Schedule of Investment Securities Classified as Current and Long-Term (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment [Line Items]
Amortized Cost	$ 8,959	$ 9,550
Gross Unrealized Gains	544	377
Gross Unrealized Losses	(43)	(127)
Total debt securities, Fair Value	9,460	9,800
Debt Securities | Tax-exempt municipal securities
Investment [Line Items]
Amortized Cost	2,998	2,911
Gross Unrealized Gains	141	93
Gross Unrealized Losses	(7)	(33)
Total debt securities, Fair Value	3,132	2,971
Debt Securities | Residential Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	20	22
Gross Unrealized Gains	1
Gross Unrealized Losses	(1)
Total debt securities, Fair Value	20	22
Debt Securities | Commercial Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	636	662
Gross Unrealized Gains	19	20
Gross Unrealized Losses	(11)	(9)
Total debt securities, Fair Value	644	673
Debt Securities | Asset-backed Securities
Investment [Line Items]
Amortized Cost	41	63
Gross Unrealized Gains	1	1
Gross Unrealized Losses		(1)
Total debt securities, Fair Value	42	63
Debt Securities | Corporate Debt Securities
Investment [Line Items]
Amortized Cost	3,402	3,474
Gross Unrealized Gains	326	223
Gross Unrealized Losses	(6)	(30)
Total debt securities, Fair Value	3,722	3,667
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | U.S. Treasury And Agency Obligations
Investment [Line Items]
Amortized Cost	372	584
Gross Unrealized Gains	8	6
Gross Unrealized Losses	(2)	(6)
Total debt securities, Fair Value	378	584
Debt Securities | U.S. Treasury And Other U.S. Government Corporations And Agencies | Mortgage-Backed Securities
Investment [Line Items]
Amortized Cost	1,490	1,834
Gross Unrealized Gains	48	34
Gross Unrealized Losses	(16)	(48)
Total debt securities, Fair Value	$ 1,522	$ 1,820