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	6 Months Ended
	Jan. 31, 2019 USD ($) $ / shares shares
Number of Shares
Nonvested at beginning of period (in shares) | shares	7,383
Granted (in shares) | shares	314
Vested (in shares) | shares	(1,083)
Forfeited (in shares) | shares	(657)
Nonvested at end of period (in shares) | shares	5,957
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	211.12
Vested, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	104.75
Forfeited, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	95.18
Nonvested, Weighted Average Grant Date Fair Value, at end of period (in dollars per shares) | $ / shares	$ 144.57
Unrecognized compensation cost related to non-vested RSUs | $	$ 641
Weighted average vesting period, in years	2 years 6 months