Fair value measurements (Details) - Recurring - USD ($) $ in Millions	Aug. 31, 2019	Aug. 31, 2018
Money Market Funds
Assets [Abstract]
Fair value of assets	$ 217	$ 227
Available-for-sale investments
Assets [Abstract]
Fair value of assets	5	1
Foreign currency forwards
Assets [Abstract]
Fair value of assets	88	52
Liabilities [Abstract]
Fair value of liabilities	6	4
Cross currency interest rate swap
Assets [Abstract]
Fair value of assets	73
Liabilities [Abstract]
Fair value of liabilities		1
Level 1 | Money Market Funds
Assets [Abstract]
Fair value of assets	217	227
Level 1 | Available-for-sale investments
Assets [Abstract]
Fair value of assets	5	1
Level 1 | Foreign currency forwards
Assets [Abstract]
Fair value of assets	0	0
Liabilities [Abstract]
Fair value of liabilities	0	0
Level 1 | Cross currency interest rate swap
Assets [Abstract]
Fair value of assets	0
Liabilities [Abstract]
Fair value of liabilities		0
Level 2 | Money Market Funds
Assets [Abstract]
Fair value of assets	0	0
Level 2 | Available-for-sale investments
Assets [Abstract]
Fair value of assets	0	0
Level 2 | Foreign currency forwards
Assets [Abstract]
Fair value of assets	88	52
Liabilities [Abstract]
Fair value of liabilities	6	4
Level 2 | Cross currency interest rate swap
Assets [Abstract]
Fair value of assets	73
Liabilities [Abstract]
Fair value of liabilities		1
Level 3 | Money Market Funds
Assets [Abstract]
Fair value of assets	0	0
Level 3 | Available-for-sale investments
Assets [Abstract]
Fair value of assets	0	0
Level 3 | Foreign currency forwards
Assets [Abstract]
Fair value of assets	0	0
Liabilities [Abstract]
Fair value of liabilities	0	0
Level 3 | Cross currency interest rate swap
Assets [Abstract]
Fair value of assets	$ 0
Liabilities [Abstract]
Fair value of liabilities		$ 0