Depreciation and amortization (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2017	May 31, 2016
Depreciation, Depletion and Amortization [Abstract]
Depreciation expense	$ 334	$ 353	$ 1,000	$ 997
Intangible asset and other amortization	79	94	244	274
Total depreciation and amortization expense	$ 413	$ 447	$ 1,244	$ 1,271