Discontinued Operations - (Loss) Income Recognized from Cross-Border Energy Lease Investments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Discontinued Operations [Line Items]
(Loss) income from discontinued operations, net of income taxes	$ 8	$ (11)	$ (319)	$ 9	$ 25	$ 15	$ 18	$ (322)	$ 67	$ 35
Cross-Border Energy Lease Investments [Member]
Schedule of Discontinued Operations [Line Items]
Operating revenue from PHI's cross-border energy lease investments								7	50	55
Non-cash charge to reduce carrying value of PHI's cross-border energy lease investments								(373)		(7)
Total operating revenue								(366)	50	48
(Loss) income from operations of discontinued operations, net of income taxes								(325)	32	33
Net (losses) gains associated with the early termination of the cross-border energy lease investments, net of income taxes								(2)	9	3
(Loss) income from discontinued operations, net of income taxes								$ (327)	$ 41	$ 36