Financial Guaranty Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions		Sep. 30, 2015		Dec. 31, 2014
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 29,633	[1]	$ 34,996
Pooled corporate obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 19,135		$ 23,621
Original Subordination (as a percent)	[2]	29.50%		30.10%
Current Subordination (as a percent)	[2]	30.80%		30.70%
Pooled corporate obligations [Member] | Collateralized loan obligations and collateral bond obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 7,299		$ 11,688
Original Subordination (as a percent)	[2]	31.10%		32.00%
Current Subordination (as a percent)	[2]	39.60%		36.90%
Pooled corporate obligations [Member] | Synthetic investment grade pooled corporate [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 7,119		$ 7,640
Original Subordination (as a percent)	[2]	21.70%		22.60%
Current Subordination (as a percent)	[2]	19.40%		20.60%
Pooled corporate obligations [Member] | TruPS CDOs [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 3,604		$ 3,119
Original Subordination (as a percent)	[2]	45.70%		45.30%
Current Subordination (as a percent)	[2]	41.60%		35.80%
Pooled corporate obligations [Member] | Market Value of CDOs of corporate obligations [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 1,113		$ 1,174
Original Subordination (as a percent)	[2]	17.00%		19.10%
Current Subordination (as a percent)	[2]	10.50%		20.70%
RMBS [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 2,601		$ 2,986
Original Subordination (as a percent)	[2]	22.60%		24.80%
Current Subordination (as a percent)	[2]	29.60%		33.90%
RMBS [Member] | Option Adjustable Rate Mortgage and Alt-A Mortgage [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 1,186		$ 1,378
Original Subordination (as a percent)	[2]	15.70%		16.30%
Current Subordination (as a percent)	[2]	10.50%		10.70%
RMBS [Member] | Subprime [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 1,215		$ 1,366
Original Subordination (as a percent)	[2]	27.20%		31.10%
Current Subordination (as a percent)	[2]	41.80%		50.50%
RMBS [Member] | Prime [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 183		$ 223
Original Subordination (as a percent)	[2]	10.90%		10.90%
Current Subordination (as a percent)	[2]	0.00%		0.00%
RMBS [Member] | Closed-end [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 17		$ 19
Original Subordination (as a percent)	[2]	0.00%		0.00%
Current Subordination (as a percent)	[2]	0.00%		0.00%
CMBS [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 1,127		$ 1,952
Original Subordination (as a percent)	[2]	28.40%		35.30%
Current Subordination (as a percent)	[2]	35.80%		43.60%
Other [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding		$ 6,770		$ 6,437
Original Subordination (as a percent)	[2]	0.00%		0.00%
Current Subordination (as a percent)	[2]	0.00%		0.00%
Radian [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	[1]	$ 4,300

[1] The September 30, 2015 total amount includes $4.3 billion net par outstanding of credit derivatives acquired from Radian Asset.

[2] 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.