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Loan Servicing (Residential Mortgage Servicing Rights Sensitivity) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Dec. 31, 2011
Mar. 31, 2011
Dec. 31, 2010
Mar. 31, 2012
Residential Mortgage Servicing Rights [Member]
Yr
Mar. 31, 2012
Fixed-Rate Residential Mortgage [Member]
Mar. 31, 2012
Adjustable Rate Residential Mortgage [Member]
Residential mortgage servicing rights at fair value $ 696 $ 563 $ 928 $ 830 $ 696    
Percentage of residential mortgage loans serviced for others         100.00% 99.00% 1.00%
Weighted average life, in years         4.5    
Prepayment speed         16.50%    
Effect on fair value of a 10% increase, prepayment speed         (39)    
Effect on fair value of a 20% increase, prepayment speed         (73)    
Weighted average discount rate         9.80%    
Effect on fair value of a 10% increase, discount rate         (25)    
Effect on fair value of a 20% increase, discount rate         $ (48)