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Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) (Derivative Mortgage Loans Commitments [Member])
Mar. 31, 2015
Minimum [Member]
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Expected loan close rate 23.00%usb_FairValueInputsExpectedMortgageLoanCloseRate
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Inherent MSR value (basis points per loan) 48.00%usb_FairValueInputsInherentMortgageServicingRightValue
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum [Member]
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Expected loan close rate 100.00%usb_FairValueInputsExpectedMortgageLoanCloseRate
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Inherent MSR value (basis points per loan) 204.00%usb_FairValueInputsInherentMortgageServicingRightValue
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Average [Member]
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Expected loan close rate 75.00%usb_FairValueInputsExpectedMortgageLoanCloseRate
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
Inherent MSR value (basis points per loan) 125.00%usb_FairValueInputsInherentMortgageServicingRightValue
/ us-gaap_FairValueByAssetClassAxis
= usb_DerivativeMortgageLoansCommitmentsMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember