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Accounts Receivable
 12 Months Ended
Dec. 31, 2018
Receivables [Abstract]  
Accounts receivable
Accounts receivable
In millions
December 31,
2018

 
2017

Freight
$
974

 
$
828

Non-freight
221

 
172

Gross accounts receivable
1,195

 
1,000

Allowance for doubtful accounts
(26
)
 
(16
)
Net accounts receivable
$
1,169

 
$
984