Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Oct. 31, 2014		Jul. 31, 2014
Available-for-sale debt securities:
Total available-for-sale securities	$ 1,978		$ 2,234
Liabilities:
Long-term debt	499		499
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Cash equivalents, primarily money market funds	431		652
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	431		652
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents, primarily money market funds	0		0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	1,222		1,209
Liabilities:
Senior notes	550	[1]	556	[1]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	647		701
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	565		466
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	10		42
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	1,222		1,209
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents, primarily money market funds	0		0
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	21		21
Liabilities:
Senior notes	0	[1]	0	[1]
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	21		21
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	21		21
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents, primarily money market funds	431		652
Available-for-sale debt securities:
Total assets measured at fair value on a recurring basis	1,674		1,882
Liabilities:
Senior notes	550	[1]	556	[1]
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Municipal bonds [Member]
Available-for-sale debt securities:
Total available-for-sale securities	647		701
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Corporate notes [Member]
Available-for-sale debt securities:
Total available-for-sale securities	565		466
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | U.S. agency securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	10		42
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Municipal auction rate securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	21		21
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Available-for-sale corporate equity securities [Member]
Available-for-sale debt securities:
Total available-for-sale securities	$ 1,243		$ 1,230

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