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Loans - Delinquency Ratio for Consumer Loan (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]    
Residential mortgage loan delinquency carried at lower of amortized cost or fair value less cost to sell $ 970 $ 803