Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended				0 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Minimum [Member]	Sep. 30, 2014 Maximum [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Potomac Electric Power Co [Member]	Sep. 30, 2013 Potomac Electric Power Co [Member]	Sep. 30, 2014 Potomac Electric Power Co [Member]	Sep. 30, 2013 Potomac Electric Power Co [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member]	Sep. 30, 2014 Delmarva Power & Light Co/De [Member]	Sep. 30, 2013 Delmarva Power & Light Co/De [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Sep. 30, 2014 Atlantic City Electric Co [Member]	Sep. 30, 2013 Atlantic City Electric Co [Member]	Jun. 30, 2013 Adjustment [Member]
Significant Accounting Policies [Line Items]
Estimated fair value of an asset			Greater than 50%													Greater than 50%
Impairment losses	$ 53		$ 53				$ 53	$ 53	$ 53
Impairment losses, after-tax							32	32	32
Long-lived assets before impairment, carrying amount	83		83
Long lived assets after impairment, carrying amount	30		30
Asset group, carrying amount, before impairment loss	70		70
Percentage of change in the estimated cash flows			10.00%
Range of discount rates					10.00%	16.00%
Percentage of change in discount rate assumptions			1.00%
Taxes included in gross revenues	85	98	246	264						81	91	233	244	4	4	12	12	0	3	1	8
Prior period item reclassification adjustment in Net cash from operating activities				267									227				157				170
Prior period item reclassification adjustment change in Net cash from operating activities				9									3				1				5
Net Cash From Operating Activities				258									224				158				165
Prior period item reclassification adjustment in cash from financing activities				179									170				89				32
Prior period item reclassification adjustment Change in cash from financing activities				9									3				1				5
Net Cash From Financing Activities				170									173				88				37
Deferred income tax liabilities																						$ 32