Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified				3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] MW	Oct. 18, 2011 Delmarva Power & Light Co/De [Member] MW	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] October 18, 2011 [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Land-Based Wind PPA [Member] Agreement MW	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Solar PPA [Member] MW Agreement	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility One [Member] MW	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Two [Member] MW	Sep. 30, 2014 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Three [Member] MW	Sep. 30, 2014 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member] Non-Utility Generators [Member] Agreement MW	Sep. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member]
Variable Interest Entity [Line Items]
Megawatts received from power purchase agreements (PPAs)									128			10																	459
Number of purchase power agreements									3			1																	3
Energy purchase maximum to be purchased												19								50	40	38
Purchased energy																$ 5	$ 4	$ 21	$ 21								$ 52	$ 54	$ 159	$ 157
Term of agreement, years												20 years
Term of agreement								Through 2033				Through 2030
Obligated purchase amount of energy produced at the facility												70.00%
Solar energy purchases										1	1	3	2	1	2
Power of fuel cell facility	30	15	30
Amount billed to distribution customers				8	7	26	13
Net power purchases with non-utility generators																							$ 56	$ 61	$ 182	$ 168
Equity ownership percentage																							100.00%		100.00%