Revenues - Receivables (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 986	$ 1,010
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross Receivables	790	846
Allowance for Doubtful Accounts	(21)	(18)
Total Accounts Receivable, net	769	828
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross Receivables	226	190
Allowance for Doubtful Accounts	(9)	(8)
Total Accounts Receivable, net	$ 217	$ 182