Related Party Transactions - BSC and PHISCO Service Companies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	$ 129	$ 132	$ 242	$ 232
PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	16	19	30	40
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	136	149	277	299
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	133	148	273	297
Related Party Transaction Capitalized Costs Support Services	14	14	25	26
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	67	60	140	122
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	67	60	138	122
Related Party Transaction Capitalized Costs Support Services	41	36	83	61
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	40	37	78	75
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	36	37	73	74
Related Party Transaction Capitalized Costs Support Services	18	24	33	46
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	41	40	83	78
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	40	39	82	77
Related Party Transaction Capitalized Costs Support Services	30	38	58	59
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	36	35	74	68
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	35	34	72	66
Related Party Transaction Capitalized Costs Support Services	26	20	43	40
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0	0
Related Party Transaction Capitalized Costs Support Services	16	19	30	40
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	52	52	103	107
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	20	22	41	43
Related Party Transaction Capitalized Costs Support Services	9	9	15	17
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	32	31	62	63
Related Party Transaction Capitalized Costs Support Services	7	9	13	17
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	38	38	75	76
Delmarva Power and Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	13	13	26	26
Related Party Transaction Capitalized Costs Support Services	9	6	14	11
Delmarva Power and Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	25	25	49	50
Related Party Transaction Capitalized Costs Support Services	5	5	9	12
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	34	33	66	67
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	11	11	21	21
Related Party Transaction Capitalized Costs Support Services	8	4	12	8
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	23	22	44	45
Related Party Transaction Capitalized Costs Support Services	$ 4	$ 5	$ 8	$ 11