Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ 1,354	$ 1,161	$ 2,332	$ 3,078
Unrealized gains on available-for-sale debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	0	1
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(22)	(33)
AOCI Attributable to Parent
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ (22)	$ (32)	$ (30)	$ (2)