Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information [Line Items]
Revenues	$ 8,343	$ 8,929	$ 7,689	$ 9,477	$ 8,812	$ 9,401	$ 8,074	$ 9,691	$ 34,438	$ 35,978	$ 33,558
Operating income (loss)	962	1,353	841	1,218	706	1,144	940	1,099	4,374	3,891	4,388
Net income attributable to common shareholders	773	772	484	907	152	731	537	583	2,936	2,005	3,779
Net income (loss)									3,028	2,079	3,869
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	4,644	4,774	4,210	5,296	5,069	5,278	4,579	5,512	18,924	20,437	18,500
Operating income (loss)	362	482	147	333	35	311	282	347	1,323	975	947
Net Income (Loss) Attributable to Parent	397	257	108	363	(178)	234	178	136	1,125	370	2,710
Net income (loss)									1,217	443	2,798
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,405	1,583	1,351	1,408	1,373	1,598	1,398	1,512	5,747	5,882	5,536
Operating income (loss)	255	328	311	276	242	323	288	292	1,171	1,146	1,323
Net income (loss)	144	200	186	157	141	193	164	165	688	664	567
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	766	778	655	900	765	757	653	866	3,100	3,038	2,870
Operating income (loss)	162	183	145	222	165	154	127	142	713	587	655
Net income (loss)	118	140	102	168	124	126	96	113	528	460	434
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	779	703	649	976	799	731	662	977	3,106	3,169	3,176
Operating income (loss)	142	91	80	220	109	103	85	177	532	474	614
Net income (loss)	99	55	45	160	71	63	51	128	360	313	307
Pepco Holdings LLC [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,107	1,380	1,091	1,228	1,115	1,359	1,074	1,249	4,806	4,798	4,672
Operating income (loss)	128	256	165	175	124	243	151	124	722	643	762
Net income (loss)	65	189	106	117	62	185	82	63	477	393	355
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	513	642	531	575	529	626	521	555	2,260	2,232	2,151
Operating income (loss)	57	127	93	84	63	110	83	54	361	313	392
Net income (loss)	26	98	64	55	36	87	52	29	243	205	198
Quarterly Financial Information, Quarterly Charges and Credits, Amount Reconciling to Previously Reported Results	6
Delmarva Power & Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	319	319	287	380	331	328	289	384	1,306	1,332	1,300
Operating income (loss)	50	51	44	72	48	51	42	49	217	190	229
Net income (loss)	31	33	30	53	30	33	26	31	147	120	121
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	274	419	274	273	254	406	265	310	1,240	1,236	1,186
Operating income (loss)	23	79	28	21	14	84	25	23	151	149	157
Net income (loss)	$ 12	$ 63	$ 14	$ 10	$ (1)	$ 61	$ 8	$ 7	$ 99	$ 75	$ 77