Retirement benefits - Narrative (Details) $ in Millions	3 Months Ended
	Nov. 30, 2024 USD ($)	Nov. 23, 2023 member
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 435
Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions	410
Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions	$ 480
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Number of members | member		53,000