Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Pension contributions					$ 120	$ 200
PHI Service Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		20			20
Additional Pension contribution	60				60
Projected benefit obligation	100
Amortization period	10 years
Net periodic benefit cost	13				13
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		10		85	10	85
Pension and other postretirement net periodic benefit cost	29		30		54	56
Pension and other postretirement net periodic benefit cost	6		6		10	12
Delmarva Power & Light Co/De [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		10		85	10	85
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		30		30	30	30
Pension and other postretirement net periodic benefit cost	29		30		54	56
Pension and other postretirement net periodic benefit cost	5		6		10	12
Atlantic City Electric Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		30		30	30	30
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions				85		85
Pension and other postretirement net periodic benefit cost	29		30		54	56
Pension and other postretirement net periodic benefit cost	11		9		19	20
Potomac Electric Power Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions				$ 85		$ 85