Investments and Marketable Securities - Changes in Unrealized Gains and Losses on Available-for-sale Securities (Detail) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Changes in unrealized gains and losses on available-for- sale securities, net of tax, recorded in accumulated other comprehensive income (loss)	$ 0

Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration