Financial Guaranty Contracts Accounted for as Credit Derivatives (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net Change in Fair Value of Credit Derivatives
Net credit derivative premiums received and receivable	$ 28,900,000	$ 59,600,000
Net ceding commissions (paid and payable) received and receivable	(100,000)	1,400,000
Realized gains on credit derivatives	28,800,000	61,000,000
Net credit derivative losses (paid and payable) recovered and recoverable	(85,700,000)	(25,600,000)
Total realized gains (losses) and other settlements on credit derivatives	(56,881,000)	35,427,000
Net unrealized gains and other settlements on credit derivatives	(633,758,000)	(271,636,000)
Net change in fair value of credit derivatives	(690,639,000)	(236,209,000)
Amount received on net par of terminated CDS exposures	200,000
Amount paid on net par of terminated CDS exposures		15,500,000
Net par of terminated CDS transactions	$ 200,000,000	$ 2,600,000,000