Fair Value Measurements (Details) - USD ($) $ in Millions		Apr. 30, 2016	Jul. 31, 2015
Liabilities:
Long-term debt		$ 500	$ 500
Short-term debt		500	0
Fair value, measurements, recurring | Estimate of fair value measurement
Assets:
Total cash equivalents		729	695
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis		1,243	1,774
Liabilities:
Senior notes	[1]	520	531
Fair value, measurements, recurring | Estimate of fair value measurement | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities		175	506
Fair value, measurements, recurring | Estimate of fair value measurement | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities		241	546
Fair value, measurements, recurring | Estimate of fair value measurement | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities		83	12
Fair value, measurements, recurring | Estimate of fair value measurement | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities		15	15
Fair value, measurements, recurring | Estimate of fair value measurement | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities		514	1,079
Fair value, measurements, recurring | Level 1
Assets:
Total cash equivalents		729	695
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis		729	695
Liabilities:
Senior notes	[1]	0	0
Fair value, measurements, recurring | Level 1 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 1 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 1 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 1 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 1 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 2
Assets:
Total cash equivalents		0	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis		499	1,064
Liabilities:
Senior notes	[1]	520	531
Fair value, measurements, recurring | Level 2 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities		175	506
Fair value, measurements, recurring | Level 2 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities		241	546
Fair value, measurements, recurring | Level 2 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities		83	12
Fair value, measurements, recurring | Level 2 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 2 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities		499	1,064
Fair value, measurements, recurring | Level 3
Assets:
Total cash equivalents		0	0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis		15	15
Liabilities:
Senior notes	[1]	0	0
Fair value, measurements, recurring | Level 3 | Municipal bonds
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 3 | Corporate notes
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 3 | U.S. agency securities
Available-for-sale debt securities:
Total available-for-sale securities		0	0
Fair value, measurements, recurring | Level 3 | Municipal auction rate securities
Available-for-sale debt securities:
Total available-for-sale securities		15	15
Fair value, measurements, recurring | Level 3 | Available-for-sale corporate equity securities
Available-for-sale debt securities:
Total available-for-sale securities		$ 15	$ 15

[1] Carrying value on our balance sheets at April 30, 2016 was $500 million and at July 31, 2015 was $500 million. See Note 5, “Current Liabilities – Short-Term Debt,” for more information.