XML 36 R27.htm IDEA: XBRL DOCUMENT
v3.21.1

Summary of Significant Accounting Policies - Additional Information (Detail) | May 09, 2021 states warehouse
--- | ---
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 809
UNITED STATES |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 559
Number of states in country | states | 45
CANADA |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 105
MEXICO |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 39
UNITED KINGDOM |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 29
JAPAN |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 29
KOREA |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 16
TAIWAN |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 14
AUSTRALIA |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 12
SPAIN |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 3
ICELAND |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 1
FRANCE |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 1
CHINA |
Summary Of Significant Accounting Policies [Line Items] |
Number of warehouses operated | 1

X
- Definition Summary Of Significant Accounting Policies [Line Items] + References No definition available. + Details
Name: | cost_SummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix: | cost_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of states the entity operates in as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of stores. + References No definition available. + Details
Name: | us-gaap_NumberOfStores
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_MX
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_GB
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_JP
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_KR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_TW
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_AU
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_ES
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_IS
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_FR
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_CN
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |