Financial Guaranty Contracts Accounted for as Insurance (Details 13) (USD $)	6 Months Ended
	Jun. 30, 2011 RatingCategories Subsidiaries Securities Policies D Companies Agreements Markets Transactions FiscalQuarters Counterparties Entities	Dec. 31, 2010	Dec. 31, 2009
Components of Net Reserves (Salvage)
Loss and loss adjustment expense reserve	$ 518,145,000	$ 562,955,000	$ 289,500,000
Reinsurance recoverable on unpaid losses	(26,000,000)	(22,300,000)
Salvage and subrogation recoverable	(307,147,000)	(1,032,369,000)
Salvage and subrogation payable	35,200,000	129,400,000
Total	220,200,000	(362,300,000)
Number of the entity's insurance subsidiaries that results in increased claims due to downgrade	1
Minimum number of rating agency considered for triggering bank termination right	1
Financial Guaranty
Components of Net Reserves (Salvage)
Salvage and subrogation recoverable	(307,100,000)	(1,032,400,000)
Salvage and subrogation payable	35,200,000	129,400,000
Total	218,100,000	(364,400,000)
Other
Components of Net Reserves (Salvage)
Total	2,100,000	2,100,000
Variable rate demand obligations
Components of Net Reserves (Salvage)
Rate basis for bank bond rate	prime rate plus
Bank bond rate, low end of range (as a percent)	2.00%
Bank bond rate, high end of range (as a percent)	3.00%
Bank bond floor rate (as a percent)	7.00%
Threshold period of bonds held by bank for right of accelerated repayment, low end of range (in days)	90
Threshold period of bonds held by bank for right of accelerated repayment, high end of range (in days)	180
Accelerated repayment period for bank bonds, low end of range (in years)	5
Par of insured variable rate demand obligations issued by municipal obligors with internal ratings of BBB- or lower	$ 1,000,000,000
Accelerated repayment period for bank bonds, high end of range (in years)	10