Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
PHI Service Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs	36.00%
PHI Service Company [Member] | 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	24,000,000	18,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	8,000,000	7,000,000
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	24,000,000	18,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	4,000,000	3,000,000
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	24,000,000	18,000,000
Pension and other postretirement net periodic benefit cost, allocated portion	4,000,000	4,000,000
Atlantic City Electric Co [Member] | Retiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$ 0	$ 0