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Properties - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 30, 2016
Property, Plant and Equipment [Line Items]      
Percentage of labor costs relating to the deconstruction of old track 20.00%    
Percentage of labor costs relating to the installation of new track 80.00%    
Percentage of assets depreciated under the group-life method 87.00%    
Total fixed assets $ 44,805 $ 44,324  
Abnormal gains and losses 154 18 $ 128
Impairment expense 24 25  
Total Equipment      
Property, Plant and Equipment [Line Items]      
Total fixed assets $ 11,092 11,606  
Life studies, frequency period 3 years    
Total Road      
Property, Plant and Equipment [Line Items]      
Total fixed assets $ 31,411 $ 30,091  
Life studies, frequency period 6 years