Numerators and Denominators Used in Computations of Basic and Diluted Earnings per Common Share (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income from continuing operations	$ 22	$ 56	$ 3	$ 29
Income from continuing operations attributable to common shareholders	21	54	1	27
Loss from discontinued operations	(7)	(20)	(30)	(31)
Loss from discontinued operations attributable to common shareholders	(7)	(19)	(29)	(30)
Net income (loss) available to common shareholders	14	35	(28)	(3)
Basic common shares (based upon weighted average)	349	348	349	348
Contingent common shares
Stock option dilution	1		1	1
Diluted common shares	350	348	350	349
Segment, Continuing Operations [Member]
Allocation to unvested restricted stock awards	(1)	(2)	(2)	(2)
Segment, Discontinued Operations [Member]
Allocation to unvested restricted stock awards		$ 1	$ 1	$ 1

Allocation to unvested restricted stock awards.

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Income Loss From Discontinued Operations Attributable To Common Stockholders

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(Loss) income from continuing operations attributable to common shareholders.

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Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests.

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Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of contingently issuable shares. Contingently issuable shares are those shares that are issuable for little or no cash contingent on certain conditions being met.

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-Glossary Contingently Issuable Shares

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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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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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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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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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