Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013 Amendments
Defined Benefit Plan Disclosure [Line Items]
Pension contributions		$ 60	$ 20		$ 120
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs				37.00%
Number of amendments, PHI approved						2
Reduction in net periodic benefit cost	16			16
Potomac Electric Power Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			0	0	0
Number of amendments, PHI approved						2
Reduction in net periodic benefit cost	18			18
Pension and other postretirement net periodic benefit cost	10	29		28	54
Pension and other postretirement net periodic benefit cost, allocated portion	4	11		11	19
Potomac Electric Power Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs				37.00%
Delmarva Power & Light Co/De [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			10		10
Pension and other postretirement net periodic benefit cost	10	29		28	54
Pension and other postretirement net periodic benefit cost, allocated portion	1	6		4	10
Delmarva Power & Light Co/De [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs				37.00%
Number of amendments, PHI approved						2
Reduction in net periodic benefit cost	13			13
Atlantic City Electric Co [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			30	0	30
Pension and other postretirement net periodic benefit cost	10	29		28	54
Pension and other postretirement net periodic benefit cost, allocated portion	2	5		6	10
Atlantic City Electric Co [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of postretirement benefit costs				37.00%
Number of amendments, PHI approved						2
Reduction in net periodic benefit cost	$ 11			$ 11