Summary of Stock Option Activity (Detail) (Employee Stock Option, USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Employee Stock Option
Shares
Outstanding at December 31, 2013	2,698
Granted	756
Exercised	(272)
Forfeited and expired	(366)
Outstanding at December 31, 2014	2,816
Expected to vest at December 31, 2014	1,335
Exercisable at December 31, 2014	1,456
Weighted-Average Exercise Price
Outstanding at December 31, 2013	$ 32.74
Granted	$ 32.20
Exercised	$ 14.25
Forfeited and expired	$ 70.30
Outstanding at December 31, 2014	$ 29.51
Expected to vest at December 31, 2014	$ 27.37
Exercisable at December 31, 2014	$ 31.47
Weighted-Average Remaining Contractual Term (years)
Outstanding at December 31, 2014	2 years 4 months 13 days
Expected to vest at December 31, 2014	3 years 5 months 27 days
Exercisable at December 31, 2014	1 year 3 months 22 days
Aggregate Intrinsic Value
Outstanding at December 31, 2014	$ 9.1
Expected to vest at December 31, 2014	4.7
Exercisable at December 31, 2014	$ 4.4

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Net number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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