Financial Guaranty Contracts Accounted for as Credit Derivatives - Narrative (Details) - Financial Instruments [Domain] $ in Millions		6 Months Ended		12 Months Ended
		Jun. 30, 2015 USD ($) Transaction		Dec. 31, 2014 USD ($)
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)		5 years 1 month		4 years 7 months 30 days
Net par outstanding		$ 32,309	[1]	$ 34,996
Gain due to change in methodology in expected recoveries		49
Gain from narrowing of spreads		207
Collateral agreed to be posted		$ 330		376
Market value collateralized debt obligations of corporate obligations [Member]
Credit Derivatives
Maximum average obligor size (as a percent)		1.00%
Maximum exposure of one industry (as a percent)		10.00%
Net par outstanding		$ 21,015		23,621
Other pooled infrastructure [Member]
Credit Derivatives
Net par outstanding		$ 2,000
Pooled infrastructure [Member]
Credit Derivatives
Number of transactions | Transaction		1
Remaining other CDS [Member]
Credit Derivatives
Net par outstanding		$ 4,800
Collateral Debt Obligations, Collateral Requirement [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped		5,300
Collateral Debt Obligations, Collateral Cap Negotiated [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped		5,100
Collateral Debt Obligations, No Cap Negotiated [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped		575
Collateral agreed to be posted		330		376
Notional amount subject to collateral based on movements in the mark-to-market valuation of the underlying exposure		238		242
Collateral posted, based on mark-to-market valuation		20		$ 25
Radian [Member]
Credit Derivatives
Net par outstanding	[1]	$ 4,300

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