Investments (Available-For-Sale Investments With Gross Unrealized Losses) (Details) - USD ($) $ in Millions	Jan. 28, 2017	Jul. 30, 2016
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	$ 35,863	$ 5,480
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(390)	(49)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	441	1,208
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(69)	(8)
TOTAL, Fair Value	36,304	6,688
TOTAL, Gross Unrealized Losses	(459)	(57)
Publicly traded equity securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	63	188
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(6)	(40)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	94	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(68)	0
TOTAL, Fair Value	157	188
TOTAL, Gross Unrealized Losses	(74)	(40)
Total fixed income securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	35,800	5,292
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(384)	(9)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	347	1,208
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(1)	(8)
TOTAL, Fair Value	36,147	6,500
TOTAL, Gross Unrealized Losses	(385)	(17)
Total fixed income securities | U.S. government securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	16,303	2,414
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(82)	(2)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	16	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	16,319	2,414
TOTAL, Gross Unrealized Losses	(82)	(2)
Total fixed income securities | U.S. government agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,430	144
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(5)	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	0	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	1,430	144
TOTAL, Gross Unrealized Losses	(5)	0
Total fixed income securities | Non-U.S. government and agency securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,107	61
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(6)	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	6	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	1,113	61
TOTAL, Gross Unrealized Losses	(6)	0
Total fixed income securities | Corporate debt securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	15,180	2,499
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(264)	(7)
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	325	1,208
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	(1)	(8)
TOTAL, Fair Value	15,505	3,707
TOTAL, Gross Unrealized Losses	(265)	(15)
Total fixed income securities | U.S. agency mortgage-backed securities
Schedule of Investments [Line Items]
UNREALIZED LOSSES LESS THAN 12 MONTHS, Fair Value	1,780	174
UNREALIZED LOSSES LESS THAN 12 MONTHS, Gross Unrealized Losses	(27)	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Fair Value	0	0
UNREALIZED LOSSES 12 MONTHS OR GREATER, Gross Unrealized Losses	0	0
TOTAL, Fair Value	1,780	174
TOTAL, Gross Unrealized Losses	$ (27)	$ 0