Operating leases (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2018 USD ($) lease	May 31, 2017 USD ($)	May 31, 2018 USD ($) lease	May 31, 2017 USD ($)	Aug. 31, 2017 USD ($)
Operating Leased Assets [Line Items]
Interval period of renewal options			5 years
Proceeds from sale-leaseback transactions			$ 0	$ 436
Charges related to facilities that were closed or relocated	$ 21	$ 25	$ 88	289
Number of leases | lease	71		71
Potential undiscounted future payments	$ 311		$ 311
Changes in reserve for facility closings and related lease termination charges [Roll Forward]
Balance at beginning of period			718	$ 466	$ 466
Provision for present value of non-cancellable lease payments on closed facilities			34		344
Changes in assumptions			7		13
Accretion expense			47		37
Other - non cash			30		0
Cash payments, net of sublease income			(159)		(142)
Balance at end of period	$ 677		$ 677		$ 718
Minimum
Operating Leased Assets [Line Items]
Initial term of operating lease			15 years
Maximum
Operating Leased Assets [Line Items]
Initial term of operating lease			25 years