New accounting pronouncements - Reconciliation of Effect of New Restricted Cash Accounting Guidance (Details) - USD ($) $ in Millions	9 Months Ended
	May 31, 2019	May 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable	$ 662	$ 675
Accrued expenses and other liabilities	(642)	16
Other non-current assets and liabilities	(171)	(110)
Net cash provided by operating activities	3,215	5,446
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(12)	27
Net increase (decrease) in cash, cash equivalents and restricted cash	62	(1,422)
Cash, cash equivalents and restricted cash at beginning of period	975	3,496
Cash, cash equivalents and restricted cash at end of period	$ 1,038	2,074
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		627
Accrued expenses and other liabilities		10
Other non-current assets and liabilities		(117)
Net cash provided by operating activities		5,385
Effect of exchange rate changes on cash, cash equivalents and restricted cash		26
Net increase (decrease) in cash, cash equivalents and restricted cash		(1,483)
Cash, cash equivalents and restricted cash at beginning of period		3,301
Cash, cash equivalents and restricted cash at end of period		1,818
Accounting standards update 2016-18 | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		48
Accrued expenses and other liabilities		6
Other non-current assets and liabilities		7
Net cash provided by operating activities		61
Effect of exchange rate changes on cash, cash equivalents and restricted cash		1
Net increase (decrease) in cash, cash equivalents and restricted cash		61
Cash, cash equivalents and restricted cash at beginning of period		195
Cash, cash equivalents and restricted cash at end of period		$ 256