Fair Value of Financial Assets and Liabilities - Composition of Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		$ 0
U.S. government and agency obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,951	3,726
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2)	(3)
Available-for-sale securities	1,951	3,727
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,998	2,260
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1	8
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(2)
Available-for-sale securities	1,995	2,266
High yield corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	570	515
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	9	19
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(16)	(3)
Available-for-sale securities	563	531
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0
Available-for-sale securities	53
Municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	948	860
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	3
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale securities	950	863
Auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29	63
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2)	(3)
Available-for-sale securities	27	60
Foreign debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,566	2,152
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(3)
Available-for-sale securities	2,564	2,155
Total fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,115	9,576
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	16	40
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(28)	(14)
Available-for-sale securities	8,103	9,602
Publicly traded equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	117	72
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	103	24
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(11)	(1)
Available-for-sale securities	209	95
Total
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,232	9,648
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	119	64
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(39)	(15)
Available-for-sale securities	$ 8,312	$ 9,697

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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