ACCOUNTS RECEIVABLE PROGRAMS (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Aug. 31, 2018	Aug. 31, 2017
Deferred purchase price receivables
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable	$ 2,932,379	$ 2,646,513
Collections	2,187,377	1,899,088
Exit from programs		(124,302)
International Marketing and Distribution \| Deferred purchase price receivables \| Domestic Country Sale of Accounts Receivable
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable		354,500
Collections		325,700
Exit from programs		83,700
Australia \| Deferred purchase price receivables
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable	0	16,914
Collections	0	13,537
Exit from programs		(33,917)
Australia \| Businesses Sold or Held for Sale
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Collections		3,700
Exit from programs		1,600
United States
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Advance payments outstanding	0
United States \| Deferred purchase price receivables
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable	2,396,780	2,251,118
Collections	1,818,781	1,635,701
Exit from programs		(90,385)
Poland
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Advance payments outstanding	12,100
Poland \| Deferred purchase price receivables
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable	535,599	378,481
Collections	368,596	249,850
Exit from programs		$ 0
Financial Institutions \| Deferred purchase price receivables
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Transfers of trade accounts receivable	$ 381,100

It represents actual amount of advance payment received on accounts receivable sold.

No definition available.

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

- Definition

It represents the amount of customer receivables returned or repurchased in the sales of accounts receivable program during the reporting period.

+ References

No definition available.

+ Details

Name:	cmc_Terminationofaccountsreceivables
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

It represents net transfer of customer accounts receivable during the period under the sale of accounts receivable programs.

+ References

No definition available.

+ Details

Name:	cmc_Transfersofaccountsreceivable
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cash Flows between a transferor and a transferee attributable to collections reinvested in revolving period transfers related to either a securitization, asset-backed financing arrangement, or similar transfer in which the transferor has continuing involvement with the transferred financial assets underlying the transaction (including, but not limited to, servicing, recourse, and restrictions on transferor's interests in the transferred financial assets).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=109247956&loc=d3e107207-111719

+ Details

Name:	us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromCollectionsReinvestedInRevolvingPeriodTransfers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_SecuritizationFinancialAssetForWhichTransferIsAccountedAsSaleLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=cmc_DeferredpurchasepricereceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=cmc_InternationalMarketingAndDistributionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cmc_DomesticCountrySaleOfAccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_AU
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=cmc_BusinessesSoldorHeldforSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_PL
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=cmc_FinancialInstitutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: