v2.4.1.9
Share Repurchase Program (Details) (USD $)
1 Months Ended 3 Months Ended 12 Months Ended
Feb. 06, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jan. 01, 2014
Shares Repurchased [Abstract]                          
BOD authorized                         120,000,000us-gaap_StockRepurchaseProgramNumberOfSharesAuthorizedToBeRepurchased
Stock repurchase program expiration date                   Dec. 31, 2017      
Share repurchases (Note 19) (shares) 2,800,000us-gaap_TreasuryStockSharesAcquired 7,736,400us-gaap_TreasuryStockSharesAcquired 8,347,000us-gaap_TreasuryStockSharesAcquired 8,320,000us-gaap_TreasuryStockSharesAcquired 7,640,000us-gaap_TreasuryStockSharesAcquired 9,858,110us-gaap_TreasuryStockSharesAcquired 7,333,788us-gaap_TreasuryStockSharesAcquired 6,122,940us-gaap_TreasuryStockSharesAcquired 5,762,800us-gaap_TreasuryStockSharesAcquired 32,043,400us-gaap_TreasuryStockSharesAcquired 29,077,638us-gaap_TreasuryStockSharesAcquired    
Average purchase price   $ 113.77us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 102.54us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 96.84us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 89.43us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 79.68us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 78.39us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 75.71us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 68.29us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 100.65us-gaap_TreasuryStockAcquiredAverageCostPerShare $ 76.26us-gaap_TreasuryStockAcquiredAverageCostPerShare    
Remaining number of shares yet to be repurchased   87,956,600us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased               87,956,600us-gaap_StockRepurchaseProgramRemainingNumberOfSharesAuthorizedToBeRepurchased      
Aggregate cost $ 327,000,000us-gaap_TreasuryStockValueAcquiredCostMethod                 $ 3,225,000,000us-gaap_TreasuryStockValueAcquiredCostMethod $ 2,218,000,000us-gaap_TreasuryStockValueAcquiredCostMethod $ 1,474,000,000us-gaap_TreasuryStockValueAcquiredCostMethod  
Stock repurchased since inception                   $ 12,600,000,000unp_StockRepurchasedSinceInceptionValue