Retirement benefits - change in plan assets (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2023	Aug. 31, 2022
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value at beginning of year	$ 6,603	$ 10,475
Employer contributions	40	45
Benefits paid	(286)	(304)
Return on assets	(1,275)	(2,477)
Currency translation adjustments	511	(1,136)
Plan assets at fair value at end of year	$ 5,594	$ 6,603