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Commitments and Contingencies (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
location
Dec. 31, 2019
USD ($)
location
Commitments and Contingencies Disclosure [Abstract]    
Environmental liability $ 54,000,000 $ 56,000,000
Current environmental liability $ 15,000,000 $ 15,000,000
Known cleanup and remediation locations and projects | location 100 110
Number of sites - representative sample | location 17  
Liability associated with those sites $ 40,000,000  
Environmental locations representative sample liability payout period, in years 5 years  
Responsible locations with another party | location 11  
Self-insured injury/damage to third parties - and above, per occurrence $ 75,000,000  
Self-insured injury/damage to third party - up to 800,000,000  
Self-insured for bodily injury and property damage to third parties above, for specific perils 1,100,000,000  
Self-insured NS owned property - and above, per occurrence $ 75,000,000  
Self-insured, percentage of potential losses covered 85.00%  
Self-insured NS owned property - up to $ 275,000,000  
Purchase commitments $ 1,100,000,000