Revenues - Accounts Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 1,008	$ 986
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	802	790
Allowance for Doubtful Accounts	(20)	(21)
Total Accounts Receivable, net	782	769
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	235	226
Allowance for Doubtful Accounts	(9)	(9)
Total Accounts Receivable, net	$ 226	$ 217