Retirement benefits - change in plan assets (Details) - Pension Plan - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2020	Aug. 31, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value at beginning of year	$ 9,131	$ 8,676
Employer contributions	38	38
Benefits paid	(333)	(363)
Return on assets/other	(31)	1,333
Currency translation adjustments	810	(552)
Plan assets at fair value at end of year	$ 9,614	$ 9,131