Income Taxes - Summary of Interest Expense (Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			$ 106
Net interest (income) expense recognized related to uncertain tax positions			165	$ (13)	$ (36)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			(13)	(31)	(50)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties Expense			86
Net interest (income) expense recognized related to uncertain tax positions			117	7	6
PECO Energy Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			0	0	0
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			0	0	1
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			6	(4)	(1)
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			0	0	0
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions			$ (1)	0	(1)
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions		$ (2)
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 0			$ (34)	$ 0