Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 8,814	$ 9,403	$ 8,076	$ 9,693	$ 8,384	$ 8,768	$ 7,665	$ 8,747	$ 35,985	$ 33,565	$ 31,366
Operating income (loss)	708	1,146	942	1,101	1,288	1,499	300	1,308	3,898	4,395	3,212
Net income attributable to common shareholders	152	733	539	585	1,880	823	95	990	2,010	3,786	1,121
Net income (loss)									2,084	3,876	1,196
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	5,069	5,278	4,579	5,512	4,657	4,750	4,216	4,878	20,437	18,500	17,757
Operating income (loss)	35	311	282	347	504	497	(427)	373	975	947	820
Net income (loss) attributable to membership interest	(178)	234	178	136	2,224	304	(235)	418	370	2,710	483
Net income (loss)									443	2,798	550
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,373	1,598	1,398	1,512	1,309	1,571	1,357	1,298	5,882	5,536	5,254
Operating income (loss)	242	323	288	292	286	404	319	314	1,146	1,323	1,205
Net income (loss)	141	193	164	165	120	189	118	141	664	567	378
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	765	757	653	866	729	715	630	796	3,038	2,870	2,994
Operating income (loss)	165	154	127	142	157	169	137	192	587	655	702
Net income (loss)	124	126	96	113	107	112	88	127	460	434	438
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	799	731	662	977	813	738	674	951	3,169	3,176	3,233
Operating income (loss)	109	103	85	177	163	124	98	228	474	614	550
Net income attributable to common shareholders									313	307	286
Net income (loss)	71	63	51	128	76	62	45	125	313	307	294
Pepco Holdings LLC [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,117	1,361	1,076	1,251	1,121	1,310	1,074	1,175	4,805	4,679
Operating income (loss)	126	245	153	126	159	285	148	180	650	769
Net income (loss) attributable to membership interest	62	187	84	65	4	153	66	140	398	362
Net income (loss)									398	362
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	531	628	523	557	510	604	514	530	2,239	2,158	2,186
Operating income (loss)	65	112	85	56	87	149	84	79	320	399	174
Net income (loss)	36	89	54	31	17	87	43	58	210	205	42
Delmarva Power & Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	331	328	289	384	330	327	282	362	1,332	1,300	1,277
Operating income (loss)	48	51	42	49	52	59	41	78	190	229	50
Net income (loss)	30	33	26	31	14	31	19	57	120	121	(9)
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	254	406	265	310	271	370	270	275	1,236	1,186	1,257
Operating income (loss)	14	84	25	23	28	79	25	25	149	157	7
Net income (loss)	$ (1)	$ 61	$ 8	$ 7	$ 0	$ 41	$ 8	$ 28	$ 75	$ 77	$ (42)