Related Party Transactions - BSC and PHISCO Service Companies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	$ 516	$ 448	$ 330
PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction Capitalized Costs Support Services	72	79	0
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	587	661	697
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	570	652	689
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	66	67	98
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	264	267	270
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	263	265	270
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	148	135	118
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	154	156	149
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	149	146	146
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	88	64	59
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	160	162	153
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	157	157	152
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	126	79	54
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	143	152	150
Pepco Holdings LLC [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	139	147	145
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	88	102	0
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
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	72	79	0
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	209	226	58
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	85	89	53
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	38	40	0
Potomac Electric Power Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	124	137	5
Other Cost and Expense, Operating			219
Related Party Transaction Capitalized Costs Support Services	33	32	0
Potomac Electric Power Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0
Other Cost and Expense, Operating			29
Related Party Transaction Capitalized Costs Support Services	0	0	0
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	152	162	32
Delmarva Power & Light Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	52	51	31
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	25	28	0
Delmarva Power & Light Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	100	111	0
Other Cost and Expense, Operating			165
Related Party Transaction Capitalized Costs Support Services	20	25	0
Delmarva Power & Light Company [Member] | Pepco Energy Services Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	0	0	0
Other Cost and Expense, Operating			9
Related Party Transaction Capitalized Costs Support Services	0	0	0
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	133	142	28
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	42	42	25
Other Cost and Expense, Operating			0
Related Party Transaction Capitalized Costs Support Services	19	20	0
Atlantic City Electric Company [Member] | PHI Service Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	90	98	0
Other Cost and Expense, Operating			135
Related Party Transaction Capitalized Costs Support Services	$ 19	$ 21	$ 0