Investments (Available-For-Sale Investments With Gross Unrealized Losses) (Details) - USD ($) $ in Millions	Jul. 28, 2018	Jul. 29, 2017
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	$ 21,093	$ 28,215
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(391)	(195)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	9,019	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(156)	(8)
TOTAL, Fair Value	30,112	29,255
TOTAL, Gross Unrealized Losses	(547)	(203)
Publicly traded equity securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	0	122
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	0	(27)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	0	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	0	122
TOTAL, Gross Unrealized Losses	0	(27)
Total fixed income securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	21,093	28,093
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(391)	(168)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	9,019	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(156)	(8)
TOTAL, Fair Value	30,112	29,133
TOTAL, Gross Unrealized Losses	(547)	(176)
Total fixed income securities | U.S. government securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	2,966	14,962
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(20)	(55)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	4,303	771
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(23)	(5)
TOTAL, Fair Value	7,269	15,733
TOTAL, Gross Unrealized Losses	(43)	(60)
Total fixed income securities | U.S. government agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	206	1,791
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(2)	(4)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	521	130
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(3)	(1)
TOTAL, Fair Value	727	1,921
TOTAL, Gross Unrealized Losses	(5)	(5)
Total fixed income securities | Non-U.S. government and agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	105	368
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(1)	(1)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	103	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	208	368
TOTAL, Gross Unrealized Losses	(1)	(1)
Total fixed income securities | Corporate debt securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	16,990	9,487
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(344)	(92)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	3,511	101
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(101)	(1)
TOTAL, Fair Value	20,501	9,588
TOTAL, Gross Unrealized Losses	(445)	(93)
Total fixed income securities | U.S. agency mortgage-backed securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	826	1,485
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(24)	(16)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	581	38
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(29)	(1)
TOTAL, Fair Value	1,407	1,523
TOTAL, Gross Unrealized Losses	$ (53)	$ (17)