Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator:
Net income-basic and diluted	$ 128us-gaap_NetIncomeLoss	$ 91us-gaap_NetIncomeLoss
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.0	163.4
Diluted weighted-average shares	165.6	165.0
Earnings per share:
Basic (in USD per share)	$ 0.78us-gaap_EarningsPerShareBasic	$ 0.56us-gaap_EarningsPerShareBasic
Diluted (in USD per share)	$ 0.77us-gaap_EarningsPerShareDiluted	$ 0.55us-gaap_EarningsPerShareDiluted
Number of anti-dilutive stock-based awards (in shares)	0.7	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	1.0
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.6

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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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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