Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Millions	Apr. 30, 2020	Jul. 31, 2019
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	$ 3,371	$ 2,116
Available-for-sale debt securities	800	824
Fair value, measurements, recurring
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	2,157	1,647
Available-for-sale debt securities	800	824
Total assets measured at fair value on a recurring basis	2,957	2,471
Fair value, measurements, recurring | Level 1
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	2,157	1,647
Available-for-sale debt securities	0	0
Total assets measured at fair value on a recurring basis	2,157	1,647
Fair value, measurements, recurring | Level 2
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	0	0
Available-for-sale debt securities	800	824
Total assets measured at fair value on a recurring basis	800	824
Fair value, measurements, recurring | Municipal bonds
Assets:
Available-for-sale debt securities	8	5
Fair value, measurements, recurring | Municipal bonds | Level 1
Assets:
Available-for-sale debt securities	0	0
Fair value, measurements, recurring | Municipal bonds | Level 2
Assets:
Available-for-sale debt securities	8	5
Fair value, measurements, recurring | Corporate notes
Assets:
Available-for-sale debt securities	765	800
Fair value, measurements, recurring | Corporate notes | Level 1
Assets:
Available-for-sale debt securities	0	0
Fair value, measurements, recurring | Corporate notes | Level 2
Assets:
Available-for-sale debt securities	765	800
Fair value, measurements, recurring | U.S. agency securities
Assets:
Available-for-sale debt securities	27	19
Fair value, measurements, recurring | U.S. agency securities | Level 1
Assets:
Available-for-sale debt securities	0	0
Fair value, measurements, recurring | U.S. agency securities | Level 2
Assets:
Available-for-sale debt securities	$ 27	$ 19