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Fair Value of the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $)
In Millions
Sep. 30, 2011
Dec. 31, 2010
Sep. 30, 2010
Dec. 31, 2009
Fixed Rate Residential Mortgage
    
Servicing Assets at Fair Value [Line Items]    
Fair value at beginning of period$ 630$ 791$ 572$ 667
Fair value at end of period630791572667
Adjustable Rate Residential Mortgage
    
Servicing Assets at Fair Value [Line Items]    
Fair value at beginning of period32312732
Fair value at end of period$ 32$ 31$ 27$ 32