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Financial instruments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Financial instruments (Details) - USD ($) $ in Millions	Feb. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019	Aug. 31, 2019
Foreign currency forwards \| Not Designated as Hedging Instrument \| Selling, general and administrative expenses
Derivatives, Fair Value [Line Items]
Gains and (losses) due to changes in fair value of derivative instruments	$ 13	$ (106)	$ (61)	$ (60)
Foreign currency forwards \| Not Designated as Hedging Instrument \| Other income
Derivatives, Fair Value [Line Items]
Gains and (losses) due to changes in fair value of derivative instruments	(7)	$ (6)	4	$ (2)
Other non-current assets \| Cross currency interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	851		851		$ 800
Fair value	42		42		73
Other current assets \| Cross currency interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	100		100
Fair value	1		1
Other current assets \| Foreign currency forwards \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	378		378		18
Fair value	7		7		1
Other current assets \| Foreign currency forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	2,873		2,873		3,485
Fair value	52		52		87
Other non-current liabilities \| Cross currency interest rate swaps \| Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	206		206
Fair value	4		4
Other current liabilities \| Foreign currency forwards \| Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional	1,265		1,265		707
Fair value	$ 9		$ 9		$ 6