Income Taxes - Summary of Interest Receivable (Payable) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Document Period End Date		Dec. 31, 2017
Net Interest Receivable Payable Related To Uncertain Tax Positions		$ 233	$ (507)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		(17)	(106)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		(3)	46
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	[1]	4	(384)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	(86)
PECO Energy Co [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		0	8
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	(1)
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net Interest Receivable Payable Related To Uncertain Tax Positions		2	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	1
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0	0
Delmarva Power and 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	1
Unrecognized Tax Benefits, Income Tax Penalties Accrued		$ 0	$ 0

[1] Change in balance attributable to Like-Kind Exchange interest payments, see Other Tax Matters for further discussion.