Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Jan. 31, 2014		Jul. 31, 2013
Available-for-sale debt securities:
Total available-for-sale securities	$ 1,666		$ 1,979
Liabilities:
Long-term debt	499		499
Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	517		489
Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	265		269
U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	71		69
Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Total Fair Value
Assets:
Cash equivalents, primarily money market funds	402		917
Available-for-sale debt securities:
Total available-for-sale securities	909		893
Total assets measured at fair value on a recurring basis	1,311		1,810
Liabilities:
Senior notes	560	[1]	560	[1]
Fair Value, Measurements, Recurring | Total Fair Value | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	517		489
Fair Value, Measurements, Recurring | Total Fair Value | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	265		269
Fair Value, Measurements, Recurring | Total Fair Value | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	71		69
Fair Value, Measurements, Recurring | Total Fair Value | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Total Fair Value | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Level 1
Assets:
Cash equivalents, primarily money market funds	402		917
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Total assets measured at fair value on a recurring basis	430		950
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring | Level 1 | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 1 | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Level 2
Assets:
Cash equivalents, primarily money market funds	0		0
Available-for-sale debt securities:
Total available-for-sale securities	853		827
Total assets measured at fair value on a recurring basis	853		827
Liabilities:
Senior notes	560	[1]	560	[1]
Fair Value, Measurements, Recurring | Level 2 | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	517		489
Fair Value, Measurements, Recurring | Level 2 | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	265		269
Fair Value, Measurements, Recurring | Level 2 | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	71		69
Fair Value, Measurements, Recurring | Level 2 | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 2 | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3
Assets:
Cash equivalents, primarily money market funds	0		0
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Total assets measured at fair value on a recurring basis	28		33
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring | Level 3 | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring | Level 3 | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	28		33
Fair Value, Measurements, Recurring | Level 3 | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	$ 0		$ 0

[1] Carrying value on our balance sheet at January 31, 2014 was $499 million and at July 31, 2013 was $499 million. See Note 6.