Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	$ 6,003,474,000	$ 5,968,712,000
Subrogation recoverable	(489,237,000)	(498,478,000)
Claim liability reported on Balance Sheet, before reinsurance	5,514,237,000	5,470,234,000
Claims [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	3,319,248,000	3,374,224,000
Subrogation recoverable	695,918,000	530,091,000
Claim liability reported on Balance Sheet, before reinsurance	4,015,166,000	3,904,315,000
Accrued Interest [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	289,865,000	0
Subrogation recoverable	69,955,000	0
Claim liability reported on Balance Sheet, before reinsurance	359,820,000	0
Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	4,324,634,000	4,895,277,000
Subrogation recoverable	138,738,000	135,610,000
Claim liability reported on Balance Sheet, before reinsurance	4,463,372,000	5,030,887,000
Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(1,488,476,000)	(1,797,805,000)
Subrogation recoverable	(1,393,848,000)	(1,164,179,000)
Claim liability reported on Balance Sheet, before reinsurance	(2,882,324,000)	(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	(441,797,000)	(502,984,000)
Subrogation recoverable	0	0
Claim liability reported on Balance Sheet, before reinsurance	$ (441,797,000)	$ (502,984,000)