Fair Value of Financial Assets and Liabilities - Unrealized Losses on Investments by Investment Category and Length of Time in Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	$ 3,368
Less than 12 Months Gross Unrealized Losses	(24)
12 Months or Greater Fair Value	52
12 Months or Greater Gross Unrealized Losses	(5)
Total Fair Value	3,420
Total, Gross Unrealized Losses	(29)
U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	938
Less than 12 Months Gross Unrealized Losses	(2)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	938
Total, Gross Unrealized Losses	(2)
U.S. corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	986
Less than 12 Months Gross Unrealized Losses	(3)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	986
Total, Gross Unrealized Losses	(3)
High yield corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	264
Less than 12 Months Gross Unrealized Losses	(9)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	264
Total, Gross Unrealized Losses	(9)
Auction rate securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	0
Less than 12 Months Gross Unrealized Losses	0
12 Months or Greater Fair Value	52
12 Months or Greater Gross Unrealized Losses	(4)
Total Fair Value	52
Total, Gross Unrealized Losses	(4)
Foreign debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	1,159
Less than 12 Months Gross Unrealized Losses	(2)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	1,159
Total, Gross Unrealized Losses	(2)
Publicly traded equity securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	21
Less than 12 Months Gross Unrealized Losses	(8)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	(1)
Total Fair Value	21
Total, Gross Unrealized Losses	$ (9)