Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (259)	$ (47)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(264)	(51)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	2	(1)
Not Designated as Hedging Instrument [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 0	$ (1)