Income taxes - additional information (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Operating Loss Carryforwards [Line Items]
Tax attributes	$ 555	$ 373
Income tax credits	91
Deferred tax assets operating loss carryforwards subject to expiration	253
Deferred tax assets operating loss carryforwards not subject to expiration	302
Valuation allowance	408	305
Income taxes paid	1,100	1,100	$ 1,300
Unrecognized tax benefits	409	269	261	$ 193
Unrecognized tax benefits would favorably impact the effective tax rate if recognized	286	237	$ 227
Decrease in unrecognized tax benefits is reasonably possible	140
Accrued Interest and penalties in income tax provision	43	34
Interest and penalties included in income tax expense	9
Unrecorded deferred tax liability for temporary differences related to foreign subsidiaries	142	$ 116
U.S. Federal
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	423
State
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	212
Non-U.S.
Operating Loss Carryforwards [Line Items]
Deferred tax assets, operating loss carryforwards	1,160
Long-term liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	250
Current liabilities
Operating Loss Carryforwards [Line Items]
Unrecognized tax benefits	$ 202