Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ 268	$ (222)	$ (294)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	270	(228)	(307)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	280	(204)	(317)
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	280	(204)	(317)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Operating Revenue [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	112	0	(270)
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	112	0	(270)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Purchased Power And Fuel [Member] | Commodity Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	168	(204)	(47)
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	$ 168	$ (204)	$ (47)