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, 2019	Jul. 31, 2018	Jul. 31, 2017
Summary of restricted stock unit activity
Nonvested, Number of shares, Beginning Balance (in shares)	7,383	8,636	9,039
Granted (in shares)	2,452	2,828	3,983
Unregistered restricted stock granted in connection with acquisitions (in shares)		75
Vested (in shares)	(3,123)	(2,960)	(3,121)
Forfeited (in shares)	(1,029)	(1,196)	(1,265)
Nonvested, Number of shares, Ending Balance (in shares)	5,683	7,383	8,636
Weighted Average Grant Date Fair Value
Nonvested, Weighted Average Grant Date Fair Value per share, Beginning Balance (in dollars per share)	$ 131.50	$ 98.76	$ 82.30
Granted (in dollars per share)	245.40	185.53	119.84
Unregistered restricted stock granted in connection with acquisitions (in dollars per share)		163.00
Vested (in dollars per share)	129.31	105.71	86.93
Forfeited (in dollars per share)	107.40	88.59	76.75
Nonvested, Weighted Average Grant Date Fair Value per share, Ending Balance (in dollars per share)	$ 186.22	$ 131.50	$ 98.76
Total tax benefit related to RSU share-based compensation expense	$ 200	$ 199	$ 179
Restricted Stock Units (RSUs)
Weighted Average Grant Date Fair Value
Total fair market value of shares vested	676	527	388
Share-based compensation for RSUs	351	326	274
Total tax benefit related to RSU share-based compensation expense	141	143	130
Cash tax benefits realized for tax deductions for RSUs	150	$ 142	$ 130
Unrecognized compensation cost	$ 961
Weighted average vesting period	3 years 1 month 6 days