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	Mar. 31, 2016 USD ($)
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	$ 1,773
Less than 12 Months Gross Unrealized Losses	(11)
12 Months or Greater Fair Value	129
12 Months or Greater Gross Unrealized Losses	(13)
Total Fair Value	1,902
Total, Gross Unrealized Losses	(24)
U.S. government and agency obligations
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	466
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	466
Total, Gross Unrealized Losses	(1)
U.S. corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	485
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	485
Total, Gross Unrealized Losses	(2)
High yield corporate debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	99
Less than 12 Months Gross Unrealized Losses	(6)
12 Months or Greater Fair Value	23
12 Months or Greater Gross Unrealized Losses	(2)
Total Fair Value	122
Total, Gross Unrealized Losses	(8)
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	23
12 Months or Greater Gross Unrealized Losses	(2)
Total Fair Value	23
Total, Gross Unrealized Losses	(2)
Foreign debt securities
Gain (Loss) on Investments [Line Items]
Less Than 12 Months Fair Value	721
Less than 12 Months Gross Unrealized Losses	(1)
12 Months or Greater Fair Value	81
12 Months or Greater Gross Unrealized Losses	(1)
Total Fair Value	802
Total, Gross Unrealized Losses	(2)
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	2
12 Months or Greater Gross Unrealized Losses	(8)
Total Fair Value	4
Total, Gross Unrealized Losses	$ (9)