Debt (Carrying Value and Estimated Fair Value of Company's Long-term Debt) (Details) - USD ($) $ in Millions	8 Months Ended
May. 08, 2016	Aug. 30, 2015
Debt Instrument [Line Items]
Total long-term debt, carrying value	$ 5,114	$ 6,135
Less current portion, carrying value	1,193	1,283
Long-term debt, excluding current maturities	3,921	4,852
Total long-term debt, fair value	5,244	6,188
Less current portion, fair value	1,238	1,284
Long-term debt, excluding current portion, fair value	$ 4,006	4,904
0.65% Senior Notes Due December 2015
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.65%
Debt instrument, maturity date	Dec. 07, 2015
Total long-term debt, carrying value	$ 0	1,200
Total long-term debt, fair value	$ 0	1,201
5.5% Senior Notes Due March 2017
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	5.50%
Debt instrument, maturity date	Mar. 15, 2017
Total long-term debt, carrying value	$ 1,099	1,099
Total long-term debt, fair value	$ 1,144	1,171
1.125% Senior Notes Due December 2017
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.125%
Debt instrument, maturity date	Dec. 15, 2017
Total long-term debt, carrying value	$ 1,099	1,098
Total long-term debt, fair value	$ 1,105	1,097
1.7% Senior Notes Due December 2019
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.70%
Debt instrument, maturity date	Dec. 15, 2019
Total long-term debt, carrying value	$ 1,196	1,195
Total long-term debt, fair value	$ 1,219	1,186
1.75% Senior Notes Due February 2020
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.75%
Debt instrument, maturity date	Feb. 15, 2020
Total long-term debt, carrying value	$ 498	497
Total long-term debt, fair value	$ 508	494
2.25% Senior Notes Due February 2022
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.25%
Debt instrument, maturity date	Feb. 15, 2022
Total long-term debt, carrying value	$ 496	496
Total long-term debt, fair value	512	484
Other Long-term Debt
Debt Instrument [Line Items]
Total long-term debt, carrying value	726	550
Total long-term debt, fair value	$ 756	$ 555

Estimated fair value of the long-term debt current portion at the balance-sheet date.

No definition available.

Name:	cost_LongtermDebtFairValueCurrentMaturities
Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Estimated fair value of the non-current portion of long-term debt at the balance-sheet date.

+ References

No definition available.

+ Details

Name:	cost_LongtermDebtFairValueNonCurrent
Namespace Prefix:	cost_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ 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 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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 210.5-02.22)
-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 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

+ Details

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

- Definition

Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.5-02.19,20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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