Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (222)	$ (294)	$ (151)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(228)	(307)	(167)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(317)	(169)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(317)	(169)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Operating Revenue [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	0	(270)	(126)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Operating Revenue [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	0	(270)	(126)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Purchased Power And Fuel [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(204)	(47)	(43)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Purchased Power And Fuel [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (204)	$ (47)	$ (43)