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Trading Assets and Liabilities - Trading Assets and Liabilities (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Security
Dec. 31, 2011
Security
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Trading assets $ 38,322 $ 38,800
Foreign bonds issued by the governments of Greece, Ireland, Italy, Portugal or Spain 0 0
Collateralized Mortgage Backed Securities [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Trading assets 13 10
Collateralized Mortgage Backed Securities [Member] | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Trading assets $ 218 $ 14