Severance - Constellation Merger-Related Severance (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Corporate Restructuring Severance Benefit Obligation [Line Items]
Beginning Balance	$ 53
Payments	(36)
Ending Balance	17
Exelon Generation Co L L C [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Beginning Balance	10
Payments	(5)
Ending Balance	5
Commonwealth Edison Co [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Beginning Balance	0
Payments	0
Ending Balance	0
PECO Energy Co [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Beginning Balance	0
Payments	0
Ending Balance	0
Baltimore Gas and Electric Company [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Beginning Balance	6
Payments	(4)
Ending Balance	$ 2