Document and Entity Information - shares	6 Months Ended
	Feb. 28, 2019	Mar. 22, 2019
Document And Entity Information [Abstract]
Trading Symbol	CMC
Entity Registrant Name	COMMERCIAL METALS CO
Entity Central Index Key	0000022444
Document Type	10-Q
Document Period End Date	Feb. 28, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--08-31
Entity Tax Identification Number	750725338
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		117,921,070