Leasing Activities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Power Delivery [Member]	Mar. 31, 2013 Other Non-Regulated [Member]	Mar. 31, 2013 Corporate And Other [Member]	Mar. 31, 2013 Phi [Member] Agreement	Jul. 01, 2013 Phi [Member] Subsequent Event [Member]	Mar. 31, 2013 Interest Expense [Member]	Mar. 31, 2013 PHI [Member]	Dec. 31, 2012 PHI [Member]
Leases [Line Items]
Lease investments	$ 869	$ 1,237							$ 869	$ 1,237
After-tax non-cash charge	377
Non-cash charge to reduce carrying value of PHI's cross-border energy lease investments	373
After-tax effect of revised lease rerun	307
After-tax non-cash charge								70
Interest benefit			12
Interest expense on uncertain tax positions	16			16	66
Maximum percentage of penalty on the amount of additional taxes due	20.00%
Number of lease termination agreements						2
Net cash proceeds						168
Net of aggregate termination payments						804
Net pre tax loss							$ 27