v2.4.1.9
Debt (Carrying Value and Estimated Fair Value of Company's Long Term Debt) (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Feb. 15, 2015
Aug. 31, 2014
Debt Instrument [Line Items]    
Total long-term debt, carrying value $ 5,030us-gaap_LongTermDebt $ 5,093us-gaap_LongTermDebt
Less current portion, carrying value 1,200us-gaap_LongTermDebtCurrent 0us-gaap_LongTermDebtCurrent
Long-term debt, excluding current maturities 3,830us-gaap_LongTermDebtNoncurrent 5,093us-gaap_LongTermDebtNoncurrent
Total long-term debt, fair value 5,143us-gaap_LongTermDebtFairValue 5,217us-gaap_LongTermDebtFairValue
Less current portion, fair value 1,203cost_LongtermDebtFairValueCurrentMaturities 0cost_LongtermDebtFairValueCurrentMaturities
Long-term debt, excluding current portion, fair value 3,940cost_LongtermDebtFairValueNonCurrent 5,217cost_LongtermDebtFairValueNonCurrent
0.65% Senior Notes due December 2015    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate (percent) 0.65%us-gaap_LongTermDebtPercentageBearingFixedInterestRate
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesZeroPointSixFiveZeroPercentDueDecemberSevenTwentyFifteenMember
 
Debt instrument, principal due date 2015-12  
Total long-term debt, carrying value 1,200us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesZeroPointSixFiveZeroPercentDueDecemberSevenTwentyFifteenMember
1,199us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesZeroPointSixFiveZeroPercentDueDecemberSevenTwentyFifteenMember
Total long-term debt, fair value 1,203us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesZeroPointSixFiveZeroPercentDueDecemberSevenTwentyFifteenMember
1,203us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesZeroPointSixFiveZeroPercentDueDecemberSevenTwentyFifteenMember
5.5% Senior Notes due March 2017    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate (percent) 5.50%us-gaap_LongTermDebtPercentageBearingFixedInterestRate
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesFivePointFivePercentDueMarchTwentySeventeenMember
 
Debt instrument, principal due date 2017-03  
Total long-term debt, carrying value 1,099us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesFivePointFivePercentDueMarchTwentySeventeenMember
1,099us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesFivePointFivePercentDueMarchTwentySeventeenMember
Total long-term debt, fair value 1,201us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesFivePointFivePercentDueMarchTwentySeventeenMember
1,223us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesFivePointFivePercentDueMarchTwentySeventeenMember
1.125% Senior Notes due December 2017    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate (percent) 1.125%us-gaap_LongTermDebtPercentageBearingFixedInterestRate
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointOneTwoFivePercentDueDecemberFifteenTwentySeventeenMember
 
Debt instrument, principal due date 2017-12  
Total long-term debt, carrying value 1,100us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointOneTwoFivePercentDueDecemberFifteenTwentySeventeenMember
1,100us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointOneTwoFivePercentDueDecemberFifteenTwentySeventeenMember
Total long-term debt, fair value 1,102us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointOneTwoFivePercentDueDecemberFifteenTwentySeventeenMember
1,095us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointOneTwoFivePercentDueDecemberFifteenTwentySeventeenMember
1.7% Senior Notes due December 2019    
Debt Instrument [Line Items]    
Debt instrument, stated interest rate (percent) 1.70%us-gaap_LongTermDebtPercentageBearingFixedInterestRate
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointSevenPercentDueDecemberTwentyNineteenMember
 
Debt instrument, principal due date 2019-12  
Total long-term debt, carrying value 1,198us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointSevenPercentDueDecemberTwentyNineteenMember
1,198us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointSevenPercentDueDecemberTwentyNineteenMember
Total long-term debt, fair value 1,194us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointSevenPercentDueDecemberTwentyNineteenMember
1,186us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_SeniorNotesOnePointSevenPercentDueDecemberTwentyNineteenMember
Other Long Term Debt    
Debt Instrument [Line Items]    
Total long-term debt, carrying value 433us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_OtherLongTermDebtMember
497us-gaap_LongTermDebt
/ us-gaap_LongtermDebtTypeAxis
= cost_OtherLongTermDebtMember
Total long-term debt, fair value $ 443us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_OtherLongTermDebtMember
$ 510us-gaap_LongTermDebtFairValue
/ us-gaap_LongtermDebtTypeAxis
= cost_OtherLongTermDebtMember