Pension And Other Postretirement Benefits (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$ 60	$ 200
Pension and other postretirement net periodic benefit cost	25	26
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		85
Pension and other postretirement net periodic benefit cost	8	11
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	10	85
Pension and other postretirement net periodic benefit cost	4	6
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	30	30
Pension and other postretirement net periodic benefit cost	5	6
Other Postretirement Benefits [Member] | PHI Service Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	20
Other Postretirement Benefits [Member] | Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		85
Other Postretirement Benefits [Member] | Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	10	85
Other Postretirement Benefits [Member] | Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$ 30	$ 30