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The maximum straight-time hours per year of the discretionary contribution under the employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Rate per hour of the discretionary contribution under employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Period of service of the employee required for employer to makes contributions in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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Namespace Prefix:	cost_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The maximum annual amount of the employer match in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

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Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of employer matching contribution on eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

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Namespace Prefix:	us-gaap-ebp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of contribution receivable from employer of participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 962
-SubTopic 325
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478873/962-325-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-05(a)(Schedule II))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 310
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478642/962-310-45-1

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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Name:	cost_EmployeeTypeAxis=cost_UnionMember
Namespace Prefix:
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