Debt - short-term borrowings (Details)	Aug. 31, 2020 USD ($)	Aug. 31, 2020 GBP (£)	Aug. 31, 2019 USD ($)
Short-Term Borrowings [Abstract]
Total short-term debt	$ 3,538,000,000		$ 5,738,000,000
2.700% Unsecured Notes Due 2019
Short-Term Borrowings [Abstract]
Face amount	$ 8,000,000,000
Stated interest rate (as a percent)	2.70%	2.70%
Total short-term debt	$ 0		1,250,000,000
2.875% Unsecured Pound Sterling Notes Due 2020
Short-Term Borrowings [Abstract]
Face amount | £		£ 700,000,000
Stated interest rate (as a percent)	2.875%	2.875%
Total short-term debt	$ 533,000,000		0
Other
Short-Term Borrowings [Abstract]
Total short-term debt	418,000,000		464,000,000
Commercial Paper
Short-Term Borrowings [Abstract]
Total short-term debt	1,517,000,000		2,400,000,000
Credit facilities
Short-Term Borrowings [Abstract]
Total short-term debt	$ 1,071,000,000		$ 1,624,000,000