Income Taxes - Summary of Interest Expense (Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ (36)	$ 391	$ (1)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	(50)	17	11
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	6	281	(20)
PECO Energy Co [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	0	(1)	(1)
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Net interest (income) expense recognized related to uncertain tax positions	$ 1	$ 0	$ 9