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Financial instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Financial instruments (Details) - USD ($) $ in Millions	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018	Aug. 31, 2018
Foreign currency forwards \| Not designated as hedges \| Selling, general and administrative expenses
Effect of Fair Value Hedges on Results of Operations [Abstract]
Gains and (losses) due to changes in fair value of derivative instruments	$ (106)	$ (164)	$ (60)	$ (183)
Foreign currency forwards \| Not designated as hedges \| Other income (expense)
Effect of Fair Value Hedges on Results of Operations [Abstract]
Gains and (losses) due to changes in fair value of derivative instruments	(6)	$ (1)	(2)	$ 33
Accrued expenses and other liabilities \| Interest rate swaps \| Designated as hedges
Derivatives, Fair Value [Line Items]
Notional					$ 250
Fair value					1
Accrued expenses and other liabilities \| Foreign currency forwards \| Not designated as hedges
Derivatives, Fair Value [Line Items]
Notional	2,807		2,807		825
Fair value	92		92		4
Other current assets \| Foreign currency forwards \| Designated as hedges
Derivatives, Fair Value [Line Items]
Notional					15
Fair value					0
Other current assets \| Foreign currency forwards \| Not designated as hedges
Derivatives, Fair Value [Line Items]
Notional	748		748		3,273
Fair value	3		3		$ 52
Other non-current liabilities \| Cross currency interest rate swap \| Designated as hedges
Derivatives, Fair Value [Line Items]
Notional	623		623
Fair value	$ 16		$ 16