v2.4.1.9
Accounts Receivable (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accounts Receivable Details [Abstract]      
Allowance for doubtful accounts $ 5,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent $ 1,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent  
Allowance for doubtful accounts - receivables not expected to be collected in one year 16,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableNoncurrent 22,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableNoncurrent  
Receivables Securitization Facility [Abstract]      
Total capacity to transfer undivided interests to investors under the receivables securitization facility 650,000,000unp_TotalTransferCapacityUndividedInterestsToInvestorsUnderReceivablesSecuritizationFacility 600,000,000unp_TotalTransferCapacityUndividedInterestsToInvestorsUnderReceivablesSecuritizationFacility  
Receivables securitization facility renewal date Jul. 29, 2014    
Receivables securitization facility duration 3 years 1 year  
Value of the outstanding undivided interest held by investors under the receivables securitization facility 400,000,000unp_ValueOutstandingUndividedInterestHeldByInvestorsUnderReceivablesSecuritizationFacility 0unp_ValueOutstandingUndividedInterestHeldByInvestorsUnderReceivablesSecuritizationFacility  
Accounts receivable supporting the undivided interest held by investors 1,200,000,000unp_AccountsReceivableSupportingUndividedInvestorHeldInterest 1,100,000,000unp_AccountsReceivableSupportingUndividedInvestorHeldInterest  
Cost of the receivables securitization facility - interest expense $ 4,000,000unp_ReceivablesSecuritizationFacilityInterestExpenseCost $ 5,000,000unp_ReceivablesSecuritizationFacilityInterestExpenseCost $ 3,000,000unp_ReceivablesSecuritizationFacilityInterestExpenseCost