COVER PAGE - USD ($) $ in Billions	12 Months Ended
	Aug. 31, 2019	Oct. 22, 2019	Feb. 28, 2019
Cover page.
Entity Interactive Data Current	Yes
Security Exchange Name	NYSE
Title of 12(b) Security	Common Stock, $0.01 par value
City Area Code	214
Entity Address, Postal Zip Code	75039
Entity Incorporation, State or Country Code	DE
Entity File Number	1-4304
Document Annual Report	true
Trading Symbol	CMC
Entity Registrant Name	Commercial Metals Company
Entity Address, Address Line One	6565 N. MacArthur Blvd.
Entity Address, City or Town	Irving
Entity Address, State or Province	TX
Entity Central Index Key	0000022444
Document Type	10-K/A
Document Period End Date	Aug. 31, 2019
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--08-31
I.R.S. Employer Identification No.	75-0725338
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		117,934,611
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Minimum Percentage of Share Ownership Deemed Affiliates			10.00%
Entity Public Float			$ 1.9
Document Transition Report	false
Local Phone Number	689-4300