Stockholders' Equity - Restricted Stock Unit Activity and Related Share-Based Compensation Expense (Details) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Oct. 31, 2017 USD ($) $ / shares shares
Number of Shares
Nonvested at beginning of period (in shares) | shares	8,636
Granted, Number of shares (in shares) | shares	226
Vested, Number of Shares (in shares) | shares	(681)
Forfeited, Number of Shares (in shares) | shares	(568)
Nonvested at end of period (in shares) | shares	7,613
Weighted Average Grant Date Fair Value
Nonvested, Weighted Average Grant Date Fair Value, at beginning of period (in dollars per shares) | $ / shares	$ 98.76
Granted, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	140.80
Vested, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	65.30
Forfeited, Weighted Average Grant Date Fair Value (in dollars per shares) | $ / shares	76.70
Nonvested, Weighted Average Grant Date Fair Value, at end of period (in dollars per shares) | $ / shares	$ 104.65
Restricted Stock Units (RSUs) [Member]
Weighted Average Grant Date Fair Value
Unrecognized compensation cost related to non-vested RSUs | $	$ 626
Weighted average vesting period, in years	2 years 2 months 12 days