Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs					36.00%
Pension and other postretirement net periodic benefit cost			$ (3,000,000)		$ 2,000,000
Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$ 0	$ 0	0	$ 0
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	0	0	0	0
Pension and other postretirement net periodic benefit cost	24,000,000		10,000,000		48,000,000	$ 28,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	7,000,000		4,000,000		15,000,000	11,000,000
Potomac Electric Power Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	0	0	0	0
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	0	0	0	0
Pension and other postretirement net periodic benefit cost	24,000,000		10,000,000		48,000,000	28,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	4,000,000		1,000,000		8,000,000	4,000,000
Delmarva Power & Light Co/De [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	0	0	0	0
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	0	0	0	0
Pension and other postretirement net periodic benefit cost	24,000,000		10,000,000		48,000,000	28,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	4,000,000		2,000,000		$ 8,000,000	$ 6,000,000
Atlantic City Electric Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$ 0	$ 0	$ 0	$ 0