Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended				12 Months Ended
	Nov. 01, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Potomac Electric Power Co [Member]	Mar. 31, 2013 Potomac Electric Power Co [Member]	Nov. 01, 2013 Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Delmarva Power & Light Co/De [Member]	Mar. 31, 2013 Delmarva Power & Light Co/De [Member]	Mar. 31, 2014 Atlantic City Electric Co [Member]	Mar. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2013 Adjustment [Member]
Significant Accounting Policies [Line Items]
Estimated fair value of an asset	Greater than 50%					Greater than 50%
Taxes included in gross revenues		$ 83	$ 84	$ 78	$ 77		$ 4	$ 4	$ 1	$ 3
Prior period item reclasification adjustment in Net cash used by operating activities			30		13			6		8
Prior period item reclasification adjustment Change in Net cash used by operating activities			(146)		37			54		23
Net Cash From (Used By) Operating Activities		284	(176)	66	24		92	48	112	15
Prior period item reclassification adjustment in cash from financing activities			30		13			6		8
Prior period item reclassification adjustment Change in cash from financing activities			542		178			32		57
Net Cash From Financing Activities		100	572	148	191		11	38	(55)	65
Deferred income tax liabilities											$ 32