Investment in Affiliates and Related-Party Transactions - Schedule of Related Party Consolidated Balance Sheet Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Corporate Joint Venture | Conrail | Accounts Payable
Related Party Transaction [Line Items]
Payable to Affiliates	$ 50	$ 213
Corporate Joint Venture | Conrail | Long-term Debt | 1.31% CSX Promissory Note due December 2050
Related Party Transaction [Line Items]
Promissory note interest rate	1.31%
Promissory notes payable to Conrail subsidiary	$ 73
Corporate Joint Venture | Conrail | Long-term Debt | 1.31% CSXT Promissory Note due December 2050
Related Party Transaction [Line Items]
Promissory note interest rate	1.31%
Promissory notes payable to Conrail subsidiary	$ 368
Corporate Joint Venture | Conrail | Long-term Debt | 2.89% CSX Promissory Note due October 2044
Related Party Transaction [Line Items]
Promissory note interest rate		2.89%
Promissory notes payable to Conrail subsidiary		$ 73
Corporate Joint Venture | Conrail | Long-term Debt | 2.89% CSXT Promissory Note due October 2044
Related Party Transaction [Line Items]
Promissory note interest rate		2.89%
Promissory notes payable to Conrail subsidiary		$ 151
Affiliated Entity | TTX | Accounts Payable
Related Party Transaction [Line Items]
Payable to Affiliates	$ 40	$ 34