Operating leases (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2017 USD ($) lease	May 31, 2016 USD ($)	May 31, 2017 USD ($) lease	May 31, 2016 USD ($)	Aug. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Interval period of renewal options			5 years
Proceeds from sale leaseback transactions			$ 436	$ 60
Charges related to facilities that were closed or relocated	$ 25	$ 16	$ 289	91
Number of leases | lease	70		70
Potential undiscounted future payments	$ 330		$ 330
Changes in reserve for facility closings and related lease termination charges [Roll Forward]
Balance at beginning of period			466	$ 446	$ 446
Provision for present value of non-cancellable lease payments on closed facilities			271		134
Assumptions about future sublease income, terminations and changes in interest rates			(7)		(34)
Interest accretion			25		27
Cash payments, net of sublease income			(100)		(107)
Balance at end of period	$ 655		$ 655		$ 466
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