| Cover | 12 Months Ended |
| Dec. 31, 2023 shares | |
| Document Information [Line Items] | |
| Document Type | 40-F |
| Amendment Flag | false |
| Document Registration Statement | false |
| Document Annual Report | true |
| Document Period End Date | Dec. 31, 2023 |
| Document Fiscal Period Focus | FY |
| Document Fiscal Year Focus | 2023 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 1-2413 |
| Entity Registrant Name | CANADIAN NATIONAL RAILWAY COMPANY |
| Entity Central Index Key | 0000016868 |
| Entity Primary SIC Number | 4011 |
| Entity Tax Identification Number | 98-0018609 |
| Entity Incorporation, State or Country Code | Z4 |
| Entity Address, Address Line One | 935 de La Gauchetiere Street West |
| Entity Address, City or Town | Montreal |
| Entity Address, State or Province | QC |
| Entity Address, Country | CA |
| Entity Address, Postal Zip Code | H3B 2M9 |
| City Area Code | 514 |
| Local Phone Number | 399-7091 |
| Title of 12(b) Security | Common shares |
| Trading Symbol | CNI |
| Security Exchange Name | NYSE |
| Annual Information Form | true |
| Audited Annual Financial Statements | false |
| Entity Current Reporting Status | Yes |
| Entity Interactive Data Current | Yes |
| Entity Emerging Growth Company | false |
| Entity Common Stock, Shares Outstanding | 643,833,245 |
| ICFR Auditor Attestation Flag | true |
| Auditor Name | KPMG LLP |
| Auditor Location | Montreal, Quebec, Canada |
| Auditor Firm ID | 85 |
| Business Contact [Member] | |
| Document Information [Line Items] | |
| Entity Address, Address Line One | 28 Liberty Street |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10005 |
| City Area Code | 212 |
| Local Phone Number | 894-8940 |
| Contact Personnel Name | C T Corporation System |
