Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net credit derivative premiums received and receivable	$ 27,000,000	$ 29,000,000
Net ceding commissions (paid and payable) received and receivable	1,000,000	0
Realized gains on credit derivatives	28,000,000	29,000,000
Net credit derivative losses (paid and payable) recovered and recoverable	(10,000,000)	(86,000,000)
Total realized gains (losses) and other settlements on credit derivatives	18,000,000	(57,000,000)
Net unrealized gains (losses) on credit derivatives	(610,000,000)	(634,000,000)
Net change in fair value of credit derivatives	(592,000,000)	(691,000,000)
Net par of terminated CDS transactions	1,000,000,000	200,000,000
Proceeds from Termination of Financial Guaranty Contracts Accounted for as Credit Derivatives	$ 1,000,000	$ 0