v2.4.1.9
Stock Split (Details) (USD $)
0 Months Ended 12 Months Ended
May 27, 2014
Dec. 31, 2014
Dec. 31, 2013
Stock Split [Abstract]      
Stock split effective date   Jun. 06, 2014  
Stock split conversion ratio 2us-gaap_StockholdersEquityNoteStockSplitConversionRatio1    
Percent of dividend in stock 100.00%unp_PercentOfDividendInStock    
Stock split record date   May 27, 2014  
Common shares, par value $ 2.50us-gaap_CommonStockParOrStatedValuePerShare $ 2.50us-gaap_CommonStockParOrStatedValuePerShare $ 2.50us-gaap_CommonStockParOrStatedValuePerShare