Discontinued Operations - Income Recognized from Cross-Border Energy Lease Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of income taxes	$ 8	$ 25	$ (322)	$ 58
Cross-Border Energy Lease Investments [Member]
Schedule of Discontinued Operations [Line Items]
Operating revenue from PHI's cross-border energy lease investments		13	7	39
Non-cash charge to reduce carrying value of PHI's cross-border energy lease investments			(373)
Total operating revenue		13	(366)	39
Income (loss) from operations of discontinued operations, net of income taxes		8	(325)	24
Net gains (losses) associated with the early termination of the cross-border energy lease investments, net of income taxes	7	9	(2)	9
Income (loss) from discontinued operations, net of income taxes	$ 7	$ 17	$ (327)	$ 33