Consolidation of Variable Interest Entities (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012 Entity days	Mar. 31, 2011	Dec. 31, 2011 Entity
Consolidated VIEs
Number of additional VIEs required to be consolidated	2
Net loss on consolidation	$ (6,100,000)
Consolidated VIEs
Number of FG VIEs	35		33
Assets	2,827,652,000		2,819,077,000
Liabilities	3,450,800,000		3,458,400,000
Total with recourse , Assets	1,742,100,000		1,757,600,000
Total with recourse , Liabilities	2,365,177,000		2,396,945,000
Without recourse, Assets	1,085,600,000		1,061,500,000
Without recourse, Liabilities	1,085,618,000		1,061,497,000
Total unpaid principal balance for the VIEs' assets that were over 90 days or more past due	1,048,100,000
Number of days VIEs' assets were past due (in days)	90
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' Assets	3,121,800,000
Change in the instrument specific credit risk of the VIEs' assets	85,900,000
Difference between the aggregate unpaid principal and aggregate fair value of the VIEs' liabilities	2,498,700,000
Gross par outstanding for FG VIEs liabilities with recourse	3,674,800,000		3,796,400,000
Contractual Maturity
2013	11,800,000
2014	114,100,000
Thereafter	3,548,900,000
Total	3,674,800,000		3,796,400,000
Net earned premiums	(17,000,000)	(19,100,000)
Net investment income	(3,200,000)	(300,000)
Net realized investment gains (losses)	1,400,000	300,000
Net change in fair value of financial guaranty variable interest entities:
Fair value gains (losses) on FG VIEs	(36,602,000)	119,601,000
Loss and LAE	3,200,000	50,700,000
Total pre-tax effect on net income	(52,200,000)	151,200,000
Less: tax provision (benefit)	(18,300,000)	53,000,000
Total effect on net income (loss)	(33,900,000)	98,200,000
Total (decrease) increase on shareholders' equity	(438,700,000)		(405,200,000)
HELOCs
Consolidated VIEs
Number of FG VIEs	8		8
Assets	572,200,000		572,900,000
Liabilities	898,700,000		907,900,000
Alt-A first lien
Consolidated VIEs
Number of FG VIEs	3		3
Assets	117,800,000		118,000,000
Liabilities	104,400,000		106,100,000
Option ARM
Consolidated VIEs
Number of FG VIEs	2		2
Assets	399,700,000		386,800,000
Liabilities	499,000,000		472,700,000
Subprime
Consolidated VIEs
Number of FG VIEs	7		5
Assets	43,000,000		49,700,000
Liabilities	230,300,000		244,700,000
Closed-end second lien
Consolidated VIEs
Number of FG VIEs	10		10
Assets	184,300,000		184,600,000
Liabilities	207,700,000		219,900,000
Automobile loans
Consolidated VIEs
Number of FG VIEs	4		4
Assets	126,900,000		155,800,000
Liabilities	126,900,000		155,800,000
Life insurance
Consolidated VIEs
Number of FG VIEs	1		1
Assets	298,200,000		289,800,000
Liabilities	$ 298,200,000		$ 289,800,000