Financial Guaranty Contracts Accounted for as Credit Derivatives (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Financial Guaranty Contracts Accounted for as Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	3 years 8 months 12 days		4 years 3 months 18 days
Net par of terminated CDS transactions	$ 2,300,000,000		$ 11,500,000,000
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	70,781,000,000		85,047,000,000
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	3,000,000		25,000,000
Pooled Corporate Obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	50,120,000,000		61,073,000,000
Original Subordination (as a percent)	31.70%	[1]	31.20%	[1]
Current Subordination (as a percent)	30.40%	[1]	28.90%	[1]
Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	29,142,000,000		34,567,000,000
Original Subordination (as a percent)	32.80%	[1]	32.60%	[1]
Current Subordination (as a percent)	33.30%	[1]	32.00%	[1]
Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	9,658,000,000		12,393,000,000
Original Subordination (as a percent)	21.60%	[1]	20.40%	[1]
Current Subordination (as a percent)	19.70%	[1]	18.70%	[1]
Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,626,000,000		5,049,000,000
Original Subordination (as a percent)	35.00%	[1]	35.70%	[1]
Current Subordination (as a percent)	30.30%	[1]	30.30%	[1]
Trust Preferred Securities Collateralized Debt Obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,099,000,000		4,518,000,000
Original Subordination (as a percent)	46.50%	[1]	46.60%	[1]
Current Subordination (as a percent)	32.70%	[1]	31.90%	[1]
Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,595,000,000		4,546,000,000
Original Subordination (as a percent)	30.10%	[1]	30.60%	[1]
Current Subordination (as a percent)	32.00%	[1]	28.90%	[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	3,200,000,000
U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	7,257,000,000		8,532,000,000
Original Subordination (as a percent)	24.20%	[1],[2]	24.10%	[1]
Current Subordination (as a percent)	30.40%	[1],[2]	32.20%	[1]
Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,381,000,000		4,060,000,000
Original Subordination (as a percent)	20.20%	[1]	19.60%	[1]
Current Subordination (as a percent)	10.40%	[1]	13.60%	[1]
Subprime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,494,000,000		4,012,000,000
Original Subordination (as a percent)	29.80%	[1]	30.10%	[1]
Current Subordination (as a percent)	52.60%	[1]	53.90%	[1]
Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	333,000,000		398,000,000
Original Subordination (as a percent)	10.90%	[1]	10.90%	[1]
Current Subordination (as a percent)	5.20%	[1]	8.40%	[1]
Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	49,000,000		62,000,000
Original Subordination (as a percent)			0.00%	[1]
CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,094,000,000		4,612,000,000
Original Subordination (as a percent)	33.30%	[1]	32.60%	[1]
Current Subordination (as a percent)	41.80%	[1]	38.90%	[1]
Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	9,310,000,000		10,830,000,000
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	983,000,000
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 6,100,000,000

[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.