Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 3) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net credit derivative premiums received and receivable	$ 33,000,000	$ 40,000,000	$ 96,000,000	$ 148,000,000
Net ceding commissions (paid and payable) received and receivable	0	1,000,000	0	3,000,000
Realized gains on credit derivatives	33,000,000	41,000,000	96,000,000	151,000,000
Termination losses	0	0	(1,000,000)	(23,000,000)
Net credit derivative losses (paid and payable) recovered and recoverable	(31,000,000)	(41,000,000)	(173,000,000)	(103,000,000)
Unrealized Gains (Losses)	(38,000,000)	1,156,000,000	(388,000,000)	830,000,000
Realized gains (losses) and other settlements	2,000,000	0	(78,000,000)	25,000,000
Net change in fair value of credit derivatives	(36,000,000)	1,156,000,000	(466,000,000)	855,000,000
Net par of terminated CDS transactions	300,000,000		1,100,000,000
Amount received on net par of terminated CDS exposures		$ 1,800,000,000		$ 9,500,000,000