Stockholders' Equity - Restricted Stock Unit Activity and Related Share-Based Compensation Expense (Details) - Restricted Stock Units (RSUs) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Oct. 31, 2018 USD ($) $ / shares shares
Number of Shares
Nonvested at beginning of period (in shares) | shares	7,383
Granted (in shares) | shares	148
Vested (in shares) | shares	(825)
Forfeited (in shares) | shares	(494)
Nonvested at end of period (in shares) | shares	6,212
Weighted Average Grant Date Fair Value
Nonvested, Weighted Average Grant Date Fair Value, at beginning of period (in dollars per shares) | $ / shares	$ 131.50
Granted, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	214.57
Vested, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	94.49
Forfeited, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	74.75
Nonvested, Weighted Average Grant Date Fair Value, at end of period (in dollars per shares) | $ / shares	$ 142.90
Unrecognized compensation cost related to non-vested RSUs | $	$ 712
Weighted average vesting period, in years	2 years 7 months 6 days