Description of Business and Summary of Significant Accounting Policies - Schedule of shares used in the computation of basic and diluted net income per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Numerator:
Net income	$ (44)	$ 1,378	$ 189	$ 34	$ (38)	$ 1,186	$ 183	$ (2)	$ 1,557	$ 1,329	$ 985
Shares used in basic per share amounts:
Weighted average common shares outstanding (in shares)									260	256	257
Shares used in diluted per share amounts:
Weighted average common shares outstanding (in shares)									260	256	257
Dilutive common equivalent shares from stock options and restricted stock awards (in shares)									4	5	4
Dilutive weighted average common shares outstanding (in shares)									264	261	261
Basic and diluted net income per share:
Basic net income 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 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
Weighted average stock options and restricted stock units that have been excluded from dilutive common equivalent shares outstanding due to their anti-dilutive effect (in shares)									1	0	3