Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016	[1]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders’ equity	$ 3,749	$ 2,816	$ 1,699	$ 1,492
Unrealized gain (loss) on available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders’ equity	1	(2)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders’ equity	(37)	(34)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders’ equity	$ (36)	$ (36)	$ (22)	$ (32)

[1] The cumulative effect adjustment to retained earnings related to the adoption of ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” as of July 31, 2016 was $331 million.