Document and Entity Information - shares	9 Months Ended
	May 31, 2017	Jun. 26, 2017
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	May 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
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		115,790,392