Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) (Interest Expense [Member], Fair Value Hedging [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 9	[1]	$ 2	[1]
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	(1)	[1]	(5)	[1]
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	1		(4)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	11	[1]	4	[1]
Designated as Hedging Instrument [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	$ 0	[1]	$ (1)	[1]

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