Stock Options Status and Activity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, January 1, 2013	2,447,475
Granted	311,539
Canceled	(7,225)
Forfeited	(14,920)
Exercised	(82,622)
Outstanding, March 31, 2013	2,654,247	2,447,475
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding, January 1, 2013	$ 20.14
Granted	$ 36.29
Canceled	$ 11.73
Forfeited	$ 14.59
Exercised	$ 19.96
Outstanding, March 31, 2013	$ 22.12	$ 20.14
Weighted Avg. Remaining Life in Years	4 years 3 months 18 days	4 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding, Beginning Balance	$ 29
Aggregate Intrinsic Value, Exercised	1
Aggregate Intrinsic Value, Outstanding, Ending Balance	$ 41	$ 29

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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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.

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

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

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including 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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Number of share options (or share units) exercised during the current period.

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