Severance and Plant Retirements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance charges recorded	$ 4	$ 1
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start	53
Payments	12
Restructuring Reserve, Period End	41
Business Acquisition, Costs Recognized Post Merger [Abstract]
Business Acquisition Charitable Contributions Per Year	7
Plant Retirement Cost [Abstract]
Inventory write down related to plant retirements	2
Exelon Generation Co L L C [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance charges recorded	4	0
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start	10
Payments	1
Restructuring Reserve, Period End	9
Plant Retirement Cost [Abstract]
Inventory write down related to plant retirements	2
Commonwealth Edison Co [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance charges recorded	0	1
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start	0
Payments	0
Restructuring Reserve, Period End	0
PECO Energy Co [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance charges recorded	0	0
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start	0
Payments	0
Restructuring Reserve, Period End	0
Baltimore Gas and Electric Company [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance charges recorded	0	0
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Period Start	6
Payments	2
Restructuring Reserve, Period End	$ 4