Derivative Instruments (Effect of Derivative Instruments Designated as Fair Value Hedges on Consolidated Statement of Operations Summary) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Apr. 30, 2011	May 01, 2010	Apr. 30, 2011	May 01, 2010
Interest Expense [Member] | Derivatives Designated as Fair Value Hedging Instruments [Member] | Interest Rate Derivatives [Member]
Gains (losses) on derivative instruments			$ 3	$ 1
Gains (losses) related to hedged items			(4)	(1)
Interest Expense [Member] | Interest Rate Derivatives [Member]
Gains (losses) on derivative instruments	26	1
Gains (losses) related to hedged items	(27)	(1)
Derivatives Designated as Fair Value Hedging Instruments [Member] | Equity Derivatives [Member] | Other Income Net [Member]
Gains (losses) on derivative instruments		3		2
Gains (losses) related to hedged items		(3)		(2)
Derivatives Designated as Fair Value Hedging Instruments [Member]
Gains (losses) on derivative instruments	26	4	3	3
Gains (losses) related to hedged items	$ (27)	$ (4)	$ (4)	$ (3)