Related Party Transactions - BSC and PHISCO Service Companies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	$ 149	$ 148	$ 431	$ 390
PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	18	15	54	45
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	177	132	458	409
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	145	133	424	406
Related Party Transaction Capitalized Costs Support Services	43	13	76	37
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	73	69	217	209
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	71	65	214	204
Related Party Transaction Capitalized Costs Support Services	47	49	148	133
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	43	37	126	114
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	41	34	120	107
Related Party Transaction Capitalized Costs Support Services	12	20	57	53
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	46	39	137	122
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	45	38	133	120
Related Party Transaction Capitalized Costs Support Services	20	30	62	88
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	43	38	122	111
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	40	36	116	107
Related Party Transaction Capitalized Costs Support Services	27	36	88	79
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	18	15	54	45
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	52	49	155	152
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	23	20	68	61
Related Party Transaction Capitalized Costs Support Services	11	14	36	29
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	26	28	84	90
Related Party Transaction Capitalized Costs Support Services	7	7	22	20
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	40	37	117	112
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	14	13	43	38
Related Party Transaction Capitalized Costs Support Services	10	12	29	26
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	24	24	73	73
Related Party Transaction Capitalized Costs Support Services	6	4	17	13
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	35	32	103	98
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	14	11	37	32
Related Party Transaction Capitalized Costs Support Services	7	10	22	22
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	21	21	64	65
Related Party Transaction Capitalized Costs Support Services	$ 5	$ 4	$ 15	$ 12