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Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Transfers and Servicing of Financial Assets [Abstract]  
Gain related to excess servicing rights sold $ 44usb_GainRelatedToExcessServicingRightsSold