Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 415	$ 203	$ 110
Maximum borrowings outstanding	597	446	366
Average interest rates, computed on a daily basis	0.33%	0.40%	0.50%
Average interest rates at year end	0.50%	0.37%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	571	254	199
Maximum borrowings outstanding	1,164	682	505
Average interest rates, computed on a daily basis	0.32%	0.37%	0.48%
Average interest rates at year end	0.53%	0.35%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	93	42	4
Maximum borrowings outstanding	552	291	165
Average interest rates, computed on a daily basis	0.32%	0.32%	0.45%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	64	35	6
Maximum borrowings outstanding	$ 180	$ 135	$ 76
Average interest rates, computed on a daily basis	0.29%	0.31%	0.43%
Average interest rates at year end	0.61%	0.31%