Investment in Affiliates and Related-Party Transactions - Equity-method Investments in Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Related Party Transaction [Line Items]
Total	$ 1,985	$ 1,879	[1]
Corporate Joint Venture | Conrail
Related Party Transaction [Line Items]
Total		1,025		$ 982
Affiliated Entity
Related Party Transaction [Line Items]
Total		1,985		1,879
Affiliated Entity | TTX
Related Party Transaction [Line Items]
Total		796		743
Affiliated Entity | Other
Related Party Transaction [Line Items]
Total		$ 164		$ 154

[1] Certain prior year data has been reclassified to conform to the current presentation.