Composition of Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
US Government Agencies Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	$ 2,743	$ 3,726
Available For Sale Securities Unrealized Gains	4	4
Available For Sale Securities Unrealized Losses	(2)	(3)
Available For Sale Securities Fair Value	2,745	3,727
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	8,820	9,576
Available For Sale Securities Unrealized Gains	41	40
Available For Sale Securities Unrealized Losses	(10)	(14)
Available For Sale Securities Fair Value	8,851	9,602
Publicly Traded Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	71	72
Available For Sale Securities Unrealized Gains	52	24
Available For Sale Securities Unrealized Losses	(4)	(1)
Available For Sale Securities Fair Value	119	95
Debt and Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	8,891	9,648
Available For Sale Securities Unrealized Gains	93	64
Available For Sale Securities Unrealized Losses	(14)	(15)
Available For Sale Securities Fair Value	8,970	9,697
US Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	2,352	2,260
Available For Sale Securities Unrealized Gains	5	8
Available For Sale Securities Unrealized Losses	(1)	(2)
Available For Sale Securities Fair Value	2,356	2,266
High Yield Corporate Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	543	515
Available For Sale Securities Unrealized Gains	23	19
Available For Sale Securities Unrealized Losses	(1)	(3)
Available For Sale Securities Fair Value	565	531
Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	825	860
Available For Sale Securities Unrealized Gains	3	3
Available For Sale Securities Unrealized Losses	0	0
Available For Sale Securities Fair Value	828	863
Auction Rate Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	63	63
Available For Sale Securities Unrealized Gains	0	0
Available For Sale Securities Unrealized Losses	(4)	(3)
Available For Sale Securities Fair Value	59	60
Foreign Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Amortized Cost	2,294	2,152
Available For Sale Securities Unrealized Gains	6	6
Available For Sale Securities Unrealized Losses	(2)	(3)
Available For Sale Securities Fair Value	$ 2,298	$ 2,155