Segment reporting - geographic data (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Aug. 31, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2020	Aug. 31, 2019	Aug. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales	$ 34,746	$ 34,631	$ 35,820	$ 34,339	$ 33,954	$ 34,591	$ 34,528	$ 33,793	$ 139,537	$ 136,866	$ 131,537
Total long-lived assets	13,342				13,478				13,342	13,478
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									2,467	2,597	2,254
Total long-lived assets	164				197				164	197
Reportable Geographical Components | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									107,701	104,532	98,392
Total long-lived assets	10,344				10,598				10,344	10,598
Reportable Geographical Components | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									12,099	12,729	13,297
Total long-lived assets	2,294				2,162				2,294	2,162
Reportable Geographical Components | Europe (excluding the United Kingdom)
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales									17,270	17,009	$ 17,594
Total long-lived assets	$ 540				$ 521				$ 540	$ 521