Revenues - Accounts Receivables, Net (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Accounts Receivable, net	$ 912	$ 986
Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables	716	790
Allowance for Credit Losses	(16)	(21)
Total Accounts Receivable, net	700	769
Non-Freight Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Receivables	224	226
Allowance for Credit Losses	(12)	(9)
Total Accounts Receivable, net	$ 212	$ 217