Investments (Summary of Investments) (Details) (USD $) In Millions	9 Months Ended		12 Months Ended
	Apr. 30, 2011		Jul. 31, 2010
Amortized Cost	$ 35,938		$ 34,746
Gross Unrealized Gains	819		609
Gross Unrealized Losses	(25)		(75)
Fair Value	36,732		35,280
U.S. Government Securities [Member]
Amortized Cost	19,785		16,570
Gross Unrealized Gains	38		42
Gross Unrealized Losses	(6)
Fair Value	19,817		16,612
U.S. Government Agency Securities [Member]
Amortized Cost	8,197	[1]	13,511	[1]
Gross Unrealized Gains	30	[1]	68	[1]
Gross Unrealized Losses	(2)	[1]		[1]
Fair Value	8,225	[1]	13,579	[1]
Non-U.S. Government and Agency Securities [Member]
Amortized Cost	2,721	[2]	1,452	[2]
Gross Unrealized Gains	14	[2]	15	[2]
Gross Unrealized Losses	(1)	[2]		[2]
Fair Value	2,734	[2]	1,467	[2]
Corporate Debt Securities [Member]
Amortized Cost	4,351		2,179
Gross Unrealized Gains	64		64
Gross Unrealized Losses	(9)		(21)
Fair Value	4,406		2,222
Asset-Backed Securities [Member]
Amortized Cost	126		145
Gross Unrealized Gains	7		9
Gross Unrealized Losses	(3)		(5)
Fair Value	130		149
Total Fixed Income Securities [Member]
Amortized Cost	35,180		33,857
Gross Unrealized Gains	153		198
Gross Unrealized Losses	(21)		(26)
Fair Value	35,312		34,029
Publicly Traded Equity Securities [Member]
Amortized Cost	758		889
Gross Unrealized Gains	666		411
Gross Unrealized Losses	(4)		(49)
Fair Value	$ 1,420		$ 1,251

[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.