Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended										9 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Line Items]
Operating Revenues		$ 8,381	$ 8,769	$ 7,623	$ 8,757	$ 7,875	$ 9,002	$ 6,910	$ 7,573				$ 33,531	$ 31,360	$ 29,447
Operating Income (Loss)		1,258	1,475	232	1,296	714	1,267	647	483				4,260	3,112	4,409
Net Income (Loss) Attributable to Common Stockholders		1,871	824	80	995	204	490	267	173				3,770	1,134	2,269
Net Income (Loss)													3,849	1,204	2,250
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 12	4,654	4,751	4,174	4,888	4,388	5,035	3,589	4,739				18,466	17,751	19,135
Operating Income (Loss)		501	500	(467)	387	94	342	(13)	415				921	836	2,275
Net (Loss) Income Attributable to Membership Interest		2,215	305	(250)	423	(41)	236	(8)	310
Net Income (Loss)													2,771	558	1,340
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		1,309	1,571	1,357	1,298	1,223	1,497	1,286	1,249				5,536	5,254	4,905
Operating Income (Loss)		286	404	319	314	217	389	324	274				1,323	1,205	1,017
Net Income (Loss)		120	189	118	141	80	37	145	115				567	378	426
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		729	715	630	796	701	788	664	841				2,870	2,994	3,032
Operating Income (Loss)		157	169	137	192	150	204	152	196				655	702	630
Net Income (Loss) Attributable to Common Stockholders		107	112	88	127	92	122	100	124				434	438	378
Net Income (Loss)													434	438	378
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		813	738	674	951	812	812	680	929				3,176	3,233	3,135
Operating Income (Loss)		163	124	98	228	190	115	59	187				614	550	558
Net Income (Loss) Attributable to Common Stockholders		76	62	45	125	103	54	31	98				307	286	275
Net Income (Loss)													307	294	288
Pepco Holdings LLC [Member] | Predecessor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues											$ 1,153				4,935
Operating Income (Loss)											105				673
Net (Loss) Income Attributable to Membership Interest											19
Net Income (Loss)											$ 19				327
Pepco Holdings LLC [Member] | Successor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		1,121	1,310	1,074	1,175	1,078	1,394	1,066	105	[1]		$ 3,643	4,679
Operating Income (Loss)		159	285	148	180	90	279	136	(411)	[1]		93	769
Net (Loss) Income Attributable to Membership Interest		4	153	66	140	30	166	52	(309)	[1]
Net Income (Loss)												$ (61)	362
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		510	604	514	530	491	635	509	551				2,158	2,186	2,129
Operating Income (Loss)		87	149	84	79	51	132	97	(105)				399	174	385
Net Income (Loss) Attributable to Common Stockholders		17	87	43	58	23	79	49	(108)
Net Income (Loss)													205	42	187
Delmarva Power and Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		330	327	282	362	303	331	281	362				1,300	1,277	1,302
Operating Income (Loss)		52	59	41	78	20	72	30	(72)				229	50	165
Net Income (Loss) Attributable to Common Stockholders		14	31	19	57	7	44	12	(72)
Net Income (Loss)													121	(9)	76
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues		271	370	270	275	275	421	270	291				1,186	1,257	1,295
Operating Income (Loss)		28	79	25	25	26	83	19	(121)				157	7	134
Net Income (Loss) Attributable to Common Stockholders		$ 0	$ 41	$ 8	$ 28	$ 8	$ 47	$ 3	$ (100)
Net Income (Loss)													$ 77	$ (42)	$ 40

[1] Amounts for March 31, 2016 reflect the PHI Successor activity for the period March 24, 2016 to March 31, 2016.