Equity and Earnings Per Share - Calculation of Earnings Per Share of Common Stock (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income (Numerator):
Net Income	$ 53us-gaap_NetIncomeLoss	$ 75us-gaap_NetIncomeLoss
Weighted average shares outstanding for basic computation:
Average shares outstanding	253	250
Adjustment to shares outstanding		1pom_AdjustmentToSharesOutstandingBasic
Weighted Average Shares Outstanding for Computation of Basic Earnings Per Share of Common Stock	253	251
Net effect of potentially dilutive shares	0	0
Weighted Average Shares Outstanding for Computation of Diluted Earnings Per Share of Common Stock	253	251
Basic and Diluted Earnings per Share
Basic and Diluted earnings per share	$ 0.21us-gaap_EarningsPerShareBasicAndDiluted	$ 0.30us-gaap_EarningsPerShareBasicAndDiluted

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Weighted average number basic shares outstanding.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or 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 sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.

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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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