Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	$ 4		$ 2
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings	15		(3)		(1)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings	3		(24)		(9)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Gain (Loss) on Swaps/Borrowings	2	[1]	(6)	[1]	0	[1]
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 Swaps/Borrowings	(16)	[1]	(15)	[1]	(6)	[1]
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ 17		$ 16

[1] For the years ended December 31, 2014 and 2013, the loss on Generation swaps included $(17) million and $16 million realized in earnings, respectively, with $4 million and $2 million excluded from hedge effectiveness testing, respectively.