Revenues - Accounts Receivable (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 860	$ 986
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	644	790
Allowance for Doubtful Accounts	(17)	(21)
Total Accounts Receivable, net	627	769
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	244	226
Allowance for Doubtful Accounts	(11)	(9)
Total Accounts Receivable, net	$ 233	$ 217