v2.4.1.9
Leases (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Future Minimum Lease Payments For Capital Leases [Abstract]      
Minimum capital lease payments - 2015 $ 253us-gaap_CapitalLeasesFutureMinimumPaymentsDueCurrent    
Minimum capital lease payments - 2016 249us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears    
Minimum capital lease payments - 2017 246us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears    
Minimum capital lease payments - 2018 224us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears    
Minimum capital lease payments - 2019 210us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears    
Minimum capital lease payments - later years 745us-gaap_CapitalLeasesFutureMinimumPaymentsDueThereafter    
Total minimum capital lease payments 1,927us-gaap_CapitalLeasesFutureMinimumPaymentsDue    
Capital lease payments - amount representing interest (407)us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments    
Capital lease payments - present value of minimum lease payments 1,520us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments    
Properties held under capital leases 2,454us-gaap_CapitalLeasedAssetsGross 2,486us-gaap_CapitalLeasedAssetsGross  
Properties held under capital leases - accumulated depreciation 1,210us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation 1,092us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation  
Lease payments related to locomotives 95.00%unp_CapitalLeasesFutureMinimumPaymentsDueLocomotives    
Future Minimum Lease Payments For Operating Leases [Abstract]      
Minimum operating lease payments - 2015 508us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent    
Minimum operating lease payments - 2016 484us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears    
Minimum operating lease payments - 2017 429us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears    
Minimum operating lease payments - 2018 356us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears    
Minimum operating lease payments - 2019 323us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears    
Minimum operating lease payments - later years 1,625us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter    
Total minimum operating lease payments 3,725us-gaap_OperatingLeasesFutureMinimumPaymentsDue    
Rent expense for operating leases with terms exceeding one month $ 593unp_RentExpenseForOperatingLeases $ 618unp_RentExpenseForOperatingLeases $ 631unp_RentExpenseForOperatingLeases