v2.4.1.9
Accumulated Other Comprehensive Income/(Loss) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]      
Balance at January 1 $ (750)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax $ (1,186)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax  
Other comprehensive income/(loss) before reclassifications (2)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax (1)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax  
Amounts reclassified from accumulated other comprehensive income/(loss) (458)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax [1] 437us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax [1]  
Net to-date other comprehensive income/(loss), net of taxes (460)us-gaap_OtherComprehensiveIncomeLossNetOfTax [2] 436us-gaap_OtherComprehensiveIncomeLossNetOfTax [2] (132)us-gaap_OtherComprehensiveIncomeLossNetOfTax [2]
Balance at December 31 (1,210)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax (750)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax (1,186)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Deferred taxes activity other comprehensive income/(loss) 291us-gaap_OtherComprehensiveIncomeLossTax (264)us-gaap_OtherComprehensiveIncomeLossTax 82us-gaap_OtherComprehensiveIncomeLossTax
Defined Benefit Plans [Member]      
Accumulated Other Comprehensive Income Loss [Line Items]      
Balance at January 1 (713)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 (1,149)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		  
Other comprehensive income/(loss) before reclassifications 10us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 (1)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		  
Amounts reclassified from accumulated other comprehensive income/(loss) (458)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1] 437us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 [1]  
Net to-date other comprehensive income/(loss), net of taxes (448)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 436us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		  
Balance at December 31 (1,161)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		 (713)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_PensionPlansDefinedBenefitMember		  
Foreign Currency Translation [Member]      
Accumulated Other Comprehensive Income Loss [Line Items]      
Balance at January 1 (37)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		 (36)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		  
Other comprehensive income/(loss) before reclassifications (12)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		 (1)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		  
Amounts reclassified from accumulated other comprehensive income/(loss) 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		  
Net to-date other comprehensive income/(loss), net of taxes (12)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		 (1)us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		  
Balance at December 31 (49)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		 (37)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= unp_ForeignCurrencyTranslationMember		  
Derivatives [Member]      
Accumulated Other Comprehensive Income Loss [Line Items]      
Balance at January 1 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		 (1)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		  
Other comprehensive income/(loss) before reclassifications 0us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		 1us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		  
Amounts reclassified from accumulated other comprehensive income/(loss) 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		 0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		  
Net to-date other comprehensive income/(loss), net of taxes 0us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		 1us-gaap_OtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		  
Balance at December 31 $ 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		 $ 0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ unp_AccumulatedOtherComprehensiveIncomeLossAxis
= us-gaap_DerivativeMember		  
[1] The accumulated other comprehensive income/(loss) reclassification components are 1) prior service cost/(benefit) and 2) net actuarial loss which are both included in the computation of net periodic pension cost. See Note 5 Retirement Plans for additional details.
[2] Net of deferred taxes of $291 million, ($264) million, and $82 million during 2014, 2013, and 2012, respectively.