Investments (Investments with Gross Unrealized Losses) (Details) (USD $) In Millions	9 Months Ended		12 Months Ended
	Apr. 30, 2011		Jul. 31, 2010
Gross unrealized losses less than 12 months, fair value	$ 3,872		$ 310
Gross unrealized losses less than 12 months	(15)		(13)
Gross unrealized losses 12 months or greater, fair value	322		812
Gross unrealized losses 12 months or greater	(10)		(62)
Total gross unrealized losses, fair value	4,194		1,122
Total gross unrealized losses	(25)		(75)
U.S. Government Securities [Member]
Gross unrealized losses less than 12 months, fair value	2,090
Gross unrealized losses less than 12 months	(6)
Gross unrealized losses 12 months or greater, fair value
Gross unrealized losses 12 months or greater
Total gross unrealized losses, fair value	2,090
Total gross unrealized losses	(6)
U.S. Government Agency Securities [Member]
Gross unrealized losses less than 12 months, fair value	819	[1]
Gross unrealized losses less than 12 months	(2)	[1]
Gross unrealized losses 12 months or greater, fair value		[1]
Gross unrealized losses 12 months or greater		[1]
Total gross unrealized losses, fair value	819	[1]
Total gross unrealized losses	(2)	[1]
Non-U.S. Government and Agency Securities [Member]
Gross unrealized losses less than 12 months, fair value	305	[2]
Gross unrealized losses less than 12 months	(1)	[2]
Gross unrealized losses 12 months or greater, fair value		[2]
Gross unrealized losses 12 months or greater		[2]
Total gross unrealized losses, fair value	305	[2]
Total gross unrealized losses	(1)	[2]
Corporate Debt Securities [Member]
Gross unrealized losses less than 12 months, fair value	606		140
Gross unrealized losses less than 12 months	(2)		(1)
Gross unrealized losses 12 months or greater, fair value	211		304
Gross unrealized losses 12 months or greater	(7)		(20)
Total gross unrealized losses, fair value	817		444
Total gross unrealized losses	(9)		(21)
Asset-Backed Securities [Member]
Gross unrealized losses less than 12 months, fair value			2
Gross unrealized losses less than 12 months
Gross unrealized losses 12 months or greater, fair value	109		115
Gross unrealized losses 12 months or greater	(3)		(5)
Total gross unrealized losses, fair value	109		117
Total gross unrealized losses	(3)		(5)
Total Fixed Income Securities [Member]
Gross unrealized losses less than 12 months, fair value	3,820		142
Gross unrealized losses less than 12 months	(11)		(1)
Gross unrealized losses 12 months or greater, fair value	320		419
Gross unrealized losses 12 months or greater	(10)		(25)
Total gross unrealized losses, fair value	4,140		561
Total gross unrealized losses	(21)		(26)
Publicly Traded Equity Securities [Member]
Gross unrealized losses less than 12 months, fair value	52		168
Gross unrealized losses less than 12 months	(4)		(12)
Gross unrealized losses 12 months or greater, fair value	2		393
Gross unrealized losses 12 months or greater			(37)
Total gross unrealized losses, fair value	54		561
Total gross unrealized losses	$ (4)		$ (49)

[1] Includes corporate debt securities that are guaranteed by the Federal Deposit Insurance Corporation (FDIC).

[2] Includes corporate debt securities that are guaranteed by non-U.S. governments.