Stock-Based Compensation Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Common Stock [Abstract]
Common Stock without par - Authorized	2,000,000,000		2,000,000,000
Common Stock without par - Outstanding	858,721,507		857,000,000
Share Based Compensation Components [Abstract]
Stock-based compensation costs	$ 46	$ 39
Exelon Generation Co L L C [Member]
Share Based Compensation Components [Abstract]
Stock-based compensation costs	0	4
Commonwealth Edison Co [Member]
Share Based Compensation Components [Abstract]
Stock-based compensation costs	0	1
PECO Energy Co [Member]
Share Based Compensation Components [Abstract]
Stock-based compensation costs	0	1
Baltimore Gas and Electric Company [Member]
Share Based Compensation Components [Abstract]
Stock-based compensation costs	$ 0	$ 1