Quarterly Financial Information - Schedule of Quarterly Financial Information (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information [Line Items]
Increase in fair value of preferred stock derivative		$ 15							$ 15
Increase in fair value of preferred stock derivative, after-tax		10
Pretax gains on sales of land	$ 46								46
Aftertax gains on sales of land	27
Income tax benefit	23	49	$ 27	$ 30	$ 13	$ 34	$ 45	$ 46	129	$ 138	$ 319
Charge to correct prior period error after-tax	7
Tax Settlement [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	(47)
Income tax benefit discontinued operations	(9)
Pepco Energy Services [Member]
Quarterly Financial Information [Line Items]
Impairment losses, pre-tax					28	53
Impairment losses, after-tax					16	32
Atlantic City Electric Co [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	15	7	7	2	4	14	4	6	31	28	19
Charge to correct prior period error after-tax	2				2
Reversed unbilled revenue, pre-tax					3
Reversed unbilled revenue, after-tax					2
Charge to correct prior period error before tax					3
Atlantic City Electric Co [Member] | Tax Settlement [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	3
Potomac Electric Power Co [Member]
Quarterly Financial Information [Line Items]
Pretax gains on sales of land	46								46
Aftertax gains on sales of land	27
Income tax benefit	36	32	18	12	10	38	28	16	98	92	79
Charge to correct prior period error after-tax	6
Interest expense on uncertain tax positions	3
Potomac Electric Power Co [Member] | Tax Settlement [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	(9)
Delmarva Power & Light Co/De [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	14	$ 9	$ 5	$ 21	$ 14	$ 13	$ 13	$ 25	49	$ 65	$ 56
Delmarva Power & Light Co/De [Member] | Tax Settlement [Member]
Quarterly Financial Information [Line Items]
Income tax benefit	$ 3								$ 3