Consolidation of Variable Interest Entities (Details) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011 Entities RatingCategories Y Statements Securities Policies D Companies Agreements Markets Subsidiaries Transactions FiscalQuarters Counterparties	Jun. 30, 2010	Jun. 30, 2011 RatingCategories Subsidiaries Securities Policies D Companies Agreements Markets Transactions FiscalQuarters Counterparties Entities	Jun. 30, 2010	Dec. 31, 2010	Dec. 31, 2009
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	762,300,000
Liabilities	4,037,600,000		4,037,600,000		4,264,200,000	762,700,000
Income statement impact of the consolidated VIEs
Net earned premiums	(18,300,000)	(15,600,000)	(37,400,000)	(21,600,000)
Net investment income	(700,000)		(700,000)
Net realized investment gains (losses)	200,000		500,000
Net change in fair value of financial guaranty variable interest entities:
Interest income	80,700,000	54,400,000	163,400,000	115,300,000
Interest expense	(36,900,000)	(20,600,000)	(76,500,000)	(44,700,000)
Net realized and unrealized gains (losses) on assets	(306,800,000)	(73,500,000)	(72,400,000)	(130,200,000)
Net realized and unrealized gains (losses) on liabilities with recourse	(5,400,000)	50,200,000	(41,300,000)	75,900,000
Net realized and unrealized gains (losses) on liabilities without recourse	86,500,000	8,600,000	(49,000,000)	14,400,000
Other income	6,900,000		20,900,000
Other expenses	(18,700,000)	(18,600,000)	(44,900,000)	(40,800,000)
Net change in fair value of financial guaranty variable interest entities	(193,676,000)	477,000	(99,771,000)	(10,113,000)
Loss and loss adjustment expenses	19,600,000	24,300,000	71,500,000	34,300,000
Total pre-tax effect on net income	(192,900,000)	9,200,000	(65,900,000)	2,600,000
Less: tax provision (benefit)	(67,500,000)	3,200,000	(23,000,000)	900,000
Total effect on net income	(125,400,000)	6,000,000	(42,900,000)	1,700,000
Total effect on shareholders' equity			(308,600,000)		(311,800,000)
Contractual Maturity
2012	8,000,000		8,000,000
2013	20,100,000		20,100,000
2014	166,400,000		166,400,000
Thereafter	3,772,000,000		3,772,000,000
Total	3,966,500,000		3,966,500,000
HELOCs
Consolidated FG VIEs
Assets	780,400,000		780,400,000		857,100,000
Liabilities	990,100,000		990,100,000		1,021,200,000
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	551,800,000		551,800,000		612,700,000
Option ARM
Consolidated FG VIEs
Assets	651,100,000		651,100,000		626,600,000
Liabilities	876,600,000		876,600,000		910,600,000
Alt-A second liens
Consolidated FG VIEs
Assets	760,600,000		760,600,000		747,400,000
Liabilities	793,400,000		793,400,000		822,000,000
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