Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative [Line Items]
Income taxes		$ 102	$ 327	$ 285	$ 690
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	[1]	4		6
Derivative, Loss on Derivative		3
Increase (Decrease) in Fair Value of Hedged Item in Price Risk Fair Value Hedge			16		9
Gain (Loss) on Fair Value Hedges Recognized in Earnings			(11)		(1)
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		16		16		$ 8
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		(31)	$ 181	120	407
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		(1)		(16)
Interest Rate Swap [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ 5		22
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 six months ended June 30, 2015, the loss on Generation swaps included $1 million realized in earnings with an immaterial amount excluded from hedge effectiveness testing.