Fair Value Measurements (Details) (USD $) | Apr. 30, 2015 | Jul. 31, 2014 |
In Millions, unless otherwise specified |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | $2,446 | | $2,234 | |
Liabilities: | | | | |
Long-term debt | 499 | | 499 | |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | | | | |
Assets: | | | | |
Cash equivalents, primarily money market funds | 770 | | 652 | |
Available-for-sale debt securities: | | | | |
Total assets measured at fair value on a recurring basis | 1,857 | | 1,882 | |
Liabilities: | | | | |
Senior notes | 542 | [1] | 556 | [1] |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Municipal bonds [Member] | | | | |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | 495 | | 701 | |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Corporate notes [Member] | | | | |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | 571 | | 466 | |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | U.S. agency securities [Member] | | | | |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | 0 | | 42 | |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Municipal auction rate securities [Member] | | | | |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | 21 | | 21 | |
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member] | Available-for-sale corporate equity securities [Member] | | | | |
Available-for-sale debt securities: | | | | |
Total available-for-sale securities | 1,087 | | 1,230 | |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | | | |
Assets: | | | | |
Cash equivalents, primarily money market funds | 770 | | 652 | |
Available-for-sale debt securities: | | | | |
Total assets measured at fair value on a recurring basis | 770 | | 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 | 1,066 | | 1,209 | |
Liabilities: | | | | |
Senior notes | 542 | [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 | 495 | | 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 | 571 | | 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 | 0 | | 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 | 1,066 | | 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 | |
|
[1] | Carrying value on our balance sheet at April 30, 2015 was $499 million and at July 31, 2014 was $499 million. See Note 6. |