Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Significant Accounting Policies [Line Items]
Incremental storm restoration cost	$ 30,000,000		$ 30,000,000
Cost incurred for storm related repair work	12,000,000		12,000,000
Capitalized storm costs	18,000,000		18,000,000
Regulatory assets	10,000,000		10,000,000
Other operation and maintenance expense	2,000,000		2,000,000
Estimated portion of incremental storm restoration cost	24,000,000		$ 24,000,000
Estimated fair value of an asset			Greater than 50%
Taxes included in gross revenues	81,000,000	$ 78,000,000	$ 164,000,000	$ 161,000,000
Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Incremental storm restoration cost	4,000,000		4,000,000
Cost incurred for storm related repair work	2,000,000		2,000,000
Capitalized storm costs	2,000,000		2,000,000
Regulatory assets	1,000,000		1,000,000
Other operation and maintenance expense	2,000,000		2,000,000
Estimated portion of incremental storm restoration cost	2,000,000		$ 2,000,000
Estimated fair value of an asset			Greater than 50%
Taxes included in gross revenues	5,000,000	4,000,000	$ 9,000,000	8,000,000
Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Incremental storm restoration cost	26,000,000		26,000,000
Cost incurred for storm related repair work	10,000,000		10,000,000
Capitalized storm costs	16,000,000		16,000,000
Regulatory assets	10,000,000		10,000,000
Estimated portion of incremental storm restoration cost	22,000,000		22,000,000
Taxes included in gross revenues	1,000,000	1,000,000	1,000,000	1,000,000
Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues	$ 76,000,000	$ 74,000,000	$ 155,000,000	$ 152,000,000