Derivative Financial Instruments - Summary of Economic Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (294)	$ (151)	$ (24)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(307)	(167)	(40)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(6)	(9)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	7	(6)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(4)	(3)	0
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	(317)	(169)	(31)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(270)	(126)	(490)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Commodity Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(47)	(43)	459
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	(9)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Operating Revenue [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	7	(6)	(10)
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Purchased Power And Fuel [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	(9)	0	0
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member] | Foreign Exchange Contract [Member] | Interest Expense [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (7)	$ (3)	$ 0