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Accounts Receivable, Net	9 Months Ended
Accounts Receivable, Net	Sep. 30, 2015
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, 2015 and December 31, 2014, $64 million and $56 million, respectively, of such allowances had been recorded. At September 30, 2015 and December 31, 2014, $51 million and $35 million, respectively, of accounts receivable were greater than 90 days old.