Leasing Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended		6 Months Ended			1 Months Ended	3 Months Ended			12 Months Ended	1 Months Ended		6 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Power Delivery [Member]	Jun. 30, 2013 Other Non-Regulated [Member]	Jun. 30, 2013 Corporate and Other [Member]	Jul. 26, 2013 Phi [Member]	Jun. 30, 2013 Phi [Member]	Mar. 31, 2013 Phi [Member]	Sep. 30, 2013 Phi [Member] Subsequent Event [Member]	Dec. 31, 2013 Phi [Member] Subsequent Event [Member]	Jun. 30, 2013 PHI [Member] Investment	Dec. 31, 2012 PHI [Member] Investment	Jun. 30, 2013 Interest Expense [Member]
Leases [Line Items]
Lease investments		$ 167	$ 1,237									$ 167	$ 1,237
Number of investment in lease portfolio												1	6
Net cash proceeds							180	693
Net of aggregate termination payments							665	1,400
Net pre tax gain / loss								14		11	3
Loss on early termination of finance leases held in trust, after tax								9		7	2
Early termination agreement of leases								Five of the six remaining lease investments
Interest expense on uncertain tax positions		16			16	66			16
After-tax non-cash charge	377
Other non-cash charge		373
After-tax effect of revised lease rerun		307
After-tax non-cash charge														70
Interest benefit				$ 12
Maximum percentage of penalty on the amount of additional taxes due	20.00%	20.00%