Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Credit risk derivative liabilities, at fair value	$ 0	$ 0
Cash plus borrowing capacity to meet future liquidity needs	736	332
Gross Derivative Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total Derivative asset	3	1
Net Derivative Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total Derivative asset	3
Delmarva Power & Light Co/De [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Credit risk derivative liabilities, at fair value	0	0
Cash plus borrowing capacity to meet future liquidity needs	736	332
Delmarva Power & Light Co/De [Member] | Gross Derivative Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total Derivative asset		1
Delmarva Power & Light Co/De [Member] | Gross Derivative Instruments [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total Derivative asset	1
Delmarva Power & Light Co/De [Member] | Net Derivative Instruments [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total Derivative asset	$ 1