Discontinued Operations - Operating Results for Cross-Border Energy Lease Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) from Discontinued Operations, Net of Income Taxes		$ 8		$ (322)
Cross-Border Energy Lease Investments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenue from PHI's cross-border energy lease investments				7
Non-cash charge to reduce carrying value of PHI's cross-border energy lease investments				(373)
Total operating revenue				(366)
Loss from operations of discontinued operations, net of income taxes				(325)
Net gains (losses) associated with the early termination of the cross-border energy lease investments, net of income taxes		7		(2)
Income (Loss) from Discontinued Operations, Net of Income Taxes		$ 7		$ (327)