Quarterly Data (Unaudited) - Quarterly Operating Results (Details) - USD ($) $ in Millions	3 Months Ended										9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016		Mar. 23, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Information [Line Items]
Operating Revenues	$ 7,875	$ 9,002	$ 6,910	$ 7,573			$ 6,702	$ 7,401	$ 6,514	$ 8,830		$ 31,360	$ 29,447	$ 27,429
Operating Income (Loss)	714	1,267	647	483			707	1,200	1,134	1,366		3,112	4,409	3,096
Net Income (Loss) Attributable to Common Stockholders	204	490	267	173			309	629	638	693		1,134	2,269	1,623
Net income												1,204	2,250	1,820
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	4,388	5,035	3,589	4,739			4,294	4,768	4,232	5,840		17,751	19,135	17,393
Operating Income (Loss)	94	342	(13)	415			230	622	703	719		836	2,275	1,176
Net (Loss) Income Attributable to Membership Interest	(41)	236	(8)	310			154	377	398	443		496	1,372	835
Net income												558	1,340	1,019
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,223	1,497	1,286	1,249			1,196	1,376	1,148	1,185		5,254	4,905	4,564
Operating Income (Loss)	217	389	324	274			217	327	243	230		1,205	1,017	980
Net income	80	37	145	115			87	149	99	90		378	426	408
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	701	788	664	841			645	740	661	985		2,994	3,032	3,094
Operating Income (Loss)	150	204	152	196			128	154	124	223		702	630	572
Net Income (Loss) Attributable to Common Stockholders	92	122	100	124			79	90	70	139		438	378	352
Net income												438	378	352
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	812	812	680	929			746	725	628	1,036		3,233	3,135	3,165
Operating Income (Loss)	190	115	59	187			144	110	99	204		550	558	439
Net Income (Loss) Attributable to Common Stockholders	103	54	31	98			74	51	44	106		286	275	198
Net income												294	288	211
Pepco Holdings LLC [Member] | Successor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	1,078	1,394	1,066	105	[1]						$ 3,643
Operating Income (Loss)	90	279	136	(411)	[1]						93
Net (Loss) Income Attributable to Membership Interest	30	166	52	(309)	[1]						(61)
Net income											$ (61)
Pepco Holdings LLC [Member] | Predecessor [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues						$ 1,153	1,126	1,336	1,119	1,354			4,935	4,808
Operating Income (Loss)						105	208	184	139	142			673	605
Net (Loss) Income Attributable to Membership Interest						19	130	91	53	53			327	242
Net income						$ 19							327	242
Potomac Electric Power Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	491	635	509	551			488	592	504	545		2,186	2,129	2,055
Operating Income (Loss)	51	132	97	(105)			123	115	83	63		174	385	349
Net Income (Loss) Attributable to Common Stockholders	23	79	49	(108)			59	60	42	26		42	187	171
Net income												42	187	171
Delmarva Power and Light Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	303	331	281	362			296	314	271	421		1,277	1,302	1,282
Operating Income (Loss)	20	72	30	(72)			46	32	24	63		50	165	207
Net Income (Loss) Attributable to Common Stockholders	7	44	12	(72)			21	15	8	32		(9)	76	104
Net income												(9)	76	104
Atlantic City Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Operating Revenues	275	421	270	291			291	386	285	334		1,257	1,295	1,210
Operating Income (Loss)	26	83	19	(121)			29	51	25	29		7	134	137
Net Income (Loss) Attributable to Common Stockholders	$ 8	$ 47	$ 3	$ (100)			$ 3	$ 22	$ 6	$ 9		(42)	40	46
Net income												$ (42)	$ 40	$ 46

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