Operating leases (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018	Aug. 31, 2018
Leases [Abstract]
Charges related to facilities that were closed or relocated	$ 29	$ 28	$ 42	$ 67
Changes in reserve for facility closings and related lease termination charges [Roll Forward]
Balance at beginning of period			964	$ 718	$ 718
Provision for present value of non-cancellable lease payments on closed facilities			1		52
Changes in assumptions			21		19
Accretion expense			20		58
Other - non cash			86		338
Cash payments, net of sublease income			(164)		(221)
Balance at end of period	$ 928		$ 928		$ 964