Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Derivative [Line Items]
Derivative, Loss on Derivative			$ 0				$ (12)
Derivative, Gain on Derivative			(6)				(2)
Derivative, Net Hedge Ineffectiveness Gain (Loss)					2
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Loss on Derivative	1	[1]	(1)	[1]	1	[1]	0	[1]
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain on Derivative	(8)				(3)
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	(4)	[1]	(4)	[1]	(12)	[1]	(13)	[1]
Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain on Derivative	(6)				6
Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ (4)		$ (4)		$ (12)		$ (12)

[1] For the three and nine months ended September 30, 2014, the loss on Generation swaps included $4 million and $12 million realized in earnings, respectively, with $2 million amount excluded from hedge effectiveness testing.