Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 236	$ 233
Unrecognized Tax Benefits, Income Tax Penalties Accrued	(17)	(17)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	(2)	(3)
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	4	4
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	1	2
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	0
Unrecognized Tax Benefits, Income Tax Penalties Accrued	$ 0	$ 0