Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended									3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended						3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2013 Adjustment [Member]	Mar. 31, 2013 Adjustment [Member]	Dec. 31, 2012 Adjustment [Member]	Dec. 31, 2011 Adjustment [Member]	Jun. 30, 2013 Non-Utility Generators [Member]	Jun. 30, 2012 Non-Utility Generators [Member]	Jun. 30, 2013 Non-Utility Generators [Member]	Jun. 30, 2012 Non-Utility Generators [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Jun. 30, 2012 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Jun. 30, 2013 Atlantic City Electric Co [Member] Non-Utility Generators [Member] MW	Jun. 30, 2012 Atlantic City Electric Co [Member] Non-Utility Generators [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member]	Oct. 31, 2011 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Fuel Cell Facility [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] Fuel Cell Facility [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Maximum [Member] Fuel Cell Facility [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] MW	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Wind PPA [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility One [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Two [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Wind PPA [Member] Wind Facility Three [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] MW	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Jun. 30, 2012 Delmarva Power & Light Co/De [Member] Solar PPA [Member] Maximum [Member]	Jun. 30, 2013 Delmarva Power & Light Co/De [Member] Land-Based Wind PPA [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Jun. 30, 2013 Potomac Electric Power Co [Member]	Jun. 30, 2012 Potomac Electric Power Co [Member]	Jun. 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												$ 53	$ 49	$ 107	$ 100					$ 53	$ 49	$ 107	$ 100
Purchase of energy	446	465	1,008	1,010								48	47	103	98					48	47	103	98											7	6	17	15
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	1	1
Power of fuel cell facility, MW																												30	15	15	3
Amount billed to distribution customers																													3	6		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	83	87	166	174												2	3	5	7					4	4	8	8																				77	80	153	159
Prior period reclassification adjustment																									1		1
Deferred tax liability					2,717	3,208	2,895	32	32	32	32																																								0
Reclassification adjustment relating to uncertain tax positions																																																$ 1