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Accounts Receivable (Tables)
 12 Months Ended
Dec. 31, 2019
Receivables [Abstract]  
Accounts receivable
In millions
December 31,
2019

 
2018

Freight
$
1,008

 
$
974

Non-freight
233

 
221

Gross accounts receivable
1,241

 
1,195

Allowance for doubtful accounts
(28
)
 
(26
)
Net accounts receivable
$
1,213

 
$
1,169