Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Significant Accounting Policies [Line Items]
Incremental storm restoration cost	$ 39,000,000		$ 39,000,000
Cost incurred for storm related repair work	15,000,000		15,000,000
Capitalized storm costs	24,000,000		24,000,000
Regulatory assets	13,000,000		13,000,000
Other operation and maintenance expense	2,000,000		2,000,000
Estimated portion of incremental storm restoration cost	10,000,000		$ 10,000,000
Estimated fair value of an asset			Greater than 50%
Taxes included in gross revenues	85,000,000	$ 85,000,000	$ 249,000,000	$ 246,000,000
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	1,000,000		$ 1,000,000
Estimated fair value of an asset			Greater than 50%
Taxes included in gross revenues	4,000,000	4,000,000	$ 13,000,000	12,000,000
Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Incremental storm restoration cost	35,000,000		35,000,000
Cost incurred for storm related repair work	13,000,000		13,000,000
Capitalized storm costs	22,000,000		22,000,000
Regulatory assets	13,000,000		13,000,000
Estimated portion of incremental storm restoration cost	9,000,000		9,000,000
Taxes included in gross revenues	0	0	0	1,000,000
Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Taxes included in gross revenues	$ 81,000,000	$ 81,000,000	$ 236,000,000	$ 233,000,000