Related Party Transactions - BSC and PHISCO Service Companies (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	$ 113	$ 99
PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	14	22
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	142	150
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	11	11
Related Party Transaction, Expenses from Transactions with Related Party	140	149
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	74	62
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	42	25
Related Party Transaction, Expenses from Transactions with Related Party	72	62
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	38	38
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	16	22
Related Party Transaction, Expenses from Transactions with Related Party	37	37
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	42	39
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	28	21
Related Party Transaction, Expenses from Transactions with Related Party	41	38
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	38	33
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	16	19
Related Party Transaction, Expenses from Transactions with Related Party	37	32
Pepco Holdings LLC [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	14	22
Related Party Transaction, Expenses from Transactions with Related Party	0	0
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	51	54
Potomac Electric Power Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	6	8
Related Party Transaction, Expenses from Transactions with Related Party	21	21
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	6	9
Related Party Transaction, Expenses from Transactions with Related Party	30	33
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	37	39
Delmarva Power and Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	5	5
Related Party Transaction, Expenses from Transactions with Related Party	13	13
Delmarva Power and Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	4	7
Related Party Transaction, Expenses from Transactions with Related Party	24	26
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	33	34
Atlantic City Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	4	4
Related Party Transaction, Expenses from Transactions with Related Party	11	11
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	4	6
Related Party Transaction, Expenses from Transactions with Related Party	$ 22	$ 23