Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	$ 6,072,323,000	$ 5,968,712,000
Subrogation recoverable	(484,152,000)	(498,478,000)
Claim liability reported on Balance Sheet, before reinsurance	5,588,171,000	5,470,234,000
Claims [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	3,183,938,000	3,374,224,000
Subrogation recoverable	815,164,000	530,091,000
Claim liability reported on Balance Sheet, before reinsurance	3,999,102,000	3,904,315,000
Accrued Interest [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	237,955,000	0
Subrogation recoverable	70,135,000	0
Claim liability reported on Balance Sheet, before reinsurance	308,090,000	0
Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	4,542,406,000	4,895,277,000
Subrogation recoverable	234,998,000	135,610,000
Claim liability reported on Balance Sheet, before reinsurance	4,777,404,000	5,030,887,000
Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(1,415,979,000)	(1,797,805,000)
Subrogation recoverable	(1,604,449,000)	(1,164,179,000)
Claim liability reported on Balance Sheet, before reinsurance	(3,020,428,000)	(2,961,984,000)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(475,997,000)	(502,984,000)
Subrogation recoverable	0	0
Claim liability reported on Balance Sheet, before reinsurance	$ (475,997,000)	$ (502,984,000)