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Accounts Receivable, Net
9 Months Ended
Sep. 30, 2017
Receivables [Abstract]  
Accounts Receivable, Net
Accounts Receivable, Net
 
Accounts receivable, net consists of freight and other receivables, reduced by an allowance for bill adjustments and uncollectible accounts, based upon expected collectibility. At September 30, 2017 and December 31, 2016, $85 million and $88 million, respectively, of such allowances had been recorded.
 
At September 30, 2017 and December 31, 2016, $80 million and $88 million, respectively, of accounts receivable were greater than 90 days old.