Quarterly Financial Information - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ 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]
Total Operating Revenue	$ 1,150	$ 1,362	$ 1,140	$ 1,371	$ 1,118	$ 1,313	$ 1,117	$ 1,330	$ 5,023	$ 4,878	$ 4,666
Total operating expenses	941	1,179	1,001	1,229	1,004	1,147	966	1,157	4,350	4,274	3,998
Operating Income (Loss)	209	183	139	142	114	166	151	173	673	604	668
Other Expenses	(65)	(43)	(59)	(59)	(66)	(53)	(53)	(52)	(226)	(224)	(239)
Income Before Income Tax Expense	144	140	80	83	48	113	98	121	447	380	429
Income Tax Expense	23	49	27	30	13	34	45	46	129	138	319
Net Income from Continuing Operations	121	91	53	53					318	242	110
Income from Discontinued Operations, net of taxes	9								9		(322)
Net Income	$ 130	$ 91	$ 53	$ 53	$ 35	$ 79	$ 53	$ 75	$ 327	$ 242	$ (212)
Earnings Per Share of Common Stock from Continuing Operations	$ 0.48	$ 0.36	$ 0.21	$ 0.21					$ 1.25
Earnings Per Share of Common Stock from Discontinued Operations	0.03								0.04
Basic and Diluted Earnings Per Share of	0.51	0.36	0.21	0.21	$ 0.14	$ 0.31	$ 0.21	$ 0.30	1.29	$ 0.96
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
Atlantic City Electric Co [Member]
Quarterly Financial Information [Line Items]
Total operating expenses	$ 252	$ 349	$ 254	$ 313	$ 246	$ 295	$ 228	$ 309	$ 1,168	$ 1,078	$ 1,066
Operating Income (Loss)	40	38	32	20	27	52	25	31	130	135	136
Other Expenses	(15)	(17)	(15)	(14)	(17)	(15)	(15)	(15)	(61)	(62)	(67)
Income Before Income Tax Expense	25	21	17	6	10	37	10	16	69	73	69
Income Tax Expense	15	7	7	2	4	14	4	6	31	28	19
Net Income	10	14	10	4	6	23	6	10	38	45	50
Total Operating Revenue	292	387	286	333	273	347	253	340	1,298	1,213	1,202
Potomac Electric Power Co [Member]
Quarterly Financial Information [Line Items]
Total operating expenses	379	497	435	493	408	462	414	469	1,804	1,753	1,705
Operating Income (Loss)	124	115	83	63	63	125	94	66	385	348	321
Other Expenses	(29)	(23)	(23)	(25)	(27)	(20)	(20)	(18)	(100)	(85)	(92)
Income Before Income Tax Expense	95	92	60	38	36	105	74	48	285	263	229
Income Tax Expense	36	32	18	12	10	38	28	16	98	92	79
Net Income	59	60	42	26	26	67	46	32	187	171	150
Total Operating Revenue	503	612	518	556	471	587	508	535	2,189	2,101	2,026
Delmarva Power & Light Co/De [Member]
Quarterly Financial Information [Line Items]
Total operating expenses	256	285	251	361	257	264	239	326	1,153	1,086	1,059
Operating Income (Loss)	47	32	24	62	51	45	40	71	165	207	185
Other Expenses	(12)	(8)	(11)	(9)	(12)	(9)	(8)	(9)	(40)	(38)	(40)
Income Before Income Tax Expense	35	24	13	53	39	36	32	62	125	169	145
Income Tax Expense	14	9	5	21	14	13	13	25	49	65	56
Net Income	21	15	8	32	25	23	19	37	76	104	89
Total Operating Revenue	$ 303	$ 317	$ 275	$ 423	$ 308	$ 309	$ 279	$ 397	$ 1,318	$ 1,293	$ 1,244