Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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	$ 1,000,000		$ 3,000,000
Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	$ 0
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0
Pension and other postretirement net periodic benefit cost	25,000,000	$ 16,000,000	73,000,000	44,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	7,000,000	5,000,000	22,000,000	16,000,000
Potomac Electric Power Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0
Pension and other postretirement net periodic benefit cost	25,000,000	16,000,000	73,000,000	44,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	3,000,000	1,000,000	11,000,000	5,000,000
Delmarva Power & Light Co/De [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0
Pension and other postretirement net periodic benefit cost	25,000,000	16,000,000	73,000,000	44,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	$ 3,000,000	$ 4,000,000	11,000,000	10,000,000
Atlantic City Electric Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			$ 0	$ 0