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Accounts Receivable
 12 Months Ended
Dec. 31, 2020
Receivables [Abstract]  
Accounts receivable Accounts receivable
In millionsDecember 31,20202019
Freight$869 $1,008 
Non-freight211 233 
Gross accounts receivable1,080 1,241 
Allowance for credit losses
(26)(28)
Net accounts receivable$1,054 $1,213