RedemptionPrice

No definition available.

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

- Definition

The redemption price, as a percentage of the principal amount, that the Company, upon certain events defined by the terms of the outstanding notes, will be required to make a purchase offer to redeem notes outstanding.

+ References

No definition available.

+ Details

Name:	cost_RedemptionPriceCertainEvents
Namespace Prefix:	cost_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

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

+ Details

Name:	us-gaap_DebtInstrumentFrequencyOfPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

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

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=cost_SeniorNotesTwoPointOneFivePercentDueMayEighteenTwentyTwentyOneDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cost_SeniorNotesTwoPointThreeZeroPercentDueMayEighteenTwentyTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cost_SeniorNotesTwoPointSevenFivePercentDueMayEighteenTwentyTwentyFourMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cost_SeniorNotesThreePercentDueMayEighteenTwentyTwentySevenMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events Subsequent Events (Details) - USD ($) $ in Millions	May 18, 2017	May 15, 2017	Dec. 07, 2012
Senior Notes [Member] \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 3,800
Redemption Price Certain Events	101.00%
1.125% Senior Notes Due December 2017
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage			1.125%
1.125% Senior Notes Due December 2017 \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount		$ 1,100
RedemptionPrice		$ 1,106
Debt Instrument, maturity date	Dec. 15, 2017
SeniorNotesTwoPointOneFivePercentDueMayEighteenTwentyTwentyOne [Domain] \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 1,000
Debt instrument, interest rate, stated percentage	2.15%
Debt Instrument, maturity date	May 18, 2021
Debt Instrument, Frequency of Periodic Payment	Interest is due semi-annually on May 18 and November 18, with the first payment due on November 18, 2017
SeniorNotesTwoPointThreeZeroPercentDueMayEighteenTwentyTwentyTwo [Member] \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 800
Debt instrument, interest rate, stated percentage	2.30%
Debt Instrument, Frequency of Periodic Payment	Interest is due semi-annually on May 18 and November 18, with the first payment due on November 18, 2017
SeniorNotesTwoPointSevenFivePercentDueMayEighteenTwentyTwentyFour [Member] [Member] \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 1,000
Debt instrument, interest rate, stated percentage	2.75%
Debt Instrument, Frequency of Periodic Payment	Interest is due semi-annually on May 18 and November 18, with the first payment due on November 18, 2017
SeniorNotesThreePercentDueMayEighteenTwentyTwentySeven[Member] [Member] \| Subsequent Event Type
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 1,000
Debt instrument, interest rate, stated percentage	3.00%
Debt Instrument, Frequency of Periodic Payment	Interest is due semi-annually on May 18 and November 18, with the first payment due on November 18, 2017