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Loan Servicing (Residential Mortgage Servicing Rights Sensitivity) (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2012
Dec. 31, 2011
Jun. 30, 2011
Dec. 31, 2010
Jun. 30, 2012
Residential Mortgage Servicing Rights [Member]
Yr
Jun. 30, 2012
Fixed-Rate Residential Mortgage [Member]
Jun. 30, 2012
Adjustable Rate Residential Mortgage [Member]
Fair value of mortgage servicing rights $ 578 $ 563 $ 879 $ 830 $ 578    
Composition of residential mortgage loans serviced for others         100.00% 99.00% 1.00%
Weighted average life, in years         4.0    
Prepayment speed         19.30%    
Effect on fair value of a 10% increase, prepayment speed         (34)    
Effect on fair value of a 20% increase, prepayment speed         (63)    
Weighted average discount rate         10.80%    
Effect on fair value of a 10% increase, discount rate         (19)    
Effect on fair value of a 20% increase, discount rate         $ (37)