Variable Interest Entities - Additional Information (Detail) $ in Millions		12 Months Ended
	Oct. 18, 2011 MW	Dec. 31, 2015 USD ($) MWh Agreement MW	Dec. 31, 2014 USD ($) MWh MW	Dec. 31, 2013 USD ($)
Delmarva Power & Light Co/De [Member]
Variable Interest Entity [Line Items]
Power produced by fuel cell facility	30
Power produced by fuel cell facility | MWh		227,113	222,948
Delmarva Power & Light Co/De [Member] | Fuel Cell Facility [Member]
Variable Interest Entity [Line Items]
Term of agreement		Through 2033
Amount billed to distribution customers, respect to energy produced by these facilities | $		$ 37	$ 36	$ 23
Delmarva Power & Light Co/De [Member] | Wind PPA [Member]
Variable Interest Entity [Line Items]
Purchased energy | $		$ 29	$ 31	30
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
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 | Agreement		1
Energy purchase maximum to be purchased		28	19
Term of agreement		Through 2030
Term of agreement, years		20 years
Obligated purchase amount of energy produced at the facility		70.00%
Solar energy purchases | $		$ 6	$ 6	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 | Agreement		3
Delmarva Power & Light Co/De [Member] | 2015 PPA [Member] | Maximum [Member]
Variable Interest Entity [Line Items]
Expected time frame for facilities to be operational		1 year
Atlantic City Electric Co [Member]
Variable Interest Entity [Line Items]
Purchase activities with non utility generators per power purchase agreements | $		$ 198	208	206
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
Number of purchase power agreements | Agreement		3
Purchased energy | $		$ 208	$ 233	$ 221