Income taxes - narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Operating Loss Carryforwards [Line Items]
Tax Cuts and Jobs Act, measurement period adjustment, income tax benefit			$ 247
Deferred tax assets, tax attributes	$ 7,467	$ 6,781
Income tax credits	97
Deferred tax assets operating loss carryforwards subject to expiration	7,100
Deferred tax assets operating loss carryforwards not subject to expiration	398
Valuation allowance	7,239	6,490
Income taxes paid	336	626	893
Unrecognized tax benefits	1,098	494	455	$ 456
Unrecognized tax benefits reported against deferred taxes	475
Unrecognized tax benefits reported against tax receivables	114
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	524	353	$ 311
Decrease in unrecognized tax benefits is reasonably possible	132
Accrued interest and penalties in income tax provision	84	58
Interest and penalties included in income tax expense	26	11
Unrecorded deferred tax liability for temporary differences related to foreign subsidiaries	118	124
Long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	594
U.S. Federal
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	670
State
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	75
Non-U.S.
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	6,600
United Kingdom
Operating Loss Carryforwards [Line Items]
Tax expense recorded from re-measurement of foreign deferred tax liabilities from changes in tax laws	$ 344	$ 139