Stockholders' Equity - Restricted Stock Unit Activity and Related Share-Based Compensation Expense (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Summary of restricted stock unit activity
Nonvested, Number of shares, Beginning Balance (in shares)	8,636	9,039	8,916
Granted (in shares)	2,828	3,983	4,072
Unregistered restricted stock granted in connection with acquisitions (in shares)	75
Vested (in shares)	(2,960)	(3,121)	(2,392)
Forfeited (in shares)	(1,196)	(1,265)	(1,557)
Nonvested, Number of shares, Ending Balance (in shares)	7,383	8,636	9,039
Weighted Average Grant Date Fair Value
Nonvested, Weighted Average Grant Date Fair Value per share, Beginning Balance (in dollars per share)	$ 98.76	$ 82.30	$ 72.48
Granted (in dollars per share)	185.53	119.84	99.30
Unregistered restricted stock granted in connection with acquisitions (in dollars per share)	163.00
Vested (in dollars per share)	105.71	86.93	78.07
Forfeited (in dollars per share)	88.59	76.75	77.03
Nonvested, Weighted Average Grant Date Fair Value per share, Ending Balance (in dollars per share)	$ 131.50	$ 98.76	$ 82.30
Total tax benefit related to RSU share-based compensation expense	$ 199	$ 179	$ 86
Restricted Stock Units (RSUs)
Weighted Average Grant Date Fair Value
Total fair market value of shares vested	527	388	288
Share-based compensation for RSUs	326	274	230
Total tax benefit related to RSU share-based compensation expense	143	130	73
Cash tax benefits realized for tax deductions for RSUs	142	$ 130	$ 92
Unrecognized compensation cost	$ 820
Weighted average vesting period	2 years 9 months 18 days