Document and Entity Information - shares	6 Months Ended
	Feb. 28, 2018	Mar. 22, 2018
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, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--08-31
Entity Tax Identification Number	750725338
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		117,004,438