Leases - changes in reserve for facility closings and related lease termination (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Changes in Reserve for Facility Closing and Related Lease Termination Charges [Roll Forward]
Balance at beginning of period	$ 466	$ 446
Provision for present value of non-cancellable lease payments on closed facilities	344	134
Assumptions about future sublease income, terminations and changes in interest rates	13	(34)
Interest accretion	37	27
Cash payments, net of sublease income	(142)	(107)
Balance at end of period	$ 718	$ 466