Number of states or provinces within a country where Costco has warehouses

No definition available.

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

- Definition

Number of warehouses operated by country

+ References

No definition available.

+ Details

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

- Definition

Percentage of Ownership Interest Acquired

+ References

No definition available.

+ Details

Name:	cost_PercentageOfOwnershipInterestAcquired
Namespace Prefix:	cost_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	cost_SummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix:	cost_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate foreign currency transaction gain (loss) (both realized and unrealized) included in determining net income for the reporting period. Excludes foreign currency transactions designated as hedges of net investment in a foreign entity and intercompany foreign currency transactions that are of a long-term nature, when the entities to the transaction are consolidated, combined, or accounted for by the equity method in the reporting enterprise's financial statements. For certain enterprises, primarily banks, that are dealers in foreign exchange, foreign currency transaction gains (losses) may be disclosed as dealer gains (losses).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 52

-Paragraph 30

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30700-110894

+ Details

Name:	us-gaap_ForeignCurrencyTransactionGainLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the difference between (a) inventory at the lower of LIFO cost or market and (b) inventory at replacement cost or at the lower of some acceptable inventory accounting method (such as FIFO or average cost), or market. If material, reflects an excess of replacement or current cost over stated LIFO value parenthetically on the balance sheet or in a note to the financial statements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(c))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph c

-Article 5

+ Details

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

- Definition

The change in the inventory reserve representing the cumulative difference in cost between the first in, first out and the last in, first out inventory valuation methods, which change has been reflected in the statement of income during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section L

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6b)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6a)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6c)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Aggregate notional amount of foreign currency exchange rate derivatives. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

+ Details

Name:	us-gaap_NotionalAmountOfForeignCurrencyDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Summary of Significant Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended					1 Months Ended	6 Months Ended
	Feb. 17, 2013	Feb. 12, 2012	Feb. 17, 2013	Feb. 12, 2012	Sep. 02, 2012	Feb. 17, 2013 Forward Foreign Exchange Contracts	Sep. 02, 2012 Forward Foreign Exchange Contracts	Jul. 31, 2012 Costco Mexico	Feb. 17, 2013 UNITED STATES	Feb. 17, 2013 CANADA	Feb. 17, 2013 MEXICO	Feb. 17, 2013 UNITED KINGDOM	Feb. 17, 2013 JAPAN	Feb. 17, 2013 TAIWAN, PROVINCE OF CHINA	Feb. 17, 2013 KOREA, REPUBLIC OF	Feb. 17, 2013 AUSTRALIA
Summary Of Significant Accounting Policies [Line Items]
Number of warehouses operated			622						448	85	32	23	13	9	9	3
Number of regions in country									41
Purchase of equity interest								50.00%
Charge to merchandise costs	$ 9	$ 3	$ 11	$ 3
Inventory LIFO reserve	97		97		108
Notional amount of forward foreign - exchange derivative						275	284
Gain (loss) on foreign currency transaction	$ 6	$ 3	$ 15	$ 23