Income taxes - unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019
Reconciliation of Unrecognized Tax Benefits
Balance at beginning of year	$ 494	$ 455	$ 456
Gross increases related to tax positions in a prior period	229	60	33
Gross decreases related to tax positions in a prior period	(52)	(23)	(53)
Gross increases related to tax positions in the current period	446	9	26
Settlements with taxing authorities	(13)	(4)	(2)
Lapse of statute of limitations	(6)	(3)	(5)
Balance at end of year	$ 1,098	$ 494	$ 455