Variable Interest Entities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 MW	Jun. 30, 2013 MW	Jun. 30, 2014 MW	Jun. 30, 2013 MW	Oct. 18, 2011 MW
Delmarva Power & Light Co/De [Member] | Fuel Cell Facility [Member]
Variable Interest Entity [Line Items]
Power of fuel cell facility	30	15	30	15	30
Amount billed to distribution customers	$ 9	$ 3	$ 18	$ 6
Delmarva Power & Light Co/De [Member] | Fuel Cell Facility [Member] | October 18, 2011 [Member]
Variable Interest Entity [Line Items]
Term of agreement			Through 2033
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			19
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		2
Delmarva Power & Light Co/De [Member] | Solar PPA [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Solar energy purchases		1		1
Delmarva Power & Light Co/De [Member] | Wind PPA [Member]
Variable Interest Entity [Line Items]
Purchased energy	7	7	17	17
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]
Equity ownership percentage	100.00%		100.00%
Atlantic City Electric Co [Member] | Non-Utility Generators [Member]
Variable Interest Entity [Line Items]
Megawatts received from power purchase agreements (PPAs)			459
Number of purchase power agreements			3
Purchased energy	49	48	108	103
Net power purchases with non-utility generators	$ 54	$ 53	$ 126	$ 107