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Income Taxes - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Operating Loss Carryforwards [Line Items]      
Loss carry-forwards exceed     $ 3,400,000,000
Percentage of payment to IRS, Tier C 12.50%    
Percentage of payment to IRS, Tier D 17.50%    
Unrecognized tax benefits 96,900,000 96,900,000 23,050,000
Interest expense recognized 0 0  
Interest accrued 0 0  
Valuation allowance 3,256,423,000 3,169,402,000  
Net operating loss carryforwards exceeds 3,400,000   3,400,000,000
Expiration period Expiring in 2029 and will fully expire in 2034    
Operating tax carryforward expiration year start 2029    
Operating tax carryforward expiration year end 2034    
U. S. federal net operating tax [Member]
     
Operating Loss Carryforwards [Line Items]      
Net operating tax carryforward 7,287,114,000    
Ambac Assurance [Member]
     
Operating Loss Carryforwards [Line Items]      
Potential payment to outstanding disputes 100,000,000    
Ambac [Member]
     
Operating Loss Carryforwards [Line Items]      
Potential payment to outstanding disputes $ 1,900,000