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Properties (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Property, Plant and Equipment [Line Items]    
Cost $ 75,620 $ 75,420
Accumulated depreciation 21,558 21,259
Net book value 54,062 54,161
Land [Member]    
Property, Plant and Equipment [Line Items]    
Cost 5,245 5,246
Net book value 5,245 5,246
Road: Rail and Other Track Material [Member]    
Property, Plant and Equipment [Line Items]    
Cost 17,693 17,620
Accumulated depreciation 6,698 6,631
Net book value $ 10,995 $ 10,989
Estimated useful life 43 years 42 years
Road: Ties [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 11,121 $ 11,051
Accumulated depreciation 3,387 3,331
Net book value $ 7,734 $ 7,720
Estimated useful life 34 years 34 years
Road: Ballast [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 5,956 $ 5,926
Accumulated depreciation 1,785 1,753
Net book value $ 4,171 $ 4,173
Estimated useful life 34 years 34 years
Road: Other Roadway [Member]    
Property, Plant and Equipment [Line Items]    
Cost [1] $ 21,058 $ 21,030
Accumulated depreciation [1] 4,386 4,329
Net book value [1] $ 16,672 $ 16,701
Estimated useful life [1] 48 years 48 years
Total Road [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 55,828 $ 55,627
Accumulated depreciation 16,256 16,044
Net book value 39,572 39,583
Equipment: Locomotives [Member]    
Property, Plant and Equipment [Line Items]    
Cost 9,322 9,375
Accumulated depreciation 3,605 3,555
Net book value $ 5,717 $ 5,820
Estimated useful life 17 years 17 years
Equipment: Freight Cars [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 2,157 $ 2,118
Accumulated depreciation 801 789
Net book value $ 1,356 $ 1,329
Estimated useful life 25 years 25 years
Equipment: Work Equipment and Other [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 1,108 $ 1,107
Accumulated depreciation 361 351
Net book value $ 747 $ 756
Estimated useful life 18 years 18 years
Total Equipment [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 12,587 $ 12,600
Accumulated depreciation 4,767 4,695
Net book value 7,820 7,905
Technology and Other [Member]    
Property, Plant and Equipment [Line Items]    
Cost 1,211 1,199
Accumulated depreciation 535 520
Net book value $ 676 $ 679
Estimated useful life 12 years 13 years
Construction in Progress [Member]    
Property, Plant and Equipment [Line Items]    
Cost $ 749 $ 748
Net book value $ 749 $ 748
[1] Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.