Supplemental financial information (Details) - USD ($)	3 Months Ended
	Nov. 30, 2017	Nov. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Effective tax rate	21.90%	17.30%
Discrete tax benefit from tax rate reduction	$ 0	$ 77,000,000
Cash paid for income taxes	45,000,000	63,000,000
Interest paid	$ 217,000,000	$ 246,000,000