Significant Accounting Policies (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended
	Oct. 31, 2011 Y MW	Mar. 31, 2013 MW	Mar. 31, 2012	Jun. 30, 2012 MW
Significant Accounting Policies [Line Items]
Purchase of energy		$ 600	$ 641
Taxes included in gross revenues		84	86
Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Number of purchase power agreements		3
Term of agreement, years		15
Equity ownership percentage		100.00%
Number of Standard Offer Capacity Agreements		3
Estimated share of payments received or made to generation companies		15.00%
Taxes included in gross revenues		3	4
Atlantic City Electric Co [Member] | Non-Utility Generators [Member]
Significant Accounting Policies [Line Items]
Megawatts received from power purchase agreements (PPAs)		459
Net power purchases with non-utility generators		54	51
Purchase of energy		54	50
Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues		4	4
Delmarva Power & Light Co/De [Member] | Fuel Cell Facility [Member]
Significant Accounting Policies [Line Items]
Term of agreement, years	21
Power of fuel cell facility, MW	30	27		3
Increments to power of fuel cell facility, MW		5
Amount billed to distribution customers		3	0
Delmarva Power & Light Co/De [Member] | Wind PPA [Member]
Significant Accounting Policies [Line Items]
Megawatts received from power purchase agreements (PPAs)		128
Purchase of energy		10	9
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility One [Member]
Significant Accounting Policies [Line Items]
Energy purchase maximum to be purchased, MW		50
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility Two [Member]
Significant Accounting Policies [Line Items]
Energy purchase maximum to be purchased, MW		40
Delmarva Power & Light Co/De [Member] | Wind PPA [Member] | Wind Facility Three [Member]
Significant Accounting Policies [Line Items]
Energy purchase maximum to be purchased, MW		38
Delmarva Power & Light Co/De [Member] | Solar PPA [Member]
Significant Accounting Policies [Line Items]
Number of purchase power agreements		1
Megawatts received from power purchase agreements (PPAs)		10
Term of agreement, years		20
Obligated purchase amount of energy produced at the facility		70.00%
Delmarva Power & Light Co/De [Member] | Solar PPA [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Solar energy purchases		1	0
Delmarva Power & Light Co/De [Member] | Land-Based Wind PPA [Member]
Significant Accounting Policies [Line Items]
Number of purchase power agreements		3
Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues		$ 77	$ 78