Commitments and Contingencies - Retained Environmental Exposures - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Jul. 31, 2010 USD ($) Facility	Dec. 31, 2012 USD ($)	Jun. 30, 2015 USD ($)
Commitments and Contingencies [Line Items]
Loss contingency liabilities			$ 12,000,000
Pepco Energy Services [Member]
Commitments and Contingencies [Line Items]
Certain allegedly unauthorized charges		$ 7,000,000
Additional compounded interest		9,000,000
Pepco Energy Services [Member] | Pending Litigation [Member]
Commitments and Contingencies [Line Items]
Certain allegedly unauthorized charges		4,000,000
Additional compounded interest		$ 5,000,000
Conectiv Energy [Member]
Commitments and Contingencies [Line Items]
Third party maximum and seller floor for environmental remediation costs	$ 10,000,000
Number of facility locations | Facility	9
Environmental remediation expense minimum	$ 7,000,000
Environmental remediation expense maximum	18,000,000
PHI [Member]
Commitments and Contingencies [Line Items]
Third party maximum and seller floor for environmental remediation costs	$ 10,000,000
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Loss contingency liabilities			4,000,000
Delmarva Power & Light Co/De [Member]
Commitments and Contingencies [Line Items]
Loss contingency liabilities			2,000,000
Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
Loss contingency liabilities			$ 6,000,000