Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Millions	Apr. 30, 2018	Jul. 31, 2017
Available-for-sale debt securities:
Available-for-sale securities	$ 462	$ 463
Fair value, measurements, recurring | Total Fair Value
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	1,288	181
Time deposits	75	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	1,825	644
Fair value, measurements, recurring | Total Fair Value | Municipal bonds
Available-for-sale debt securities:
Available-for-sale securities	46	63
Fair value, measurements, recurring | Total Fair Value | Corporate notes
Available-for-sale debt securities:
Available-for-sale securities	394	382
Fair value, measurements, recurring | Total Fair Value | U.S. agency securities
Available-for-sale debt securities:
Available-for-sale securities	7	3
Fair value, measurements, recurring | Total Fair Value | Municipal auction rate securities
Available-for-sale debt securities:
Available-for-sale securities	15	15
Fair value, measurements, recurring | Total Fair Value | Available-for-sale securities
Available-for-sale debt securities:
Available-for-sale securities	462	463
Fair value, measurements, recurring | Level 1
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	1,288	181
Time deposits	0	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	1,288	181
Fair value, measurements, recurring | Level 1 | Municipal bonds
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 1 | Corporate notes
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 1 | U.S. agency securities
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 1 | Municipal auction rate securities
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 1 | Available-for-sale securities
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 2
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	0	0
Time deposits	75	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	522	448
Fair value, measurements, recurring | Level 2 | Municipal bonds
Available-for-sale debt securities:
Available-for-sale securities	46	63
Fair value, measurements, recurring | Level 2 | Corporate notes
Available-for-sale debt securities:
Available-for-sale securities	394	382
Fair value, measurements, recurring | Level 2 | U.S. agency securities
Available-for-sale debt securities:
Available-for-sale securities	7	3
Fair value, measurements, recurring | Level 2 | Municipal auction rate securities
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 2 | Available-for-sale securities
Available-for-sale debt securities:
Available-for-sale securities	447	448
Fair value, measurements, recurring | Level 3
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	0	0
Time deposits	0	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	15	15
Fair value, measurements, recurring | Level 3 | Municipal bonds
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 3 | Corporate notes
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 3 | U.S. agency securities
Available-for-sale debt securities:
Available-for-sale securities	0	0
Fair value, measurements, recurring | Level 3 | Municipal auction rate securities
Available-for-sale debt securities:
Available-for-sale securities	15	15
Fair value, measurements, recurring | Level 3 | Available-for-sale securities
Available-for-sale debt securities:
Available-for-sale securities	$ 15	$ 15