Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Derivative [Line Items]
Income taxes		$ 340		$ 115	$ 625	$ 805
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	[1]	6			12
Derivative, Loss on Derivative			$ 3
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge				(13)		(4)
Gain (Loss) on Fair Value Hedges Recognized in Earnings				16		15
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		(10)			(10)		$ (8)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		173		$ (36)	293	371
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge	[1]				0	0
Interest Expense [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge		14			(3)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ (8)			15
Interest Rate Swap [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	[1]				$ 0	(1)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Loss on Derivative						$ (1)

[1] For the nine months ended September 30, 2015, the loss on Generation swaps included $1 million realized in earnings with an immaterial amount excluded from hedge effectiveness testing.