Advance Limit as Percent of Eligible Trade Accounts Receivable Transferred

No definition available.

Name:	cmc_AdvanceLimitasPercentofEligibleTradeAccountsReceivableTransferred
Namespace Prefix:	cmc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents actual debt to capitalization ratio for an applicable date.

+ References

No definition available.

+ Details

Name:	cmc_DebttoCapitalizationRatio
Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents actual interest coverage ratio for an applicable date.

+ References

No definition available.

+ Details

Name:	cmc_InterestCoverageRatio
Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

It represents maximum debt to capitalization ratio stated in the debt covenant.

+ References

No definition available.

+ Details

Name:	cmc_MaximumDebttoCapitalizationRatio
Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

This represents minimum interest coverage ratio applicable to current period stated in debt covenant.

+ References

No definition available.

+ Details

Name:	cmc_MinimumInterestCoverageRatio
Namespace Prefix:	cmc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Periodic Payments, as Percent of Original Principal Amount

+ References

No definition available.

+ Details

Name:	cmc_PeriodicPaymentsasPercentofOriginalPrincipalAmount
Namespace Prefix:	cmc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Transfer of Accounts Receivable Program, Face Amount

+ References

No definition available.

+ Details

Name:	cmc_TransferofAccountsReceivableProgramFaceAmount
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Transfers of Accounts Receivable Outstanding

+ References

No definition available.

+ Details

Name:	cmc_TransfersofAccountsReceivableOutstanding
Namespace Prefix:	cmc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

+ Details

Name:	us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Weighted average interest rate of long-term debt outstanding calculated at point in time.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=cmc_CmcpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmc_U.S.ProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmc_U.S.ProgramwithConsentofCMCRVandProgramAdministrativeAgentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmc_PolandProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cmc_A300MillionNotesat5.375dueJuly2027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cmc_A350millionnotesat5.75dueApril2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cmc_A330MillionNotesAt4875DueMay2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MediumTermNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmc_A2022TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmc_A2018TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

CREDIT ARRANGEMENTS (Narrative) (Details)	9 Months Ended
CREDIT ARRANGEMENTS (Narrative) (Details)	May 31, 2019 USD ($)	May 31, 2019 PLN (zł)	Aug. 31, 2018 USD ($)	Jul. 31, 2017 USD ($)	May 31, 2013 USD ($)
CMCP
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	$ 71,700,000	zł 275,000,000.0
Revolving credit facility, amount drawn	0		$ 0
Stand by letters of credit outstanding amount	1,300,000		1,100,000
Revolving credit facility
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	350,000,000.0
Revolving credit facility, maximum borrowing capacity	600,000,000.0
Revolving credit facility, amount drawn	$ 0		0
Minimum interest coverage ratio	2.50
Maximum debt to capitalization ratio	0.60
Actual interest coverage ratio	5.53	5.53
Actual debt to capitalization ratio	0.47	0.47
Stand-by letters of credit
Debt Instrument [Line Items]
Revolving credit facility current borrowing capacity	$ 50,000,000.0
Stand by letters of credit outstanding amount	3,000,000.0		3,300,000
U.S. Program
Debt Instrument [Line Items]
Transfer of accounts receivable program limit	200,000,000.0
U.S. Program with Consent of CMCRV and Program Administrative Agent
Debt Instrument [Line Items]
Transfer of accounts receivable program limit	300,000,000.0
Poland Program
Debt Instrument [Line Items]
Transfer of accounts receivable program limit	$ 57,400,000	zł 220,000,000.0
Advance limit as percent of eligible trade accounts receivable transferred (percent)	90.00%	90.00%
Advances outstanding under transfer of receivables programs	$ 25,300,000		$ 12,100,000
2027 Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 300,000,000.0
Weighted average interest rate	5.375%	5.375%		5.375%
2026 Notes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 350,000,000.0
Weighted average interest rate	5.75%	5.75%
2023 Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 330,000,000.0
Weighted average interest rate	4.875%	4.875%			4.875%
Term Loans \| Revolving credit facility
Debt Instrument [Line Items]
Weighted average interest rate	4.115%	4.115%
Periodic payments, as percent of original principal amount (percent)	1.25%
Term Loans \| 2022 Term Loan \| Revolving credit facility
Debt Instrument [Line Items]
Debt instrument, face amount	$ 150,000,000.0
Term Loans \| 2018 Term Loan \| Revolving credit facility
Debt Instrument [Line Items]
Debt instrument, face amount	$ 180,000,000.0