Document and Entity Information	12 Months Ended
	Dec. 31, 2019
Document And Entity Information [Abstract]
Document Type	6-K
Document Period End Date	Dec. 31, 2019
Amendment Flag	false
Entity Registrant Name	CANADIAN NATIONAL RAILWAY CO
Entity Central Index Key	0000016868
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY