Income Taxes - Summary of Interest Expense (Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ (13)	$ (36)	$ 391
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	(31)	(50)	17
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	7	6	281
PECO Energy Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	0	0	(1)
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 0	$ 1	$ 0