Revenues - Schedule of Accounts Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 1,045	$ 970
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables gross	855	810
Allowance for Doubtful Accounts	(18)	(17)
Total Accounts Receivable, net	837	793
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables gross	218	186
Allowance for Doubtful Accounts	(10)	(9)
Total Accounts Receivable, net	$ 208	$ 177