Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total net revenue	$ 988	$ 2,925	$ 1,165	$ 886	$ 842	$ 2,541	$ 1,016	$ 778	$ 5,964	$ 5,177	$ 4,694
Cost of revenue	231	304	246	196	183	237	206	183
All other costs and expenses	838	1,006	899	747	669	860	788	656
Operating income from continuing operations	(81)	1,615	20	(57)	(10)	1,444	22	(61)	1,497	1,395	1,242
Net income	$ 49	$ 1,200	$ (21)	$ (17)	$ 24	$ 964	$ 13	$ (30)	$ 1,211	$ 971	$ 979
Basic net income (loss) per share (in dollars per share)	$ 0.19	$ 4.68	$ (0.08)	$ (0.07)	$ 0.09	$ 3.76	$ 0.05	$ (0.12)	$ 4.72	$ 3.78	$ 3.73
Diluted net income (loss) per share (in dollars per share)	$ 0.18	$ 4.59	$ (0.08)	$ (0.07)	$ 0.09	$ 3.70	$ 0.05	$ (0.12)	$ 4.64	$ 3.72	$ 3.69