Income taxes - additional information (Details) - USD ($) $ in Millions		12 Months Ended
	May 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
Operating Loss Carryforwards [Line Items]
U.S. statutory federal tax rate			25.70%	35.00%	35.00%
Tax Cuts and Jobs Act Of 2017, discrete tax benefit			$ 307
Tax Cuts And Jobs Act Of 2017, provisional income tax expense (benefit)			(125)
Tax Cuts and Jobs Act, provisional income tax benefit due to remeasurement of deferred tax liabilities			648
Transition tax, provisional discrete tax expense	$ 679		523
Tax attributes			2,351	$ 555
Income tax credits			58
Deferred tax assets operating loss carryforwards subject to expiration			2,100
Deferred tax assets operating loss carryforwards not subject to expiration			227
Valuation allowance			2,226	408
Income taxes paid			600	1,100	$ 1,100
Unrecognized tax benefits			456	409	269	$ 261
Unrecognized tax benefits would favorably impact the effective tax rate if recognized			331	286	$ 237
Decrease in unrecognized tax benefits is reasonably possible			24
Accrued Interest and penalties in income tax provision			87	43
Interest and penalties included in income tax expense			44
Unrecorded deferred tax liability for temporary differences related to foreign subsidiaries			127	$ 142
U.S. Federal
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards			426
State
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards			43
Non-U.S.
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards			8,500
Long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits			482
Current liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits			$ 61
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
U.S. statutory federal tax rate		21.00%