Investments (Available-for-Sale Investments With Gross Unrealized Losses) (Details) - USD ($) $ in Millions	Jan. 27, 2018	Jul. 29, 2017
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	$ 30,015	$ 28,215
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(267)	(195)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	11,729	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(167)	(8)
TOTAL, Fair Value	41,744	29,255
TOTAL, Gross Unrealized Losses	(434)	(203)
Publicly traded equity securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	10	122
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(1)	(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	10	122
TOTAL, Gross Unrealized Losses	(1)	(27)
Total fixed income securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	30,005	28,093
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(266)	(168)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	11,729	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(167)	(8)
TOTAL, Fair Value	41,734	29,133
TOTAL, Gross Unrealized Losses	(433)	(176)
Total fixed income securities | U.S. government securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	11,553	14,962
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(96)	(55)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	5,804	771
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(44)	(5)
TOTAL, Fair Value	17,357	15,733
TOTAL, Gross Unrealized Losses	(140)	(60)
Total fixed income securities | U.S. government agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,152	1,791
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(5)	(4)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	559	130
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(5)	(1)
TOTAL, Fair Value	1,711	1,921
TOTAL, Gross Unrealized Losses	(10)	(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	136	368
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	0	(1)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	203	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(1)	0
TOTAL, Fair Value	339	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	16,003	9,487
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(146)	(92)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	4,287	101
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(87)	(1)
TOTAL, Fair Value	20,290	9,588
TOTAL, Gross Unrealized Losses	(233)	(93)
Total fixed income securities | U.S. agency mortgage-backed securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,161	1,485
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(19)	(16)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	876	38
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(30)	(1)
TOTAL, Fair Value	2,037	1,523
TOTAL, Gross Unrealized Losses	$ (49)	$ (17)