Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commonwealth Edison Co [Member]
Short-term Debt [Line Items]
Average borrowings	$ 461	$ 415	$ 203
Maximum borrowings outstanding	$ 684	$ 597	$ 446
Average interest rates, computed on a daily basis	0.53%	0.33%	0.40%
Average interest rates at year end	0.89%	0.50%	0.37%
Exelon Corporate [Member]
Short-term Debt [Line Items]
Average borrowings	$ 499	$ 571	$ 254
Maximum borrowings outstanding	$ 739	$ 1,164	$ 682
Average interest rates, computed on a daily basis	0.53%	0.32%	0.37%
Average interest rates at year end	0.88%	0.53%	0.35%
Exelon Generation Co L L C [Member]
Short-term Debt [Line Items]
Average borrowings	$ 1	$ 93	$ 42
Maximum borrowings outstanding	$ 50	$ 552	$ 291
Average interest rates, computed on a daily basis	0.49%	0.32%	0.32%
Baltimore Gas and Electric Company [Member]
Short-term Debt [Line Items]
Average borrowings	$ 37	$ 64	$ 35
Maximum borrowings outstanding	$ 210	$ 180	$ 135
Average interest rates, computed on a daily basis	0.48%	0.29%	0.31%
Average interest rates at year end	0.87%	0.61%	0.31%