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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Liability Activity [Abstract]      
Current portion $ 208us-gaap_LossContingencyAccrualCarryingValueCurrent   $ 249us-gaap_LossContingencyAccrualCarryingValueCurrent
Environmental [Abstract]      
Beginning balance at January 1 182us-gaap_AccrualForEnvironmentalLossContingencies 171us-gaap_AccrualForEnvironmentalLossContingencies  
Accruals 19us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses 6us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses  
Payments (10)us-gaap_AccrualForEnvironmentalLossContingenciesPayments (11)us-gaap_AccrualForEnvironmentalLossContingenciesPayments  
Ending balance at December 31 191us-gaap_AccrualForEnvironmentalLossContingencies 166us-gaap_AccrualForEnvironmentalLossContingencies  
Current portion, ending balance at December 31 58us-gaap_AccruedEnvironmentalLossContingenciesCurrent 52us-gaap_AccruedEnvironmentalLossContingenciesCurrent  
Personal Injury [Member]      
Liability Activity [Abstract]      
Beginning balance 335us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
294us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Current year accruals 23us-gaap_LossContingencyAccrualProvision
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
23us-gaap_LossContingencyAccrualProvision
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Changes in estimates for prior years (6)unp_LossContingencyAccrualCarryingValueChangeInPriorYears
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
(6)unp_LossContingencyAccrualCarryingValueChangeInPriorYears
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Payments (53)us-gaap_LossContingencyAccrualCarryingValuePayments
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
(17)us-gaap_LossContingencyAccrualCarryingValuePayments
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Ending balance 299us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
294us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Current portion 70us-gaap_LossContingencyAccrualCarryingValueCurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
78us-gaap_LossContingencyAccrualCarryingValueCurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= unp_PersonalInjuryMember
 
Asbestos [Member]      
Liability Activity [Abstract]      
Beginning balance 126us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
131us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
 
Payments (1)us-gaap_LossContingencyAccrualCarryingValuePayments
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
(2)us-gaap_LossContingencyAccrualCarryingValuePayments
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
 
Ending balance 125us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
129us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
 
Current portion $ 7us-gaap_LossContingencyAccrualCarryingValueCurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember
$ 9us-gaap_LossContingencyAccrualCarryingValueCurrent
/ us-gaap_LossContingenciesByNatureOfContingencyAxis
= us-gaap_AsbestosIssueMember