Revenues - Accounts Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 1,101	$ 1,010
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	861	846
Allowance for Doubtful Accounts	(20)	(18)
Total Accounts Receivable, net	841	828
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	269	190
Allowance for Doubtful Accounts	(9)	(8)
Total Accounts Receivable, net	$ 260	$ 182