Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total net revenue	$ 994	$ 3,272	$ 1,502	$ 1,016	$ 864	$ 2,912	$ 1,339	$ 910	$ 6,784	$ 6,025	$ 5,196
Cost of revenue	281	354	285	247	229	305	246	198
All other costs and expenses	866	1,134	984	779	835	1,006	899	747
Operating income	(153)	1,784	233	(10)	(200)	1,601	194	(35)	1,854	1,560	1,418
Net income	$ (44)	$ 1,378	$ 189	$ 34	$ (38)	$ 1,186	$ 183	$ (2)	$ 1,557	$ 1,329	$ 985
Basic net income (loss) per share (in dollars per share)	$ (0.17)	$ 5.30	$ 0.73	$ 0.13	$ (0.15)	$ 4.62	$ 0.72	$ (0.01)	$ 5.99	$ 5.18	$ 3.83
Diluted net income (loss) per share (in dollars per share)	$ (0.17)	$ 5.22	$ 0.72	$ 0.13	$ (0.15)	$ 4.53	$ 0.70	$ (0.01)	$ 5.89	$ 5.09	$ 3.78