Revenues - Accounts Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 980	$ 986
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	756	790
Allowance for Doubtful Accounts	(16)	(21)
Total Accounts Receivable, net	740	769
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade Accounts Receivable, gross	250	226
Allowance for Doubtful Accounts	(10)	(9)
Total Accounts Receivable, net	$ 240	$ 217