Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Millions	Oct. 31, 2018	Jul. 31, 2018
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	$ 1,084	$ 1,464
Available-for-sale debt securities:
Available-for-sale debt securities	448	452
Fair value, measurements, recurring
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	512	1,143
Available-for-sale debt securities:
Available-for-sale debt securities	448	452
Assets, Fair Value Disclosure	960	1,595
Fair value, measurements, recurring \| Level 1
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	512	1,143
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
Assets, Fair Value Disclosure	512	1,143
Fair value, measurements, recurring \| Level 2
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	0	0
Available-for-sale debt securities:
Available-for-sale debt securities	448	452
Assets, Fair Value Disclosure	448	452
Fair value, measurements, recurring \| Level 3
Assets:
Cash equivalents, primarily money market funds and savings deposit accounts	0	0
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
Assets, Fair Value Disclosure	0	0
Municipal bonds
Available-for-sale debt securities:
Available-for-sale debt securities	13	31
Municipal bonds \| Fair value, measurements, recurring
Available-for-sale debt securities:
Available-for-sale debt securities	13	31
Municipal bonds \| Fair value, measurements, recurring \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
Municipal bonds \| Fair value, measurements, recurring \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	13	31
Municipal bonds \| Fair value, measurements, recurring \| Level 3
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
Corporate notes
Available-for-sale debt securities:
Available-for-sale debt securities	420	412
Corporate notes \| Fair value, measurements, recurring
Available-for-sale debt securities:
Available-for-sale debt securities	420	412
Corporate notes \| Fair value, measurements, recurring \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
Corporate notes \| Fair value, measurements, recurring \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	420	412
Corporate notes \| Fair value, measurements, recurring \| Level 3
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
U.S. agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	15	9
U.S. agency securities \| Fair value, measurements, recurring
Available-for-sale debt securities:
Available-for-sale debt securities	15	9
U.S. agency securities \| Fair value, measurements, recurring \| Level 1
Available-for-sale debt securities:
Available-for-sale debt securities	0	0
U.S. agency securities \| Fair value, measurements, recurring \| Level 2
Available-for-sale debt securities:
Available-for-sale debt securities	15	9
U.S. agency securities \| Fair value, measurements, recurring \| Level 3
Available-for-sale debt securities:
Available-for-sale debt securities	$ 0	$ 0

Fair Value Assets Measured On Recurring Basis Abstract.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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