Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Millions	Oct. 31, 2019	Jul. 31, 2019
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	$ 1,630	$ 2,116
Available-for-sale debt securities	825	824
Fair value, measurements, recurring
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	1,145	1,647
Available-for-sale debt securities	825	824
Total assets measured at fair value on a recurring basis	1,970	2,471
Fair value, measurements, recurring | Level 1
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	1,145	1,647
Available-for-sale debt securities	0	0
Total assets measured at fair value on a recurring basis	1,145	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	825	824
Total assets measured at fair value on a recurring basis	825	824
Fair value, measurements, recurring | Level 3
Assets:
Cash equivalents, primarily time deposits, savings deposit accounts, and money market funds	0	0
Available-for-sale debt securities	0	0
Total assets measured at fair value on a recurring basis	0	0
Fair value, measurements, recurring | Municipal bonds
Assets:
Available-for-sale debt securities	3	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	3	5
Fair value, measurements, recurring | Municipal bonds | Level 3
Assets:
Available-for-sale debt securities	0	0
Fair value, measurements, recurring | Corporate notes
Assets:
Available-for-sale debt securities	790	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	790	800
Fair value, measurements, recurring | Corporate notes | Level 3
Assets:
Available-for-sale debt securities	0	0
Fair value, measurements, recurring | U.S. agency securities
Assets:
Available-for-sale debt securities	32	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	32	19
Fair value, measurements, recurring | U.S. agency securities | Level 3
Assets:
Available-for-sale debt securities	$ 0	$ 0