Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Oct. 18, 2011 MW	Mar. 31, 2014 MW	Mar. 31, 2013 MW
Delmarva Power & Light Co/De [Member] | Fuel Cell Facility [Member]
Variable Interest Entity [Line Items]
Term of agreement, years	21 years
Power of fuel cell facility	30	30	9
Amount billed to distribution customers		$ 9	$ 3
Delmarva Power & Light Co/De [Member] | Land-Based Wind PPA [Member]
Variable Interest Entity [Line Items]
Megawatts received from power purchase agreements (PPAs)		128
Number of purchase power agreements		3
Delmarva Power & Light Co/De [Member] | Solar PPA [Member]
Variable Interest Entity [Line Items]
Megawatts received from power purchase agreements (PPAs)		10
Number of purchase power agreements		1
Energy purchase maximum to be purchased		14
Term of agreement, years		20 years
Term of agreement		through 2030
Obligated purchase amount of energy produced at the facility		70.00%
Solar energy purchases		1
Delmarva Power & Light Co/De [Member] | Solar PPA [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Solar energy purchases			1
Delmarva Power & Light Co/De [Member] | Wind PPA [Member]
Variable Interest Entity [Line Items]
Purchased energy		10	10
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility One [Member]
Variable Interest Entity [Line Items]
Energy purchase maximum to be purchased		50
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility Two [Member]
Variable Interest Entity [Line Items]
Energy purchase maximum to be purchased		40
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility Three [Member]
Variable Interest Entity [Line Items]
Energy purchase maximum to be purchased		38
Atlantic City Electric Co [Member]
Variable Interest Entity [Line Items]
Number of purchase power agreements		3
Equity ownership percentage		100.00%
Atlantic City Electric Co [Member] | Non-Utility Generators [Member]
Variable Interest Entity [Line Items]
Megawatts received from power purchase agreements (PPAs)		459
Purchased energy		59	54
Net power purchases with non-utility generators		$ 72	$ 54