Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	[1]	$ 2
Derivative, Loss on Derivative			$ 9
Derivative, Gain on Derivative			(7)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Loss on Derivative	[1]	0	0
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain on Derivative		17
Fair Value Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Loss on Derivative	[1]	0	(1)
Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain on Derivative		$ (15)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings			$ (1)

[1] For the three months ended March 31, 2015, the loss on Generation swaps included $1 million realized in earnings with an immaterial amount excluded from hedge effectiveness testing.