Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Reconciliation of activity for Level 3 assets
Beginning balance	$ 59	$ 87	$ 245
Settlements at par	(18)	(28)	(158)
Ending balance	41	59	87
Short Term Debt Investments [Member]
Reconciliation of activity for Level 3 assets
Beginning balance	0	0	151
Settlements at par	0	0	(151)
Ending balance	0	0	0
Long-Term Investment [Member]
Reconciliation of activity for Level 3 assets
Beginning balance	59	87	94
Settlements at par	(18)	(28)	(7)
Ending balance	$ 41	$ 59	$ 87

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant