Financial Guaranty Contracts Accounted for as Credit Derivatives - Credit Derivatives Net Par Outstanding (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Financial Guaranty Contracts Accounted for as Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	4 years		4 years 1 month 15 days
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 51,318,000,000		$ 54,482,000,000
Original Subordination (as a percent)	0.00%	[1]
Current Subordination (as a percent)	0.00%	[1]
Pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	35,326,000,000
Original Subordination (as a percent)	31.40%	[1]
Current Subordination (as a percent)	31.60%	[1]
Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	17,634,000,000
Original Subordination (as a percent)	32.40%	[1]
Current Subordination (as a percent)	36.10%	[1]
Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	9,759,000,000
Original Subordination (as a percent)	21.60%	[1]
Current Subordination (as a percent)	20.30%	[1]
Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,690,000,000
Original Subordination (as a percent)	47.20%	[1]
Current Subordination (as a percent)	41.30%	[1]
Trust Preferred Securities Collateralized Debt Obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,436,000,000
Original Subordination (as a percent)	45.40%	[1]
Current Subordination (as a percent)	33.70%	[1]
Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,807,000,000
Original Subordination (as a percent)	23.60%	[1]
Current Subordination (as a percent)	30.60%	[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	2,500,000,000
U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	5,637,000,000
Original Subordination (as a percent)	24.40%	[1]
Current Subordination (as a percent)	29.20%	[1]
Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,520,000,000
Original Subordination (as a percent)	19.10%	[1]
Current Subordination (as a percent)	7.60%	[1]
First mortgage, subprime
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,837,000,000
Original Subordination (as a percent)	30.60%	[1]
Current Subordination (as a percent)	51.30%	[1]
Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	258,000,000
Original Subordination (as a percent)	10.90%	[1]
Current Subordination (as a percent)	1.80%	[1]
Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	22,000,000
CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,822,000,000
Original Subordination (as a percent)	33.50%	[1]
Current Subordination (as a percent)	42.50%	[1]
Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	7,533,000,000
Pooled Infrastructure Transactions [Member]
Net Par Outstanding on Credit Derivatives
Number of transactions	2
Other Transactions [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	5,000,000,000
Financial Guaranty Contracts Accounted For As Credit Derivatives Outstanding Principal Amount Rated BIG	500,000,000
AAA
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	35,157,000,000		38,244,000,000
AAA | Pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			37,321,000,000
Original Subordination (as a percent)			31.50%	[1]
Current Subordination (as a percent)			30.60%	[1]
AAA | Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			19,323,000,000
Original Subordination (as a percent)			32.40%	[1]
Current Subordination (as a percent)			34.00%	[1]
AAA | Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			9,754,000,000
Original Subordination (as a percent)			21.60%	[1]
Current Subordination (as a percent)			20.00%	[1]
AAA | Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			2,690,000,000
Original Subordination (as a percent)			47.20%	[1]
Current Subordination (as a percent)			41.10%	[1]
AAA | Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			2,000,000,000
Original Subordination (as a percent)			24.40%	[1]
Current Subordination (as a percent)			30.50%	[1]
AAA | CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			3,744,000,000
Original Subordination (as a percent)			33.50%	[1]
Current Subordination (as a percent)			42.50%	[1]
Internal Credit, BB plus Rating [Member] | Trust Preferred Securities Collateralized Debt Obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			3,554,000,000
Original Subordination (as a percent)			45.50%	[1]
Current Subordination (as a percent)			32.90%	[1]
Internal Credit, BB minus Rating [Member] | Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			2,609,000,000
Original Subordination (as a percent)			19.20%	[1]
Current Subordination (as a percent)			8.60%	[1]
Internal Credit AA Minus Rating [Member] | First mortgage, subprime
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			2,930,000,000
Original Subordination (as a percent)			30.50%	[1]
Current Subordination (as a percent)			51.90%	[1]
Internal Credit CCC Rating [Member] | Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			264,000,000
Original Subordination (as a percent)			10.90%	[1]
Current Subordination (as a percent)			3.20%	[1]
Internal Credit, B Plus Rating [Member]
Net Par Outstanding on Credit Derivatives
Current Subordination (as a percent)			0.00%	[1]
Internal Credit, B Plus Rating [Member] | Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			23,000,000
Original Subordination (as a percent)			0.00%	[1]
BBB
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	4,304,000,000		4,161,000,000
BBB | U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			5,826,000,000
Original Subordination (as a percent)			24.40%	[1]
Current Subordination (as a percent)			30.10%	[1]
Internal Credit A- Rating [Member]
Net Par Outstanding on Credit Derivatives
Original Subordination (as a percent)			0.00%	[1]
Current Subordination (as a percent)			0.00%	[1]
Internal Credit A- Rating [Member] | Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			7,591,000,000
Internal Credit AA Plus Rating [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding			$ 54,482,000,000

[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.