Stockholders' Equity - Stock-Option Activity and Related Share-Based Compensation Expense (Details) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jan. 31, 2019 USD ($) $ / shares shares
Number of Shares
Options outstanding, beginning balance (in shares) | shares	5,154
Options granted, number of shares (in shares) | shares	64
Options exercised, number of shares (in shares) | shares	(1,129)
Options canceled or expired, number of shares (in shares) | shares	(214)
Options outstanding, ending balance (in shares) | shares	3,875
Weighted Average Exercise Price Per Share
Weighted average exercise price per share, Beginning Balance (in dollars per share) | $ / shares	$ 120.26
Options granted, weighted average exercise price per share (in dollars per share) | $ / shares	225.47
Options exercised, weighted average exercise price per share (in dollars per share) | $ / shares	97.08
Options canceled or expired, weighted average exercise price per share (in dollars per share) | $ / shares	128.23
Weighted average exercise price per share, Ending Balance (in dollars per share) | $ / shares	$ 128.30
Exercisable (in shares) | shares	2,358
Exercisable, Weighted average exercise price per share (in dollars per share) | $ / shares	$ 109.10
Employee Stock Option
Weighted Average Exercise Price Per Share
Unrecognized compensation cost related to non-vested share based compensation expense | $	$ 45
Expected weighted average vesting period to recognize compensation cost related to share based compensation expense, in years	2 years 3 months 18 days