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Accounts Receivable, Net
12 Months Ended
Dec. 31, 2016
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 December 31, 2016 and 2015, $88 million and $74 million, respectively, of such allowances had been recorded.

At December 31, 2016 and 2015, $88 million and $50 million, respectively, of accounts receivable were greater than 90 days old.