Subsequent Events (Narrative) (Details) (Howell [Member], USD $) In Millions, unless otherwise specified	0 Months Ended
Oct. 17, 2013
Howell [Member]
Subsequent Event [Line Items]
Business Divestiture Disposal Price	$ 58.5

This represents disposal price of a business unit or asset during divestiture.

No definition available.

Name:	cmc_BusinessDivestitureDisposalPrice
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration