New accounting pronouncements - Reconciliation of Effect of New Restricted Cash Accounting Guidance (Details) - USD ($) $ in Millions	6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable	$ 682	$ 599
Accrued expenses and other liabilities	(542)	188
Other non-current assets and liabilities	(104)	(52)
Net cash provided by operating activities	1,195	3,208
Effect of exchange rate changes on cash, cash equivalents and restricted cash	0	56
Net increase (decrease) in cash, cash equivalents and restricted cash	34	(1,508)
Cash, cash equivalents and restricted cash at beginning of period	975	3,496
Cash, cash equivalents and restricted cash at end of period	$ 1,009	1,988
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		592
Accrued expenses and other liabilities		182
Other non-current assets and liabilities		(72)
Net cash provided by operating activities		3,176
Effect of exchange rate changes on cash, cash equivalents and restricted cash		44
Net increase (decrease) in cash, cash equivalents and restricted cash		(1,552)
Cash, cash equivalents and restricted cash at beginning of period		3,301
Cash, cash equivalents and restricted cash at end of period		1,749
Accounting Standards Update 2016-18 [Member] | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade accounts payable		7
Accrued expenses and other liabilities		6
Other non-current assets and liabilities		20
Net cash provided by operating activities		32
Effect of exchange rate changes on cash, cash equivalents and restricted cash		12
Net increase (decrease) in cash, cash equivalents and restricted cash		44
Cash, cash equivalents and restricted cash at beginning of period		195
Cash, cash equivalents and restricted cash at end of period		$ 239