Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ (507)	$ (288)
Unrecognized Tax Benefits, Income Tax Penalties Accrued	(106)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	46	80
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	(384)	(210)
Unrecognized Tax Benefits, Income Tax Penalties Accrued	(86)
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	8	3
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	(1)	(1)
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	1	20
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	0	3
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	1	24
Unrecognized Tax Benefits, Income Tax Penalties Accrued	0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions	$ 2
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		$ (34)