Quarterly Financial Information - Schedule of Quarterly Financial Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information [Line Items]
Total operating revenue	$ 1,118	$ 1,313	$ 1,117	$ 1,330	$ 1,091	$ 1,344	$ 1,051	$ 1,180	$ 4,878	$ 4,666	$ 4,625
Total operating expenses	1,004	1,147	966	1,157	936	1,109	906	1,047	4,274	3,998	4,084
Operating Income (Loss)	114	166	151	173	155	235	145	133	604	668	541
Other Expenses	(66)	(53)	(53)	(52)	(58)	(60)	(62)	(59)	(224)	(239)	(220)
Income from Continuing Operations Before Income Tax Expense	48	113	98	121	97	175	83	74	380	429	321
Income Tax Expense Related to Continuing Operations	13	34	45	46	39	65	30	185	138	319	103
Net Income from Continuing Operations					58	110	53	(111)	242	110	218
(Loss) Income from Discontinued Operations, net of taxes						8	(11)	(319)		(322)	67
Net Income (loss)	35	79	53	75	58	118	42	(430)	242	(212)	285
Basic and Diluted Earnings Per Share of Common Stock:
(Loss) Earnings Per Share of Common Stock from Continuing Operations					$ 0.23	$ 0.44	$ 0.21	$ (0.47)		$ 0.45
(Loss) Earnings Per Share of Common Stock from Discontinued Operations						$ 0.04	$ (0.04)	$ (1.35)		$ (1.31)
(Loss) Earnings Per Share of Common Stock	$ 0.14	$ 0.31	$ 0.21	$ 0.30	$ 0.23	$ 0.48	$ 0.17	$ (1.82)	$ 0.96	$ (0.86)
Cash Dividends Per Share of Common Stock	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 0.27	$ 1.08	$ 1.08	$ 1.08
Potomac Electric Power Co [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	471	587	508	535	475	605	469	477	2,101	2,026	1,948
Total operating expenses	408	462	414	469	410	476	389	430	1,753	1,705	1,691
Operating Income (Loss)	63	125	94	66	65	129	80	47	348	321	257
Other Expenses	(27)	(20)	(20)	(18)	(24)	(23)	(23)	(22)	(85)	(92)	(83)
Income from Continuing Operations Before Income Tax Expense	36	105	74	48	41	106	57	25	263	229	174
Income Tax Expense Related to Continuing Operations	10	38	28	16	17	40	20	2	92	79	48
Net Income (loss)	26	67	46	32	24	66	37	23	171	150	126
Delmarva Power & Light Co/De [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	308	309	279	397	312	296	266	370	1,293	1,244	1,233
Total operating expenses	257	264	239	326	258	249	235	317	1,086	1,059	1,079
Operating Income (Loss)	51	45	40	71	54	47	31	53	207	185	154
Other Expenses	(12)	(9)	(8)	(9)	(9)	(10)	(10)	(11)	(38)	(40)	(37)
Income from Continuing Operations Before Income Tax Expense	39	36	32	62	45	37	21	42	169	145	117
Income Tax Expense Related to Continuing Operations	14	13	13	25	17	14	9	16	65	56	44
Net Income (loss)	25	23	19	37	28	23	12	26	104	89	73
Atlantic City Electric Co [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	273	347	253	340	258	396	271	277	1,213	1,202	1,198
Total operating expenses	246	295	228	309	229	341	242	254	1,078	1,066	1,079
Operating Income (Loss)	27	52	25	31	29	55	29	23	135	136	119
Other Expenses	(17)	(15)	(15)	(15)	(15)	(17)	(18)	(17)	(62)	(67)	(66)
Income from Continuing Operations Before Income Tax Expense	10	37	10	16	14	38	11	6	73	69	53
Income Tax Expense Related to Continuing Operations	4	14	4	6	5	13	4	(3)	28	19	18
Net Income (loss)	$ 6	$ 23	$ 6	$ 10	$ 9	$ 25	$ 7	$ 9	$ 45	$ 50	$ 35