Fair Value of Financial Assets and Liabilities - Composition of Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
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	$ 2,449	1,951
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(8)	(2)
Available-for-sale securities	2,441	1,951
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,257	1,998
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(10)	(4)
Available-for-sale securities	2,248	1,995
High yield corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	307	570
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(22)	(16)
Available-for-sale securities	287	563
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20	53
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale securities	20	53
Municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	731	948
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1	2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available-for-sale securities	732	950
Auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27	29
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(2)	(2)
Available-for-sale securities	25	27
Foreign debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,332	2,566
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(9)	(4)
Available-for-sale securities	2,323	2,564
Total fixed income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,123	8,115
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4	16
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(51)	(28)
Available-for-sale securities	8,076	8,103
Publicly traded equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	126	117
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	40	103
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(8)	(11)
Available-for-sale securities	158	209
Total
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,249	8,232
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	44	119
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(59)	(39)
Available-for-sale securities	$ 8,234	$ 8,312

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
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