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Securities Available for Sale - Additional Information (Detail) (USD $)
Jun. 30, 2011
Dec. 31, 2010
Jun. 30, 2011
Trading Assets
Jun. 30, 2011
Mortgage-backed Securities, Issued by Private Enterprises
Other Than Temporarily Impaired Securities
Jun. 30, 2010
Mortgage-backed Securities, Issued by Private Enterprises
Other Than Temporarily Impaired Securities
Schedule of Available-for-sale Securities [Line Items]          
Fair value of pledged securities available for sale $ 4,500,000,000 $ 6,900,000,000      
Trading assets and cash equivalents, pledged     1,100,000,000    
Repurchase agreements 2,253,000,000 2,180,000,000 1,000,000,000    
Available for sale securities, fair market value       $ 193,000,000 $ 1,000,000