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Composition of the Company's Loan Portfolio (Parenthetical) (Detail) (USD $)
In Millions
Jun. 30, 2011
Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans carried at fair value $ 449 $ 492
Commercial Portfolio Segment
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans carried at fair value 4 4
Commercial Portfolio Segment | Commercial and Industrial
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans carried at fair value 4 4
Residential Mortgage Loans
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans carried at fair value 445 488
Residential Mortgage Loans | Residential Nonguaranteed
   
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans carried at fair value $ 445 $ 488