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, 2013
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	$ 2,744
Less than 12 Months Unrealized Losses	(17)
12 Months or Greater Fair Value	67
12 Months or Greater Unrealized Losses	(5)
Total Fair Value	2,811
Total, Gross Unrealized Losses	22
US Government Agencies Debt Securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	787
Less than 12 Months Unrealized Losses	(3)
12 Months or Greater Fair Value	0
12 Months or Greater Unrealized Losses	0
Total Fair Value	787
Total, Gross Unrealized Losses	3
US Corporate Debt Securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	823
Less than 12 Months Unrealized Losses	(3)
12 Months or Greater Fair Value	0
12 Months or Greater Unrealized Losses	0
Total Fair Value	823
Total, Gross Unrealized Losses	3
High Yield Corporate Debt Securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	190
Less than 12 Months Unrealized Losses	(7)
12 Months or Greater Fair Value	0
12 Months or Greater Unrealized Losses	0
Total Fair Value	190
Total, Gross Unrealized Losses	7
Municipal Obligations
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	139
Less than 12 Months Unrealized Losses	(1)
12 Months or Greater Fair Value	0
12 Months or Greater Unrealized Losses	0
Total Fair Value	139
Total, Gross Unrealized Losses	1
Auction Rate Securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	0
Less than 12 Months Unrealized Losses	0
12 Months or Greater Fair Value	67
12 Months or Greater Unrealized Losses	(5)
Total Fair Value	67
Total, Gross Unrealized Losses	5
Foreign Debt Securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	805
Less than 12 Months Unrealized Losses	(3)
12 Months or Greater Fair Value	0
12 Months or Greater Unrealized Losses	0
Total Fair Value	805
Total, Gross Unrealized Losses	$ 3