Derivative Financial Instruments - Summary of Proprietary Trading Activities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			$ (151)	$ (230)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives			(158)	(235)
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	$ 15	$ 0	$ 17	(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				$ (1)