Fair Value of Financial Assets and Liabilities - Unrealized Losses on Investments by Investment Category and Length of Time in Continuous Unrealized Loss Position (Detail) $ in Millions	Sep. 30, 2015 USD ($)
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	$ 2,885
Less than 12 Months Gross Unrealized Losses	(32)
12 Months or Greater Fair Value	74
12 Months or Greater Gross Unrealized Losses	(15)
Total Fair Value	2,959
Total, Gross Unrealized Losses	(47)
U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	321
Less than 12 Months Gross Unrealized Losses	(1)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	321
Total, Gross Unrealized Losses	(1)
U.S. corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	1,103
Less than 12 Months Gross Unrealized Losses	(5)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	1,103
Total, Gross Unrealized Losses	(5)
High yield corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	239
Less than 12 Months Gross Unrealized Losses	(17)
12 Months or Greater Fair Value	30
12 Months or Greater Gross Unrealized Losses	(5)
Total Fair Value	269
Total, Gross Unrealized Losses	(22)
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	25
12 Months or Greater Gross Unrealized Losses	(2)
Total Fair Value	25
Total, Gross Unrealized Losses	(2)
Foreign debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	1,220
Less than 12 Months Gross Unrealized Losses	(8)
12 Months or Greater Fair Value	0
12 Months or Greater Gross Unrealized Losses	0
Total Fair Value	1,220
Total, Gross Unrealized Losses	(8)
Publicly traded equity securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	2
Less than 12 Months Gross Unrealized Losses	(1)
12 Months or Greater Fair Value	19
12 Months or Greater Gross Unrealized Losses	(8)
Total Fair Value	21
Total, Gross Unrealized Losses	$ (9)