Financial Guaranty Contracts Accounted for as Credit Derivatives (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Financial Guaranty Contracts Accounted for as Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	3 years 10 months 24 days		3 years 8 months 12 days
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 60,879		$ 70,781			$ 60,879
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]
Proceeds from Termination of Financial Guaranty Contracts Accounted for as Credit Derivatives	14.0				0.7	15.0		1.0
Pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	42,097		50,120			42,097
Original Subordination (as a percent)	31.70%	[1]	31.70%	[1]		31.70%	[1]
Current Subordination (as a percent)	31.10%	[1]	30.40%	[1]		31.10%	[1]
Collateralized loan obligation/collateral bond obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	22,954		29,142			22,954
Original Subordination (as a percent)	31.90%	[1]	32.80%	[1]		31.90%	[1]
Current Subordination (as a percent)	34.20%	[1]	33.30%	[1]		34.20%	[1]
Synthetic investment grade pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	9,626		9,658			9,626
Original Subordination (as a percent)	21.60%	[1]	21.60%	[1]		21.60%	[1]
Current Subordination (as a percent)	19.70%	[1]	19.70%	[1]		19.70%	[1]
Synthetic high yield pooled corporate
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,690		3,626			2,690
Original Subordination (as a percent)	47.20%	[1]	35.00%	[1]		47.20%	[1]
Current Subordination (as a percent)	41.10%	[1]	30.30%	[1]		41.10%	[1]
Trust Preferred Securities Collateralized Debt Obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,716		4,099			3,716
Original Subordination (as a percent)	46.10%	[1]	46.50%	[1]		46.10%	[1]
Current Subordination (as a percent)	33.50%	[1]	32.70%	[1]		33.50%	[1]
Market value collateralized debt obligations of corporate obligations
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,111		3,595			3,111
Original Subordination (as a percent)	31.20%	[1]	30.10%	[1]		31.20%	[1]
Current Subordination (as a percent)	32.70%	[1]	32.00%	[1]		32.70%	[1]
Maximum average obligor size (as a percent)	1.00%					1.00%
Maximum exposure of one industry (as a percent)	10.00%					10.00%
Other Pooled Infrastructure Transactions [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,000					3,000
U.S. RMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	6,634		7,257			6,634
Original Subordination (as a percent)	24.30%	[1]	24.20%	[1]		24.30%	[1]
Current Subordination (as a percent)	29.90%	[1]	30.40%	[1]		29.90%	[1]
Option ARM and Alt-A first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,112		3,381			3,112
Original Subordination (as a percent)	20.00%	[1]	20.20%	[1]		20.00%	[1]
Current Subordination (as a percent)	10.10%	[1]	10.40%	[1]		10.10%	[1]
Subprime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,195		3,494			3,195
Original Subordination (as a percent)	30.10%	[1]	29.80%	[1]		30.10%	[1]
Current Subordination (as a percent)	51.70%	[1]	52.60%	[1]		51.70%	[1]
Prime first lien
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	302		333			302
Original Subordination (as a percent)	10.90%	[1]	10.90%	[1]		10.90%	[1]
Current Subordination (as a percent)	5.20%	[1]	5.20%	[1]		5.20%	[1]
Closed end second lien and HELOCs
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	25		49			25
Original Subordination (as a percent)			0.00%	[1]
CMBS
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	3,816		4,094			3,816
Original Subordination (as a percent)	33.40%	[1]	33.30%	[1]		33.40%	[1]
Current Subordination (as a percent)	41.50%	[1]	41.80%	[1]		41.50%	[1]
Other
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	8,332		9,310			8,332
Pooled Infrastructure Transactions [Member]
Net Par Outstanding on Credit Derivatives
Number of transactions	3					3
Other Transactions [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	5,300					5,300
Financial Guaranty Contracts Accounted For As Credit Derivatives Outstanding PrincipalAmount Rated BIG	$ 0.5					$ 0.5

[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.