Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 318	$ 219
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	0	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Net Interest Income Expense Related To Uncertain Tax Positions	0	0	0
Unrecognized Tax Benefits, Income Tax Penalties Expense	$ 0	$ 0	$ 0