Subsequent Events (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 28, 2012
Subsequent Events [Abstract]
Net proceeds from the termination of interest rate swap agreements	$ 53

Net proceeds from the termination of interest rate swap agreements.

No definition available.

Name:	cmc_Netproceedsfromterminationofinterestrateswaps
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant