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Properties (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2020
USD ($)
item
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Property, Plant and Equipment [Line Items]      
Cost $ 75,420 $ 74,246  
Accumulated depreciation 21,259 20,330  
Net book value $ 54,161 53,916  
Depreciable asset classes description We currently have more than 60 depreciable asset classes, and we may increase or decrease the number of asset classes due to changes in technology, asset strategies, or other factors.    
Total repairs and maintenance expense $ 2,000 2,300 $ 2,500
Non-cash impairment charge 278    
Land [Member]      
Property, Plant and Equipment [Line Items]      
Cost 5,246 5,276  
Accumulated depreciation  
Net book value 5,246 5,276  
Road: Rail and Other Track Material [Member]      
Property, Plant and Equipment [Line Items]      
Cost 17,620 17,178  
Accumulated depreciation 6,631 6,381  
Net book value $ 10,989 $ 10,797  
Estimated useful life 42 years 42 years  
Road: Ties [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 11,051 $ 10,693  
Accumulated depreciation 3,331 3,186  
Net book value $ 7,720 $ 7,507  
Estimated useful life 34 years 34 years  
Road: Ballast [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 5,926 $ 5,752  
Accumulated depreciation 1,753 1,669  
Net book value $ 4,173 $ 4,083  
Estimated useful life 34 years 34 years  
Road: Other Roadway [Member]      
Property, Plant and Equipment [Line Items]      
Cost [1] $ 21,030 $ 20,331  
Accumulated depreciation [1] 4,329 4,056  
Net book value [1] $ 16,701 $ 16,275  
Estimated useful life [1] 48 years 48 years  
Total Road [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 55,627 $ 53,954  
Accumulated depreciation 16,044 15,292  
Net book value $ 39,583 38,662  
Term of Depreciation Studies 6 years    
Equipment: Locomotives [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 9,375 9,467  
Accumulated depreciation 3,555 3,434  
Net book value $ 5,820 $ 6,033  
Estimated useful life 17 years 18 years  
Equipment: Freight Cars [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 2,118 $ 2,083  
Accumulated depreciation 789 779  
Net book value $ 1,329 $ 1,304  
Estimated useful life 25 years 25 years  
Equipment: Work Equipment and Other [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 1,107 $ 1,081  
Accumulated depreciation 351 322  
Net book value $ 756 $ 759  
Estimated useful life 18 years 18 years  
Total Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 12,600 $ 12,631  
Accumulated depreciation 4,695 4,535  
Net book value $ 7,905 8,096  
Term of Depreciation Studies 3 years    
Technology and Other [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 1,199 1,136  
Accumulated depreciation 520 503  
Net book value $ 679 $ 633  
Estimated useful life 13 years 12 years  
Construction in Progress [Member]      
Property, Plant and Equipment [Line Items]      
Cost $ 748 $ 1,249  
Accumulated depreciation  
Net book value $ 748 $ 1,249  
Minimum [Member]      
Property, Plant and Equipment [Line Items]      
Number of depreciable asset classes | item 60    
[1] Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.