Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (31)	$ (259)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(33)	(264)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(20)	(267)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(50)	(100)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 30	$ (167)