Investments (Available-For-Sale Investments With Gross Unrealized Losses) (Details) - USD ($) $ in Millions	Oct. 28, 2017	Jul. 29, 2017
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	$ 28,476	$ 28,215
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(138)	(195)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	8,340	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(122)	(8)
TOTAL, Fair Value	36,816	29,255
TOTAL, Gross Unrealized Losses	(260)	(203)
Publicly traded equity securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	54	122
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(6)	(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	54	122
TOTAL, Gross Unrealized Losses	(6)	(27)
Total fixed income securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	28,422	28,093
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(132)	(168)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	8,340	1,040
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(122)	(8)
TOTAL, Fair Value	36,762	29,133
TOTAL, Gross Unrealized Losses	(254)	(176)
Total fixed income securities | U.S. government securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	16,719	14,962
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(66)	(55)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	3,602	771
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(27)	(5)
TOTAL, Fair Value	20,321	15,733
TOTAL, Gross Unrealized Losses	(93)	(60)
Total fixed income securities | U.S. government agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,696	1,791
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(4)	(4)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	222	130
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(2)	(1)
TOTAL, Fair Value	1,918	1,921
TOTAL, Gross Unrealized Losses	(6)	(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	316	368
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(1)	(1)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	41	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	357	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	8,129	9,487
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(45)	(92)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	4,209	101
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(86)	(1)
TOTAL, Fair Value	12,338	9,588
TOTAL, Gross Unrealized Losses	(131)	(93)
Total fixed income securities | U.S. agency mortgage-backed securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,562	1,485
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(16)	(16)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	266	38
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(7)	(1)
TOTAL, Fair Value	1,828	1,523
TOTAL, Gross Unrealized Losses	$ (23)	$ (17)