Derivative Financial Instruments - Summary of Gains and Losses on Hedges (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Gain (Loss) on Fair Value Hedges Recognized in Earnings		$ 0		$ 1
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net		(11)	$ 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, Gain (Loss) on Derivative, Net	[1]	0	(3)
Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]			(2)	$ 5
Interest Expense [Member] | Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net		(12)	(3)
Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]			(1)	(8)
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]
Derivative, Gain (Loss) on Derivative, Net	[1]	$ 0	2
Gain (Loss) on Fair Value Hedges Recognized in Earnings			$ (4)		(8)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]			(4)	(7)
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Fair Value Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]			$ 0	$ 1

[1] For the three and six months ended June 30, 2015, the loss on Generation swaps included $0 million and $1 million realized in earnings, respectively, with an immaterial amount excluded from hedge effectiveness testing. For the three and six months ended June 30, 2014, the loss on Generation swaps included $4 million and $8 million realized in earnings, respectively, with an immaterial amount excluded from hedge effectiveness testing.