Fair Value of Financial Assets and Liabilities - Composition of Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Gross Unrealized Gain		$ 0
U.S. government and agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,726	2,191
Available-for-sale Securities, Gross Unrealized Gain	4	10
Available-for-sale Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale securities	3,727	2,200
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,260	1,480
Available-for-sale Securities, Gross Unrealized Gain	8	10
Available-for-sale Securities, Gross Unrealized Loss	(2)	0
Available-for-sale securities	2,266	1,490
High yield corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	515	486
Available-for-sale Securities, Gross Unrealized Gain	19	34
Available-for-sale Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale securities	531	519
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	2
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale Securities, Gross Unrealized Loss	0	0
Available-for-sale securities	0	2
Municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	860	1,032
Available-for-sale Securities, Gross Unrealized Gain	3	3
Available-for-sale Securities, Gross Unrealized Loss	0	0
Available-for-sale securities	863	1,035
Auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	63	74
Available-for-sale Securities, Gross Unrealized Gain	0
Available-for-sale Securities, Gross Unrealized Loss	(3)	(4)
Available-for-sale securities	60	70
Foreign debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,152	1,270
Available-for-sale Securities, Gross Unrealized Gain	6	9
Available-for-sale Securities, Gross Unrealized Loss	(3)	0
Available-for-sale securities	2,155	1,279
Total fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,576	6,535
Available-for-sale Securities, Gross Unrealized Gain	40	66
Available-for-sale Securities, Gross Unrealized Loss	(14)	(6)
Available-for-sale securities	9,602	6,595
Publicly traded equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	72	47
Available-for-sale Securities, Gross Unrealized Gain	24	41
Available-for-sale Securities, Gross Unrealized Loss	(1)	(1)
Available-for-sale securities	95	87
Total
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,648	6,582
Available-for-sale Securities, Gross Unrealized Gain	64	107
Available-for-sale Securities, Gross Unrealized Loss	(15)	(7)
Available-for-sale securities	$ 9,697	$ 6,682