credit Derivatives	1,000,000				0
Pooled Corporate Obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	46,239,000,000		50,120,000,000
Original Subordination (as a percent)	31.90%	[1]	31.70%	[1]
Current Subordination (as a percent)	31.20%	[1]	30.40%	[1]
Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	26,342,000,000		29,142,000,000
Original Subordination (as a percent)	32.30%	[1]	32.80%	[1]
Current Subordination (as a percent)	34.00%	[1]	33.30%	[1]
Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	9,592,000,000		9,658,000,000
Original Subordination (as a percent)	21.60%	[1]	21.60%	[1]
Current Subordination (as a percent)	19.70%	[1]	19.70%	[1]
Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,690,000,000		3,626,000,000
Original Subordination (as a percent)	47.20%	[1]	35.00%	[1]
Current Subordination (as a percent)	41.10%	[1]	30.30%	[1]
Trust Preferred Securities Collateralized Debt Obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,967,000,000		4,099,000,000
Original Subordination (as a percent)	46.40%	[1]	46.50%	[1]
Current Subordination (as a percent)	33.40%	[1]	32.70%	[1]
Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,648,000,000		3,595,000,000
Original Subordination (as a percent)	29.70%	[1]	30.10%	[1]
Current Subordination (as a percent)	31.70%	[1]	32.00%	[1]
Maximum average obligor size (as a percent)	1.00%
Maximum exposure of one industry (as a percent)	10.00%
Other Pooled Infrastructure Transactions [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,100,000,000
U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	6,984,000,000		7,257,000,000
Original Subordination (as a percent)	24.20%	[1],[2]	24.20%	[1]
Current Subordination (as a percent)	30.20%	[1],[2]	30.40%	[1]
Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,259,000,000		3,381,000,000
Original Subordination (as a percent)	20.10%	[1]	20.20%	[1]
Current Subordination (as a percent)	10.20%	[1]	10.40%	[1]
Subprime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,360,000,000		3,494,000,000
Original Subordination (as a percent)	29.90%	[1]	29.80%	[1]
Current Subordination (as a percent)	52.50%	[1]	52.60%	[1]
Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	318,000,000		333,000,000
Original Subordination (as a percent)	10.90%	[1]	10.90%	[1]
Current Subordination (as a percent)	5.20%	[1]	5.20%	[1]
Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	47,000,000		49,000,000
Original Subordination (as a percent)			0.00%	[1]
CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,983,000,000		4,094,000,000
Original Subordination (as a percent)	33.30%	[1]	33.30%	[1]
Current Subordination (as a percent)	42.00%	[1]	41.80%	[1]
Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	8,694,000,000		9,310,000,000
Pooled Infrastructure Transactions [Member]
Net Par Outstanding on Credit Derivatives
Number of transactions	3
Remaining other CDS
Financial Guaranty Contracts Accounted for as Credit Derivatives
Financial Guaranty Contracts Accounted For As Credit Derivatives Outstanding PrincipalAmount Rated BIG	717,000,000
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 5,600,000,000

[1] 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.

[2] 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.