| Document and Entity Information | Jun. 04, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | CSX CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000277948 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Jun. 4, 2021 |
| Entity Incorporation State Country Code | VA |
| Entity File Number | 1-08022 |
| Entity Tax Identification Number | 62-1051971 |
| Entity Address, Address Line One | 500 Water Street |
| Entity Address, Address Line Two | 15th Floor |
| Entity Address, City or Town | Jacksonville |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 32202 |
| City Area Code | (904) |
| Local Phone Number | 359-3200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $1 Par Value |
| Trading Symbol | CSX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
