Investments (Summary of Available-for-Sale Investments) (Details) - USD ($) $ in Millions	Jan. 27, 2018	Jul. 29, 2017
Schedule of Investments [Line Items]
Amortized Cost	$ 55,716	$ 58,225
Gross Unrealized Gains	777	762
Gross Unrealized Losses	(434)	(203)
Fair Value	56,059	58,784
Net unsettled available-for-sale investments, purchases (sales)	(3)	(30)
Total fixed income securities
Schedule of Investments [Line Items]
Amortized Cost	54,792	57,045
Gross Unrealized Gains	80	208
Gross Unrealized Losses	(433)	(176)
Fair Value	54,439	57,077
Total fixed income securities | U.S. government securities
Schedule of Investments [Line Items]
Amortized Cost	17,506	19,880
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(140)	(60)
Fair Value	17,366	19,823
Total fixed income securities | U.S. government agency securities
Schedule of Investments [Line Items]
Amortized Cost	1,722	2,057
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(10)	(5)
Fair Value	1,712	2,052
Total fixed income securities | Non-U.S. government and agency securities
Schedule of Investments [Line Items]
Amortized Cost	340	389
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	339	388
Total fixed income securities | Corporate debt securities
Schedule of Investments [Line Items]
Amortized Cost	31,508	31,626
Gross Unrealized Gains	80	202
Gross Unrealized Losses	(233)	(93)
Fair Value	31,355	31,735
Total fixed income securities | U.S. agency mortgage-backed securities
Schedule of Investments [Line Items]
Amortized Cost	2,106	2,037
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(49)	(17)
Fair Value	2,057	2,023
Total fixed income securities | Commercial paper
Schedule of Investments [Line Items]
Amortized Cost	1,414	996
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	1,414	996
Total fixed income securities | Certificates of deposit
Schedule of Investments [Line Items]
Amortized Cost	196	60
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	196	60
Publicly traded equity securities
Schedule of Investments [Line Items]
Amortized Cost	924	1,180
Gross Unrealized Gains	697	554
Gross Unrealized Losses	(1)	(27)
Fair Value	$ 1,620	$ 1,707