Stockholders' Equity - Stock-Option Activity and Related Share-Based Compensation Expense (Details) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Oct. 31, 2018 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	(890)
Options canceled or expired, number of shares (in shares) | shares	(169)
Options outstanding, ending balance (in shares) | shares	4,159
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	97.90
Options canceled or expired, weighted average exercise price per share (in dollars per share) | $ / shares	128.19
Weighted average exercise price per share, Ending Balance (in dollars per share) | $ / shares	$ 126.33
Exercisable (in shares) | shares	2,331
Exercisable, Weighted average exercise price per share (in dollars per share) | $ / shares	$ 105.63
Employee Stock Option
Weighted Average Exercise Price Per Share
Unrecognized compensation cost related to non-vested share based compensation expense | $	$ 54
Expected weighted average vesting period to recognize compensation cost related to share based compensation expense, in years	2 years 4 months 24 days