Significant Accounting Policies - 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		1 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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Adjustment [Member]	Mar. 31, 2013 Adjustment [Member]	Dec. 31, 2012 Adjustment [Member]	Dec. 31, 2011 Adjustment [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Sep. 30, 2012 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Sep. 30, 2012 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2012 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member] MW	Sep. 30, 2012 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member]	Sep. 30, 2012 Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member]	Sep. 30, 2012 Delmarva Power & Light Co/De [Member]	Oct. 31, 2011 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] Maximum [Member]	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] Maximum [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] MW	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility One [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Two [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Three [Member] MW	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] MW	Sep. 30, 2012 Delmarva Power & Light Co/De [Member] Solar PPA [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member] Land-Based Wind PPA [Member]	Sep. 30, 2013 Potomac Electric Power Co [Member]	Sep. 30, 2012 Potomac Electric Power Co [Member]	Sep. 30, 2013 Potomac Electric Power Co [Member]	Sep. 30, 2012 Potomac Electric Power Co [Member]	Sep. 30, 2013 Potomac Capital Investment Corporation [Member] Adjustment [Member]
Significant Accounting Policies [Line Items]
Number of purchase power agreements														3																									1		3
Megawatts received from power purchase agreements (PPAs)																		459														128							10
Net power purchases with non-utility generators																$ 61	$ 56	$ 168	$ 156
Purchase of energy	579	648	1,587	1,658												54	53	157	151											4	4	21	20
Energy purchase maximum to be purchased, MW																																		50	40	38
Term of agreement, years														15 years										21 years															20 years
Obligated purchase amount of energy produced at the facility																																							70.00%
Solar energy purchases																																					1	1	2	2
Power of fuel cell facility, MW																								30	15	15	3
Amount billed to distribution customers																									7	13		1	1
Equity ownership percentage												100.00%		100.00%
Number of Standard Offer Capacity Agreements														3
Estimated share of payments received or made to generation companies														15.00%
Taxes included in gross revenues	98	103	264	275								3	6	8	13					4	4	12	12																			91	93	244	250
Prior period reclassification adjustment																							1
Deferred tax liability					$ 2,717	$ 3,208	$ 2,895	$ 32	$ 32	$ 32	$ 32																																			$ 0