Financial Guaranty Contracts Accounted for as Credit Derivatives (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012		Jun. 30, 2012		Dec. 31, 2011
Financial Guaranty Contracts Accounted for as Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	3 years 10 months 24 days				4 years 3 months 18 days
Net par of terminated CDS transactions	$ 600,000,000		$ 800,000,000
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	78,443,000,000		78,443,000,000		85,047,000,000
Original Subordination (as a percent)	0.00%	[1]	0.00%	[1]
Current Subordination (as a percent)	0.00%	[1]	0.00%	[1]	0.00%	[1]
Pooled corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	55,791,000,000		55,791,000,000		61,073,000,000
Original Subordination (as a percent)	32.10%	[1]	32.10%	[1]	31.20%	[1]
Current Subordination (as a percent)	29.60%	[1]	29.60%	[1]	28.90%	[1]
Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	32,210,000,000		32,210,000,000		34,567,000,000
Original Subordination (as a percent)	33.10%	[1]	33.10%	[1]	32.60%	[1]
Current Subordination (as a percent)	32.70%	[1]	32.70%	[1]	32.00%	[1]
Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	10,453,000,000		10,453,000,000		12,393,000,000
Original Subordination (as a percent)	20.90%	[1]	20.90%	[1]	20.40%	[1]
Current Subordination (as a percent)	19.00%	[1]	19.00%	[1]	18.70%	[1]
Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,898,000,000		4,898,000,000		5,049,000,000
Original Subordination (as a percent)	35.40%	[1]	35.40%	[1]	35.70%	[1]
Current Subordination (as a percent)	30.30%	[1]	30.30%	[1]	30.30%	[1]
Trust Preferred Securities Collateralized Debt Obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,319,000,000		4,319,000,000		4,518,000,000
Original Subordination (as a percent)	46.50%	[1]	46.50%	[1]	46.60%	[1]
Current Subordination (as a percent)	31.90%	[1]	31.90%	[1]	31.90%	[1]
Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,911,000,000		3,911,000,000		4,546,000,000
Original Subordination (as a percent)	33.00%	[1]	33.00%	[1]	30.60%	[1]
Current Subordination (as a percent)	28.50%	[1]	28.50%	[1]	28.90%	[1]
Maximum average obligor size (as a percent)	1.00%		1.00%
Maximum exposure of one industry (as a percent)	10.00%		10.00%
U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	7,902,000,000		7,902,000,000		8,532,000,000
Original Subordination (as a percent)	24.10%	[1],[2]	24.10%	[1],[2]	24.10%	[1]
Current Subordination (as a percent)	31.50%	[1],[2]	31.50%	[1],[2]	32.20%	[1]
Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,701,000,000		3,701,000,000		4,060,000,000
Original Subordination (as a percent)	20.10%	[1]	20.10%	[1]	19.60%	[1]
Current Subordination (as a percent)	11.80%	[1]	11.80%	[1]	13.60%	[1]
Subprime
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,778,000,000		3,778,000,000		4,012,000,000
Original Subordination (as a percent)	29.60%	[1]	29.60%	[1]	30.10%	[1]
Current Subordination (as a percent)	53.60%	[1]	53.60%	[1]	53.90%	[1]
Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	367,000,000		367,000,000		398,000,000
Original Subordination (as a percent)	10.90%	[1]	10.90%	[1]	10.90%	[1]
Current Subordination (as a percent)	7.10%	[1]	7.10%	[1]	8.40%	[1]
Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	56,000,000		56,000,000		62,000,000
Original Subordination (as a percent)					0.00%	[1]
CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,270,000,000		4,270,000,000		4,612,000,000
Original Subordination (as a percent)	33.50%	[1],[2]	33.50%	[1],[2]	32.60%	[1]
Current Subordination (as a percent)	41.00%	[1],[2]	41.00%	[1],[2]	38.90%	[1]
Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	10,480,000,000		10,480,000,000		10,830,000,000
Pooled infrastructure transactions
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	7,400,000,000		7,400,000,000
Number of transactions	3		3
Remaining other CDS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 3,100,000,000		$ 3,100,000,000

[1] esents 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. E

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