Income taxes - unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2023	Aug. 31, 2022	Aug. 31, 2021
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 1,110	$ 1,098	$ 494
Gross increases related to tax positions in a prior period	12	63	229
Gross decreases related to tax positions in a prior period	(19)	(51)	(52)
Gross increases related to tax positions in the current period	12	21	446
Settlements with taxing authorities	(7)	(19)	(13)
Lapse of statute of limitations	(2)	(2)	(6)
Balance at end of year	$ 1,106	$ 1,110	$ 1,098