Discontinued Operations - Operating Results for Cross-Border Energy Lease Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations, net of income taxes	$ 0	$ (11)	$ 0	$ (330)
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		2		7
Non-cash charge to reduce carrying value of PHI's cross-border energy lease investments				(373)
Total operating revenue		2		(366)
Income from operations of discontinued operations, net of income taxes		(6)		(325)
Net losses associated with the early termination of the cross-border energy lease investments, net of income taxes		(9)		(9)
Loss from discontinued operations, net of income taxes		$ (15)		$ (334)