Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Numerator:
Net income-basic and diluted	$ 86	$ 61
Denominator:
Weighted-average common shares outstanding	162,277	162,940
Adjusted weighted-average shares	163,145	163,670
Earnings per share:
Basic	$ 0.53	$ 0.38
Diluted	$ 0.53	$ 0.38
Number of anti-dilutive stock based awards	6,215	6,919
Nonvested shares
Denominator:
Effect of stock-based awards	541	526
Stock Options
Denominator:
Effect of stock-based awards	327	204

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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