Capital stock (Details) - USD ($) shares in Millions	12 Months Ended
	Aug. 31, 2021	Aug. 31, 2020	Aug. 31, 2019	Apr. 30, 2017
Equity, Class of Treasury Stock [Line Items]
Cost of stock repurchased	$ 110,000,000	$ 1,589,000,000	$ 4,160,000,000
Stock repurchased during current fiscal year, value	$ 110,000,000	$ 103,000,000	$ 339,000,000
Shares of common stock reserved for future issuances (in shares)	71
June 2018 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Share repurchase program, authorized maximum amount				$ 10,000,000,000
Shares repurchased during period (in shares)		30
Cost of stock repurchased		$ 1,500,000,000
Stock repurchase program, remaining authorized amount to be purchased	$ 2,000,000,000