Income taxes - additional information (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Operating Loss Carryforwards [Line Items]
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		$ 523
U.S. statutory federal tax rate	21.00%	25.70%	35.00%
Tax Cuts and Jobs Act Of 2017, discrete tax benefit	$ 89
Tax Cuts and Jobs Act, measurement period adjustment, income tax expense (benefit)	(247)
Tax attributes	6,687	$ 2,351
Income tax credits	61
Deferred tax assets operating loss carryforwards subject to expiration	6,400
Deferred tax assets operating loss carryforwards not subject to expiration	248
Valuation allowance	6,638	2,226
Income taxes paid	900	600	$ 1,100
Unrecognized tax benefits	455	456	409	$ 269
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	311	331	$ 286
Decrease in unrecognized tax benefits is reasonably possible	16
Accrued Interest and penalties in income tax provision	47	87
Interest and penalties included in income tax expense	40
Unrecorded deferred tax liability for temporary differences related to foreign subsidiaries	127	$ 127
U.S. Federal
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	3,100
State
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	159
Non-U.S.
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	23,700
Long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 499