Financial Guaranty Contracts Accounted for as Credit Derivatives - Distribution of Credit Derivative Net Par Outstanding by Internal Rating (Details) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
		Jun. 30, 2015		Dec. 31, 2014
Credit Derivatives
Net Par Outstanding		$ 32,309	[1]	$ 34,996
Internal Credit Rating, AAA [Member]
Credit Derivatives
Net Par Outstanding		18,018		21,817
Internal Credit Rating, AA [Member]
Credit Derivatives
Net Par Outstanding		5,688		5,398
Internal Credit Rating, A [Member]
Credit Derivatives
Net Par Outstanding		2,319		1,982
Internal Credit Rating, BBB [Member]
Credit Derivatives
Net Par Outstanding		2,784		2,774
BIG [Member]
Credit Derivatives
Net Par Outstanding	[2]	$ 3,500		$ 3,025
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar		100.00%		100.00%
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member] | Internal Credit Rating, AAA [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar		55.80%		62.30%
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member] | Internal Credit Rating, AA [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar		17.60%		15.40%
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member] | Internal Credit Rating, A [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar		7.20%		5.70%
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member] | Internal Credit Rating, BBB [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar		8.60%		8.00%
Credit Concentration Risk [Member] | Derivative, Aggregate Notional Amount [Member] | BIG [Member]
Credit Derivatives
Percentage of installment premiums denominated in currencies other than the U.S. dollar	[2]	10.80%		8.60%
Radian [Member]
Credit Derivatives
Net Par Outstanding	[1]	$ 4,300
Radian [Member] | BIG [Member]
Credit Derivatives
Net Par Outstanding	[2]	$ 933

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

[2] The June 30, 2015 BIG amount includes $933 million net par outstanding of credit derivatives acquired from Radian Asset.