Consolidation of Variable Interest Entities (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011 Statements Entities Y RatingCategories Counterparties Securities Agreements Policies D Subsidiaries Markets Companies FiscalQuarters Transactions	Jun. 30, 2010	Jun. 30, 2011 RatingAgency RatingCategories Subsidiaries Counterparties Securities Agreements Policies D Markets Companies FiscalQuarters Entities Transactions	Jun. 30, 2010	Dec. 31, 2010
Consolidated VIEs
Expected reversal in fair value of gains (losses) in FG VIEs	$ 0		$ 0
Number of additional VIEs required to be consolidated	8		8
Total consolidated VIEs	35
Increase in FG VIEs' assets	254,800,000
Increase in FG VIEs' liabilities	305,200,000
Net loss on consolidation	95,300,000
Number of VIEs whose debt was fully paid off	2
Total unpaid principal balance for the VIEs' assets that were over 90 days or more past due	1,245,400,000		1,245,400,000		1,199,100,000
Change in the instrument specific credit risk of the VIEs' assets	861,900,000	44,100,000	478,700,000	95,400,000
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' liabilities	2,663,800,000		2,663,800,000		2,053,000,000
Number of quarters lag in financial results of consolidated VIEs	1		1
Correction of a misclassification					676,900,000
Consolidated FG VIEs
Assets	3,492,204,000		3,492,204,000		3,657,481,000
Liabilities	4,131,400,000		4,131,400,000		4,368,100,000
Income statement impact of the consolidated VIEs
Net earned premiums	(18,300,000)	(10,700,000)	(37,400,000)	(21,600,000)
Net investment income	(400,000)		(700,000)
Net realized investment gains (losses)	200,000		500,000
Net change in fair value of financial guaranty variable interest entities	(174,286,000)	(27,392,000)	(54,685,000)	(36,305,000)
Loss and loss adjustment expenses	16,900,000	10,100,000	67,600,000	34,200,000
Total pre-tax effect on net income	(175,900,000)	(28,000,000)	(24,700,000)	(23,700,000)
Less: tax provision (benefit)	(61,600,000)	(9,800,000)	(8,600,000)	(8,300,000)
Total effect on net income	(114,300,000)	(18,200,000)	(16,100,000)	(15,400,000)
Total effect on shareholders' equity			(342,600,000)		(371,400,000)
Contractual Maturity
2012	15,600,000		15,600,000
2013	24,400,000		24,400,000
2014	193,500,000		193,500,000
Thereafter	2,791,100,000		2,791,100,000
Total	3,024,600,000		3,024,600,000
HELOCs
Consolidated FG VIEs
Assets	780,400,000		780,400,000		857,100,000
Liabilities	1,092,100,000		1,092,100,000		1,126,100,000
Alt-A first lien
Consolidated FG VIEs
Assets	173,600,000		173,600,000
Liabilities	165,400,000		165,400,000
Subprime
Consolidated FG VIEs
Assets	466,200,000		466,200,000		528,700,000
Liabilities	555,600,000		555,600,000		616,500,000
Option ARM
Consolidated FG VIEs
Assets	651,100,000		651,100,000		626,600,000
Liabilities	850,900,000		850,900,000		909,400,000
Alt-A second liens
Consolidated FG VIEs
Assets	760,600,000		760,600,000		747,400,000
Liabilities	807,100,000		807,100,000		818,400,000
Automobile loans
Consolidated FG VIEs
Assets	333,300,000		333,300,000		486,800,000
Liabilities	333,300,000		333,300,000		486,800,000
Life insurance
Consolidated FG VIEs
Assets	327,000,000		327,000,000		304,800,000
Liabilities	327,000,000		327,000,000		304,800,000
Credit card loans
Consolidated FG VIEs
Assets					106,100,000
Liabilities					$ 106,100,000