Stockholders Equity - Additional Information (Detail) (USD $) In Billions, except Share data in Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Stockholders Equity Note [Line Items]
Common shares outstanding plus shares underlying outstanding stock awards, including all stock-based awards outstanding, including estimated forfeiture	483	483
Net unrecognized compensation cost related to unvested stock-based compensation arrangements	$ 2.2
Net unrecognized compensation cost related to unvested stock-based compensation arrangements, weighted average recognition period (in years)	1 year 1 month 6 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Period Type:	duration