Retirement benefits - Narrative (Details) $ in Millions	6 Months Ended
	Feb. 28, 2025 USD ($)	Nov. 23, 2023 member
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 441
Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions	410
Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions	$ 470
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Number of members | member		53,000