Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 2,129	$ 587	$ 735	$ 1,349
Restricted cash	373	358	252	247
Restricted cash included in other long-term assets	178	177	191	185
Total cash, cash equivalents and restricted cash	2,680	1,122	1,178	1,781
Accrued Expenses [Abstract]
Compensation-related accruals	744	1,052
Taxes accrued	396	414
Interest accrued	357	337
Exelon Generation Co L L C [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	483	303	575	750
Restricted cash	153	146	122	153
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	636	449	697	903
Accrued Expenses [Abstract]
Compensation-related accruals	277	422
Taxes accrued	229	222
Interest accrued	53	65
Commonwealth Edison Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	403	90	65	135
Restricted cash	155	150	77	29
Restricted cash included in other long-term assets	166	163	174	166
Total cash, cash equivalents and restricted cash	724	403	316	330
Accrued Expenses [Abstract]
Compensation-related accruals	135	171
Taxes accrued	61	83
Interest accrued	119	110
PECO Energy Co [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	380	21	20	130
Restricted cash	7	6	6	5
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	387	27	26	135
Accrued Expenses [Abstract]
Compensation-related accruals	50	58
Taxes accrued	2	3
Interest accrued	37	37
Baltimore Gas and Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	195	24	8	7
Restricted cash	1	1	1	6
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	196	25	9	13
Accrued Expenses [Abstract]
Compensation-related accruals	52	78
Taxes accrued	19	26
Interest accrued	46	46
Pepco Holdings LLC [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	39	131	54	124
Restricted cash	36	36	37	43
Restricted cash included in other long-term assets	11	14	17	19
Total cash, cash equivalents and restricted cash	86	181	108	186
Accrued Expenses [Abstract]
Compensation-related accruals	92	101
Taxes accrued	73	117
Interest accrued	51	49
Potomac Electric Power Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	19	30	18	16
Restricted cash	33	33	34	37
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	52	63	52	53
Accrued Expenses [Abstract]
Compensation-related accruals	32	28
Taxes accrued	54	90
Interest accrued	25	23
Delmarva Power and Light Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	6	13	3	23
Restricted cash	0	0	1	1
Restricted cash included in other long-term assets	0	0	0	0
Total cash, cash equivalents and restricted cash	6	13	4	24
Accrued Expenses [Abstract]
Compensation-related accruals	18	19
Taxes accrued	5	14
Interest accrued	8	8
Atlantic City Electric Company [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	8	12	4	7
Restricted cash	3	2	2	4
Restricted cash included in other long-term assets	11	14	17	19
Total cash, cash equivalents and restricted cash	22	28	$ 23	$ 30
Accrued Expenses [Abstract]
Compensation-related accruals	14	15
Taxes accrued	8	8
Interest accrued	$ 13	$ 12