New accounting pronouncements - Reconciliation of Effect of New Restricted Cash Accounting Guidance (Details) - USD ($) $ in Millions	3 Months Ended
	Nov. 30, 2018	Nov. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable	$ 1,097	$ 1,043
Accrued expenses and other liabilities	(341)	(216)
Other non-current assets and liabilities	(54)	13
Net cash provided by operating activities	460	1,003
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(6)	29
Net increase (decrease) in cash, cash equivalents and restricted cash	208	(1,424)
Cash, cash equivalents and restricted cash at beginning of period	975	3,496
Cash, cash equivalents and restricted cash at end of period	$ 1,183	2,072
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		1,011
Accrued expenses and other liabilities		(222)
Other non-current assets and liabilities		9
Net cash provided by operating activities		961
Effect of exchange rate changes on cash, cash equivalents and restricted cash		24
Net increase (decrease) in cash, cash equivalents and restricted cash		(1,471)
Cash, cash equivalents and restricted cash at beginning of period		3,301
Cash, cash equivalents and restricted cash at end of period		1,830
Accounting Standards Update 2016-18 | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		32
Accrued expenses and other liabilities		6
Other non-current assets and liabilities		4
Net cash provided by operating activities		42
Effect of exchange rate changes on cash, cash equivalents and restricted cash		5
Net increase (decrease) in cash, cash equivalents and restricted cash		47
Cash, cash equivalents and restricted cash at beginning of period		195
Cash, cash equivalents and restricted cash at end of period		$ 242