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Accounts receivable (Tables)
12 Months Ended
Dec. 31, 2014
Notes To Financial Statements [Abstract]  
Accounts receivable
In millions December 31,20142013
Freight  $777$675
Non-freight    160 147
Gross accounts receivable   937 822
Allowance for doubtful accounts   (9) (7)
Net accounts receivable  $928$815