Financial Guaranty Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 20,014	$ 25,594
Pooled corporate obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 12,653	$ 17,523
Original Subordination (as a percent)	[1]	28.30%	29.20%
Current Subordination (as a percent)	[1]	33.00%	32.30%
Pooled corporate obligations [Member] | Collateralized loan obligations and collateral bond obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 3,006	$ 5,873
Original Subordination (as a percent)	[1]	29.70%	30.90%
Current Subordination (as a percent)	[1]	55.80%	42.30%
Pooled corporate obligations [Member] | Synthetic investment grade pooled corporate [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 7,116	$ 7,108
Original Subordination (as a percent)	[1]	21.70%	21.70%
Current Subordination (as a percent)	[1]	19.40%	19.40%
Pooled corporate obligations [Member] | TruPS CDOs [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 2,531	$ 3,429
Original Subordination (as a percent)	[1]	45.30%	45.80%
Current Subordination (as a percent)	[1]	44.00%	42.60%
Pooled corporate obligations [Member] | Market Value of CDOs of corporate obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 0	$ 1,113
Original Subordination (as a percent)	[1]	0.00%	17.00%
Current Subordination (as a percent)	[1]	0.00%	30.10%
RMBS [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 1,229	$ 1,526
Original Subordination (as a percent)	[1]	25.10%	24.10%
Current Subordination (as a percent)	[1]	40.70%	37.40%
RMBS [Member] | Option Adjustable Rate Mortgage and Alt-A Mortgage [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 289	$ 351
Original Subordination (as a percent)	[1]	9.50%	10.50%
Current Subordination (as a percent)	[1]	13.10%	12.70%
RMBS [Member] | Subprime [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 925	$ 981
Original Subordination (as a percent)	[1]	27.70%	27.70%
Current Subordination (as a percent)	[1]	45.30%	45.20%
RMBS [Member] | Prime [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 0	$ 177
Original Subordination (as a percent)	[1]	0.00%	10.90%
Current Subordination (as a percent)	[1]	0.00%	0.00%
RMBS [Member] | Closed-end [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 15	$ 17
Original Subordination (as a percent)	[1]	0.00%	0.00%
Current Subordination (as a percent)	[1]	0.00%	0.00%
CMBS [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 384	$ 530
Original Subordination (as a percent)	[1]	44.80%	44.80%
Current Subordination (as a percent)	[1]	58.40%	52.60%
Other [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 5,748	$ 6,015
Original Subordination (as a percent)	[1]	0.00%	0.00%
Current Subordination (as a percent)	[1]	0.00%	0.00%

[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.