Name:	cost_EBPMinimumAgeOfParticipants
Namespace Prefix:	cost_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

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

Percentage of increase in eligible compensation contributed for participant automatically enrolled in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

No definition available.

Name:	cost_EmployeeBenefitPlanParticipantContributionAutomaticIncreaseDeferralRate
Namespace Prefix:	cost_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of minimum pretax annual compensation that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), is permitted to contribute to total pretax annual compensation.

No definition available.

Name:	cost_EmployeeBenefitPlanParticipantContributionPretaxMinimumAnnualCompensationToTotalCompensationPercentage
Namespace Prefix:	cost_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of eligible compensation contributed for participant automatically enrolled 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

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

Percentage of maximum pretax annual compensation that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), is permitted to contribute to total pretax annual compensation.