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Investment Securities - Significant Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Determined to be Other-Than-Temporarily Impaired (Detail) (Available-for-Sale Securities [Member], Mortgage-Backed Securities Residential [Member])
 12 Months Ended
Dec. 31, 2014
Non-Agency Prime [Member] | Minimum [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 7.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime probability of default rates 3.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime loss severity rates 15.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Non-Agency Prime [Member] | Maximum [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 20.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime probability of default rates 7.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime loss severity rates 60.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Non-Agency Prime [Member] | Average [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 16.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime probability of default rates 4.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Lifetime loss severity rates 47.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyPrimeMember
Non-Agency Non-Prime [Member] | Minimum [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 1.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime probability of default rates 6.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime loss severity rates 40.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Non-Agency Non-Prime [Member] | Maximum [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 10.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime probability of default rates 14.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime loss severity rates 75.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Non-Agency Non-Prime [Member] | Average [Member]
  
Assumption Ranges for Available-for-Sale Non-Agency Mortgage-Backed Securities Other-Than- Temporarily Impaired [Line Items]  
Estimated lifetime prepayment rates 5.00%us-gaap_FairValueInputsPrepaymentRate
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime probability of default rates 9.00%us-gaap_FairValueInputsProbabilityOfDefault
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember
Lifetime loss severity rates 56.00%us-gaap_FairValueInputsLossSeverity
/ us-gaap_DebtSecurityAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_InformationByCategoryOfDebtSecurityAxis
= us-gaap_AvailableforsaleSecuritiesMember
/ us-gaap_RangeAxis
= us-gaap_WeightedAverageMember
/ us-gaap_UnderlyingAssetClassAxis
= usb_NonAgencyNonPrimeMember